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  • Na, Young-Nam  (2)
  • 1
    Online Resource
    Online Resource
    Acoustical Society of America (ASA) ; 2012
    In:  The Journal of the Acoustical Society of America Vol. 131, No. 4_Supplement ( 2012-04-01), p. 3488-3488
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 131, No. 4_Supplement ( 2012-04-01), p. 3488-3488
    Abstract: This study attempts to investigate the fluctuation of underwater acoustic signals due to internal waves (IWs) off the east coast of Donghae, Korea. Sea experiment was performed with thermistor strings, a sound source, and an array of hydrophones. Based on the thermistor string data, the IWs have characteristics of typical periods of 10-20 minutes, amplitudes of 10-20m, and a duration of 1-2 hours. The IWs were analyzed as they moved from offshore to the coast at a speed of 70 cm/sec. Underwater acoustic signals (CW 80 - 800Hz) also show obvious energy fluctuations with the IWs. Through an analysis of these acoustic signals, fluctuations of periods of 15 minutes are located in time domain. As mixed layer depth varies with time, it may cause travel time difference of acoustic signals. This travel time differences causes fluctuation of acoustic signals in range-independent stratified ocean structure. The spectrum characteristics of the acoustic signals show the possibility that acoustic waves may react to the IWs through mechanisms such as mode coupling and travel time fluctuation.
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    RVK:
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 2012
    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) ; 2012
    In:  The Journal of the Acoustical Society of America Vol. 131, No. 4_Supplement ( 2012-04-01), p. 3498-3498
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 131, No. 4_Supplement ( 2012-04-01), p. 3498-3498
    Abstract: It is difficult to efficiently produce high-intensity acoustic/ultrasonic waves in air with a conventional piezoelectric transducer because of the huge acoustic impedance mismatch between solid-state transducers and air. In this work, the mechanoacoustic efficiency of a thin-plate flexural mode transducer is analytically compared with that of a conventional 1/4ƛ thickness mode vibrator. Radiation and internal mechanical quality factors are applied in the analysis. In the case of the thickness mode piezoelectric vibrator, the radiation quality factor does not depend on design factors, but only on material properties. Consequently, the mechanoacoustic efficiency of the thickness mode vibrator depends only on the material properties, and is less than 3% for most piezoelectric ceramics. For a thin-plate flexural mode transducer, the radiation quality factor can be controlled by the aspect ratio of the thin-plate, which is one of design parameters. Theoretically, the mechanoacoustic efficiency of the flexural mode transducer can be designed to be nearly 100% at the resonance frequency. By experimental analysis, the mechanoacoustic efficiency of the micro-machined transducer was about 65.9%, and the overall electroacoustic efficiency was 58.4% in the resonance. The transducer arrays designed based on this analysis have been successfully applied in parametric array applications in air.
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    RVK:
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 2012
    detail.hit.zdb_id: 1461063-2
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
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