In this paper we propose a compact size rectangular implantable tri-band patch antenna for biotelemetry applications. Rogers RT6010 is used as substrate and superstrate material. The resonant frequency is further lowered by using a shorting pin which also reduces patch resistance. For excitation 50-ohm microstrip line is used. The antenna operates in MICS band (402405) MHz, ISM band (902-928) MHz and (2.4-2.48) GHz at 402 MHz, 915 MHz and 2.4 GHz. The gain of the antenna is 2.05 dBi, 2.67 dBi and 5.39 dBi with bandwidth of 120 MHz, 166 MHz and 190 MHz at relevant frequencies when simulated in a fat layer box. SAR values are within allowable limits. The simulated results show that the antenna is an excellent choice for implantable applications as it can be used for data transmission, wakeup signal and wireless power transfer by using three frequency bands

Amjal, Tahmina

Malik, Nabeel Ahmed

Sant, Paul

Ur Rehman, Masood

English

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     Malik, N. A., Amjal, T., Sant, P. and Ur Rehman, M. (2020) A Tri-Band Implantable Antenna for Biotelemetry Applications. In: 5th International Conference on UK-China Emerging Technologies (UCET), Glasgow, UK, 20-21 August 2020, ISBN 9781728194882 (doi:10.1109/UCET51115.2020.9205362).  This is the author’s final accepted version.  There may be differences between this version and the published version. You are advised to consult the publisher’s version if you wish to cite from it.  http://eprints.gla.ac.uk/223278                              Deposited on: 08 October 2020         Enlighten – Research publications by members of the University of Glasgow http://eprints.gla.ac.uk   A Tri-band Implantable Antenna for BiotelemetryApplicationsNabeel Ahmed MalikDeparment of Computer Science andTechnology, University of BedfordshireLuton, UKnabeel.malik@study.beds.ac.ukPaul SantDeparment of Computer Science andTechnology, University of BedfordshireLuton, UKpaul.sant@beds.ac.ukTahmina AjmalDeparment of Computer Science andTechnology, University of BedfordshireLuton, UKtahmina.ajmal@beds.ac.ukMasood Ur-RehmanJames Watt School of EngineeringUniversity of GlasgowGlasgow, UKmasood.urrehman@glasgow.ac.ukAbstract—In this paper we propose a compact size rectangularimplantable tri-band patch antenna for biotelemetry applications.Rogers RT6010 is used as substrate and superstrate material.The resonant frequency is further lowered by using a shortingpin which also reduces patch resistance. For excitation 50-ohmmicrostrip line is used. The antenna operates in MICS band (402-405) MHz, ISM band (902-928) MHz and (2.4-2.48) GHz at 402MHz, 915 MHz and 2.4 GHz. The gain of the antenna is 2.05 dBi,2.67 dBi and 5.39 dBi with bandwidth of 120 MHz, 166 MHz and190 MHz at relevant frequencies when simulated in a fat layerbox. SAR values are within allowable limits. The simulated resultsshow that the antenna is an excellent choice for implantableapplications as it can be used for data transmission, wakeupsignal and wireless power transfer by using three frequencybands.Index Terms—Biotelemetry, Patch Antenna, Implantable sen-sors, Wireless power transferI. INTRODUCTIONWith recent developments in technology and wireless com-munication, biotelemetry has gained a lot of attention and hasbecome a major part of our everyday life [1]–[3]. Implantablemedical devices and sensors are used in biotelemetry. Theyare capable of monitoring patient psychological signals inreal time which saves a lot of time and money that waspreviously spent on such facilities in hospitals [4]–[7]. Thereare a number of such devices including: blood sugar levelmonitoring, cardiac pacemakers, defibrillators, retinal implantsand capsule endoscopy etc. [8]–[14]. All these devices andsensors rely on an antenna for communication with externaldevice to receive and transmit data. So, any issues withoverall antenna performance would have a direct impact onsystem efficiency. At higher frequencies the signal distortionrate increases so the operating frequency of the implantableantenna should be as low as possible. The size of the antennais also important, but if we decrease the size the resonantfrequency will increase to a higher value, so careful consid-eration needs to be given to these matters. As the antennahas to operate inside the human body, the safety of humanbody tissue is a big challenge as well. The battery life ofimplantable devices should be as long as possible so thatsurgery is not needed very frequently to replace the batteries.On the other hand, wireless power transfer techniques can beused to power the implantable sensors by introducing an extrafrequency band for the implantable antenna. More generallythe selection of antenna for biotelemetry is a challengingtask. According to the literature, several antennas