DesignofNovelS-ShapedQuad-BandAntennafor MedRadio/WMTS

Hindawi Publishing CorporationInternational Journal of Antennas and PropagationVolume 2012, Article ID 564092, 12 pagesdoi:10.1155/2012/564092

Application Article

Design of Novel S-Shaped Quad-Band Antenna forMedRadio/WMTS/ISM Implantable Biotelemetry Applications

Chih-Kuang Wu,1 Tsung-Fu Chien,2 Chin-Lung Yang,1 and Ching-Hsing Luo3

1 Department of Electrical Engineering, National Cheng Kung University, Tainan 701, Taiwan2 Department of Electrical Engineering, Southern Taiwan University, Tainan 710, Taiwan3 Department of Electrical Engineering and Institute of Nanotechnology and Microsystems Engineering,National Cheng Kung University, Tainan 701, Taiwan

Correspondence should be addressed to Chin-Lung Yang, [email protected]

Received 8 April 2012; Revised 31 May 2012; Accepted 3 June 2012

Academic Editor: Hon Tat Hui

Copyright © 2012 Chih-Kuang Wu et al. This is an open access article distributed under the Creative Commons AttributionLicense, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properlycited.

A novel S-shaped quad-band planar inverted-F antenna (PIFA) is proposed for implantable biotelemetry in the Medical DeviceRadiocommunications Service (MedRadio) band (401–406 MHz), Wireless Medical Telemetry Service (WMTS) band (1427–1432 MHz), and industrial, scientific, and medical (ISM) bands (433-434 MHz and 2.4–2.4835 GHz). The proposed antennareveals compact dimension of 254 mm3 (10 × 10 × 2.45 mm3) and is composed of three substrates and a superstrate, which areconstructed from an S-shaped radiator (layer 1) and two twin radiators of spiral structures (layer 2 and layer 3). The optimalantenna characteristics were measured in the ground pork skin, and the measured bandwidths are 150 MHz for the MedRadio andISM bands (433 MHz), 52 MHz for the WMTS band, and 102 MHz for the ISM band (2.4 GHz), respectively. The characteristicsof proposed antenna are enough to support the applications of implantable body area networks (BAN) for biotelemetry and cancompletely cover main available frequency bands of BAN for biotelemetry below 3 GHz.

1. Introduction

Recently, researches of the implantable biotelemetry for earlydiagnosis of diseases and monitoring various physiologicalparameters had been reported. For such a biotelemetrysystem, these implantable antennas are applied to establishwireless communication links between implantable medicaldevices and exterior instruments for biotelemetry applica-tions. These wireless communication links were operated atseveral frequency bands, and all these bands were presentedin body area networks (BANs) [1]. In addition, in recentyears, as an emerging ICT technology, BAN had caughtsignificant attention. One of the many applications of BANis in medical environment where conditions of patients arecontinuously monitored in real time. The range of medicaldevice and systems being implanted into the human bodyis increasing rapidly. Among literatures, an intraocularimplantable antenna [2] and a conformal ingestible capsule

antenna [3] were investigated at Wireless Medical Teleme-try Service (WMTS) band (1.4 GHz). The implantableantenna for intracranial pressure (ICP) monitoring [4] andImplantable slot dipole conformal flexible antenna [5]were presented for industrial, scientific, and medical (ISM)band (2.45 GHz). Planar antennas operating at the Med-ical Implant Communication Service (MICS) band (402–405 MHz) were discussed in [6–8]. Rectenna applicationof miniaturized implantable antenna [9] was developed forMICS band and two ISM bands (433 MHz and 2.4 GHz).Furthermore, an implantable antenna with pyramidal struc-ture operating at Medical Device RadiocommunicationsService (MedRadio) band (401–406 MHz) and ISM band(2.4 GHz) was performed in [10]. However, as mentionedabove, there are no results of research that can completelycover main available frequency bands of BAN for bioteleme-try below 3 GHz. In addition, the Federal Communications

2 International Journal of Antennas and Propagation

Commission (FCC) created the MedRadio Service incorpo-rating the existing MICS band and including the adjacent“wing” bands at 401-402 MHz and 405-406 MHz.

