Types of a fingerprint scanner for a smartphone: principle of operation

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Modern smartphones are equipped with systems that allow biometric authentication to unlock the display. The main types of fingerprint verification module are discussed below, as well as the pros, cons, and how they work.

What is a fingerprint reader?​

This term refers to a smartphone design element that identifies the wearer by reading and analyzing the papillary layer on the finger. To do this, the hardware component takes biometric data, and specialized programs check and compare it with a sample stored on the device.

The papillary pattern is formed even before the birth of a person, without changing throughout his life. Therefore, the fingers have a unique set of depressions and bulges, as well as a difference in the characteristics of the skin. Due to this feature, when reading biometric information, the scanner detects the presence of heat, electrical capacity, or both.

Types of fingerprint scanner​

Mobile device manufacturers integrate capacitive, optical, and ultrasonic fingerprint identifiers. Each of them differs in design, in its inherent way of obtaining biometrics and in the conditions for successful verification.

Capacitive Scanner​

It functions thanks to semiconductors that are attached to the back of the reading section. When the finger touches the scanner, the capacitance changes, by which the distance between the papillary layer and the reading plane is determined. In elevated areas, it is less, and in the place of the presence of depressions, it is more. Thanks to this, a papillary pattern is created, which the software turns into a picture and compares it with the picture saved during setup in the database.

The capacitive view of the scanner has a relatively low cost and quickly reads the print of a leaning finger, performing the procedure at an arbitrary angle of inclination. But due to its massiveness, it is difficult to implement it under the display, so manufacturers place the module on the back or side of the mobile device. If your finger is wet with liquid or covered in dirt, the reading will not be performed correctly.

Optical scanner​

Acts by forming a two-dimensional image of the papillary pattern. The module can be designed as a contact area or embedded directly into the display of a mobile device.

Contact area​

The design resembles that of the capacitive variety of fingerprint scanners. However, the device operates using reflection technology, when a finger applied to a surface is affected by light emitted from a built-in source. Some of the photons are reflected, falling on the camera that collects them. Thanks to this process, a two-dimensional fingerprint scheme is created.

As an advantage, the contact pad quickly reads the information and compares the card to the sample. And its small size allows manufacturers to mount the fingerprint module under the display or directly in it. However, when scanning a dirty finger, errors are generated and the structure is poorly protected from damage.

Scanner inside the display​

It works like a contact pad, differing in design features. For example, during the manufacture of a smartphone, a hole is drilled in a certain area of the screen. A reading element with a comparable size is inserted there at a certain step in the technological process. Its coordinates are chosen in such a way that during standard operation of the gadget, the scanner plane acts as a display.

When the user needs to unlock the screen by scanning a fingerprint, the test area will be highlighted, allowing accurate finger placement. And because of the clear boundaries, any shifts are fraught with an error in the formation of a map of papillary lines. Finally, the display brightness in the test area is increased to provide a suitable light output.

The small-sized module does not pose a problem by reading your fingerprint under the hardened glass on the screen. But the reading area is definitely limited, and in bright light, scanning is not possible the first time. If the module is damaged, in the place of its presence the display will stop responding to touching fingers. Also, an in-screen fingerprint scanner is difficult to integrate into an IPS-type matrix.

Ultrasound Scanner​

Uses ultrasound waves to verify the fingerprint. The wave emitted by it hits the finger, and then is reflected and flies back to the module. Through this process, the depth of the depressions and the height of the protrusions on the papillary layer are measured. Since biometrics are checked without a separate reading area, the scanning is done at the expense of the screen.

The ultrasonic version of the fingerprint scanner generates an ultra-high-quality fingerprint card, preventing hackers from illegally gaining access to the mobile device's system. Also, the module is able to determine the human pulse. However, the devices containing it are quite expensive, and cracks that have penetrated deep into the protective glass will not allow using the scanner.

It is impossible to read the fingerprint, having covered the smartphone display with a protective glass, and for the successful completion of the operation, you will need to put your finger on a strictly defined area.