Acoustic supercoupling with compressibility-near-zero effective material properties




Byrne, Matthew Scott

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Supercoupling is a widely-researched topic in wave engineering, which has been used to build coupling channels that can, in principle, support total transmission and complete phase uniformity, independent of the length of the channel. This has generally been accomplished by employing dispersion in media that display a near-zero index. In the field of acoustics, prior works have required the presence of periodic embedded resonators, such as membranes or Helmholtz resonators, in order to observe near-zero properties. Here we show, theoretically and experimentally, that supercoupling can occur in an acoustic channel without the presence of embedded resonators. A compressibility-near-zero (CNZ) acoustic channel was observed to show remarkable properties analogous to those found in electromagnetics. Furthermore, by employing higher-order modes, we demonstrate the realization of effective soft boundary conditions in air, which are exploited to produce uniform phase in the coupling channel. In the second chapter of this work, we show that these concepts can be extended to realize a novel acoustic power divider, which permits the tunneling of acoustic power to an arbitrary number of output ports, where the phase shift with respect to the input signal can be selected to be either 0 or 180 degrees. We also present analytical and numerical models, which describe the behavior of the power divider, and conclude with an analysis that describes the limitations and trade-offs that occur due to losses as the device size is scaled.


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