Therefore, design of an antenna with multiband andgood radiating performance suitable for implanting intohuman body has already become a big challenge for design-ers. In the past literatures, for effectively reducing the volumeof implantable antennas, most of the implantable antennaswere designed by the uses of planar inverted-F antenna(PIFA) structures [4, 6–9, 11]. Hence, in this paper, to meetthe requirements of quad band, a PIFA antenna with S-shaped and two stacked twin spiral stripes was constructedon three layer substrates to lengthen effective current path.Meanwhile, a superstrate was also tightly covered on the topof proposed antenna for avoiding tissue erosion. But in [7–9], for lengthening the current path, the authors used feedpoint to connect layer 1 and layer 2. However, unlike thesereports, we connected layer 1 with layer 2 via short pin andconnect feed point with layer 2 directly to excite more modesand tune the impedance matching.

The proposed antenna with S-shaped and two stackedtwin spiral stripes can excite four resonant frequencies whichwere at MedRadio band, WMTS band, and two ISM bands.The details of proposed antenna design and tuning mech-anism will be discussed in Section 2. For verifying multi-band implantable antenna, the emulating tissue had beendeveloped, such as skin gel [11] and minced pork leg [6]. Inthis paper, owing tothat the characteristics of pork skin aremore similar to human skin, ground pork skin was adoptedas the emulated human tissue to verify the quad-bandimplantable antenna and the measured results were investi-gated. In addition, the electrical properties of ground porkskin will be shown in Section 3. Moreover, the simulated 10 gaveraged specific absorption rate (SAR) satisfies the limita-tion of the American National Standards Institute (ANSI/IEEE) for short-distance biotelemetry [12]. Detail results ofthe proposed antenna structure were simulated and mea-sured in the quad band and presented in Section 4.

2. Antenna Design

2.1. Structure of Antenna. Using the Ansoft simulation soft-ware high-frequency structure simulator (HFSSTM), a novelquad-band antenna was designed for the biotelemetryapplications (MedRadio/WMTS/ISM). As shown in Figure 1,the proposed antenna is constructed with four-layered stackstructures, the substrate and superstrate are all Rogers 3210with the thickness of 0.635 mm, loss tangent of 0.0027, anddielectric constant of 10.2. The proposed antenna is com-posed of a ground plane, three radiating elements (layer 1,layer 2 and layer 3), three substrate layers, and a superstratelayer. In addition, the layer 1 is a radiator of S-shaped stripe,and layer 2 and layer 3 are twin radiators of spiral stripesstructure. The feed point is directly connected to lower partof layer 2, the short pin connect layer 1, and the upper partof layer 2. Layer 1 and the lower part of layer 2 are alsoconnected through via 1. The lower part of layer 2 and layer3 are connected through via 2, and the upper part of layer 2and layer 3 are connected through via 3.

However, for the purpose of tuning the impedancematching of the proposed antenna, the dimension of upperpart of spiral structure in layer 3 (denoted as t) is chosen totune the impedance matching of MedRadio band. Andthe dimension of lower part of spiral structure in layer 2(denoted as f ) is chosen to tune the impedance matchingof two ISM bands. Besides, the hook-shaped radiator locatedon the lower part of layer 3 can be considered as an opencapacitive tuning stub. Hence, by varying the length of hook(denoted as s), the impedance matching of WMTS band canbe tuned.

2.2. Characteristics of Antenna. Figure 2 shows the simulatedsurface current distribution for the proposed antenna. It canbe seen from Figure 2(a) that the current-flow path excitesa fundamental resonant frequency to cover MedRadio band(401 MHz). Moreover, from the surface current distributionof Figure 2(b), it can be seen that the current-flow pathexcites another fundamental resonant frequency to coverISM band (433 MHz). Consequently, utilizing the S-shapedwith stacked spiral strip on PIFA structure can excite dualresonant frequencies and that can achieve wider bandwidthby the combination of the two close resonant frequencies [6].Hence, that can obtain wider bandwidth of 168 MHz (320–488 MHz) at a return loss of 10 dB to cover MedRadio band(401 MHz) and ISM band (433 MHz).

