P. Hauptmann et al., USING THE QUARTZ MICROBALANCE PRINCIPLE FOR SENSING MASS CHANGES AND DAMPING PROPERTIES, Sensors and actuators. A, Physical, 37-8, 1993, pp. 309-316
A brief summary of the most important development steps of a special c
rystal sensing technique is presented. Then, a lumped-element equivale
nt circuit model is introduced that describes the near-resonance elect
rical characteristics of a quartz-crystal microbalance (QCM) simultane
ously loaded by a surface mass layer and contacting analyte. This mode
l predicts that surface mass accumulation causes a shift of the resona
nce peak while increasing the density-viscosity product of the sensiti
ve layer. These two effects cause both a translation and a decrease of
the resonance peak. Experimental results are given which demonstrate
interactions between sensitive materials (adsorbates) coated on the qu
artz crystal and various solvent vapours (analytes). Different polymer
s, modified ethanolamines and compounds with long alkyl-chains are use
d as coatings. Two of these coated sensors show an anomalous effect: t
he exposure to solvent vapours results in an increase of frequency bec
ause of the effective mass decrease. The apparent discrepancy implies
that the physical properties of the film must change, requiring a more
detailed characterization of the coated quartz.