June 3rd 2020: AWSensors is pleased to announce the release of its new Technology Note on Quartz Crystal Microbalance with Dissipation entitled “AWSensors QCMD“.
Summary of the Note
Advanced Wave Sensors is a company that designs, develops, and manufactures ultra-sensitive sensing systems based on the quartz crystal microbalance with dissipation (QCMD) measurement technology. In this Note the technology basics are explained.
Introduction
At the core of the QCMD technology is a piezoelectric resonator, typically made of quartz, that is excited to oscillate at its resonance frequency in the thickness-shear mode by applying an alternating current through the electrodes deposited on its surface.
With the resonator oscillating in the thickness shear mode, its two surfaces move in the opposite directions, as indicated by the arrows in Figure 2. The wavelength of the shear wave, λ, is therefore twice the thickness of the sensor, λ = 2d . Because λf = c , where c = √(Gq/rhoq) , is the speed of shear sound in the material and f is the frequency, the resonance frequency of such a resonator is given by fn = nc/2d = (n/2d) √(Gq/rhoq), where Gq is the shear modulus of quartz, rhoq is its density, and n is the (odd) overtone order. The same expression may be derived formally by solving the equations describing the propagation of shear waves in elastic media subject to appropriate boundary conditions, as discussed in ref. 1. Plugging in 29×109 Pa for the shear modulus of AT quartz and 2650 kg/m3 for the density, one obtains a frequency of ~ 5 MHz for a thickness of ~ 330 um at the fundamental, where n = 1.
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Other References
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QCMD: What is it?
QCMD stands for Quartz crystal microbalance (QCM) with dissipation measurements (QCMD) and is a sensing technique that relies on measuring resonance properties (resonance frequency and quality factor) of piezoelectric resonators, or sensors. Learn more.
QCMD: What it is used for?
QCMD measurements can be used to measure minute changes in sensor mass, arising, for example, from the deposition of a thin film on the surface of the sensor, as well as other properties of such films (e.g., viscoelasticity), or to monitor the properties of the environment of the sensor (liquid or gas).
