Übertragungssystem für Schallwellen und Verfahren zum Übertragen von Schallwellen auf einen rohrförmigen Körper

摘要

An acoustic wave transmission system comprises an acoustic wave generating metal tubular member (12) for converting information about the bottom of a borehole, which is obtained by a bottom hole sensor (21), into an acoustic wave. The acoustic wave generating metal tubular member includes a acoustic wave generating mechanism (25) having at least a magnetostrictive oscillator (26), which is mounted in a recess (28) formed in an outer wall of the acoustic wave generating metal tubular member, and on which a compressive load is imposed by means of a pre-load mechanism using a vise (29). The magnetostrictive oscillator is constructed of a stack of thin plates each made of a metal magnetostrictive material having a property of increasing its dimensions when magnetized, the thin plates being bonded together by a heat-resistant adhesive. The magnetostrictive oscillator can thus have a buckling strength large enough to resist the compressive load imposed thereon by the pre-load mechanism and a stress due to a strain caused in itself. The acoustic wave generating metal tubular member further includes an excitation current supplier (24) for supplying either a rectangular, sinusoidal, or triangular alternating excitation current modulated with the information about the bottom of the borehole and having a frequency that is half the carrier frequency of the acoustic wave, or a series of excitation pulses modulated with the information about the bottom of the borehole and having a pulse repetition rate that is equal to the carrier frequency of the acoustic wave, to an excitation winding wound around the magnetostrictive oscillator.