1

Compact and Flexible Wide-Band Antenna for Intraoral Tongue-Drive Systemfor People with Disabilities

Abdul Basir, Student Member, IEEE, Muhammad Zada, and Hyoungsuk Yoo, Senior Member, IEEE

Abstract—This paper presents a compact and flexible folded dipole an-tenna with stable and wide-bandwidth characteristics for the applicationof an intraoral tongue-drive system (iTDS) designed for use by peoplewith severe disabilities. The proposed antenna, with an exceptionallysmall size of 20 mm x 4.4 mm x 0.025 mm, was designed to overcome thechallenges of space-suitability and detuning that occur due to the variableconditions of the oral environment of the mouth by providing stable andwideband antenna properties. The substantial reduction in the size ofthe antenna was achieved by introducing slots and meandering the armsof the radiator. Performance was analyzed in open- and closed-mouthscenarios using a realistic model of the human head. Maximum simulatedimpedance bandwidths of 163% and 151% were observed for the closed-and open-mouth cases, respectively. The proposed design showed lowerspecific absorption rate values (addressing safety concerns) with higherrealized gain values in both scenarios compared to the current state-of-the-art iTDS antennas. In order to validate the simulation results, invivo and in vitro measurements were taken for the reflection coefficientand radiation patterns, respectively. The results prove that the proposedantenna can work efficiently in the dynamic environment of the mouthand is therefore a good candidate for iTDS application.

Index Terms—Folded dipole, flexible, intraoral tongue drive system,meandering, wideband.

I. INTRODUCTION

TETRAPLEGIA may result from spinal cord injury, amyotrophiclateral sclerosis, or stroke [1]. People with tetraplegia cannot

perform tasks such as controlling computers, smartphones, andwheeled mobility apparatus without assistance. The adoption ofassistive technologies allows tetraplegic people to improve theirfunctional competences and level of independence. However, thesetechnologies are subject to limitations in terms of their compatibility,robustness, how intuitive they are to use, and invasiveness [2].

The tongue-drive system (TDS) is a wireless tongue-operated assis-tive technology, which is non-invasive, secure, flexible, and robust. ATDS exploits the propensity of the human tongue to retain movementability after spinal cord injury or other neural disease due to its directconnection with the brain via the hypoglossal nerve [3], [4]. A TDSsystem incorporates magnetic sensors that are attached to a dentalretainer in the case of intraoral TDS (iTDS) or mounted outside themouth around the cheeks in the case of extraoral TDS (eTDS). Avery small magnetic tracer is implanted in the tip of the tongue bytongue piercing for permanent use or, for short-term use, attachedwith glue. Magnetic variations produced around the tracer due totongue movements are detected by magnetic sensors and wirelesslytransmitted by the intraoral antenna to an exterior receiving deviceworn by the user. This external device executes the requisite signal-processing algorithms and generates user-defined control commandsfor performing tasks such as controlling a wheelchair or accessingand operating computers or smartphones [1]–[4].

The development of robust wireless communication between anintraoral antenna and an external device is challenging due to thenumber of factors that can cause signal degradation or loss; these

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.)Authors are with the Department of Biomedical Engineering, Hanyang

University, Seoul 04763, South Korea (e-mail: hsyoo@hanyang.ac.kr).

(a)

(b) (c)

4.0

Port

0.3

4.0

0.5

1.0

1.5

Polyimide

PDMS

Copper

Capacitor

20

4.4 Via-1

Via-2

Fig. 1. Geometry of the wideband folded dipole antenna [Units: mm]. (a)Radiating patch (b) Back view. (b) Side view.

TABLE IPROPOSED WORK VERSUS STATE OF THE ART.

Ref.Antenna

type

Freq.

(MHz)

Antenna Size

(mm3)

BW

(%)

Gain

(dBi)

SAR

(W/kg)

Net input

power (mW)

Flexible

?

