Fingerprint scanners aren’t just reserved for the very top-tier smartphones these days, with even many budget phones packing the tech these days. Technology has moved on a lot from the early days too, becoming faster and more accurate in their readings. With all that in mind, let’s take a look at how the latest fingerprint scanners work and what the differences are.
Biometric Fingerprint Scanners
Nothing is completely secure. Locks can be picked, safes can be broken into, and online passwords can be guessed sooner or later. How, then, can we protect the things that we value? One way is to use biometrics fingerprints, iris scans, retinal scans, face scans, and other personal information that is more difficult to forge. Not so long ago, if you'd had your fingerprints taken, chances are you were being accused of a crime; now, it's innocent people who are turning to fingerprints to protect themselves. And you can find fingerprint scanners on everything from high-security buildings to ATM machines and even laptop computers. Let's take a closer look at how they work!
Why are fingerprints unique?
It's pretty obvious why we have fingerprints the tiny friction ridges on the ends of our fingers and thumbs make it easier to grip things. By making our fingers rougher, these ridges increase the force of friction between our hands and the objects we hold, making it harder to drop things. You have fingerprints even before you're born. In fact, fingerprints are completely formed by the time you're seven months old in the womb. Unless you have accidents with your hands, your fingerprints remain the same throughout your life.
What makes fingerprints such a brilliant way of telling people apart is that they are virtually unique: fingerprints develop through an essentially random process according to the code in your DNA (the genetic recipe that tells your body how to develop). Because the environment in the womb also has an effect, even the prints of identical twins are slightly different. While it's possible that two people could be found who had identical fingerprints, the chances of this happening are so small as to be virtually negligible. In a criminal case, there are usually other pieces of forensic evidence that can be used with fingerprints to prove a person's guilt or innocence beyond a reasonable doubt. Where fingerprints are being used to control access to something like a computer system, the chances of a random person having just the right fingerprint to gain entry are, generally speaking, too small to worry about and much less the chance of someone guessing the right password or being able to break through a physical lock.
Enrollment and verification
Suppose you're in charge of security for a large bank and you want to put a fingerprint scanning system on the main entry turnstile where your employees come in each morning. How exactly would it work?
There are two separate stages involved in using a system like this. First, you have to go through a process called enrollment, where the system learns about all the people it will have to recognize each day. During enrollment, each person's fingerprints are scanned, analyzed, and then stored in a coded form on a secure database. Typically it takes less than a half-second to store a person's prints and the system works for over 99 percent of typical users.
Once enrollment is complete, the system is ready to use and this is the second stage, known as verification. Anyone who wants to gain access has to put their finger on a scanner. The scanner takes their fingerprint, checks it against all the prints in the database stored during enrollment, and decides whether the person is entitled to gain access or not. Sophisticated fingerprint systems can verify and match up to 40,000 prints per second!
How fingerprints are stored and compared
When fingerprints were first used systematically for a criminal investigation in 1900, by Sir Edward Henry of the Metropolitan Police in London, England, they were compared slowly and laboriously by hand. You took a fingerprint from a crime scene and another fingerprint from your suspect and simply compared them under a magnifying glass or microscope. Unfortunately, fingerprints taken under different conditions can often look quite different the one from the crime scene is much more likely to be incomplete or smudged and comparing them to prove that they are identical sometimes takes great skill. That's why forensic scientists developed a reliable system for matching fingerprints where they looked for between eight and sixteen distinct features. In the UK, two fingerprints need to match in all sixteen respects for the prints to be judged the same; in the United States, only eight features need to match.
When a computer checks your fingerprints, there obviously isn't a little person with a magnifying glass sitting inside, comparing your fingerprints with all the hundreds or thousands stored in the database! So how can a computer compare prints? During enrollment or verification, each print is analyzed for very specific features called minutiae, where the lines in your fingerprint terminate or split in two. The computer measures the distances and angles between these features a bit like drawing lines between them and then uses an algorithm to turn this information into a unique numeric code. Comparing fingerprints is then simply a matter of comparing their unique codes. If the codes match, the prints match, and the person gains access.
How fingerprint scanners work
Having your fingerprints taken at a police station involves pressing your fingers onto an ink pad and then rolling your fingers onto paper to leave a clean impression on the page. Your prints are also stored on a computer database so the police can check if you've committed any known crimes or if you do so in the future.
But when fingerprints are being used to control access to buildings and computer systems, more sophisticated methods have to be used: a computer has to scan the surface of your finger very quickly and then turn the scanned representation into a code it can check against its database. How does this happen?
There are two-three ways of scanning fingers
1. Optical Scanner
Optical fingerprint sensors have been around for a while. The way an optical scanner works is by shining a bright light over your fingerprint and taking a digital photo. The light-sensitive microchip makes the digital image by looking at the ridges and valleys of the fingerprint, turning them into 1’s and 0’s, and creates the user’s own personal code. The disadvantage to this, while highly unlikely, is that a digital photo can be replicated.
