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Additional recommended knowledge
It is well known that properties of viscoelastic fluid are characterised in shear rheology with a shear modulus G, which links shear stress Tij and shear strain Sij
There is similar linear relationship in extensional rheology between extensional stress P, extensional strain S and extensional modulus K:
Detail theoretical analysis indicates that propagation of sound or ultrasound through a viscoelastic fluid depends on both shear modulus G and extensional modulus K, . It is convinient to introduce a combined longitudinal modulus M:
There are simple equations that express longitudinal modulus in terms of acoustic properties, sound speed V and attenuation α
Acoustic rheometer measures sound speed and attenuation of ultrasound for a set of frequencies in Mhz range. These measurable parameters can be converted into real and imaginary components of longitudinal modulus.
This type of rheometers works at much higher frequencies than others. It is suitable for studying effects with much shorter relaxation times than any other rheometer.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Acoustic_rheometer". A list of authors is available in Wikipedia.|