Dresden 2003 – scientific programme

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CPP: Chemische Physik und Polymerphysik

CPP 22: POSTER C

CPP 22.48: Poster

Thursday, March 27, 2003, 12:00–14:00, ZEU/250

Emission of longitudinal sound from shear resonating quartz crystals — •Katrin Wondraczek and Diethelm Johannsmann — Institute of Physical Chemistry, TU Clausthal, Arnold-Sommerfeld-Str. 4, D-38678 Clausthal-Zellerfeld

In the use of quartz crystals as microbalances, there is a systematic problem related to the emission of longitudinal sound. The latter is readily transmitted by liquids. When the longitudinal component is reflected at opposing interfaces, a standing wave in the cuvette is generated, introducing systematic errors. The longitudinal wave can be tracked by changing the distance or angle between the reflector and the quartz surface. To do so, we used an ultrasonic hydrophone as a reflecting surface and as a detector for longitudinal sound at different harmonics of a 5 MHz quartz crystal. We found interferences between longitudinal and transverse sound at several overtones. Further experiments were done using a different surface roughness and morphology of the quartz electrode contacting the liquid. We discuss two different models to explain the experimental findings: one model basing on energy trapping and bending of the oscillating quartz crystal, the second model dealing with extensional components in the motion of the quartz related to piezoelectric stiffening.