Piezoelectric transducers for air-coupled operation in the frequency range 0.3-2.5 MHz

Abstract

Use of non-contact techniques to produce and sense acoustic vibrations in the megaherzt frequency range are increasing. Higher frequencies provide higher spatial resolution while non-contact operation is an important improvement for rapid NDE scanning, analysis of materials that can not be wetted or touched, "in-situ" NDE appplications, etc. The approach we present in this paper is based on the use of piezoelectric transducers for both signal generation and reception. It is based on the use of a stack of quarter-wavelength matching layers to improve both the efficiency and the frequency band. To this end it is extremely important to find materials having: very low attenuation, very low acoustic impedance and the thickness requiered for the working frequency of the transducer. Piezoceramics and 1-3 connectivity piezocomposites are studied and compared. Plane and focused transducers are presented.