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CHAPTER 2

REVIEW OF THE PAST WORK

2.1 Introduction:

Many researchers have exploited nanotechnology application to the field of

electronics communication, in particular antenna development for its miniaturization (size

reduction) and bandwidth enhancement. Based on their research, they have published their

findings in the form of research papers and articles. Several theoretical modelling, simulation

and experimental investigations have found in understanding the use of nanotechnology

techniques used in the development of patch and carbon nanotube antennas in wireless

communication systems. So, the detailed literature survey is made and presented in this

chapter on modelling, simulation and experimental validation of nanotechnology enabled

antennas from 1939 to till date. Based on the literature survey, formulation of the research

problem is presented here.

2.2 Literature survey: Nanotechnology Concepts and Applications in Electronics

The achievements in the synthesis of nanostructured materials enabled scientists to

explore the physical, chemical and electronic properties for various applications in the field

of nanoelectronics, nanooptics and chemical sensing. The advantages of nanomaterials based

sensors are fast response, small size, high selectivity and portability compared to existing

bulky sensors. In this context, Stephanie A. Hooker [1] in 2002 of Business Communications

Co., Inc., USA have presented a paper that discusses development of gas sensors that detect

NH3, NOx, VOCs, and CO2 using nano-sized aluminum powders (< 100 nm). The sensors are

able to detect indoor air pollutants with very low power and high sensitivity operation.

In 2004, Dr. Ashutosh Sharma et al. [2] explains nanotechnology is that area of

research and development which is truly interdisciplinary in nature. Research at nanoscale is

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unified by the need to gain knowledge on nanotechnology tools and techniques, as well as

information on the physics affecting atomic and molecular interactions. Electronics,

mechanical engineers, material scientists and medical researchers are working with

biologists, physicists and chemists in this new realm. The literature explains the possibilities

to create newer innovations which can create significant impact in areas such as high end

computing, healthcare, electronic communication systems etc. The authors also explain

nanostructured magnetic particles and thin films coated substrates for magnetic recording

data, cellular phones, credit cards, microwave devices and opto-electronic application

including polymer displays.

In the year 2005, Mohammad U. Mafuz and Kazi M. Ahmed [3] have highlighted the

importance of nanotechnology in the development of wireless sensor networks (WSN) for

probable exploitation in environment monitoring and pollution control. They reviewed micro-

nano-scale wireless sensor networks in terms of reduced size, low cost, less maintenance, less

analysis time, and increased sensitivity. They highlighted the requirement of ultra wideband

(UWB) radio technology to indicate its possible potential to be used in wireless sensor

networks using nanotechnology.

In the year 2005 Alen Rae in his special report of Microsystems and Nanosystems [4],

describes nanotechnology is like a toolkit for the electronic industry that allows us to make

nanomaterials with special properties modified by ultra-thin particle size, crystalline,

structure or surfaces. These nano-materials become commercially important when they give a

cost and performance advantage over existing products or allow us to create new products.

The paper presents areas in nanotechnology with specific impact on semiconductors, passive

components, display materials, packaging IC and MEMS devices, substrate, power delivery,

conductive adhesives etc. This paper addresses key issues of nanotechnology importance to

electronic industry.

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Charles P. Poole, Jr. and Frank J. Owens [5] in 2009 describe nanotechnology as a

relatively new field deals with various structures of matter having dimensions of the order of

a billionth (1×10-9

) of a meter. The fundamental physics and chemistry changes when bulk

solid material converted to a nanometer range. They give the example of semiconducting

material in the order of the wavelength of the electrons or holes that carry current. The

electron structure of the system completely changes results in the quantum dot laser presently

used to read compact disks (CDs). This illustrates the electron structure is strongly influenced

by the number of dimensions that of the nanosized and the electron structure is strongly

influenced by the number of dimensions that are nanosized. The changes in electronic

properties with size result in major changes in the optical properties of nanosized materials.

This illustrates nanotechnology for semiconductor application for compact disks.

In 2007, Ermolov V. et al. [6] presented review paper on nanotechnology application

to wireless devices and communications. They have outlined the importance of

nanotechnology solution for radio in particular antennas. Basically, antennas are made from

bulk materials that increase electromagnetic dissipation. The antenna geometry can be

optimized using numerical solutions but at the cost of reduced performance. The authors

suggest the radical enhancement of the performance could come from nanotechnology by

tailoring magnetic nanoparticles to reduce loss and tune the electrical permittivity and

permeability to optimal values. Such material is not appearing conventionally in nature, is

attractive for antennas, filters and near field imaging. The authors also explain application of

nanotechnology to semiconductor memories, power and thermal management, simulations,

manufacturing and environment etc.

During 2007 researchers Prabir K. Patra et al. [7] have successfully demonstrated the

use of nanotechnology in developing textile based carbon nanotube flexible antenna for

2.4 GHz application. They claim that their research using nanotechnology in controlled

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deposition and patterning of carbon nanotube on flexible substrates can open doors to a

number of exciting applications in the field of flexible/wearable electronics, flexible

displays,, batteries, communication devices such as wearable antennas and RFID devices.

They have successfully realized inkjet printing of carbon nanotube ink on various flexible

substrates such as fabric, paper and transparency.

M.D. Balachandran et al. in 2008 [8], have published their research work in electronic

letters that demonstrates application of nanotechnology in developing SnO2 capacitive sensor

integrated with microstrip patch antenna for wireless detection of ethylene gas for status of

fruits and vegetable at various stages of their ripening. By monitoring the change in resonant

frequency and return loss of the antenna, concentration of the ethylene gas is detected

wirelessly. They claim that unlike other reported sensors, their developed ethylene sensor is

fabricated at room temperature with SnO2 nanoparticles as the active dielectric layer. Their

proposed antenna sensor is a low cost, passive and planar that can be easily integrated with

passive RFID tags.

G. Sundararajan and Tata Narasinga Rao [9] in the year 2009, discusses

nanotechnology based product development in India. The authors describe nanotechnology

application oriented research in India primarily on energy, environment and healthcare

related areas. For example IISc Bangalore has developed and transferred nanotechnology

based gas-flow sensors know-how to an American start-up company. The paper also

discusses development of nanocrystalline ZnO powder based varistors for lightening arrestor

application, developed by International Advanced Research Centre for Powder Metallurgy

and New materials (ARCI), Hyderabad, India. The article reviews nanomaterials and

nanotechnology, and its benefits to society through Indian scientific and industrial

community over the last decade.

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In [10] during 2009, Mitesh R. Parmar et al. have developed alcohol sensing

nanostructured copper oxide thin film using nanotechnology tools and techniques. They have

fabricated nanostructured copper oxide thin film alcohol sensor using reactive DC magnetron

sputtering technique. The thin film sensor has been characterized using nanotechnology tools

like X-ray Diffraction, energy dispersive X-ray analysis, X-ray photo-spectroscopy and field

emission microscopy. The grain size of copper oxide film found to be in the range 40-65 nm

range. The so developed thin sensor has almost linear response for different ethanol

concentrations.

2.3 Magneto-Dielectrics: Antenna Miniaturization and Bandwidth Enhancement

In 1986, David M. Pozar [11] made a detailed analysis of slot and aperture coupled

microstrip antenna. The approach is based on the reciprocity theorem and uses exact Greens

functions for the grounded dielectric slab in a moment method solution for the unknown

currents. The method is applied to two antenna structures namely slot and aperture coupled

patch antennas. The theoretical analysis and measurements are quite closer.

David M. Pozar [12] in 1992 listed wide applications of microstrip patch antennas that

is being used in radar, communication, altimeter, navigation systems for aircraft and ship

platform to mobile satellite telephone, mobile radio system for land vehicles platform,

including direct broadcast TV, remote sensing radars systems in satellite platform.

US patent number 5,334,941 [13] published by King D.J in the year 1994 explains

how resonant frequency decreases when positioning of nonmagnetic dielectric as superstrate

on patch of antenna. The fringing fields on the surface of the resonator couples capacitively

with the superstrate, results in shift of the transmission resonant frequency peak of the

antenna.

Hwang Y. et al. [14] in 1995 demonstrated enhanced gain of

an inverted F antenna loaded with a very high permittivity substrate. Due to high dielectric

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loading in PIFA, radiation loss occurs. To overcome this problem a layer of superstrate with

higher permittivity material was added on the antenna. Measurements show that the size of

the antenna can be reduced without sacrificing the antenna radiation efficiency. The gain-

enhancement mechanism, bandwidth, and antenna radiation gain and patterns are presented

and discussed.

In 1997, authors Lo T.K. et al. [15] have designed, developed and conducted

experiment on aperture coupled microstrip patch antenna on high dielectric substrate for 1.66

GHz. For gain enhancement, he added appropriate superstrate substrate on the patch of

antenna. He observed miniaturization of antenna took place without change in other

parameter like bandwidth. His experiment demonstrates loading of high dielectric constant

material to antenna will reduce the size of antenna to one fifth of that of the conventional

antenna.

In 2000, R.C. Hansen and M. Burke [16] have investigated a new material with

permittivity, permeability and low loss to antennas. Unlike permittivity, permeability does

not reduce the patch bandwidth. Such substrates offer an important advantage: the patch

resonant length is reduced by µ1/2

so that a smaller patch will have the same bandwidth as a

patch with permittivity only.

In [17] during 2001 Ramesh Garg et al. highlight the most popular types of patch

antennas: microstrip line, coaxial probe, aperture coupling, and proximity coupling.

Microstrip feed line and coaxial probe are direct contact with patch type, where as aperture

and proximity coupled type are non-contacting type. He explains that it is easy to fabricate

contact type, where as it is difficult in case of non-contacting type antennas.

Hai Dong et al. [18] in 2004 prepared magnetic nano composite material by mixing

the cobalt ferrite nanoparticles with epoxy/anhydride matrix for high Q embedded inductor.

Usually embedded inductor suffers from low Q-factor and high parasitic effect due to

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substrate proximity. For embedded inductor application in personal electronics and electronic

equipments and devices, it is desirable to decrease the loss of core material in order to

achieve high Q. The loss of core material is increased with large ferrite grain size and

resistivity. In order to reduce the core loss the authors have prepared the inductor substrate

using nano phase ferrite that reduces the resistivity of the substrate material.

A lot of research is carried out on magneto-dielectrics in terms of theoretical and

experimental analysis. Hossein Mosallaei and Kamal Sarabandi [19] in 2004 have

demonstrated application of magneto-dielectric metamaterials for improving the performance

and achieving miniaturization of antennas. They proved that the magneto-dielectric meta-

substrates provide a great advantage in the design of miniaturized planar antennas with

superior radiation and bandwidth characteristics. They conclude that utilizing both dielectric

and magnetic materials allows for simultaneous use ease of antenna impedance matching and

miniaturization.

