The fingerprint sensor has been a feature used to unlock smartphones for a long time. If my memory serves me right, the first time the fingerprint reader was used on a large scale was with the iPhone 5S, launched in 2013. Since then, we have used passwords, PINs or drawing patterns on the screen less and less to unlock our electronic devices.
Over these nearly 10 years, the fingerprint sensor has appeared in various positions on the smartphone. Integrated into the Power button on the front and side, on the back and now it’s being placed under the screen. But do you know how the fingerprint sensor works? In this article we will explain how the magic happens.
Two types of technologies
The fingerprint sensor is a biometrics technique. As such, the sensor analyzes a specific physical characteristic of the person. In this case, the fingerprint pattern of one or more fingers. The idea is to uniquely identify the user, preventing unauthorized people from having access to the device.
Currently, fingerprint readers use two types of technology: optical and ultrasonic.
Optical digital sensor
The optical digital sensor is the most common type. This was the technology used in the first smartphones with the function. Currently, the optical digital sensor can be found in older smartphones or in entry and/or intermediate models. This makes the device cost a little less.
In practice, the sensor will scan your fingerprint. It does this by shining a light onto the surface of your finger. This light is emitted precisely from the scanner’s working area. It could be the surface of the Power button or that circle found on the back of some smartphones.
This light enables the scanner to create a digital image of the fingerprint pattern. If this pattern matches the image that is already stored on the device, unlocking takes place.
This is the same technology used in ATMs, for example. Or in the “point” equipment, used in some companies or public offices, where employees register the time of entry and exit from work. It is simply a little box that emits light to identify fingerprint patterns.
Ultrasonic digital sensor
The ultrasonic digital sensor is the most modern and efficient version of the technology. It does not use a light to create a 2D image of your fingerprint. But rather ultrasonic waves that are much more accurate and efficient.
When you place your finger over the fingerprint sensor, it emits an ultrasonic wave that interacts with the skin of your finger. This ultrasonic wave identifies the ridges and valleys of a fingerprint more accurately. The result is a 3D image of your fingerprint, almost like a map.
Another advantage of ultrasonic sensors is that they can read your fingerprint even if your fingers are dirty, wet or greasy. In addition, the ultrasonic digital sensor can be installed under some surfaces. Among them are metals, glass and OLED screens.
Finally, the security of the ultrasonic digital sensor is also higher, as it is much more difficult to fool it. In the optical sensor, in theory, it is enough to have a 2D image of the digital one. In the ultrasonic sensor it is necessary to model a finger in 3D with the same fingerprint pattern registered in the device.
Fingerprint sensor under the screen
The next trend in the smartphone world is installing fingerprint sensors under the screen. This is only possible thanks to ultrasonic wave technology, as we saw in the previous topic. But is it really a good idea?
Currently, installing a fingerprint sensor under the screen makes the device more expensive to mount. That’s why we find this type of technology only on premium smartphones (or premium intermediates).
In addition, you need to be much more careful with the screen of the device. After all, if it breaks, you will not only need to change the screen, but also the fingerprint sensor. And while the component works properly even if the screen has scratches, the same does not happen if it is cracked.
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