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Ultrasonic fingerprint scanners: how do they work?
After a few years lurking in backroom prototypes and inside a few quickly forgotten handsets, ultrasonic fingerprint sensors are ready for prime time. The technology is built into Samsung’s flagship Galaxy S10 and Galaxy S10 Plus, making the technology almost guaranteed to be securing millions of thumbprints by the year’s end.
In December 2018, Qualcomm announced its 3D ultrasonic in-display fingerprint sensor. This technology is enabled in devices using the company’s Snapdragon 855 platform as an option if the manufacturer wants to include the extra hardware. Ultrasonic fingerprint technology has its own pros and cons versus traditional capacitive scanners and even other in-display fingerprint designs. Here’s everything you need to know.
How ultrasonic fingerprint scanners work
Qualcomm’s 3D in-display ultrasonic fingerprint scanner is based on what used to be called Sense ID. Rather than existing photographic or capacitive-based fingerprint scanners, ultrasonic fingerprint scanners make use of very high-frequency ultrasonic sound. You can’t hear it, but these waves are used to map out the details of the user’s fingerprint. Fortunately, there’s no need to swipe, just touch the finger to the sensor like the top of the line capacitive fingerprint scanners.
To actually capture the details of a fingerprint, the hardware consists of both a transmitter and a receiver. An ultrasonic pulse is transmitted against the finger that is placed over the scanner. Some of this pulse’s pressure is absorbed and some of it is bounced back to the sensor, depending upon the ridges, pores and other details that are unique to each fingerprint.
There isn’t a microphone listening out for these returning signals. Instead, a sensor that can detect mechanical stress is used to calculate the intensity of the returning ultrasonic pulse at different points on the scanner. Scanning for longer periods of time allows for additional depth data to be captured, resulting in a highly detailed 3D reproduction of the scanned fingerprint.
Qualcomm notes that there’s about a 250-millisecond latency for unlocking, roughly equivalent to capacitive fingerprint scanners. The sensor has about a 1 percent error rate, which again is pretty comparable to other scanners.
Pros of ultrasonic fingerprint vs capacitive scanners
Ultrasonic fingerprint technology works very differently to capacitive fingerprint scanners, which are only able to reproduce 2D images. 3D details are much more difficult to forge or fool than a 2D image, making the ultrasonic system much more secure. It goes without saying that ultrasound is also much more secure than optical fingerprint scanners, which have all but fallen out of favor.
In-display scanners like those inside the OnePlus 6T and Huawei Mate 20 Pro are optical not ultrasonic.
Another added perk of this ultrasonic fingerprint scanner technology is that it allows the fingerprint scanner to still operate through thin materials, such as glass, aluminum, or plastic. The sensor is just 0.15 millimeters thick and can scan through up to 800 µm of glass and up to 650 µm of aluminum. Therefore, the scanner can be embedded under the case or under the display as we’re seeing in the Samsung Galaxy S10, allowing for a more discrete look and thinner bezels.
Because the sensor uses ultrasonic waves, the sensor can also double up as a health tracker that can record heart rate and blood flow. Additionally, there’s less chance of damaging the sensor or exposing it to external tampering, and sweat or moisture on the finger won’t interfere with the scanning process either.
Scanning is just half the process
Of course, there’s still plenty to be done with this fingerprint data and keeping it secure is an equally important part of the system.
As will all biometric security systems, processing and security highly sensitive personal information security are key. Qualcomm’s processors are built with dedicated security tools, including Cryptographic Accelerators, Key Provisioning Security, and a Trusted Execution Environment. This ensures that the processing and storage of sensitive data are kept well away from malicious applications. Other Arm-based processors offer TrustZone hardware isolation for similar levels of protection.
Qualcomm’s setup is also designed to support the Fast Identity Online (FIDO) Alliance protocols, which can be used for online password-less authentication. FIDO does this without transferring any of the confidential fingerprint information to the cloud or through networks that could be compromised.
Ultrasonic fingerprint scanners certainly have a number of advantages of existing capacitive implementations and given the prevalence of Qualcomm processors in mobile products. 3D ultrasonic fingerprint scanners are now ready for prime time and it’s possible that we’ll see many more manufacturers adopt this technology throughout 2019.