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Acoustic metamaterials are artificially fabricated materials designed to control, direct, and manipulate sound waves as these might occur in gases, liquids, and solids. The hereditary line into acoustic metamaterials follows from theory and research in negative index material. Furthermore, with acoustic metamaterials controlling sonic waves can now be extended to the negative refraction domain.〔 Control of the various forms of sound waves is mostly accomplished through the bulk modulus ''β'', mass density ''ρ'', and chirality. The density and bulk modulus are analogies of the electromagnetic parameters, permittivity and permeability in negative index materials. Related to this is the mechanics of wave propagation in a lattice structure. Also materials have mass, and instrinsic degrees of stiffness. Together these form a resonant system, and the mechanical (sonic) resonance may be excited by appropriate sonic frequencies (for example pulses at audio frequencies).〔 ==History== (詳細はVictor Veselago in 1967, but not realized until some 33 years later. John Pendry produced the basic elements of metamaterials during the last part of the 1990s. His materials were combined and then negative index materials were realized first in the year 2000 and 2001 which produced a negative refraction thereby broadening possible optical and material responses. Hence, research in acoustic metamaterials has the same goal of broader material response with sound waves.〔Nahin, P.J., Spectrum, IEEE, Volume 29, Issue 3, March 1992 Page(s):45–〕〔 〕〔 〕〔〔 〕〔 〕〔Negative refraction (electromagnetic) first demonstrated by D. Smith, S. Shultz, and R. Shelby (2000–2001)〕 Research employing acoustic metamaterials began in the year 2000 with the fabrication and demonstration of sonic crystals in a liquid.〔 This was followed by transposing the behavior of the split-ring resonator to research in acoustic metamaterials.〔 After this double negative parameters (negative bulk modulus ''β''eff and negative density ''ρ''eff) were produced by this type of medium.〔 Then a group of researchers presented the design and tested results of an ultrasonic metamaterial lens for focusing 60 kHz.〔 The earlier studies of acoustics in technology, which is called acoustical engineering, are typically concerned with how to reduce unwanted sounds, noise control, how to make useful sounds for the medical diagnosis, sonar, and sound reproduction and how to measure some other physical properties using sound. Using acoustic metamaterials the directions of sound through the medium can be controlled by manipulating the refractive index. Therefore, the traditional acoustic technologies are extended and may eventually cloak certain objects from acoustic detection. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Acoustic metamaterials」の詳細全文を読む スポンサード リンク
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