Patent ID: 7848798
Filing Date: 2010-12-07
Classification: A61B,G06K

Abstract:
1. Sensor assembly for determining the condition of a structure, especially for confirming if a measured fingerprint is on a live finger, by measuring characteristics of close to the structure surface, the sensor comprising: a current source; at least four electrodes at chosen positions relative to each other, said positions providing at least two relative distances between the electrodes, wherein a chosen first pair of said at least four electrodes constitutes current supply electrodes, and a chosen second pair of said at least four electrodes constitutes pickup electrodes, and of which at least one does not constitute a current supply electrode; a measuring instrument coupled to said at least four electrodes for measuring the impedance between said chosen pair of pickup electrodes for providing a value characterizing the structure; wherein said sensor is adapted to store a predetermined set of values characterizing a chosen condition for said structure; wherein said sensor is adapted to compare said characteristics from each of said at least one pair of pickup electrodes with said set of predetermined values for detecting if said structure is in a certain condition, and the sensor assembly is adapted to alternating coupling of at least one current supply and measuring instrument to different electrode pairs with different distances between them, for measuring characteristic values at different depths in said structure; and wherein the supplied current is oscillating within a chosen frequency range and said sensor is adapted to measure the impedance at each pickup electrode and to compare the imaginary and real parts of the impedance signals as functions of the applied frequency, by determining the slope of the resulting curve, and to compare this slope with a predetermined set of slopes indicating a live finger.