Anti-symmetric flexural modes for the detection of humidity variation.

Antisymmetric flexural (ASF) modes are guided acoustic modes propagating along the apex line of a wedge with particle motion that is antisymmetric about the midplane bisecting the apex angle. This paper describes experimental observations in applying ASF modes for the detection of moisture variation. In our setup, the wedge tip is coated with a thin layer of hygroscopic film for the absorption of moisture, so the phase velocity of the ASF mode is influenced by the changing humidity of the surrounding air.