Attenuation of edge reflections in plates and bars in flexure by a graded impedance interface

Abstract

Experimental results will be presented showing that it is possible to reduce reflections at the edges of plates and bars by using a graded impedance interface. A perfect impedance mismatch at the boundaries results in 100% reflection of waves, hence the motivation for using a graded impedance interface. An aluminum bar, a lucite bar (2 ft×1 in.×1 in.), and a viscoelastic strip (2 ft×1 in.×0.5 in.) are glued at the edges of a steel plate (2 ft×2 ft×1 in.), in order to achieve the graded impedance interface. The center point impulse excitation response is measured, and the peaks in the velocity response give a measure of the intensity of the reflected waves. A reflection coefficient R is defined based on a one-dimensional wave model. R is as low as 0.17 for the steel plate with the graded impedance interface mentioned above. Similar results are obtained for a steel bar, for which a value of R=0.31 is obtained by the same type of impedance grading. The reduction in R for both bars and plates is superior to that obtained using dry or wet sand as a vibration absorption mechanism.