[6]Patch 2400 60 x 13 x 0.75 18.8 -10.6 N/A N/A No

PIFA 2400 60 x 13 x 0.75 29.2 -14 N/A N/A No

[7] Loop 2450 25 x 18 x 5 3.3 -21 N/A N/A No

[9]

PIFA433

17.2 x 8 x 2.63531.8 -28.2 179.7 (10-g) 11.12 No

915 21.7 -24.5 160.7 (10-g) 12.4 No

Dipole433

42 x 10 x 2.6357.4 -19.1 48.68 (10-g) 41.1 No

915 11.5 -14.4 26.10 (10-g) 76.6 No

This

workDipole 915 20 x 4.4 x 0.025 163 -17.5 108.25 (1-g) 14.8 Yes

include power absorption by the mouth at higher radio frequencies(RF), the dynamic environment of operation due to the movement ofthe tongue and jaw, and exposure to saliva. Another major challenge isthe selection of an operating frequency for an intraoral antenna as thishas a direct impact on the performance of the antenna. Performancecan worsen due to frequency-dependent problems including the sizeof the antenna (which must be small enough to fit comfortablyonto a dental retainer), and at higher frequencies, attenuation of theRF signal by surrounding tissue, and antenna impedance mismatch[5]. Studies in which successful wireless communication has beenestablished between an intraoral antenna and an external unit [6],[7] have required a high (2.4 GHz) operating frequency, narrowbandwidth, and a large antenna. The 2.4 GHz frequency bandis crowded, more vulnerable to human-body attenuation, and caninterfere with the operation of other medical devices which commonlyuse this band. Researchers in [4], [5], and [8] discussed iTDSdevices in detail, but did not address the challenges of antennadesign or safety concerns related to potential power absorption inthe user’s mouth. Moreover, all the aforementioned studies werefocused entirely on system implementation, providing no in-depthanalysis of the intraoral antenna. Recently in [9], we suggested twodual band antennas: folded dipole and slotted planer inverted F-antenna (PIFA) for the ISM bands of 433 and 915 MHz. However,the dipole antenna exhibited narrow bandwidths at both the resonancefrequencies. Owing to the complex and variable behavior of themouth, the antenna may detune from the desired operating bands.

2

Frequency (GHz)

Step-1 Step-3

(a)

(b)

-30

-20

-10

0

0 0.5 1 1.5 2 2.5

Ref

lect

ion

Co

effi

cien

t (d

B)

Frequency (GHz)

Step-2 Step-3 Step-4 Matching Capacitor

(Step-1)

(Step-2)

(Step-3)

(Step-4)

Fig. 2. Optimization steps and the related S11 for the proposed widebandantenna. (a) Proposed antenna evolution steps: Step-1, printed dipole withoutslots; Step-2, creating horizontal slots on arms; Step-3, vertically slitting thearms from center; and Step-4, creation of vertical slots at the horizontaledges of the dipole arms. (b) The corresponding reflection coefficients ofthe involved steps.

Step-1 Step-2

Step-3 Proposed design

21.89

19.7018.3917.0815.7714.4513.1410.807.896.585.273.962.641.330.02

Jsurf

[A/m]

Y

X

Fig. 3. Current distributions of the optimization steps at 915 MHz.

Therefore, stable and wideband antennas are highly recommendedfor robust operation of iTDS system. Additionally, the performanceof the PIFA is degraded due to low gain values and low radiationefficiencies at both the resonances.

Several studies suggest implantable antennas [10]–[12] but inmost cases the efficiency and gains of an implantable antenna areinsufficient for effective iTDS application. Additionally, implantabledevices severely detune when the surrounding environment of theantenna is changed. Therefore, researchers have suggested ultra-wideband antennas to minimize the detuning due to change inthe operating scenarios [13]. Unlike antennas implanted in a fixedand stable position in the human body, intraoral antennas must bedesigned to consider the constantly changing positions of the jaw andtongue which vary in shape and position during speech, breathing,and swallowing, all of which can easily detune the antenna.

To overcome these challenges, we designed a compact and flexiblewideband dipole antenna with stable impedance-matching character-istics at the Industrial, Scientific, and Medical (ISM) frequency band,915 MHz. This band provides better radiation performance, lowerSAR values, and sufficient bandwidth with small sized antenna. Thesubstantial antenna-size reduction is accomplished by meanderingboth antenna arms, which lengthens the current flow path on theradiator. The antenna was designed on a thin substrate layer offlexible polyimide, and coated with Polydimethylsiloxane (PDMS).PDMS provides both flexibility and avoids short circuits caused byexposure to saliva, thereby ensuring biocompatibility. The flexible

-60

-50

-40

-30

-20

-10

0

0.5 1 1.5 2 2.5

Tota

l E

ffic

ien

cy (

dB

)

Frequency (GHz)

Step-1 Step-2Step-3 Proposed (Simulation)Measured (Minced pork)

Fig. 4. Simulated total efficiencies against frequency of the proposed antennafor the design steps and measured efficiency of the fabricated prototype.

