OPTIMIZATION & APPLICATION OF ELECTRO- DYNAMIC ULTRASONIC WAV E TRANSDUCERs*

First, let me describe briefly what I have in mind when I talk about electrodynamic ultrasonic wave transducers. There are a number of trans-ducers which I would put in this class including the capacitive microphone-type transducers, which are based on an electrodynamic phenomenon as opposed to piezoelectric phenomena. However, I am going to focus my attention on a particular type of electrodynamic device, the electromagnetic acoustic wave transducer or EMAT for short. I wi ll describe electromagnetic acoustic wave generation and, hopefully, will show you how transducers based on this phenomenon have been understood in rather great detail. It is then up to all of us to try and apply this information to solve NDE problems. With this background information, I hope that you will feed back to me ideas so that we can work together on applications. Figure l shows a typical measurement setup when using an electromagnetic acoustic wave transducer or EMAT. One takes a pulse of radio frequency current, at a frequency of a few megaHertz and having an amplitude of a few amps pea