Development Of The Flexible Textile Conformal Antennas And Investigation Of The Radiation Properties

Wearable devices are promising to be used in many areas such as medical and health care fields,military and public security fields,engineering fields,sports and entertainment fields.For instance,smart combat uniforms are possible to increase the convenience of communication during battle and provide vital signal monitoring for the soldiers.In addition,the functions of position and tracking make the strategic deployment and rescue operation easier.In health care domain,wearable devices are possible to monitor the physiological signals of patients remotely.The data captured by wearable devices will be used in illness prediction and medical assistant,which will increase the efficiency and reduce the cost of medical treatment.In the applications mentioned above,antenna is able to transmit the signal in real-time wirelessly which is one of the indispensable electronic components.The antenna which works in wireless body area network is called wearable antenna.The requirements of wearable antennas are comfortable,lightweight,hard to be noticed and less obstructive.Therefore,traditional materials which are rigid and heavy are required to be replaced by new materials which are soft and flexible in wearable antenna fabrication.Textile material is one of the desirable new materials for wearable antennas since the reasonable price and convenient access approach.Nevertheless,there are still several challenges for wearable textile antenna in practical.First of all,conductive layers in textile antennas have periodical air gaps and the woven structures are anisotropic.Therefore,investigating the effects of woven structure on antenna properties is necessary.Secondly,the shape of the flexible antenna and gap between the antenna and human body are varying during movement which also affects the antenna performance.Thus,it is also necessary to make the antenna input matching less sensitive to antenna deformation.Thirdly,a human body behaves as an inhomogeneous lossy antenna platform with a high dielectric permittivity which significantly impacts the antenna performance and wireless communication.Therefore,it is necessary to take the impact of human body into account in the antenna design process.The main objective of this study is to develop novel textile antennas,and to investigate the effects of textile structures,bending and human body on antenna properties at the same time.Four different types of textile antennas were developed and studied as follows:?1?A textile conformal dipole antenna was designed to work at the frequency of 915 MHz.The radiation elements of the antenna were adhered directly onto the stitched polyester fabric substrate to get the conformal effect.The measured S₁₁ of the antenna at the resonant frequency was-15.3 dB and the measured antenna gain was 3.4 dBi.The measured results showed that the antenna had good performance with the return loss value and typical omnidirectional radiation patterns.To investigate the effect of textile structure on the antenna performance,models for stitched and plain weave structures were built and the value of root mean square?RMS?surface error was calculated using integration methods.Then an acceptable range of operation frequencies versus RMS was marked out for estimating the reliability of textile substrate.Finally,the relationships between the critical frequencies and fabric parameters such as yarn thickness and density were studied.?2?Dipole antenna has omnidirectional radiation performance.To decrease the effects of antenna radiation on human body,textile microstrip antennas with small back lobes and big front lobes in their radiation patterns were developed in the second part of the study.The microstrip antennas were integrated into three-dimensional orthogonal woven fabrics for higher textile structure integration.In order to investigate the effects of woven structures on three-dimensional woven microstrip antenna properties,six single patch microstrip antennas with different woven structures were fabricated.The measured results of the six samples showed that the antennas with warp yarns perpendicular to the feed direction had lower resonant frequencies and radiation strength than the antennas with warp yarns parallel to the feed direction.According to the current distribution of the antennas,the current concentrated into the inner warp yarns of the microstrip antenna conductive layers,and the current went up to the weft yarns to cross the air gaps between the warp yarns in the antenna with warp yarns perpendicular to the feed direction.That increased the current path and resulted in a decrease in the resonant frequencies.Furthermore,a dual-polarized microstrip antenna with two orthogonally placed ports was developed based on three-dimensional woven structure.There were 102 MHz shared operating bandwidth and isolation of 17.2 dB between the two ports,and the antenna had desirable radiation patterns and gains for both port 1 and port 2.The measured results indicated that the two ports of the antenna were possible to be used simultaneously with less interference.?3?In order to achieve the requirements of high speed and large capacity communication,an ultra-wideband antenna integrated into three-dimensional orthogonal woven structure was developed in the third part of the study.The measured-10 dB bandwidth of the three-dimensional ultra-wideband antenna was 10.3 GHz over the frequency range from 2 GHz to 13 GHz,the measured gains of the antenna in its operating frequency bandwidth were reasonable for three-dimensional woven antennas,and the radiation patterns of the antenna were approximate omnidirectional.In addition,the specific absorption rate of the ultra-wideband antenna was simulated to evaluate the radiation safety of the antenna,and the simulated results were acceptable according to the standard.The variations of the measured antenna radiation properties were indistinctive when the antenna was under bending,indicating that the antenna is suitable to be used on human body which is curved at the surface.?4?Passive antennas have more advantages of low power consumption in wearable system,for instance,radio frequency identification?RFID?tag antenna could be excited by the power from the reader antenna,it is battery-free and suitable to be labeled on mobile object in wearable monitoring system.Therefore,a textile conformal circularly polarized passive RFID tag antenna was developed in the fourth part of study.A corner-truncated square patch with a shorting pin and an inductive feed network were used to achieve circular polarization and conjugate impedance matching,ground plane was applied to decrease the influence of human body.The RFID tag antenna had ideal properties for both in-air and on-body conditions.The measured best axial ratio values of the antenna were 2.1 dB and 2.2 dB for in-air and on-body conditions,and the corresponding read ranges were 9.1 m and 8.4 m.In conclusion,four types of wearable textile antennas which were textile conformal dipole antenna,three-dimensional woven microstrip antenna,three-dimensional woven ultra wideband antenna,and textile conformal circularly polarized passive RFID tag antenna were developed and investigated in this study.The radiation properties of the antennas were compared and analyzed by modeling,calculating and simulating,the effects of textile structures on antenna properties were investigated systematically at the same time.This study is a comprehensive work in wearable textile antenna field,which provides data and theoretical support to further study.