Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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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
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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.
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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.
