VISVESVARAYA TECHNOLOGICAL UNIVERSITY

JNANA SANGAMA, BELGAUM-590018

A Seminar Report

On

“FUEL CELL TECHNOLOGY”

A Seminar report submitted in partial fulfillment of the requirements for the VIII Semester degree of Bachelor of Engineering in Electrical & Electronics Engineering of Visvesvaraya Technological

University, Belgaum

Submitted by:

SHRUTHI NAIK T A (1RN08EE049)

Under the Guidance of

Ms.Swetha Asst. Professor

Department of Electrical & Electronics Engineering

RNS Institute of Technology

Channasandra, Uttarahalli-Kengeri main Road, Bangalore-560 061

2011-2012

RNS Institute of Technology

Channasandra, Uttarahalli-Kengeri main Road,

Bangalore-560 061

DEPARTMENT OF ELECTRICAL & ELECRONICS ENGINEERING

CERTIFICATE

Certified that the Seminar on topic “Fuel Cell Technology ” has been successfully presented at RNS Institute of Technology by Shruthi naik T A, bearing USN 1RN08EE049, in partial fulfillment of the requirements for the VIII Semester degree of Bachelor of Engineering in Electrical & Electronics

Engineering of Visvesvaraya Technological University, Belgaum during academic year 2011-2012. It is certified that all corrections/suggestions

indicated for Internal Assessment have been incorporated in the report deposited in the departmental library. The Seminar report has been approved as it satisfies

the academic requirements in respect of Seminar work for the said degree.

Ms .Swetha Mrs. Sumathi. S

Asst. Professor Associate Professor and HOD

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DECLARATION

I, Shruthi naik T A [USN: 1RN08EE049], student of VIII Semester BE,

in Electrical & Electronics Engineering, RNS Institute of Technology hereby

declare that the Seminar entitled “FUEL CELL TECHNOLOGY” has been

carried out by me and submitted in partial fulfillment of the requirements for the

VIII Semester degree of Bachelor of Engineering in Electrical & Electronics

Engineering of Visvesvaraya Technological University, Belgaum during

academic year 2011-2012.

Date : Shruthi naik T A

Place : Bangalore USN: 1RN08EE049

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ACKNOWLEDGEMENT

I owe my deepest thanks to Ms.swetha, the Guide of the project, for guiding and correcting various documents of mine with attention and care. She has taken pain to go through the report and make necessary correction as and when needed.

I would also thank my Institution and my faculty members without whom this project would have been a distant reality. I also extend my heartfelt thanks to my family and well as friends for their full hearted support.

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Table of ContentsAbstract.................................................................................................................1

1.Introduction........................................................................................................2

2.Landmines..........................................................................................................3

3.Mine Types........................................................................................................4

Anti-tank......................................................................................................4

Anti-personnel.............................................................................................4

Chemical type:.............................................................................................4

4.Recent Improvements in Landmine Technology...............................................6

Scatterable mines.........................................................................................6

Hard to detect landmines.............................................................................6

Blast resistant mines....................................................................................6

Magnetic, geophonic, seismic, photosensitive fusing.................................6

Off-route, wide area and anti-helicopter mines...........................................7

Controlled “smart” minefields....................................................................7

5.Mine Detection Techniques...............................................................................8

Ground penetrating radar (GPR):................................................................9

X-ray backscatter technology:...................................................................10

Infrared imaging system:...........................................................................15

Acoustic/seismic detection:.......................................................................16

Biological detectors or Biosensors:...........................................................17

Nuclear quadrupole resonance (NQR):.....................................................18

6.Conclusion.......................................................................................................21

References...........................................................................................................22

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Abstract

A literature review of the technologies being investigated for the detection of non-metallic landmines has been conducted. Although several approaches, at various stages of research, have been identified as having potential, no single approach is currently capable of operating in all environments nor against all types of mines.