T.D. Xiao et al. [20] in 2005 have synthesized and characterized two types of nano

composite magneto-dielectric thick films of Co-Silica-BCB and Ni-Zn ferrite-epoxy that are

suitable for miniaturization of high frequency inductor, capacitor and antenna applications.

Both materials have shown permeability and permittivity of 10 at GHz frequency range

making it a good candidature for embedded inductor and antenna. Both retain high

permeability at 1-2 GHz range.

P. Markondeya Raj et al. in 2005 [21] have demonstrated preparation of magneto-

dielectric substrate and fabrication of inductor on this substrate using screen printing

technique. The nano particles of ferrite were dispersed into a commercial epoxy to form a

thick paste. The paste is then screen printed onto a FR4 substrate to a thickness of 125

microns. The composition of organic paste consists of 50-70% nano particles uniformly

dispersed in an epoxy resin. Then the epoxy is cured to form a dense solid at 1400C

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temperature for a period of 30 minutes. The inductor is patterned on this magneto-dielectric

film using sputtering to a thickness of 3 microns using etch-back process.

In 2006, John D. Kraus et al. [22] explains geometry of microstrip patch antenna. In

its most basic form, a microstrip patch antenna consists of a radiating metallic patch on one

side of a dielectric substrate, which has a metallic ground on the other side. The patch is

generally made of conducting material such as copper or gold. The radiating patch and feed

lines is usually photo etched on the dielectric substrate. The most common board is a dual

copper coated FR4 substrate. The microstrip antennas may have a square, rectangular,

circular, triangular or elliptical shape.

In 2006, researchers Kyung-Woon Jang and Kyung-Wook Paik [23] fabricated

embedded capacitor on organic substrate (printing circuit board) using a simple screen

printing technique. Also they have discussed drawback of capacitor fabrication using

techniques like vacuum deposition, spin coating, tape casting etc. The disadvantages with

above techniques are high processing temperature, high cost, waste of materials, non-uniform

thickness control etc. leads to parasitic inductance occurrence. Hence they used screen

printed technique to fabricate capacitor on organic material where embedded capacitor pastes

have the advantage of that capacitors can be formed locally on desired part via mask pattern

using a screen printing method. However screen printing technique have problem of high

tolerance because the edge of a screen print layer is generally thicker than its centre due to

surface tension of mask.

Alireza Foroozesh and Lotfollah Shafai [24] in 2006 have verified magneto-dielectric

substrate as superstrate substrate for probe feed antenna miniaturization. The magneto-

dielectric layer of 1 mm thickness with a permittivity and permeability are assumed to be 10,

is added just beneath the high permittivity dielectric superstrate, with an air gap height of 8.9

mm between magneto-dielectric material and patch of the antenna. The result shows that the

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resonance frequency shifts down from 7.35 GHz to 7.15 GHz that indicates antenna size

reduction.

Many researchers studied, developed and experimentally validated artificial magnetic

materials with properties that do not exist in natural materials. In 2006, researchers Kevin

Buell et al. [25] have developed a microstrip antenna up to 2.5 GHz and tested to demonstrate

the potential application of embedded circuits‟ magnetic metamaterials substrate. Their

simulation result indicates that with commercially available low-dielectric materials and

standard 5-mil commercially available processing technology, magnetic metamaterials

produced by their technique can be designed with an operating frequency of up to 10 GHz

with permeability in 1-5 range.

Other researchers who proposed magneto-dielectric substrate for antenna

miniaturization are Kyeong-Sik Min and Viet-Hong Tran [26] in the year 2006. The antenna

structure is meander line type designed for 433.92 MHz and has omnidirectional radiation

pattern for mobile RFID system or Ubiquitous Sensor Networks (USN). The advantage of

using meander line technique is to one more time reduce the size and utilize whole volume of

the antenna in addition to size reduction from magneto-dielectric substrate. The authors

discuss miniaturization factor or refractive index given by n = (ɛrµr)1/2

. In order to achieve

small size of antenna, in addition to permittivity, permeability should be varied above one.

The permeability in a material can be varied by properties of Ni-Zn material.

Francis Eugene Parsche [27] in US patent publication (2010) has disclosed that

magneto-dielectric layer operates with an infinite passband or bandwidth, as the magneto-

dielectric material offers a perfect reflection less boundary to free-space. This is because the

wave impedance in magneto-dielectric layer is the same as free-space if ɛr=µr>1 and

ɛair=µair=1. The author has demonstrated small rationally polarized omni-directional antenna

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with reduced size and increased bandwidth which may be used in high frequency applications

like portable phones, and other mobile communication systems.

In 2008 Yasushi Shirakata et al [28] have confirmed the possibility and feasibility of

miniaturizing the rod antenna by loading the developed magnetic composite material. The

developed composite material consists of Ni78Fe22 or Zn5Ni75Fe20 fine 150 nm thickness

flakes dispersed in thermosetting polymer. They found that magnetic loss decreases with an

increase in stirring time and the minimum value can be obtained when the agglomerated

particles decrease and most particles are deformed into flakes. The effect of wavelength

shortening and low loss characteristics are verified by the experimental results. The

resonance frequency of the antenna shifted from 1.8 GHz to 1 GHz, hence the size reduction.

Some of the researchers have developed magnetic materials using silicone or/and

Benzocyclobutene (BCB) as dielectric material with Co2Z magnetic powder for wearable

conformal RFID tag antenna working at 480 MHz in bio-monitoring applications.

In 2008, Li Yang et al. [29] synthesized a magnetic substrate using the above

mentioned polymer matrix and magnetic powder to produce a 1.3 mm thickness magnetic

substrate. They have fabricated a folded bow-tie meander line dipole antenna on the magnetic

material. Their experimental results show that the resonant frequency of the antenna is shifted

down by 22 MHz with a centre frequency of 458 MHz, with a drop in gain from -4.63 to -

7.37 dBi. The flexible substrate enables the RFID tag module‟s application in wireless health

monitoring and pharmaceutical drug bottle tracking.

Constantine A. Balanis [30] in 2009, explained antenna as a device designed for

radiating or receiving radio waves. The author highlights antenna in particular microstrip

patch antennas have several advantages like light weight, low cost, low volume, small size,

and easy to fabricate using photolithographic printed circuit technology, and are widely used

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in many practical applications like aircraft, satellite, spacecraft, missile, mobile, GPS, RFID,

Wi-Max and Radar etc.

In 2009, Guo-Min Yang et al. [31] have designed, fabricated and tested antennas with

self-biased ferrite magnetic properties film at 1.2 GHz. They have prepared NiCo-ferrite film

onto 15 micron thin transparency. The thickness of the film is about 2 micron by spin spray

plating technique prepared at a low temperature of 900

C. Measurement on magnetic

rectangular inset-fed patch antennas demonstrates that the resonant frequency shifted down

word over a tuning range of 12-40 MHz, which indicates the self-biased magnetic film do

lead to miniaturized antenna by shifting down the resonance frequency. The bandwidth of the

antenna is enhanced by 3 MHz to 11 MHz over non-magnetic antenna. In addition to antenna

size reduction efficiency of antenna is increased from 41% to 74%.

In 2009, Nevin Altunyurt et al. [32] in their conference paper have highlighted

realization of magneto-dielectric substrates through material synthesis. Also, they have

highlighted the characteristics of magneto-dielectric that are useful for applications in

microwave frequency range. When nano scale nickel and cobalt particles mixed with

insulating matrix like epoxy, the end product i.e. magneto-dielectric material will have low

eddy current, low hysteresis, high permeability, cancellation of magnetic anisotropy of the

individual particles leading to smaller skin depth, enhanced material softness, high

permittivity and stable frequency properties at high frequencies.

Researchers Jae-Sik Kim et al. [33] in 2009 have investigated high frequency electro-

magnetic properties of Ba3Co2Fe24O41 ceramics for small antenna applications in 210 MHz

frequency range. Essentially Ba3Co2Fe24O41 are hexagonal ferrites can have high permeability

overcome a Snoek‟s limitation. They demonstrated that permeability and permittivity of the

ferrite ceramic can be decreased or increased with sintering temperature. Ba3Co2Fe24O41

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ceramics were synthesized by solid-state reaction method and microwave characteristic was

estimated by network analyzer.

Leo Kempel et al. [34] in 2009 presented a research article that explains radiation by a

magneto-dielectric loaded microstrip patch antenna. The authors studied placement of

inductors and magneto-dielectric nano composite material along the centerline spine of a

rectangular patch antenna. It was found that the inductor increases the resonant frequency

while magneto-dielectric substrate decreases the resonant frequency, and when loops forming

the inductors are disrupted, the radiation performance of the antenna is similar to that of the

case with only a magneto-dielectric load.

In 2010, T. Danny Xiao et al. [35] in their US patent publication have shown

successful fabrication of nanostructured micro-inductors using different techniques like

physical vapor deposition (e.g., RF sputtering, EB-PVD), paste or screen-printing, spin-

coating assisted with an energy source in the form of a heater or energy beam, CVD, or sol-

gel. They have fabricated 2 to 6 turns or windings of patterned high frequency spiral

inductors on Ni-Zinc/Ferrite Epoxy paste and Co/Sio2/Ferrite nano composite. The nano

composite comprising ferrite nanoparticles, embedded in an insulator matrix (e.g., a polymer,

ceramic).

Kunal Borah and Nidhi Saxena Bhattacharyya in 2010 [36] have prepared magneto-

dielectric material using nano cobalt ferrite inclusions as potential substrate for patch

antennas for permittivity characterization at X-band using in touch superstrate method.

Superstrate method is based on measurement on the shift in resonant frequency when

microstrip patch antenna is loaded with superstrate. They have successfully demonstrated

interesting characteristics of nano Co-ferrite magneto-dielectric composite material as

substrate for antenna miniaturization.

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G.M. Yang et al. [37] in 2010 have tested loading effect of self biased magnetic films

on patch antennas for antenna miniaturization and bandwidth enhancement. On either side of

the radiating element with self biased NiCo-ferrite thin films forms magneto-dielectric

substrate/superstrate sand witch structure. The geometry of the antenna designed to operate at

2.1 GHz. It is a conventional line feed patch antenna on alumina substrate. The 3 micron

copper layer was deposited using physical vapor deposition system. These magnetic patch

antennas shows an enhanced bandwidth of >200% over the non-magnetic substrates at 2.1

GHz. The omnidirectional radiation pattern is greatly enhanced over unloaded antenna.

