Research On The Wireless Test System Of Passive Wireless Saw Sensor

Sensor as a modern science and technology at the forefront of technology, has been widely used in aerospace, industrial manufacturing, consumer electronics and other fields. Surface acoustic wave(SAW) sensor has high Q, low-cost, passive wireless and other characteristics, therefore, it is very suitable for very harsh environment, such as,high temperature, high pressure, high-speed rotation, or confined space to wirelessly detect temperature, strain, torque, pressure and other factors’ changes. Wireless test system is one of the key technologies of passive SAW sensor in practical applications and toward handheld technology, high speed, low power consumption, long-distance and other direction. Therefore, research on passive wireless SAW sensor test system has a very important significance.Firstly, this paper analyzed the equivalent circuit model and sinusoidal steady-state response of 315 MHz and 433 MHz SAW sensor. Using a microwave signal source,oscilloscope, RF switch and other equipment to build a test system of SAW sensor’s time domain signal, measured and analyzed the characteristics of 433 MHz SAW sensor signal in time domain and frequency domain, as well as the influence of different transmission time, transmission frequency, transmission power and other conditions.According to the characteristics of the sensor signal, this paper studied on a new test method of SAW sensor, and used LABVIEW virtual instrument, microwave signal source, Keithley 2182 nanovoltmeter and other relevant experimental instrument to build a principle verification platform, the results show that this test method was able to accurately measure the resonant frequency of the SAW sensor.Secondly, according to this new test method of SAW sensor, this paper designed the overall scheme of the test system, and elaborated hardware/software design,production, testing and other processes of each system’s module. System includes a micro control unit, transmitting unit, receiving unit, a radio frequency switch and an antenna. Transmitting unit used direct digital frequency synthesizer and double frequency amplifier module to achieve a small step sweep function in the vicinity of the resonant frequency of SAW sensor. Receiving unit used a low noise amplifier, power detector and programmable DC amplifier to achieve the sensor signal’s amplification,detection, and other functions. Micro control unit used MSP430 microcontroller toprovide control signals required for the system, the internal ADC module collected envelope signal of the sensor, LCD module displayed information such as the resonant frequency of the sensor. In order to facilitate real-time communication between the computer and the MSP430 microcontroller, using MATLAB software GUI designed a graphical interface for the test system.Finally, this paper measured 433 MHz SAW sensor in wired temperature test and wireless distance test using passive SAW sensor test system based on MSP430 microcontroller, the results show that when this system transmitting power was 5 dBm,it could wirelessly test within 10 mm distance, and the sample standard deviation was6.963 kHz. By contrast based on vector network analyzer(VNA) built SAW sensor test system, the results show that the MSP430 microcontroller SAW sensor test system was feasible, and its measurement was reliable.