Moreover, from the surface current distribution ofFigure 2(c), it can be found that two current null exist in thecurrent-flow path, this confirms that the resonant frequency(at WMTS band) is the higher-order mode of 433 MHz inFigure 2(b). Furthermore, from the surface current distrib-ution of Figure 2(d), three current null can be found in thecurrent-flow path, this confirms that the mode (at ISM band)is also the higher order mode of 433 MHz in Figure 2(b).

2.3. Principle of Tuning Antenna. As shown in Figure 1, at theupper part of layer 3, it is constructed as a capacitiveloading [13] and simulated return loss of the proposedantenna implanting into pork skin with various t is shownin Figure 3. Clearly, the resonant frequency and bandwidthat MedRadio band (401 MHz) can be adjusted and enhancedthrough changing the magnitude of t. Meanwhile, simulatedreturn loss of the proposed antenna implanting into porkskin with various position of feed point (parameter f ) isshown in Figure 4. Obviously, the position of feed pointcan determine the resonance of two ISM bands (433 MHzand 2.4 GHz) and enhance the impedance matching andbandwidth for ISM band (433 MHz). And the ISM band(2.4 GHz) is the higher order mode of ISM band (433 MHz).However, it is a convenient tuning mechanism for ISMband (433 MHz) and ISM band (2.4 GHz) by changing theposition of feed point (parameter f ). Therefore, the opti-mal parameters (t = 5.5 mm, f = 2.2 mm) were obtainedfor achieving dual-resonant frequencies of 347 MHz and441 MHz, respectively. The wide bandwidth of 168 MHz(320–488 MHz) is achieved owing to the combination ofthe two close resonant frequencies. In addition, changingthe magnitude of parameter s of hook-shaped tuning stub

International Journal of Antennas and Propagation 3

Layer 1

Layer 2 Layer 3

Ground

Ground

Layer 1

Feed

2.54

Substrate

Layer 2

Layer 3

Substrate

Substrate

Superstrate

Short

Via 3Via 2Via 1

10

Feed

10

Via 3

Via 2Via 1

Feed

Via 3

Via 2

1

1

1

1

9.4

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2

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7.5

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8.4

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1.5

1.5

3.7 Feed

0.5

0.5

3.2 Short

Short

Short

Via 1

0.3

0.30.3

0.3

0.3

t0.7

S

f

X

Z

X

Z

Y

Unit: mm

0.8

Y

Figure 1: Geometry of the proposed antenna.

can change capacitance. As shown in Figure 5(a), for WMTSband (1.427 GHz), as the magnitude of parameter s increasesprogressively, the inductive impedance will gradually shift tothe capacitive impedance. As shown in Figure 5(b), for theresonant frequency of WMTS band, changing the magnitudeof s is an effective tuning method, and the behavior of reso-nance shifting does not affect other two resonance frequen-cies of ISM band. Hence, the impedance matching can beimproved by using an open capacitive stub which connectsin shunt with the spiral structure of lower part of layer2. Therefore, the optimal parameter (s = 5.5 mm) wasobtained for achieving resonant frequency of WMTS band(1.427 GHz). In addition, adjusting the magnitude of s canalso tune the resonant frequency to 1.395–1.4 GHz, which isanother spectrum block of WMTS band. Thus, the WMTSband of proposed antenna can be tuned to demandedspectrum block through this tuning mechanism. The four

resonances can be fine tuned by varying the lengths of allspiral stripes to increase or decrease the effective length ofcurrent path and do impedance matching.