This report describes the latest research being undertaken in the field of landmine detection. Of particular interest is research into the detection of non-metallic anti- personnel landmines. The problem of detecting these small landmines is not trivial and although currently no solution is available, many new technologies are under investigation. The most promising technologies that have been identified for future application in landmine detection are: ground probing radar, synthetic aperture radar, X-ray backscatter, electro-optical imaging, differential acoustics and nuclear magnetic resonance/ nuclear quadrupole resonance.

It is most unlikely that a panacea in the form of a single detector will be found. A more probable outcome is for a combination of several detectors, selected for a particular application, to be deployed in the search for the landmines. This 'super' detector would require image processing to provide shape information. Future research should therefore be directed to developing the identified technologies and to study means of combining the individual output data to enhance the system detection capabilities.

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Introduction

The landmine problem requires a multi-faceted approach. It is not only a technological problem, it is also a political one. Efforts to clean up landmines already in the ground are futile while they continue to be placed twenty times faster than they are being removed. Landmines are inexpensive and far too readily available. It is estimated that there are 300 million stored in warehouses awaiting sale and deployment. Many of these are in countries with very active arms exporting industries.

Canada is leading a political initiative to bring about a worldwide ban on anti-personnel landmines. Even if that initiative is successful, it is not realistic to expect it will completely stop landmines from being produced and used, since they are so inexpensive and easy to make. However, the scope and magnitude of the problem would be greatly reduced if a serious effort were to be made now.

As of 1999, the only artificial systems employed by the U.S. military for the detection of buried landmines were metal detectors. Although these detectors can sense as little as 0.5 grams of metal, and thus maintain a high detection probability, they cannot distinguish between a firing pin or a piece of scrap metal. Furthermore, modern landmines can be constructed without metallic parts and would therefore not be detected with current technology. An ideal sensor would be able to detect the actual explosive material (e.g. TNT, RDX) rather than detect parts used in the construction of the landmine. It would need to be sensitive but also specific so as not to result in a large number of false positive hits that would slow down the clearing process.

The US State Department has concluded that “The impact of landmines on a developing economy is tremendous... it is common to lay mines around key economic installations such as electric plants and power lines, water treatment plants, main roads, major market centers and government buildings. These are key installations required to support a rebuilding economy...as a consequence, economic reconstruction is delayed.”

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Landmines

An explosive device which lay dormant for a long period of time, and then it is suddenly triggered into action by the presence of an unsuspecting a target.

The triggering action may be simple or complex. Stepping on a mine and applying pressure to the initiating mechanism provides a simple trigger. A more complex trigger is associated with a magnetic or seismic detector incorporated in the mine fuse. Whatever the triggering mechanism, it is the difficulty in detecting the precise location of a mine and the inability of a mine to differentiate between friend and foe that makes this weapon extremely dangerous. In addition, as traditional designated minefields are becoming more common, the hazard is increased.

The danger associated with landmine continues into the post war period. The proliferation in the use of landmines in places such as Cambodia, Somalia, the Middle East and Afghanistan has resulted in an unprecedented problem. It is estimated that to clear the land mines from Afghanistan alone using the present labor intensive procedures would take many years. For the 300 civilians that are killed or maimed per month that is too long a time.

The enormity of the problem is that the detection of landmines presents in both a conflict and in peace time necessitates that improved techniques be developed to locate these landmines. Presently, the usual approach to mine detection relies on careful mine sweeping employing metal detectors and magnetometers. If the existence of a mine is suspected the region is prodded with a non-metallic probe to verify the exact location of the mine. The procedure is labor intensive, tedious, time consuming and hazardous. In addition, the emergency of low metal content mines has reduced the practicality of these techniques. Plastic mines and the proposed future case less mines will render these techniques useless.

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Mine Types

Landmines can be divided into two distinct groups:

Anti-tank

Anti-personnel

An anti-personnel mine is normally buried under a small amount of soil (<20mm), covered by grass and twigs, or lying on the ground surface. Anti-tank landmines may be laid on the surface or buried to depths of approximately 100mm.

An anti-personnel mine can be as small as 60mm in diameter and 60mm in height. An Anti-tank mine is much larger with a diameter at 200mm and a height of over 100mm. these differences affect the ease with which each of these types of mines can be found.

