Nonlinear propagation of focused ultrasound beams from a wide-angle aperture
Sound pressure amplitudes of the first three harmonics in finite-amplitude CW ultrasound beams are measured along and across the beam axis in fresh water. The sound source is a 1.6 MHz focused transducer with a circular aperture of 73 mm in diameter and a focal length of 75 mm. The source pressure amplitude is supposed to be distributed uniformly. The aperture half-opening angle of 29° exceeds the upper limit of the applicability of the paraxial approximation, so the present authors propose a beam model equation using the oblate spheroidal coordinate system for theoretical prediction [J.Acoust.Soc.Am. 107, 3035-3046 (2000)]. Numerical solutions of the model equation are overall in good agreement with the experiment. Thus, the supported validity of the model equation allows us to further study nonlinear propagation of ultrasonic pulses from a strongly focusing source. It has been determined numerically that the direct wave from the center of the source has a crucial effect on forming a shock-like spike in the post-focal region.
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Document Type: Research Article
Publication date: May 1, 2000
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- Acta Acustica united with Acustica, published together with the European Acoustics Association (EAA), is an international, peer-reviewed journal on acoustics. It publishes original articles on all subjects in the field of acoustics, such as general linear acoustics, nonlinear acoustics, macrosonics, flow acoustics, atmospheric sound, underwater sound, ultrasonics, physical acoustics, structural acoustics, noise control, active control, environmental noise, building acoustics, room acoustics, acoustic materials, acoustic signal processing, computational and numerical acoustics, hearing, audiology and psychoacoustics, speech, musical acoustics, electroacoustics, auditory quality of systems. It reports on original scientific research in acoustics and on engineering applications. The journal considers scientific papers, technical and applied papers, book reviews, short communications, doctoral thesis abstracts, etc. In irregular intervals also special issues and review articles are published.
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