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What is fingerprint scanning technology and how does it work

With technology literally at our fingertips now, fingerprint scanning technology is more relevant now than ever before. A close look at what this technology entails…

How does fingerprint scanning technology work and how has it revolutionised our lives today.

Nov 12, 2019    By Team YoungWonks *

At a time when smartphones have become omnipresent, it is indeed interesting to note how fingerprint scanning has come to be an increasingly important feature in many of these phones. So in this blog, we shall look at what fingerprint scanning technology is all about and how we have to come to depend on it mainly thanks to its use in our smartphones and even laptops/ computers. 

 

What is a fingerprint

Before we delve into this subject, let’s start by looking at what is a fingerprint.  

A fingerprint refers to an impression left by the friction ridges of a human finger. They are easily deposited on surfaces like glass or metal or polished stone by the natural secretions of sweat from the eccrine glands that are present in epidermal ridges. Deliberate impressions of fingerprints can be formed by ink or other substances and passed on to a relatively smooth surface such as a fingerprint card. Usually, fingerprint records contain impressions from the pad on the last joint of fingers and thumbs, though fingerprint cards also typically record portions of lower joint areas of the fingers. 

Human fingerprints are detailed, nearly unique, difficult to change, and remain the same over the life of an individual, making them ideal long-term markers of human identity. This is why they are used for identification purposes. Not only are fingerprints used by police and other authorities to identify individuals, but today’s  fingerprint scanning technology has also made it possible for smartphones, laptops and several other gadgets to identify their rightful users. 

 

What is a fingerprint scanner 

Broadly speaking, fingerprint scanners are security systems of biometrics (the field of study which aims to identify or recognise people based on traits they have). As mentioned above, fingerprints are rather unique and hence, they are used to unlock doors and in other security applications where access is controlled and monitored closely. During the 2010s, fingerprint scanners became a common feature on mobile phones. Nowadays, they are also being used in laptops. 

 

How fingerprint scanning technology works

Fingerprint image acquisition is the most important step in an automated fingerprint authentication system, as it assesses the final fingerprint image quality, which has a crucial impact on the overall system performance.The question then is how is this fingerprint assessed? The answer is: using fingerprint sensors that these scanners come fitted with.  

A fingerprint sensor is an electronic device used to capture a digital image of the fingerprint pattern. The captured image is called a live scan. The live scan is digitally processed to come up with a unique biometric template (a collection of extracted features) which is stored and used for matching. Once this is done, there are matching algorithms that are used to compare these previously stored templates against candidate fingerprints for authentication purposes. In order to do this either the original image must be directly compared with the candidate image or certain features must be compared.

Today, there are different types of fingerprint readers in the market, but the basic idea behind each is to measure the physical difference between ridges and valleys of the fingerprint and thus ascertain an individual’s identity.

 

a. Optical fingerprint scanners 

These are the oldest method of capturing and comparing fingerprints. Like the name suggests, an optical fingerprint scanner dwells on capturing an optical image, basically a photograph, and uses algorithms to identify unique patterns on the surface, such as ridges or unique marks, by analyzing the lightest and darkest areas of the image.

Like smartphone cameras, these sensors have a finite resolution, and the higher the resolution, the finer details the sensor can detect about a finger, increasing the level of accuracy and thus, security. However, these sensors capture much higher contrast images than a regular camera. They usually have a very high number of diodes per inch to capture these details up close. Also, because it’s dark when the finger is placed on the scanner, the optical scanner incorporates arrays of LEDs as a flash to light up the picture while scanning. The problem with this though is that this design is bulky for smartphones, which typically tend to be rather slim. Another drawback is that optical scanners are easy to cheat. Since the scanner is only capturing a 2D picture, prosthetics and other pictures of good enough quality can be used to work around this technique of detection. So these scanners aren’t secure enough to trust our most sensitive details with. This is also why they are slowly being phased out now. 

