Due to the strong damping properties of air, low frequencies in the kHz range are used in air-coupled ultrasonic testing. It is therefore all the more important that the ultrasonic transducers have a particularly high sensitivity in order to ensure high penetration and improved resolution. We achieve this, among other things, by installing preamplifiers in the receiver search unit as well as by using the SONOTEC piezo composite technology, which enables a flexible use of the matching materials in our CFC and CF probes.