Full Band Gaps of Sonic Crystals Made of Acrylic Cylinders in Air –Numerical and Experimental Investigations–

By introducing a common parameter space for sonic crystals and photonic crystals, we have classified them uniformly. Both are artificial crystals made of a periodic array of scatterers with a lattice constant of approximately a half wavelength. Then, we predicted that sonic crystals composed of solid cylinders in air have full band gaps with a filling ratio larger than 0.44, developing a finite-difference time-domain (FDTD) method numerically to analyze acoustic wave propagation in a finite periodic structure. Next, we constructed in air a two-dimensional array of 10 ×10 acrylic cylinders with a radius of 10.2 mm and a lattice constant of 24.0 mm, and observed a full band gap between 6.8 kHz and 9.5 kHz with a transmission ratio smaller than -25 dB using a tone burst, which agrees well with the numerical predictions. To our knowledge, no other report of clear and direct measurements of the full band gap of sonic crystals made of solid scatterers in air has been published.