Theory of the resonant method for determining the complex shear modulus of liquid

Shear elasticity should appear at high megahertz frequencies according to existing fluid theories. However, low-frequency (100 kHz) shear elasticity in all liquids independently of their viscosity and polarity was discovered for the first time in our team. It was assumed that a low-frequency viscoelastic relaxation process exists in liquids. It is possible that dynamic movements of large groups of molecules appear by low-frequency shear action on the liquid layer. Therefore, further comprehensive detailed studies of low-frequency shear elasticity by various methods are of fundamental importance for the physics of liquids. A piezoelectric crystal of rectangular shape for shear action on the studied liquid layer at low frequencies is used in the resonance method. A liquid layer covered with a solid cover-plate is applied to the horizontal face of the piezoelectric quartz. The liquid layer experiences dynamic shear deformations when the piezoelectric quartz oscillates at a resonant frequency and a shear wave is excited in this liquid layer. The general solution to the problem of interaction of the oscillatory system “the piezoelectric quartz - the interlayer of the liquid - the coverplate” is considered in the work. The values of the real shear modulus and the mechanical losses angle are calculated from the parameters of the shear wave.