Some of researchers demonstrated miniaturization capability of the magneto-dielectric

substrate validated by an aperture coupled microstrip patch antenna loaded with synthesized

ferrite compound. In 2010, S. Deepak Ram Prashath et al. [38] have validated antenna

miniaturization by placing 2 mm thickness ferrite magneto-dielectric material above the

slot/aperture of the feeding structure of the antenna lower substrate. The electromagnetic

energy passes through the ferrite magneto-dielectric material and coupled to the patch making

it to radiate. They have shown that the loading of ferrite material increases effective

permeability and permittivity of the combination and hence shifts the resonant frequency

from 1.77 GHz to 1.49 GHz with increase in return loss characteristics from -10.39 dB to

-19.89 dB. The authors also discussed limitations of magneto-dielectric material to higher

frequencies in terms of sneok‟s limit, where saturation magnetization will be the magnetic

resonance frequency limiting factor. If saturation magnetization increased for the given

material, the magnetic resonance frequency of the magneto-dielectric material can be shifted

to higher frequencies.

C. Niamien et al. [39] in 2010 have developed ultra-miniature UHF antenna using

magneto-dielectric material and meander lines operating at lower band around 470 MHz for

TV signal reception. They used a commercial magneto-dielectric material called MF-114 for

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size reduction of the antenna. The electrical properties of this material are: dielectric constant

of 11.2, permeability of 2.1, dielectric loss of material is 0.05, magnetic material loss of 0.066

at 500 MHz. The researchers are able to reduce the size of antenna with this material is

around the size of λ0/41. Here the magneto-dielectric material is used as superstrate on

meander lines.

Many researchers have done a lot of work in exploiting the magnetism in nano

particles. Jaakko V.I. Timonen et al. [40] in 2010 have reviewed theory of magnetism in nano

particles by characterizing the electromagnetic properties of magnetic nano composite

materials. Conventional magnetic materials used in the electronic communication devices are

ferrites which are micrometer-size in nature. These micron size materials have small

saturation magnetization. Therefore, applications developed using these materials will have

poor performance at GHz frequencies. The ferromagnetic resonance frequency has to be well

above the designed operation frequency to avoid losses and to have significant magnetic

response. The authors have demonstrated by using nano particles saturation magnetization

can be increased sufficiently in the frequency range 1-14 GHz applications.

In 2010, researchers David Souriou et al. [41] have presented a new magneto-

dielectric material called M1 with low loss in UHF band. They fabricated magneto-dielectric

material by doping indium with Ni-Zn-Co ferrites nano powders by conventional co-

precipitation method. They have compared their M1 with commercial magneto-dielectric

material called MF114 by fabricating slot antenna for 100 MHz to 700 MHz range in UHF

band. A shorted small meandered slot antenna called M-CSA of 15×15 mm2 and integrated

on a PCB of 130×230 mm2. It is based on a ¼ wavelength slot shorted on the right ground

plane with a co-planar feeding line. They found that when slot antenna is loaded with M1

material there is a down frequency shift from 716 MHz to 484 MHz, and for commercial

antenna there is a down frequency shift from 716 MHz to 515 MHz. Thus they have obtained

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a size reduction of about 30% with the two materials with better efficiency results for M1

material.

In 2010 researchers David Souriou et al. [42] have experimentally studied

electromagnetic properties of nickel-zinc ferrites based magneto-dielectric materials make

them potential candidates for telecommunication applications. In their study, nano-sized

particles of spinel ferrite were prepared by co precipitation method. An optimized material

was obtained after adequate heat treatment and partial filling of the porosity by epoxy resin.

The material shows constant permeability and permittivity in the frequency range 0.1 GHz –

0.7 GHz. The refractive index n is close to 3.75. The electromagnetic properties shows that

this material could be used in the design of miniaturized antenna in the VHF-UHF range of

frequency (300 MHz – 700 MHz).

In 2010, researchers C. Niamien et al. [43] proposed an ultra-miniature planar

meander antenna that integrates a magneto-dielectric material as superstrate. The authors

have compared two superstrate: one is commercially available MF114 magneto-dielectric

substrate and other is their own fabricated magneto-dielectric substrate called Material 85.

The properties of materials at 500 MHz are: MF-114 material is having a permittivity of 11.2,

permeability of 2.1, whereas material 85 is having a permittivity of 4.9 and permeability of

5.6. The miniaturization factor for MF114 is 4.8 whereas for material 85 is 5.2. The antenna

fabricated with MF114 resonates at 462 MHz, whereas antenna with material 85 resonates at

456 MHz. It is summarized that with MF114 material the bandwidth is 3.3% and efficiency

of 17. In case of material 85 the antenna able to achieve a bandwidth of 2.5% and efficiency

of 24%. The main application of antenna is in DVB-T in the 470 MHz frequency band.

In 2011 Guo-Min Yang et al. [44] have fabricated ferrite-dielectric-ferrite magneto-

dielectric sandwich substrate to realize antenna for size reduction and bandwidth

improvement for WLAN and Bluetooth bands at 2.46 GHz. They have prepared magneto-

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dielectric material by NiCo-ferrite films deposited onto two sides of the Rogers Duroid6010

dielectric material. The inset feed antenna structure is fabricated on the top surface of the

magneto-dielectric material. Measurements on magnetic patch antennas demonstrate that the

operating central resonant frequency can be varied downward over a tuning of 190% of the

antenna bandwidth. This indicates the self biased magnetic films do lead to reduce the size of

antenna by shifting down the resonance frequency.

In 2011, Manouan Aka Constant Niamien et al. [45] have proposed a small antenna

over magneto-dielectric substrate for DVB-T/H reception application. They fabricated a

simple monopole printed on FR4 substrate with permittivity of 4.4, permeability of 1, and

material loss of 0.01 with a thickness of 0.8 mm. In order to reduce the antenna size the strip

line is folded and increased the number of meanders to decrease the resonant frequency. A 3

mm thick block of a commercial magneto-dielectric material called MF-114 is placed over

the antenna as a superstrate. The result shows that the antenna is ten times smaller than a

classical monopole antenna. The antenna exhibits a bandwidth of 15 MHz with a gain of -4.5

dBi around 470 MHz.

In 2011, researchers Kunal Borah and Nidhi S. Bhattacharyya [46] have developed

two magneto-dielectric materials using nano ferrite composites cobalt-ferrite/LDPE and

Nickel ferrite/LDPE for miniaturization of antenna in X-band applications. They have

prepared the 2.1 mm height magneto-dielectric substrate by mixing synthesized average 10

nm size CoFe2O4 nano particles in LDPE matrix and average 12 nm size NiFe2O3 in PDPE

matrix. On these substrates 15.7×14.9 mm2 and 5.71×6.9 mm2 dimension patch antennas are

fabricated. The antennas are excited through probe feeding technique. From antenna radiation

characterization it is found that there is a small shift in resonant frequency indicating antenna

size reduction. The radiation pattern shows antenna has negligible side lobes and back lobe

with directional behavior.

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G. Le Fur et al. [47] in 2010 have experimentally validated effect of magneto-

dielectric material loaded on notch antenna designed for 1.08 GHz operation by simulation

and experimental measurements. The result shows that the resonant frequency is down

shifted from 960 MHz to 740 MHz corresponds to a miniaturization of 23%. They conclude

that the small piece of magneto-dielectric load has to be placed on the slot open end. The

radiation efficiency is slightly reduced (around 10%) in spite of antenna miniaturization and

material loss, which are low.

Jungyub Lee et al. [48] in 2012 have designed and experimentally demonstrated a

small antenna for mobile handsets using a new magneto-dielectric material, used to resonate

around 2 GHz. They have processed magneto-dielectric material using Co2Y(Fe2O3, BaCo3,

Co3O4, additive oxides) powders mixed with ZrO2 to get hexagonal ferrite powder. This is

ball milled and then polyvinyl alcohol binder is added and is heated below 4500 C to get final

material. The material is characterized and antenna is fabricated on magneto-dielectric

substrate for mobile handset application. The result shows that magneto-dielectric chip

antenna has not only miniaturization effects but also more improved bandwidth compared to

the one of the dielectric chip antenna at the same frequency.

The miniaturization of a patch antenna using magneto-dielectric substrate is presented

by Yu Yu Kyi et al. [49] in 2012. They used magneto-dielectric developed by Temasek

Laboratories @ NUS. A U-shaped patch is printed on the magneto-dielectric material whose

permittivity and permeability values are of the same values. The measured result shows its

operating frequency at 192 MHz, therefore demonstrates its effectiveness of the size

reduction of 45% decreased in dimension compared to the antenna design with FR4 loading.

In [50] Inframats web site, it is clearly explained background and applications of nano

magnetics. The consolidation of high density nano composite materials is a critical step

towards magnetic material. An isolated nano composite particle possesses very high

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anisotropy and demagnetizing effect. For nano composites materials, the soft material

integration interaction mostly due to the exchange coupling of the neighborhood material

interaction tends to average the anisotropy of each individual particle, resulting higher

permeability. A critical parameter, the exchange coupling of magnetic moments of the two

particles can be coupled. A nano composite consisting of a magnetic phase and an insulating.

The latest development in the fabrication of magneto-dielectric is in 2014 by Kunal

Borah et al. [51] for design of light weight microstrip antenna in X band. They have modified

the substrate structure by incorporating a step profile along the radiating edges of the patch.

Their design is tested for both dielectric and magneto-dielectric substrates. The result shows

an enhanced S11, parameter, -10 dB bandwidth and directivity compared to planar substrate

antennas. The magneto-dielectric substrate shows a miniaturization factor of 3.14 and

bandwidth enhancement along with weight reduction. They have prepared the magneto-

dielectric material by synthesizing 5% VF nickel ferrite/LDPE mixture.

2.4 Nanofilm (Ultra-Thin Patch) Antennas

It is understood that very thin metallic films have a much higher resistivity than a bulk metal

because of electron scattering from thin metal surface. The resistivity of the bulk metal will

be same if the thickness of metal is very large compared to electron mean-free-path.

However, when the film thickness is on the order of the electron mean-free-path, then the role

of electron scattering becomes dominant. K. Fuchs [52] in 1937 considered the general form

of the solution of the Boltzmann equation for the case of conducting film and found the film

conductivity σf in terms of the bulk conductivity σ, the film thickness t, and the electron-

mean-free-path p: σf = (3tσ/4p)[ln(p/t)+0.04228] for t<<p. According to the Fuchs-

Sondheimer theory, the surface resistance Rs of a metallic film is decreased as the thickness

of the film is increased. The Fuchs theory helps to model antennas nano film patch for

simulation by calculating the nano film surface resistance theoretically.

33

In 1986 Raymond Justice [53] in his US patent no 4,571,592 has highlighted his

invention on effect of skin depth to make microwave device resonate at more than the one

frequency determined by the dimensions of the discontinuity defined by the conductive

material. It is highlighted that a conductive material having a thickness equal to its skin depth

functions as a high dielectric constant material at frequencies below the microwave frequency

that defines the skin depth. Skin effect is the tendency of current density in a conducting

material at microwave frequencies to be concentrated near the surface of the conducting

material there by effectively increasing the resistance of the conductive material at

microwave frequencies. Their invention is applicable to slot antennas, cavity backed

antennas, and transmission line stubs, and is further applicable to other microwave devices

utilizing skin depth/effect to make device resonant at more than one frequency.

