Propagation and excitation of membrane waves loaded by air

Membrane waves at ultrasonic frequencies can be excited in thin stretched foils. In this paper the effects of surrounding air load on the propagation and attenuation properties of membrane waves are discussed. The air-mass loading makes the membrane waves slightly dispersive. Attenuation, in the case where the membrane wave does not radiate to the air, is mainly due to the viscous and thermal-conductivity losses in a thin boundary layer on the membrane surface. The electrostatic-excitation method is discussed in detail and includes the derivation of the voltage-transfer function. Theoretical results are compared with the measurements.