Figure 1.

Vibrations elicited as two etched silicon surfaces, consisting of an array of truncated pyramids, with spatial periods of 276 (left) and 416 microns (right), are scanned across the finger at 20 mm/s. Vibrations (top plots) were recorded using a Hall Effect Transducer.⁷ As can be seen, both from the raw traces and the spectrograms, the two surfaces elicit vibrations that differ in their spectral content. The peak frequency of the vibrations is linearly related to the scanning speed and inversely related to the spatial period of the surface (approximately 72 and 48 Hz for the two surfaces at the nominal scanning speed).