Metamaterial-Loaded Compact High-Gain Dual-Band Circularly ... · Antenna System for Multiple Biomedical Applications Muhammad Zada, Izaz Ali Shah, and Hyoungsuk Yoo, Member, IEEE

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This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/TAP.2019.2938573, IEEETransactions on Antennas and Propagation

IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION 1

Metamaterial-Loaded Compact High-Gain Dual-Band Circularly Polarized ImplantableAntenna System for Multiple Biomedical Applications

Muhammad Zada, Izaz Ali Shah, and Hyoungsuk Yoo, Member, IEEE

Abstract—This communication presents a metamaterial (MTM) loadedcompact dual-band circularly polarized (CP) antenna system suitablefor multiple bio-telemetric applications. The proposed antenna systemoperates in the industrial, scientific, and medical (ISM) bands withcenter frequencies: 915 MHz (902–928 MHz) and 2450 MHz (2400–2480MHz). The integration of an MTM structure with epsilon very largeproperty on the superstrate layer of the antenna produces significant gainenhancement and strong CP behavior at both the operating frequencies.The key features of the proposed antenna system are its compactsize (7 mm × 6 mm × 0.254 mm), dual-band CP characteristics,significantly high gain values (-17.1 and -9.81 dBi in the lower andupper bands, respectively), and slot-less ground plane that reduces thecomplexity and backscatter radiation. The performance of the MTM-loaded antenna system is validated experimentally. The antenna isfabricated and integrated with dummy electronics and batteries andis enclosed in a 3D printed device. The hermetically sealed device istested in minced pork muscle to validate the simulation results. Themeasured impedance bandwidths of 35.8% and 17.8% are obtained inthe lower and upper ISM bands, respectively. The specific absorptionrate of the antenna system is evaluated at both frequencies in differenttissues. Additionally, to determine the wireless communication range, thelink margin is estimated at data rates of 100 kbps and 1 Mbps.

Index Terms—Axial ratio, circular polarization, ISM bands, linkmargin, miniaturization, metamaterial.

I. INTRODUCTION

Recent research advances have enabled the use of wirelesslylinked implantable medical devices (IMDs) as control devices (e.g.,implanted sensors, drug infusion devices, artificial vision, and organcontrol) or stimulators (nerve stimulators, defibrillators, cochlearimplants, and leadless pacemaker) to improve the lifestyle of patients[1]. A key component of the wirelessly linked IMDs is the integratedimplantable antenna, which facilitates bidirectional communicationwith the external control equipment. The design of implantableantennas has attracted significant research interest, as they mustsatisfy the requirements of miniaturization, biocompatibility, patientsafety, sufficient radiation efficiency, and circular polarization (CP).The CP characteristic of an antenna is essential for high-qualitycommunication with the external environment to compete humanactivities and postural movements. In order to fit easily within thedevices used in bio-telemetric applications, the antenna must bedesigned with minimum size and volume. However, miniaturizationdegrades the antenna’s gain and efficiency. Many researchers haveproposed and developed various antenna designs to meet theserequirements [1]–[6], [9], [10]. Recently in [11], we designed a tripleband antenna system that was intended for biotelemetry and wirelesspower transfer system. The miniaturization, impedance matching, andbandwidth enhancement of the antenna were achieved by inserting aslot in the ground plane. However, small gain values were observed inthe desired direction of propagation at all the frequency bands due tothe dominant back scatter radiations from the ground slot. The backscatter radiations can severely detune the antenna when integratedwith microelectronics [12].

This work was supported by the Basic Science Research Program throughthe National Research Foundation of Korea funded by the Ministry ofEducation, Science and Technology under Grant 2019R1A2C2004774.

(Corresponding author: Hyoungsuk Yoo.)The authors are with the Department of Biomedical Engineering, Hanyang

University, Seoul 04763, South Korea (e-mail: [email protected]).

Isometric view

Side view

Exploded view

Heart

Large

intestine

Small

intestine

Scalp

Stomach

MTM

Bat

teri

es5

mm

Fig. 1. Overview of human anatomy and the proposed MTM-loaded antennasystem.