An anti-personnel mine is designed to kill or maim dismounted troops where as an anti-tank mine is designed to destroy or disable track or wheeled vehicles. Thus we see that anti personnel mine are more dangerous and destructive in nature.

There also exists a third kind of mine:

Chemical type: It is mainly designed to dispense smoke, fumes or more dangerous biological or chemical agents, which may cause dizziness or temporary damage. Severe mines might also cause death. Thus this kind of mines cannot be underestimated.

Anti-personnel mines came into widespread use during the Second World War. They were intended to stop the theft of anti-tank mines. Anti-tank mines were intended to destroy battle tanks, but they could be easily seen by foot soldiers, who stole them and implanted them in their own minefields. Anti-tank mines were originally unexploded artillery shells with their fuses exposed. The first

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anti-personnel mines had the capacity to explode with the weight of a foot. During the Cold War, a number of technological advances were made and the use of these weapons spread.

Anti-personnel mines are not indispensable military tools. According to 1996 RED CROSS study, military experts examining 26 wars where anti-personnel mines were used concluded that mines did not lead to a strategic advantage in war. The reality is that mines do more to create fear and cause suffering in civilian populations than they do to deter the movement of soldiers. According to the United Nations, landmines are at least 10 times more likely to kill or injure a civilian after a conflict than a combatant during hostilities. Once mines have been laid, they are completely indiscriminate in their action.  Unless cleared, they continue to have the potential to kill and maim long after the actual fighting has ceased.

In addition, AP mines are often used by warring parties to purposefully induce terror in villages and communities. This is a far stretch from the stated defense uses of AP mines and it affects civilians already caught in the crossfire of surrounding battles.

The major producers of anti-personnel landmines in the last 25 years have included the United States, Italy, the former Soviet Union, Sweden, Vietnam, Germany, Austria, the former Yugoslavia, France, China and the United Kingdom. The most commonly found mines around the world were from China, Italy and the former Soviet Union.

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Recent Improvements in Landmine Technology

As better, more sophisticated mines are developed, their detection and neutralization become more complex and dangerous. A wide variety of anti-personnel landmines currently exist, necessitating the development of extremely complex detection devices.

Scatterable mines : Scatterable mines can be deployed remotely using artillery or aircraft. This reduces the time and labor required to deploy a surface-laid minefield. In battle, troops can be easily surrounded by scatterable mines. Improvements in sensors and warheads have resulted in scatterable mines with higher kill probabilities. The scatterable mines themselves are fitted with self-neutralizing features which cause them to detonate automatically after a pre-set time delay. Unfortunately these light weapons, as with all landmines, can shift during weather changes. Since scatterable mines are not laid in marked rows, they are extremely difficult to plot and locate in the event that the self-neutralization feature is not included or fails.

Hard to detect landmines : Many modern mines are made of plastic or other non-metal materials, with minimal metal content. While the technology exists to detect even the smallest traces of metal, this level of sensitivity results in a very high rate of false alarms in mine detection. In some mine detectors, the mineral content of certain soils can mask the minimum-metal landmine, limiting the usefulness of a hand-held metal detector. To date, there is no simple, inexpensive solution.

Blast resistant mines : Some mines have been constructed to resist explosive shock, thus making them more resistant to neutralization by explosion.

Magnetic, geophonic, seismic, photosensitive fusing : Sensors that can select targets for destruction have been introduced into mines. This complicates their removal. For example, the MI mine is fused by close proximity to the vehicle’s metallic body. The vehicle wheels or tracks do not have to pass directly over the mine. The mine can be placed in the centre of the road so that it explodes underneath the centre of the

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vehicle when the vehicle’s body passes over it. The use of multiple sensors makes it even harder to fool or decoy the mine.

Off-route, wide area and anti-helicopter mines : These types of mines can also be well hidden and camouflaged. Their detection has not been addressed by any current system. These mines are designed to fire against the side of a target as it passes within sensor range. Off-route anti-personnel mines can be particularly dangerous to deminers because they are typically designed to project a field of fragments that can injure or kill whole groups of people. Improved detection systems for demining will have to cover significantly more ground, especially around roads and paths where off-route mines are used.

