Fingerprint Scanners - How It Works

What is a Fingerprint Scanner and How It Works

We all have seen fingerprint scanners, they are everywhere as smartphones have launched it as an basic security feature. Most simple explanation to fingerprint scanner would be that you touch it with your finger and reads your fingerprint, matches and tells you if it is the one it has stored as authentic or not.

Basic Explanation:

Everyone has patterns of friction ridges on their fingers, and it is this pattern that is called the fingerprint. Fingerprints are uniquely detailed, durable over an individual's lifetime, and difficult to alter. Because there are countless combinations, fingerprints have become an ideal means of identification.

The fingerprint scanner detects these patterns and forms a unique key and then matches them with the already stored keys.

How exactly do they work and how they found their way onto so many consumer devices?

Every  fingerprint scanners has the same job but they work differently. So, here are types of scanners and their working.

Types of Scanners:

• Optical scanners take a visual image of the fingerprint using a digital camera.
• Capacitive or CMOS scanners use capacitors and thus electrical current to form an image of the fingerprint. This type of scanner tends to excel in terms of precision.
• Ultrasonic fingerprint scanners use high frequency sound waves to penetrate the epidermal (outer) layer of the skin.
• Thermal scanners sense the temperature differences on the contact surface, in between fingerprint ridges and valleys.

Optical Scanners:

Optical scanners use visible light to capture a more traditional image of your fingertips but these are uncommon at least in portable devices due to their bulk size. It then uses algorithms to detect unique patterns on the surface, such as ridges or marks, by analyzing the lightest and darkest areas of the image. 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 Scanner:

You’ll find this type of scanner on the front and back of smartphones and even used as part of cutting-edge in-display variants. Well as it turns out typical fingerprint readers use the same principle of capacitance as track pads and touchscreens. So if you check out How Touch Screen Works you'll know that they typically function by detecting the difference in charge between the lower layer of your skin which is conductive and the phone screen itself .

Fingerprint readers adapt this concept for personal identification by cramming lots of tiny conductive plates into the space just below the scanner surface. They're narrower than the ridge that make up your fingerprints. When you place your finger tip against the reader, the sensors can tell which portions of your finger the ridges are touching the sensor and which are not because the small valleys are further away from the sensor which decreases the capacitance the tiny place will pick up the reader can use these differences in capacitance to form a virtual image of the ridges of your fingerprint. 

Now these scanners have actually been on phones since 2007 but only they really took off when Apple released touch ID with the iPhone 5s in 2013. 

Ultrasonic fingerprint scanner:

Ultrasonic fingerprint readers have the potential to be the next big thing. These works somewhat similarly to a bats echolocation the way they work out the shapes of objects in the dark. Ultrasonic pulses emanate from the reader and hit the ridges of your fingerprints then variations in the return signal are used to construct a scan. Ultrasonic sensors not only have the advantage of a cool marketing friendly name but they can also work through other materials allowing them to be seamlessly embedded underneath the phone surface for a slicker look or it appeared through the crud of moisture on your hands for better reliability than there are capacitive counterparts.

Thermal scanners:

Thermal scanners use heat to create the image of your fingerprint. As you press your finger on the scanner, the device measures the temperature of the ridges touching the sensors. The “valleys” formed between the ridges don’t make contact with the scanner and aren’t measured. The scanner creates the image by using the contrast between the temperature of these ridges and valleys. Because this type of scanner relies on heat, a temperature difference of at least one degree must exist between the surface of your finger and the ambient room temperature for it to operate properly.

Final Word

Fingerprint scanners sounds great right but while many people originally thought, fingerprint sensors is a highly secure technology perhaps because of their association with spy films they certainly aren't foolproof no matter exactly which variety you're using. 

Think of how the scanner on your phone will work even though you don't place your finger on it in exactly the same position every time this is because they only require a good-enough partial match to decided this your finger. Now this allows it to recognize you from many different angles but it also means there's a small chance of a false positive. Even though master fingerprints are typically secured in some way, like how Apple encrypts the touch ID fingerprint and stores it locally. 

It's still possible to defeat fingerprint readers using artificial moles that can be created if say some miscreant gets to hold a fingerprints that you left on a glass.
So while the technology is super convenient there are holes that have led most smartphone operating systems to also require a password or PIN which is especially important if you're one of the few dozen or so people in the world that were born without fingerprints.

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