Experimental Studies on Sonic-Crystal Defect-Mode Waveguides Composed of a Periodic Chain of Single-Defects

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We have obtained the following results according to the purpose and plan of the research described in the application documents. In this report, a waveguide composed of a periodic chain of single-defects, or point-defects, are called a defect-mode waveguide.(1) Two methods to analyze the temporal and frequency characteristics of defects in an artificial crystal, namely, an internal excitation method which investigates them by exciting impulse, or burst sound pressure in a defect, and an external method by an excitation of a defect from the outside of the crystal.(2) Spatial confinement and frequency characteristics of a single-defect, or point-defect, embedded in a sonic crystal are investigated by both the external and internal methods, and the theoretical and experimental results had a good coincidence.(3) Temporal responses and frequency characteristics of two adjacent single-defects, which compose elementary parts of defect-mode waveguides, are investigated by FDTD simulations of t … More he wave propagation, by experimental external excitation method and by a coupled-mode theory. Well quantitatively agreed results indicated validity of the three methods.(4) Straight waveguides with and without a sharp bend composed of a chain of single defects proved to have a good 100% transmission in the pass-band by means of a FDTD simulation and an experimental external excitation.(5) Transmission characteristics of long defect-mode waveguides, which have a sharp bend and a branch or a crossroads, were measured by the ultrasonic waves of a frequency of 20〜40 kHz in air. The following items were confirmed, namely their high transmission per lattice constant in the pass band, and a high suppression in the forbidden band outside the pass band, and a good branching characteristics.(6) A high 50% mode coupling was obtained between a straight defect-mode waveguide and a neighboring defect-mode waveguide which has a sharp bend to remove from the former waveguide.(7) We have established a new coupled-mode theory which describes the behaviors of an arbitrary number of coupled modes of a chain of defect-modes. Quantitative preciseness of the results deduced by this theory was confirmed by the FDTD simulation and the experimental results described above. Less