Ultrasonic fingerprint sensor: what it is, how it works and what it does

An ultrasonic fingerprint sensor is a biometric component that employs ultrasonic waves to capture and compare the topography of a finger's skin against a stored template. Unlike optical or capacitive sensors, ultrasonic technology penetrates the superficial layers of the skin, allowing it to distinguish a genuine fingerprint from a superficial replica.

Operating principle

The sensor's emitter projects an ultrasonic pulse toward the contact surface. The wave reflects with varying intensity depending on the skin's microtopography: fingerprint ridges absorb part of the energy, while valleys (grooves) reflect it with greater amplitude. A receiver converts this reflection pattern into a digital image that is matched against the fingerprint registered during initial setup.

Under-display integration

In current mobile devices, the ultrasonic sensor is located in the screen, i.e., beneath the touch panel. This arrangement eliminates the need for a dedicated physical button and preserves the visual continuity of the surface. The user places a finger on the designated area of the glass, and the sensor operates through the panel layers.

Operational characteristics

• Immediate unlock: reading and verification are completed in a short time, allowing direct access to the phone without complications or perceptible delays.
• Complementarity with facial authentication: the ultrasonic sensor typically coexists with a facial unlock system, offering the user two biometric access paths.
• Security: ultrasonic penetration into the skin makes it difficult to use fake or wet fingerprints, reinforcing the reliability of the unlock.

Applications

Its primary application is mobile device unlock, although the same principle is used in enterprise terminals, physical access systems, and, in some contexts, transaction authentication.

Scope and limitations

• The reading area is smaller than that of a surface-level optical sensor, so finger placement must be relatively precise.
• The presence of thick or textured screen protectors may attenuate the ultrasonic signal and degrade the recognition rate.
• The sensor requires a clean contact surface; excess grease or moisture can alter the wave reflection.

Interpretation in a product

When a device's technical sheet states fingerprint_sensor = ultrasonic under display, it indicates that the fingerprint authentication mechanism is integrated beneath the touch panel and that the manufacturer positions it as a secure and immediate access path, complementary to facial unlock. It does not, by itself, imply superior resistance to other sensor types, but rather a design choice oriented toward aesthetic integration and verification speed.

"The ultrasonic in-screen fingerprint sensor and facial unlock let you access your phone directly, without complications or delays."

Source: product feature description, amazon.es (confidence 0.95).