The Surface Acoustic Wave Temperature Sensing System Using Phased-array Antenna

Temperature detection is ubiquitous.Because of the characteristics of passive and wireless,surface acoustic wave(SAW)sensor is especially suitable for the occasion that wireless sensing is needed,the test environment is complex and the test condition is poor.In light of the problems encountered in practical application of temperature sensing system,in this paper,the phased-array antenna is applied to the temperature measurement system,and the SAW temperature sensing system with phased-array antenna is designed and tested.First of all,the principle of SAW sensor temperature sensing is analyzed,and the single-ended SAW resonator is used for temperature sensing.The echo characteristics and the theoretical method of temperature measurement of the resonator sensor are analyzed.Then,the phased-array antenna is analyzed by MATLAB simulation for its working principle,the formula of feed phase difference of the homogeneous linear phased-array antenna and the rectangular planar phased-array antenna are derived,and the passive phased-array antenna is adopted and the specific structure of the antenna is introduced.Based on the analysis above,linear and planar phasedarray antenna are simulated by HFSS software,a phased-array antenna experimental test system is built,and the test results show that the phased-array antenna can improve the gain and control beam direction.Next,the scheme of temperature measurement is determined according to the characteristics of sensor's echo signal,and the reader is designed based on the analysis.The speed of frequency conversion is improved by providing the reference signal for the source by direct digital synthesizer(DDS),and using mixer to convert the echo signal down to intermediate frequency.The sampling rate is increased by the alternate sampling technology of three ADCs inside the MCU.And the optimized scheme of frequency sweep is used to improve the sweep speed.Finally,the realization of SAW temperature sensing system using phased-array antenna is introduced.The performance parameters of the reader are tested,including temperature measurement time,temperature measurement precision,temperature measurement range and measurement distance.The function of phased array antenna in the system is tested by setting up an experimental test system.The test results show that using phased-array antenna can improve the measuring distance and realize the space division multiple access of temperature sensor.What's more,the temperature measurement system is used to measure the temperature of the same frequency sensors of multiple sensors in different azimuths simultaneously.The results show that the SAW temperature sensing system using phased-array antenna can realize multi-point temperature measurement at the same time.