TABLE ICOMPARISON OF THE PROPOSED DUAL-BAND ANTENNA WITH THE

EXISTING LITERATURE

Ref. Size (mm3)Freq.

(MHz)

BW

(%)

Gain

(dBi)

1-g SAR

(W/kg)

10-g SAR

(W/kg)CP? Device?

[2] 34.3 x 1.95 x 0.3 402 35.0 -23.7 219.0 47.0 No No

[3] 34 x 30 x 0.8 2450 6.20 -9.0 ---- ---- No No

[5] 10 x 10 x 0.4 2450 57.0 -9.0 131.0 ---- No No

[6] 10 x 10 x 0.6920 23.1 -31.8 699.0

---- Yes No2450 47.9 -27.6 568.0

This

work7 x 6 x 0.254

915 17.8 -17.1 576.1 54.5Yes Yes

2450 35.8 -9.81 524.3 50.2

BW= bandwidth, CP= circular polarization, Freq. = Frequency

TABLE I

COMPARISON OF THE PROPOSED DUAL-BAND ANTENNA WITH EXITING LITERATURE

Various techniques were proposed for the gain enhancement ofthe implantable antennas. In [2], a relatively large size planar dipolewith a high gain of -23.7 dBi and low specific absorption rate (SAR)in the Med-Radio band (401–406 MHz) was proposed. However, itsachieved gain value still need to be improved and the antenna sizeshould be miniaturized to fit easily within small implantable devices.In some other works, the implantable antenna gain was improved byusing a combination of hemispherical lenses and parasitic rings [3]or by introducing external structures such as printed grid surfaces[4]. This inclusion of external structures, however, restricted theimplantation of the entire antenna system inside the human body.An alternative approach was proposed by Das et al. [5] wherein 3-dB gain improvement and good impedance matching was achievedby the inclusion of metamaterial (MTM) structures. However, in theirwork, the antenna communicated over a single frequency band (2.45GHz) only, which was a busy band. Hence, the antenna operating inthis band could suffer significant losses during propagation in tissuescompared to the lower frequency bands. Moreover, the antenna waslinearly polarized, which could create polarization mismatch with theexternal controlling device. Additionally, the study lacked system-level consideration and coupling with the device components usedfor bio-telemetric applications. In [6], the authors used a reactiveimpedance substrate, which widened the impedance bandwidth and



2 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION

(a) (b)

(c)

(d)

L1 L2 L2

L3

L6

L6

L7

L6

W2

W3

W4

L5

L4

L4

L8

D2

W1

D1

W5

L9

W7

W6

MTM Unit cellMTM surface

Copper

Rogers 6010

Feed (PEC)

Shorting pin (PEC)

Substrate

Feed Shorting pin

H1

H1Superstrate

Fig. 2. Profile of the MTM-loaded antenna (Units: mm). (a) Radiating patch.(b) Ground plane. (c) Exploded view. (d) Side view.

TABLE IICOMPLETE PARAMETERS OF PROPOSED MTM-LOADED ANTENNA

(UNITS: mm)TABLE II

COMPLETE PARAMETERS OF PROPOSED ANTENNA (Units: mm)

Variable Value Variable Value Variable Value

L1 3.8 L8 7.0 W6 0.2

L2 1.2 L9 2.9 W7 0.8

L3 1.6 W1 6.0 D1 0.3

L4 0.4 W2 2.0 D2 0.2

L5 0.8 W3 0.8 H1 0.25

L6 1.4 W4 0.4 -- --

L7 1.8 W5 3.4 -- --

improved the axial ratio (AR) behavior in both the operating bands.However, the antenna exhibited low gain values of -31.8 and -27.6dBi at 920 and 2450 MHz, respectively, and had a relatively largesize.