2.4. Experiment Setup. The simulated and measured envi-ronment of the proposed implantable antenna is embeddedin the container (55 × 55 × 20 mm3) filled with the groundpork skin. In addition, the proposed antenna is placed at4 mm [14] in depth inside the container. Furthermore, thecoaxial cable is fixed in the cover of container for fixing theembedded depth in the container. The detailed structure anddimension of the container are shown as Figure 6. Themeasured S11 values were obtained by the use of the Agilent8753E network analyzer. And the RF signal generator (SMC100A) and spectrum analyzer (HP N9304B) were usedto measure the received power. As shown in Figure 7, in


Ground

Feed

Feed

FeedVia 1

Via 1 Via 2Via 2

Via 3 Via 3Layer 1

Short

Short

Short

Layer 2 Layer 3

z

zz

z

Y Y

YY

X X

XX

z

zz

Ground

Feed

Feed

FeedVia 1

Via 1 Via 2 Via 2

Via 3 Via 3Layer 1

Short

Short

Short

Layer 3Layer 2

(Hook shapedtuning stub)

XX

X X

Y Y

Y Y

Jsurface (A/m)5.0000e+0014.1553e+0013.4534e+0012.8700e+0012.3852e+0011.9822e+0011.6474e+0011.3691e+0011.1378e+0019.4558e+0007.8584e+0006.5309e+0005.4276e+000

Jsurface (A/m)5.0000e+0014.1553e+0013.4534e+0012.8700e+0012.3852e+0011.9822e+0011.6474e+0011.3691e+0011.1378e+0019.4558e+0007.8584e+0006.5309e+0005.4276e+000

Ground Layer 1

Layer 3Layer 2

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Feed

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Via 1

Via 3Via 3

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Current null

Current null

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z

z

z

z

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Layer 1

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Short

Layer 3Layer 2


Current null

Current null

Current null

X X

XX

Y

Y Y

Y

(a) (b)

(c) (d)

Figure 2: The simulated surface current distribution of the proposed antenna at (a) MedRadio band (401 MHz), (b) ISM band (433 MHz),(c) WMTS band (1.427 GHz), and (d) ISM band (2.4 GHz).

a real environment, the communication link between theimplanted proposed transmitting antenna and the one-quarter wavelength exterior receiving monopole antenna wassetup.

3. The Electrical Properties ofGround Pork Skin

Because the proposed antenna needs to be embedded insideemulating tissue to verify the characteristics of implant forbiomedical telemetry, the specifications of emulating tissuemust be similar to realistic human tissue for measurement ofimplantable antenna. In order to develop a test environmentfor multiband operation, skin gel [11] and pork leg [6] had

been introduced for emulating skin tissue. However, forverifying the multiband antenna, the development of skingels is quite inconvenient due to that one skin gel can onlyused for one special band. And the relative permittivity ofpork leg is much higher than that of human skin, and theconductivity of pork leg is also much higher than that ofhuman skin and muscle.

It measures the relative permittivity and conductivity ofground pork skin in a container, whose volume is 120 ×120 × 45 mm3, by using Agilent 85070E dielectric probe kitand Agilent 8753E network analyzer. The relative permit-tivity and conductivity of the ground pork skin (the testtissue) are measured from 0.1 GHz to 3.1 GHz for 301 fre-quency points. The comparison of relative permittivity andconductivity of the pork skin, skin, and muscle [15–17]


0

−5

−10

−15

−20

0.3 0.4 0.5

Frequency (GHz)

t = 0.5 mmt = 1.5 mm

t = 3.5 mmt = 5.5 mm

S 11

(dB

)

Figure 3: Simulated return loss for parameter of t in pork skin.

