Ultrasound scattering theory

It is very interesting that large molecules, such as proteins, behave as particles and can be described by ultrasound scattering theory in the very long wavelength limit. Scattering theory is vindicated by the precise and repeatable nature of the data available for these molecules. In particular, it should be pointed out that the molecular adiabatic compressibility is insensitive to individual bonds and is the sum of the intrinsic compressibility of the primary structure (the amino acid sequence), cavities in the tertiary structure and interaction with the solvent (Kharakoz and Sarvazyan, 1993). Velocity and attenuation spectroscopy relate to different aspects of the molecule... 

In the past, ultrasound has not been widely used in studies of food emulsions. This is probably because the scientist would have to build his/her own measurement cell, specify and assemble the required transducers and electronics, transfer the data to a computer for analysis, and implement the quite complex scattering theory required for data analysis. These start-up requirements have meant that scientists more interested in ultrasonics than food emulsions have... 

In non-ideal mixtures, or systems where scattering of ultrasound is significant, the above equations are no longer applicable. In these systems the ultrasonic properties depend on the microstructure of the system, and the interactions between the various components, as well as the concentration. Mathematical descriptions of ultrasonic propagation in emulsions and suspensions have been derived which take into account the scattering of ultrasound by particles [20-21]. These theories relate the velocity and attenuation to the size (r), shape (x) and concentration (0) of the particles, as well as the ultrasonic frequency (co) and thermophysical properties of the component phases (TP). 

Flocculation can also be detected directly using ultrasonic methods. During the flocculation process the ultrasonic properties change significantly and are not consistent with theory for spherical drop scattering. This is because a network has been formed, and at present there is no suitable theory to describe the propagation of ultrasound through such a structure. 

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