3D-5 Mode Coupling Behavior of Neighboring Single-Defects and Defect-Mode Wave Guides in a Sonic Crystal Made of Acrylic Resin Cylinders in Air

We have numerically investigated wave propagations through various types of defect-mode waveguides constructed in two-dimensional (2D) sonic crystals made of acrylic resin cylinders in air. The prominent features of these wave guides were summarized as follows: (1) quasi-perfect transmission of sound waves, and (2) good impedance matching at both the inlet and outlet with no practical reflections of the incident waves and the guided waves. These two features overcome the drawbacks of the conventional line-defect wave guides in sonic crystals. For example, the transmissions of straight and bending defect-mode waveguides fabricated in 2D sonic crystals of 11 times 11 and 15 times 11 acrylic resin cylinders in air are 0.0 dB and 1.5 dB respectively. The transmission is not less than 0 dB due to a slight concentration of the guided waves during transmission. It is considered that the fundamentals of traveling waves in these defect-mode wave guides originate from the mode coupling between adjacent or neighboring single-defects (point-defects). First in this report, we investigate numerically mode coupling behavior of two neighboring single-defects in the central part of 13 times 11 acrylic resin cylinders in air using an elastic FDTD method. The results show a double periodic and complete energy exchange between them. One period is equal to that of resonant mode itself localized in one of neighboring single-defects. The other is a long one depending on the coupling strength. Detailed temporal behavior of the energy exchange is analyzed not only numerically but also using movies of two-dimensional acoustic field distribution, in order to explain the mechanism of the traveling modes over a line of single-defects. Second, a wave guide bend, two- and three-port power dividers are constructed by branching a defect-mode wave guide, and their traveling waves are discussed based on the mode-coupling behavior of the neighboring single-defects