MXPA01000173A - Method for detecting living human skin - Google Patents

Abstract

The characteristic curve of the skin surface impedance as function of the frequency of an alternating current voltage is measured by applying said voltage to one or more electric conductors which are galvanically or capacitively coupled to the surface of the skin and modifying the frequency, and then compared with a previously generated reference curve. If the characteristic shapes of said characteristic curves coincide to a large extent, the surface of the skin is recognized as forming part of living tissue.

Description

PROCEDURE FOR THE LIVE RECOGNITION OF HUMAN LEATHER FIELD AND BACKGROUND OF THE INVENTION - In modern admission and access authorization systems *, among other things, fingerprinting can be used for identification. An essential condition of this is security against fraud. In particular, they should be prevented from having access to pass clearance, counterfeit fingers or cut fingers. It is therefore essential jointly to verify with the digital impression that the person with that fingerprint lives. In WO 95/26 013 different methods for the electronic identification of persons are described, with which in addition to the taking of a diary impression it can be determined if the person v; Lve.

These methods include pulsing frequency or electrocardiogram signals, measurement of the oxygen content of the blood, skin temperature, blood pressure or mechanical properties of the skin surface. SUMMARY OF THE INVENTION It is the task of the present invention to present a simple method for the in vivo recognition of human skin that is especially suitable to be applied in conjunction with a digital pressure sensor.

This task is solved with the procedure with the features described in claim 1. Other conformations are derived from the dependent claims. In the method according to the invention, it is used that the living human skin possesses a characteristic layer structure. With a decisive significance for the invention presented here is that these layers have clearly different electrical conductive capacities. If these layers are found in an electric field of an array of electrodes, a capacitive resistive system is formed with a fully characteristic frequency course. In the attached figure, diagrams are represented in which are expressed the ohmic resistance (real part of the impedance) or the capacity (proportional to the imaginary part of the impedance) for different conditions with respect to the logarithm of the frequency of the applied voltage. In the basic measurement an index finger placed on a layer of silicon covered with oxide is used and the impedance of this arrangement is measured. In the diagrams on the left side, groups of curves for different finger states have been drawn. The curve marked 1 is for a wet finger, curve 2 for a normal finger and curve 3 in points, for a dry finger. The curve 4 superior in points, establishes the measurement of the topping of a central finger. The diagrams on the left side represent characteristic lines for different test persons. It is easily recognizable that the course of these characteristic curves itself is largely independent of the state of the person and of the person tested, JiiS TSj GC ci xu (BH tß IlO L £ 1.0 6 ci C3,3TciC? €? X 'X LXCcl C * 6X course of the ohmic resistance curve This course is only difficult to imitate with an artificial finger, in case of a severed finger, the course of the curve drastically changes due to the death of the skin tissue Next, we must now describe how this characteristic impedance course can be used to verify the authenticity and life status of the finger used.In a first step, a characteristic reference line is first generated.The frequency course can be directly measured here. , as in the applied finger or also the time course of a measurement signal can be applied.An example for the last method is the application of a voltage jump on the electrodes and the measurement of the temporal urso of the load current. The corresponding characteristic lines look completely different, but in principle they have equal value since they are co-related by means of a Fourier transformation. Which method has to be applied depends on the corresponding application. In case of high demands on the security of identification, they can for example evaluate the real and imaginary part of the impedance course. In a simple use, the use of the absolute impedance trace is enough since this value can be obtained by a simple obtaining of the measurement current. Preferably, the characteristic line of reference is generated in such a way that it represents an average course of the impedance curve. This can for example be achieved by means of multiple curves taken under different conditions. Preferably, the reference characteristic line is used especially for each person to be identified later. The impedance values selected in the selected field of the alternate voltage frequency are stored, for example, together with the characteristics (Municias) of the finger pressure. It can then be compared with the values stored in the finger print control, both the finger print itself, as well as the characteristic line for live recognition. Since only slight variations between different people are determined or established (see the diagrams on the right side of the figure), it is also possible to use a single reference curve for all the persons to be identified. In the comparison of a current characteristic line with those stored reference characteristic lines, in any case large variations or limits of tolerance that can be allowed, instead of depending on the measurement of the dependence of a single or pure sinusoidal oscillation, are presented. You can also use the frequency accumulation.

