Acoustic Meta-Structure Transmission Loss Characterization via an Impedance Tube and the Transfer Matrix Approach

Abstract

Abstract This paper proposes a new meta-structure bandgap depth measurement method that considers energy absorption rather than discrete structural response. By applying measurement techniques previously reserved for acoustic property characterization, this novel method aims to characterize acoustic meta-structures by their transmission loss (TL). Transmission loss is the ratio of incident energy to transmitted energy from a structure. One extensively defined testing method for determining acoustic transmission loss involves using an impedance tube or a tube outfitted with transducers flush to its inside wall on either side of a sample holder, along with a source and termination on either end of the tube. Using the transfer matrix approach and transfer functions computed from the impedance tube transducers, the pressure and particle velocity at one point in space and time can be related to that of another point in space and time. In the end, a transfer matrix can be determined, which contains information about how much energy is absorbed, reflected, and transmitted by a structure over an entire range of frequencies. By outfitting an impedance tube to accept acoustic meta-structure samples, this same method can determine the transmission loss versus frequency exhibited by such a structure. This information can be used to directly observe and measure the band gap depth of an acoustic meta-structure.