Ultrasonic fingerprint sensor: how it beats an optical one

An ultrasonic fingerprint sensor is an in-display sensor that reads your fingerprint pattern with ultrasound and builds a 3D map of it. It is faster and more reliable than an optical one, especially with wet fingers.

Ultrasound reads the ridges of a finger

In plain words

An optical sensor is like a photographer taking a picture of your finger through backlit glass: it works, but water drops and bright sunlight get in the way. An ultrasonic one is like a ship's sonar that "sees" the seabed with sound: it feels the ridges and valleys of your finger even through drops of water or dirt.

How it works

An ultrasound emitter plate sits under the screen.
It sends sound waves up through the glass to your finger.
The ridges and valleys of the pattern reflect the sound differently.
The sensor builds a 3D map of the fingerprint.
The system compares it with the saved template and unlocks the phone.

An ultrasonic sensor works like sonar

Where you'll see it

Ultrasonic sensors are used in Samsung Galaxy S flagships and some models from other brands (notably those using Qualcomm 3D Sonic sensors). Optical ones are in most mid-range phones. Side-mounted capacitive ones sit in the power button of budget and rugged models.

Does it matter when buying

Moderately. Side-mounted capacitive sensors in the button are also fast and reliable. An ultrasonic sensor works better with wet hands and does not light up your finger with a bright flash at night. A screen protector can interfere with an ultrasonic sensor - choose a compatible one.

Myths

Myth: An in-display sensor is always worse than a button. Reality: Ultrasonic models are as fast as side-mounted ones.
Myth: Ultrasound is dangerous. Reality: The power is tiny and safe.

FAQ

Why does the sensor not work with my new screen protector?

Thick glass or bubbles block the ultrasound - you need a compatible protector.

Which is more secure - fingerprint or face?

A fingerprint is more secure than face recognition with a regular camera; 3D face scanning is comparable.

Can an ultrasonic sensor be fooled?

It is much harder than with an optical one, because it sees the ridges.