Optical fingerprint scanners are the oldest method of capturing and comparing fingerprints. As the name suggests, this technique relies on capturing an optical image — essentially a photograph. Just like smartphone cameras, these sensors have a finite resolution. The higher the resolution, the finer details the sensor can discern about your finger, increasing the level of security. However, these sensors capture much higher contrast images than a regular camera. Optical scanners typically have a very high number of diodes per inch to capture these details up close. Of course, it’s very dark when your finger is placed over the scanner. The scanners, therefore, incorporate arrays of LEDs or even your phone’s display as a flash to light up the picture come scan time. Capacitive fingerprint sensors are what are often referred to as physical fingerprint sensors. An easy way to identify them is if they’re not on a screen.
An optical scanner works by visual detection, as opposed to physical detection in capacitive scanners. These scanners rely on capturing an image and then forming a pattern out of it by gauging the light and dark areas. Think of it as a photocopy machine detecting text.
A small camera on the bottom of the sensor then takes this “photograph” and compares it to an existing record to determine if the fingerprint is authorised. These scanners are quick and usually accurate, but can also be easy to fool. Since the key to the lock here is actually a 2D image, a good, high resolution exact image of your fingerprint may be enough to get past an optical fingerprint scanner. This is the reason these scanners are not considered the safest, even if they are quick and accurate.
Ultrasonic fingerprint sensors
The third type of fingerprint scanner is one that isn’t found on a number of devices, but is the most advanced and also much more secure than optical sensors. Ultrasonic sensors are also often seen below displays in phones like the iQOO 9 Pro. Under an ultrasonic fingerprint scanner is an ultrasonic transmitter and a receiver. The transmitter throws an ultrasonic pulse towards the sensor’s contact surface when you place a finger on it. The pulse is bounced off at different rates when it comes into contact with an uneven surface like our fingers. Ridges on our fingers bounce the pulse back to the receiver, while cavities absorb the pulse. This uneven data that is sent back to the receiver forms a 3D pattern of our fingerprint. This data is then matched with the correct 3D data to authorise a finger.
Unlike capacitive and optical scanners, Ultrasonic scanners are the only kind to make a 3D image ofyour fingerprint data and then compare it with records. This makes it the hardest to beat among the three.
If you decide you want an under-display scanner you need to then look at the advantages and disadvantages of optical and ultrasonic scanners. Phones with optical fingerprint scanners will often be less expensive and also faster to unlock. If you don’t travel much in public transport, or if the device in question will stay indoors most of the time, you can get by with an optical scanner. However, if the device contains sensitive information, and security is a top priority, even if it means higher costs, you should be looking at phones with ultrasonic fingerprint scanners.