| Nowadays,mobile health is becoming popular in the advanced medical treatment.Different from the traditional medical treatment,mobile Health has the characteristics of high efficiency and low cost,and can monitor in real time.As an extremely important part of implantable mobile healthy devices,implantable antennas are key elements for data exchange in vivo and in vitro.Different from wired communications,wireless ones through implantable antennas can greatly alleviate the pain of patients in medical treatment.Due to the fact that the human body is a mobile object working in a harsh environment,polarization mismatch between transceiver units is inevitable.Circularly polarized(CP)antennas can address these issues,and greatly enhance the robustness and fault tolerance.In addition,with the increase of people’s requirements for implantable devices’ function,implantable antennas with multi operating modes also have important research value.This thesis was supported in part by the Science and Technology Planning Project of Guangdong Province under Grant No.2015B010101006,No.2014A010103014,No.2017xm057,and in part by the National Natural Science Foundation of China under Grant No.61372008,the following work mainly targets on the investigation of implantable antennas for harsh medical communication environments:(1)Wideband circularly polarized implantable antenna fed by CPW.In order to adapt to the variable electromagnetic environments of the human body,a wideband circularly polarized antenna fed by Coplanar Waveguide(CPW)is proposed in the 2.45-GHz ISM band.The advantages of CPW are the large bandwidth,and the ease of fabrication with single-layer metal conductors.Circular polarization is achieved by cutting asymmetrical slots in the antenna.The simulated impedance and AR bandwidths are 2.24 GHz(1.15–3.39 GHz,98.68%)and 920 MHz(2.29–3.21 GHz,33.45%)with broadband performance.Via the performance analysis of parameters,the antenna illustrates a good robustness.The measurement results showed 1.26 GHz(2.17–3.43 GHz,45%)impedance bandwidth,slightly deviating from the simulation results.Circular polarization is introduced in this design to address the polarized mismatch issue in medical communication.But,in real applications,there is still a mismatch between leftand right-handed circularly polarized antennas.So,the following work adopts the idea of reconfiguration to design an implantable antenna with switchable circularly polarized states.(2)Left-and right-handed circularly polarized reconfigurable implantable antenna.The slots and shorting pins are employed in the proposed antenna for the miniaturization,operating at 2.45-GHz ISM band.To obtain the dual circularly polarized mode,PIN diodes are used as switches to change the polarized states of the antenna.The dimensions of the antenna are 8.9 mm × 6.6 mm × 1.27 mm(74.6 mm3).The simulated impedance and AR bandwidths are 520 MHz(2.11–2.63 GHz,21.9%)and 150 MHz(2.38–2.53 GHz,6.1%)with a peak gain of-23.9 d Bi,respectively.The half-power beamwidth(HPBW)covers at least70°.The 3-d B AR beamwidth(ARBW)covers at least 80°.The measured results showed that the impedance bandwidth is 620 MHz(2.12–2.74 GHz,25.5%).Through the measurement of the external CP antenna,the optimization of the polarized match of the antenna can be achieved in the band from 2.27 to 2.61 GHz.In the above designs,the antennas work in single state.With the rise of people’s demand,multi-band and multi-function implantable antennas have become a research hotspot.Not only off-body communication between in-vivo and in-vitro devices,but also in-body communication between in-vivo devices are needed.Therefore,circularly polarized dual-band and dual-radiation implantable antenna is investigated to meet the needs of multi-mode antennas.(3)Circularly polarized antenna with dual radiated modes.Based on the microstrip antenna,the slots and slow-wave structures are employed to lower the resonant frequency.By loading the shorting pin,different operating modes of the microstrip antenna are excited.The proposed antenna operates in the 915-MHz ISM band for omnidirectional in-body communication and in the 2.45-GHz ISM band for directional circularly polarized off-body communication.Simulation shows that at 915 MHz,the impedance bandwidth of the antenna is 70 MHz(0.87–0.94 GHz,7.7%),and at 2.45 GHz,the antenna has an impedance bandwidth of 300 MHz(2.38–2.68 GHz,11.3%)with a 3-d B AR bandwidth of 130 MHz(2.38–2.51 GHz,5.3%).From simulation of the far field,at 915 MHz,the proposed antenna has an omnidirectional gain of –28.2 d Bi,and its HPBW covers 109° on the E-plane with an out-of-roundness of 0.44 d B on the H-plane.At 2.45 GHz,the antenna has a directional RHCP gain of –22.9 d Bi with a HPBW of 77° and a ARBW of 80°.Via measurements,the impedance bandwidths are 100 MHz(0.87–0.97 GHz,10.8%)and 690 MHz(2.21–2.90 GHz,27%),respectively.Finally,it was verified in the microwave anechoic chamber that this antenna realized two radiation modes.Three circularly polarized implantable antennas proposed in this research have the characteristics of small size,broadband,robustness and multi-mode.It can be used in mobile medical communication systems.It is hoped that the relevant research content of this work would be helpful to the design of circularly polarized implantable antennas. |
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