 

b. Capacitive scanners

Capacitive scanners are the most commonly used type of fingerprint scanners. As the name suggests, the capacitor is the key component here. Capacitive fingerprint scanners use arrays of small capacitor circuits to collect data about a fingerprint as opposed to creating the traditional image of a fingerprint. Since capacitors can store electrical charge, one can track the details of a fingerprint by connecting them to conductive plates on the surface of the scanner. The charge stored in the capacitor will change a bit when a finger’s ridge is placed on the conductive plates, and an air gap will leave the charge at the capacitor relatively unchanged. The changes are tracked with an op-amp integrator circuit and then recorded by an analog-to-digital converter.  Once captured, the digital data can be examined to look for distinctive fingerprint attributes, which can be saved for comparison at a later date. The results here can’t be copied with a photo and it’s quite tough to cheat with a prosthetic too, given that different materials will record slightly different changes in charge at the capacitor. 

So it is important to note that these scanners are not easy to fool; in fact, they are found inside most smartphones these days, as they are the most secure. The only real security risks then are hardware or software hacking. Bear in mind that having a big enough array of these capacitors - usually hundreds if not thousands in a single scanner - helps it come up with a highly detailed image of the ridges and valleys of a fingerprint using just the electrical signals. And like the optical scanner, more capacitors make it a higher resolution scanner, thus enhancing the level of security. 

These scanners were quite expensive until recently mainly due to the larger number of components in the detection circuit. Some early versions reduced the number of capacitors required by using “swipe” scanners, which would gather data from a smaller number of capacitor components by quickly refreshing the results as a finger is pulled over the sensor. But this method was not reliable and needed many attempts to scan the result correctly. These days though, the simple press and hold design is way more popular. Not only can we read fingerprints with these scanners, but the new models boast gesture and swipe functionality as well. These can be used as soft button support to act as navigation keys, force sensing capabilities, or as a way to communicate with other UI elements. Many higher-end smartphones have a wider variety of swipe and navigation features using their fingerprint scanners, and this technology is expected to become cheaper over time. 

 

c. Ultrasonic scanners

They are the latest fingerprint scanning technology in the smartphone space with the Le Max Pro smartphone being the first one to declare that it was using it in their models. Another key part of the design in these phones are  Qualcomm and its Sense ID technology. Here the hardware capturing the details of a fingerprint consists of both an ultrasonic transmitter and a receiver. An ultrasonic pulse is transmitted against the finger that is placed on the scanner. While some of the pulse is absorbed, some is bounced back to the sensor, as per the ridges, pores and other details unique to each fingerprint.

Now there is no microphone listening to these returning signals, but there’s a sensor recognising mechanical stress that calculates the intensity of the returning ultrasonic pulse at different points on the scanner. Scanning for longer periods of time means that additional depth data can be captured, resulting in a highly detailed and more accurate 3D reproduction of the scanned fingerprint. The 3D nature of the capture technique makes it an even more secure alternative. 

In December 2018, Qualcomm announced its 3D ultrasonic in-display fingerprint sensor; it been used inside Samsung’s flagship Galaxy S10 and Galaxy S10 Plus. On one hand, these scanners are ideal as they can be hidden easily under the display, thus allowing for thinner-than-ever-before bezels in these phones. The problem, however, is that ultrasonic scanners are not as quick as other scanners, not as yet. Ultrasonic technology also doesn’t always work well with some screen protectors, which can in turn restrict the scanner from reading fingerprints correctly. Plus, since ultrasonic scanners are hidden under the display, the waves have to travel through the display’s backplane, glass, and protective cover before reaching the finger. Adding extra layers, such as a screen protector can thus hinder the technology from working correctly. The good thing, however, is that the sensor can be placed elsewhere by the manufacturer and doesn’t need any special display production techniques; except for making sure the panel is thin enough for the detection to happen. 

 

d. Optical-capacitive scanners

Like ultrasonic fingerprint scanners, here too the sensors doing the scanning are hidden in the display. But the optical part requires line-of-sight in order to the lit up the space around your finger. So this technique can work only with OLED displays, where there are gaps in the backplane. Of course, it is still more secure than a basic optical scanner, since a capacitive measurement is detecting if and when a real finger is being pressed up next to the screen. Moreover, one can also scale up the scanner size, providing a much bigger area in which to detect your fingerprint.