Controlled “smart” minefields : Mines are under development which use electronic command to allow more control over the minefield, with sections being turned off and on. Jamming signals, access to electric power and high failure rates make these less effective.

Mine Detection Techniques7

Metal detectors were first used, after their invention by the Polish officer  Józef Kosacki. Allies used his invention, known as the Polish mine detector, to clear the German mine fields during the Second Battle of El Alamein when 500 units were shipped to Field Marshal Montgomery.

The first step in manual demining is to scan the area with metal detectors, which are sensitive enough to pick up most mines but which also yield about one thousand false positives for every mine. Some mines, referred to as minimum metal mines, are constructed with as little metal as possible - as little as 1 gram (0.035 oz) - to make them difficult to detect. Mines with no metal at all have been produced, but are rare. Areas where metal is detected are carefully probed to determine if a mine is present; the probing must continue until the object that set off the metal detector is found.

Various detection technologies are currently used, each with limits or flaws. Dogs and other "sniffers" have high ongoing expenses, are subject to fatigue, and can be fooled by masked scents. Metal detectors are sensitive to metal mines and firing pins but cannot reliably find plastic mines. Infrared detectors effectively detect recently placed mines, but they are expensive and limited to certain temperature conditions. Thermal neutron activation detectors are accurate but are large for field use, slow, and expensive. In early attempts, ground-penetrating radar was sensitive to large mines, had good coverage rate at a distance, and with signal processing, could discriminate antitank mines from clutter such as rocks beneath the ground surface. This type of radar, however, remains expensive, cannot detect antipersonnel mines because its resolution is too low, and frequently records false alarms from clutter sources.

The major innovative techniques are:

Electromagnetic methods

Acoustic/seismic methods

Chemical vapor detection methods

Bulk explosives detection methods

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Ground penetrating radar (GPR):

GPR sensor, also used for landmine detection, operates by transmitting pulses of ultra high frequency radio waves down into the ground through a transducer or antenna. These GPR sensors have the advantage of having the capability to detect plastic cased mines. The transmitted energy is reflected from various buried objects or distinct contacts between different earth materials. The antenna then receives the reflected waves and stores them in the digital control unit. The ground penetrating radar antenna (transducer) is pulled along the ground by hand or behind a vehicle. When the transmitted signal enters the ground, it contacts objects or subsurface with different electrical conductivities and dielectric constants. Part of the ground penetrating radar waves reflect off of the object or interface; while the rest of waves pass through to the next interface. The control unit present in the antenna system registers the reflections against the ground surface and then amplifies these signals.

However, the presence of clutter in the mine data hinders the detection accuracy of landmines. The clutter varies with soil and environmental conditions and leads to false alarms in mine detection. Therefore it becomes necessary to overcome the clutter effects when processing the GPR data for detecting small, shallow objects. Other radar approaches include generating continuous frequencies in a narrow band or bands, either by discrete steps, continuous sweeping or chirping (a short burst of sweep frequencies). Synthetic aperture radar (SAR) utilizes multiple antenna locations to improve resolution of the resulting image, essentially creating a larger antenna from multiple smaller antennas. Bi static impulse radar emits a short burst of energy which incorporates a broad range of frequencies on a single transmit antenna.

Kempen and Sahli together proposed an ARMA model for clutter estimation. The technique models the GPR signal return as given in the equation below

Erec'd (k) E

r*d (k) * (hc (k) ht (k)) n

This represents the relationship between the radiated electric field and the received one, where hc (k) and ht (k) are the impulse response of the clutter and

target, respectively and n represents the measurement noise. The removal of Erad (k) the emitted signal, by deconvolution is the first step in the algorithms.

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This deconvolution can be performed after the clutter reduction. The technique then estimates a small amount of known clutter samples with the ARMA model. Kalman filtering can also be used to estimate the parameters of the clutter, where the parameters are considered as being constant with some fluctuations. The Kalman filtering method was found to give better results, reducing most of the clutter to zero, while preserving the shape of the original signal.