James G. Evans et al. [54] in US patent no 5,598,168 during 1997 has explained how

effectiveness of a Microstrip antenna at any frequency can be improved by making the

antenna patch thickness sufficiently small less than skin effect of the radiating patch. The

skin effect causes shielding to electromagnetic wave and losses in the conductor. According

to their invention the radiating patch has a thickness sufficiently small to be substantially

transparent to radiation over a range of frequencies at which the antenna operates. This

allows the larger current at inner surface of the patch facing dielectric substrate, and hence

adds its effect on radiation to the current at the upper patch surface. Hence, their invention

overcomes the undesirable effect of conductive material between upper and inner surfaces of

microstrip antennas shielding the radiation produced or sensed by the currents in the inner

surface.

William B. Robbins and Timothy S. Skogland [55] in 1998, describes their invention

on microstrip patch antenna that utilize a radiating conductive layer having thickness of a

fraction of a skin depth of the conductive element. In their invention the antenna having a

34

conductive layer for the radiating patch of less than one skin depth in thickness results in the

conductive layer exhibiting a higher resistance. This higher resistance is a result of higher

ohmic losses in the metallization layer of the antenna that dissipates more energy. The higher

resistance lowers the quality factor Q value of the antenna, thereby increasing the bandwidth

of the antenna. Higher bandwidth is often desirable in microstrip antennas, which are

inherently narrow bandwidth antennas. Further the inventors explain that the greater

bandwidth makes the antenna more tolerant to variations in manufacturing without

compromising the operation of the antenna.

Apart from CNT and CNT-ink composites as radiating patch, research is done on

using superconducting materials as patch element of microstrip antenna. Superconducting

materials have low resistance and low power loss compared to their counterpart copper

materials. When Superconducting material used in patch antenna, the efficiency of the

antenna increases. Michael J. Lancaster et al. [56] in 1998 have fabricated „H‟ shaped

Superconducting radiating patch that uses aperture feed technique, and copper based

reference antenna. The antennas are designed for 4.5 GHz. The Superconducting antenna

performance is analyzed in terms of resonance frequency, losses and efficiency. The

resonance frequency of H antenna is slightly higher than copper patch antenna. For H antenna

the conductor losses are less compared to copper antenna. Efficiency is higher in H antenna

compared to copper based reference antenna.

In 2001, H.-D. Liu et al. [57] presented experimental validation of copper nano film

exhibiting higher resistance when compared with bulk copper metal. The researchers have

grown ultra-thin copper film less than 40 nm on 500 nm thick SiO2 on Silicon (100) substrate

in an ultra high vacuum chamber with a base pressure of 5×10-10

torr. The sheet resistance Rs

(Ω/square) was measured. The result shows that, when the film thickness is less than 10 nm,

the sheet resistance is almost infinity. When the film thickness increased from 10 to 41 nm,

35

the result shows resistivity of 2.67 µΩ cm. The results suggest that for film thickness greater

than 10 nm, the resistivity rapidly decreases with increasing thickness of the film as

continuous film forms, and gradually levels off to approximately 1.5 times bulk copper

resistivity at thickness equal to electron mean-free-path. The paper helps us to model ultra-

thin copper patch modelling for antenna simulation and fabrication.

Thin films plays very important role in applications involving sensors, MOSFETs and

ultra-thin (nanofilm) for antenna-on-chip. In 2003, Samuel Y. Liao [58] explained electrical

properties of metals of very thin films. Under the circumstances, if the thickness of metallic

film is very large compared to its electron mean-free-path (for copper it is 42 nm and for

silver it is 58 nm), the resistivity is nearly same as that of thick metal. However, when the

film thickness is on the order of the electron mean-free-path, then its resistivity increases. The

reason for variation in surface resistivity is electron scattering becomes dominant. According

to the Fuchs-Sondheimer theory, as the thickness of film increases, the surface resistance

decreases.

Radio frequency identification (RFID) is a rapidly developing RF tag technology that

uses RF signal for automatic identification of objects without the restriction of line of sight.

Many RF tags use coils made of copper or aluminum. Recently other metals are also used due

to the requirement of low cost tags at large volumes. Pavel V. Nikitin et al. [59] in 2005 have

studied RFID tag antennas made from silver ink at UHF. They have compared and analyzed

RFID antennas at UHF when an antenna is made either from silver ink or from copper.

Copper has higher conductivity but it is expensive, while silver ink is not as conductive as

copper but is inexpensive and can be printed in affordable way on thin substrates. Authors

have printed straight dipole and meandered dipole antennas on dielectric substrate using

copper and silver ink. After conducting experiment, the result shows that antenna parameters

and RFID tag performance change differently for different antenna types when copper is

36

replaced with silver ink. Overall, modern nano silver ink materials present an attractive low

cost option for RFID tags for UHF applications.

There has been increasing research on nano sized films for their mechanical and

electrical properties since metal nano films are being used increasingly in the modern

microelectronics and MEMS technology. Also, there are fewer studies on thin films

compared to dielectric thin films. Most of the research result shows that the thermal

conductivity and electrical conductivity of the thin films are less than their corresponding

bulk state materials. In 2006 Zhang Xing et al. [60] made experimental studies of thermal and

electrical properties of platinum nanofilm. In their experiment the platinum film of thickness

15 nm with a length of 8.9 µm, and width of 496 µm is deposited on silicon substrate by

nanotechnology tool called electron beam physical vapor deposition system. After

performing experiment they have drawn the following conclusions: The thermal conductivity

and electrical conductivity of the nano film thickness of 15 nm are much less than those of

the bulk material for the temperature range between 80 K and 340 K. They are 27 %, 10 %,

and 16 % of the corresponding bulk values at 300 K respectively. At 28 nm thickness the

thermal and electrical conductivity increases at the temperature range 80 K to 340 K. In

summary thermal and electrical conductivity increases with increase in thickness of the

platinum nano film.

Apart from nano metal inkjet printing technology for antenna fabrication, there is a lot

of research on antenna using conducting polymer as radiating element that uses screen print

technology for fabrication. Conducting polymers has attracted for their potential applications

in microelectronics. Conducting polymers have advantage of lower surface mass, easy

processing, chemical manipulation for changing the electromagnetic parameters etc over

common microwave conducting materials like copper, silver etc. Hatem RMILI et al. [61] in

2006 have reported the design, simulation and fabrication of rectangular microstrip fed

37

proximity coupled patch antenna for X-band application using conducting polymer called

Pani (polyaniline). The radiating Pani patch is printed by a screen printing technique. The

measured and simulated result shows that Pani Antenna resonates around 10 GHz is

satisfying concerning matching, bandwidth and the gain in comparison to copper based patch

antenna.

Some of the nanotechnological applications such as antenna patch fabrication on

substrate using inkjet print technology are an interesting alternative to conventional

photolithography. The advantages of printing include the ease of mass production, low cost

and flexibility. After printing the patch it is necessary to sinter the patch in order to get good

conductivity and avoiding oxidation. There are different techniques in sintering such as

radiation-conduction convection heating, laser sintering, oven etc. However these techniques

require longer time, costly and complex. Thus there is a clear need for a fast, cost effective

and simple that would allow the sintering of the printed structures by selective heating of

only the printed conductive material. Microwave heating technique is one that fulfills these

requirements. Jolke Perelaer et al. [62] in 2006 have fabricated silver nanoparticles ink strip

lines, parallel lines, squares and antennas of thickness 4.1 µm on Kapton of 100µm substrate,

using inkjet printing technique. After going through microwave radiation sintering, the

measurements indicates, the resistivity of printed structures is 3×10-7

Ωm, which is 5 % of the

value of bulk silver. Also it is observed that this method shortens the sintering time of silver

nanoparticles by a factor of 20.

In 2006, Saeed I. Latif et al. [63] have studied effect of multi-layer copper conductor

on performance of probe fed square ring microstrip patch antenna on a foam substrate. A

square ring antenna is a miniaturized antenna has two edges the inner and outer, where

currents become excessively large and cause excessive ohmic losses, which reduces the

antenna gain. To overcome this problem researchers have used multiple thin copper layers

38

rather than a single layer of thickness ranging from 5 µm to 35 µm in commercial substrates.

The antenna is simulated and recorded directivity for each thickness in steps of 2 µm from 3

µm to 19 µm. The simulated results show the gain was increased with directivity

enhancement of the small antennas. By increasing the stacked copper layer, the resistive

losses decreases, hence the improvement in the gain and directivity.

In 2007, Bong Kyun Park et al. [64] have developed the conductive ink containing

copper nanoparticles with a size of 45 8 nm by polyol process. The copper ink continuous and

smooth lines were printed onto glass substrate. Upon the heat treatment at 325 0C for one hour in

vacuum, the films become very conductive as particles underwent significant sintering. The resistivity

of films was 17.2 × 10-6

Ω cm, which was just about ten times larger than bulk copper‟s

resistivity. This experiment demonstrate copper conductive ink could serve as an attractive

alternative to conventional photolithography for direct patterning conductive patch for

antenna applications at low cost.

Also research is made on antenna made of transparent conductive film for mobile

terminals. Ning Guan et al. [65] in 2007 have fabricated one half of a bow-tie dipole antenna

patch made up of ultra thin transparent conductive film on glass substrate for 2.4 GHz

frequency. The antenna is made up of ITO and FTO, as well as copper as a reference with

different patch thicknesses. The sheet resistivity of ITO film varies from 19.8 Ω/□ to 1.3 Ω/□,

and the one for the FTO films does from 5.7 Ω/□ to 1.9 Ω/□. After experimental investigation

it is found that the gain is lowered from 4.4 dB to 0.2 dB, efficiency increases from 46% to

93 % at 2.4 GHz, as the sheet resistivity of the film decreases from 19.8 Ω/□ to 1.3 Ω/□. The

experiment demonstrates the transparent conductive films can provide a useful means for the

antenna employed in mobile terminals.

U. Schmid and H. Seidel [66] in 2007 have studied effect of temperature on the

electrical performance of titanium/platinum (Ti/Pt) thin films thickness ranging from 24 nm

39

to 105 nm on SiO2/Si substrates. At 300 0C there is decrease in film resistivity independent of

film thickness that is thicker films. At 450 0C film resistivity increases that is highest at low

film thickness. The study assists us in proper and reliable design of metallization systems or

functional thin-film elements operating under high temperature environmental conditions. It

should be noted that researchers have deposited Ti/Pt thin films on SiO2/Si using

nanotechnology tool called electron-beam evaporation system.

