Abstract:

The sound velocity and attenuation in perspex (poly methyl methacrylate) and in reson (hydroxyl terminated polybutadiene) are determined as functions of frequency and temperature using ultrasonic pulse technique. The importance of these materials comes from the need to examine their impedance match with water and to measure their attenuation coefficients over an extended range of frequency. A pair of transducers was placed in a small tank full of water and used to transmit and receive a 2.5-MHz pulse. The temperature of the water was varied using a temperature controlled heater (or cooler). The signal was captured with and without the material sample being inserted in the transmit/receive water path, using a digital storage oscilloscope (DSO), and then processed on a PC to obtain its FFT and to compute and plot the variation of the velocity of sound in the sample material as well as its absorption coefficient. The accuracy of the method was first checked and proved to be quite good by obtaining results for perspex and comparing them with the known published data. The measurements were then repeated for reson. A frequency range of ~1--5 MHz was covered. The lowest considered temperature was 10 (degrees)C and the largest was 40 (degrees)C.