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.
Lamb wave propagation in a surface-stubbed phononic-crystal plate is investigated numerically and experimentally.
Results show that the complete band gaps and flat bands of elastic waves exist in the structure. By using laser ultrasonic
techniques, the experimental measurements demonstrate the evidence of the band gaps and resonances at the band-edge
frequencies. In addition, a frequency range associated with the deaf bands is found. Based on the verified band gaps and
deaf bands, waveguiding effects in the structure with a line defect are characterized. Furthermore, a sharply bent
waveguide is then designed and fabricated to experimentally demonstrate frequency selection for broadband Lamb
This study presents a novel method based on the surface acoustic wave (SAW) sensor, for monitoring the thickness of a silicon membrane in real time during wet etching. Similar to accelerometers and pressure sensors, some micro-electro-mechanical systems (MEMS) devices require the thickness of silicon membranes to be known precisely. Precisely controlling the thickness of a silicon membrane during wet etching is important, because the thickness strongly affects post-processing and device performance. Moreover, the proposed surface acoustic wave sensor allows the thickness of a silicon membrane to be monitored from a few μm to hundreds of μm in situ, which depends on the periodicity of interdigital transducers (IDT). A novel method, which differs from any in previous work on etch-stop techniques, is developed in-situ for monitoring the thickness of a silicon membrane during wet etching. In summary, the proposed method for measuring the thickness of a silicon membrane in real time, is highly accurate; is simple to implement, and can be mass-produced. This work also describes the principles of the method used, detailed process flows, the method of taking measurements and the simulated and experimental results. The theoretical and measured values differ by an error of less than 2.50μm, so the results closely agree with each other.