Live finger detection by four-point measurement of complex impedance
First Claim
1. Sensor assembly for determining the condition of a structure so as to confirm whether the structure is constituted by skin and living tissue, the sensor assembly comprising:
- at least four electrodes, of whichat least two electrodes constitute current supply electrodes which are connected to a current source for providing a current or voltage to said structure, wherein the current or voltage is oscillating within a chosen frequency range, andat least two electrodes constitute pickup electrodes of which at least a first pickup electrode is connected to a measuring instrument for measuring at least one parameter value relating to the impedance of the structure; and
wherein said sensor assembly is adapted to alter which electrodes constitute current supply electrodes and/or which electrodes constitute pickup electrodes between different measurements so as to alter the distance(s) between the current supply electrodes and/or the pickup electrodes to thereby alter the depths of the structure at which the measurements are performed;
wherein said sensor assembly is further adapted to (1) store a predetermined set of values characteristic of at least one certain condition of the structure, and (2) compare the at least one measured parameter value with the predetermined set of values for determining whether the structure is in said certain condition;
wherein said sensor assembly is adapted to measure the impedance at each pickup electrode, andwherein said sensor assembly is adapted to compare imaginary and real parts of impedance signals as functions of the applied frequency.
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Accused Products
Abstract
A method and sensor assembly for determining the condition of a structure, especially for confirming if a measured fingerprint is on a live finger, measures characteristics of close to the structure surface. The sensor includes a first pair of current supply electrodes coupled to a current source, providing an electrical current to the skin, at least two pickup electrodes at chosen and different positions relative to the current supply electrodes, at least a first of the pickup electrodes being coupled to an instrument for measuring the voltage between the first pickup electrode and at least one of the pickup or current supply electrodes, storage for a predetermined set of values characterizing a certain condition of the surface, and means for comparing the characteristics from each pickup electrode with the measurements of the other pickup electrodes and with the predetermined set of characteristics for determining the surface condition.
15 Citations
6 Claims
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1. Sensor assembly for determining the condition of a structure so as to confirm whether the structure is constituted by skin and living tissue, the sensor assembly comprising:
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at least four electrodes, of which at least two electrodes constitute current supply electrodes which are connected to a current source for providing a current or voltage to said structure, wherein the current or voltage is oscillating within a chosen frequency range, and at least two electrodes constitute pickup electrodes of which at least a first pickup electrode is connected to a measuring instrument for measuring at least one parameter value relating to the impedance of the structure; and wherein said sensor assembly is adapted to alter which electrodes constitute current supply electrodes and/or which electrodes constitute pickup electrodes between different measurements so as to alter the distance(s) between the current supply electrodes and/or the pickup electrodes to thereby alter the depths of the structure at which the measurements are performed; wherein said sensor assembly is further adapted to (1) store a predetermined set of values characteristic of at least one certain condition of the structure, and (2) compare the at least one measured parameter value with the predetermined set of values for determining whether the structure is in said certain condition; wherein said sensor assembly is adapted to measure the impedance at each pickup electrode, and wherein said sensor assembly is adapted to compare imaginary and real parts of impedance signals as functions of the applied frequency. - View Dependent Claims (2, 3, 4, 5, 6)
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Specification