NONCONTACT EXCITATION OF HIGH-Q ACOUSTIC RESONANCES IN GLASS PLATES

The applications of magnetic direct, a noncontact technique for genera ting acoustic waves, are limited by poor transduction efficiency. This letter describes an approach for substantially improving the transduc tion efficiency by application of a transduction format, enhanced dire ct magnetic generation, that utilizes continuous wave resonances and t hin film generation. Glass plates coated with thin films of aluminium have been used as free-standing acoustic cavities to generate resonanc es with high transduction efficiencies and Q factors. These acoustic r esonances have been excited without mechanical contact and their origi n and characteristics are discussed with respect to resonances in 530 mu m thick aluminized silica plates. The consequences of magnetic dire ct generation applied to thin metal films, as opposed to bulk metal, a re also discussed, particularly with respect to high operating frequen cies and acoustic Q factors. It is possible that novel sensors and tim e standards may be constructed by exploiting this approach. (C) 1998 A merican Institute of Physics.