The coexistence of pressure waves in the operation of quartz-crystal shear-wave sensors

Abstract

It is demonstrated that an AT-cut quartz crystal driven in the thickness-shear-wave mode and typically used as a sensor to monitor the viscoelastic shear-wave properties of a fluid also produce longitudinal pressure waves. Unlike the shear wave, these waves are capable of long-range propagation through the fluid and of reflection at its boundaries, notably at an outer fluid-air interface. They introduce a component into the measured electrical impedance and resonance frequency shift of the crystal, which reflects the setting up of cyclic pressure-wave resonances in the fluid. This has important implications for the practical employment of these crystal as sensors. Under appropriate conditions, as demonstrated for water and n-octane, it is possible to determine the propagating properties of sound waves in a fluid simultaneously with the viscoelastic shear-wave properties. These experiments are supported by an analysis of the appropriate hydrodynamic equations for waves in the crystal-fluid system, which predicts electrical characteristics in close agreement with those found experimentally.

Detection of Liquid Penetration of a Micropillar Surface Using the Quartz Crystal Microbalance

“…In water, the wave decay length is 180 ± 20 nm for a 10 MHz QCM, 40 which is much smaller than the heights of the micropillars and the liquid film thickness in this research. Therefore, the responses of the QCM are insensitive to the height and configuration of the liquid volume, 41 i.e., there is no significant difference in the responses of complete wetting (liquid film) and Wenzel states.…”

Evaporation of binary mixtures and precision measurement by crystal resonator

“…The amplitude of the spikes varies but the wave form is quite similar during evaporation. Physically the acoustic wave is due to unavoidable longitudinal crystal oscillation triggered along with the shear motion of the resonator, and will resonate with the free surface [34]. Specifically the longitudinal wave emits from the crystal surface, travels upward, and then reflects at the free surface.…”

The Development of an Amperometric Biosensor Based on the Assembly of Genetically Engineered Enzymes for the Detection of Explosives

“…After recording the characteristics of the crystal in air, 1 ml of phosphate buffer solution at pH 7.1 was introduced to the cell forming a layer about 2 mm deep on the crystal. Care was taken to avoid trapping air at the crystal face and a PTFE cone was then inserted into the liquid surface to remove unwanted compression waves ( 16 ). After allowing the measured impedance to stabilise, a volume of enzyme-bearing buffer solution was introduced into the cell and the electrical impedance recorded at 30 second intervals until no further change took place.…”