Method for measurement of shear-wave impedance in the MHz region for liquid samples of approximately 1 ml

Abstract

A method for measuring both the real and imaginary parts of complex shear-wave impedance Z_s* for low viscosity liquids using a planar AT-quartz resonator (thickness shear) in an RF bridge network between 2 and 34 MHz, is described. This technique employs a PLL circuit and permits continuous quantitative recording of the sample impedance (probe volume below 1 ml). The mechanical vibration amplitude at the transducer-liquid interface is in the Angstrom range, preventing any heating and structural damage effects. Incremental Z_s-resolution is better than 50 kg m^-2 s^-1 ( approximately 1% of water impedance at 6 MHz), as is demonstrated by test measurements on different newtonian liquids. These measurements show that Z_s* values determine quantitatively the shear quartz resonator parameters. This method permits measurements of interface and surface layer properties.