Research On Stretchable Flexible Microstrip Antenna Based On Defective Ground Structure

In recent years,stretchable flexible electronic technology has been widely used in flexible sensors,wearable devices and other new electronic devices.Among them,the wearable physiological monitoring system based on flexible sensor has great application potential in health monitoring.As the key component of the system data transmission link,the flexibility of the RF antenna is an important part of the related system research.Microstrip antennas have been widely used in wireless signal transmission in integrated sensing systems due to the advantages of concise structure,easy realization of low profile and miniaturization.Although the flexibility can be achieved by using intrinsically flexible conductive materials,the poor impedance characteristics of this material can easily lead to the degradation of the antenna performance.By graphical structure design of conventional conductive materials such as metal,the overall deformation of the antenna can be realized through structural deformation while achieving good impedance characteristics.However,the stretchable structure widely used in the current structural flexible design strategy has the problem of low stretchability and filling rate,which restricts the further improvement of its mechanical stretchability and radiation characteristics.In this thesis,the application of fractal structure in stretchable microstrip antenna is studied.The main research contents are as follows:1.In view of the shortcomings of the current stretchable structures used to realize the flexibility of the antenna structure in terms of the stretchability and the structure filling rate,a microstrip antenna radiation patch and ground plane structure based on Hilbert fractal curve is proposed.The mechanical stretchability and electromagnetic performance of the design were simulated by the finite element method,and the influence of structural parameters such as Hilbert curve order and line width on the performance of the antenna was investigated in detail,and the optimal structural parameters for subsequent experiments were determined.2.A flexible microstrip antenna based on a second-order Hilbert curve is experimentally fabricated,and the S parameters of the antenna are characterized under stretching and bending conditions.The experimental results show that the fabricated microstrip antenna can achieve mechanical stretchability of 40%,and its resonant frequency decreases gradually with the increase of the amount of stretching,and there is a good linear relationship between the resonant frequency and the amount of stretching.The influence of bending deformation on S parameter is not obvious.The antenna can still maintain good electromagnetic characteristics after 80 times of cyclic stretching test.The tensile deformation has no obvious effect on the radiation characteristics of the antenna,and the antenna maintains a gain of more than 2.2 d B along the +z direction at different tensile rates.3.Based on the designed flexible antenna,a wireless strain sensing system is constructed.Based on the linear correlation between antenna resonant frequency and tensile rate,the correlation law between radiated power and tensile strain is established.By receiving the fixed frequency signal transmitted by flexible antenna and analyzing its radiated power,the wireless perception of strain is realized.The experimental results show that the system can realize the sensing of strain within 30% at a distance of 2 meters.On this basis,by attaching the flexible antenna to the knee,wrist,elbow and other different joint parts of the human body,the monitoring of a variety of motion postures is realized,and the application feasibility of the system in human motion monitoring is further explored.