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  • Comparative Studies. Non-European Languages/Literatures  (13)
  • 1
    Online Resource
    Online Resource
    Evaluation of the resolution of a metamaterial acoustic leaky wave antenna
    Acoustical Society of America (ASA) ; 2016
    In:  Journal of the Acoustical Society of America Vol. 139, No. 4_Supplement ( 2016-04-01), p. 2182-2182
    Details
    In: Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 139, No. 4_Supplement ( 2016-04-01), p. 2182-2182
    Abstract: Acoustic antennas have long been utilized to directionally steer acoustic waves in both air and water. Typically these antennas are comprised of arrays of active acoustic elements which are electronically phased to steer the acoustic profile in the desired direction. A new technology, known as an acoustic leaky wave antenna, has recently been shown to achieve directional steering of acoustic waves using a single active transducer coupled to a transmission line passive aperture. The leaky wave antenna steers acoustic energy by preferential coupling to an input frequency and can be designed to steer from backfire to endfire, including broadside. This paper provides an analysis of resolution as a function of both input frequency and antenna length. Additionally, the resolution is compared to that achieved using an array of active acoustic elements. [This work was supported by ONR.]
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.4950489
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 2016
    detail.hit.zdb_id: 1461063-2
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  • 2
    Online Resource
    Online Resource
    Effect of waveguide impedance on radiation in underwater acoustic leaky wave antennas
    Acoustical Society of America (ASA) ; 2015
    In:  Journal of the Acoustical Society of America Vol. 137, No. 4_Supplement ( 2015-04-01), p. 2265-2265
    Details
    In: Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 137, No. 4_Supplement ( 2015-04-01), p. 2265-2265
    Abstract: Leaky wave antennas (LWAs) have been examined for decades as a way to steer electromagnetic waves as indexed by input frequency, enabling rapid video scanning of an environment with a simple compact device. Recently, an LWA device constructed of a rigid waveguide with open shunts was shown to produce a similar steering effect for acoustic waves in air [Naify et al., Appl. Phys Lett. 102, 203508 (2013)] . The shunts serve two purposes, to couple acoustic energy from the waveguide to the surrounding area, as well as control directionality of the radiated wave by changing the impedance, and thus modulating the phase speed of the waves in the waveguide. While this impedance contrast of the waveguide wall relative to that of the surrounding fluid is very large for an air background, when designing a structure for use in water the material of the waveguide can drastically change the directionality of the radiation profile. This study examines the effect of waveguide wall impedance on directionality of an acoustic LWA using both numerical and finite element methods. Three material impedance conditions are examined, including acoustically rigid, and two materials with finite impedance. [Work sponsored by the Office of Naval Research.]
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.4920266
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 2015
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  • 3
    Online Resource
    Online Resource
    Holographic metamaterial using an acoustic leaky wave antenna
    Acoustical Society of America (ASA) ; 2016
    In:  Journal of the Acoustical Society of America Vol. 139, No. 4_Supplement ( 2016-04-01), p. 2182-2182
    Details
    In: Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 139, No. 4_Supplement ( 2016-04-01), p. 2182-2182
    Abstract: Acoustic antennas in the form of active phased arrays have long been utilized to steer acoustic waves in both air and water. Although acceptable, these antennas form electrically complex, bulky structures. Acoustic leaky wave antennas have recently emerged as a method to achieve directional steering using a minimal number of active transducers coupled to an analog metamaterial aperture. In this study, a two-dimensional air-acoustic leaky wave antenna, coupled to only four sources, is shown to steer acoustic energy within a full three-dimensional space while also providing significant savings in terms of size, weight, and cost. By careful selection of the analog geometry, the aperture has the capability to produce a wide range of holographic acoustic images.
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.4950490
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 2016
    detail.hit.zdb_id: 1461063-2
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  • 4
    Online Resource
    Online Resource
    Evaluation of the resolution of a metamaterial acoustic leaky wave antenna
    Acoustical Society of America (ASA) ; 2016
    In:  The Journal of the Acoustical Society of America Vol. 139, No. 6 ( 2016-06-01), p. 3251-3258
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 139, No. 6 ( 2016-06-01), p. 3251-3258
    Abstract: Acoustic antennas have long been utilized to directionally steer acoustic waves in both air and water. Typically, these antennas are comprised of arrays of active acoustic elements, which are electronically phased to steer the acoustic profile in the desired direction. A new technology, known as an acoustic leaky wave antenna (LWA), has recently been shown to achieve directional steering of acoustic waves using a single active transducer coupled to a transmission line passive aperture. The LWA steers acoustic energy by preferential coupling to an input frequency and can be designed to steer from backfire to endfire, including broadside. This paper provides an analysis of resolution as a function of both input frequency and antenna length. Additionally, the resolution is compared to that achieved using an array of active acoustic elements.
