Why Does Fingerprint Recognition Will Failure With Wet Hand?

2018-08-06
Why does fingerprint recognition will failure with wet hand?

On the one hand, most smartphones today use images formed by uneven fingerprint lines. When the finger is pressed on the glass plate, since the fingerprint is textured, the line is convex, and the glass plate is contacted to form a mark; and the lines are concave between the lines, and the glass plate cannot be contacted, and no trace can be formed. In this way, a light and dark stripe pattern is formed on the glass plate. But when the finger is wet, there is a water film on the surface of the fingerprint, which fills the concave portion between the lines. In this way, when the finger is pressed onto the glass plate, there will be no light and dark stripes, and the fingerprint is naturally unrecognizable.

On the other hand, the current high utilization rate in mobile phones is mainly capacitive. Capacitive fingerprint recognition technology is of course working with the current sensing of the human body; it is understood that the fingerprint technology of the capacitive technology is coated with a long and narrow electrode. When the finger touches the surface of the sensor, the human body's fingerprint and the sensor surface are due to the human body electric field. A coupling capacitor is formed. For high-frequency current, the capacitor is a direct conductor, so the finger draws a small current from the surface of the contact point. This current flows out of the surrounding electrode and flows through the surrounding electrode. The current is proportional to the distance from the fingerprint to the periphery. The controller calculates the touch fingerprint by accurately calculating the current ratio. Because water has conductive properties, when the wet hand touches the sensor, the current on the surface of the finger is affected by the water on the finger, which causes the fingerprint to be inaccurate or not good.


Therefore, fingerprint products will indicate the acceptable humidity range of their products to avoid identification failure. For  example, as a profess fingerprint lock manufacturer, Fipilock will note that the humidity range of fingerprint lock is 40% RH-90%RH.And it will also remind consumers to wipe the rain and then use the padlock after the rain.

Little friends, have you got it?

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