New Type of Vibration Dampers Utilising the Effect of Acoustic 'Black Holes'
One of the well-known ways of damping resonant flexural vibrations of different engineering structures or their elements, e.g. finite plates or bars, is to reduce reflections of flexural waves from their free edges. In the present paper, a new efficient method of reducing edge reflections is described that utilises gradual change in thickness of a plate or a bar from the value corresponding to the thickness of the basic plate to almost zero. It is proposed to use specific power-law shapes of plates of variable thickness (wedges) that ideally provide zero reflection even for negligibly small material attenuation – the so-called 'acoustic black hole effect'. In particular, for powers m ≥ 2 – in free wedges, and m ≥ 5/3 – in immersed wedges, incident flexural waves become trapped near the edge and do not reflect back. Since, because of ever-present edge truncations in real manufactured wedges, the corresponding reflection coefficients are always far from zero, to make up for real wedges and make the systems more efficient it is proposed to deposit absorbing thin layers on wedge surfaces. It is shown that the deposition of thin damping layers on the wedge surfaces can dramatically reduce the reflection coefficients. Thus, the combination of a wedge with power-law profile and of thin damping layers can utilise the acoustic 'black hole' effect resulting in very effective damping systems for flexural vibrations.
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Document Type: Research Article
Publication date: 2004-09-01
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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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