Abstract
We describe an acoustic impedance matching method that permits perfect sound transmission between waveguides of different impedances as set by their cross sectional areas. Impedance matching in this case is based on extraordinary acoustic transmission mediated via a Helmholtz resonator embedded at the junction between the dissimilar waveguides. Perfect transmission occurs at the Helmholtz resonance frequency. However, perfect transmission between different impedance waveguides requires that the two-neck Helmholtz resonator be asymmetric with different areas and lengths of the necks that couple to each waveguide.
Highlights
A method is described of achieving perfect sound transmission between two acoustic waveguides with different impedances via the use of an asymmetric two-neck Helmholtz resonator
This impedance-matching scheme is based on the phenomenon of extraordinary acoustic transmission demonstrated previously1,2 using a two-neck Helmholtz resonator (HR) embedded between identical waveguides
Many are closely aligned with the surface plasmon model in that the resonant effect is due to evanescent surface waves on the textured surface on the barrier adjacent to the perforation
Summary
A method is described of achieving perfect sound transmission between two acoustic waveguides with different impedances via the use of an asymmetric two-neck Helmholtz resonator. This impedance-matching scheme is based on the phenomenon of extraordinary acoustic transmission demonstrated previously using a two-neck Helmholtz resonator (HR) embedded between identical waveguides. In earlier work the phenomenon of EAT mediated by a two-neck Helmholtz resonator embedded between two identical waveguides was demonstrated in which 100% transmission was predicted computationally at the HR resonant frequency.. This work explores the ability of resonant structures to act as impedance-matching elements, a topic which is well established in electrical transmission lines. Demonstration here of the need for an asymmetric coupling agent may have parallels in optics where there is considerable research in the ability of plasmonic or resonant antenna structures to impedance match at interfaces between optical media of different refractive indices.
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