Research On Algorithm For SAW Sensor Based On Delay Line Theory

Currently, the Surface Acoustic Wave (SAW) sensor has received considerableattention for its advantages such as wireless and passive. SAW sensor based on delayline has also received more attention from many fields, especially the logistics fieldbecause of its sensing and labels. But the most challenging problem of the developmentof this kind of sensor system is demodulation. A variety of complex factors affect theaccuracy of the demodulation, so studying echo signal demodulation method of SAWsensor based on delay line is critical.First, the research progress of the demodulation method of the delay line SAWtemperature sensor and the demodulation methods are analyzed in this paper. Therefore,a kind of demodulation method with combination of time delay demodulation and phasedemodulation was proposed. In this paper, main research contents are as follows:①SAW sensor system based on delay line is introduced and the program of thesystem are analyzed in this paper. Then the paper introduces the measurement principleof SAW sensor based on delay line and especially discusses phase ambiguity of phasemeasurement. Theoretical analysis shows that the combination of delay measurementand phase measurement can uniquely determine the measurement and overcome thephase ambiguity problem.②The characteristics of the echo signal is studied. The echo signal has thewaveform characteristics of waveform relative stability and controllability and thecharacteristics of input frequency invariance. The paper analyzes the non-strictquadrature demodulator and the non-strict coherence condition can cause demodulationerrors. Experimental studies have shown that all kinds of errors will reduce the accuracyof the quadrature demodulator and affect phase measurement accuracy, seriously, fail inphase measurement.③The paper focuses on the demodulation method of the delay line SAWtemperature sensor. The paper analyzes and compares several baseband I/Q signalpreprocessing methods to select the flatting way of twice average in neighborhood field.Then the paper discusses baseband I/Q signal waveform positioning methods and solvesmuch more high-accuracy waveform positioning with introduction of the concept of the“centroid” to measure the baseband pulse waveform position. Combining smoothingmethod and waveform positioning method of echo signal, a high-accuracy and strong anti-noise demodulation algorithm that would be suitable to SAW temperature sensorbased on delay line is proposed with phase measurement. Echo signal demodulationmethod is tested through the experiment system. The experimental results show that thedemodulation method can surely realize the high precision temperature.The experimental results show that the demodulation method resolves theambiguity of phase measurement and achieves the high precision and strong anti-noiseability of the demodulator of SAW temperature sensor based on delay line with centroidposition and phase measurement. These findings are useful for the similar SAW sensortowards a practical significance.