-35

-30

-25

-20

-15

-10

-5

0

0.5 1 1.5 2 2.5

Ref

lect

ion

co

effi

cien

t (d

B)

Frequency (GHz)

Coating = 0.1 mm Coating = 0.3 mm

Coating = 0.5 mm Coating = 0.7 mm

Coating = 0.9 mm Coating = 1 mm

Fig. 5. Influence of PDMS coating’s thickness on the performance of theproposed antenna.

antenna can be easily integrated with a dental retainer, and isresilient to damage from the variable environment of the mouth.The results and characteristics of the proposed antenna are discussedin detail, in terms of reflection coefficients, optimization technique,radiation performance, SAR, and wireless link analysis. Moreover,for validation of the simulated reflection coefficients, we conductedmeasurements with the fabricated prototype in the mouth of a user inboth open- and closed-mouth scenarios. The radiation patterns weremeasured in a 3D head model and minced pork to pretend the effectof human mouth tissue in both open- and closed-mouth cases. Theperformance of the proposed broadband antenna is contrasted withthe contemporary state-of-the-art in Table I. It can be seen that theproposed antenna performed better in terms of bandwidth, gain, SAR,and antenna size than any of the iTDS antennas presented in [3], [6],and [7].

II. METHODOLOGY

A. Wide-Band Antenna Design and Optimization

To avoid the occurrence of detuning due to exposure to salivaand movement of the jaws and tongue, we designed a widebandfolded dipole with meandered symmetrical arms operating at 915MHz. The front and back geometry of the suggested antenna areshown in Figs. 1(a) and (b), respectively. To achieve the desiredresonance frequency and wide impedance bandwidth, the radiatingpatch consists of meander lines that extend the path for current flow,assisting in antenna-size reduction. To provide flexibility, a polyimide(εr = 4.3 and tanδ = 0.004) of 19.8 mm x 4.2 mm in size with athickness of 0.025 mm was selected for the substrate of the proposedantenna, providing resilience and robustness to potential damage thatcould emanate from the movement of the jaw and tongue duringswallowing. A 50-ohm feed was applied from the center of theradiating patch to the ends of the arms, as indicated in black in thefigure . The whole antenna was coated with a 0.1 mm thick layerof PDMS on each side to avoid short circuits due to exposure to

3

Antenna

Mo

uth

cav

ity

3D head model

(a)

AntennaAntenna

Antenna

(b) (c)

Antenna

(d) (e)

(f) (g)

mm-scaleFabricated

prototypes

PDMS

coating

Capacitor

Fro

nt

vie

w

Air box

Fig. 6. Simulations and measurements environments. (a) Simulation setupfor realistic closed-mouth. (b) Simulation setup for realistic open-mouth. (c)Fabricated prototype of the proposed antenna. (d) Open-mouth measurementsetup for reflection coefficient. (e) Closed-mouth measurement setup forreflection coefficient. (f) Head model with saline solution for radiation patternmeasurement. (g) Minced pork with cavity for radiation patterns measurement.

saliva and thereby provide biocompatibility. For stable impedancematching, an 11 pF capacitor was used at the rear of the antenna andconnected with the two crossed ends of the arms, as depicted in theyellow region in Fig. 1(b). The overall size of the proposed antennawas 20 mm x 4.4 mm x 0.025 mm, the smallest (smaller than anyof the current state-of-the-art iTDS antennas) antenna is able to offerstable input impedance and wideband characteristics in both open-and closed-mouth scenarios.

The proposed antenna’s optimization and evolution were achievedin four successive steps as shown in Fig. 2(a); corresponding re-flection coefficients are shown in Fig. 2(b). As can be seen fromthe evolution steps, we started simply from a basic dipole withtwo slotless arms. The S11 of Step 1 was resonating at a highfrequency (above 3 GHz) with narrow bandwidth. Then, we inserteda 0.3 mm horizontal slot in the middle of both arms, as depictedin Step 2. Although the current flow path at this point has doubledin comparison with that in Step 1, the S11 is highly unstable. InStep 3, five symmetrical vertical slots were inserted into each arm,which lengthened the current path and enabled the achievement of thedesired band. However, the S11 was just below -10 dB with narrowimpedance bandwidth, so, to achieve impedance matching and thedesired wide bandwidth, we inserted more vertical slots from lateraledges as shown in Step 4. The reflection coefficient was stabilized(S11 < -10 dB) by completely meandering the arms. Bearing inmind the nature of the human mouth, we attached a capacitor at theends of the arms for further impedance matching. Parametric analysiswas used to determine appropriate values for the capacitor and theinserted slots. A more stable impedance match and super widebandwere achieved (S11 <-20 dB) at a capacitance of 11 pF, enabling theproposed antenna to function inside the dynamic oral environment.

