Focusing Ultrasound with an Acoustic Metamaterial Network

Department of Mechanical Science and Engineering and Beckman Institute of Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA.
Physical Review Letters (Impact Factor: 7.51). 06/2009; 102(19):194301. DOI: 10.1103/PhysRevLett.102.194301
Source: PubMed


We present the first experimental demonstration of focusing ultrasound waves through a flat acoustic metamaterial lens composed of a planar network of subwavelength Helmholtz resonators. We observed a tight focus of half-wavelength in width at 60.5 kHz by imaging a point source. This result is in excellent agreement with the numerical simulation by transmission line model in which we derived the effective mass density and compressibility. This metamaterial lens also displays variable focal length at different frequencies. Our experiment shows the promise of designing compact and lightweight ultrasound imaging elements.

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    • "Another distinctive feature is the frequency-dependent anisotropy (or directivity) observed in their spatial wave patterns [6] [7] [8] and the ability to feature a negative refractive index [9] [10] [11]. A number of metamaterial architectures have also been proposed to design acoustic lenses [12] [13] [14] and attain subwavelength imaging [15] [16]. "
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    • "acoustic properties such as negative effective mass density and/or bulk modulus. These metamaterials are compelling in view of the possibility of using negative refraction to design flat superlenses that can beat the diffraction limit [3]. Different from the acoustic metamaterial, the elastic metamaterial is a structured composite with a solid host matrix, which can support both longitudinal and transverse waves. "
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    • "In the case of electromagnetic properties, a revolution started a decade ago with the experimental realisation of Veselago's predictions [1] on hypothetical materials with negative refractive index [2] [3], and related applications such as to the design of sub-wavelength lens [4] and electromagnetic cloaks [5]. Similar concepts have also been explored to create materials with unusual acoustic properties, including negative effective mass density for acoustic focusing [6]. These properties contrast with those of most conventional materials. "
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