In this communication, a compact dual-band implantable antennasystem with enhanced gain and circular polarization characteristicsin the 915 and 2450 MHz industrial, scientific, and medical (ISM)bands is presented for use in multiple bio-telemetric applications.The MTM technique [5], [7]–[10], [13] is used to improve the gainand AR behavior of the proposed planar inverted-F antenna (PIFA)system. An MTM unit cell consisting of a 2 × 2 array with epsilon-very-large (EVL) property is designed on the superstrate layer of theproposed antenna. In addition to the improvement in AR behaviorwith the MTM surface, gain improvements of approximately 2 and1.5 dB are observed at 915 and 2450 MHz, respectively. To the bestof our knowledge, the achieved gain is the highest value obtainedto date, for implantable antennas with the smallest size of 7 mm× 6 mm × 0.254 mm (10.6 mm3). A detailed comparison withrecent studies is presented in Table I. The MTM-loaded PIFA isintegrated with dummy electronic components for demonstrating thepractical usability of the device in bio-telemetric applications, asshown in Fig. 1. The device is simulated inside a homogeneousphantom and in different body tissues of a realistic human model. Theintegrated antenna system’s performance is validated experimentallyin the minced pork muscles, and the measured results are found to

Large

intestine

Small

intestine

Patch Ground Substrate

Antenna prototype

Min

ced

po

rk Minced pork

Phantom

(a)

(b)

Heart

10

0

Antenna system

30

0

Radiation box

Duke

model

Head

MTM structure

An

ten

na

inte

gra

ted

wit

h

du

mm

y e

lect

ron

ics

VNA

cable

Device

top view

Sealed

device

Fig. 3. Analysis setups for the MTM-loaded antenna system. (a) Simulationenvironments. (b) Fabricated prototypes and measurement setups for thereflection coefficient, AR behavior, and radiation pattern.

be in reasonable agreement with the simulated results. Additionally,the link-budget analysis of the antenna system is estimated fordifferent tissues, to investigate its capability for communication inbio-telemetric applications.

II. METHODOLOGY

A. Design of the MTM-Loaded Antenna System

The schematic of MTM-loaded CP implantable antenna is pre-sented in Fig. 2. The antenna has a compact size of 7 mm × 6mm × 0.254 mm and consists of a serpentine-shaped radiating patchwith a full ground plane. The coaxial feed and shorting pin withdiameters of 0.6 and 0.4 mm, respectively, are placed at appropriatepositions on the ground plane. The designed antenna is employedon substrate and superstrate layers. A Rogers RT/duriod 6010 witha dielectric constant (εr) of 10.2, loss tangent (tanδ) of 0.0035,and thickness 0.127 mm is used as the substrate and superstratelayer. The high-dielectric superstrate material decouples the antennafrom the lossy surroundings and stabilizes the effective permittivityfluctuations around the antenna [5]. Moreover, to improve the antennagain and AR behavior, a finite array of MTMs consisting of 2 × 2unit cells is designed on the existing superstrate layer of the proposedantenna. An additional dielectric slab is not required to load the MTMunit cell, which ensures a greater level of compactness to fit insidethe IMDs used for bio-telemetric applications. The detailed designparameters of the antenna are presented in Table II.

In practical scenarios, the IMDs contain not only the antenna, butalso microelectronic components such as sensors, circuitry, and powersources (batteries). Therefore, the designed antenna is integratedwith dummy electronic components to constitute the device archi-tecture. Fig. 1 shows the integration of the antenna with the devicecomponents. The device contains an implantable antenna, sensorpacks, micro-electronics, and two alkaline batteries of height 2.1 mmand diameter 6.5 mm. The electronic components and batteries areconsidered to be perfect electric conductors and the sensor pack is ofRoger RT/duriod 6010. All components of the device are encased ina biocompatible ceramic alumina (Al2O3) container with εr of 9.8and thickness 0.2 mm.



IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. –, NO. –, – 2019 3

(b)(a)

Skin

box

PEC

PEC

PMC

PMC

Wave port

11 mm

Rad

iation

bo

x

Skin

box

Unit cell MTM unit cell

Real (𝜀)

Imaginary (𝜀)

Fig. 4. (a) Simulation setup for the 2 × 2 elements unit cell. (b) Effectivepermittivity of the MTM unit cell.

Fig. 5. Comparison of the simulated and measured reflection coefficients ofthe MTM-loaded antenna system in different human body tissues.

