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Quartz crystal microbalance based on torsional piezoelectric resonators
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Image of FIG. 1.
FIG. 1.

Mounting of the resonators: (a) two-pin mounting (b) mounting on a pin and an O-ring around the waist. (c) Configuration of the electrodes.

Image of FIG. 2.
FIG. 2.

Frequency shift of the resonator after small drops of a polymer dispersion (solids content: 55%) were deposited on the resonator. The frequency shift was determined after drying, whereas the droplet volume was measured before the application of the drop. The mass of the dried droplets was .

Image of FIG. 3.
FIG. 3.

(Color online) Variation of sensitivity with location of the load. Small drops (as in Fig. 2) of identical volume were deposited on the side of the cylinder at a variable distance from the edge, . The amplitude of oscillation depends on as (where is the length of the cylinder). Since the sensitivity scales as the square of amplitude, one finds a decrease of with increasing distance from the edge. The dashed line is a fit to , with as the fit parameter.

Image of FIG. 4.
FIG. 4.

Time resolved measurement of the drying of a film. The film was applied by dipping the resonator into the bulk dispersion. After dip coating, the film was removed from the face of the cylinder with tips because droplets had formed after dipping. The progress of drying is reflected both (a) in the decrease of mass and (b) in the decrease of softness . Panels (c) and (d) display the conversion to thickness and to viscous compliance .

Image of FIG. 5.
FIG. 5.

Results of a biofouling experiment. The resonator was exposed to a dispersion of Pseudomonas fluorescens cells (DSMZ 147). The decrease in frequency corresponds to an equivalent Sauerbrey thickness of . The Sauerbrey thickness is not necessarily equal to the geometric thickness because of roughness and softness. Note, however, that the increase in bandwidth is much less than the decrease in frequency. Accordingly, the resonator operates in the Sauerbrey regime and is expected to sense the entire cell. This is in contrast to thickness-shear resonators, which would only sense the bottom part of the cell layer.

Image of FIG. 6.
FIG. 6.

Wine-glass deformation of the cylinder, caused by the anisotropy of the crystal (much exaggerated). This type of motion is superimposed onto the torsional displacement.


Generic image for table
Table I.

Resonator characteristics


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Quartz crystal microbalance based on torsional piezoelectric resonators