optical fingerprint scanner
As the name suggests, an optical scanner involves the use of optics (light) to capture and scan fingerprints on a device. Essentially, the scanner works by capturing a digital photograph of the fingerprint and then using algorithms to find unique patterns of lines and ridges, spread across the different lighter and darker areas of the image. This digital photograph is a 2D depiction of the different patterns of ridges and lines present on the finger, and since it comprises of details in the darker sections of the image as well, the same is lit-up using a light source, typically an LED, to capture a detailed image. The quality of the image sensor plays a crucial role in getting a high-definition and detailed image of the fingerprint, which would make it easier to extract more data from the image, increasing security.
Optical Scanners have been prevalent in the early days of fingerprint authentication technology, and are nowadays, rarely used on most smartphones, except for a few budget-friendly ones. The possible reasons for a fall in the adoption of optical scanners seem to be – the bulky circuitry design that makes it difficult for manufacturers to fit it into a smaller form factor design, or the low-level of security offered with the 2D picture of the fingerprint, which can be easily tricked using prosthetics or high-resolution pictures.
2. Capacitive Fingerprint Scanners
capacitive fingerprint scanner
Going by the name, one can get an idea of the involvement of capacitors in Capacitive Scanners. For those unaware, a capacitor is an electronic component that stores electrical energy in an electric field. In case you’re wondering about its role in Capacitive Scanners, it’s important to first understand that unlike optical scanners, which capture a 2D image of the fingerprint, capacitive scanners capture different details of the fingerprint using just the electrical signals. For this, it uses a series of tiny capacitors circuits, arranged in an array, to store data of the captured fingerprints. During the process of enrolment, the change in fingerprint patterns (ridges and lines) causes a change in the registration process, as the charge would be different for a finger placed over the capacitive plate and different for the air gap between the ridges and lines. This change, in the charge of the capacitor, is further determined using an op-amp (Operational Amplifier), and then recorded with the help of an ADC (Analogue-to-Digital Converter).
Once a fingerprint is captured, all its related data is further analyzed for unique fingerprint information and then saved for comparison at the time of user authentication, in the future. Since no 2D image capturing is involved in this process, the fingerprint data is far more secure than the data from an Optical Scanner. And therefore, a Capacitive Scanner cannot be easily tricked with the help of prosthetics or photographs of the fingerprint, which is why these scanners are more popular and widely used across a wide range of smartphones currently in the market.
3. Ultrasonic Fingerprint Scanners
Ultrasonic fingerprint scaner
It is the newest fingerprint scanning technology, that has started to appear in smartphones, recently. Unlike the other two types of fingerprint scanners, which involve the use of light or capacitor, an ultrasonic scanner, on the other hand, utilizes a very high-frequency ultrasonic sound. Additionally, it also requires the use of a combination of an ultrasonic transmitter and an ultrasonic receiver. The process involves the use of an ultrasonic pulse, which is sent through the ultrasonic transmitter towards the finger resting on the scanner. As soon as this pulse strikes the finger, some part of it is transmitted, while some part is reflected back. This reflected pulse is then picked up by an ultrasonic receiver, which depending upon the intensity of the pulse, captures a 3D depiction of the fingerprint. This change in the intensity of pulse is caused due to the texture of the finger, which constitutes ridges and lines.
To be able to pick the change in intensity of the reflected ultrasonic pulse, the ultrasonic receiver takes into consideration the mechanical stress of the fingerprint on the scanner. The longer a finger stays on the scanner, the more details it can capture, and produce a detailed 3D depiction of the fingerprint. However, a drawback of this type of fingerprint scanning method is that it is not as fast as the other methods of fingerprint scanning. On the other hand, the scanner does a great job of allowing manufacturers to get rid of or minimize the bezels around the screen, which is only possible because the scanner can be easily implemented under the display.
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