The slitting of patch extends the current paths and stabilizes the

R1 L1 C1 R2 L2 C2 R3 L3 C3 C4 Cp Lp

20 3.1 8.2 25 9.7 4.6 40 3 2.8 11 4.8 5.1

Parameters (Units: Ω, nH, pF)

Term1

Z= 50 Ohm

Fig. 7. (a) Equivalent circuit for the proposed antenna. (b) Correspondingvalues of the components used in the circuit.

Fig. 8. Comparison of the simulated and measured reflection coefficient inopen and closed mouth scenarios.

input impedance by balancing the current distributions. The currentdistributions on the proposed antenna for each optimization step at915 MHz are shown in Fig. 3. The currents are flowing in the samedirection on both arms, constitute as λ/2 dipole mode. Initially,the current distribution on arms was inhomogeneous, which led toimpedance instability. After each design step, the current distributionbecame more and more homogeneous, which stabilized the inputimpedance of the antenna and a wideband is achieved. Meanderingthe patch of the antenna is also affecting the efficiency of theantenna. The radiation efficiency of the antenna greatly dependingon the surface area of the conducting patch. Meandering reducesthe conducting area; hence, the radiation efficiency decreases. Thetotal efficiency of the antenna against frequency is shown in Fig. 4.The figure reveals that the total efficiency of the antenna around 900MHz is reduced after each designing steps. Although, the radiationefficiency of the antenna follows the same trend, but the totalefficiency does not necessarily follow the trend across widebandas it also depends on other antenna parameters. However, the totalefficiency of the optimized antenna is stable (-27.1– -17.3 dB) acrossthe wideband.

Thin PDMS was used for miniaturization and to insulate theantenna from the direct contact with the surrounding tissue andsaliva. To achieve further miniaturization, thinner insulating layersare preferred. Although, the use of thinner insulating layers shiftingthe resonance to lower frequencies, yet enough thickness is requiredfor long time protection. To evaluate the robustness of the antennafor long time protection and usability, the thickness of the PDMS

4

(c) (d)

(a) (b)

Units: dBi

Y

X

Z

X

Fig. 9. Propagation direction of the proposed antenna from the mouth [Units:dBi]. (a) Open mouth. (b) Closed mouth. (c) E–plane simulated and measuredradiation pattern. (d) H–plane simulated and measured radiation pattern.

coating was parametrically analyzed as shown Fig. 5. It is evidentfrom the figure that as the thickness of the insulating layer (PDMS)increased, the wideband shifts to higher frequencies. However, theantenna maintained the wideband characteristic, and antenna is stillresonating at 915 MHz for up to thickness of 0.9 mm. It is worthmentioned that the PDMS coating is equally applied at each side ofthe proposed antenna.

B. Simulation and Measurement Environment

The proposed wideband folded dipole antenna was evaluated usingAnsoft HFSS software, with the setups shown in Fig. 6(a) and (b)used for open- and closed-mouth scenarios, respectively. An air boxwith dimensions of 63 mm x 50 mm x 15 mm was inserted for theapproximation of the open-mouth scenario. The proposed antenna issuggested for curved shaped iTDS. In real life application, the iTDSantennas are integrated with dental retainer and placed in front ofthe teeth attached to the lower jaw. Therefore, in simulations andin vivo measurements, the proposed antenna is placed in front ofthe teeth in the realistic head model and human subject’s mouth,respectively. We evaluated the performance of the antenna in termsof the radiation pattern, reflection coefficients, and SAR in eachscenario. For verification of the simulation results obtained from thesescenarios, the proposed antenna was fabricated on the aforementionedPolyimide substrate and coated with a thin layer of biocompatiblePDMS as depicted in Fig. 6(c). The measurement of the reflectioncoefficient was conducted in the subject’s mouth for open- and closed-mouth cases using the vector network analyzer as visualized inFig. 6(d) and (e), respectively. In contrast, the radiation pattern wasmeasured in an anechoic chamber in the 3D head model and mincedpork to represent the properties of human mouth tissue. The antennawas placed in the mouth of the 3D head model which was filledwith saline (having similar dielectric properties to the human mouth)for the approximation of open-mouth performance as depicted in Fig.6(f). For the closed-mouth approximation, a curved cavity was formedin the minced pork and the antenna was placed inside the cavity asshown in Fig. 6(g).

