Designing and evaluating transducers for narrowband ultrasonic spectroscopy

Introduction of new composite materials in aerospace applications has created a demand for an efficient NDE technique. Ultrasonic resonance inspection is especially suitable for the inspection of multilayered structures. In our previous work we have described the principle of narrowband ultrasonic spectroscopy (NBUS), where the surface of an inspected structure is scanned with a resonant transducer whose frequency response is monitored in a narrow frequency band. This paper is concerned with optimizing the NBUS setup consisting of a piezoelectric transducer coupled to a multi-layered structure. Differences in the electrical impedance of a piezoelectric transducer caused by variations of parameters of the inspected structure are estimated using an equivalent circuit model and a finite element analysis. The theoretical analysis presented in the paper results in design guidelines for NBUS transducers.