2. Capacitive Scanner
In today’s world, capacitive fingerprint scanners are more common and found on phones. Similar to the capacitive touchscreen, it measures your finger by using human conductivity, creating an electrostatic field, and creating a digital image based on the electrostatic field.
To go into more detail, the capacitive fingerprint scanner uses tiny capacitor array circuits that track the detail of a fingerprint. It uses the ridges of your fingerprint that are placed over the conductive plates which change the charge stored in the capacitor, while the valleys leave the charge on the capacitor unchanged. An operational amplifier integrator circuit tracks these changes that can then be recorded by an analog-to-digital converter, where this digital data can be analyzed.
This technology is a lot harder to bypass since an image cannot get past a capacitive fingerprint sensor and other materials will record different changes in charge on the capacitor. While it is more expensive, it’s also more complex and secure.
As we become more advanced and IOT keeps growing, accurate data collection via sensors becomes more important. Smartphones are the best example of how sensors are quickly changing the way we go about our days. After all, it was only a few years ago that phones didn’t have touchscreen or fingerprint applications on them.
3. Ultrasonic scanner
The third type of fingerprint reader is called an ultrasonic scanner because it uses high-frequency sound waves (ultrasound) to "map" your finger instead of light. If you have a new Samsung smartphone, you'll probably find it has one of these built under the display, which you can use to unlock the phone or secure access to your apps and data. According to Samsung, ultrasonic scanners are more secure (because they scan fingerprints in three dimensions) and work better outdoors (in bright light or low temperatures) than optical scanners, though they tend to be slower than capacitive scanners.
What happens during a scan?
Unlike ordinary digital photos, scans have to capture exactly the right amount of detail brightness, and contrast so that the individual ridges and other details in the fingerprint can be accurately matched to scans taken previously. Remember that fingerprints might be used as evidence in criminal trials, where a conviction could result in a long jail sentence or even the death penalty. That's why "quality control" is such an important part of the fingerprint scanning process.
Here's how the process works with a simple optical scanner:
- A row of LEDs scans bright light onto the glass (or plastic) surface on which your finger is pressing (sometimes called the platen).
- The quality of the image will vary according to how you're pressing, how clean or greasy your fingers are, how clean the scanning surface is, the light level in the room, and so on.
- Reflected light bounces back from your finger, through the glass, onto a CCD or CMOS image sensor.
- The longer this image-capture process takes, the brighter the image formed on the image sensor.
- If the image is too bright, areas of the fingerprint (including important details) may be washed out completely like an indoor digital photo where the flash is too close or too bright. If it's too dark, the whole image will look black and details will be invisible for the opposite reason.
- An algorithm tests whether the image is too light or too dark; if so, an audible beep or LED indicator alerts the operator and we go back to step 1 to try again.
- If the image is roughly acceptable, another algorithm tests the level of detail, typically by counting the number of ridges and making sure there are alternate light and dark areas (as you'd expect to find in a decent fingerprint image). If the image fails this test, we go back to step 1 and try again.
- Providing the image passes these two tests, the scanner signals that the image is OK to the operator (again, either by beeping or with a different LED indicator). The image is stored as an acceptable scan in flash memory, ready to be transmitted (by USB cable, wireless, Bluetooth, or some similar method) to a "host" computer where it can be processed further. Typically, images captured this way are 512×512 pixels (the dimensions used by the FBI), and the standard image is 2.5 cm (1 inch) square, 500 dots per inch, and 256 shades of gray.
- The host computer can either store the image on a database (temporarily or indefinitely) or automatically compare it against one or many other fingerprints to find a match.
What can you use fingerprint scanning for?
Fingerprint scanning is the most popular biometric technology and it's easy to see why. We store more and more information on our computers and share it, online, in ever more risky ways. Much of the time, our bank information and personal details are protected by just a few hastily thought-out numbers in our passwords. Anyone can use their credit or debit card to get money from an ATM (automated teller machine) if they know just four numbers!
In the future, it will be much more common to have to confirm your identity with biometric information: either your fingerprint, a scan of the iris or retina in your eye, or a scan of your face. Some laptop computers and most smartphones now use fingerprint scanning to make them more secure. Large banks, such as Bank of America and JP-Morgan Chase, have introduced fingerprint authentication as part of the sign-in process for their smartphone apps. Soon we could be seeing fingerprint scanners on ATMs, in airport security scanners, on checkouts in grocery stores, in electronic voting systems, and perhaps even replacing the keys in our (self-driving) automobiles!
Some people don't like the sound of a Big Brother society where you have to do everything with your fingerprints and it's true that there are important issues of privacy. But humans have always used bio-metrics for personal identification: we tell one another apart chiefly by recognizing one another's faces and voices. Worry about the drawbacks, by all means, but don't forget the advantages too: your information should be much more secure from criminals and you'll never again have the problem of losing your keys or forgetting your password!
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