| US 7,567,690 B2 | ||
| Method of determining the living character of an element carrying a fingerprint | ||
| Jean-Christophe Foundeur, Levallois-Perret (France); Joel-Yann Fourre, Couveciennes (France); and Laurent Lambert, Paris (France) | ||
| Assigned to Sagem Securite, Paris (France) | ||
| Appl. No. 10/539,822 PCT Filed Dec. 19, 2003, PCT No. PCT/FR03/03803 § 371(c)(1), (2), (4) Date Feb. 03, 2006, PCT Pub. No. WO2004/061757, PCT Pub. Date Jul. 22, 2004. |
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| Claims priority of application No. 02 16735 (FR), filed on Dec. 20, 2002. | ||
| Prior Publication US 2006/0140456 A1, Jun. 29, 2006 | ||
| Int. Cl. G06K 9/00 (2006.01); G06F 7/04 (2006.01) | ||
| U.S. Cl. 382—124 [382/115; 340/5.52; 340/5.53; 340/5.82; 340/5.84] | 9 Claims |
| 4. A fingerprint sensor adapted to determine a living character of a finger carried by a person, the sensor comprising:
(a) at least four electrodes, wherein at least two of the said at least four electrodes have smaller surfaces than the other
two of the said four electrodes with larger surfaces;
(b) means for measuring impedances at least between on the one hand, two electrodes with smaller surfaces and on the other
hand, two electrodes with larger surfaces;
(c) means for determining one curve among several curves, each of said several curves satisfies a law of variation of an impedance
Z measured by said two electrodes with smaller surfaces or by said two electrodes with larger surfaces, as a function of the
surface area (S) of the electrodes covered by the fingerprint of a finger at a time t, that is, Z=fDt(S), said one curve being determined by selecting the curve containing the point with the coordinates (first predetermined
surface area, measured impedance); and
(d) means for checking that the point defined by the unselected surface area and the other unselected impedance measurement
values belongs to an area of tolerance situated around said one curve.
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