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  • 11
    Online Resource
    Online Resource
    Acoustical Society of America (ASA) ; 1997
    In:  The Journal of the Acoustical Society of America Vol. 102, No. 3 ( 1997-09-01), p. 1296-1309
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 102, No. 3 ( 1997-09-01), p. 1296-1309
    Abstract: A noncontact acoustical system has been developed which measures Young’s modulus of solid materials at high temperature with ⩽0.05% accuracy. The system employs capacitive (or electrostatic) transducers to excite and detect vibrations of millimeter-sized resonant tuning forks, whose resonance frequencies alter with changing temperature and material properties. The use of tuning forks in their fundamental symmetric modes of vibration provide resonances of high Q’s and eliminate irreversible frequency and drift effects that occur with other forms of resonator. The use of noncontact capacitive transducers reduces the damping and stresses that otherwise occur with contacting transducers, and allows the system to be simply and accurately modeled. Both single crystal silicon tuning forks, and those manufactured from hydrided and unhydrided Zr–2.5%Nb, were investigated at temperatures up to 700 °C. The measured responses of silicon forks confirmed the system accuracy, and suggested that single-crystal silicon be standardized as a calibration material for acoustical measurement systems. Results obtained with Zr–2.5%Nb tuning forks allowed an accurate quantitative analysis of the effects of hydride dissolution and precipitation on Young’s modulus, and confirmed that Young’s modulus of hydrided Zr–2.5%Nb decreases in proportion to free hydrogen concentration. This experimental system should prove valuable for accurate modeling of high-temperature material transformations in solids.
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    RVK:
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 1997
    detail.hit.zdb_id: 1461063-2
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  • 12
    Online Resource
    Online Resource
    Acoustical Society of America (ASA) ; 1986
    In:  The Journal of the Acoustical Society of America Vol. 80, No. 1 ( 1986-07-01), p. 1-12
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 80, No. 1 ( 1986-07-01), p. 1-12
    Abstract: The radiated pressure fields of axisymmetric ultrasonic transducers have been measured experimentally at a single frequency to a high resolution. Results in both the nearfield and farfield have been compared to the prediction of theory in three dimensions, developed to examine transducers vibrating with an arbitrary amplitude and phase distribution across their front face. Good correlation was obtained for polyvinylidene fluoride (PVDF) radiators, assuming plane-piston-type behavior. For lead zirconate titanate (PZT) transducers, marked amplitude variations with radius across the disk face were encountered, and these needed to be modeled theoretically to obtain good agreement with experiment. Other predictions of theory which are of interest to applications involving acoustical imaging are presented.
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    RVK:
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 1986
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  • 13
    Online Resource
    Online Resource
    Acoustical Society of America (ASA) ; 2003
    In:  The Journal of the Acoustical Society of America Vol. 114, No. 3 ( 2003-09-01), p. 1435-1449
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 114, No. 3 ( 2003-09-01), p. 1435-1449
    Abstract: This paper presents a study of the radiated ultrasonic fields of capacitive micromachined ultrasonic transducers (often referred to as cMUTs) in air. These fields were modeled theoretically and then compared to the experimental near-field amplitude variations and directivity patterns of square cMUTs. The good agreement between theory and experiment indicates that the devices can be approximated to plane piston radiators. The fields of multiple elements driven in phase on the same silicon substrate are presented, where again comparison is made to theory. The results indicate that individual elements are unaffected by radiation through the silicon substrate from adjacent devices. It will also be demonstrated that it is possible to use the knowledge of these fields to develop air-coupled ultrasonic surface imaging systems.
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    RVK:
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 2003
    detail.hit.zdb_id: 1461063-2
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  • 14
    Online Resource
    Online Resource
    Acoustical Society of America (ASA) ; 1987
    In:  The Journal of the Acoustical Society of America Vol. 81, No. 1 ( 1987-01-01), p. 196-197
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 81, No. 1 ( 1987-01-01), p. 196-197
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    RVK:
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 1987
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  • 15
    Online Resource
    Online Resource
    Acoustical Society of America (ASA) ; 2021
    In:  The Journal of the Acoustical Society of America Vol. 150, No. 1 ( 2021-07-01), p. 74-81
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 150, No. 1 ( 2021-07-01), p. 74-81
    Abstract: Metamaterials exhibiting Fabry–Pérot resonances are shown to achieve ultrasonic imaging of a sub-wavelength aperture in water immersion across a broad bandwidth. Holey-structured metamaterials of different thickness were additively manufactured using a tungsten substrate and selective laser melting, tungsten being chosen so as to create a significant acoustic impedance mismatch with water. Both broadband metamaterial behavior and sub-wavelength imaging in water are demonstrated experimentally and validated with finite element simulations over the 200–300 kHz range.
