Loop filters as resonant elements for acoustic metamaterials and stop band structures

Two geometries of acoustic loop filters side-loaded onto waveguides are explored using audio-frequency impulse response measurements. Finite element modeling is used to elucidate the interference mechanisms in each loop filter configuration. These simulations also yield transmission amplitude results, which are in good agreement with those determined experimentally. The ability to create broad forbidden transmission regions is demonstrated by the use of a sub-wavelength spaced series of slightly detuned filters. Finally, the phase information from the impulse response measurements is analyzed to show that regions of negative bulk modulus exist at frequencies in the vicinity of the loop interference minima. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4797501]