Elastic waves in thin films
Thin film technology for RF filters

Increased frequency and miniaturization have been major trends throughout the development of mobile telephony. The former makes it possible to increase bandwidth, and the latter to increase the number of bands in a device.

By switching from an electromagnetic wave to an elastic wave, the wavelength is divided by around 100,000. This means that miniaturization is easier using elastic waves than electromagnetic waves. Since the wavelength $\lambda =v_s\text{/}f$ decreases with frequency $f$...