If You’re into The Movie Industry, You’re Well Aware That Fingerprint Sensors Have Been Used for Decades As An Oddball Technology In Thrillers; until A Few Years Ago, They Were Only Used In Products Used In Military Facilities. 

Gradually, these fingerprint sensors made their way to police stations and buildings that required high security, and they were even used in some keyboards of laptops and smartphones.

Nowadays, these sensors are also used in not-so-expensive phones, and in some consumer products such as tablets and smartphones, these sensors have been used under the screen.

Today, security experts use fingerprint sensors to improve the security level of a building, which are ready-made devices that can be deployed in companies.

These devices receive people’s fingerprints in different ways. For this reason, you should have general information about their performance when using or purchasing them.

In this article, we will briefly examine this issue, and at the end, we will discuss the advantages and disadvantages of these security systems.

Each person’s fingerprint is unique.

The fingerprint is one of nature’s complex and strange designs, so the fingerprints of no two people in the world are the same. Even twins have their fingerprints.

This is why security experts describe fingerprints as the internal identification card of humans, which can be easily used. Fingerprints are known as small ridges of skin that are located on the fingers and have never been removed from the structure of the human body because the pattern of peaks and valleys on the fingers makes it easier to use objects and hold them in hand.

In the same way, the tire’s tread pattern helps the tire stick to the road surface better.

Similar to different organs in the human body, these bumps are formed through a combination of genetic and environmental factors. The genetic code in the DNA specifies the general instructions for how the skin is created. Still, these ridges form entirely randomly, so people’s fingerprints differ.

Although the genetic code in DNA gives cells general instructions on how to form the skin while the embryo is developing, as we mentioned, how these ridges form is based on random events, in addition to countless factors that contribute to the formation of a unique fingerprint, many environmental parameters influence its shape.

Just like certain weather conditions that shape clouds into different structures, the process of fingerprint formation and development is so irregular that there has never been a chance for an exact pattern to form twice in human history.

Recognizing fingerprint analysis has formed the foundation of criminology and information security research. As a result, fingerprints are unique for each human being, and even identical twins do not have identical fingerprints.

In a situation where the development of printing two fingerprints may look the same at first glance, expert security experts and people who work in digital criminology can use advanced software to identify the clear and distinct differences in fingerprints.

More specifically, a fingerprint scanner collects print samples and compares them to the recorded pieces, acting as an analyzer to distinguish different fingerprints.

On what technique do optical fingerprint sensors work?

Fingerprint scanning systems perform this critical process based on two primary techniques. First, they take an image of your finger and determine whether the pattern of ridges and valleys in the fingerprint image matches the fingerprint pattern in the previously scanned images.

There are different ways to take a picture of someone else’s finger. The most common solutions used by security companies and smartphone manufacturers are optical scanning and capacitance scanning. Both technologies provide the same result but do so in different ways.

At the heart of an optical sensor is a CCD charge-coupled device, the same optical sensor system used in digital cameras and video recording. A CCD can be an array of light-sensitive diodes called photosites that produce electrical signals in response to light photons.

During this process, each photocell of a pixel records a small point representing the light that hit that point, and in total, the bright and dark pixels form an image of the scanned area (for example, a fingerprint).

Scanning begins when you place your finger on a unique glass screen so that a CCD camera captures the fingerprint. In general, scanners have their light source, usually light-emitting diodes illuminating the bumps on the finger.

The CCD system creates an inverted image of the finger, with darker areas representing more reflected light (finger ridges) and lighter areas representing less reflected light (valleys between ridges). However, before comparing the scanned image with the previously stored data, the scanner processor must ensure that the CCD has captured a clear picture.

Next, the processor checks the average dark pixels or overall values ​​in a small sample and rejects it if the image is too dark or bright. If the idea is rejected, the scanner adjusts the exposure time so the light enters better. Next, it repeats the evaluation process until the person approves the image.

If the surface is dark, the scanner system determines the image resolution limit for the clarity of fingerprint scanning. Then the processor performs the image scanning process in several straight lines horizontally and vertically. If the fingerprint image is of good resolution, the lines perpendicular to the ridges of the fingerprint show alternating sections of dark and light pixels.

All these processes are done in less than a minute, and if the fingerprint is approved (in the entry and exit system or on the phone), everything goes according to the user’s wishes.

What is the working mechanism of capacitive fingerprint scanners?

Like optical scanners, capacitive fingerprint scanners create an image of the ridges and valleys that make up the fingerprint. However, capacitors use electric current instead of light. These sensors consist of one or more semiconductor chips that have a set of small cells. Each cell in semiconductor chips consists of two plates covered with an insulating layer.

These cells are as wide as a fingertip. The sensor is connected to an integrator circuit, an electrical circuit wrapped around an inverting operational amplifier. The inverting amplifier is a complex semiconductor device with several transistors, resistors, and capacitors.