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.4950755
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 2016
    detail.hit.zdb_id: 1461063-2
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  • 5
    Online Resource
    Online Resource
    Acoustic Scattering Cancellation: an Alternative to Coordinate Transformation Scattering Reduction
    Acoustical Society of America (ASA) ; 2016
    In:  Journal of the Acoustical Society of America Vol. 139, No. 4_Supplement ( 2016-04-01), p. 2183-2183
    Details
    In: Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 139, No. 4_Supplement ( 2016-04-01), p. 2183-2183
    Abstract: Coordinate transformations have been extensively studied as a means to hide an object immersed in a fluid from an acoustic field. The coordinate transform approach relies on coatings with non-uniform and typically anisotropic material properties to guide an acoustic wave around the object. Acoustic scattering cancellation is an alternative approach that relies on modal cancellation within a desirable bandwidth to significantly reduce the acoustic scattering cross-section of an object. We present a direct comparison, using coatings with similar layer thicknesses and material properties, demonstrating that scattering cancellation achieves a similar level of scattering reduction compared to coordinate transforms, but with much thinner coatings. Furthermore, we present experimental results demonstrating significant reductions in the scattering cross-section of neutrally buoyant elastic cylinders suspended in an aqueous environment. Omnidirectional scattering reduction is obtained using a single isotropic coating through modal cancellation of the monopole and dipole modes of the cylinders. The modal cancellation is achieved by carefully tuning the coating’s material properties and thickness such that the combined cylindrical object and coating exhibit effective medium properties identical to water. The scattering cancellation is close to 15 dB over a broad bandwidth for all reduced frequencies below ka ≅ 1.
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.4950493
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 2016
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  • 6
    Online Resource
    Online Resource
    Superresolution using an acoustic vortex wave antenna
    Acoustical Society of America (ASA) ; 2016
    In:  Journal of the Acoustical Society of America Vol. 140, No. 4_Supplement ( 2016-10-01), p. 3102-3102
    Details
    In: Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 140, No. 4_Supplement ( 2016-10-01), p. 3102-3102
    Abstract: Acoustic waves, like their electromagnetic counterpart, exhibit a diffraction limit, which restricts the ability to resolve or generate fine structures in the pressure field. Previously proposed methods to overcome this limit, and therefore achieve superresolution, have mainly been limited to operating within the near-field region of the aperture. In this work, we describe how far-field superresolution can be achieved using shaped acoustic vortices, created by utilizing the topological diversity of an acoustic vortex wave antenna. Theoretical and numerical results will be presented for the design of an acoustic vortex wave antenna with arbitrary planar arrangement which is capable of generating superresolved far-field features in the radiated acoustic pressure. Variation of the antenna geometry enables different shaped acoustic vortex patterns to be achieved, which propagate from the near-field into the far-field through an arrangement of stable integer mode vortices. Despite the total aperture size being less than a wavelength in diameter, the proposed acoustic vortex wave antenna is shown to achieve far-field superresolution with feature sizes 4-9 times smaller than the resolution limit. Several examples will be presented and discussed in detail. [Work supported by the Office of Naval Research.]
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.4969678
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 2016
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  • 7
    Online Resource
    Online Resource
    Anisotropic acoustic metafluid for underwater operation
    Acoustical Society of America (ASA) ; 2016
    In:  The Journal of the Acoustical Society of America Vol. 139, No. 6 ( 2016-06-01), p. 3325-3331
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 139, No. 6 ( 2016-06-01), p. 3325-3331
    Abstract: The paper presents a method to design and characterize mechanically robust solid acoustic metamaterials suitable for operation in dense fluids such as water. These structures, also called metafluids, behave acoustically as inertial fluids characterized by anisotropic mass densities and isotropic bulk modulus. The method is illustrated through the design and experimental characterization of a metafluid consisting of perforated steel plates held together by rubber coated magnetic spacers. The spacers are very effective at reducing the effective shear modulus of the structure, and therefore effective at minimizing the ensuing coupling between the shear and pressure waves inside the solid effective medium. Inertial anisotropy together with fluid-like acoustic behavior are key properties that bring transformation acoustics in dense fluids closer to reality.
