Abstract
A parametric array (PA) loudspeaker generates highly directional sound beams by exploiting the PA phenomenon. Before such loudspeakers were fabricated from stepped plate transducers, arrays of small ultrasonic radiators were employed. A stepped plate transducer generates broadband PA sound by exploiting the multi-resonance characteristics of its structure, even though it has only a single radiator. However, the design process is difficult because the plate must be thicker than the steps. In this study, we present a new method for fabrication of stepped plate PA loudspeakers (SPPALs); we employ a Langevin transducer, a circular aluminum plate, and composite polymer steps. The new stepped plate is fabricated by molding the composite steps on a flat plate. This is unlike the conventional stepped plate, in which both the plate and steps are made of the same metal. Using this method, although the radiation plate is thinner than the steps, such stepping is associated with minimal changes in the natural frequency and mode shape. Therefore, the SPPAL design process is simplified. We experimentally confirmed that the new stepped plate exhibited the desired bending mode. The SPPALs exhibited a maximum sound pressure of 61 dB at 2 m and a half-power beam width of < 5°; the sound was highly directional.
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