 

Uses of fingerprint scanning technology

Fingerprints were used as signatures in ancient Babylon in the second millennium BCE. By 246 BCE, Chinese officials were impressing their fingerprints into the clay seals used to seal documents. By 650, the Chinese historian Kia Kung-Yen stated that fingerprints could be used as a means of authentication. In fact, a Fingerprint Bureau was set up in Kolkata, India, in 1897, in order to use fingerprints for the classification of criminal records. Across the world, fingerprint evidence is key to solving a crime. 

Today, fingerprint scanners have become quite a secure alternative to remembering  several usernames and passwords. Two of the first smartphone manufacturers to include fingerprint recognition in their phones were Motorola with the Atrix 4G in 2011, and Apple with the iPhone 5S on September 10, 2013. In addition to fingerprint access on smartphones, fingerprints are being used for validating overall electronic registration, to provide access to office spaces, cashless catering and even library access. Since the year 2000, electronic fingerprint readers are being used for security applications such as log-in authentication for the identification of computer users. In 2006, fingerprint sensors became a popular feature in the notebook PC market. Built-in sensors in laptops, such as ThinkPads, VAIO, HP Pavilion and EliteBook laptops, and others also work as motion detectors for document scrolling, like the scroll wheel.

 

Advantages and disadvantages of fingerprint scanning technology

Fingerprint scanning technology has several advantages. For one, it allows fast and easy one-finger access to unlock devices. As mentioned earlier, it is a good way to identify unique individuals and it is not easy to fake fingerprints and break the system. Also, unlike your signature, you can’t forget your fingerprint. 

But at the same time, there are a few disadvantages. It is tough to crack the system but fingerprint identification is not completely foolproof. Also, if someone has got finger injuries, then they can interrupt successful fingerprint scanning and can deny access and cause confusion among authorized users. Dirty fingers (and germs) can interfere with the scanning of the fingerprint. Especially in the manual labour industry where employees work with their hands, their fingers may get rough or scratched which could lead to a misinterpretation/ misreading. Similarly, if an employee has not placed his/ her fingerprint in the right spot, the fingerprint scanner can get confused and incorrectly reject the employee’s fingerprint.

Optical scanners can’t always tell the difference between a picture of a finger and the finger itself, and capacitive scanners can be fooled by a mold of a person’s finger. Even the scanners that have additional pulse and heat sensors to verify if the person who the finger belongs to is alive, can be fooled by a gelatin print mold over a real finger. To make these security systems more reliable, it is recommended to combine the biometric analysis with a conventional means of identification, such as a password (in the same way an ATM requires a bank card and a PIN code). 

The cost of the hardware and software needed for efficient fingerprint scanning is not exactly low; although it is expected to become much cheaper in the coming days. 

Another factor is if your prints get stolen. Now if we lose our credit card or accidentally tell somebody our secret PIN number, we can still get a new card or change our code. But if somebody steals our fingerprints, it’s trickier than that. For one, we wouldn't be able to use our prints as a form of identification until we have made sure all copies have been destroyed. This is particularly true when it comes to official / government records. 

 

Road Ahead 

Taking the fingerprint recognition one step ahead, some gadgets (read iPhones and Windows laptops) and security systems also have facial recognition. This is a technology capable of identifying or verifying a person from a digital image or a video frame from a video source. There are multiple ways in which facial recognition systems work, but in general, they work by comparing selected facial features from given visual with faces within a database. Although it is contactless and non-invasive when compared to fingerprint scanning, its accuracy as a biometric technology is lower than fingerprint recognition. 

It can also be rather cumbersome to use especially on mobile phones. For instance, when the user is driving, accessing/ unlocking the phone with facial recognition requires one to keep the phone directly in front of one’s face and this can distract the user while driving as opposed to fingerprint access which is relatively easier to achieve in such a situation. 

On the other hand, incorporating facial recognition in office laptops is far more productive as they are typically opened and worked upon on flat surfaces and typically have only one user. 

 

*Contributors: Written by: Vidya Prabhu / Lead image by: Leonel Cruz

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