The presented report discusses the principle of a parametric coupled ultrasonic-array which utilizes the nonlinearity of the pressure-density relationship of air to produce a highly directed audible sound.
Furthermore, the development of a system, that amplitude-modulates an audio-signal of a CD- or a MP3-player on to the carrier-frequency of 40 kHz is built. A loudspeaker transduces this ultrasound-signal into the air and that way produces directed audible sound. In addition to that, the determination of the directional characteristic is shown (see Figure 2) and compared with the theoretical calculation.
In order to turn the loudspeaker in different directions, a positioning-device including two stepper-motors is constructed. Finally, the whole system is packed in a tight device (see Figure 1).
July 31, 2008