Anyone with the latest iPhone or Android knows that fingerprint scanning has officially hit the mainstream. But how does that process work, and how accurate can it really be? Here’s a closer look at fingerprint scanning and how it works.

fingerprint scannerFingerprint scanning falls under the umbrella of biometrics, the measure of your physical form and/or behavioral habits, generally for the sake of identifying you before you are granted privileged access to something. Other examples of biometrics include handwriting, voiceprints, facial recognition, and hand structure scanning.

It’s said that humans have tiny ridges and valleys all along the inside surface of their hands for the sake of friction; our fingerprints are meant to act as treads that allow for us to climb and enjoy an improved grip on the things we carry. Who really knows though. Regardless, we have fingerprints, and they happen to be different for each of us due to both genetic and environmental factors.

That’s extremely useful for security and law enforcement in general. With a fingerprint scanner, you can know if anyone whose fingerprints are on record touched a particular object. Finger print scanners can get an image of someone’s finger in many ways, but the two most common methods are optical scanning and capacitance scanning.

Optical scanners use a charged coupled device (CCD), which is the same light sensor system commonly found in digital cameras and camcorders. A CCD is just a collection of light-sensitive diodes called photosites that receive light photons and generate an electrical signal in response. When you place your finger on the glass plate of a fingerprint scanner, the scanner’s light source illuminates the ridges of your finger and the CCD generates an inverted picture of your fingerprint in which the ridges are lighter and the valleys are darker. So long as the image is sufficiently bright and crisp, the scanner will then proceed to compare the print to other prints on file.

capcitive fingerprint scanningCapacitive fingerprint scanners function slightly differently but create the same output. They use electrical current to sense the print instead of light, so they’re built with one or more semiconductor chips containing and array of cells which are each made up of two conductor plates covered with an insulating layer. A capacitor is formed out of these plates, plus the surface of the finger acts as the third capacitor plate. Basically, the scanner reads how the voltage outputs coming from the finger are different due to the difference in distance from the valleys and ridges to the capacitors and generates from this an image of a fingerprint. These systems are apparently harder to trick and can be built to be more compact.

Once the fingerprint registers, it must be analyzed to see if it matches with any other prints recorded in the system. This occurs by comparing specific features of fingerprints referred to as the minutiae. These points are generally areas where ridge lines end or where one ridge splits into two. To get a match, the scanner system simply has to find a sufficient number of minute patterns that the two prints have in common.


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