Laser-Ultrasonic Investigation on Lamb Wave Band Gaps in Two-Dimensional Phononic Crystal Plates

Abstract

Abstract - Phononic crystals (PCs) commonly consisted of two materials with huge contrasted elastic properties and mass densities are generally studied in theory such as the finite element method for many difficulties in the experiments. In this paper, the laser-ultrasonic non-destructive testing is introduced to investigate the propagation of Lamb waves in two-dimensional PCs plates. The existence of band gaps for low order Lamb wave modes is demonstrated experimentally. Crucial parameters such as the thickness of PCs plate and the periodical arrangement of scatterers are discussed in detail for the influence of location of band gaps. The finite element analysis agrees well with the result of laser-ultrasonic measurement. The extraordinary transmission properties such as acoustic band gaps in PCs have been attracted extensive interest because of the great potential applications. Due to the coupling of longitudinal and transversal strain components at the plate boundaries with complex wave vectors, Lamb waves in PC plate are more interesting and complicated. We investigate theoretically and experimentally the propagation of Lamb waves in two-dimension (2D) PC plates. The PCs are created by patterning air filled holes in the aluminum thin plates. The transmission properties of Lamb waves in PC plate are calculated employed the finite element method. The dispersion curves depict Lamb wave band gaps in the created PCs. Prominently, the periodical arrangement of scatterers strongly modifies the location of Lamb wave band gaps. The PC with scatterers patterned squarely shows three absolute forbidden bands, while the PC with scatterers patterned triangularly presents one partial forbidden band and two absolute forbidden bands in low frequency domain. Lamb wave band gaps altering along structural parameters such as the thickness of PC plates and filling ratio are further studied in this work. On the basis of calculations, 2D PC plates are manufactured. Through laser-ultrasonic measurements, acoustic band gaps in the PC plates are observed experimentally, which confirms the existence of Lamb wave band gaps in 2D PC plates. The transmit power spectra (TPS) detected in the experiments are in good agreement with the calculate results.