Research On Signal Extraction Of Wireless Passive LC Sensor Based On Reflection Coefficient

Since the simple structure and low cost,wireless passive LC sensors can be widely used in agriculture,medical,aerospace and other fields.A lot of research has been focused on wireless passive LC sensors at home and abroad,but it has been very difficult to extract the signals of wireless passive LC sensors.The current signal extraction methods for wireless passive LC sensors mainly include the maximum impedance real part method,the phase-dip method,the Fourier transform method for the imaginary part of the impedance,and the measurement S11 parameter(reflection coefficient)method.This paper introduces several common signal extraction methods to provide a reference for the measurement of wireless passive LC sensors.When measuring wireless passive LC sensors,draw the equivalent circuit diagram of the circuit and calculate the equivalent input impedance at the readout coil.Analyzing the zeros and poles of the input impedance can get the relationship between the sensor's resonant frequency and the maximum point of the real part of the impedance and the phase-dip point.And then select a resonant frequency point that is easy to measure for measuring.Based on the S11 parameter measurement theory,this paper designs a portable wireless passive LC sensor measurement system.Generally,a vector network analyzer is used when measuring the S11 parameters of the sensor,but because the vector network analyzer is expensive and bulky,it is not easy to actually measure.Therefore,this paper aims to design a portable measurement device that can replace the vector network analyzer.This paper uses AD9910 as the frequency sweep source,AD8302 to measure the reflection coefficient,and STM32 microcomputer as the main control chip to design a high-precision,low-cost sensor measurement system.At the same time,a set of upper computer software is designed.The upper computer software is designed based on the state machine using Lab VIEW language.The original data measured by the circuit is sent to the host computer through serial communication,and the final result is displayed in the form of curves or text after a series of processing.This paper also proposes a wireless passive multi-parameter LC sensor decoupling method,and designs a wireless passive LC temperature-pressure dual-parameter sensor to verify the method,and the results show that the method can be widely used in multi-parameters Decoupling of LC sensor.At present,the decoupling of multi-parameter LC sensors is to first determine a parameter,and then substitute this parameter into a new equation to calculate other parameters.The method proposed in this paper takes into account the mutual interference of temperature and pressure,so it is more versatile.This method is verified by designing a temperature and pressure composite measurement system.The test results show that at 25 ?and 1000 ?,the maximum absolute difference between the temperature and the actual temperature obtained by decoupling by this method is only 2.12 ? and 20.99 ? respectively.From 25 ? to 300 ?,the average relative error after decoupling temperature and pressure is only 2.89% and 4.07% respectively.The average relative error after decoupling temperature and pressure in the range of 300 ? to 1000 ? is only 1.25% and 4.74%,respectively.This method can also be extended to the decoupling of sensors with three or more parameters.