Transmission Peak and Its Suppression of Ultrasound Travelling through Layered Structures Comprised of Cu and Ag in a Liquid

Abstract

We observed the transmission peak and its suppression of ultrasound travelling through layered structures in a liquid at the frequency range of stop band. The layered structures are comprised of bilayers of Cu and Ag. Each layer has the thickness of 0.50 mm. When the number of bilayers is small, a peak of transmission rate occurs at 2.08 MHz. However, this peak is suppressed when the total number of bilayers increases. This suppression of the peak originates in the stop band determined by the unit bilayer (Cu/Ag). Making use of the effective reflection coefficient, we obtain the transmission rate precisely including the suppression of the peak of transmission rate at 2.08 MHz. The suppression is a characteristic feature of layered structures comprised of only bilayers. We elucidate this feature by the deviation of the effective reflection coefficient from the usual reflection coefficient at the interface between the layered structure and the liquid. When the layered structure has an extra layer, the suppression does not occur. This situation is similar to the case of homogeneous materials such as the Cu plate or the Ag plate.