Reseach On SAW Wirless Temperature Sensors Test

Sensors, used to collect information, play an important role in information technology. Among them, passive wireless sensorsarecapable of workingunder severe conditions, such as in rotating parts, high-temperature and humid environment. At the same time, as it requires no power and can be easily maintained, the passive wireless sensor has played an increasingly important role in information systems. Among the passive wireless sensor, the passive wireless surface acoustic wave(SAW) sensor, with simple structure, high sensitivity, reliability and low cost, hasattracted increasing attention these years. This thesis, aiming at the passive wireless SAW sensor, present a study of the antenna design and the associated detection systems of it.First, a designed miniaturized patch antenna working in the 915 MHz passive wireless SAW sensor will be presented in this work. The optimized antenna, with the center frequencyat 915 MHz, has the size of 21.4mm × 21.3mm. Because ofradiation patch slot and the miniaturizing technology of shorted load used in it, the antenna, compared with other antenna without the miniaturizing technology operating at the same frequency, has achieved a reduction of 80.4% in size.The simulation result shows that when the antennaⅠresonates at 914.8MHz,S11=-38.5d B,-10 d B bandwidth=4MHz, gain=-9.14 d Bi. The test result shows thatantenna-Ⅰachieves-10 d B bandwidth=5.5 MHz, gain=-7.86 d Bi, when operating at 915 MHz. On the basis of the antenna-Ⅰ,after changing theshape of the sloton the radiation patch and using the meandered slot to further reduce the size of the antenna,theantenna-Ⅱ has been created. The size of the radiation patch is 15.9mm×15.3mm and has a reduction of 85.4% in size, compared with other antenna without the miniaturizedtechnologyoperating at the same frequency. The simulation result shows that antenna Ⅰ achieved S11=-24.8 d B,-10 d B bandwidth=5 MHz, gain=-15.699 d Bi when resonating at 914.8MHz. And the test result shows thatantenna- Ⅰ achieved-10 d B bandwidth=4.6MHz, gain=-11.1d Bi, when operating at 915 MHz.Secondly, based on vector network analyzer, a passive wireless SAW sensor test platform has been built.Thetime-domain gating of the original test dataeffectively suppressed the happening of the multiplicative and additive noise, sothe SNR of the test result was improved a lot.This test platform and the designed sensor antennasmentioned above have also been used to conduct a wireless passive SAW sensor distance test, and the result shows that when yagi-uda antennais at-5d Bm output power level, the antenna-Ⅰcan achieve wireless detecting in the distance of 120 cm, and the antenna-Ⅱcan achieve 80 cm.Finally, based on the platform, the temperature characteristic of the passive wireless SAW sensor has been tested. The result shows that, with the temperature increases from 35 ℃ to 184 ℃, the quartz SAW sensorwhich depend on the designedantennas resonant frequency decreases monotonically from915.349 MHz to913.871 MHz. And the Test result shows that when the temperature increased from 183℃to 573.9℃,the SAW sensor resonantfrequency decreases monotonically from 217.575 MHz to 216.225 MHz.