0

−5

−10

−15

−20

0.3 0.4 0.5

Frequency (GHz)

S 11

(dB

)

f = 4.2 mmf = 3.2 mmf = 2.2 mm

(a)

0

−5

−10

−15

2.3 2.4

Frequency (GHz)

S 11

(dB

)

2.5 2.6

f = 4.2 mmf = 3.2 mmf = 2.2 mm

(b)

Figure 4: Simulated return loss for parameter of f in pork skin (a) at ISM (433 MHz) band, (b) at ISM (2.4 GHz) band.

is shown in Figures 8(a) and 8(b). And the variability inthe relative permittivity and conductivity of skin, muscle,and pork skin at MedRadio band, WMTS band, and two ISMbands is listed in Table 1. It can be found that the permittivityof ground port skin is close to human skin and very suitable

to act as an emulating tissue. In addition, the simulatedreturn loss of proposed antenna implanted into pork skinand skin is shown in Figure 9, which shows that the simulatedresults are consistent in pork skin and skin. Hence, in thispaper, the ground pork skin was adopted as the test tissue


Table 1: Comparison of electrical properties of tissues at MedRadio, WMTS, and two ISM bands.

TissuesMedRadio (401 MHz) ISM (433 MHz) WMTS (1.427 GHz) ISM (2.4 GHz)

εr σ (S/m) εr σ (S/m) εr σ (S/m) εr σ (S/m)

Pork skin 46.6 0.66 46.5 0.67 42.3 1.08 40.3 1.63

Skin 46.8 0.69 46.1 0.7 39.6 1.04 38.1 1.44

Muscle 57.1 0.79 56.9 0.89 54.1 1.15 52.8 1.71

Relative permittivity: εr ; conductivity: σ .

100

50

0

−50

1.3 1.4 1.5 1.6

Impe

dan

ce (Ω

)

Frequency (GHz)

Re (s = 5.5 mm)Im (s = 5.5 mm)Re (s = 4.5 mm)

Im (s = 4.5 mm)Re (s = 3.5 mm)Im (s = 3.5 mm)

(a)

0

−10

0

0.5 1.51 2 2.5

−20

−30

Frequency (GHz)

S 11

(dB

)

s = 3.5 mms = 4.5 mms = 5.5 mm

(b)

Figure 5: Simulated return loss for parameter of s in pork skin (a) impedance, (b) S11.

4 mm55 mm

55 mm

Coaxial cable

Hot melt adhesive

Shrink tube

Filled with groundpork skin

Antenna

Quartz glass(thickness of 1 mm)

Seal tape(isolation)

Figure 6: The structure and dimension of the container.


1 m

Proposed antennaembedded inside pork skin

RF signal generator(SMC 100 A)

Spectrum analyzer(HP N9304B)

Figure 7: Measurement of received power at 1 m away from the proposed implanted antennas (delivered power is 1 mW).

0 0.5 1.51 2 2.5

Frequency (GHz)

3

SkinMusclePork skin

80

70

60

50

40

30

Rel

ativ

e pe

rmit

tivi

ty

(a)

0

0

0.5

0.5

1.5

1.5

1

1

2

2

2.5

2.5

Frequency (GHz)

3

Con

duct

ivit

y (S

/m)

SkinMusclePork skin

(b)

Figure 8: Comparison of human skin, human muscle, and pork skin: (a) relative permittivity and (b) conductivity.

due to that all the characteristics of the pork skin and skinare very similar.

4. Results and Discussion

The fabricated quad-band PIFA antenna is shown in Figure10. As the proposed antenna was implanted into the groundpork skin (the emulated human tissue), the simulated andmeasured return loss results are shown in Figure 11. Andgood agreement can be found between the measured andsimulated results. Moreover, the results of measured returnloss reveal good impedance matching in the MedRadio band(401 MHz) and the ISM band (433 MHz) with impedance

bandwidth of 150 MHz (338–488 MHz), the WMTS band(1.427 GHz) with impedance bandwidth of 52 MHz (1.41–1.462 GHz), and the ISM band (2.4 GHz) with impedancebandwidth of 102 MHz (2.373–2.475 GHz). The peek direc-tivity, radiation efficiency, and peek gain results of proposedantenna are shown in Table 2.

In Figure 12, as the antenna was simulated implantedinto the skin, the simulated three-dimension far-field peakgain is −22 dBi for 401 MHz, −23 dBi for 433 MHz, −17 dBifor 1.427 GHz, and −16 dBi for 2.4 GHz, respectively. Mean-while, by using the Ansoft simulation software HFSS, thesimulated 10 g averaged specific absorption rate (SAR) distri-bution of proposed antenna implanted into the skin is shownin Figure 13. Whereas the delivered power is assumed to


Table 2: The peek directivity, radiation efficiency, and peek gain results of proposed antenna.

