The Quartz Crystal Microbalance in Soft Matter Research

Part of the series Soft and Biological Matter pp 247-286


Point Contacts and Contact Stiffness

  • Diethelm JohannsmannAffiliated withInstitute of Physical Chemistry, Clausthal University of Technology Email author 

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If an external object (such as a sphere) touches the resonator surface across a contact with a diameter much below the wavelength of sound and, also, much below the size of the particle, one can infer the stiffness of the contact from the frequency shift. The situation is particularly transparent for particles, which are heavy enough to be clamped in space by inertia, so that they do not follow MHz motion of the resonator. In this case, the frequency shift is positive and proportional to the contact stiffness. Smaller particles give rise to coupled resonances. Coupled resonances can be viewed as absorption lines in shear-wave spectroscopy.