Elastic Constants by the Ultrasonic Pulse Echo Method

The elastic constants of single-crystal KCl and NaI have been measured by means of the ultrasonic pulse echo method using a wide-band amplifier to display the unrectified echo pattern directly. The experimental results agree with previous measurements made using other techniques. From detailed observations of successive echoes, made possible by the wide-band receiving unit, it was determined that the pulse was attenuated at the front, and at the same time elongated, due to reflection from the specimen-transducer interface. This effect turns out to be just what one would expect theoretically, and is responsible for the so-called ``transit-time error.'' The transit-time error may be as large as one vibration period of the fundamental frequency in the pulse, and is most pronounced for crystal samples in which the acoustic impedance is the same as that of the quartz transducer.