An airborne parametric array

The development of a prototype parametric speaker comprised of 37 piezo-speakers, also known as “acoustic flashlight” is described. The sound pressure along the axis was measured for both the primary (38.5 kHz ultrasonic) signal and the secondary (demodulated) signal. Comparison with the theory for an equivalent piston radiating at the same frequency and the simulation of the piezo speakers as simple sources in the same hexagonal arrangement was made. The absorption coefficient and the radiation patterns of the primary and secondary signal were also measured. All the measurements and the simulation agree with the corresponding theories. The demodulated (audio frequency) signal behaves in the near field of the speaker in the same way (that of an equivalent piston) as the primary (ultrasonic frequency) signal, which results in the inheritance of its high directivity.