B. Simulation and Measurement Environments

The finite-element method based high-frequency structural simula-tor (HFSS) and finite-difference time domain based XFdtd Remcomwere used for the antenna design and analysis. Initially, the antennasystem was simulated at a depth of 4 mm in a homogeneous skin boxsurrounded by a radiation box of dimensions 300 mm × 300 mm ×300 mm. The properties (permittivity and conductivity) of the skintissues were set to be frequency dependent for the entire band used inthe simulations. The antenna system was then implanted at differentbody tissue locations such as the scalp, heart, stomach, and small andlarge intestines of a realistic human model in Remcom, as shownin Fig. 3(a). The simulation results were validated by fabricatedprototype of the antenna system. The fabricated MTM-loaded antennawas integrated with dummy circuitry and two batteries enclosed in a3D printed device. The reflection coefficient, AR behavior, and gainpatterns were measured by placing the hermetically sealed device inthe minced pork muscle, as depicted in Fig. 3(b).

C. Operating Principal of the MTM-Loaded Antenna System

As discussed in detail by Lovat et al. [7] that MTM superstrate withEVL (|εr|� 1) and mu very large (|µr|� 1) properties are requiredto improve the directivity and broadside gain of the magnetic dipoleand electric dipole sources, respectively. Moreover, work presentedin [8] described that if a grounded MTM structure of permittivityεr and permeability µr is excited by a wave source, the normalizedbroadside power PN (0) can be expressed as

PN (0) =K2

0

8π2η0η2r(1)

whereK0 = ω

√µ0ε0 (2)

Fig. 6. (a) Comparison of the simulated and measured AR behavior with andwithout MTM structure. (b) Simulated and measured gain comparison withand without MTM structure.

η0 =

√µ0

ε0(3)

ηr =

√µr

εr(4)

these equations show that if we made high the relative permittivityof the MTM structure or low the characteristic/intrinsic impedance,directive radiation can be obtained, which leads to gain enhance-ment in the desired direction of propagation. Thus, high effectivepermittivity values are suitable for enhancing directivity and gainof the antennas based on the leaky wave concept [7]. Furthermore,MTM structure has been applied to circular polarized micro-stripantennas in the free space to enhance the antenna gain and ARbehavior [9], [10]. These enhancements are due to two factors.First, placing the MTM structure above the radiating patch resultsin additional electromagnetic coupling between the radiating patchand the meta-surface, thus enhancing the AR bandwidth. Second,the MTM improves the field distribution, which enlarge the effectiveaperture of the antenna [13].

In this study, the unit cell of the MTM structure was analyzedby applying two perfect electric and magnetic conductive boundarieseach to the walls of the radiation box, which was placed at a distanceof 1 mm from each side of the skin phantom, as illustrated in Fig.4(a). As described in [5], [7]–[10], a grounded MTM superstratewith EVL properties is required to improve the broad-side gain ofthe magnetic dipole source. Here, we simulated the MTM-loadedimplantable antenna in a homogeneous skin phantom. The charac-teristics and effective medium parameters of the unit cell, such asthe effective permittivity and permeability were extracted using theKramers–Kronig algorithm [14]. It can be seen from Fig. 4(b) that inthe desired frequency range, the effective permittivity values of theMTM superstrate are very high, and they vary in the range of 20 to30. Thus, this MTM structure with these EVL properties can be usedfor improving the gain and AR behavior of the antenna.

III. RESULTS AND DISCUSSION

The simulated and measured results for the return loss character-istics of the MTM-loaded implantable antenna system are illustrated



4 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION

0o

(b)

90o

180o 270o

(a)

0o 90o

180o 270o

Jsurf [A/m]79.40

67.22

57.63

48.02

38.44

28.85

19.25

9.66

0.00X

Y

Fig. 7. Distributions of the simulated surface currents on the radiating patchof the MTM-loaded antenna system at different phases: 00, 900, 1800, and2700. (a) 915 MHz. (b) 2450 MHz.

