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Why do sweaty fingers cause fingerprint lock recognition to fail?

Technology Exchange 05 Dec 2019 09:17 Source: Door Lock World
Fingerprint lock recognition sensitivity is one of the important indicators of fingerprint lock product performance and user experience, but in real life, fingerprint locks are always susceptible to external factors. For example, sweaty fingers or too wet fingerprint collection window will cause fingerprint lock recognition to fail. What is the reason for this?
To understand why fingerprint sweating can cause fingerprint lock recognition to fail, you must first understand the basic principles of fingerprint recognition technology.
Fingerprints are regular but different lines on the skin of the front of a human finger. The points formed by the interruption, bifurcation or turning in the fingerprint are the detail feature points, and these detail feature points provide confirmation information for the uniqueness of the fingerprint. The fingerprint recognition sensor records the direction of the fingerprint pattern and digitizes it to form a key and unlock it.
At present, fingerprint locks can collect fingerprints in two main ways: optical and capacitive (semiconductor). The optical fingerprint head obtains fingerprint information by calculating the distance between the grooves and ridges of the fingerprint and the collection window. When the finger is sweaty or the collection window has moisture, it will affect the transmission and distance of the light, resulting in the obtained fingerprint information and the original The stored information is incorrect, so the fingerprint lock recognition fails.
Capacitive (semiconductor) fingerprint locks are more advanced than optical fingerprint locks, but there are also cases where recognition fails after being wet. Speaking of capacitive fingerprint locks, the principle should be able to associate the working principle of capacitive screens, which use the human body's current induction to work.
Capacitive (semiconductor) fingerprint lock Fingerprint recognition sensors are plated with long and narrow electrodes. When the finger is pressed against the fingerprint collection window, because the human body is an electric field, the user's fingerprint pattern and the sensor surface will form a coupling capacitor. In terms of current, capacitance is a direct conductor, so a finger will draw a small current from the contact point. This current is flowing from the surrounding electrodes, and the current flowing through the surrounding electrodes is proportional to the distance from the fingerprint to the surroundings. The controller calculates the data related to the touch pattern through accurate calculation of the current ratio.
To put it simply, where the user's fingerprint goes, there will be "power on" and "leakage", and the sensor will respond. Therefore, when the fingers are sweaty or the collection window has water stains, since the water is conductive, when the user uses fingerprint recognition, the current will be affected, so the above calculation is not allowed, and the natural recognition fails.
Therefore, when a fingerprint lock user enters a fingerprint for the first time, try to keep the finger and the fingerprint collection window dry and clean, so as to enter a correct and clean fingerprint; when the user unlocks with the fingerprint, wipe the finger and the collection window to avoid the fingerprint lock failure Case.
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