The functional details of this device itself are a detailed and complete article. But here, for a clear understanding of the performance of fingerprint sensors, provide a simple explanation to obtain a capacitor.

Like any amplifier, an inverting op-amp changes current based on other current fluctuations.

In other words, this amplifier changes the supply voltage of the device. This change is based on the relative voltage of the two inputs, which are the inverting terminal and the non-inverting terminal.

In this case, the non-inverting terminal is connected to the ground, and the inverting terminal is connected to the primary voltage source and the feedback circuit. The feedback loop, which is also connected to the output of the amplifier, consists of two conductor plates.

As you may have noticed, two conductive plates form a primary capacitor, an electrical component capable of storing charge. The finger surface acts as a third plate capacitor separated by insulating layers from the cell structure for the ridges and by air voids for the depressions.

Changing the distance between the plates of the capacitor (by moving the finger closer or further away from the conductive plates) changes the total capacity of the capacitor (the ability to store charge). For this reason, the capacitor under the finger’s ridges has a greater degree than the capacitor under the depressions.

For fingerprint scanning, the processor first closes the reset switch for each cell to short the input and output of each amplifier and balance the integrator circuit. The capacitors are charged when the button is opened again, and the processor applies a constant load to the integrator circuit.

The capacitor capacity of the feedback circuit affects the amplifier’s input voltage and the amplifier’s output voltage.

Since the distance between the sensor plate and the finger is a factor in changing the capacitance of the capacitor, the ridges on the finger lead to a different voltage output than its depressions.

In this case, the processor of the capacitor scanner reads this voltage output and determines the peak or trough voltage. By reading all the voltages in an array of sensor units, the processor can piece together an overall picture of the fingerprint, similar to an image captured by an optical scanner.

The main advantage of the capacitive fingerprint sensor is that instead of the light and dark pattern that visually creates an image of the fingerprint, it captures and makes the fingerprint.

This makes the process of tricking the scanner more difficult. Also, since a semiconductor chip is used instead of a CCD unit, capacitive scanners are more compact and smaller than optical fingerprint sensors.

What is the process of analysis and review used by scanners?

In movies and TV series, you’ve probably seen that automatic fingerprint analyzer sensors usually overlay different fingerprint images to find a match for a specific fingerprint.

However, the above method is not an accurate mechanism for comparing fingerprints, as a minor blemish can make two images look the same. Because of this, you rarely get a completely accurate picture of a fingerprint.

In addition, using the whole fingerprint image in comparative analysis requires a lot of processing power, which causes the battery of mobile devices to drain quickly.

In contrast, most fingerprint scanner systems compare specific features of fingerprints, commonly known as details. And in general, researchers or innovative software focus on the points in the fingerprint where the ridge lines end or where a ridge splits into two parts.

Then, in general, this set of distinctive features is sometimes called typical. Scanner software uses complex algorithms to identify, analyze and analyze these details.

The main idea is to use the relative positions of the artifact with the details inside that help to analyze the data better. The main idea is to measure intimate parts and points like we use the stars in the sky for positioning.

To obtain a match, the scanner system does not need to find the entire detail pattern in the received and recorded samples but only a sufficient number of delicate prints repeated in both images.

What are the advantages and disadvantages of fingerprint sensors?

There are several ways that a security system can verify the identity of a person trying to enter a system. Most of the systems confirm or reject the identity of people based on the following three questions.

•  what do you have
•  what do you know
•  who are you

To get through the “what have you” system, you’ll need some “token,” which could be an ID card with a magnetic stripe. A “who are you” design looks for physical evidence that you are who you claim to be through a fingerprint, voice, or iris pattern. The “What do you know” system will ask you to enter a password or PIN.

“Who are you” systems, such as fingerprint scanners, have significant advantages over other methods, the most important of which are the following:

•  Their physical characteristics are more difficult to forge than systems based on identity cards.
•  You cannot guess the fingerprint pattern, but it is possible to think of the password.
•  You can’t forget your fingerprint, which is the case with the password.

Although the above systems are efficient, they are not infallible and have disadvantages. Optical scanners cannot always distinguish between a fingerprint and the finger itself, and capacitive scanners can sometimes be fooled by a template made from an individual’s fingerprint.

If someone can access 3D printers and obtains a user’s fingerprint, they can fool the scanner. Some scanners have additional pulse and thermal sensors to check if the finger is real or fake, but such systems can also be fooled by printing fingerprints on gelatin.

To make these security systems more reliable, combine biometric analysis with a standard identification tool such as a password (in the same way, an ATM requires a bank card and a PIN code).

The main problem with biometric security systems is when someone steals identity information. If you lose your credit card or accidentally tell someone your secret PIN, you can always get a new card or change your code.

On the other hand, if someone steals your fingerprints, you’re done with nothing. Despite the disadvantages we mentioned, fingerprint scanners and biometric systems are excellent tools for identification. They will likely become an integral part of people’s daily lives, just like keys, ATM cards, and passwords are today.