What are the benefits of measuring at several frequencies simultaneously?
Simultaneous measurement of multiple overtones is required to model viscoelastic properties and extract correct thickness for films outside the Sauerbrey region. With the Q-Sense E4 system, 14 incoming parameters (7 frequencies and 7 dissipation values) per sensor provide a well-determined model of the particular film properties. Moreover, the different overtones give information about the homogeneity of applied layers: as the detection range out from the crystal surface decreases with increasing overtone number, abnormal frequency behaviour suggests vertical variations in film properties. The fact that the detection range out from the crystal surface decreases with increasing frequency is also used by the modeling software to calculate accurate thickness of films that do not fully couple to the oscillation of the crystal. For rather soft films, containing much water (films made of large proteins for example), you will not get accurate thickness information without measuring at several