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.4950754
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 2016
    detail.hit.zdb_id: 1461063-2
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  • 8
    Online Resource
    Online Resource
    Experimental studies of sound propagation over vertical and slanted paths in a turbulent atmosphere
    Acoustical Society of America (ASA) ; 2019
    In:  The Journal of the Acoustical Society of America Vol. 145, No. 3_Supplement ( 2019-03-01), p. 1661-1661
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 145, No. 3_Supplement ( 2019-03-01), p. 1661-1661
    Abstract: Sound propagation over vertical and slanted paths differs from horizontal paths due to the height dependence of turbulence parameters and atmospheric stratification. Vertical and slanted paths are important for several applications, such as localization of unattended aerial systems (UASs) with ground-based acoustic microphone arrays, detection of ground-based sources with elevated arrays, and the effect of atmospheric turbulence on sonic booms. This paper describes a comprehensive experiment on near-vertical sound propagation conducted over five days in September 2018 at the National Wind Technology Center (NWTC), located near Boulder, CO. The experiment involved the NWTC 135-m meteorological tower with meteorological instruments installed at 17 heights. Nine microphones were located on three horizontal booms attached to the tower at different heights, and a speaker was placed on the ground. Two reference microphones where located near the speaker. About 65% of the time, the speaker transmitted nine or twelve tones. During the remaining time, 6-ms chirps were transmitted. A preliminary analysis of the signal statistics is presented and compared with theoretical predictions.
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.5101100
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 2019
    detail.hit.zdb_id: 1461063-2
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  • 9
    Online Resource
    Online Resource
    Interferometric measurements of supersonic projectile acoustic signatures
    Acoustical Society of America (ASA) ; 2020
    In:  The Journal of the Acoustical Society of America Vol. 148, No. 4_Supplement ( 2020-10-01), p. 2570-2570
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 148, No. 4_Supplement ( 2020-10-01), p. 2570-2570
    Abstract: Supersonic projectiles cause disturbances in the air that propagate and coalesce to form acoustic signatures. In the far-field, these signatures approach ideal N-waves. However, near the projectile these signatures are closely related to the projectile's shape. To study the generation and formation of acoustic signatures from supersonic projectiles, an experiment was conducted using optical methods. A z-type schlieren imaging system and laser interferometer were used in conjunction with acoustic sensors to measure the pressure field surrounding supersonic projectiles of various sizes and shapes. The rate of change of the phase difference recorded by the interferometer is inverted to obtain the ballistic pressure field by assuming cylindrical symmetry and using an inverse Abel transform. The accuracy of these reconstructed time series is evaluated by comparing N-wave parameters, such as period and peak pressure, with analytical results derived from the Whitham F-function. Improved rise time resolution obtained from the interferometric measurement is demonstrated by comparison with recordings from standard condenser microphones. Advantages of measuring acoustic signatures near the projectile by interferometric methods are discussed.
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.5147132
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 2020
    detail.hit.zdb_id: 1461063-2
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  • 10
    Online Resource
    Online Resource
    Designing beampatterns with tapered leaky wave antennas
    Acoustical Society of America (ASA) ; 2017
    In:  The Journal of the Acoustical Society of America Vol. 141, No. 5_Supplement ( 2017-05-01), p. 3574-3575
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 141, No. 5_Supplement ( 2017-05-01), p. 3574-3575
    Abstract: Leaky wave antennas (LWAs) have been shown to be an effective tool for frequency-steerable wave radiation in both the electromagnetic and acoustic wave regimes. LWA’s operate by modifying the impedance on a waveguide such that refraction occurs out of the waveguide at an angle corresponding to Snell’s Law. For a LWA with uniform leaking parameter across the waveguide length, that leakage angle is constant. Using analytical techniques, and by careful geometric design of the waveguide impedance, the leaked beampattern can be tailored. The process of the tapering process for an acoustic LWA is discussed here, and notional examples are presented including sidelobe reduction. [Work supported by the Office of Naval Research.]
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.4987601
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 2017
    detail.hit.zdb_id: 1461063-2
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