have beenproposed for implantable applications. A wideband circularlypolarized implantable patch antenna for ISM band medicalapplication was proposed in [15]. A 0.635 mm layer of RogersRO6010 (r = 10.2; tan δ = 0.0023) is used as substrate andsuperstrate material. The overall volume of the antenna is 122mm3 and it operates at 2.4 GHz. The antenna is simulated inskin layer. Slots are etched in the patch and two shorting pinsare used to adjust the resonant frequency. The bandwidth ofthe antenna is 21%, having a peak gain of -33 dBi. The gainof the antenna is low compared to its relatively large size andhigher resonant frequency.Li Rongqiang, et al. presented a compact broadband antennawith dual-resonance for implantable devices in [16]. Rogers6010 (r = 10.2; tan δ = 0.0023) is used as substrate materialwith thickness of 0.635 mm. A shorting pin is used to lower theantenna frequency. The size of the antenna is 23×16.4×1.27mm3. The antenna shows a peak gain of -34.9 dBi with abandwidth of 52 MHz at 0.402 MHz when simulated in a skinlayer phantom model. The bandwidth of the antenna is quitenarrow. A flexible implantable antenna on PMDS substrate isproposed in [17]. The antenna is simulated in a three-layerphantom model. The overall size of the antenna is 242 mm3.The bandwidth of the antenna is 500 MHz with a peak gainof -20.8 dBi. A miniaturized implantable Planar inverted Fantenna is proposed in [18]. The antenna is designed on a 0.75mm thick layer of alumina which is also used as superstratewith a thickness of 0.5 mm. A shorting pin is used to lowerthe antenna frequency. The overall volume of the antennais 125 mm3. The antenna has a bandwidth of 180 MHzwith a gain of -4.5 dB at 2.45 GHz. The antenna operatingfrequency could be lowered when compared to the antennaslarge size. Shang et al. proposed an implantable dual bandplanar inverted F antenna in [19]. The antenna substrate andsuperstrate material is Rogers 3010 with a thickness of 0.5.The overall dimensions of the antenna are 9×11×0.5 mm3. At402 MHz and 2.4 GHz the peak gain of the antenna is 38.8dBi and 18.6 dBi whereas the bandwidth is 152 MHz and170 MHz at relevant frequencies. In this paper we proposean implantable antenna which operates on three frequenciesand has small size, high gain and low specific absorption rate(SAR). This paper is structured as follows: Section I detailsthe importance of implantable devices, implantable antennasand recent research on implantable antennas. In section II thedesign of proposed antenna is given. Section III explains theresults and analysis and conclusions are drawn in last section.II. IMPLANTABLE ANTENNA DESIGNThe antenna patch and ground plane are shown in Fig. 1(a) and (b). The antenna is designed on a 0.25 mm thick layerof Rogers RT6010 (r = 10.2; tan δ = 0.0023) substrate. Thesuperstrate layer is also used for human body tissue safety andto lower the operating frequency. The superstrate layer materialand thickness is same as the substrate. Copper cladding is usedfor the antenna ground plane and patch material. The antennais excited by a 50-ohm microstrip line. Overall dimensionsof antenna are 6×5×0.5 mm3. The perspective view of theantenna is shown in Fig. 2(a). Slots are etched onto the patchto elongate the current path which makes physically smallantenna an electrically large antenna. The insertion of slots(a) (b)Fig. 1: (a)Antenna patch (b) Antenna ground planein the patch introduces more electrical resistance which isreduced by a shorting pin P(x= -0.97; y = 1.5). The shortingpin also helps to lower the operating frequency. Slots are alsointroduced in the ground plane to adjust the resonant frequencyand to achieve the wider bandwidth. Simulation of the antenna(a) (b)Fig. 2: (a)Antenna perspective view (b) Antenna in fat boxwas performed using CST Microwave Studio software. Thesimulated antenna design is placed inside a (60×60×60) mm3fat layer box to analyze the antenna performance as shownin Fig. 2(b). The antenna detail dimensions are presented inTable I.TABLE I: Antenna dimensionsParameter Unit(mm) Parameter Unit(mm) Parameter Unit(mm)L 6 L7 0.3 W4 0.3L1 0.2 L8 0.2 W5 0.2L2 0.1 L9 0.9 W6 0.275L3 1.4 W 5 W7 0.2L4 2.9 W1 2.151 W8 0.3L5 2 W2 3.8 W9 2.95L6 5.05 W3 0.425III. RESULTS AND DISCUSSIONThe antenna was first simulated in free space and then in afat layer model. The simulation results are listed below.Fig. 3: Antenna return loss plotA. Return loss (S1,1)The return loss(S1,1) of an antenna is a measure of antennatransmitted power and reflected back power. The lower thevalue of S1,1, the lower the reflected back power and thehigher the transmitted power. The standard for an antenna toresonate on a specific frequency is that the value of S1,1 shouldbe less than or equal to -10 dB (S1,16 -10). The return lossof the antenna in free