A high frequency shear wave impedance spectrometer for low viscosity liquids

Abstract

A method for measuring the complex shear viscosity spectra of low viscosity liquids in the frequency range 6-120 MHz is described. Details of the resonator cell, based on a thickness shear (AT-cut) quartz resonator as central device, and of the RF bridge circuit for the compensation of the unloaded capacitance of the resonator are presented. A measuring and data-evaluation procedure that allows the careful consideration of spurious higher order vibration modes and also of intrinsic cell losses is discussed. Sources of experimental error are shown and the usability of the method is illustrated by reference measurements. The complex viscosity spectrum of n-dodecanol is displayed and its relaxation frequency is compared with the value resulting from broad-band acoustical attenuation spectrometry.

High-Frequency Shear Viscosity of Low-Viscosity Liquids

“…We identified this technique unsuitable for quantitative investigations because of difficulties to embrace edge effects due to the finite size of the oscillating plate. We thus used a thickness shear resonance method (D) to measure the complex shear viscosity of liquids with low η s in the frequency range from 6 MHz to 130 MHz [30]. [9,14,22,23]; (b) torsional crystal viscometer [24][25][26]; (c) oscillating plate viscometer [27]; (d) thickness shear resonator technique [28][29][30]: 1, liquid sample; 2, BT-cut quartz crystal; 3, fusedquartz rod; 4, cylindrical torsional quartz transducer; 5, cuvette; 6, oscillating plate; 7, thickness shear vibrating AT-cut quartz disk…”

“…Due to the small penetration depth d p of viscosity waves, sample volumes V s < 1 cm 3 are required with both resonator cells. The beveled AT-cut quartz transducer disks, with diameter 2r q = 15 mm and thickness d q = 1 mm, were covered by thin (<1 μm) chromium/gold layers, serving Schematic of the thickness shear resonance spectrometer used in the complex shear-viscosity measurements [30]: 1, beveled vibrating AT-cut quartz; 2, gold layers connecting the quartz disk (1) with the electronic circuit; 3, liquid under test; 4, O-ring; 5, flexible electric contact wire; 6, electronic bridge circuit with 7, center-tapped RF transformer; TD tuning diode; FET field effect transistor; R 1 , R 2 , multi-turn potentiometers; 8, vector network analyzer with S, R, M, signal output, reference, and measurement ports, respectively, as well as 9, signal splitter; 10, pre-amplifier; PC process control computer The inset shows on a logarithmic scale the transfer function of a thickness shear resonator when loaded with water at 25 • C. The full line is the graph of the principal resonance peak; dashed lines display the first four higher order modes as electrodes for the connection of the devices to the electronic apparatus. Before each measurement, the cells were carefully cleaned using reagent grade acetone and/or isopropanol as well as deionized and additionally distilled water.…”

Complex Strain-Optical Coefficient Measurements by Means of Polarization Analysis of a Diffracted Light by Longitudinal Ultrasound

“…[6][7][8] The method has been applied to observe the relaxation of the LiClO 4 -propylene carbonate solutions 7) and imidazolium-based ionic liquids. 8) Therefore development of methods to measure to obtain complex strain-optical coefficients in the corresponding frequency range of the shear modulus measurement method is highly desired.…”

A new method for wideband characterization of resonator-based sensing platforms

“…11 Hence, various modifications to simple oscillator circuits are reported which use automatic gain control 10,12 or parallel capacitance compensation techniques. 13 It is very difficult to maintain the accuracy of the measurements under reduced Q conditions and, therefore, a careful calibration of the oscillator circuit is required. This calibration in oscillator based circuits may require expensive instruments such as network analyzers.…”