Parametric array in air

Abstract

An experimental investigation of the parametric array in air was conducted using a circular piston transducer which produced spherically spreading, collinear, primary beams at frequencies of 18.6 and 23.6 kHz. Since source levels were not strong (about 110 dB re 0.0002 μbar at 1 ft), the 5−kHz difference frequency signal generated by the parametric array was relatively weak. Because of space limitations, all measurements were made in the nearfield of the array. Spurious difference frequency signals resulting from intermodulation distortion in the receiving system were suppressed by judicious choice of electronic components and by the addition of an acoustical filter in front of the microphone. The classic properties of the parametric array were observed. The 5−kHz beam was narrow, and no minor lobes were evident. The propagation curve first increased with increasing range, reached a broad maximum, and then gradually decreased. Theoretical predictions were based on a perturbation solution of Burgers’ equation and on the integral solution of the inhomogeneous wave equation. Comparison of measured results with these predictions conclusively demonstrated the existence of the parametric array in air. Beam patterns and propagation data obtained for the second−harmonic and sum−frequency signals also confirmed theoretical predictions. Subject Classification: 25.35.

Are some people suffering as a result of increasing mass exposure of the public to ultrasound in air?

“…Audiosonic spotlights [154,155] use intense ultrasound to generate zones into which audio frequency sound is contained, so that exhibition booths, museums etc. can have audio commentary contained in front of the exhibit without leaking to neighbouring ones.…”

Generating dual beams from a single steerable parametric loudspeaker

“…When two primary frequencies (PFs) are transmitted from an ultrasonic transducer, new frequency components, such as the difference frequency (DF), sum frequency, and higher order harmonics, are generated due to nonlinear acoustic effects. Furthermore, as a result of the absorption in air, the PFs, sum frequency, and higher order harmonics decay more rapidly than the DF [4]. More importantly, the DF is audible and still exhibits a narrow directivity pattern, which can be modeled by an end-fire array of virtual sources [2,5].…”

Actively created quiet zones by parametric loudspeaker as control sources in the sound field

“…Since the first experiment on the parametric array in air implemented by Bennet and Blackstock [3], the development of the parametric loudspeaker has attracted much attention in audio engineering [4]- [8]. A localized sound field or a private listening space can be created by the parametric loudspeaker through the self-demodulation of finite-amplitude modulated ultrasonic waves resulting form nonlinear interaction in air.…”