| By providing personalized and intelligent medical services,such as consistent monitoring,remote diagnosis and treatment,health prediction and so on,e-health is expected to cause a dramatic shift in wellness management.It can effectively mitigate the deficiency in medical resources,hence marketing opportunities will thoroughly expand.Wireless body area network(WBAN)can establish short-range,low power,and highly reliable wireless communications in the vicinity of,or inside a human body using wearable and implantable sensors and other portable devices.This technology is a key solution to realize e-health because it is capable of sampling,processing and communicating vital physiological parameters as well as receiving real-time feedback from the user and medical personnels without causing any discomfort.Therefore,WBAN has attracted more and more attention.This dissertation revolves around the WBAN and mainly focuses on the research of wearable antennas and capacitive human body communication(HBC).The study of wearable antennas is facing many technical challenges,such as miniaturization,multi-band,multi-function,and safety issue and so on.To solve these problems,several methods are proposed in this dissertation,including a novel capacitively coupled feeding technique using patch antenna for circular polarization,a size reduction technique for patch antennas based on the structure and mode symmetry,and a design methodology of dual-band dual-mode antenna using stacked patch structure.Based on the above methods,a variety of novel and high-performance wearable antennas are proposed.The capacitive HBC is a novel non-radio-frequency(non-RF)wireless communication technique,which uses the human body as the transmission medium for electrical signals.This technique is superior to the conventional RF wireless communication techniques in that it has a lower path loss,higher efficiency,wider signal coverage and higher security and so on.There are a variety of technical challenges regarding the study of capacitive HBC,such as the discrepancy in measurement schemes,the difficulties in modeling,numerical simulation and extraction of circuit parameters.In view of these issues,a novel measurement system is built up to emulate the realistic capacitive HBC channels.In addition,the full-wave analysis and equivalent circuit model are employed to investigate the operation principle,communication ability,and the influence of electrode structure and surroundings.The main contributions of this dissertation are summarised as below:1.A miniaturized circularly polarized(CP)wearable antenna is designed with the human body effect taken into consideration.Rather than employing a complex four-feed network to provide the phase shifts of 0°,90°,180°,and 270°,a novel capacitively coupled feeding technique using patch antenna for circular polarization is proposed,and it is implemented to design a planar quadruple inverted-L wearable antenna.Similar to the conventional quadrifilar helix antennas,the proposed antenna also features a wide beamwidth and low back radiation.The overall size in wavelength is only 0.19λ0×0.19λ0×0.04λ0.The antenna performances,specific absorption rate(SAR)and link budget are investigated in wearable environment.Compared with the published designs,the proposed antenna exhibits superior performances.2.A size reduction technique based on the structure and mode symmetry is studied and implemented for patch antennas.Using this technique,a novel compact dual-band antenna is presented for wearable applications,and its size only 1/8 that of conventional cir-cular patch antenna.In addition,a higher resonant mode is excited by slitting an open-ended quarter-wavelength slot.The proposed antenna has a simple structure and it can achieve reliable on-body perform ances.3.To solve the technical challenges in multi-band multi-functional wearable antenna design,a design methodology of dual-band dual-mode antenna using stacked patch structure is proposed.It is demonstrated that by etching slots properly,the coupling between the stacked patches can be reduced,keeping their impedance matching performances and radiation patterns unaffected.Based on this key technique,a novel dual-band dual-mode antenna is proposed.This antenna can generate vertically polarized omnidirectional radiation patterns for on-body links and broadside radiation patterns for off-body links although it requires only one feed port.The proposed antenna features wide impedance bandwidths,a low profile,good omnidirectivity and stable radiation patterns.4.Based on the above design methodology,an improved design with miniaturized form factor is proposed.In this design,the lower patch resonants at the monopolar patch mode,and it is capacitively coupled fed by a probe and shorted to the ground plane at the center.Such configuration not only reduces the coupling with the corner-truncated square patch at the upper layer,but also leads to a small form factor.In addition,a transition from feeding post to microstrip line is utilized in this design to avoid the discomfort caused by the direct touch between the coaxial probes and human body surface.Therefore,this antenna can be directly attached to the human body.With a miniaturized size of 0.18λ0×0.18λ0×0.04λ0,the proposed antenna can simultaneously achieve the properties of dual-band resonance,dual-mode radiation and dual polarization.In addition,it can generate vertically polarized omnidirectional radiation patterns for on-body links and CP broadside radiation patterns for off-body links.The antenna performances,SAR and link budget analysis are studied in both the on-body and off-body links.This antenna exhibits outstanding performances compared with the reported designs.5.A systematic study of the capacitive HBC based on experimental measurement,numerical simulation and equivalent circuit model is presented.To emulate the realistic capacitive HBC scenario,a novel measurement system is built up using portable devices,and its validity has been confirmed by conventional measurement setup.Then a complete numerical model is established and full-wave analysis is performed to verify the measurement results and to analyze the mechanism of signal transmission.The effect of electrode configuration on the input impedances and path gains of HBC channels is also studied using full-wave analysis.Based on the analysis of the simulated E-field distribution around and inside the body model,an equivalent circuit model is proposed.The circuit parameters are extracted using the finite element method,and the effect of human body is considered.Finally,the transmission capability along the human body and the influence of surroundings are investigated.Therefore,a variety of technical issues such as measurement,modeling and numerical simulation,establishment of equivalent circuit and extraction of circuit parameters are well addressed. |