In 2008 Theodore K. Anthony [67] has designed, simulated, and fabricated a

prototype 20 GHz co-planar proximity coupled microstrip patch antenna on single silicon (Si)

wafer substrate for military applications. Initially antenna is simulated to resonate at 20 GHz.

The constructional feature of this antenna is it uses silicon substrate with height of 500

micron, dielectric constant of 11.9 and very low conductivity. The antenna structure is copper

metalized to a thickness of 2 micron on Si wafer. The antenna finds application in high data

rate transmission in chip level communication system.

Danideh A. et al. [68] in 2008 have demonstrated use of single FR4 substrate

co-planar proximity coupled microstrip patch antenna that gives wide bandwidth. The

antenna structure and ground lies on the same plane i.e. on top side of substrate, where as

microstrip feed line etched on bottom side of substrate. The antenna is designed to optimized

resonance that gives wide bandwidth with multi frequency resonance.

In 2008 Ning Guan et al. [69] have studied radiation characteristics of two kinds of

antenna namely planar inverted F antenna (PIFA) and monopole antenna, made of transparent

conductive films at 2.4 GHz. The conductive film thicknesses are in several nano meters.

These two antennas are most popular antennas used in small mobile devices. The advantage

of using conductive transparent film antenna is they can be installed on the surface or the

display window of the mobile devices without much visible design problem. The interference

from other electric parts can also be suppressed because of the location of antenna. It is found

40

that the film resistance influences the performance more strongly for the PIFA than for the

monopole antenna due to the cavity-like behavior of the former.

Nano-electromagnetic domain is a rapidly growing field due to nano materials size

and their application in electromagnetic at very high frequencies, ranging from GHz to THz

where wave length is very small. Examples for nano-electromagnetic applications are: nano-

waveguides, nano-antennas, semiconductors, nano scale resonators etc. In 2009, W.G.

Whittow et al. [70] have designed and simulated sheets of nano metamaterials. The

simulation result shows that the nano metamaterials show the behavior of the reflection and

transmission coefficients of an antenna. The resonant frequency of antenna can decrease or

increase depending upon the geometry of nano sheet metamaterials. Based on simulation

result, researchers have deposited few 2 mm×4 mm dipole antennas on 1 mm thick glass

substrate and 60 µm porous dielectric using nanotechnology tool called vacuum evaporation

system. The thickness of silver layer is ranging from 200 nm to 500 nm and on top of it there

is 50 nm gold layers is deposited to prevent silver oxidation. Around 30-40% of the dipole

surface area is covered by holes. The holes can be varied using different fabrication processes

and film thicknesses. The result shows that when gaps are added to a dipole, the resonance

frequency increases logarithmically. When holes are added to a metal disc the resonance

frequency decreases. This helps to design wearable antennas which require light weight,

flexible and to allow skin to breathe.

Matti Mantysalo and Pauliina mansikkamaki [71] during 2007 have studied inkjet

deposited antenna in 2.4 GHz ISM band applications to demonstrate the capability of printed

electronics. The researchers have designed inset feeding type antenna structure with a

dimension of 32 mm × 32 mm on 1.62 mm thickness substrate for 2.45 GHz. One antenna

was manufactured by etching and two by inkjet printing. Printed antennas are attached on top

of the substrates. The printed thick and thin antennas have a thickness of 2.5 µm and 500 nm.

41

The experimental results show that very high conductivities close to those of the bulk metals

were achieved using printed technique. However, the profile of printed structures was much

thinner than that of etched line, which increases their resistance. It was found that antenna

bandwidth remains almost the same. However, the antenna gain is decreased that indicates

decrease in operating range. Also it was demonstrated that as film thickness is less than the

skin depth, printed electronics have relatively good potential for many RF applications.

CNT nano composites are used in patch antenna as a radiating element to enhance

bandwidth. Many researchers have worked on depositing pure CNT arrays directly on copper

patch of the antenna to enhance the radiation parameters. Qi Zhu et al. [72] in 2009 have

studied radiation effect of vertical MWCNT arrays grown on silicon substrate by exciting the

CNT arrays with microstrip patch antenna and patch antenna arrays. The CNT arrays were

grown by chemical vapor deposition method (CVD). The CNT array has very uniform

distributions of height and diameter (20 µm × 20 nm). The authors have constructed a

reference rectangular patch antenna for comparison. From experimental results it is found

that by incorporating vertical aligned CNT arrays with a length of 20 µm, the radiation

pattern and intensities of the antennas are significantly modified.

There has been a growing interest in using conducting polymers (CP) for patch

antennas. The purpose of using CP is to exploit the plastic like material as a radiating patch of

antenna. Akhilesh Verma et al. [73] in 2009 have explored the possibility of using CP called

Polypyrrole (Ppy) for application at microwave frequencies in particular as a radiating patch

on a planar patch antenna. A 2 GHz rectangular probe fed patch antenna is designed. Two

antennas were fabricated: one is with Ppy and other with copper as conducting patch. Both

Ppy and copper were pasted on Plexiglas with glue. The experimental result shows that Ppy

antenna resonates at 2.18 GHz with a gain and conduction efficiency of 5.01 dB and 60%,

where as copper antenna resonates at 2.2 GHz with a gain and conduction efficiency of 6.26

42

dB and 80%. The significance of results is it might be possible to use CPs in passive

microwave applications.

Nanotechnology also offers clean environment friendly manufacturing process, where

conventional fabrication processes like etching copper from antenna produces chemical

wastes. Recently printing silver nano particle paste becomes popular due to its environment

friendly fabrication process. Bo Gao and Mathew M.F. Yuen [74] in 2009 have printed silver

paste as a RFID tag antenna on 50 µm PET films using screen printing technology. Authors

have fabricated two types of antennas, dipole based and quasi-isotropic antennas to evaluate

the effects of skin depth on RFID tag performance. The results show 10 µm thickness tag

antenna presents the minimal turn on power of 22 dBm and 18 dBm which is enough for

most applications. This present thinner printed silver paste RFID tag antenna is a potential

solution for low cost UHF RFID tags.

A.K. Sowpati et al. [75] during 2010 have shown in their research that inkjet printing

of nano silver ink on polyphenylene substrate is able to produce enough conductivity can

produce antenna performance against Rogers copper foil structure. In the fabrication of

antenna they used silver nano ink as conductive radiating part of the antenna. The thickness

of the conductive part is about four times of skin depth at the operating frequency. The inkjet

printing was performed by Fujifilm Dimatix DMP-2831 printer. The measurement result

shows that with five printings of inkjet of nano silver ink can produce even better return loss

was achieved with the reference antenna. The reason is conductivity difference of the copper

foil and printed nano silver ink is not very big. In addition, the skin effect for silver for 2.4

GHz is about 1.3 micron. Thus it confirms that the printing thickness of 5.5 micron should

thus be enough to produce optimum return loss performance. It also confirms that as

thickness increases efficiency and gain also increases up to reference antenna copper patch

thickness.

43

The use of nano materials for antenna applications is increasing over the past few

years. Fabio Urbani et al. [76] in 2012 have reported fabrication of microstrip patch antenna

with an ultra thin iron film as radiating patch. The 10 nm ultra thin iron patch was fabricated

on a double side polished silicon substrate by depositing Fe layer of approximately 10 nm

using resistively heated thermal evaporation system. The researchers have selected aperture

coupled microstrip antenna, since it simplifies the feeding method of the antenna by

overcoming the need to electrically connect the 10 nm ultra thin patch with a coplanar bulk

17 micron metallic microstrip line, which in turn significantly minimizes practical fabrication

difficulties such as ensuring a reliable electrical contact. The feeding technique allows

electromagnetic coupling between patch and feed without physical contact. The fabricated

antenna shows excellent performance in terms of bandwidth. The patch provides the antenna

with a bandwidth of 1 GHz at resonant frequency of 14.5 GHz. They classified these

antennas as Ultra Wide Band (UWB), useful in system-on-chip applications.

In 2010 Akhilesh Verma et al. [77] have reported use of conducting polymers namely

Ppy (Polypyrrole) and PEDOT-PSS (Poly 3, 4 ethylenedioxthiophene Poly Sterene

Sulfonate) as radiating patch of antenna. The researchers have designed and fabricated Ppy

and PEDOT-PSS films of thickness 90 µm and 7 µm printed on 200 µm Arylite substrate on

Rogers substrate. They have selected probe-fed antenna designed for 6 GHz. Also they have

fabricated probe-fed copper based reference antenna for comparison. The experimental result

shows that despite very low DC conductivities and thickness of the CP patches, reasonable

antenna performance at microwave frequencies was observed with relatively low radiation

efficiencies. The result clearly confirms the potential of polymer as antennas.

In low power communication devices such as wireless sensors operating in harsh

chemical or gas environmental areas copper patch of antenna become corrode or get oxidized

and hence degrade in its performance. To avoid corrode or oxidation of radiating part of

44

antenna, many have done research on employing MWCNTs as radiating element instead of

copper patch. Many researchers have demonstrated ability of CNT‟s interaction with

electromagnetic waves. Taha A. Elwi et al. [78] in 2010 prepared MWCNT based ink. There

are several potential applications of these MWCNT inks are in interconnecting

microelectronic chips, RFIDs, transmission lines and patch antennas. The use of MWCNT

ink to fabricate antennas could represent a new way to develop multifunctional antennas

given the good electrical conductivity of the carbon nano structured materials. There are

several methods to make thin films of MWCNT ink such as filtration, spin coating, drying

from solvent, screen printing and ink jet printing. Except ink jet printing technique, it is very

difficult to achieve antenna dimensions and shapes with other printing methods. The authors

have fabricated inset feed type microstrip antennas from MWCNT ink on different substrates

using ink jet process based on a micro spray nozzle controlled by piezoelectric actuation

common in commercial printers. From their experimental results it is found that there is a

remarkable enhancement in the bandwidth ranging from 2.2% to 5.6% as compared to 1.1%

to 3% for their identical copper based antennas. This is 45% more than the copper antennas.

However MWCNT antennas have lesser gain compared to their counterpart copper antenna

due to low conductivity of CNTs. Another important observation made is there is no change

in shape of far field radiation pattern. This research suggest that MWCNT based antennas are

viable for short and medium range wireless communication and sensor networks in

environments which are not suitable for conventional conductors like copper and silver.