MedRadio (401 MHz) ISM (433 MHz) WMTS (1.427 GHz) ISM (2.4 GHz)

Peek directivity 0.33202 0.423772 1.99281 2.21578

Radiation efficiency 0.019269 0.0119228 0.00909009 0.0109045

Peek gain 0.00639769 0.00505254 0.0181148 0.024162

0 0.5 1.51 2 2.5

Frequency (GHz)

S 11

(dB

)−5

−10

0

−15

−20

−25

Pork skinHuman skin

Figure 9: Simulated return loss of proposed antenna implanted into pork skin and skin.

Layer 1

Layer 2 Layer 3

Superstrate

Figure 10: Fabricated quad-band implantable PIFA antenna.


ISMband

ISMband

WMTSband

MedRadioband

SimulationMeasurement

0 0.5 1.51 2 2.5

Frequency (GHz)

S 11

(dB

)

−5

−10

0

−15

−20

−25

Figure 11: Simulated and measured return loss for the proposed antenna implanted in ground pork skin.

Y

Z

X

−2.1940e+001−2.3042e+001−2.4144e+001−2.5247e+001−2.6349e+001−2.7452e+001−2.8554e+001−2.9656e+001−3.0759e+001−3.1861e+001−3.2963e+001−3.4066e+001−3.5168e+001

Total gain (dB)

(a)

Y

Z

−2.2965e+001−2.4122e+001−2.5280e+001−2.6438e+001−2.7595e+001−2.8753e+001−2.9910e+001−3.1068e+001−3.2225e+001−3.3383e+001−3.4541e+001−3.5698e+001−3.6856e+001

X

Total gain (dB)

(b)

Y

Z

Y

X

−1.7227e+001−1.8207e+001−1.9188e+001−2.0168e+001−2.1148e+001−2.2128e+001−2.3109e+001−2.4089e+001−2.5069e+001−2.6049e+001−2.7030e+001−2.8010e+001−2.8990e+001

Total gain (dB)

(c)

Y

Z

−1.6169e+001−1.7194e+001−1.8219e+001−2.2318e+001−2.3343e+001−2.4368e+001−2.5393e+001−2.6418e+001−2.7443e+001−2.8468e+001−1.9244e+001−2.0268e+001−2.1293e+001

Total gain (dB)

X

(d)

Figure 12: Simulated three-dimensional antenna radiation patterns (delivered power = 1 W), (a) 401 MHz, (b) 433 MHz, (c) 1.427 GHz,and (d) 2.4 GHz.


Table 3: Comparison of the measured received power between the proposed antenna and [14].

Antennas Delivere power (mW) Gain (dBi) Radiation efficiency Distance (m) Receive power (dBm)

Reference [14] MICS (402 MHz) 8.8 N/A 0.16% 0.3 −30

MedRadio (401 MHz) 1 −22 1.93% 1 −51

ISM (433 MHz) 1 −23 1.19% 1 −50

WMTS (1.427 GHz) 1 −17 0.91% 1 −46

ISM (2.4 GHz) 1 −16 1.1% 1 −44

40

30

20

10

0

40

30

20

10

0

0 010 102020

X (mm) Z (mm)

10-g averagedSAR (W/kg)

−30 −30−20 −20

−10 −10

3.91e+013.55e+01

2.84e+012.49e+012.13e+011.78e+011.42e+011.07e+017.11e+003.55e+000.00e+00

3.20e+00

(a)

40

30

20

10

0

40

30

20

10

0

010

20

X (mm)

010

20

Z (mm)


3.95e+013.59e+013.23e+012.87e+012.51e+012.15e+011.79e+011.44e+011.08e+017.18e+003.59e+000.00e+00

