Experimental studies on two-dimensional defect-mode waveguides in a sonic/phononic crystal

Defect-mode waveguides (DMWGs) were constructed removing every second scatterer from a sonic/phononic crystal along, an intended waveguide path. The host crystal was composed of a square array of acrylic resin cylinders in air with a diameter of 5.0 mm. The lattice constant was 6.25 mm with a Bragg reflection at around 27.6 kHz at room temperature. Various shapes of DMWGs were fabricated, and their transmission spectra were measured using a network analyzer with a high-frequency speaker, i.e., a tweeter, and a wideband microphone. The theoretically expected band-pass spectra of DMWGs were confirmed experimentally as follows. (1) A clear passband of the DMWG was observed at a normalized frequency of between 0.545 and 0.590 with a transmission per lattice constant of -0.52 dB. (2) The passband was not influenced significantly by the, existence of a bend, a branch, or a crossroads in the DMWG. The DMWG was verified to work not only as a novel acoustic waveguide but also as a good band-pass filter.