Research On Wireless Capsule Endoscope Antennas For Biomedical Applications

Now,digestive tract disease is becoming global high-incidence one.It is particularly important to adopt effective detection methods,preventing and treating this kind of disease.Wireless capsule endoscopes have attracted more and more attention as they offer significant advantages in achieving noninvasive examination of the digestive tract.As the key component in communication between the wireless capsule endoscopes and external devices,the performance of the antennas takes a critical role in enhancing the quality of communication.Due to the fact that the capsule antennas need to go through the lossy tissues with different electromagnetic properties when passing through the human digestive tract and their locations and postures are arbitrary in the process,the communication between the internal and external devices would be failed.Therefore,it is of great value and significance to carry out the relevant research.This dissertation was supported in part by the Science and Technology Planning Projects of Guangdong Province(No.2015B010101006,No.2014A010103014,No.2017xm057),and in part by the National Natural Science Foundation of China(61372008),the following research is carried out mainly about the wireless capsule endoscope antennas for biomedical applications:(1)A broadband circularly polarized wireless capsule endoscope antenna.Considering the polarization mismatch caused by the change of capsule position and posture in the working process of human digestive tract,a circularly polarized capsule antenna with broadband characteristic is designed.The proposed antenna consists of two pairs of crossed dipole arms and two rectangular coupling patches.By introducing a winding path on the dipole arm,the dimensions of the antenna can be reduced.Each pair of dipole arms is connected with a threequarter ring-shaped phase delay line,resulting in a 90° phase difference.The circular polarization characteristic of the antenna is further optimized by loading rectangular patches.Space saving is achieved by conforming the antenna to the inner surface of the capsule.The antenna has the dimensions of 18 × 15 × 0.254 mm3 with a –10-d B impedance bandwidth of38.5%(2.31–3.41 GHz)and a 3-d B axial ratio bandwidth of 37.5%(2.36–3.45 GHz).In addition to data transmission,the ingestible capsule endoscope devices also perform other functions such as wireless energy transferring.Therefore,multi-band antennas need to be implemented for such devices,realizing multiple tasks.Due to the variable working environment,the antennas should be broadband with robust performance.Therefore,broad dual-band wireless capsule endoscope antenna for data communication and wireless energy transmission is presented.(2)A broad dual-band wireless capsule endoscope antenna.By etching four rectangular slots and two C-shaped slots on the patch,multiple different resonant modes are introduced,covering 915-MHz and 2.45-GHz ISM bands with broad impedance bandwidths of 46.0%(0.82–1.31 GHz)and 48.2%(1.89–3.09 GHz),and the maximum gains of –24.4 d Bi and –35.1d Bi.Similar to the previous antenna,this antenna saves space inside the device by being conformal to the device with the dimensions of π ×(5.42-5.32)× 11 mm3.In this work,the relevant parameters are analyzed.And the effects of different capsule shell materials,thicknesses and electronic components on the performance of the antenna are evaluated,and the physical fabrication and verification are carried out.In addition,an analysis of the link budget of the antenna is carried out.Due to the complex and changeable human environment,and the first two antennas only achieve a single radiation state,their radiation communication ranges are limited,their ability to resist the influence of the rotation and position changes of the capsule devices still has certain limitations.Therefore,a reconfigurable wireless capsule endoscope antenna with quasiisotropic radiation pattern is developed.(3)A radiation pattern reconfigurable wireless capsule endoscope antenna.The antenna adopts a composite structure,consisting of two conformal arms and a PIFA structure.The miniaturization is achieved by the introduction of shorting pin and arc current path,and the reconfiguration of two different states is implemented by loading PIN diodes on the conformal arms.The different states of the antenna present different radiation properties,and both states operate in the 915-MHz ISM band with an impedance bandwidth of 0.88–0.95 GHz(7.6%).The radiation patterns of the two states are complementary,with a significant gain improvement in the weakest region of radiation in one of the two states after reconfiguration,presenting quasi-isotropic radiation behavior in the single-layer human tissue phantom,with a maximum gain of –17.9 d Bi as well as a gain variation range of only 4.5 d Bi.Furthermore,this dissertation presents the working principle of the antenna,analyzes the influence of critical parameters and electromagnetic compatibility,and evaluates the SAR values and communication distance.The wireless capsule endoscope antennas proposed in this dissertation have the advantages of miniaturization,circular polarization,high robustness and reconfigurable radiation pattern.It is hoped that the related research in this dissertation can provide a reference for the design of wireless capsule endoscope antennas.