Researches On In-vivo And In-vitro Wideband Conformal Antennas For Body Area Network Applications

The continuous development of wireless communication technology has promoted the wide application of communication devices in the field of bio-detection,especially within the medical field of human-centered body area network.As an important device of the wireless communication module in medical detection,the performance of the in-vivo and in-vitro antenna is related to the communication quality between the implantable device and the in vitro receiving device.Among them,the bandwidth characteristics are related to the transmission rate and accuracy of detection results.Therefore,it is crucial to study the in-vitro and in-vivo antennas with broadband characteristics.In addition,the antenna conformal structure is also studied and designed in order to make the antenna better integrated on the device surface.The main work of the paper is as follows.(1)An implantable broadband conformal capsule antenna is designed.The antenna is placed in an implantable capsule device with a radius of 5 mm.The capsule wall is composed of a flexible biocompatible material,polyimide,which isolates the antenna from human tissue.The antenna has an inverted F structure with a conformal metal patch at the top of the capsule,which is connected to the grounding plate below the capsule through a metal pin,thus achieving quarter-wavelength resonance.In addition,the top metal patch is constructed on PET-ITO(PET: polyethylene terephthalate;ITO: indium tin oxide)in a "bow-tie" structure to ensure a certain light transmission while widening the bandwidth.The antenna has an impedance bandwidth of 127.2%(0.57-2.56GHz),covering in the ISM(Industrial Scientific Medical)and WMTS(Wireless Medical Telemetry Service)bands.(2)A conformal broadband equiangular spiral antenna based on ring coupling is designed.First,a wideband right circularly polarized antenna is built based on the principle of equiangular Archimedean spiral antenna for receiving signals inside the human body.A reflector plate is placed under the antenna in order to realize the unidirectional radiation of the antenna and reduce the influence of external circuits.In order to improve the performance of circularly polarized radiation in the low frequency band,an open ring is introduced below the radiating patch using coupling ring.The antenna is conformally designed.Simulation results show that the introduction of this open ring can make the antenna widen the circular polarization bandwidth and improve the gain without increasing the size.Finally,the ring-coupled spiral antenna with planar surface is processed and tested.The results show that the impedance bandwidth of the antenna is 76.9%(0.96-2.16GHz).The 3-dB axial ratio bandwidth is 55.2%(1.14-2.01GHz).The gain of the antenna in the circular polarization bandwidth is greater than 7.5 dBic.(3)Based on the previous two parts of the study,the evaluation of the in-vivo and in-vitro transmission links was carried out.In this case,the in-vivo capsule antenna is used as the transmitting antenna and the conformal binary spiral antenna array is used as the receiving antenna.The calculation results show that the whole antenna system is capable of stable transmission at a transmission rate of 100kb/s over a distance of 1m,which is suitable for suitable body domain network applications.