Fingerprint sensor Technology in Mobile Phones

Fingerprint sensor Technology in Mobile Phones

Fingerprints have long been used to identify people. The reason for this is the uniqueness of a fingerprint. A few years ago, the fingerprint sensor in smartphones was still something special. Nowadays it is available in numerous devices and has almost become a matter of course.

Fingerprint sensors are used for quick and easy unlocking of the devices by the user. Compared to other systems, e.g. PIN, password or pattern entry, the process is much simpler and significantly more secure.

A distinction is made between semi-automatic and fully automatic fingerprint sensors. With the semi-automatic sensors, the finger must be swiped over a sensor field in order to record the entire fingertip. What we know from smartphones today are fully automatic sensors, where the fingertip can simply be placed on.

Methods for scanning Finger Print: 

There are two common methods of scanning the fingerprint: optical and capacitive. Optical fingerprint sensors are the most common in smartphones. A finger is placed on the glass plate, which serves as a prism, for identification. The papillary ridges (bumps) of the fingerprint come into contact with the glass.

The valleys (grooves) in between are filled with air and in this way do not touch the glass plate. A light source then illuminates the finger so that the prism reflects the light rays onto an image sensor. The reflection is disturbed where the rays hit the elevations.

The image sensor creates a two-dimensional photo of the impression. Optical fingerprint sensors are the most common in smartphones. A finger is placed on the glass plate, which serves as a prism, for identification.

The papillary ridges (bumps) of the fingerprint come into contact with the glass. The valleys (grooves) in between are filled with air and in this way do not touch the glass plate. A light source then illuminates the finger so that the prism reflects the light rays onto an image sensor.

The reflection is disturbed where the rays hit the elevations. The image sensor creates a two-dimensional photo of the impression. Optical fingerprint sensors are the most common in smartphones. A finger is placed on the glass plate, which serves as a prism, for identification. The papillary ridges (bumps) of the fingerprint come into contact with the glass.

The valleys (grooves) in between are filled with air and in this way do not touch the glass plate. A light source then illuminates the finger so that the prism reflects the light rays onto an image sensor. The reflection is disturbed where the rays hit the elevations.

The image sensor creates a two-dimensional photo of the impression. The valleys (grooves) in between are filled with air and in this way do not touch the glass plate. A light source then illuminates the finger so that the prism reflects the light rays onto an image sensor.

The reflection is disturbed where the rays hit the elevations. The image sensor creates a two-dimensional photo of the impression. The valleys (grooves) in between are filled with air and in this way do not touch the glass plate.

A light source then illuminates the finger so that the prism reflects the light rays onto an image sensor. The reflection is disturbed where the rays hit the elevations. The image sensor creates a two-dimensional photo of the impression.

When the smartphone is unlocked, a comparison is made in seconds to determine whether the applied pattern matches the stored data. For high-quality sensors, ultrasound or infrared is used in addition to the optical sensors. It is thus possible to recognize whether the owner of the fingerprint is alive in the identification.

Properties such as pulse, blood circulation and thermal image are also examined.

The capacitive sensors are based on electrical charge. In this case, there is a conductive silicon layer on the fingerprint scanner and a network of tiny capacitors underneath. These sit on a sensor chip. If the finger is placed on the silicon layer, the electrical charge changes.

This only happens in the places where the finger grooves rest. Where there are no grooves, the load remains the same. With the help of an operational amplifier with an integrated circuit and an analog-to-digital converter, the whole thing is converted into a digital image of the fingerprint.

The fingerprint sensor is therefore used for identification. One cannot assume that it is completely free of errors, as is the case with other biometric methods. The biggest mistakes when using biometric procedures are false acceptance and false rejection.

The False Acceptance Rate

The False Acceptance Rate (FAR) is the probability with which an unauthorized person will be accepted on the basis of similar biometric characteristics. The false rejection rate (FRR) is the probability with which an authorized person will be denied access because the requirements for matching biometric characteristics are handled too rigidly.

The aim is to bring both parameters (FAR, FRR) into an acceptable relation to the security level.

 

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