A FULLY AUTOMATED PRECISE MEASUREMENT SYSTEM FOR SOUND-VELOCITY AND INTERNAL-FRICTION IN SOLIDS DOWN TO LIQUID-HELIUM TEMPERATURES USING THE VIBRATING REED TECHNIQUE

The design and fabrication of a fully automated, computer controlled, precise measurement system for sound velocity and internal friction us ing the vibrating reed technique is described in detail. Relative vari ation of sound velocity and internal friction has been measured using automatic frequency locking. A detailed description of the apparatus i s given. The associated electronics that took care of quite a few prob lems in getting a good lock-in condition have bees highlighted. With a bath cryostat and sample insert, measurements were made down to liqui d helium temperatures with a temperature control accuracy better than 10 mK. The resonance frequency and the peak amplitude were recorded as a function of temperature which in turn provided temperature variatio n of sound velocity and internal friction with a relative accuracy bet ter than 1 parr in 10(4) and 1.5%, respectively. Precise nature of the results obtained using this setup is highlighted for a specimen of an amorphous alloy near it's Curie temperature. (C) 1997 American Instit ute of Physics.