Modern state and perspectives of bulk acoustic wave composite resonators

The review of the modern state and the perspectives of bulk acoustic wave composite resonators is presented. Special attention is paid to the following topics: what composite resonators are, modern composite resonators including multifrequency resonators, the thin-film resonators with and without acoustic isolation from the substrate. A particular review of the microwave bulk acoustic spectroscopy of the materials - the measurements of attenuation and elastic coefficients is presented.