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If active piezoelectric materials are used as inclusions in a phononic crystal (PC), a stop band can be changed to a pass band or vise versa just by electric switching. Here, we make a use of the property to create an active waveguides in an elastic body in a certain frequency range. The advantages of the wave-guiding are that no permanent geometry or material change is needed and that somewhat arbitrarily-shaped waveguides can be formed actively in PC structures. At the operating frequencies, a piezoelectric PC at an open-circuit state forms a stop band while a PC at a closed-circuit state forms a pass band. Therefore, a part of a piezoelectric PC at a closed-circuit state makes a waveguide through which elastic waves can pass.

Phononic crystal; Active; Wave-guiding