The Delta f-Delta R QCM technique: an approach to an advanced sensor signal interpretation

The frequency shift and the resistance change of a quartz crystal microbala nce (QCM) coated with a viscoelastic film and working in a viscous liquid a re analysed. It is shown that the measurement of the resistance provides ad ditional information for an advanced signal interpretation. With the measur ement of both values, viscoelastic contributions to the frequency response can be discovered. We present a method, which allows sufficiently accurate estimation of the complex sheer modulus of the coating. With this value the impedance approximation can be applied to calculate the film thickness mor e accurate than with those equations based on the assumption of thin rigid films. (C) 2000 Elsevier Science Ltd. All rights reserved.