(a) (b)

Fig. 10. Average SAR distributions over 1 g of tissue at 915 MHz. (a) Closedmouth. (b) open mouth.

C. Equivalent Circuit Model

A wideband antenna is considered to be a radiating element withclosely associated resonances in which some parts of the adjacentlyoccurring bands overlap. In terms of resonance, each frequencyband can be modelled as parallel connected RLC lumped elements.However, for wideband, multiple parallel RLCs (tank circuits) areconnected in cascade fashion with closely adjacent bands. The equiva-lent lumped element circuit model for the proposed antenna, shown inthe Fig. 7, was primarily based on the widely used degenerative Fostercanonical model and was designed using ADS software [12]. Here,Lp and Cp represent the inductance and capacitance, respectively,when the antenna is operating at basic mode (lower frequency).The remaining higher resonances are realized using three RLC tankcircuits connected in cascade fashion. Parameters R1, R2, and R3represent the radiation resistance of each related resonance. Themiddle RLC circuit (R2, L2, C2) controls the lower side of thewideband, the right RLC tank (R3, L3, C3) controls the higherfrequencies, and the left RLC tank (R1, L1, and C1) adjusts matchingwithin the band. The capacitor shown in the figure , C4, representsthe loaded capacitor when the antenna is capacitively loaded. Therespective values of the circuit model components are given in theembedded table in Fig. 7.

III. RESULTS AND DISCUSSIONS

The objective of this study was to design a wideband stableimpedance-matched antenna, operating at 915 MHz and of a suitablesize for an iTDS device, which would work perfectly inside the dy-namic human-mouth environment. The simulation and measurementof the proposed antenna were carried out using the setups shownin Fig. 6 in an Ansoft HFSS finite element method-based simulatorand in subject’s mouth, respectively. The reflection coefficient of theantenna is depicted in Fig. 8. It can be seen that the proposed an-tenna maintained wideband and stable impedance matching for bothscenarios in both simulations and measured results. The simulatedbandwidth was 151% (813–2200 MHz) and 163% (700–2194 MHz)for the open- and closed-mouth cases, respectively. The measurementof the reflection coefficient was performed inside the mouth of the’test subject’, and the measured bandwidth of the proposed antennaremained in good agreement with simulated scenarios, with widebandwidth values of 142% (820–2120 MHz) and 181% (720–2380MHz) for the open- and closed-mouth cases, respectively. From theseresults, we conclude that the proposed antenna can indeed be usedfor iTDS in the variable environment of the mouth.

To fulfill the propagation-direction requirement for iTDS applica-tion, we plotted the radiation patterns and direction of propagationas shown in Figs.9(a)–(d). Figures 9(a) and (b) show the satisfactionof the conditions for the required application as the antenna ispropagating outside of the mouth. The comparison of simulated andmeasured radiation polar patterns for the open- and closed-mouth

5

TABLE IILINK BUDGET CALCULATION FOR THE PROPOSED WIDEBAND ITDS

ANTENNA.

Par. detail value Par. detail value

fr Frequency 915 MHz PL Path loss (dB) Adjustable

Br Tx data rate 250/24 kbps NF Noise figure 3.5 (dB)

OOK Mod. scheme 100% SNR Signal to noise ratio 12.0 (dB)

Pt Tx EIRP 25 μWNo

Noise power

density

-203.9

dBm/HzGt Tx Gain -17.5/-18.9 dBi

TABLE IILINK BUDGET CALCULATION PROPOSED WIDEBAND iTDS ANTENNA SYSTEM

k

k k

k

Ver. detail value Ver. detail value

f Frequency 915 MHz PL Path loss (dB) Adjustable

Br Tx data rate 250/24 kbps NF C/No 3.5

OOK Mod. scheme 100% SNR Signal to noise ratio 12.0

Pt Tx EIRP 25 μWNo

Noise power

density

-203.9

dBm/HzGt Tx Gain -17.5/-18.9 dB

TABLE IILINK BUDGET CALCULATION PROPOSED WIDEBAND iTDS ANTENNA SYSTEMFig. 11. Link budget analysis for the proposed iTDS antenna at 915 MHz.

cases at 915 MHz in azimuthal and elevation planes are shown inFigs. 9(c) and (d), respectively, and both are in close agreement witheach other. The maximum peak realized gains observed in simulationand measurement were -17.5 and -17.96 dBi in the open-mouth cases,and -18.94 and -19.42 dBi in the close-mouth cases, respectively.

