Frequency response of different couplant materials for mounting transducers

Sensors often are piezoelectric crystal transducers that convert movement (a variation of pressure) into an electrical voltage. Several non-destructive techniques involve the use of transducers, such as sonic testing, tomography, acoustic emission and pulse-impact echo. There are different types of transducers according to their different aims and applications, but in all cases the mounting of a sensor is an essential requirement in order to record good quality data-a good acoustic coupling between the transducer and the surface of the structure has to be ensured. It is common practice to use Cyanoacrylate adhesive glue (e.g. superglue) for most applications, but the authors found its use problematic during temporary installations due to the difficulties encountered to remove the sensor at the end of the experiment. For this reason, a study has been carried out to investigate possible alternative couplant materials. Eight different materials have been selected, and their amplitude of response in terms of time-domain and the frequency-domain has been compared. A final evaluation based on several pre-defined criteria has then been obtained, showing the feasibility of 'plasticine' as a valid alternative to superglue.