Research And Design Of Wireless Capsule Endoscope Antenna

With the continuous development of electronic communication technology and the medical industry,wireless capsule endoscopy(WCE)system that combines biomedical functions has been born.As an important part of the WCE system to communicate with external receiving devices,antennas are becoming more and more important.Due to the complex environment of the human gastrointestinal tract,it is a huge challenge to design a capsule antenna that can achieve stable communication with external receiving device.In this article,four ingestible capsule antennas are designed,and the main subjects include:1.Firstly,an ultra wideband(UWB)capsule antenna is designed,which is composed of a meandering dipole attached to the inner wall of the capsule.The working band of the antenna covers 0.915 GHz,2.45 GHz industrial,scientific and medical(ISM)frequency band and 1.4GHz wireless telemetry service(WMTS)frequency band,and the impedance bandwidth reaches 0.75-3.28 GHz.The broadband characteristics ensure that the antenna can work in the required frequency band even if it is detuned in the complex environment inside the human body,making it applicable to WCE system.The antenna is fed by a lumped port.According to the simulation results,the capsule antenna can realize the function of ultra wideband,which verifies the rationality of the design.2.In view of the single function of the capsule antenna mentioned above,a capsule antenna with working band covering 0.403 GHz,0.413GHz(Med Radio)and 0.433 GHz ISM band is designed,which is also applicable to WCE system.Four metal strips were added to the inner wall of the capsule,and a diode was added in the center of each metal strip.The directional radiation in four different directions can be realized by controlling the on-off of the diode.For the feeding,the antenna uses coaxial feed.The simulation results show that the design can realize the reconfiguration of the radiation pattern in 0.403-0.433 GHz.Compared with the first capsule antenna,the gain of the antenna has been improved,and the radiation performance has been greatly improved.3.The two capsule antennas designed before are linearly polarized antennas.Because the position of the linear polarized capsule antenna in the human body is not fixed,it will lead to polarization mismatch and multipath loss.Therefore,two circularly polarized capsule antennas working in 0.915 GHz ISM band are designed for WCE system,which are antenna 1and antenna 2.By attaching L-shaped metal strip on the inner wall of the capsule and adding two metal cylinders inside the capsule,circularly polarized waves are generated.Antenna 2 is obtained by rotating antenna 1 180 ° around z-axis.Antenna 1 and antenna 2 can only realize circularly polarized radiation in limited range of xoy plane.The simulation results show that the design achieves circular polarization radiation,and has a wide impedance and axial ratio bandwidth.At the same time,the gain of the antenna is further improved.4.In order to obtain more stable omnidirectional radiation performance and achieve omnidirectional circularly polarized radiation in a wider azimuth plane,the fourth omnidirectional circularly polarized capsule antenna working in 0.915 GHz ISM band is proposed.The antenna is composed of antenna 1 and antenna 2,and the horizontal and vertical copper strip sizes are optimized.It can not only achieves stable omnidirectional radiation performance in the horizontal plane,but also maintain circular polarization performance(AR < 3 d B)in a very wide range of elevation angle ?(49°?144°),making it a strong candidate for WCE system in the future.The feeding part is the same as the former two,both of which adopt coaxial feeding.The experimental results show that the design has stable omnidirectional circularly polarized radiation performance.However,the maximum radiation direction of the fourth capsule antenna designed in this paper is ? =101°,which is due to the asymmetry of the antenna structure relative to the xoy plane.In order to make the maximum radiation surface of the antenna coincide with the xoy plane,the structure of the antenna is optimized.The simulation results show that the performance of the improved antenna achieves the expected results.