TABLE IIITRANSMISSION PARAMETERS FOR THE WIRELESS LINK-BUDGET

ANALYSIS

TABLE III

TRANSMISSION PARAMETERS FOR WIRELESS

LINK-BUDGET ANALYSIS

Variable Description Value

fr Resonance frequency (MHz) 915/2450

Pt Tx input power (dBW) -46

Gr Gain of the Rx antenna (dBi) 2

Gt Gain of the Tx antenna (dBi) -17.1/-9.81

PL Path loss (dB) Distance dependent

d Distance (m) 1-20

in Fig. 5. As can be seen from the figure, the system resonates inthe 915 and 2450 MHz bands, with maximum measured impedancebandwidths of 17.8% and 35.8% in the lower and upper ISM bands,respectively. The simulation setups for the proposed antenna systemin a homogeneous skin box and in different tissues (scalp, heart,stomach, small intestine, and large intestine) of a realistic humanmodel are shown in Fig. 3(a). The heterogeneous environment hasnegligible effect in the lower frequency band (915 MHz), while asmall shift occurs in the upper band (2450 MHz), which may be dueto the variations in the electrical properties and asymmetrical loadeffect red of the body tissues [12].

The simulated and measured AR and gain comparisons between theimplantable PIFA and MTM-loaded PIFA are illustrated in Fig. 6(a)and (b). The integration of the MTM structure leads to considerableCP behaviors at the corresponding frequency bands, as shown in Fig.6(a). The simulated 3-dB AR bandwidths of the unloaded antennaare observed to be 15.3% and 11.8% in the lower and upper ISMbands, respectively. The MTM-loaded antenna system exhibits ARbandwidths of 21.3% and 17.14% in the lower and upper bands,respectively. The measured AR behavior is closely correlated withthe simulated scenarios. The simulated and measured gain versusfrequency analysis is shown in Fig. 6(b), the gain enhancement uponloading the MTM structure can be observed clearly. Gain enhance-ments of approximately 2 and 1.5 dB are observed at the lower andupper frequency bands, respectively. A similar gain enhancement canbe observed from the measured gain behavior at both the resonancefrequencies.

Regardless of the axial behavior, the CP mechanism can alsobe realized by analyzing the surface current distributions. Fig. 7represents the simulated current distributions on the radiating patch ofthe MTM-loaded antenna at the corresponding resonance frequencies(915 and 2450 MHz) for four different phases (00, 900, 1800, and

Fig. 8. Simulated and measured gain patterns in the E-plane (azimuthal) andH-plane (elevation) for the MTM-loaded antenna system at: (a) 915 MHz. (b)2450 MHz.

(a) (b)

Fig. 9. Analysis of the simulated wireless communication link budget at 915MHz in different body tissues for different data rates. (a) 100 kbps. (b) 1Mbps.

2700). At both the operating frequencies for 00 phase, the currentdensity is dominant in +Y direction (upward), while for the 900

phase, the dominant currents are toward +X direction (rightward).However, the predominant currents for the 1800 and 2700 are foundin equal magnitude and opposite phase with 00 and 900, respectively.Thus, the predominant currents are rotating in clockwise direction,which shows that the polarization sense for the proposed MTM-loaded antenna is left-hand circular polarization.

Fig. 8 demonstrates the radiated far-field gain patterns in therealistic human scalp, heart, stomach, and small and large intestines,and those measured in the minced pork muscle at the correspondingoperating frequencies. As can be seen from the figure, the gainpatterns are nearly omni-directional in both E and H planes; however,the maximum direction of propagation is outside from the anatomicalmodel as required for the implantable antenna systems. The gain-patterns were measured in an anechoic-chamber, as shown in Fig.3(b). The maximum realized gain values of the MTM-loaded antennasystem were observed in the skin phantom as -17.1 and -9.81 dBi inthe lower and upper ISM bands, respectively, which are the highestgain values obtained to date with the smallest antenna size comparedto the recently published implantable antennas.

The link-budget was calculated to determine the communicationability of the proposed antenna system. The proposed implantableantenna system was considered as a transmitter (Tx) with an inputpower of 25 µW, and a dipole antenna with a constant gain (Gr) of



IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. –, NO. –, – 2019 5

394.8

345.4

296.1

246.7

197.4

148.0

98.7

49.3

W/kg

0.0

(a)

576.1

504.4

432.2

360.1

288.8

215.6

144.7

72.2

W/kg

0.0

581.3

508.6

436.1

363.3

290.6

218.0

145.3

72.6

W/kg

0.0

405.2

354.6

303.9

253.2

202.6

151.9

101.3

50.6

W/kg

0.0

(b)

Fig. 10. Simulated SAR distributions over 1–g of tissue in an anatomicalhuman model at 915 MHz: (a) Without MTM. (b) With MTM.

