A Single SAWR Sensor System to Monitor Both Dynamic Strain and Temperature

Dynamic strain and temperature are critical physical quantities to be monitored in industrial environments to assure safe operational conditions and to diagnose for required maintenance. Dynamic strain and temperature feedback signals are particularly important for equipment and structural health monitoring (SHM) applications in aerospace, automotive, power generation, and advanced manufacturing. Challenges presented by dynamic strain sensing include sensor adhesion, packaging, stability, and temperature cross-sensitivity. Surface acoustic wave resonator (SAWR) sensors have demonstrated the ability to function under a variety of industrial/harsh environmental conditions for monitoring quantities, such as temperature, strain, vibration, gases, and neutron flux. SAWR sensors have the added benefits of being compact in size and capable of wireless and battery-free operation. In further exploring the versatility of SAWR devices and sensors, this article reports on the utilization of a single SAWR device that can simultaneously measure temperature and dynamic strain using a power spectral technique. Since the SAWR sensitivity to dynamic strain is also dependent on temperature, using the inherent temperature sensing capability of the SAWR itself offers an excellent method for selecting the appropriate strain sensor calibration curve. Once the temperature is known and the appropriate strain calibration curve is selected, real-time tracking of the strain magnitude can then be obtained from the relative amplitude of the SAWR dynamic strain spectral components to the main resonant peak. To demonstrate this method, SAWRs were initially calibrated for temperature and dynamic strain from room temperature (RT) to 190 °C and subjected to 500 Hz dynamic strain test signals ranging from 11 to $26~\mu \varepsilon $ . The accuracy of the SAWR-measured temperature remains within 2 °C of a reference thermocouple for temperatures greater than 100 °C, resulting in an overall strain discrepancy of less than 4% when compared to a commercial strain gauge.