Audio and ultrasonic transducers based on electrothermomechanical film (ETMF)

A transducer material consisting of foamized plastic, called electrothermomechanical film (ETMF), is introduced. The film has conductive electrodes on at least one side, so it can be used with either an electrostatic or electrodynamic driving force. The film can be used both as a transmitter and a receiver at audio and ultrasonic frequencies, also in hydroacoustical applications. Lumped-component and one-dimensional distributed-parameter models are developed to examine the behavior of the film. Frequency responses and sensitivities predicted by the models are compared with measured data. Audio applications of the film as a loudspeaker (tweeter and full-range) are introduced with data collected from prototypes. Means of controlling radiation pattern and frequency response are briefly discussed. Applications of the film as a microphone, hydrophone, and hydroacoustic source for audio and ultrasonic frequencies are mentioned