Development of a Sound Directional Device Based on Ultrasound Modulation and Transducer Array Optimization

The sound directional system utilizes the directional transmitting of ultrasonic wave to realize the directivity of sound, which has a wide application in civil and military fields. An optimized sound directional device is developed in this article. The signal modulation algorithms with single-frequency and broadband frequency input are theoretically analyzed. The modulation coefficients on sound distortion are evaluated. The sound fields are simulated and show that the sound emitting areas are $0.09\pi $ and $0.16\pi $ for the 16- and 10-mm-diameter transducers in 40 kHz, indicating that the 16-mm transducer has better sound directivity. The hardware of sound directional device is established, and the signal modulation is realized by DSP programming. Sound directivity and distortion evaluation principle is proposed, which provides a guidance of ultrasound modulation determination and transducer array optimization. Sound distortion measurement is conducted, and the second-order approximate square root (SASR) is adopted in the proposed hardware. Finally, the sound directional system is compared with the current sound directional array. Experiments show that the total harmonic distortion (THD) is 15.44% of $7\times 7$ array. The sidelobe amplitude intensity of $7\times 7$ array is 71.4 dB and lower than 87.9 dB of the commercial array, demonstrating that the sound emitting of $7\times 7$ array in sidelobe is in high suppression. The sound main beam emitting angle of $7\times 7$ array is 117°, which is significantly lower than 175° of the Audfly array. Therefore, the $7\times 7$ array shows a better sound directivity.