Acoustic Hyperlens Research Articles

Experimental demonstration of a three-dimensional acoustic hyperlens for super-resolution imaging

Acoustic hyperlenses have recently attracted much attention for promising applications in various fields. Yet the experimental realization of an acoustic hyperlens working in a real three-dimensional (3D) world is still lacking. Here, we theoretically propose and experimentally demonstrate a 3D acoustic hyperlens capable of producing super-resolution imaging for broadband airborne sound. A simple nonresonant metamaterial is designed as a practical implementation that simultaneously ensures tessellation of the curved surface and deep-subwavelength resolution. We analyze the dispersion relationship of the designed metamaterial that converts the evanescent waves into radially propagating modes based on positive extreme anisotropy. The effectiveness of our mechanism is demonstrated both numerically and experimentally via the production of 3D magnifying super-resolution imaging of small objects containing subwavelength patterns within a broad frequency range. We envision the realization of a 3D acoustic hyperlens to offer possibilities for the design of acoustic super-resolution imaging devices and their application in diverse scenarios ranging from medical ultrasound imaging to noninvasive evaluation.

An Acoustic Hyperlens with Negative Direction Based on Double Split Hollow Sphere

This study develops a new acoustic negative-refraction metamaterial that utilizes a synthesized double split hollow sphere (DSHS) for its unit cell. Recent relevant research has affirmed the concept that acoustic metamaterials can show unusual behavior that has not been observed in nature previously. However, as some hypothetical metamaterial designs have material properties not found in nature, the realization of practical metamaterials requires practical and complicated models. As a contribution to the development of acoustic metamaterials, the present study proposes a new anisotropic unit structure that encompasses Helmholtz resonators. This structure is referred to as the DSHS, is easy to manufacture, and has the advantage in that it uses the natural medium in its original form. By drawing the equifrequency or isofrequency contours of the designed two-dimensional (2D) anisotropic unit structure using the Floquet–Bloch’s principle, the properties of the present metamaterial can be understood. Numerical simulations are also conducted to identify and present the characteristics of the presented acoustic metamaterial. Through these, a new refraction phenomenon is identified that deviates from Snell’s law, and an acoustic hyperlens is numerically implemented that overcomes the diffraction limit.

Shape-adaptable hyperlens for acoustic magnifying imaging

Previous prototypes of acoustic hyperlens consist of rigid channels, which are unable to adapt in shape to the object under detection. We propose to overcome this limitation by employing soft plastic tubes that could guide acoustics with robustness against bending deformation. Based on the idea of soft-tube acoustics, acoustic magnifying hyperlens with planar input and output surfaces has been fabricated and validated experimentally. The shape-adaption capability of the soft-tube hyperlens is demonstrated by a controlled experiment, in which the magnifying super-resolution images remain stable when the lens input surface is curved. Our study suggests a feasible route toward constructing the flexible channel-structured acoustic metamaterials with the shape-adaption capability, opening then an additional degree of freedom for full control of sound.

Metamaterials and imaging.

Resolution of the conventional lens is limited to half the wavelength of the light source by diffraction. In the conventional optical system, evanescent waves, which carry sub-diffraction spatial information, has exponentially decaying amplitude and therefore cannot reach to the image plane. New optical materials called metamaterials have provided new ways to overcome diffraction limit in imaging by controlling the evanescent waves. Such extraordinary electromagnetic properties can be achieved and controlled through arranging nanoscale building blocks appropriately. Here, we review metamaterial-based lenses which offer the new types of imaging components and functions. Perfect lens, superlenses, hyperlenses, metalenses, flat lenses based on metasurfaces, and non-optical lenses including acoustic hyperlens are described. Not all of them offer sub-diffraction imaging, but they provide new imaging mechanisms by controlling and manipulating the path of light. The underlying physics, design principles, recent advances, major limitations and challenges for the practical applications are discussed in this review.

Acoustic metamaterials by bending layered structures

In this talk, basic concepts of metamaterials for acoustic imaging and wave manipulation using layered structures will be introduced. Starting from periodically layered structures, we can easily construct metamaterials with large anisotropy which is very useful to obtain sub-wavelength resolution in acoustic imaging. By geometric scaling the layered structure in a fixed direction, an acoustic hyperlens can be obtained so that the image with subwavelength details can be progressively magnified and exit the lens as far-fields. We have now further developed different geometric transformations by bending the layered structures to achieve a variety of wave manipulations including negative refraction in the effective medium regime, acoustic cloaking, and tunneling with a density-near-zero material.

Bandwidth and resolution of super-resolution imaging with perforated solids

Recent experiments on acoustic superlens and hyperlens found anisotropic metamaterials constructed from periodic perforated solids can be used for super-resolution imaging. Here, we present a theoretical study on the operational bandwidth of these imaging devices using the emerging framework of transformation acoustics. Within the transformation approach, both the microstructural superlens and hyperlens can be discussed using the transfer matrix method on the same footing. We show that the geometrical structure of the periodic metamaterials induces that an acoustics hyperlens has a very wide operational frequency bandwidth with its subwavelength resolution limited by the ratio of image magnification while an acoustics superlens has a very deep subwavelength resolution limited only by the periodicity of the perforations but intrinsically working at a narrow frequency bandwidth. Such investigation will become useful for designing future transformation acoustical imaging devices.

A holey structured acoustic metamaterial

The resolution of acoustic imaging system is restricted by diffraction limit. To beat this limit, early research shows acoustic metamaterials that can manipulate acoustic waves artificially and may act as lens to achieve subwavelength resolution. However, these solutions suffer significant loss therefore lack convincing experimental demonstration. Recent study suggested that arrays of metallic nanorods or nanowire can be used as lens for optical imaging at subwavelength resolution. Similar acoustic hyperlens designs have also been explored, and latest experimental result provided resolution of wavelength/7. Here presented is a holey structured endoscope which supports the transmission of the otherwise-evanescent waves over distances, therefore beating diffraction limit and achieving deep subwavelength imaging. Experimental demonstration shows clear image with feature size of wavelength/50. Such a metamaterial endoscope brings new perspectives to the applications of medical ultrasonography, sonar and ultrasonic non-destructive evaluation.

