Variables in the use and design of acoustic emission transducers

Experiments to verify the applicability of a theory explaining the resonant behavior of a couplant/multilayer acoustic emission transducer system are presented. The study focuses on the effect of the piezoelectric transducer on measured acoustic emission parameters. The transducer is coupled to the structure being monitored via a thin coupling layer (oil or grease) with the piezoelectric element faced by a protective shoe. A series of equations presenting the theory of transducer response is given and the experimental procedure is outlined. Theory and experiental results for both five layer and six layer systems are given with six layer theory shown to be applicable to the transmission of longitudinal acoustic waves into an acoustic emission transducer. Multilayer transmission theory has important applications in the design of transducers where performance can be optimized and components selected to give a specific frequency response. Applications to non-destructive testing technology are foreseen.