TABLE IVDETAILED PERFORMANCE OF THE MTM-LOADED ANTENNA SYSTEM IN

DIFFERENT HUMAN TISSUES

Tissue

category

Frequency

(MHz)

Bandwidth

(MHz)

Gain

(dBi)

1-g Net-

input power

without

MTM (mW)

1-g Net-

input power

with MTM

(mW)

10-g Net-input

power without

MTM

(mW)

10-g Net-

input power

with MTM

(mW)

Skin

/Scalp

915

2450

101

163

-17.13

-9.81

2.776

3.052

4.052

4.853

36.67

39.82

48.97

58.10

Small

Intestine

915

2450

101

193

-19.1

-11.85

2.865

3.227

3.781

4.316

33.75

34.58

43.82

47.07

Heart915

2450

84

144

-19.78

-12.3

2.752

3.313

3.948

5.071

31.56

36.91

44.88

51.63

Large

Intestine

915

2450

76

139

-20.26

-12.93

3.169

3.505

4.831

6.650

35.89

38.48

53.40

66.74

Stomach 915

2450

95

151

-21.8

-14.4

2.957

3.664

4.343

5.579

33.94

38.27

49.16

60.04

TABLE IV

DETAILED PERFORMANCE OF THE ANTENNA IN DIFFERENT TISSUES

2 dBi was considered as a receiver located at a distance d from theTx. The additional parameters used for the link-budget calculationare presented in Table III. The Friis formula was used to calculatethe link budget, considering various losses [15]. Figs. 9(a) and (b)demonstrate the distance versus margin for the proposed antennasystem in different body tissues at 915 MHz with bit rates of 100kbps and 1 Mbps, respectively. It has been observed that the antennasystem exhibits successful transmission for d > 10 and d ≥ 6 m atbit rates of 100 kbps and 1 Mbps, respectively. Thus, the proposedantenna system fulfills the requirements of low and high-data rateapplications and can be used in multiple implantable biomedicalapplications.

To evaluate the safety of the proposed MTM-loaded antennasystem, the SAR distributions over 1-g of tissues in the scalp andheart of a realistic human model without and with MTM structurewere evaluated and shown in Figs. 10(a) and (b), respectively. Foran input power of 1 W, the maximum 1-g average SAR in theheart tissues at 915 MHz was observed to be 405.2 and 581.1W/kg with and without MTM, respectively. The SAR reductionand gain enhancement with MTM structure is due to the formationof displacement currents in the surrounding tissues of the antennasystem [16]. The detailed performance of the MTM-loaded antenna,e.g., bandwidth, gain, and maximum allowable net input power withand without MTM in different human tissues using the XFdtd-basedsimulator Remcom are presented in Table IV. According to Table??, the 1-g net input power for the heart without and with MTMstructure are 2.75 and 3.94 mW, which are very far from the 25µW value specified for implantable antennas under the IEEE safetyregulations.

IV. CONCLUSION

This paper addressed the design, analysis, and experimental valida-tion of an MTM-loaded compact CP implantable antenna system withenhanced gain and AR characteristics, for multiple bio-telemetricapplications. Gain enhancement and substantial AR bandwidth wereachieved at the desired frequency bands, with a compact size of7 mm × 6 mm × 0.254 mm compared to the other implantableantennas. The integrated antenna with dummy electronics and batter-ies was simulated in different tissues of a realistic human model todemonstrate its use in multiple applications. The simulation resultswere validated experimentally by placing a hermetically sealed devicecontaining the MTM-loaded antenna, dummy circuitry, and batteriesin minced pork muscles. The measured results (reflection coefficientsand gain patterns) were found to be in reasonable agreement with thesimulated results.

REFERENCES

[1] A. Kiourti and K. S. Nikita, “A review of implantable patch antennasfor biomedical telemetry: Challenges and solutions,” IEEE AntennasPropag. Mag., vol. 54, no. 3, pp. 210–228, June 2012.