Taha A. Elwi et al [79] during 2010 fabricated a dual frequency, square spiral

microstrip patch antenna constructed from MWCNTs ink deposited on a thin flexible FR4

substrate. The fabricated antenna operates at 1.2276 GHz for wearable Global Positioning

System applications and 2.47 GHz for wearable Multichannel Multipoint Distribution

Services. The MWCNT ink is used as radiating patch. Before fabrication the antenna is

45

simulated to evaluate and optimize return loss, matching impedance, resonance frequency,

bandwidth, and far-field radiation pattern. The authors synthesized and processed MWCNT

using chemical vapor deposition system. Then the pure MWCNT is mixed with sodium

cholate to form MWCNT ink. An inkjet printer is used to print antenna structure on flexible

FR4 substrate. The MWCNT patch is fed through an N-type female SMA coaxial cable to the

50 Ω matching point by silver point. Also copper based antenna is fabricated for performance

comparison. The experimental result shows that MWCNT-epoxy antenna resonates at 1.2276

GHz and 2.47 GHz and copper antenna resonates at 1.25 GHz and 2.53 GHz. The

comparison point out that MWCNT-epoxy antenna bandwidth is about 3% which is wider

than antenna made from copper. The MWCNT-epoxy antenna offers larger gain bandwidth

product compared to patch antenna based on copper.

Yijun Zhou et al. [80] in 2010 have developed polymer-carbon nanotube sheets for

realizing conformal load bearing antennas. Polymer is a rubber like structure has good RF

properties like high dielectric constant and low loss tangent, and desirable mechanical

properties like conformal, flexible and lightweight. The antennas built with polymer based

material finds applications in small aircrafts and body worn. However, there is a challenge in

metallization of patch on polymer substrates due to their hydrophobic nature and peeling

under stain or tensile stresses. To address this problem the authors have embedded vertically

aligned carbon nanotubes within the polymer composite to achieve a CNT sheet having high

structural compatibility. The vertically aligned 200 µm × 100 nm apart CNTs are synthesized

by CVD process. The rectangular patch antenna is designed for 2.25 GHz. A 31 mm × 31 mm

CNT sheet is deposited on 56 mm × 56 mm PDMS-MCT polymer substrate using spin

coating. The CNT embedded polymer is cured to form polymer coated CNT sheet. The

experiment is conducted by bent and stretching the antenna. The result shows that the antenna

resonates at 2.25 GHz with a gain of 5.6 dB which is 0.8 dB lesser that of an ideal patch

46

made of perfect electric conductor such as copper. The work demonstrates CNT-polymer

patch antenna is most suitable for conformal and flexible antennas without losing required

radiation properties for an antenna.

Many researchers have studied effect of inkjet printed conductive patch thickness on

antenna performance. In 2010, Virtanen, J et al. [81] have fabricated silver nano ink based

RFID tag using inkjet printing technology on 50 µm thick kapton polymide film. Totally four

layers of patch were printed with each layer thickness of 1 µm thickness. The experimental

results show that as the conductor thickness increases the performance of tag in terms of gain

and efficiency also increases. However after two layer thickness the performance decreases.

Also, the cost become greater than benefits after two layer thickness, since more silver ink

and printing time is needed.

The conductivity and thickness of the radiating patch affects performance of the

antenna. Generally the patch thickness should be at least a couple of skin depths for good

performance. However researchers proved that, planar antennas based on conducting

polymers thickness less than skin depth exhibit acceptable performance despite a low

conductivity. Akhilesh Verma et al. [82] in 2010 have designed 4.5 GHz patch antennas

using copper patch and Ppy polymer patch. The Ppy patch thickness is less than its calculated

skin depth. The experimental studies suggest that reasonable antenna performance is possible.

A lot of study is made on conductivity of copper nanoparticles thin films.

Akihiro Yabuki and Norzafriza Arriffin [83] in 2010 have prepared a 20 nm diameter

copper nanoparticles thin film at low temperature. The copper nanoparticles paste were

coated onto a glass substrate and annealed under various conditions to investigate the effects

of various atmospheric conditions such as air, nitrogen gas at different annealing temperature.

The measurement shows a low resistance of 2 × 10-5

Ω cm which is suitable for most

electronic systems application.

47

In the past few years, the synthesis of copper nanoparticles has attracted much

attention because of its huge potential for replacing expensive nano silver inks utilized in

conductive printing. However the biggest problem in utilizing copper nanoparticles is their

inherent tendency to oxidize in ambient conditions. Shlomo Magdassi, et al. [84] in 2010

have performed a research on preventing oxidation of nanoparticles by coating inorganic

materials such as silica on copper nanoparticles. This works as preventive layer against

oxidation. This opens new possibilities for applications in printed electronics such as printed

antennas, solar cells, RFID tags etc.

Fred Lacy [85] in 2011 has demonstrated experimentally and proposed a theoretical

modelling of the size of an object that can have an effect on its properties. The important

property of any thin film for electrical and electronics application is its electrical resistivity.

The electrical resistivity of a thin film will become larger as the thickness of that film

decreases in size. Further, the electrical resistivity will also increase as the temperature

increases. The electrical resistivity that the material has when it is in bulk form is not the

resistivity that the material has when it is nano sized. It is understood that this change occurs

because the mean free path of conduction electrons is reduced due to increased scattering

effect. So, the electrical resistivity and other properties of thin films may behave differently

than expected if the thickness of the material becomes sufficiently small. Paper in [85] helps

us to model, design and fabricate antenna with ultra-thin (nanofilm in the range 1-100 nm)

patch antenna.

Ashraf Shamseldin Yahia et al. [86] in 2011 have carried out modelling and

simulation studies on nanotechnology based RFID tag antennas with nano copper ink, nano

silver ink and nano gold ink as conductors. They have compared nano-ink antennas and

traditional ones. Also they have discussed inkjet printing technology and its advantages in

antenna production. In traditional lithography process unwanted/excess conductive material is

48

being removed. However, in inkjet printing technology the conductive nano-ink is sprayed in

the form of single ink droplets from printer‟s nozzles to the desired position, therefore no

wastage of conductive material is created. This makes inkjet printing economical fabrication

process and environmental friendly process, because no toxic chemicals are used as in

common etching process. However, the main concern of the antenna designer is the

conductor losses when circuits are produced using printed technologies. The authors have

discussed skin depth dependencies and VSWR variation of nano-ink printed antennas on

frequency. From the modelling and simulation studies, authors conclude that skin depth is

critical in high speed applications and high frequency devices such as microwave antennas.

The patch layer thickness should be sufficiently large. The silver-ink is the best ink to be used

in antenna printing.

In 2011 Gelza M. Barbosa et al. [87] have presented their work on X-band microstrip

patch antennas using carbon nanotubes in the form of buckypaper and silver epoxy

composites added on copper radiating patch. The inset feeding type patch antennas are

fabricated for 10 GHz with a patch dimension of 10 mm by 11.8 mm on Rogers 5880

dielectric substrate of thickness 0.787 mm, after modelling and optimized simulation. The

experimental result shows that reference antenna resonates at 10.34 GHz. The antenna

covered with silver epoxy resonates at 10.35 GHz with a return loss of -9.7 dB. The antenna

covered with MWCNT bucky paper resonates at 10.45 GHz with a return loss of -27.2 dB.

The antenna covered with MWCNT-silver epoxy composite resonates at 10.18 GHz with a

return loss of -16 dB. In comparison MWCNT-epoxy composite present enhanced bandwidth

than other types of antenna, without overall gain loss.

In 2011, Alexander Kamyshny et al. [88] made a review on application of metal based

inkjet inks for printed electronics. The review explain copper, aluminum and silver nano

particle based inks for applications in the development of solar cells, thin film transistors,

49

OLEDs, Electroluminescent devices, RFID tags etc. The paper also explains the common

words that are being used in nanotechnology synthesis and measurements: electrical

resistivity, sintering, nano particle ink preparation and processing etc. It concludes that

copper and aluminum based inks are less developed or have yet to be developed, compared to

silver nano particle ink.

Zhiliang Zhang et al. [89] during 2011 have synthesized high concentration silver

nano particles which are low cost and high conductivity. Silver nano particles conductive inks

were prepared and a series of electro-circuits including RFID antenna were fabricated by

inkjet printer on paper substrate. After thermal treatment at 160 0C for 30 minutes the

resistivity of printed electro-circuits is found to be in the range between 9.18 × 10-8

µm and

8.76 × 10-8

µm. The wireless transmission was achieved with RFID antenna. The results

promise enormous potential for the manufacture of flexible electro-circuits, low cost

electrodes and sensor devices.

In 2011, M.J. Roo-Ons et al. [90] have presented a novel rectangular patch solar

antenna mounted on the surface of s commercially available solar module. The patch

comprises a thin sheet of clear polyester with a conductive coating. The amorphous silicon

solar cells in the module are used as both a photovoltaic generator and the antenna ground

plane. The experimental result shows the antenna provides a peak gain of 3.96 dBi in the 3.4

to 3.8 GHz range without compromising the light transmission in the module. A comparison

is made between copper and transparent conductor in terms of antenna and solar

performance. The measured gain values are appropriate for wireless communications and

sensor networks.

In 2010, Fabio Urbani et al. [91] have reported patch antennas composed of nano

films – chromium or aluminum of 15 nm, and titanium or nickel of 20 nm thicknesses

deposited on silicon substrate for X-band applications. The antenna they have selected was

50

aperture coupled microstrip patch antenna where there is no direct contact between nano

thickness patch and bulk copper microstrip line. The nanofilm patch was excited by

electromagnetic coupling between microstrip feed line and nano film patch. The antenna

structure consists of FR4 bottom substrate and top silicon substrate. The researchers have

fabricated four different antennas with four different ultra thin (nano film) patches:

chromium, aluminum, nickel and titanium – all of equal surface areas. All films are deposited

using thermal and electron beam evaporation deposition systems. Chromium and aluminum

were deposited to 15 nm thickness using thermally evaporation, while nickel and titanium

were deposited for 20 nm thickness using electron beam system. Out of four antennas,

experimental result of aluminum patch is encouraging. The aluminum patch antenna

resonates at 11.5 GHz shows a bandwidth of 660 MHz with a return loss (RL) of -17 dB,

while other antennas classified as resonators since they resonate at 12 GHz above -10 dB and

hence they can‟t meet the definition of antenna. The nano film antennas are attractive for a

wide range of potential communication applications including system-on-chip and inter IC.

Rapid developments in wireless communications coupled with recent progress in nano

structure materials for microwave devices resulted in a growing interest for antenna

designers. Nano scale materials are promising candidates provide new properties that were

not possible in bulk materials. Electrically conductive ink based on nanoscale material is one

such example. In recent years carbon nanotubes (CNTs) are attracted as potential candidates

for electromagnetic radiators due to CNTs fascinating electrical parameters. The ohmic losses

in CNTs are low due to ballistic transport characteristics. There are two types of CNTs: One

is single wall CNT (SWCNT) and other is multi wall CNT (MWCNT). The advantage of

using CNT like MWCNT as conductive ink instead of copper for microstrip patch antenna

gives main benefits like lower mass density and high resistivity against corrosion. In 2012

researchers Taha Elsayed Taha et al. [92] have modeled and simulated a square spiral

51

microstrip patch antenna using MWCNT ink and compared with reference antenna made

from copper. They modeled patch shaped as square spiral trace truncated horizontally on a

FR4 substrate. The proposed antenna operates at 1.22 GHz for wearable GPS applications

and 2.47 GHz for wearable multichannel multipoint distribution services. The simulation

result shows that for 1.22 GHz application MWCNT antenna resonates at 1.2276 GHz with a

return loss of -12 dB against copper antenna that resonates at 1.25 GHz with a return loss of -

13 dB. For 2.47 GHz application MWCNT resonates at 2.47 GHz with a return loss of -27

dB, while copper antenna resonates at 2.53 GHz with a return loss of -13 dB. Hence in

conclusion, MWCNT nearly matches the performance of copper patch antenna.

