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  • 2005-2009  (3)
  • Comparative Studies. Non-European Languages/Literatures  (3)
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  • 2005-2009  (3)
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  • Comparative Studies. Non-European Languages/Literatures  (3)
RVK
  • 1
    Online Resource
    Online Resource
    Acoustical Society of America (ASA) ; 2009
    In:  The Journal of the Acoustical Society of America Vol. 126, No. 4_Supplement ( 2009-10-01), p. 2225-2225
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 126, No. 4_Supplement ( 2009-10-01), p. 2225-2225
    Abstract: The presence of echo returns from the rough interface of two layered medium, and the clutter of volume scattering hinders the detection of target buried in heterogeneous media. The situations are often raised in ultrasonic breast tumor diagnosis and underwater acoustic buried mine detection. This work investigates the application of monostatic single channel iterative time reversal in mitigating the difficulties with a numerical study. Simulations based on pseudospectral finite-difference time-domain method are performed with a sphere buried in the heterogeneous media of lower layer, a transmitter is situated at the upper homogeneous domain, and the interface position is normally distributed. A wideband signal is launched to initiate the process, and the time-reversed echo received at same position is emanated as renewed interrogation pulse for next iteration. Some field snapshots are taken and the echo is recorded in each iteration. The results illustrate as the number of iteration increases, small volume scattering is eliminated, and rough interface reverberation is suppressed relatively. The echoes will converge to a narrowband waveform corresponding to an object’s dominant resonance mode. The detection of target is achieved by exploiting this important acoustic signature. [Work supported by the CAS Innovation Fund.]
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    RVK:
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 2009
    detail.hit.zdb_id: 1461063-2
    Location Call Number Limitation Availability
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  • 2
    Online Resource
    Online Resource
    Acoustical Society of America (ASA) ; 2009
    In:  The Journal of the Acoustical Society of America Vol. 125, No. 4_Supplement ( 2009-04-01), p. 2702-2702
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 125, No. 4_Supplement ( 2009-04-01), p. 2702-2702
    Abstract: Iterative time reversal process will gradually lead echo waves to converge to a dominant narrowband resonant mode of the target and enhance the return level in noisy and reverberant environment. This technique is used in bottom target detection and an experiment has been performed in the Yellow Sea, China. The experiment is in a monostatic configuration, and the target, which is a 53 cm external diameter and 260 cm long stainless steel cylindrical shell with concrete interior, is resting on the seafloor, and the directional transceiver, which is a transmitter and receiver couple, is located right above the target. First, a broadband interrogation pulse is launched, and the echo is measured and a bandpass filter is applied to avoid transceiver response peak, then the signal is time reversed and retransmitted, and repeat above procedures iteratively. The bottom reverberation will gradually be suppressed, and the center frequency of converged signal corresponds to a target resonance frequency, which is different from inhomogeneous bottom response in no target case. The existence of target is determined by this important acoustic signature, and the results illustrate the feasibility of this method. [Work partially supported by the CAS Innovation Fund.]
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    RVK:
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 2009
    detail.hit.zdb_id: 1461063-2
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
  • 3
    Online Resource
    Online Resource
    Acoustical Society of America (ASA) ; 2009
    In:  The Journal of the Acoustical Society of America Vol. 126, No. 6 ( 2009-12-01), p. 3049-3056
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 126, No. 6 ( 2009-12-01), p. 3049-3056
    Abstract: The time domain implementation of the transfer-matrix method developed by Song and Bolton [J. Acoust. Soc. Am. 107, 1131–1154 (2000)] for measuring the characteristic impedance and wave number of porous materials is described in this paper. The so called Butterworth impulse is generated in a standing wave tube with a flat frequency response over a wide frequency range. With only two microphone measurements, the transfer matrix of porous layers can easily be determined through the calculation of complex amplitudes of incident, reflected, and transmitted pulses. The procedure has been used to measure the acoustical properties of a fiber material, and good agreement was found between measured acoustical pro perties and predicted results by Delany and Bazley [Appl. Acoust. 3, 105–116 (1971)] semiempirical formulas. Although the error associated with the sample-edge constraint still remains, the new method has a better frequency response as a result of the system calibration process, and the optimal inter-microphone distance is no longer required compared to the frequency domain implementation.
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    RVK:
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 2009
    detail.hit.zdb_id: 1461063-2
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
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