Though several advances are made in the Sensor industry, Ultra wideband GPR sensors have been accepted as popular radar for the detection of landmines. GPR systems are usually of two types: Vehicle-mounted and Hand-held GPR systems. The vehicle mounted GPR systems attaches the GPR and EMI sensors in the front of a vehicle and collects the data as the vehicle moves. The vehicle has a constant moving speed and relatively stable sensor to ground distance so that the mine signature is consistent. Handheld systems have GPR sensors located at the tip of a hand-held unit. The background characteristics in the hand-held GPR sensors are non stationary and vary with soil conditions and soil types.

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THE IMPULSE GPR SYSTEMImpuls

egenerator

tx

processorVisual

display

A/D conve

rtor

Pulse extender

rx

landmine

Linear Prediction technique has been proposed by Ho to model the GPR data in the frequency domain. The linear prediction model is given by the following equations:

Where x(n) is a vector sample of the GPR data at location n and P is the prediction order, X (n-1) = [x (n-1), x (n-2) x (n-P)] is a collection of P past input vector samples and a(n) = [a1(n), a2(n)aP(n)] T is a vector of the linear prediction

coefficients at location n. the linear prediction coefficients are obtained by minimizing є H є, giving

Where the superscript H represents the complex conjugate transpose operation. The resulting error is given by

weighting matrix can be used to find the LP coefficients to improve performance.

The advantage of using frequency domain techniques in that sub banding can be used to improve the detection accuracy of the system. Sub banding decomposes each frequency domain vector sample x (n) into M frequency bands that produce test statistic i'(n) for each sub band. The resulting test statistic is

obtained by taking the geometric mean of M test statistics as given by

where i'(n) represents the test statist*c for each sub band index i and (n) represents the

resultant test statistic .

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Flowchart showing the basic working of a GPR system

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X-ray backscatter technology:

By passing the photons through the object the detection of buried landmine can be done by x-ray. The production of high resolution image of buried landmine resulted because of the wavelength of x-ray variety in compare with the size of landmine. The principle of detection by x-ray can be done by passing the photons through the object and the backscatter of x rays may still be used to provide information about buried irradiated objects. The backscatter exploits the fact that mines and soils have slightly different mass densities and effective atomic numbers that differ by a factor of about two. To detect buried object it is necessary to use low-energy incident photons, but soil penetration of photons backscatter devices is poor. This limits detection to shallow mines whose depth is less than 10 cm deep. Also the time required to obtain surface image is long. The x-ray technique is sensitive to source/detector standoff variations and ground-surface fluctuations. Furthermore it is difficult to achieve high spatial resolution by x-ray.

The underlying basic principle being:

When X-rays pass through matter they will be attenuated, i.e. absorbed or scattered. The probability of scattering is in the back direction. This probability depends inversely on the absorption power of the material to the incident and to the backscattered x rays. Organic materials typically absorb only a small fraction of the x rays, so that the scatter probability is high. Metals typically are strongly absorbing, and the scatter probability is low. Thus, organic materials are bright and metallic objects are dark in the image.

The major advantages of this method are as follows:

1.The information depth is sufficient to detect all regularly placed mines.2. The XBT is able to detect metal-free landmines also along with metallic mines. 3. The landmines buried in a variety of soil conditions including various types of vegetation will be detected with XBT.

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The schematic diagram shows an x-ray back scatter system

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Infrared imaging system:

Infrared images of sufficient temperature and spatial resolution to detect anomalies in the ground introduced by the presence of a landmine are commercially available from numerous sources. All bodies emit infrared radiation that is related to the temperature of a body. In order to detect objects using a thermal imaging system a difference in the emitted infrared radiation is required. This can be caused by either a temperature difference between the object and the background or an emittance difference of bodies at the same temperature.

