Shear wave reflectance method

In the methods of the preceding section, the propagation of a shear wave into the viscoelastic liquid is not observed directly only its effect on the propagating surface is detected and measured. On the other hand, if the damping is not too severe, so that a wave train of several maxima and minima is perceptible, the wavelength and attenuation can be measured directly, as described in this section. The sample must be sufficiently large so that the waves are attenuated before they can experience reflection. 

The characteristic impedance method with reflection of a shear wave from a quartz surface as described for liquids in Chapter 5 may also be used for soft solids in the megacycle range. In this case, where reflection occurs at an angle, there should be direct contact between the quartz and the sample. 

Determination of the viscosity coefficients from the mechanical wave propagation and attenuation in the ordered nonatic phase is probably the closest to the first principles methods. The shear impedance technique is based on measuring the reflection and attenuation of ultrasonic shear waves [90-92]. The conqtlex shear impedance of the nematic sample, Zn = Rn + iXn, is determined from the complex... 

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