Accumulations of that type, for example pulse forms (rectangular pulses, pulses similar to closures or similar) are often easily generated as pure sine wave oscillations. By suitable filtration the area in which the accumulated frequencies remain can be limited to a certain interval width. The measured values or characteristic lines obtained correspond to an average of measurement values with sinusoidal excitation. If the interval width of the accumulated frequencies is selected sufficiently small, it will be possible with this simplified method to generate sufficiently satisfactory characteristic lines or to take them from a current measurement. In the identification of each person, the characteristic line considered is measured and compared with the line of reference characteristic. If a sufficient match is presented and the specific measurement values of the person (the minutia of the finger print) also coincide with the reference values, it is worth identifying the person and obtaining the authorization of admission or access. Such a characteristic line comparison can be performed in a manner. known under evaluation of the difference of the function values. One can for example add or integrate the difference of the values of the characteristic lines to each frequency, the absolute amount of these differences add or integrate them or determine the maximum of these differences. The accuracy of the comparison can also be increased when comparing the logarithms or the first derivations of the characteristic lines. The method according to the invention can be performed on a finger pressure sensor using an electrical conductor in the sensor. For this a sensor is used in which on or under a support surface to receive a finger impression, electrical conductors have been placed, which when placed the tip of the finger come into direct contact with the surface of the skin (coupling galvanic) or enter a certain distance to the surface of the skin (capacitive coupling). In the latter case, for example, between the conductor and the finger support surface, a dielectric layer is used as a protective layer or cover. For the measurement, only one conductor or two electrically isolated conductors can be used. If only one conductor is used, the applied finger acts as a junction to the ground potential. In the use of two electrical conductors, the conductors are preferably placed at a certain distance, which is greater than the thickness of the epidermis. The process is therefore allowed to be carried out with conductors having a distance from each other of at least 2 mm. It suffices if the conductors are two metallic plates of an approximate size of 10 mm2 According to the desired resolution of the measurement, much smaller measurements can be used. The measurement of the impedance can be carried out in a manner known per se, where it should only be observed that the measurement method also selected as a result sufficient for the purpose pursued. In case the method is used in a finger pressure sensor, the conductor or the conductors are arranged for fixing the recognition in life, preferably at the edge of the positioning surface for the fingertip. Since the sensor as a rule is already structured by electrically conductive sensor elements, only these sensor elements can also be used for carrying out the described method. The process can therefore also in principle also be carried out with previously conventional sensors, using suitable electronic means.

Claims (4)

1. NOVELTY OF THE INVENTION Having described the invention as above, property is claimed as contained in the following 1.
2. Procedure for the recognition in life or live of the human being, characterized in that in the area of a skin surface in contact with at least one electrical conductor "or an electrical conductor and placed at a predated distance, in which it is applied to an electric conductor an electric potential of a frequency accumulation or an electric alternating voltage with a variable frequency, in which is obtained with a measurement made with that potential of the real part and the imaginary part of the electrical impedance as a function of time or as a function of the frequency or absolute magnitude of the electrical impedance as a function of time or as a function of the frequency, and in which the coincidence of the function obtained with a reference function is proved. with claim 1, characterized in that the electric potential is an accumulation or superposition of frequencies, which produces a pulse of tension or a jump of tension.
3. 3. Method according to claim 1, characterized in that the electric potential is an accumulation of frequencies in a limited range. Method according to one of Claims 1 to 3, characterized in that a region of a pixeX surface contacting at least two electrical conductors or at a certain distance gives at least two electrical conductors, where the electrical conductors are located. electrically isolated from one another and arranged at a distance from each other of at least 2 mm.