Audio parametric arrays in air.
Mark F. Hamilton · The Journal of the Acoustical Society of America · 2009
Following Westervelt’s discovery and theoretical description of the parametric acoustic array reported at the 1960 meeting of the ASA at Brown Univ., and the measurements in both water and air at ultrasonic frequencies, confirming Westervelt’s predictions qualitatively, reported by Bellin and Beyer at that same meeting, it was not until 1973 that Bennett and Blackstock reported convincing quantitative comparisons of theory and experiment for a parametric array in air. While their experiments produced difference frequencies in the audio range, not until the late 1990s did application of the parametric array to directional audio transmission in air achieve any commercial success. This presentation will briefly review the history of developments leading up to modern-day audio parametric arrays. Challenges associated with transducer performance, signal processing, and acoustical measurements specific to audio parametric arrays in air will be described. Features of several audio parametric arrays currently on the market will be discussed. Finally, results will be presented from an ongoing collaboration between the author’s group at Univ. of Texas at Austin and Professor Pierre Khuri-Yakub’s group at Stanford Univ. to create audio parametric arrays in air using capacitive micromachined ultrasonic transducers to transmit the ultrasonic primary beams.