Research On Small Antennas For Monitoring Contact Stress In Slit With SAW

In many special circumstances such as high temperature,high pressure or extremely narrow environments,it is inconvenient to transmit signal through wired connection directly and wireless communication becomes the only way.Because of the good acoustoelectric conversion and high efficiency energy storage characteristics with small size,SAW passive sensor has been developed to monitor the changes of contact stress in the metal slit so that a small atenna is needed.As the entrance and exit of signal transmission,antennas used in the SAW system will directly determine the transmission performance.It has important practical significance in measuring the contact stress in the slit,achieving SAW signal passive wireless transmission under the background of metal environment.In this paper,the SAW signal wireless transmission has been studied according to the application background.And specific contents are listed as follows:The chain circuit of SAW sensing system is analyzed and the minimum gain of the antenna should be 0.72 dBi.The characteristics of various small antennas are compared and because of the resistance to metal interference and low profile requirements,the microstrip antenna is finally chosen to be miniaturized.The usual miniaturization methods of microstrip antenna including high dielectric constant,short-circuit loading and meandering technologies are discussed.A novel microstrip antenna with one short-circuit probe and an S-type slot on the surface of the radiation patch has been presented and the microstrip line has also been designed.The frequency of the small inverted-F microstrip antenna is 990 MHz.Based on the theoretical analysis,the structural parameters of short-circuit loading and meandering are simulated and optimized respectively and theoretical conclusions are verified by simulation at last.The influence of different grounding plate size on the radiation performance of the antenna has been investigated.And by changing the slot length of the radiation patch,the grounding plate of the antenna can be integrated with the metal part outside the metal slit effectively so as to avoid the deterioration of the antenna performance from the smaller size of grounding plate.The final size of the small inverted-F microstrip antenna is 45 mm * 45 mm * 7mm,70% less than the conventional size with the gain of 1.4dBi.A wireless test system has been constructed to realize the SAW signal transmission in this paper.The miniaturized microstrip antenna has been tested in the system.It is useable in wireless monitoring and transfer signal in real-time.The transmission signal has been analyzed by MATLAB program.