−30 −30−20 −20

−10 −10

(b)

0

20

40

60

0

20

40

60

010

20

Z (mm)

010

20

X (mm)


5.87e+015.34e+014.81e+014.27e+013.74e+013.20e+012.67e+012.14e+011.60e+011.07e+015.34e+000.00e+00

−30−30−20−20

−10−10

(c)

80

0

20

40

60

0

20

40

60

80

010

20

Z (mm)0

1020

X (mm)


7.68e+016.98e+016.29e+015.59e+014.89e+014.19e+013.49e+012.79e+012.10e+011.40e+016.98e+010.00e+00

−30 −30−20 −20

−10 −10

(d)

Figure 13: Simulated 10 g averaged SAR distribution (delivered power = 1 W, SAR calibration line was placed at Y = 0 mm), (a) 401 MHz,(b) 433 MHz, (c) 1.427 GHz, and (d) 2.4 GHz.

be 1 W, the maximum simulated 10 g averaged SAR valueis about 39.1 W/kg at 401 MHz, 39.5 W/kg at 433 MHz,58.7 W/kg at 1.43 GHz, and 76.8 W/kg at 2.4 GHz, respec-tively, which need to meet the regulated SAR limitation(2.0 W/kg) restricted by American National Standards Insti-tute (ANSI/IEEE) regulation for short-distance biotelemetry[12]. Therefore, the delivered power of proposed antennamust be reduced to less than 26 mW, then that can satisfythe limitation of 2 W/kg SAR for quad band in this paper.

As shown in Figure 7, in a real environment, the com-munication link between the implanted proposed transmit-ting antenna and the one-quarter wavelength exterior receiv-ing monopole antenna was setup. As the communicationlink distance was 1 m and 1 mW was delivered to the pro-posed antenna, the experimental measured received powerreveals about −51 dBm at 401 MHz, −50 dBm at 433 MHz,

−46 dBm at 1.427 GHz, and −44 dBm at 2.4 GHz, respec-tively. In [14], the communication link was built between theimplanted antenna and exterior dipole, and distance betweentwo antennas is smaller than 30 cm. As shown in Table 3, theradiation efficiency of proposed antenna is almost more than[14] ten times, and the delivered power of proposed antennaonly about the one ninth of [14]. Moreover, the distanceof this paper is more than [14] three times and the gainof the four bands of proposed antenna is remarkably high.Consequently, it can be concluded that the link budget ofproposed antenna is enough to support the applications ofmultiband in the biotelemetry.

As listed in Table 4, compared to previous reports ofimplantable antennas, almost all the previous implantableantennas presented single [2–8], dual [10, 11], and tripleband [9] operations; however, only the proposed antenna


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790

MIC

S(4

02M

Hz)

132

−27

4m

mN

/AN

o

Ref

eren

ce[7

]P

IFA

190

MIC

S(4

02M

Hz)

50−2

65

mm

N/A

No

Ref

eren

ce[8

]P

IFA

122

MIC

S(4

02M

Hz)

122

−26

N/A

N/A

No

Ref

eren

ce[9

]P

IFA

245

MIC

S(4

02M

Hz)

115

−7N

/A55×

55×

20N

oIS

M(4

33M

Hz)

−11

ISM

(2.4

GH

z)70

−15

Ref

eren

ce[1

0]P

yram

idal

spir

al24

77M

edR

adio

(401

MH

z)IS

M(2

.4G

Hz)

N/A

N/A

−29

−19

N/A

π×

402×

110

Yes

Ref

eren

ce[1

1]P

IFA

1266

MIC

S(4

02M

Hz)

ISM

(2.4

GH

z)10

117

0−2

8−1

03

mm

N/A

No

Pro

pose

dA

nte

nn

aP

IFA

245

Med

Rad

io(4

01M

Hz)

ISM

(433

MH

z)15

0−2

2−2

34

mm

55×

55×

20N

oW

MT

S(1

.427

GH

z)52

−17

ISM

(2.4

GH

z)10

2−1

6


presents quad-band operation. Obviously,although the pro-posed quad-band antenna only occupies a volume of254 mm3 (10 × 10 × 2.54 mm3), the proposed antennareveals wider bandwidth and higher gain than the previousdesigns of antenna.

