[Explained] Optical vs Ultrasonic In-Display Fingerprint Scanner

by: - Last updated on: July 30th, 2019

Fingerprint scanners on smartphones have gone mainstream over the past few years. They are now not just limited to the top-of-the-line smartphones but are also available on the mid-range and budget smartphones.

A possible reason for this has to do with the improvements in technology in recent years. This has, eventually, made it easier for smartphone manufacturers to implement fingerprint scanners on entry-level smartphones. From the very first optical-type fingerprint scanners to the capacitive to the newest of the lot, in-display fingerprint scanners, there is a lot that has changed and improved, with the basic idea behind the technology being the same.

Optical vs Ultrasonic in display fingerprint scanner

In this article, we take a look at two of the most commonly used types of in-display fingerprint scanners on smartphones — Optical vs Ultrasonic in-display fingerprint scanners.

If you are an Android smartphone user, chances are that you have already heard about the ‘in-display’ fingerprint scanning technology found on most smartphones these days. The traditional (Capacitive) fingerprint scanning technology popular in the early days of inception requires a separate module on the device (either in the home/power button or on the back). But an in-display fingerprint scanner does not have such requirements. Instead of having a module attached or built-in to any other hardware component on the device, it has the scanner located in/under the display. And therefore, the name.

Optical In-Display Fingerprint Scanners

Optical in-display fingerprint scanners capture a 2D image of the fingerprint and use it later for comparison at the time of authentication. The captured image must be a high-resolution image with sharp details highlighting the lighter and darker regions of the fingerprint. This image would eventually allow for an accurate depiction of the fingerprint with unique patterns of ridges and lines. For this reason, the scanner requires a backlight to illuminate the darker regions of the fingerprint. This also helps to capture the details clearly in high-resolution, and create an accurate depiction of the fingerprint. If you use a smartphone that uses Optical in-display fingerprint scanner, you should notice a light emerging out of the display when you register your fingerprint for the first time or use it to unlock your smartphone.

optical in display fingerprint scanner

A major drawback with optical in-display fingerprint scanners is that they cannot be implemented on LCD-based displays. This is because LCDs require a backlight to light up the pixels, which obstructs the scanner and makes it difficult to capture an accurate image of the fingerprint. However, its implementation is far easier on LED-based displays, as these displays light up themselves and do not require a backlight.

Ultrasonic In-Display Fingerprint Scanners

In Ultrasonic in-display fingerprint scanners, an ultrasonic sound wave is used to capture a detailed image of the fingerprint. Unlike the Optical in-display fingerprint scanner that captures a 2D image of the fingerprint and requires an additional backlight to capture details of darker regions, ultrasonic in-display fingerprint scanners manage to capture a more detailed 3D depiction of the fingerprint. For this, they use a combination of an ultrasonic transmitter and receiver, which transmits and receives the ultrasonic waves and in-turn helps in capturing a detailed image of the fingerprint.

ultrasonic in display fingerprint scanner

Let me give you a rundown of the process. The ultrasonic transmitter initially transmits an ultrasonic wave on to the fingertip resting on the scanner. And, as soon as this wave strikes the finger, a part of it is reflected, while the remaining is transmitted further. The reflected ultrasonic wave is then picked up by the ultrasonic receiver. Depending on the intensity of the pulse, the receiver generates a 3D depiction of the fingerprint in high-resolution, along with its depth data. The reason for the change in intensity of the pulse has to do with the presence of ridges and pores on the finger, and the ultrasonic receivers do a good job at depicting the changes accurately, by analyzing the mechanical stress put on the sensor.

Comparison

When compared with the Optical in-display fingerprint scanner, the Ultrasonic in-display scanning technology does appear a bit slow. This is both during registering and authenticating a fingerprint. However, that is considering the existing implementation of ultrasonic scanners on smartphones like Samsung Galaxy S10. With the current rate of improvements and developments in technology, it is likely that an improved version of the ultrasonic in-display fingerprint scanner with faster unlock speeds and increased security should soon appear on a smartphone. Qualcomm is one of the pioneers when it comes to Ultrasonic fingerprint tech and they insist that the tech is getting faster.

The delay in registering and authenticating, which appears to be a drawback of the Ultrasonic scanner, also happens to be one of its plus points. As the delay in the process has to do with the kind of accuracy and precision that the scanner has to offer. The Ultrasonic in-display fingerprint scanner captures a more detailed, accurate, and a 3D depiction of the fingerprint. While the 2D image of the Optical scanner lacks sufficient details and its related data. It is this lack of details in Optical scanners that make it comparatively less secure than Ultrasonic sensors. It has been proven that 2D depiction is relatively easier to fool with prosthetics or a high-resolution 2D image, than a 3D equivalent.

Another advantage that the Ultrasonic in-display fingerprint scanners possess over their counterpart is that they can be installed under thick glasses (and even metals), which increases their application and the scope of use, in the future.

Conclusion

On comparing both, the Ultrasonic in-display fingerprint scanning tech comes out on the top. Mainly because it captures the 3D image of the fingerprint, which is more accurate and secure over the 2D image captured by the Optical in-display fingerprint scanners. And although the process of registering and authenticating fingerprints on Ultrasonic scanners is not quite there yet, it is not far away from being a more reliable and faster authentication mechanism.

Despite the advantages and the growing popularity of Ultrasonic in-display fingerprint scanners, the Optical in-display scanners are not going away anytime soon and will be seen on smartphones in the future, especially the low-budget smartphones. A possible reason for which could be that, with the current scenario and the state of technology, implementing a reliable Ultrasonic in-display fingerprint scanner on low-budget smartphones does not seem feasible for a lot of smartphone manufacturers.

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