Characteristic gap to estimate the range of squeeze-film damping. The characteristic gap g
* is normalized to the fundamental mode of vibration (n = 1) at H
* = 0.5 (dashed line). It is the cantilever-surface gap, where the frequencies (blue triangles) and quality factors (red circles) dropped to, respectively, 93.4% and 77.8% of their initial values. The range of the squeeze-film damping can be estimated by calculating 2 · H
*, i.e., H = 1 for the fundamental mode. The means ± SD (N = 3) are shown, mode numbers n are indicated on the top axis.