Calibration of Air-Coupled Ultrasonic Transducers

Air-coupled ultrasonic transducers working at frequencies over 100 kHz have been widely used in the past for NDT applications and are a very attractive alternative when test specimens cannot enter in contact with water. In these cases, and in order to determine transducer performance it is sufficient to measure transducer two-way insertion loss and signal to noise ratio. However, in the recent years, new applications are being developed for different fields. In these novel uses, the precise knowledge of the actual amplitude of the pressure field is demanded. However, such measurements are not simple nor straightforward. This work presents a simple procedure to measure the transducer sensitivity in transmission mode (Pa/V) and in reception mode (V/Pa) using mixed water-coupled air-coupled procedure that can be easily implemented in any ultrasonic lab. As an application example, the procedure is applied to 0.65 MHz wide band transducers. The transmission and reception sensitivities are presented here. As verification of the technique, the combined transmission-reception sensitivity is then calculated and compared with direct measurements