Measurement of the speed of sound in ethanol/water mixtures

Ethanol/water mixtures are used commonly as a propagation medium in test objects to calibrate the measurement facilities of ultrasound (US) imaging systems. The speed of sound c in the mixture should be known, preferably with an accuracy of +/-0.1% where clinical measurements to +/-1% are required. This article describes measurements of c in several ethanol/water mixtures over a range of temperatures using a simple pulse superposition technique, which gives an estimated measurement uncertainty of 0.1%. The measurements show that, at 20 degrees C, a mixture of 9.5 +/- 0.25% ethanol by volume in distilled water is required to give a speed of 1540 +/- 1.5 m s(-1). However, to achieve this accuracy, the temperature of the mixture must be maintained in the range 20 degrees +/- 0.75 degrees C.