A multilayered acoustic hyperlens with acoustic metamaterials

The acoustic hyperlens can be realized by an alternating layered structure of water and fluid with negative mass density. Based on this alternating layered principle, we propose that an acoustic metamaterial consisting of three layers in water background can be designed to replace the fluid with negative mass density. The effective mass density and bulk modulus of the system which is composed of acoustic metamaterial and water are functions of the frequency. The effective mass density of such a system is close to the negative mass density of the fluid at a specific frequency; thus an acoustic metamaterial hyperlens can be achieved.

A holey-structured metamaterial for acoustic deep-subwavelength imaging

For classical waves such as light or sound, diffraction sets a natural limit on how finely the details of an object can be recorded on its image. Recently, various optical superlenses based on the metamaterials concept have shown the possibility of overcoming the diffraction limit1,2,3,4,5,6,7. Similar two-dimensional (2D) acoustic hyperlens designs have also been explored8,9,10. Here we demonstrate a 3D holey-structured metamaterial that achieves acoustic imaging down to a feature size of λ/50. The evanescent field components of a subwavelength object are efficiently transmitted through the structure as a result of their strong coupling with Fabry–Pérot resonances inside the holey plate. This capability of acoustic imaging at a very deep-subwavelength scale may open the door for a broad range of applications, including medical ultrasonography, underwater sonar and ultrasonic non-destructive evaluation.

Acoustic lenses to shout about

An acoustic hyperlens that is able to magnify and image objects much smaller than the probing wavelength promises new applications in sonar imaging.

Experimental demonstration of an acoustic magnifying hyperlens

Acoustic metamaterials can manipulate sound waves in surprising ways, which include collimation, focusing, cloaking, sonic screening and extraordinary transmission. Recent theories suggested that imaging below the diffraction limit using passive elements can be realized by acoustic superlenses or magnifying hyperlenses. These could markedly enhance the capabilities in underwater sonar sensing, medical ultrasound imaging and non-destructive materials testing. However, these proposed approaches suffer narrow working frequency bands and significant resonance-induced loss, which hinders them from successful experimental realization. Here, we report the experimental demonstration of an acoustic hyperlens that magnifies subwavelength objects by gradually converting evanescent components into propagating waves. The fabricated acoustic hyperlens relies on straightforward cutoff-free propagation and achieves deep-subwavelength resolution with low loss over a broad frequency bandwidth.

Resonances of Acoustic Waves Interacting with an Elastic Seabed

Journal of Computational AcousticsVol. 09, No. 03, pp. 1079-1093 (2001) ICTCA'99 PapersNo AccessRESONANCES OF ACOUSTIC WAVES INTERACTING WITH AN ELASTIC SEABEDMARGARETE S. FOKINA and VLADIMIR N. FOKINMARGARETE S. FOKINAInstitute of Applied Physics, Russian Academy of Sciences, 46, Ulyanov Str., Nizhny Novgorod, 603950, Russia Search for more papers by this author and VLADIMIR N. FOKINInstitute of Applied Physics, Russian Academy of Sciences, 46, Ulyanov Str., Nizhny Novgorod, 603695, Russia Search for more papers by this author https://doi.org/10.1142/S0218396X01001352Cited by:5 PreviousNext AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack CitationsRecommend to Library ShareShare onFacebookTwitterLinked InRedditEmail AbstractAn exact expression for the reflection coefficient is obtained with the Thomson–Haskell technique for the geoacoustical model of an ocean bottom consisting of an elastic homogeneous sediment layer overlying an elastic half-space. Characteristic equations for explicit determination of the position of each individual resonance contribution to the reflection coefficient are derived. Analytical expressions for the angular and frequency resonance positions are found. The resonance expression for the reflection coefficient is written in the form of a sum of resonance terms. Comparison between resonance theory and exact calculations for the elastic layer covering the elastic half-space is presented. The results of resonance formalism show excellent agreement with exact theory in all the cases.Presented at ICTCA'99, the 4th International Conference on Theoretical and Computational Acoustics, May 1999, Trieste, Italy. FiguresReferencesRelatedDetailsCited By 5An Acoustic Hyperlens with Negative Direction Based on Double Split Hollow SphereJung Sik Choi and Gil Ho Yoon17 June 2019 | Journal of Theoretical and Computational Acoustics, Vol. 27, No. 02Analytical solutions for the resonance response of Goupillaud-type elastic media using z -transform methodsG.A. Gazonas and A.P. Velo1 Jan 2012 | Wave Motion, Vol. 49, No. 1Effect of ground variability on acoustic-to-seismic transfer function and false alarms in landmine detectionVladimir N. Fokin, Margarita S. Fokina, James M. Sabatier and Zhiqu Lu1 Aug 2006 | The Journal of the Acoustical Society of America, Vol. 120, No. 2Effect of variability of soil physical properties on clutter and false alarms in land mine detectionVladimir N. Fokin, Margarita S. Fokina, James M. Sabatier, Ning Xiang and Wheeler B. Howard3 August 2004 | Radio Science, Vol. 39, No. 4Estimation of sea bottom parameters from the angle-frequency resonances of the reflection coefficientV. N. Fokin and M. S. Fokina1 Sep 2003 | Acoustical Physics, Vol. 49, No. 5 Recommended Vol. 09, No. 03 Metrics History Received 8 July 1999 Revised 7 September 2000 PDF download