Piezoelectric Microbalance

See also: Balance

A piezoelectric Microbalance makes it possible to measure very weak Masse S by measuring the change of Fréquence associated of a piezoelectric Cristal . Because of its excellent factor of quality, quartz is the material more used for this system of measurement. One speaks then about microbalance to quartz crystal (in English Quartz hook microbalance or QCM ).

The principle is the suivant : a piezoelectric Cristal undergoes a Oscillation following a piezoelectric stimulation applied by electrodes. Its frequency of Résonance of the crystal is correlated with its mass. Any addition or withdrawal of mass causes a slip of the frequency of résonance  ; by measuring this difference in frequency $\backslash \; Delta\; f$, one can calculate the difference in mass $\backslash \; Delta\; m$ thanks to the relation of Sauerbrey :

$\backslash \; Delta\; F\; =\; \{-2\; \backslash \; Delta\; m\; f\_0^2\; \backslash \; over\; has\; \backslash \; sqrt\; \{\backslash \; rho\_q\; \backslash \; mu\_q\}\}$

where $f\_0$ is the intrinsic frequency of resonance of the crystal, $A$ the active surface of the crystal (between the electrodes), $\backslash \; rho\_q$ the density of material (for example the quartz) and $\backslash \; mu\_q$ the modulus of rigidity of material.

The measurement of the slip of the frequency is very precise. This system thus makes it possible to measure very weak differences in mass. In Biology, this system makes it possible for example to measure the deposit of cell S on the crystal.

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