Hanspeter Loertscher, Bert Grandia, Jan Strycek, and Willem A. Grandia Transducer Workshop Abstract Water, the most commonly used couplant in ultrasonic testing, may not be compatible with certain materials and manufacturing processes. QMI Inc. has therefore developed transducers and instrumentation for the industrial ultrasonic testing and c-scanning through the ambient air. Transducers and technique are presented, together with results from actual applications. Air-coupled Transducers 3. Airscan Apparatus and Technique 4.
Water is the most frequently used couplant in immersion and squirter scanning techniques.
However, these techniques are not compatible with some industrial processes and water may cause permanent damage and contamination to many materials. Couplants are being used as a sound propagation medium between the transducers and the part under inspection. Although air is a reasonably good sound carrier in the frequency region of interest, it poses a major obstacle. The acoustic impedance of air differs so much from the acoustic impedances of transmitter and test parts, that most acoustic energy is being reflected, and only a very small fraction of that energy penetrates in and out of the part and the transducers. In current commercial applications, we use mainly thickness-mode type, piezoelectric elements.