A Miniature Layered SAW Contact Stress Sensor for Operation in Cramped Metallic Slits

Resumo

Based on passive and wireless surface acoustic wave (SAW) sensing technology, a sensor terminal was designed to measure the contact stress in a cramped metallic slit with less than 0.5 mm in width. A layered structure of force-sensitive element with 0.5 mm in total thickness was put forward to package SAW resonator. Thin films with elasticity and flexibility were adopted to transfer load effectively between rigid surfaces. A flexible transmission line with double-stub structure and a patch microstrip antenna were used to realize the wireless interrogation to the sensor. The force-sensitive element model was built and simulated with FEA software (COMSOL Multiphysics). The sensor prototype exhibited significant linear and repeatable frequency shifts for the loads in the range of 0–4 MPa. The linearity error was ±3% of full-scale output (FSO), and the accuracy was ±1.25% FSO. The usage of elastic films in force-sensitive element caused hysteresis in output, but the hysteresis error was controlled in an acceptable range of ±3.8% FSO.