In 2012, Ahmad Mohammadi et al. [93] have presented the development and design

of electromagnetically coupled (also called proximity coupled) feed patch antenna as a

biosensor. The sensor system consists of a two layer FR4 substrate based circular patch

antenna coated with MWCNTs for absorbing bio-molecules. The best antenna is chosen

based on simulation results. In their work, the researchers used a rectangular plastic cover

with 2 cm thickness plastic cover attached to the top of patch antenna as a liquid holder. The

centre of the liquid holder is drilled around the patch to allow interaction between sensor and

liquid under test. Then ethanol was applied in to the liquid holder at the top of the antenna

faced carbon nanotubes. The key factor to determine resonant frequency change in patch

antenna is the effective dielectric constant of MWCNTs, conductive epoxy, FR4 substrate

and liquid under test is the effective dielectric constant of the whole system. During

experiment it is found that there is a change in the resonant frequency before and after

applying the ethanol liquid on the patch. This shift in frequency indicated antenna with

carbon nanotube can be used as antenna sensor.

Few researchers presented a systematic approach for producing microstrip patch

antennas using state of art inkjet printing techniques utilizing silver nano particles conductive

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ink printed by DMP-2800 Dimatix Fujifilm materials printer. Yahiea Al-Naiemy et al. [94] in

2012 have designed an antenna for 2.45 GHz that is very common band widely used in

wireless systems. The antenna is simulated using CST and HFSS software for performance.

Based on simulation result, the antenna is fabricated using silver nano particles ink by inkjet

printing technology and reference copper patch antenna on Rogers RO 3203 substrate. The

silver ink printed film/patch is cured in the temperature range 1200C to 150

0C for better

conductivity and to avoid oxidation, which may lead to conductivity reduction that degrades

the antenna performance. The experimental results show that silver inkjet printed antenna

resonates at 2.44 GHz with a bandwidth of 80 MHz and gain of 4.6 dB, while copper antenna

resonates at 2.37 GHz with a bandwidth of 41 MHz and gain of 5.9 dB. This literature study

provides an easy to follow optimized systematic methodology for producing microstrip

antennas using inkjet printing technology.

In 2012, Yi Li et al. [95] have reported a direct write inkjet printing technique for

fabricating a flexible antenna on textile for use in smart textile applications such as wearable

systems. The entire inkjet printed 2.4 GHz dipole antenna is constructed by printing a single

conductive silver nanoparticles dispersion ink on three different flexible substrates. Then it is

wired by the silver epoxy to SMA connector for VNA measurements of impedance and

frequency measurements. Measurements show resonant frequency peaks less than 2.45 GHz

due to length of wire connected to SMA connector. This can be corrected by reducing the

length of the dipole antenna. Also, if antenna is bent, the frequency shifts up according to

meander dipole antenna theory. The research concludes inkjet printed stretchable conductive

tracks have been made on stretchable textile.

Recently researchers have reported application of carbon nanotubes in frequency

tuning of patch antenna. Peter J. Burke and Christopher Rutherglen [96] in 2012 have grown

semiconducting carbon nanotube as radiating patch on oxide layer of substrate. The resonant

53

frequency of the antenna can be tuned electrically by adjusting appropriate sections of its

back-gate, thus altering the effective size of the patch antenna and radiation beam direction

can be formed and steered.

Noble metal such as copper thin film on transparent insulating substrate like SiO2 is

technologically important in the power supply electrodes for display included integrated

electron emitter. Copper films are promising and used in many electronic devices. Copper has

become the choice of the next generation interconnection material replacing aluminum too.

Copper has strong advantages such as lower resistivity and stress voiding phenomena

compared to aluminum alloys. The room temperature resistivity of copper is 40% lower than

aluminum. Many researchers have reported on the production of copper thin films using

different methods, while they also modified these film properties such as electrical, optical

and mechanical properties. In 2013, K. Khojier and H. Savaloni [97] have reported physical

vapor deposition to deposit copper thin films of different thickness and have investigated the

dependence of film resistivity and nano structure on film thickness. Copper films of different

thickness between 20 to 270 nm were produced on glass substrate. The result shows that

increase in film thickness causes increase in grain size, roughness, concentration of carriers

and decreasing of resistivity, hall coefficient and mobility. Again, this study helps us to study

the property of copper nanofilm in terms of its resistivity.

Recently it is found that nano particle based materials such as nano particulate inks

made from silver nano particles are promising candidates for printing micro electrodes,

flexible antennas, organic thin film transistors, RFID tags, batteries and bio-circuits.

Researchers Krishnamraju Ankireddy et al. [98] have printed coplanar folded slot antenna on

Kapton substrate and sintered at 240 0C to get better conductivity. The antenna is fed by

SMA connector with a characteristic impedance of 50 Ω that is connected to antenna using

silver paste instead of solder to avoid damaging the printed surface with the hot soldering tip.

54

A reference antenna made of copper also fabricated using traditional photolithography

process. From experimental result it is found that the coplanar folder slot antenna printed on

Kapton showed an excellent performance that matched well with that of the copper reference

antenna. The experimental result helps us to fabricate future flexible printed antennas using

metallic nano-inks.

In 2013 Nicholas A. Vacirca et al. [99] have fabricated dipole antennas made from

onion-like carbon (OLC) and MWCNT films for 2.4 GHz, a commonly used frequency in

wireless applications such as WiFi, WiMax, Bluetooth as well as others. In more recent

literatures, OLC which have large surface area, been studied for THz applications. To create

the OLC and CNT antennas, the films were cut in to two strips of 3 mm width by 30 mm

length. The two strips were arranged with a gap of 2.5 mm and attached to borosilicate glass

slides of 1 mm thickness (ɛ = 4.6), with a small amount of adhesive to form the arms of the

dipole antenna. A gold plated SMA connector was fixed to the glass substrate using hot melt

glue. From experiment it is found that OLC antenna exhibited a lower conductivity with poor

return loss than MWCNT dipole antenna. However CNT antenna had a higher peak gain. In

conclusion carbon film antennas represent a promising alternative to traditional metallic

antennas while maintaining sufficient antenna performance to be used in modern wireless

applications. The very flexible and conformal nature will also extend their application in to

flexible and wearable wireless applications.

In military wireless systems are integrated onto an army vehicle or a soldiers pack,

uniform of handheld device. The antennas for these systems are often visually compromising

and cumbersome to the soldier. Antennas fabricated from standard conductors such as copper

shows tear and wear due to lack of durability and thus are limited in their placement to areas

on the uniform or pack, that see minimal flexing and bending. Many researchers worked on

overcome tear and wear problem by depositing carbon nanotube instead of copper. Steven D.

55

Keller and Amir I. Zaghloul [100] in 2013 have fabricated and measured a variety of CNT

thread and sheet antenna designs, as well as on the development of an innovative

multifunctional CNT patch antenna/gas sensor. By comparing these prototypes to a reference

antenna constructed from copper antenna, the researchers were able to evaluate the benefits

and tradeoffs of employing bulk CNT materials as the radiating elements in army antenna

designs. First, CNT dipole and loop antennas were fabricated, measured, and compared with

copper dipole antenna. The measured results from prototypes are reasonably well with

reference antenna. Next, aperture coupled microstrip patch antenna is employed in order to

avoid physical connection between CNT patch and bulk copper feed line. The patch antenna

constructed from 5 µm thick CNT sheet exhibited 2.05 dBi gain against 5.6 dBi gain of

reference copper patch antenna. The reduction gain suggest that since copper is 17 µm

thickness, it will have more gain, and there is reduction in the performance of CNT based

patch antenna. Currently researchers are working on CNT patch antenna to improve its

performance.

Rabindra N. Das et al. [101] in their literature have presented printable nano

composites that provide a simple solution to build electronic circuits on low cost flexible and

conformal substrates. Various types of nanocomposite printing techniques are explained by

fabricating the nanocomposite on flexible plastics. The result shows that ink-jet printing and

subsequent metal layer is suitable for inductors where as screen or contact printing is suitable

for conductive adhesives for interconnect applications. Capacitors, resistors, ZnO and

magnetic materials can use either ink-jet or screen/contact print process. The result suggests

that printable nanocomposite may be attractive for displays, e-papers, keyboards, RF

structures, medical devices etc.

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2.5 Carbon Nanotube: RF Model and Antenna

Paul L. McEuen et al. [102] in 2002 have studied properties of carbon nanotubes in

terms of their conductivities. The results show that single wall carbon nanotube (SWCNT)

can be classified as metal type and semiconducting type. Metallic types SWCNTs have

conductivities and current densities that meet or exceed the best metals, where as

semiconducting SWCNTs have mobilities and transconductances that meet or exceed the best

semiconductors. This clearly makes them very promising candidates for electronic

applications like in sensing, building FETs and fabricating dipole antennas.

In 2003, P. J. Burke [103] has developed a RF circuit model for single wall carbon

nanotubes. The carbon nanotube is modeled as nano transmission line that includes kinetic

inductance (Lk=16 nH/µm), electrostatic capacitance (CE=50 aF/µm) and quantum

capacitance (CQ=100 nF/µm). From these values the wave velocity in CNT and characteristic

impedance of CNT are computed. The characteristic impedance is found to be 12.5 kΩ.

These values help in modelling carbon nanotube as antenna.

Many researchers have worked on modelling and analysis of carbon nanotube for RF

antenna. G.W. Hanson [104] in 2005 has investigated fundamental properties of dipole

transmitting antennas formed by carbon nanotubes using integral equation. Properties such as

input impedance, current distribution, and radiation pattern have been discussed and

comparisons have been made to a copper antenna having the same dimension. It is found that,

due to properties of the CNT conductivity function, and its relationship to Plasmon effects,

some properties of the CNT antennas are quite different from the case of an infinity thin

copper antenna of the same size and shape. Important conclusions are CNT antennas have

high input impedance and exhibit very low efficiencies.

