Acoustic waveguide frequency-selective demultiplexing realized by Helmholtz-resonator-mediated extraordinary acoustic transmission

An acoustic frequency-selective Y-shaped waveguide splitter based on in-line Helmholtz resonators is demonstrated analytically via a modified transfer matrix method, computationally through finite element simulations using COMSOL, and experimentally by an impulse response measurement. This demultiplexer arrangement consists of a single input waveguide that splits into two output waveguides in a Y-configuration. Each output arm has a single tuned Helmholtz resonator embedded in-line along the length of the waveguide. The Helmholtz resonators in each arm consist of a single cavity with two necks—one directed toward the input and output sides of the guide. The phenomenon of extraordinary acoustic transmission results in near perfect transmission of sound along each output arm in a narrow frequency interval at the Helmholtz resonant frequency. The Helmholtz resonance and hence the demultiplexed frequencies are determined by the physical dimensions of the resonator. Using a single Helmholtz resonator in each output arm means that the system is more compact compared to other proposed schemes using either side-loaded Helmholtz resonators or stubs. The experimental results are in good agreement with the computational predictions.