Abstract
ABSTRACTThis paper presents a FEM analysis of a membrane-based Surface Acoustic Wave (SAW) sensor. The sensor is a 2.45GHz Reflective Delay Line (R-DL) based on Lithium Niobate (LiNbO3). As the wave propagation time is much smaller than the typical time constant of the phenomena to be monitored (deformation, temperature change etc.), the analysis can be performed in three successive steps. First, a static FEM study of the complete sensor (housing included) is carried out, to compute the temperature, stress and strain fields generated in the sensitive area by the measured parameters (pressure, temperature, etc.). Then, a dynamic electro-mechanical study of the R-DL is performed. The simulation takes the previously computed fields into account, which makes it possible to compute the sensor sensitivity to the measured parameters. The model takes advantage of the periodicity of the components of the R-DL to compute phenomenological parameters (Coupling-of-Mode parameters), which can later on be used to compute the electrical response of the sensor (step 3). In this paper, we focus on the first two steps. The COM parameters are extracted, under simultaneous thermal and mechanical stresses. Especially, the sensor sensitivity is obtained from the evolution of the velocity, under various stress configurations.
Highlights
Surface acoustic wave (SAW) devices use interdigital transducers (IDT, comb shaped electrodes) to generate waves at the surface of a piezoelectric substrate
This paper reports an efficient and accurate computational procedure for designing SAW sensors using the finite element method; it is demonstrated on a sensor sensitive to both pressure and temperature
A static simulation of the complete sensor is carried out to consider the effect of the measurand
Summary
Surface acoustic wave (SAW) devices use interdigital transducers (IDT, comb shaped electrodes) to generate waves at the surface of a piezoelectric substrate. The velocity of the generated waves changes with the surface state (stress and strain, mass deposition or temperature), which makes it possible to use these devices as sensors by arranging the IDTs in delay lines or resonator structures. Due to their simplicity, it is possible to build robust SAW sensors. The socalled coupling of mode (COM) parameters are extracted from the simulation of a simplified infinite grating of electrodes [8,9] These phenomenological parameters are computed for all the surface states present in the acoustic path The whole set of COM parameters is computed to illustrate the general computation procedure, as described above
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