5. Conclusion

A novel quad-band PIFA antenna is presented for bioteleme-try, which can achieve a bandwidth of 150 MHz for MedRa-dio (401 MHz) and ISM (433 MHz), a bandwidth of 52 MHzfor WMTS band (1.427 GHz), and a bandwidth of 102 MHzfor ISM band (2.4 GHz). Moreover, the results of 1 g averagedSAR distribution of proposed antenna meet the regulatedSAR limitation restricted by ANSI/IEEE for these four bands.Furthermore, a reliable communication link with distanceof 1 m has been setup and demonstrated. The proposedantenna can excite four resonance frequencies by changingthe parameters t, f , and s easily and further achieve precisefrequency-controlling mechanism for quad-band opera-tions. Finally, compared to the results in the past literatures,only the proposed antenna can completely cover main avail-able frequency bands of BAN for biotelemetry below 3 GHz.Therefore, the proposed antenna is enough to support theapplications of multiband implantable antenna for bio-telemetry.

Acknowledgment

This work was supported by the National Science Council,Taiwan, under Grants of NSC 100-2220-E-006-012.

References

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[6] C. M. Lee, T. C. Yo, F. J. Huang, and C. H. Luo, “Bandwidthenhancement of planar inverted-f antenna for implantablebiotelemetry,” Microwave and Optical Technology Letters, vol.51, no. 3, pp. 749–752, 2009.

[7] W. C. Liu, F. M. Yeh, and M. Ghavami, “Miniaturizedimplantable broadband antenna for biotelemetry communi-cation,” Microwave and Optical Technology Letters, vol. 50, no.9, pp. 2407–2409, 2008.

[8] W. C. Liu, S. H. Chen, and C. M. Wu, “Bandwidth enhance-ment and size reduction of an implantable pifa antennafor biotelemetry devices,” Microwave and Optical TechnologyLetters, vol. 51, no. 3, pp. 755–757, 2009.

[9] F. J. Huang, C. M. Lee, C. L. Chang, L. K. Chen, T. C. Yo, andC. H. Luo, “Rectenna application of miniaturized implantableantenna design for triple-band biotelemetry communication,”IEEE Transactions on Antennas and Propagation, vol. 59, no. 7,pp. 2646–2653, 2011.

[10] F. Merli, L. Bolomey, J. Zurcher, G. Corradini, E. Meurville,and A. K. Skrivervik, “Design, realization and measurementsof a miniature antenna for implantable wireless communica-tion systems,” IEEE Transactions on Antennas and Propagation,vol. 59, no. 10, pp. 3544–3555, 2011.

[11] T. Karacolak, A. Z. Hood, and E. Topsakal, “Design of a dual-band implantable antenna and development of skin mim-icking gels for continuous glucose monitoring,” IEEE Trans-actions on Microwave Theory and Techniques, vol. 56, no. 4, pp.1001–1008, 2008.

[12] “IEEE standard for safety levels with respect to humanexposure to radio frequency electromagnetic fields, 3 KHz to300 GHz,” IEEE Standard C95.1-2005, 2005.

[13] C. R. Rowell and R. D. Murch, “A capacitively loaded PIFAfor compact mobile telephone handsets,” IEEE Transactions onAntennas and Propagation, vol. 45, no. 5, pp. 837–842, 1997.

[14] J. Kim and Y. Rahmat-Samii, “Implanted antennas insidea human body: simulations, designs, and characterizations,”IEEE Transactions on Microwave Theory and Techniques, vol.52, no. 8, pp. 1934–1943, 2004.

[15] C. Gabriel, S. Gabriel, and E. Corthout, “The dielectric pro-perties of biological tissues: I. Literature survey,” Physics inMedicine and Biology, vol. 41, no. 11, pp. 2231–2249, 1996.

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