The thermal properties of mines are different from the surrounding medium. This means that a contrast can be expected for surface laid mines when the environment and weather conditions are favorable. For buried mines the contrast occurs due to disturbances in the ground conditions. An object buried in soil change the conditions in the ground. The presence of an object alters the migration of water, which introduces a change in thermal conductivity and heat capacity, as these properties are dependent on the moisture content.

The infrared imagery depend on landmine type, soil type and compaction, moisture, shadow and time of day. However, over the long term the thermal properties of the disturbed soil will return to their natural state. This means that after mines have been buried for a long period of time, the only ones that can be detected are those that are buried within 10 cm of the surface. Also, vegetation will obscure the ground surface and dissipate thermal contrast making it difficult to detect by IR.

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Acoustic/seismic detection:

Acoustic-to-seismic wave-coupling approach to detect buried land mines. Acoustic sound waves penetrate the soil surface to generate seismic waves within the soil.

These seismic waves cause the mine to vibrate and resonate, producing a displacement velocity field at the ground surface above the mine. This displacement can be measured by a laser vibrometer or UHF radar

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Biological detectors or Biosensors:

The biosensor, or artificial dog nose, which identifies mines has now a new and civilian owner, Biosensor Applications Sweden AB, based in Orebro. The company has considerably strengthened its financial resources, currently by 5 million US dollars, and intends to raise further capital on the stock exchange. 

Bofors, the arms company, started development of the biosensor in 1995. Investing about 5 million US dollars, within two years the company quickly developed the first prototype. In this prototype, an apparatus collects 100 litres of air which are then concentrated to a drop of water. The biosensor then "sniffs" the drop to tell whether it contains explosives. Finally, a computer gives the results. 

Biosensor Applications plans to have a second generation prototype ready in 1999, which will then be subjected to extensive testing and verification. The prototype can identify TNT, the explosive in by far the most anti-personnel mines in the world. 

Mine dogs are very useful but have drawbacks. The dogs must be trained, they can make mistakes and they can work for only a short period at a time. This is where the artificial dog nose comes in--equipment which can be used round the clock and with falling production costs. The biosensor is estimated to cost around 30,000 US dollars. 

Biosensor Applications have begun cooperation with the mine clearance company Mechem in South Africa, but the system will also be available for purchase by Non Governmental Organizations (NGO) and governments. 

Biosensors technology can also be used to detect narcotics and the kinds of explosives which may be used by terrorists at airports, for example. These applications will probably be more lucrative for the company. But the first artificial dog nose is designed to identify mines. 

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Nuclear quadrupole resonance (NQR):

In NMR, nuclei with spin ≥ 1/2 have a magnetic dipole moment so that their energies are split by a magnetic field, allowing resonance absorption of energy related to the difference between the ground state energy and the excited state. In NQR, on the other hand, nuclei with spin ≥ 1 , such as  14N, 35Cl and 63Cu, also have an electric quadrupole moment so that their energies are split by an electric field gradient, created by the electronic bonds in the local environment. Since unlike NMR, NQR is done in an environment without a static (or DC) magnetic field, it is sometimes called "zero field NMR". Many NQR transition frequencies depend strongly upon temperature.

Any nucleus with more than one unpaired nuclear particle (protons or neutrons) will have a charge distribution which results in an electric quadrupole moment. Allowed nuclear energy levels are shifted unequally due to the interaction of the nuclear charge with an electric field gradient supplied by the non-uniform distribution electron density (e.g. from bonding electrons) and/or surrounding ions. The NQR effect results when transitions are induced between these nuclear levels by an externally applied radio frequency (RF) magnetic field. The technique is very sensitive to the nature and symmetry of the bonding around the nucleus. The energy level shifts are much larger than the chemical shifts measured in NMR. Due to symmetry, the shifts become averaged to zero in the liquid phase, so NQR spectra can only be measured for solids.

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Schematic view of NQR detection.

14N spin inside a landmine explosive is excited by RF wave, and then emits NQR signal.

When RF wave with a specific frequency is irradiated, the wave is adsorbed by the nuclear spins and then re-emitted after the irradiation. Equation (1) shows the NQR Hamiltonian of 14N, which is the resonant spin in NQR landmine detection.

