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Wet fingers can confuse fingerprint sensors. Today’s detectors either scan
the fingerprint optically or measure the variation of capacitance across a
fingerprint pad. Now researchers at NTT in Japan have come up with a watertight
idea. Their sensor consists of an array of tiny silicon bumps, each mounted on a
pair of pressure-sensing electrodes. The tightly packed bumps give the array a
high enough resolution for individual ridges on your finger to push the bumps
down, so the sensor records every ridge and crevice of your fingerprint.