A wide-band in-air parametric array source composed of a circular plate with steps and a Langevin transducer with a horn

Parametric array (PA) sources generate a directional sound beam, via the PA phenomenon. Practical PA sources, such as PA loudspeakers, have high power consumption, low sound quality, and high cost. The stepped-plate transducer, which consists of a Langevin transducer, a horn, and a radiating plate with steps, can provide high intensity sound and a highly directional sound beam in the acoustic axis. This study investigated the use of a stepped-plate transducer to make a PA source with high directivity and a wide bandwidth. A stepped-plate transducer that had two different resonance frequencies (f(1) = 77.5 kHz, f(2) = 87.4 kHz) was designed for wide bandwidth, and the three different heights of the steps on the plate (t(s1) = 2.28 mm, t(s2) = 2.14 mm, t(s3) = 2.02 mm) were intended to provide high directivity sound beams. The fabricated stepped-plate transducer demonstrated a 50 +/- 3 dB sound pressure level for the difference frequency wave in the 4-19 kHz frequency range (with equalization), and 4.2-5.1 degrees of HPBW was shown for the highly directional sound beam.