Sound propagation velocity experiments

The velocity of sound propagation in a material is simply related to the stiffness constants and density. It is a very convenient method in practice and gives simple and unambiguous results in the case of oriented glassy polymers, as in the work of Treloar on polymethylmethacrylate. From a single experiment, two of the five elastic constants may be determined. The principle of the method is shown in Fig. 1. 

Ultrasound is used to obtain information about the properties of a material by measuring the interaction between a high frequency sound wave and the material through which it propagates. This interaction depends on the frequency and nature of the ultrasonic wave, as well as the composition and microstructure of the material. The parameters most commonly measured in an ultrasonic experiment are the velocity at which the wave travels and the extent by which it is attenuated. To understand how these parameters are related to the properties of foods it is useful to consider the propagation of ultrasonic waves in materials in general. 

In the experiments considered later, water is used as the liquid. Since water has a relatively high impedance, a compression wave of high amplitude is generated. The abruptly generated pressure wave propagates through the tube with the velocity of sound, provided the influence of the elastic tube walls can be neglected. 

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