Design optimization and experimental verification of wireless IDT based micro temperature sensor

This paper presents the prediction and measurement of the phase response from a wireless surface acoustic wave (SAW) device for temperature sensing applications. This wireless sensor consists of two or more arrays of an interdigital transducer (IDT) and reflector pair with different IDT-reflector distances. Pulse modulated signals are transmitted from a remote reader system and their echoes an returned with different time delays due to the different IDT-reflector distances. Corresponding intermediate frequency signals are generated in a mixer and their phase differences are calibrated to temperature values. Using the coupled-mode theory of SAWs, the phase characteristic relative to temperature was examined. The effect of the relative distances between the two reflector arrays is demonstrated. The influence of the phase reversal location, which produces multiple temperature values for a given phase difference, is also discussed and a simple solution is illustrated. This sensor is coupled with a small planar antenna, which will be well suited for applications that require passive and conformal sensors.