Design and fabrication of a gradient-index phononic quartz plate lens

This paper presents results on the numerical and experimental studies of focusing of Lamb waves in an AT-cut quartz gradient-index phononic crystal (GRIN PC) plate lens. The band structures of square-latticed AT-cut quartz phononic crystal plates with different filling ratios are analyzed using the finite element method. The anisotropic properties of the lowest anti-symmetric Lamb mode are discussed. Then, the design of an AT-cut quartz based GRIN PC plate lens is addressed. In the micro-fabrication, the deep reactive ion etching (Deep-RIE) process with a laboratory-made etcher was utilized to fabricate the GRIN PC plate lens on an 80μm thick AT-cut quartz plate. Interdigital transducers were fabricated directly on the quartz plate to generate plate waves and a vibro-meter was used to detect the wave fields. The measured results on the focusing are in good accordance with the numerical predictions. Results of this study may serve as a basis for developing an active micro plate lens and related devices.