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Nowadays 1-3-type PZT composite transducers are widely used for underwater parametric array (PA) sound source since they can generate highly directional acoustic beam with high intensity, which is the requirements for the PA acoustic phenomenon that results from nonlinearity of a medium. Thanks to the relatively small mechanical quality factor of 1-3 PZT composite, the transducer using it can generate high intensity sounds by relatively low input voltage in the relatively wide frequency band around its resonance frequency. The low mechanical quality factor, however, increase the internal mechanical loss inside the transducer. Consequently, the acoustic radiation efficiency may be lower than expected. In this paper, a dual-resonant-frequency PZT rods are integrated into a thinner polymer plate. Then, the radiation surface increases to enhance radiation power efficiency. The PZT rods with two different lengths, are integrated in the process of molding a polymer plate. The fabricated transducer are operated with the out-of-phase driving method for a dual resonance transducer to generate direct sound beam with a wide frequency bandwidth. The sound pressure levels (SPLs) of the primary waves of the first and second resonant frequencies were 197 dB and 203 dB (re = 1μP), respectively, at 9 m. The acoustic radiation efficiencies at 98 kHz and 135 kHz were 50% and 33%, respectively. The DFW generated by the PA had an SPL of 150 dB (re = 1μP @ 30 kHz) and a high directivity of 3.4° half-power beam width.

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A parametric array (PA) loudspeaker is a highly directional audio source that might grant one's convenience if it is used with mobile devices. However, conventional PA loudspeakers is almost impossible to apply in mobile devices using a battery because of the large power consumption and large device size. In this study, a PA loudspeaker system (PALS) was fabricated and evaluated to show that those difficulties could be overcome to apply it to mobile devices. In order to construct a PALS for demonstration, a power amplifier and signal-processing unit should also be properly designed and built. The PA source transducer should also be designed and built for a mobile device application. These components were integrated into a single PALS. The PALS generated a 125-dB primary wave and 62 dB of a different frequency wave (DFW) through the PA at 0.45 m in a 3 m × 3 m × 2 m semi-anechoic chamber. We confirmed that the half-power bandwidth (HPBW) formed a 6° beam at 83 kHz of DFW and 90 kHz of the primary wave (PW), and the HPBW formed a 7.3° beam at 5 kHz of DFW and a 7.1° beam at 10 kHz of DFW, respectively. Lastly, the power required was 6.65 W without a matching circuit, and 3.25 W with such a circuit.