| 摘要 |
<p>1447873 Wave-energy impedance transition measurement BOLT BERANEK & NEWMAN Inc 1 Oct 1973 [16 Oct 1972] 45735/73 Heading H4D Impedance transistions in a medium are measured by transmitting wave energy into it in a predetermined direction, receiving the energy returned from the medium, deconvolving the transmitted and received energy to produce a reflection impulse-response function, and integrating this function to provide an impedance-transition measurement which may be compared with properties of known media to identify the nature of the medium. The waveenergy may be acoustic, visible or invisible light, radio, microwave or heat. The invention is applicable to seismic exploration, non- destructive testing of laminates, and medical diagnosis. In the Fig. 1 embodiment for investigating the nature and gas content of marine sediments 5, an acoustic pulse source 1 and receivers 2, 3 are supported by a frame 4. Clock pulse generator 6 and the receiver 2 position are adjusted such that the wave travel times from source 1 to a receiver and between receivers are integral multiples of the clock pulse interval, to simplify received signal processing. Closure of switch 8 triggers source 1 and the sweep of a CRO 10 on which the receiver signals are monitored. The receiver signals are sampled, preferably at the Nyquist minimum rate, at intervals defined by the clock pulses and are recorded at 20, 21. From the samples the downgoing (transmitted) and returning waveforms are computed. The two computed waveforms are then convolved, the convolution result is integrated with respect to time, and the resulting acoustic impedance measure is displayed as a function of the wave travel time in the sediments 5. Source 1 may be directional and actuated repeatedly so that successive waveform signals can be averaged to enhance the signal-to-noise ratio. Mechanical or electronic scanning of transducer arrays is also envisaged. The apparatus may be towed by a ship. A single receiver movable vertically may be used instead of the two receivers shown. Receiver signal samples are obtainable by analysis of a photograph of the CRO display.</p> |
