Air coupled ultrasonic transducers: Design and applications

Based upon piezoelectric composite materials, air-coupled ultrasonic probes with frequencies above 100kHz were developed. These probes have a bandwidth larger than 50% and we obtained a dynamic range than 100dB. The essential part of the probes is a piezoelectric composite (1-3-configuration) developed and fabricated at the IZFP. The piezoelectric composites (acoustic impedance 6 to 10 MRayl) are characterized by a high electro-acoustic coupling coefficient k2= 0.7,better acoustic matching to a gas or a liquid compared to a piezoelectric ceramic (acoustic impedance 35 MRayl) and a low mechanical quality factor. To further improve the efficiency of air-coupled probes, pressurized air-shoes and traveling wave transducers are in current development.