The operation of the antenna inside the mouth is critical due to itsdirect contact with mouth tissue and the effects of the power absorbedby those tissues. For the safety of iTDS users, the maximum SAR isrestricted to less than 2 and 1.6 W/kg over 10 g and 1 g of tissue,respectively. In this study, we calculated the SAR and maximumallowable power over 1 g of tissue and set the net input power tobe 1 W in the simulations. Figure 10 shows the SAR distributionsover 1 g of tissue at 915 MHz for open- and closed-mouth scenarios.The maximum SAR of 120.09 and 108.25 W/kg was recorded at themaximum allowed power values of 13.3 and 14.8 mW for closed-and open-mouth scenarios, respectively. These values satisfy bothinternational and national safety guidelines, and as such, the proposedantenna was proven to operate safely inside the variable environmentof the mouth.

For the assessment of communication range over which theproposed antenna can efficiently communicate with other devices,is evaluated through link budget analysis. Reflections, scattering,absorption, path loss, and mismatch losses are the associated factorsaffecting the communication link. The link margin is the differencebetween the power required for a signal to reach a distant receiverand available radiated power at the transmitter (Tx) end and can becalculated according to Friis equations [3]. The Tx output power isset as 25 µW, which is the maximum permissible power (EIRP) forwireless body area network (WBAN) IoTs. Based on the parametersfor iTDS system and the proposed antenna parameters are presentedin Table II. Based on these parameters the link budget is calculated, asdepicted in Fig. 11. The link margin is fixed as 35 dB. The proposedantenna can effectively communicate for the worst scenario (closed-mouth) over distances of at least 20 m at a data rate of 250 kbps and36 m at 24 kbps.

IV. CONCLUSION

In this study, we presented the design, analysis, and experimentalvalidation of a small flexible folded dipole antenna by considering the

dynamic behavior and anatomy of the mouth, and the curve shape ofthe iTDS device. The proposed antenna maintained stable widebandbehavior with the smallest footprint of 20 mm x 4.4 mm x 0.025mm at an operating frequency of 915 MHz. This frequency band wasselected as it is less vulnerable to power absorption by mouth tissue,provides a good radiation performance, and offers improved availabil-ity compared to the busy 2.4 GHz band that also suffers significantpower absorption in the mouth. The simulations and measurementswere performed in both closed- and open-mouth scenarios. In theclosed-mouth tests at 915 MHz, stable broad bandwidths of 163%and 181% were observed for the simulations and measurements,respectively, whereas in the open-mouth tests stable broad bandwidthsof 151% and 142% was observed for simulations and measurements,respectively. The realized peak gains were -17.5 and -18.94 dBi forthe open- and closed-mouth cases, respectively. Additionally, for thesafety of future iTDS users, the SAR was calculated, and values werefound to be well below the safety guidelines. The simulation andmeasurement results prove that the proposed antenna is appropriate,and indeed, advantageous, for application in iTDS devices whichtransmit data from the mouth to external receptors.

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[3] F. Kong, M. Zada, H. Yoo, and M. Ghovanloo, “Adaptive matchingtransmitter with dual-band antenna for intraoral tongue drive system,”IEEE transactions on biomedical circuits and systems, vol. 12, no. 6,pp. 1279–1288, 2018.

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[5] H. Park and M. Ghovanloo, “Wireless communication of intraoraldevices and its optimal frequency selection,” IEEE transactions onmicrowave theory and techniques, vol. 62, no. 12, pp. 3205–3215, 2014.

[6] F. Kong, C. Qi, H. Lee, G. D. Durgin, and M. Ghovanloo, “Antennas forintraoral tongue drive system at 2.4 ghz: design, characterization, andcomparison,” IEEE Transactions on Microwave Theory and Techniques,vol. 66, no. 5, pp. 2546–2555, 2018.

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[9] M. Zada and H. Yoo, “Miniaturized dual band antennas for intra-oraltongue drive system in the ism bands 433 mhz and 915 mhz: Design,safety, and link budget considerations,” IEEE Transactions on Antennasand Propagation, vol. 67, no. 9, pp. 5843–5852, Sep. 2019.

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

[11] A. Kiourti and K. S. Nikita, “Miniature scalp-implantable antennas fortelemetry in the mics and ism bands: design, safety considerations andlink budget analysis,” IEEE Transactions on Antennas and Propagation,vol. 60, no. 8, pp. 3568–3575, 2012.

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