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  • 1
    Online-Ressource
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    Field characterization of an air-coupled micromachined ultrasonic capacitance transducer
    Acoustical Society of America (ASA) ; 1997
    In:  The Journal of the Acoustical Society of America Vol. 101, No. 1 ( 1997-01-01), p. 315-322
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 101, No. 1 ( 1997-01-01), p. 315-322
    Kurzfassung: Investigations into the field characteristics of an air-coupled ultrasonic capacitance transducer have been performed for a range of transducer configurations. The field of a 2-MHz bandwidth silicon backplate capacitance transducer has been scanned in air using a 1-mm-diam miniature detector at frequencies of up to 1.5 MHz. The radiated peak sound-pressure field is compared to theory based on a plane piston approach for various driving signals, namely pulsed and tone burst excitation. Aperture modifications, such as an annulus and a zone plate, have also been investigated and the devices have been shown to behave as predicted by theory.
    Materialart: Online-Ressource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.418011
    RVK:
    EQ 1000
    Sprache: Englisch
    Verlag: Acoustical Society of America (ASA)
    Publikationsdatum: 1997
    ZDB Id: 1461063-2
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  • 2
    Online-Ressource
    Online-Ressource
    Recent developments in air-coupled ultrasonic capacitive transducers for NDE
    Acoustical Society of America (ASA) ; 1998
    In:  The Journal of the Acoustical Society of America Vol. 103, No. 5_Supplement ( 1998-05-01), p. 2833-2833
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 103, No. 5_Supplement ( 1998-05-01), p. 2833-2833
    Kurzfassung: A new design of an air-coupled capacitive ultrasonic transducer has been developed that could have potential for use in NDE experiments, particularly when the pulse-echo method is employed. The design is based on a standard capacitive transducer, except the newly developed device has two concentric, backplate elements with a common membrane. Each of the elements is electrically isolated from the other, allowing one to be used as a source of ultrasound, while the other is used as a detector. This yields a device containing both a source and receiver of ultrasound within the same structure. Experiments have shown that the device performance depends on which of the elements is selected to be source and receiver, size of the bias voltage employed, surface of the backplates, and membrane material utilized. Initial studies have shown that the device is capable of detecting the front face echo from various material samples, and these results are contained within this paper. There has also been some investigation of the signal quality when capacitive devices have been placed within an enviroment containing a range of pressures above standard atmospheric pressure. Applications of this work include measurements in high-pressure gas pipelines.
    Materialart: Online-Ressource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.421386
    RVK:
    EQ 1000
    Sprache: Englisch
    Verlag: Acoustical Society of America (ASA)
    Publikationsdatum: 1998
    ZDB Id: 1461063-2
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 3
    Online-Ressource
    Online-Ressource
    Ultrasonic tomographic imaging of temperature and flow fields in gases using air-coupled capacitance transducers
    Acoustical Society of America (ASA) ; 1998
    In:  The Journal of the Acoustical Society of America Vol. 104, No. 6 ( 1998-12-01), p. 3446-3455
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 104, No. 6 ( 1998-12-01), p. 3446-3455
    Kurzfassung: A pair of air-coupled ultrasonic capacitance transducers with polished metal backplates have been used to image temperature and flow fields in gases using ultrasonic tomography. Using a filtered back-projection algorithm and a difference technique, cross-sectional images of spatially variant changes in ultrasonic attenuation and slowness caused by the presence of temperature and flow fields were reconstructed. Temperature fields were produced in air by a commercial soldering iron, and the subsequent images of slowness variations used to reconstruct the air temperature at various heights above the iron. When compared to measurements made with a thermocouple, the tomographically reconstructed temperatures were found to be accurate to within 5%. The technique was also able to resolve multiple heat sources within the scan area. Attenuation and velocity images were likewise produced for flow fields created by an air-jet from a 1-mm-diam nozzle, at both 90 and 45 degrees to the scanning plane. The fact that temperature and flow fields can be measured in a gas without the need to insert any measuring devices into the image region is an advantage that may have many useful applications.
    Materialart: Online-Ressource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.423928
    RVK:
    EQ 1000
    Sprache: Englisch
    Verlag: Acoustical Society of America (ASA)
    Publikationsdatum: 1998
    ZDB Id: 1461063-2
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  • 4
    Online-Ressource
    Online-Ressource
    The capacitance transducer as a standard ultrasonic source in solids
    Acoustical Society of America (ASA) ; 1995
    In:  The Journal of the Acoustical Society of America Vol. 97, No. 3 ( 1995-03-01), p. 1650-1659
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 97, No. 3 ( 1995-03-01), p. 1650-1659
    Kurzfassung: An air-gap capacitance transducer with a guard ring has been used as a standard source of wideband ultrasound in solid material. Theoretical and experimental displacement waveforms have been compared, indicating that this capacitance source is characterized by a simple transduction mechanism. The bandwidth can be altered from a sharp transient to a steplike response, while the polarity can be reversed, all through simple changes in the excitation voltage and without damage to the sample. An example of the transducer acting as a source in a dielectric material is also presented.
    Materialart: Online-Ressource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.412104
    RVK:
    EQ 1000
    Sprache: Englisch
    Verlag: Acoustical Society of America (ASA)
    Publikationsdatum: 1995
    ZDB Id: 1461063-2
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  • 5
    Online-Ressource
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    Measurement of elastic constants in composite materials using air-coupled ultrasonic bulk waves
    Acoustical Society of America (ASA) ; 1996
    In:  The Journal of the Acoustical Society of America Vol. 99, No. 4 ( 1996-04-01), p. 2116-2123
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 99, No. 4 ( 1996-04-01), p. 2116-2123
    Kurzfassung: This paper presents numerical simulations and experimental measurements of longitudinal and shear bulk waves in composite materials, generated and detected with an air-coupled ultrasonic system. The transfer function of an anisotropic absorbing layered plate immersed in air is computed with the transfer matrix method, and the waveforms produced by transmission through a plate are simulated from the convolution of a reference waveform and the impulse response of the plate. The calculated waveforms compare well to those recorded experimentally, confirming that the waveforms recorded experimentally have the correct characteristics. It is demonstrated that it is possible to identify longitudinal and shear modes. Results are presented showing how this data may be used to recover the stiffness matrix of composite materials, using the angular variation of velocity of both modes.
