Characterisation of a Wireless Passive Surface Acoustic Wave Strain Sensor

Wirelessly interrogated surface acoustic wave (SAW) sensors can operate passively and in harsh conditions reliably. The interrogation process of the signal measurement chain provides the power to excite the sensor and hence establish the sensors response in a passive manner. Development of wireless passive SAW sensors allows investigation of their potential to quantify physical measurands such as strain in aggressive environments. Wireless SAW strain measurement is shown to be advantageous over wired strain measurement alternatives where instrumentation at the sensor site can be prohibitive to strain measurement technology integration in certain application areas. In this paper, a one port SAW resonator (SAWR) strain sensor is presented and is shown to exhibit highly sensitive and linear responses to applied strain. The principle operation of the Trinity SAW is outlined and the processes involving the instrumentation of the packaged devices are discussed. Wireless strain measurement is demonstrated using a packaged SAW device that is calibrated using the standardised strain testing system developed in-house. The system facilitates a standardised and repeatable method for testing. This allows for both individual sensor performance and detailed comparative analysis between test sensors. A range of strain level performance assessments are presented and cross sensitivity at elevated temperatures is demonstrated and discussed. The performance of the SAW technology is shown to have equivalent sensitivity performance when compared to an industry standard strain gauge device. The work presented in this paper demonstrates the potential for SAW strain sensors to be integrated in real engineering applications such as process monitoring and tool condition monitoring in the future.