| Surface Acoustic Wave(SAW)sensors are passive sensors with the advantages of small size and easy installation compared to conventional sensors.SAW sensors can be applied to the measurement of physical quantities such as temperature,strain,torque and pressure,and have a wide range of applications in the fields of biochemistry,aerospace,energy and power.The advantages of online monitoring in harsh environments are particularly obvious.However,SAW sensors are passive sensors that do not actively output measurement signals themselves and require a suitable signal interrogation system to excite and read the sensors to obtain measurement representations.The form of signal transmission between the interrogation system and the sensor is an important factor affecting the application of the sensor.Therefore,the development of a wireless type of SAW sensor interrogation system is of great importance to realize the wireless passive application of SAW sensors.In this paper,we design,develop and study a wireless interrogation system for SAW sensors with the goal of realizing wireless passive measurement of SAW sensors.First,a wireless interrogation system for resonant SAW sensors is designed,and the design is developed and implemented in the hardware physical layer and software manipulation layer.Based on this,the influence of various measurement parameters on the measurement results in the wireless interrogation system is studied,and the interval of each parameter selection in the wireless measurement system is obtained.Finally,the designed general-purpose wireless interrogation system is experimentally studied for temperature measurement with a resonant temperature sensor as an example;the results show that the system can not only accurately and effectively realize wireless measurement of temperature at a single location,but also realize wireless measurement of temperature distribution at multiple locations through sensor arrays.The specific studies are as follows:First,a temperature test system based on resonant SAW sensors is designed.The system is based on the design concept of software design radio(SDR),with the use of the software toolkit GNU Radio and the USRP-B210 RF daughter board produced by Ettus,using a microcontroller to control the T/R switch to send a sinusoidal pulse excitation signal and receive the sensor response signal,and the result of the coherent averaging method to noise reduction of the received signal,to achieve the extraction of the SAW sensor resonant frequency extraction.Subsequently,the effects of various measurement parameter changes in the wireless interrogation system on the response signal of the SAW sensor are investigated.The influence of excitation frequency,excitation duration,gain and distance between antennas on the response signal of SAW sensor is summarized.The results show that the closer the excitation frequency is to the intrinsic frequency of the sensor,the higher the energy of the sensor response signal;the "charging" duration is related to the resonant frequency of the sensor design,and for the SAW sensor with the resonant frequency near 433MHz used in this experiment,the optimal "charging For the SAW sensor with resonant frequency around 433MHz used in this experiment,the best"charging" time is 2.5-3us;to ensure that the frequency identification will not be mixed,the best excitation frequency is ±0.075MHz from the center frequency of the SAW sensor;when using 1 Ocm omnidirectional antenna,the system wireless test distance can reach 0.8m.Finally,the designed general-purpose wireless interrogation system is experimentally studied for temperature measurement with a resonant temperature sensor as an example.The temperature measurement effect of the interrogation system for single sensor and sensor array is verified.The results show that for a single SAW sensor,the relative temperature measurement error of the wireless interrogation system is within 3%;for a frequency division multiple access sensor array,the wireless interrogation system can identify the resonant frequency of each sensor and output its corresponding temperature value in real time and accurately. |
