Design, simulation, and testing of wireless temperature sensor
William D. Suh, K. Alfoni Jose, Vijay K. Varadan, Vasundara V. Varadan · Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE · 2001
Remote monitoring and control of temperature is very important for many industrial applications. This paper presents the numerical simulation and its comparison with measurement of phase response from a wireless Surface Acoustic Wave temperature sensor. This wireless microsensor consists of two or more arrays of IDTs and reflectors on a piezoelectric substrate with different IDT-reflector spacing. Pulse modulated signals are transmitted from a remote reader system and their echoes are returned after traveling through the device with different time delays. The same reader is used to receive the signal and corresponding IF signals are generated in a mixer and their phase differences are calibrated to temperature values. Using coupled-mode theory, the phase characteristics relative to temperature was analyzed. The effect of relative distance between the two reflector arrays is demonstrated. The influence of 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. The analysis has shown that a very high sensitivity of 20.74°/°C or a temperature resolution of 0.05°C with 1° phase measurement resolution can be achieved using the present measurement system.