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Fingerprint Scanners: How Do They Work?

Fingerprint readers have been on the market many years now, and during that time there has been an immense growth in terms of what they can do and how. But what kind of fingerprint readers are out there?

Optical Reader

Optical scanners are the oldest method of capturing and comparing fingerprints, using the same light sensor systems used in digital cameras, called a charge coupled device

The scanner uses an internal light source to create shadows on the fingerprint surface allowing the sensor to map the ridges and valleys. If the image is to dark or too light, the scanner can adjust the exposure time to let more or less light in, ready to try again.

Due to the low security of only capturing a 2D picture which can easily be fooled and the need for large hardware to accommodate a light, optical readers are not commonly used in modern technology. They are however very cost effective and can act as a good entry level reader in cases where security is not a high concern.

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Capacitive reader

Capacitive scanners are the most common type of fingerprint used today due to their ability to be very thin, allowing them to be easily installed in even the thinnest hardware devices. Like optical scanners, capacitive scanners generate images of the grooves and images making up a fingerprint. The difference is that instead of using light tiny capacitor circuits, connected to conductive plates are used which gauge depth changes in an object making them perfect for accurately reading fingerprints.

Due to the detail these readers can obtain, they are infinitely harder to fool compared to optical readers. Unlike with optical readers, capacitive readers can’t be fooled with an image and are harder to fool with prosthetics due to the slight difference in pressure of different materials.

Ultrasonic Reader

Ultrasonic readers are the latest fingerprint capturing technology to be used and can even be used with wet or oily fingers. The general principle is similar to 3D ultrasounds of unborn babies. Using ultrasonic pulses, which are absorbed/bounced back to the sensor depending on the individual ridges, valleys and pours the reader can map a high detail 3D image of the fingerprints. This process allows each fingerprint to have an even higher degree of uniqueness as well as being just about impossible to forge, even with the highest grade of professional equipment.

Another advantage of these concept readers is the ability to be hidden behind and operate underneath a solid surface. This would allow the reader to be concealed behind a glass, aluminium or even steel surface allowing for a device to offer more flexibility in terms of its design.

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Recent developments – In-display fingerprint technology

Touch ID was first introduced to smartphones by Apple when they released the iPhone 5s and since then have been embedded to home buttons and mounted to the backs of devices. Most commonly this is achieved using capacitive readers under certain parts of the phone such as the home button. However, with the changing technology and design features seen in mobile phones such as ‘all screen’ handsets, in-display technology that is embedded under a smartphones display is becoming increasingly more important.

Despite optical scanners being the oldest method of capturing and comparing fingerprints, they are currently being revamped and used in in-display fingerprint technology (ultrasonic readers can also be used). Chinese brand Vivo have recently started to introduce this technology by embedded an optical sensor under a smartphones display and instead of coming with its own light source, something that previously made it quite bulky and inappropriate for use with smartphones, uses the light omitted from the devices display panel. Unfortunately this is currently only supported on devices with OLED and AMOLED displays but is still a working progress