Experimentally study of a sharp bending wave-guide constructed in a sonic-crystal slab of an array of short aluminum rods in air

We have made a sonic-crystal slab (SCS) of a square-array of 16×12 short Al rods between a pair of parallel Al plates in air, as an alternative of a 2D sonic crystal. The observed full band-gap was between 15.1-18.8 kHz below -20dB, although the lower and higher boundaries were not sharp enough as 2D sonic crystals. An acoustic wave-guide was constructed in the SCS with a sharp bend. We have measured the intensities of the sound waves traveled along the wave-guide and the leaky waves which propagated straight, without turning the bend. Especially at the center of the full band-gap of the SCS, about 17 kHz, the sound waves were well guided and the ratio of the guided waves to the leaky waves was 22 dB. We have reported here the first experimentally measured characteristics of a pair of acoustic coupled waveguides constructed in an SCS. The coupling between the sound waves travelling along the waveguides was almost uniform inside of the full band-gap of the SCS. They functioned as a 3∼4 dB unidirectional acoustic coupler.