. The Bell System technical journal . onal wave is generated by a torsionalquartz crystal soldered or glued to the end of the rod. These wavestra\el to the free end of the rod and are reflected back to the crystalwhere they are detected, amplified, and displayed on a cathode ray ^ This method is described by H. J. McSkimin, in a paper before the Ac-oustical Soc. of Am. in October, 1951. 130 THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1952 oscilloscope. Echoes due to end to end reflections also appear, beingattenuated by normal acoustic losses until they are undetectable by thetime the next puls
. The Bell System technical journal . onal wave is generated by a torsionalquartz crystal soldered or glued to the end of the rod. These wavestra\el to the free end of the rod and are reflected back to the crystalwhere they are detected, amplified, and displayed on a cathode ray ^ This method is described by H. J. McSkimin, in a paper before the Ac-oustical Soc. of Am. in October, 1951. 130 THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1952 oscilloscope. Echoes due to end to end reflections also appear, beingattenuated by normal acoustic losses until they are undetectable by thetime the next pulse is applied. With only air surrounding the rod, a phase reference and amplitudereference are obtained for the first received wave (or subsequent echoesif greater sensitivity is desired). The rod is then immersed a definitelength in the litiuid to be measured, as shown in Fig. 4, with, a resultingphase retardation and amplitude reduction. These are measured by em-ploying the experimental circuit shown by Fig. 5. In order to allow the. Fig. 4—Photograph of complete torsional wave measuring equipment. MECIIAXICAL PROPftETIES OF POLYMERS 131 use of one crystal for both receiving and transmitting, the crystal is putin the bridge circuit of Fig. 5 where a resistance and capacity are usedto bahuice out the transmitted pulse so that it will not overload theamplifier. The relatively weak voltages generated by the incomingacoustic waves pass through directly. The gate circuit provides pulsesof radio freciuencj^ voltage at repetition rates in the range of 20 to 100per second with a synchronizing voltage supplied to the oscilloscope forthe horizontal sweep. The frequency range of the device is from 20 to200 kc. Both glass and nickel-iron rods were used, the latter having avery low frequency-temperature coefficient. With a 100-kc quartz REFERENCE
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