[2] R. Lesnik, N. Verhovski, I. Mizrachi, B. Milgrom, and M. Haridim,“Gain enhancement of a compact implantable dipole for biomedicalapplications,” IEEE Antennas Wirel. Propag. Lett., vol. 17, no. 10, pp.1778–1782, Oct. 2018.

[3] S. Alamri, A. AlAmoudi, and R. Langley, “Gain enhancement ofimplanted antenna using lens and parasitic ring,” Electron. Lett., vol.52, no. 10, pp. 800–801, May 2016.

[4] S. Zhu, S. Almari, A. O. AlAmoudi, and R. J. Langley, “Implantedantenna efficiency improvement,” 7th European Conference on Antennasand Propagation (EuCAP), pp. 3247–3248, April 2013.

[5] S. Das and D. Mitra, “A compact wideband flexible implantable slotantenna design with enhanced gain,” IEEE Trans. Antennas Propag.,vol. 66, no. 8, pp. 4309–4314, Aug. 2018.

[6] G. Samanta and D. Mitra, “Dual band circular polarized flexible im-plantable antenna using reactive impedance substrate,” IEEE Trans.Antennas Propag., vol. 67, no. 6, pp. 4218–4223, June 2019.

[7] G. Lovat, P. Burghignoli, F. Capolino, and D. R. Jackson, “Combina-tions of low/high permittivity and/or permeability substrates for highlydirective planar metamaterial antennas,” IET Microw. Antennas Propag.,vol. 1, no. 1, pp. 177–183, February 2007.

[8] B. Majumder, K. Krishnamoorthy, J. Mukherjee and K. P. Ray, “Compactbroadband directive slot antenna loaded with cavities and single anddouble layers of metasurfaces,” IEEE Trans. Antennas Propag, vol. 64,no. 11, pp. 4595–4606, Nov. 2016.

[9] S. X. Ta and T. K. Nguyen, “AR bandwidth and gain enhancements ofpatch antenna using single dielectric superstrate,” Electronics Letters.,vol. 53, no. 15, pp. 1015–1017, July 2017.

[10] K. Agarwal, Nasimuddin and A. Alphones, “Wideband circularly po-larized AMC reflector backed aperture antenna,” IEEE Trans. AntennasPropag., vol. 61, no. 3, pp. 1456–1461, March 2013.

[11] M. Zada and H. Yoo, “A miniaturized triple-band implantable antennasystem for io-telemetry applications,” IEEE Transactions on Antennasand Propagation, vol. 66, no. 12, pp. 7378–7382, Dec. 2018.

[12] I. A. Shah, M. Zada, and H. Yoo, “Design and analysis of a compact-sized multiband spiral-shaped implantable antenna for scalp implantableand leadless pacemaker systems,” IEEE Transactions on Antennas andPropagation., vol. 67, no. 6, pp. 4230–4234, June 2019.

[13] N. Nasimuddin, Z. N. Chen and X. Qing, “Bandwidth enhancementof a single-feed circularly polarized antenna using a metasurface:metamaterial-based wideband CP rectangular microstrip antenna.,” IEEEAntennas and Propagation Magazine., vol. 58, no. 2, pp. 39–46, April2016.

[14] Z. Szabo, G. Park, R. Hedge and E. Li, “A unique extraction ofmetamaterial parameters based on KramersKronig relationship,” IEEETrans. Microw. Theory Tech., vol. 58, no. 10, pp. 2646–2653, Oct. 2010.

[15] C. Liu, Y.-X. Guo, and S. Xiao, “Capacitively loaded circularly polarizedimplantable patch antenna for ISM band biomedical applications,” IEEETransactions on Antennas and Propagation, vol. 62, no. 5, pp. 2407–2417, May 2014.

[16] R. Das and H. Yoo, “Application of a compact electromagnetic bandgaparray in a phone case for suppression of mobile phone radiationexposure,” IEEE Transactions on Microwave Theory and Techniques,vol. 66, no. 5, pp. 2363–2372, May 2018.

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Metamaterial-Loaded Compact High-Gain Dual-Band Circularly ... · Antenna System for Multiple Biomedical Applications Muhammad Zada, Izaz Ali Shah, and Hyoungsuk Yoo, Member, IEEE