CA2193029A1 - Device for detecting the presence of a live fingerprint - Google Patents

Abstract

In fingerprint technology, a concern is the use of models or severed finger tipsfor unauthorized access. Herein, a fingerprint sensing device is disclosed for distinguishing images of live fingerprints from those of other images. The device has a flat surface for receiving a finger; an infrared light source for irradiating a finger placed on the surface, and, a detector for detecting the infrared light and determining a state of the imaged fingertip.

Description

- 219302g Device for Detecting the Presence of a Live Fingerprint This invention relates generally to fingerprint detection and more particularly to a device for detecting if a finger placed on a surface is a "live" finger.

Background of the Invention In a fing,~l~,linl input transducer or sensor, the finger under investigation isusually pressed against a flat surface, such as a side of a glass plate, and the ridge and o valley pattern of the finger tip is sensed by a sensing means such as an interrogating light beam.
Various optical devices are known which employ prisms upon which a finger whose print is to be identified is placed. The prism has a first surface upon which a finger is placed, a second surface disposed at an acute angle to the first surface through which the 1 S fingerprint is viewed and a third illumination surface through which light is directed into the prism. In some cases, the illumination surface is at an acute angle to the first surface, as seen for example, in US Patents 5,187,482 and 5,187,748. In other cases, the illumination surface is parallel to the first surface, as seen for example, in US Patents 5,109,427 and 5,233,404. Fingerprint identification devices of this nature are generally used to control the building-access or information-access of individuals to buildings, rooms, and devices such as computer terminals.

Another type of fingerprint capture device absent the optical components presentin the prior art, heretofore described based on illumination of the finger tip, is a device proposed in United States patent number 4,353,056 in the name of Tsikos issued October 5, 1982; Tsikos discloses an alternative kind of fingerprint sensor that uses a capacitive sensing approach. The described sensor has a two dimensional, row andcolumn, array of capacitors, each comprising a pair of spaced electrodes, carried in a sensing member and covered by an insulating film. The sensors rely upon deformation to the sensing member caused by a finger being placed thereon so as to vary locally the spacing between capacitor electrodes, according to the ridge/trough pattern of the fingerprint, and hence, the capacitance of the capacitors. In one arrangement, the capacitors of each column are connected in series with the columns of capacitorsconnected in parallel and a voltage is applied across the columns. In another arrangement, a voltage is applied to each individual capacitor in the array. Sensing in 5 the respective two arrangements is accomplished by detecting the change of voltage distribution in the series connected capacitors or by measuring the voltage values of the individual capacitances resulting from local deformation. To achieve this, an individual connection is required from the detection circuit to each capacitor.

o Both the optical and capacitive type of devices are known to perform adequately, however, in certain instances, these device can be "fooled" or circumvented. Forexample, in the instance where a suitable copy or flexible mould of a fingerprint is made, this copy can be presented to a fingerprint input device to gain unauthorised access to a system that is to be protected. In other instances a finger may be removed from an individual and used by an other, to gain unauthorised access to a highlyrestricted area or computer system. Yet in another instance, a fingerprint may unknowingly be recorded and this recorded print presented is a suitable form to an input device to gain unauthorised entry.

It is therefore an object of this invention, to provide a device that is capable of detçrrnining if a finger placed thereon, is "alive".

Summaly of the Invention In accordance with the invention there is provided a fingerprint sensing device comprising a substantially flat surface for receiving a finger;
means for detecting an image or information related to a fingerprint on said finger;
and, means for detenninin~ within predetermined limits, if said finger is a live finger.

- - -Detailed Description There are several methods to differentiate a live finger from a severed finger or a facsimile of a finger or fingerprint. For example with the use of a piezo electric sensor installed on a platen surface of a fingerprint device, one can monitor for the 5 presence of a pulse being received from a live finger. While this method may be suitable in some instances, it may be circumvented if an unauthorized user attempts to use a sonic pulse generator to mimic a real pulse from a live finger. Yet another method which overcomes this limitation, is to monitor the presence of live blood in the finger itself. This can be done by irr~ tin~ a finger with a suitable light source, o i.e. infrared light (IR) and detecting the amount of light (IR) that passes through the irradiated finger. It has been noted that skin perfused with blood is more tr~n~mis~ive than tissue which is necrotic.

Thus, this invention provides an inexpensive simple device for achieving this end. An IR source such as an LED is placed at the finger guide area of a finger print scanner. This can be done in either the optical and capacitive input devices. An IR
receiver is placed across from the emitter as shown in the accompanying figure. When a finger is placed on the platen, the infrared light emitted from the light source is scattered through the skin, causing a glowing effect. The infrared light received by the 20 collector is proportional to the infusion of blood in the fingertip.

In yet a third less preferred embodiment the CO2 emission at the skin surface may be monitored with a solid state gas monitor.

Claims (3)

1. A fingerprint sensing device comprising: a substantially flat surface for receiving a finger;
means for detecting an image or information related to a fingerprint on said finger;
and, means for determining within predetermined limits, if said finger is a live finger.

2. A fingerprint sensing device as defined in claim 1, wherein the means for determining if a finger is alive finger comprises a light source for irradiating a finger placed on the substantially flat surface; and, means for detecting some of the light that has passed through the irradiated finger.

3. A fingerprint sensing device as defined in claim 2, wherein the light source is an infrared light source, and wherein the detector is capable of detecting infrared light.