Influence of surface conductivity on sensitivity of acoustic wave gas sensors based on multilayered structures

The influences of the surface conductivity on the velocity of an acoustic wave (AW) in a multilayered material are studied theoretically with the transfer matrix method and the conductivity sensitivity of the AW sensor is presented. It is found that the velocity of the AW increases with decreasing surface conductivity and vice versa. The result is used to explain the abnormal response of AW sensors, in which the central frequencies of AW sensors increase after they sorb the detected gases. Meanwhile, the conductivity sensitivity is found to be related to the dielectric constants of the multilayered material and the electromechanical coupling coefficient of the sensor. Finally, the sensitivities of AW sensors based on multilayered structures are optimized by considering the influences of the surface conductivities of the sensors with different initial conductivities and thicknesses of the sensitive layers.