Study Of Time Domain Readout Method On LC Passive Wireless Sensors

Based on the principle of magnetic coupling,LC passive wireless sensor could transform the measured parameters into resonant frequency of the sensor,then the readout coil could detect it wirelessly.LC passive wireless sensor has the characteristics of simple structure,no power supply and so on,which could be applied in a variety of harsh environments,such as high temperature and pressured,closed,rotating environment.However,most researches on LC passive wireless sensors focus on the sensor nodes,the researches on readout mode of resonant frequency are relatively few.This thesis is devoted to the research on the time domain readout method of LC passive wireless sensor,using the readout characteristics of time domain readout method to measure the sensitive parameters quickly.The main contents are as follows.Firstly,the basic theory of LC passive wireless sensor is systematically analyzed,and the basic principle of time domain LC passive wireless sensor readout method is deeply discussed.Results show that the time domain readout method has a short measurement period and could quickly measure the resonant frequency of LC passive wireless sensor,but it is difficult to obtain the effective signal,the processing circuit is complex and the implementation is difficult to achieve.Secondly,A new type of time domain LC sensor readout method is proposed.The circuit consists of switch which could release voltage signal with coupled oscillating information.Then the voltage signal is converted into complex frequency domain through the Fast Fourier Transform menthod in order to calculate the maximum imaginary part of the equivalent impedance of readout system.The resonant frequency of the LC passive wireless sensor could be determined at the same time.The results show that the method could accomplish the precise measurement of the resonant frequency of LC passive wireless sensor.According to the principle of Fast Fourier Tansform algorithm,the measured resolution depends on the sampling frequency and sampling points of voltage signal.Morever,time domain readout method is not sensitive to the coupling coefficient k,so there is no restricted by coupling distance.Thirdly,an integrated LC passive wireless sensor time domain readout system is designed and implemented.FPGA is proposed as the main control system,the oscillating voltage signal is obtained by high-speed ADC chip,then Fast Fourier Transform algorithm is executed in order to calculate the maximum imaginary part of the equivalent impedance of readout system,and the waveform of the resonant frequency is displayed by display system.Results show that the system could realize low power-consumption readout of the resonant frequency of the LC passive wireless sensor.The error of the capacitance calculated by the resonant frequency is controlled within 5%.The total time of single measurement is 647.378?s,the power consumption of single measurement is 960 m W,and the measurement distance is up to 1.5cm.This thesis focuses on the readout method of LC passive wireless sensor,and a new time domain readout system of LC passive wireless sensor is proposed and implemented.Through theoretical analysis and experimental measurement,the system could effectively measure the resonant frequency of the sensor.In addition,the time domain readout method could realize the real-time measurement of resonant frequency of multiple LC passive wireless sensors,which provides theoretical support and scheme demonstration for the practical application of time domain readout system of LC sensors.