In this paper, we propose novel cleaning equipment using a waveguide mode, which we call the Megatube. By using the waveguide, it is possible to supply ultrasonic waves at a distance from the sound source without spreading loss and generate cavitation by controlling the input power and dissolved gas concentration. The sound pressure distribution in the waveguide was simulated using the finite-difference time-domain (FDTD) method. Ultrasonic waves propagate along the waveguide without spreading loss and have a periodic waveguide mode. The sound pressure level emitted from the waveguide was measured to confirm the absorption of ultrasonic waves which was found to decrease by 56%/m. One of the loss factors is the absorption by water in a nonlinear sound field. The dependence of the absorption of ultrasonic waves on the input power to the sound source and the dissolved gas concentration was investigated.
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