Broadband ultrasonic transducer for a artificial bat head

The Chiroptera - inspired Robotic Cephaloid (CIRCE) project is an interdisciplinary cooperation of several European research groups to investigate the sonar system of bats. Special challenges are the development of suitable pinna shapes to optimize the biosonar as well as the development of suitable ultrasonic transducers. The bandwidth, the sensitivity (receiver), the transmit efficiency (transmitter) as well as the overall insertion loss have to be equal to their corresponding values of living bats. In order to develop the pinna shapes, the first step was to scan the ears of various species of bats and examine the reflection and diffracting behavior on the 3D ear model by means of finite elements simulations. These results were verified by measurements on real ear models. In addition an ultrasonic receiver with a transducer area of 1 square centimeter was designed and integrated into the pinna model. A new type of piezoelectric polymer film (EMFi foil) was used as transducer material. It has a resonance frequency of about 300 kHz, allowing a sensor with a passband from 50 to 150 kHz. With the same material, an ultrasonic transmitter was developed for the emission of pulse signals with a sound pressure level of more than 90 dB in a distance of 1m. This transducer has also a bandwidth of 50 to 150 kHz. We will discuss the simulation results for various designs of transmitters and receivers as well as corresponding measurement results.