    Materialart: Online-Ressource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.415398
    RVK:
    EQ 1000
    Sprache: Englisch
    Verlag: Acoustical Society of America (ASA)
    Publikationsdatum: 1996
    ZDB Id: 1461063-2
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 6
    Online-Ressource
    Online-Ressource
    Ultrasonic capacitance transducers for flow and temperature tomography in air
    Acoustical Society of America (ASA) ; 1998
    In:  The Journal of the Acoustical Society of America Vol. 103, No. 5_Supplement ( 1998-05-01), p. 2833-2833
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 103, No. 5_Supplement ( 1998-05-01), p. 2833-2833
    Kurzfassung: Capacitance transducers have been constructed that can operate at frequencies of up to 2 MHz in air, over a wide bandwidth, and with good efficiency. These have been used to propagate signals in air across regions containing variations in air flow and temperature. A source and receiver pair were scanned along a set of projections under computer control, allowing various ray paths across a chosen cross section to be selected. For each location, the received waveform was digitized and recorded, and the propagation time determined from cross-correlation techniques. The data were then used to form tomographic images, which corresponded to variations in either temperature or flow speed, both of which affect the local acoustic velocity. In one experiment, an air-jet was imaged at various distances from the nozzle. In another, the temperature variations in air above a hot metal tip were determined. Images will be shown for both sets of experiments, and the usefulness of the technique discussed.
    Materialart: Online-Ressource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.421384
    RVK:
    EQ 1000
    Sprache: Englisch
    Verlag: Acoustical Society of America (ASA)
    Publikationsdatum: 1998
    ZDB Id: 1461063-2
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 7
    Online-Ressource
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    Ultrasonic air-coupled capacitance transducers using thin mica films
    Acoustical Society of America (ASA) ; 1998
    In:  The Journal of the Acoustical Society of America Vol. 103, No. 5_Supplement ( 1998-05-01), p. 2833-2833
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 103, No. 5_Supplement ( 1998-05-01), p. 2833-2833
    Kurzfassung: Micromachined air-coupled capacitance transducers have been manufactured using anisotropically etched silicon backplates and commercially available mica films. Devices developed using 20-μm-thick insulating layers have yielded frequencies of up to 400 kHz. However, new devices using mica with a thickness of approximately 4 μm will deliver characteristics similar to existing transducers employing polymeric dielectric films. This will result in wideband behavior and bandwidths extending from approximately 100 kHz to 2 MHz. Mica-based devices have several advantages over capacitance transducers with polymer films due to the robust physical characteristics exhibited by this type of material. Improved thermal characteristics and lower porosity allow this type of device to be employed in a variety of conditions in which the performance of the polymer films would be impaired. Results of experiments performed in air at a range of temperatures from ambient to 400 °C will be presented. This will demonstrate the versatility of such devices in terms of both sensitivity and bandwidth.
    Materialart: Online-Ressource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.421385
    RVK:
    EQ 1000
    Sprache: Englisch
    Verlag: Acoustical Society of America (ASA)
    Publikationsdatum: 1998
    ZDB Id: 1461063-2
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 8
    Online-Ressource
    Online-Ressource
    A study of materials at high temperature using miniaturized resonant tuning forks and noncontact capacitance transducers
    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
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 102, No. 3 ( 1997-09-01), p. 1296-1309
    Kurzfassung: 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.
    Materialart: Online-Ressource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.420095
    RVK:
    EQ 1000
    Sprache: Englisch
    Verlag: Acoustical Society of America (ASA)
    Publikationsdatum: 1997
    ZDB Id: 1461063-2
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 9
    Online-Ressource
    Online-Ressource
    Limitation of algal growth by iron deficiency in the Australian Subantarctic Region
    American Geophysical Union (AGU) ; 1999
    In:  Geophysical Research Letters Vol. 26, No. 18 ( 1999-09-15), p. 2865-2868
    Details
    In: Geophysical Research Letters, American Geophysical Union (AGU), Vol. 26, No. 18 ( 1999-09-15), p. 2865-2868
    Materialart: Online-Ressource
    ISSN: 0094-8276
    URL: Article
    DOI: 10.1029/1998GL002284
    Sprache: Englisch
    Verlag: American Geophysical Union (AGU)
    Publikationsdatum: 1999
    ZDB Id: 2021599-X
    ZDB Id: 7403-2
    SSG: 16,13
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  • 10
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    Release and bioavailability of C, N, P Se, and Fe following viral lysis of a marine chrysophyte
    Wiley ; 1997
    In:  Limnology and Oceanography Vol. 42, No. 7 ( 1997-11), p. 1492-1504
    Details
    In: Limnology and Oceanography, Wiley, Vol. 42, No. 7 ( 1997-11), p. 1492-1504
    Materialart: Online-Ressource
    ISSN: 0024-3590
    URL: Article
    DOI: 10.4319/lo.1997.42.7.1492
    Sprache: Englisch
    Verlag: Wiley
    Publikationsdatum: 1997
    ZDB Id: 2033191-5
    ZDB Id: 412737-7
    SSG: 12
    SSG: 14
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