Fingerprint Cards turns to mirrors in a new biometric in-display sensor patent

Fingerprint Cards has received a U.S. patent for an optical biometric sensor with angled mirrors imbedded in an active portion of a display.

The design gets more biometric information from fingerprints in the form of greater resolution using a display that has a protective glass or transparent epoxy layer. That layer is a common feature on portable devices like phones and watches, but also on access control systems.

Most of those devices have capacitive biometric sensors, which have been adequate to most identification tasks to date. The problem is that capacitive sensors require close proximity to the surface of a fingerprint in order to record the ridges and whorls with the higher fidelity that is increasingly required.

Even the thin protective layer used on electronic devices reduces a capacitive sensor’s effectiveness.

Fingerprint Cards’ patent gets around the problem of excess depth between a fingerprint and the sensor by collapsing that distance using mirrors.

Light illuminating a fingerprint bounces off the skin’s surface down through apertures to two sets of extremely small, angled mirrors. In some configurations of the patented device, LCD backlight is enough to do the illumination. A secondary source, though, is also described in the patent.

The apertures can be set among LCD components, but in at least one option, the apertures are more or less free floating. In this case, the biometric sensors are set among the LCD components.

The first mirrors reflect light rays at a 90-degree angle across the layer in which the sensors are set to the second set of mirrors, which bounce the rays at a 90-degree angle down to sensors.

This design gives a sensor a longer focal length without having to increase the distance between the sensor and the subject — the fingerprint.

Novel fingerprint feature extraction and subject positioning patents

Two other biometric patent applications from Fingerprint Cards, for ‘single-feature fingerprint recognition’ and an ‘authentication method for an electronic device’, have also been published by the USPTO.

The first is an attempt to match features beyond minutiae for less complex fingerprint matching algorithms, while the second describes a system for using finger-position as a means of enhancing protection against biometric spoof attacks.

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