Many researchers made comparison between CNT and copper in terms of

conductivity at nano thickness level. George W. Hanson [105] in 2006 has modeled carbon

57

nanotube as an infinity thin tube appropriate for the frequencies of interest. The CNTs current

is compared with the current on solid and tubular copper antennas having similar or

somewhat larger radius values. It is found that for radius values on the scale of nanometers,

CNT‟s exhibit smaller losses than cylindrical copper antennas having same dimensions

assuming the bulk value of copper conductivity. Thus if radius values on the order of a

nanometer are necessary, for instance, as part of a nanoelectronics circuit, CNT‟s may be an

appropriate choice as an antenna or interconnect.

Some researchers have studied fundamental properties of dipole antennas formed by

finite length CNT‟s in THz, IR, and optical bands using integral equations utilizing an axial

quantum mechanical conductance. Jin Hao and George W. Hanson [106] in 2006 have

investigated armchair CNT dipole antenna in infrared and optical regime. It is found that,

within a certain frequency span in the GHz-THz range, finite length CNT dipoles resonate at

approximately integer multiples of one-half of a plasma wavelength. Outside of this range,

current resonances are strongly damped. In the optical range, antenna properties are strongly

modulated by interband transitions. Dipole antennas have high input impedances which may

be beneficial for connecting to nano electronic circuits and exhibit very low efficiencies due

to their extremely small radius.

Peter J. Burke et al. [107] during 2006 have discussed some of the properties of

carbon nanotube as microwave and mm-wave antennas. It concludes that the only analytical

theory available for antenna properties actually does not apply at all in the small-diameter

limit assumed. When the diameter is nanometer, the antenna behavior is quite distinct.

In 2006 P.J. Burke et al. [108] presented quantitative predictions of nanotubes and

nanowires as antennas. They have studied nanotube antennas input reactance and resistance,

radiation resistance, as a function of frequency and nanotube length. Also they developed a

circuit model for a transmission line made of two parallel nanotubes which has applications

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for nano-interconnect technology. The study concludes with advantage of nanotube antenna

in terms of better impedance patch between nano devices and free air. However, the

disadvantage is lower efficiency.

In 2007, Prabhakar R. Bandaru [109] has reviewed electrical properties and

applications of carbon nanotube structures. The author has discussed SWCNT and MWCNT

properties like electrical conductivity, superconductivity, thermoelectric, photoconductivity

and luminescence and its applications. The application includes CNT interconnect, CNTFET,

CNT high frequency electronics, CNT field emitters, and CNT biochemical sensors. Finally

the paper concludes that CNTs could be embraced into silicon fold as another nanostructured

material.

Carbon nanotubes are interesting components for further miniaturization of electrical

circuits and can be used as signal transmission lines as well as for antenna elements. Usually

in antenna theory the metallic conductors are treated as perfect electric conductors. This

assumption does not hold at nanoscale dimensions. Here the inherent materials losses are

considerable and impose limitations to copper or aluminum at nanoscale. CNTs exhibit

ballistic transport over length of several µm and relaxation time of about 50 times greater

than in copper. This offers the applicability of CNTs for the transmission and reception of

electromagnetic signals. N. Fichtner et al. [110] during 2008 have investigated carbon

nanotube antennas using thin wire Hallen integral equation (IE). It is found that nanoantennas

either of copper or of CNT exhibit inherently a very high resistance per unit length. However

for CNT a lower resistance may be achievable due to doping of CNTs. The low efficiency of

nano antennas restrict the signal transmission to very short distances as present in e.g. chip to

chip or on-chip communication systems.

Chris Rutherglen and Peter Burke [111] in 2009 present a discussion of the

electromagnetic properties of carbon nanotubes as interconnects and antenna. In the area of

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interconnects, circuit models developed are agree when the realms of application overlap. In

the area of antenna, the topic is too new for there to be many specific predictions of antenna

properties.

Terahertz (THz) waves are the next frontier in science and technology fields such as

radar and microwave communications, far-infrared nonlinear optics, coherent control of

materials, and generation of THz pulse trains. Wang Yue et al. [112] in 2009 have

investigated the properties of THz emission from metallic, single walled CNT dipole antenna

to generate THz radiation based on armchair CNT. In spite of the low emission power, the

CNT antenna attracts much attention and expands the bandwidth of high frequency.

Carbon nanotubes are characterized by slow wave propagation and high characteristic

impedance due to the additional kinetic inductive effect. In 2009, A.M. Attiya [113] used this

property of CNT to introduce resonant dipole antennas with dimensions much smaller than

traditional half-wavelength dipole antenna in THz bands. They conclude that, this property

has less effect at lower frequency bands. The relation between resonant mechanism of CNT

bundle antenna and the surface wave propagation on this bundle structure is discussed. The

complex surface wave propagation has a significant attenuation coefficient at lower

frequency band. This reduces the active part of the dipole length. The lowest frequency that

can be suitable for a CNT antenna is nearly 100 GHz.

In 2009 Wu Qun et al. [114] have investigated the radiation characteristics of metal

single walled zig-zag carbon nanotubes as a dipole antenna at THz wave range. The

numerical results demonstrate that the CNTs antenna can operate in THz wave range. It is

also found that due to the slower wave velocity on the CNTs the conductivity properties of

the zig-zag carbon nanotubes, the CNT antenna exhibits very high input impedance that will

be beneficial to match to high impedance device. Another significant conclusion is the CNT

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antenna exhibit oscillations periodically and much different from the conventional metal thin

wire antenna.

Recently the advancements in graphene (unrolled CNT) based electronics opened

door to electromagnetic communications in the nano scale. In 2010, Josep Miquel Jornet and

Ian F. Akyildiz [115] have analyzed the properties of CNTs as nano-dipole antenna and

graphene based nano-patch antenna. The results show that for a maximum antenna size in the

order of several hundred nanometers, both a nano-dipole and nano-patch antenna will be able

to radiate electromagnetic waves in the terahertz band (0.1 – 10 THz).

2.6 Electromagnetic Simulation Software

IE3D is a full wave method of moments (MoM) based electromagnetic tool used for

the design of 3D and planar structures like microwave filters and patches antennas. In our

research work we have used Mentor Graphics IE3D Electromagnetic simulation software

version 14.65, 2010 [116]. In IE3D we have modeled nanotechnology enabled magneto-

dielectric antenna for size reduction and bandwidth enhancement. Also, we have used IE3D

to model nanofilm (10-9

thickness) as a radiating patch of microstrip patch antenna for

bandwidth enhancement, without change in operating frequency.

2.7 Formulation of Research Problem

From the above detailed literature review, we found the research is done on the

following:

Nanotechnology is being used in developing electronic devices such as sensors, nano

CMOS transistors, memory technologies and wireless devices.

In wireless communication system, nanotechnology is focused on developing planar

inductors, capacitors and electronic microstrip patch antennas for various applications

61

The vital issues for patch antennas are size reduction, good impedance match and

wide bandwidth

Most microstrip patch antenna design for size reduction are based on either use of

high dielectric material (εr > 1 and µr = 1) or optimizing the conductive parts of

antenna. However use of high dielectric substrate increase the Q-factor of antenna and

thus reduces bandwidth. Use of optimized conductive parts results in possible

reduction in radiation efficiency.

To overcome above problem, researchers exploited nanotechnology to create a new

substrate material for antenna, called Magneto-Dielectric, where εr and µr values are

greater than one. For size reduction and bandwidth improvement, magneto-dielectric

material is loaded on the antenna in the form of substrate or superstrate film on the

patch or above the slot in aperture coupled antenna. The loaded magneto-dielectric

film shifts the antenna resonance frequency of the reference patch antenna to lower

frequencies (shifting left) with considerable improvement in return loss and

bandwidth, thus demonstrates antenna miniaturization and bandwidth enhancement.

In developing Magneto-Dielectric substrate, most of the researchers used Nickel-

Zinc-Ferrite and other nanocomposite material.

Also, research is done on altering the antenna patch properties without disturbing

dielectric substrate properties for bandwidth enhancement by replacing thick metal

patch with metal nanoparticles ink, conductive polymers and ultrathin metals.

Study is made on carbon nanotube based antennas.

Through literature survey we observed the following shortcomings in past research

work on nanotechnology enabled antenna development:

In magneto-dielectric material development for antenna, most of the researchers used

only Nickel-Cobalt-Ferrite nanocomposite.

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Magneto-Dielectric for antenna is not modeled for all the possible values of εr and µr

Expensive substrates such as Duroid are used for patch antenna

Nanofilm for antennas are not analyzed, modeled and simulated according to metals

theoretical approaches.

Nanofilms are developed and fabricated only with silver, aluminum, titanium and

Nickel but not Copper.

Most the work on CNT antenna is made in developing theoretical approach and

modelling but less practical approach.

In view of the above observation we propose the following:

Study of nanotechnology in electronics

Study of wireless device namely microstrip patch antenna

Use of new materials for antenna size reduction, enhancement in bandwidth and

improvement in impedance match.

Modelling of magneto-dielectric substrate for all possible values of εr and µr and

simulation of the antenna.

Use of glass epoxy substrate which is low cost and easily available material in the

market

Use of simple available instruments for fabrication and measurements such as

thermally evaporated physical vapor deposition system, screen printers etc.

Based on theoretical approach, develop nanofilm model and simulate the antenna for

radiation performance.

Use of copper as nanofilm and fabrication of prototype antenna.

Further theoretical study on CNT antennas.

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In view of the above discussion, a systematic study of nanotechnology in electronics

is carried out in the following steps:

Study of nanotechnology, techniques and tools.

Study of electronic microstrip patch antenna components: substrate, radiating patch

and feeding techniques.

Study of magneto-dielectric as antenna substrate.

Magneto-dielectric substrate modelling and simulation for antenna performance in

terms of size reduction and bandwidth enhancement using IE3D simulator.

Magneto-dielectric film preparation by mixing ceramic ferrite nanoparticles and

epoxy resin & hardener.

Study on fabricated prototype magneto-dielectric loaded probe fed circular patch and

aperture coupled microstrip patch antennas.

Study of nanofilm/ultra-thin based patch antennas.

Modelling and simulation of silver and copper nanofilm (ultrathin) aperture coupled

and proximity fed microstrip patch antennas in IE3D simulator.

Studies on fabrication of prototype nanofilm antennas using nanotechnology systems

like screen printing, physical vapor deposition and RF-sputtering. Use of scanning

electron microscope to determine the patch thickness.

Experimental studies on antenna radiation performance in terms of resonant

frequency, bandwidth, return loss and gain.

Comparing nanotechnology enabled antenna and standard reference antenna.

Study on Carbon nanotube, its RF model and applications in antenna development.

The next chapter discusses about the methodology, experimental and radiation

measurement setup, vector network analyzer, electromagnetic simulation package IE3D,

nanotechnology tools like physical vapor deposition (PVD) system, RF sputtering system,

screen printing deposition system and scanning electron microscope.