Theory of high overtone bulk acoustic wave resonator as a gas sensor

A one-dimensional model analysis based on the high overtone bulk acoustic wave resonator (HEAR) spectroscopy theory is developed for the description of the operation of gas sensors. The sensor model consists of a thin film transducer with film electrodes located on the face surface of the low acoustic loss material plate with the other surface of the plate covered with a gas sensitive layer. The model implies the fact that the thickness of this layer increases due to gas absorption resulting in the frequency change of the resonator. It was found analytically that the sensor sensitivity increases a hundred times when the initial thickness of the layer is close to a quarter of the acoustic wavelength