Ferroelectrets: ultrasonic transducer for a biomimetic sonar system

A two layer ultrasonic transmitter made of a ferroelectret material with a diameter of 1.5 cm was developed for emitting a chirp signal with a sound pressure level of more than 90 dB at a distance of 1 m for an artificial bat head. Compared to a single layer transmitter. the resonance frequency of a two layer stack actuator is shifted down to 100 kHz. This frequency shift enables the transmitter half-power bandwidth to be in the range of 30-200 kHz. With the same material, an ultrasonic receiver with a diameter of 1 cm was designed. The ferroelectric material in combination with a special pre-amplifier allows an equivalent acoustic noise level of 45 dB and a sensitivity of 500 /spl mu/V/Pa. This sensor matches the bandwidth of the transmitter. In addition, we investigate the nonlinear acoustic behaviour of the ferroelectric material by applying 2D finite element simulations of various transducer designs. Therewith, we fully solve the piezoelectric partial differential equation including the complex geometric structure of cellular ferroelectric films. In our paper, we discuss the measurement results for various designs of transmitters and receivers as well as corresponding simulation data.