| 摘要 |
An acoustical gauge is disclosed for measuring the distance between an acoustic wave transmitting and receiving or sensing port and the surface of a material. One device disclosed comprises a Y-shaped tube where the bottom of the Y ends in the sensing port. During operation of the gauge, an acoustic wave is produced in the first branch of the Y, travels to the intersection point of the branches and then propagates down the stem, i.e., the channel which is the bottom of the Y and out the sensing port. As the standing wave encounters the hydraulic impedance created by the distance between the sensing port and location of the reference surface near the sensing port, a complex interaction of standing and travelling waves are set up. At the Y intersection a resultant wave formed by the interference of the original wave produced with the feedback from the hydraulic impedance encountered at the sensing port, is investigated and measured for phase or amplitude variation. These measurements can be calibrated in terms of distance between the sending port and the reference surface.
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