How finger print scanner works

 How finger print scanner works




Some scanners rely on light other electricity and still other on sound to map the ridge and valleys of your fingers

Capacitive “electronic sensor” are popular in smartphone because they are small, accurate and fast, but optical and ultrasonic techonologies have the advantage of enabling in display scanning

Optical fingerprint scanner

These work as digital camera

It take picture of your finger and sends that picture for processing 

The following is general idea

1. The  scanner shines light onto your finger using LED and take picture 

2. If pixel value of the photo is too dark or light it adjust exposure and tries again

3. If picture is clear, the image can be processed

These scanner used in police station, airplane and secure trace

Smartphones use this technology in in display fingerprint scanner (some use optical or ultrasonic sensor) under screen to get image

Capacitive fingerprint scanner

When you put yourfinger on capacitive scanner

It using tiny amount of electricity to measure the distance between different parts of your finger and the scanner

Inside scanner are row of capacitors, each of which carries electrical charge

If the capacitor is below one of ridge it can hold more charge since its coming into contact with your skin

If its below valley capacitor will remain in contact with air, which does not allow it to store much extra charge

You can think of capacitor as pixel in camera if one holding more of charge , that can be interpreted as a ridge area, while other are read as valley

Taken as a whole, this get you an image of fingerprint that is just as accurate as one from optical sensor and even more secure

Ultrasonic fingerprint scanner

Ultrasonic scanner fire out a  high frequency pulse of sound that then bounce off the user’s fingerprint back to receiver a sensor that can measure mechanical stress

Sensor is looking at intensity of returning pulse at different point on the finger and can use that data to calculate where the ridge and valleys are

Wave masure depth of valleys in a fingerprint ,the resulting map is 3D

These scanner are slower

Can work as under display finger print scanner

Analyzing storing and using fingerprint

After image is captured

Software will check if fingerprint matches authorized user

Based in “minutiae” points of finger where some ridge line terminate or split

Each feature assigned position relative ot other detected minuatiae and scanner software make a map tat can be represented as number

Number is essentially the encoded fingerprint


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