space and in 1mm, 2mm and 4mm fatlayer versions is shown in Fig. 3. It can be seen in the Fig. 3that the antenna is resonating on three frequencies which are402 MHz, 915 MHz and 2.4 GHz when placed inside the fatlayer. The -10 dB bandwidth of the antenna is 120, 166 and190 MHz at resonant frequencies.B. Antenna Radiation Pattern and GainThe radiation pattern of the antenna gets deformed whenplaced inside a lossy medium like human body tissues. Thereare a number of parameters which affect the antenna radiationpattern such as power absorption, reflection and refractionfrom tissue boundaries, antenna bending and antenna position-ing inside the body. The 3D radiation pattern of the antennaat 0.402, 0.915 and 2.4 GHz is shown in Fig. 4 (a), (b) and(c) whereas the E-plane and H-plane radiation pattern of theantenna at resonant frequencies is shown in Fig. 5 (a) and (b)when antenna is placed inside fat layer.(a) (b) (c)Fig. 4: Antenna 3D radiation pattern (a) at 402 MHz (b) at915 MHz (c) at 2.4 GHz(a) (b)Fig. 5: (a)E-plane radiation pattern of the antenna (b) H-planeradiation pattern of the antennaIt can be seen in Fig. 4 and 5 that the antenna has aomnidirectional radiation pattern which is required in medicalimplants. The gain of the antenna at 402 MHz is 2.05 dBi,2.67 dBi at 915 MHz and 5.39 dBi at 2.4 GHz when antennais simulated in fat layer box.C. Antenna Current DistributionThe current distribution of the antenna at 402 MHz, 915MHz and 2.4 GHz is shown in Fig. 6 (a), (b) and (c). Thecurrent is more at lower half of the patch at 402 MHz whileat 915 MHz the current is more in the patch middle section.The current is more in the left lower part of the patch at 2.4GHz. If the current path is altered at maximum current positionit will effect the resonant frequency by shifting it to a higheror lower value.(a) (b) (c)Fig. 6: Antenna current distribution (a) at 402 MHz (b) at 915MHz (c) at 2.4 GHzD. Specific Absorption Rate (SAR)The electromagnetic radiations from the antenna could harmhuman body tissue. So, the SAR should be within allowedlimits. There are two standards that are used for SAR. Ac-cording to IEEE C95.1-1999 standard the SAR should be lessthan 1.6 W/kg averaged over 1g cubic volume of tissue andaccording to IEEE C95.1-2005 standard the SAR should beless than 2 W/kg averaged over 10g cubic volume of the tissue[20]. We have calculated 1g avg. SAR using CST MicrowaveStudio when input power is 0.5W which is shown in Fig.7 (a), (b) and (c). The value of SAR at 0.402, 0.915 and 2.4(a) (b) (c)Fig. 7: Antenna 1g avg. SAR (a) at 402 MHz (b) at 915 MHz(c) at 2.4 GHzTABLE II: Proposed Antenna Comparison with Previous WorkReference Size(mm3) Frequency(GHz) Gain(dBi) Bandwidth (MHz) Shorting pin used SAR 1g avg. (W/Kg)[15] 9.8×9.8×1.27 2.4 -33 540 YES 486[16] 23×16.4×1.27 0.402 -34.9 52 YES 284.5[17] 11×11×2 2.4 -20.8 500 NO 356.4[18] 10×10×1.25 2.45 -4.5 180 YES 113.5[19] 9×11×0.5 0.402; 2.4 -38.8; -18.6 152; 170 YES 719; 746Proposedwork6×5×0.5 0.402; 0.915; 2.4 2.05; 2.67; 5.39 120; 166; 190 YES 123.3; 189.9; 797.5GHz is 123.3 W/kg, 189.9 W/kg and 797.5 W/kg which seemshigher than the maximum allowed limits. To meet the SARrequirements the maximum allowed input power at resonantfrequencies should be less than 12.9, 8.4 and 2 mW [21]. So,the SAR values for this antenna are within allowed limits. Thecomparison of proposed antenna with previous work is givenin Table II.IV. CONCLUSIONWe have presented a compact size tri-band implantableantenna operating at 402 MHz, 915 MHz and 2.4 GHzfor biotelemetry applications. Slots are etched in the patchand ground plane to adjust the operating frequency. Fur-ther frequency adjustment and patch resistance reduction wasachieved by inserting a shorting pin between the patch andground plane. The antenna performance was analyzed using afat layer model. The antenna gives a peak gain of 2.05 dBi,2.67 dBi and 5.39 dBi with SAR values within permissiblelimits. The antenna can be used for data transmission, wakeupsignal and wireless power transfer by using its three frequencybands. The comparison Table II shows that this antenna is thebest choice to be used in implantable medical devices.REFERENCES[1] Q. H. Abbasi, K. Qaraqe, A. Alomainy, and M. U. Rehman, Advances inbody-centric wireless communication: Applications and state-of-the-art.The Institution of Engineering and Technology, 2016.[2] M. Ur-Rehman, M. Adekanye, and H. 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A Tri-Band Implantable Antenna for Biotelemetry Applications

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A Tri-band Implantable Antenna for Biotelemetry Applications

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A Tri-Band Implantable Antenna for Biotelemetry Applications

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