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    RVK:
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 2021
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  • 16
    Online Resource
    Online Resource
    Acoustical Society of America (ASA) ; 2004
    In:  The Journal of the Acoustical Society of America Vol. 115, No. 5 ( 2004-05-01), p. 2021-2031
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 115, No. 5 ( 2004-05-01), p. 2021-2031
    Abstract: This paper presents a method of calculating the pressure at any point emerging from a plane piston of polygonal shape in an infinite baffle. This is achieved by calculation of the impulse response as a time-stepped function, and considering the effect of each edge of the polygon in turn. The pressure is found from the convolution of this function with the time derivative of the piston velocity multiplied by the density of the propagation medium. Calculated pressure fields are shown for both a series of sources shaped as regular polygons, and for a source with an irregular shape. It is shown that the approach could be useful for the calculation of radiated fields from sources of arbitrary shape.
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    RVK:
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 2004
    detail.hit.zdb_id: 1461063-2
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  • 17
    Online Resource
    Online Resource
    Acoustical Society of America (ASA) ; 2005
    In:  The Journal of the Acoustical Society of America Vol. 117, No. 4_Supplement ( 2005-04-01), p. 2386-2386
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 117, No. 4_Supplement ( 2005-04-01), p. 2386-2386
    Abstract: Thin and flexible electrostatic loudspeakers have been constructed, which can be curved into different shapes. This allows some interesting geometries to be explored, at frequencies in the range 10 kHz to 100 kHz. The research has compared the radiated fields measured experimentally with those predicted using established theory. The theoretical approach uses a new geometrical formulation to more efficiently predict radiated field patterns, where the curved surface is considered as a series of elements at specific angles to the beam axis. These elements can be of increased width compared to previous methods, making the approach computationally efficient. It is also a more robust approach than the traditional impulse response methods, in situations where the source size is comparable to the radiated wavelengths in air. Predictions could be made for both continuous and transient excitation. A comparison between theory and experiment has demonstrated that interesting field patterns can be generated. For instance, focussed sound fields can be produced using concave shapes, with predictable focal positions which are not at the center of curvature. These and other geometries will be described.
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    RVK:
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 2005
    detail.hit.zdb_id: 1461063-2
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  • 18
    Online Resource
    Online Resource
    Acoustical Society of America (ASA) ; 2003
    In:  The Journal of the Acoustical Society of America Vol. 114, No. 2 ( 2003-08-01), p. 759-766
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 114, No. 2 ( 2003-08-01), p. 759-766
    Abstract: This paper describes the use of air-coupled ultrasonic tomography for the simultaneous measurement of flow and temperature variations in gases. Air-coupled ultrasonic transducers were used to collect through-transmission data from a heated gas jet. A transducer pair was scanned in two-dimensional sections at an angle to the jet, and travel time and amplitude data recorded along various paths in counter-propagating directions. Parallel-beam tomographic reconstruction techniques allowed images to be formed of variations in either temperature or flow velocity. Results have been obtained using heated jets, where it has been shown that it is possible to separate the two variables successfully.
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    RVK:
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 2003
    detail.hit.zdb_id: 1461063-2
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  • 19
    Online Resource
    Online Resource
    Acoustical Society of America (ASA) ; 1996
    In:  The Journal of the Acoustical Society of America Vol. 100, No. 4_Supplement ( 1996-10-01), p. 2730-2730
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 100, No. 4_Supplement ( 1996-10-01), p. 2730-2730
    Abstract: A new type of ultrasonic immersion transducer has been designed and constructed that has a wide bandwidth when used in water. It is a capacitive (electrostatic) device, using a micromachined backplate and a thin mica metallized membrane. It will be demonstrated that the field pattern of the device can be plotted experimentally using a miniature hydrophone, and the results will be compared favorably to theoretical predictions. The device has been produced as a plane piston, and also as a focusing device using both an annular transducer and a zone plate. The device has none of the ringing associated with piezoelectric devices, and hence is suitable for a wide range of applications.
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    RVK:
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 1996
    detail.hit.zdb_id: 1461063-2
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  • 20
    Online Resource
    Online Resource
    Acoustical Society of America (ASA) ; 2004
    In:  The Journal of the Acoustical Society of America Vol. 115, No. 4 ( 2004-04-01), p. 1546-1556
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 115, No. 4 ( 2004-04-01), p. 1546-1556
    Abstract: A new formulation is presented for the prediction of the signals transmitted by a rectangular acoustic source, and detected by a finite-sized rectangular receiver. This problem is encountered in measurements where the receiver is of a finite size compared to the shortest wavelength emitted by the source. The paper examines this problem theoretically, and a new formulation is presented in which the geometrical aspects are considered in some detail. The result is a simplified approach, in which the overall impulse response can be obtained from a combination of certain contributions defined geometrically. Theoretical field predictions are compared to experimental measurements for ultrasonic signals radiated into air, to demonstrate the usefulness of the approach.
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    RVK:
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 2004
    detail.hit.zdb_id: 1461063-2
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