Internet Enabled Consumer Devices

How do fingerprint sensors work?

24 September 2020
Fingerprint sensors is a key biometric technology that has become a staple in smartphones and becoming important in other security areas. Source: TE Connectivity

It is increasingly difficult to keep both physical locations and digital data secure in this modern age. Thieves can pick locks or force entry. Hackers can steal passwords or employ a number of other intrusions.

Biometric data is slowly becoming a key that cannot be lost, or password that is impossible to replicate. Biometrics such as facial recognition and retina patterns are great tools, but it is the fingerprint that has become the most ubiquitous. Smartphones and other wearables use fingerprint sensors to increase device security, and fingerprint sensors are also gaining traction for high security access to buildings or facilities.

Optical finger sensors

An optical scanner takes a digital photo of a fingerprint in a scanner under a bright light. By seeing the ridges and valleys of the fingerprint, a digital image is made by the light-sensitive microchip, which converts the digital image data into binary code. Comparing the code of the reference versus that of finger on the scanner determines access. Though there is a very rare chance of it, the digital image can be artificially replicated and fed to the sensor.

Capacitive fingerprint sensors

The most commonly used scanners are capacitive fingerprint sensors; most smartphones rely on this technology. Just like a capacitive touchscreen, an electrostatic field is generated by the measure of a finger’s conductivity, and based on that electrostatic field, a digital image is generated.

Tiny capacitor array circuits in the capacitive fingerprint sensors help track the details of the fingerprint. The charge stored in the capacitor is changed by the conductive plates that use fingerprint ridges. The valleys of a fingerprint are filled with nonconductive air, which determines the conductivity of the finger in the sensor. Changes are tracked by an operational amplifier integrator and then an analog-to-digital converter is used to record and analyze this digital data.

It is difficult to bypass this technology because the capacitive fingerprint sensor doesn't register images, and if any other material is used, then different changes will be recorded in charge on the capacitor. This is why these types of sensors more expensive, but more secure and complex.

Installing a fingerprint scanner in a building

To understand the installation of the fingerprint scanner, consider that you are the security head of a large building, and you aim to install a fingerprint scanner at the main entrance. Two different phases are involved in integrating this type of system.

In the first phase is a process known as enrollment, in which the system needs to learn about the employee that must be recognized. During the process, fingerprints of every employee are stored in the coded form on a secure database after careful scanning and analysis. Individual finger scans take less than second, and it has an accuracy rate greater than 99%. However, neither fingerprint sensor technology will work in facilities where workers or visitors have dirty hands.

After the completion of the enrollment process, there is the second phase that is known as verification. Employees or visitors who want to enter will need to scan their finger. The fingerprint taken by the scanner is checked against the fingerprints stored in the database during the enrollment process. Systems can often monitor hundreds or thousands of sensors at a time.

Conclusion

With ever-evolving IoT technology, it is more significant to collect accurate data using sensors. One of the best examples is a smartphone that helps us to understand how quickly our scanning ways and methods have changed over time. Looking back a few years ago, mobile phone were operated with a button. Smartphones are evolving fast, as are the sensing technologies that are in use in them.

To contact the author of this article, email GlobalSpecEditors@globalspec.com


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