Q is the nuclear quadrupole coupling constant of the resonant spin. IZ , IY and IZ

are the spin operator and VXX,VYY and VZZ are the electric field gradients around the spin to each directions. Since the electric field gradient is unique to each molecule structure, NQR frequency is also unique to each molecule.

One major concern in development of a NQR sensor is its sensitivity to the NQR response of a given mass of explosive. The objective is to have the capability to detect small quantities of explosives at maximum distances from the antenna. The sensitivity of an NQR sensor is dependent on the pulse sequence parameters (pulse peak amplitude, width and spacing, and number of pulses), the transmitted carrier frequency, the characteristics of the receive antenna (thermal noise, gain and ratio of antenna diameter to explosive

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diameter, similar to a solenoid “filling factor”) and receiver electronics (thermal noise in preamplifiers). Since the NQR signal voltage induced on the sensor decreases rapidly with increasing axial distance between the receive antenna and the explosive, the antenna should be designed to be as close as practical to the explosive. For a confirmation sensor, the antenna can be placed to rest on the ground directly over the mine. However, a priori knowledge of the burial depth (i.e., soil overburden) and location of a buried mine will be imprecise. The uncertainty in depth is dependent on the tactics used by those employing the mines. The location uncertainty is due to limitations of the primary sensor suite, which results in both cross-track and down-track errors. The sensor must be designed (e.g., selection of antenna diameter) to accommodate these uncertainties. Also, the average temperature of the main charge explosive in the mine must be estimated and input to the sensor for determining the optimal carrier frequency and pulse sequence parameters for transmission. An accuracy of about + 5ºC is needed. The average temperature is used since the explosive will have a temperature gradient across it due to the difference between the surface temperature and the temperatures at various depths in the ground caused by solar heating.

Experiments are being designed at the U.S. Army NVESD NQR laboratory to compare two fundamentally different NQR antenna designs; antennas comprising of low and high inductance. A comparison of sensitivity to received NQR signal as well as susceptibility to electric fields and practical design issues will be performed between a typical low inductance and high inductance antenna. Another concern in development of a NQR sensor is its ability to discriminate RF noise and interference from the NQR signal. Experiments are being designed to improve the isolation of NQR single sided antennas from RF noise and interference whilst maintaining maximum NQR signal sensitivity. Investigations as to how best to mitigate RF noise and interference using a passive NQR antenna and an extra receive channel digitizer will also be undertaken.

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Conclusion

After having known all the technologies stated above being investigated for the detection of non-metallic landmines, we infer a few things. The most important of them being that no approach is currently capable of operating in all environments nor against all kind of mines. Thus the requirement is for a combination of several detectors, selected for a particular application to be deployed in the search for the landmines. This would enhance the detection capabilities.

All of the above technologies have operational limitations which may include poor penetration in particular soil types (ground probing radar, synthetic aperture radar, differential acoustics), inadequate discrimination in background clutter (ground probing radar, synthetic aperture radar, electro-optical imaging, differential acoustics and nuclear magnetic resonance/nuclear quadrupole resonance), height sensitivity (ground probing radar, synthetic aperture radar, X-ray backscatter, and differential acoustics), size (synthetic aperture radar, X-ray backscatter, electro-optical imaging), and cost (particularly synthetic aperture radar and X-ray backscatter). To alleviate these constraints, two approaches have been proposed. By operating detectors in conjunction, the strengths of a particular detector may be able to compensate for the weaknesses of another detector. This could also help to reduce the false alarm rate. The chosen detectors would depend on the specific environmental constraints. Such a marriage of detectors will require an increased effort into data fusion research so that the information gained by each detector can be efficiently and effectively combined. It should not be forgotten that many metallic landmines still remain to be found and therefore advanced metal detectors should continue to be a part of demining operations.

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References

www.collegeseminars.com www.ndt.net www.acoustics.org “A REVIEW OF LANDMINE DETECTION” by J.A.WASCHL

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