Volume specific characterization of human skin by electrical immitance
This invention relates to a sensor assembly and a method for measuring characteristics of a surface, preferably skin, comprising a first pair of current supply electrodes coupled to a current source, providing an electrical current to the skin, at least one pickup electrodes at chosen positions relative to the current supply electrodes, at least a first of said pickup electrodes being coupled to an instrument for measuring the voltage between said first pickup electrode and at least one of the pickup or current supply electrodes.
1. Method for inspecting whether an object consists of living skin, the method comprising the following steps:
measuring electrical characteristics of two outer layers of skin, wherein said two outer layers of skin comprise respectively a stratum corneum and living skin,
comparing the measured electrical characteristics with corresponding, known characteristics of skin of a living or a dead finger, wherein the measurements of electrical characteristics in the two skin layers is characterized in
applying an alternating current or voltage with at least one frequency to the skin between two current supply electrodes,
measuring a complex voltage as a function of frequency between one of said current supply electrodes and a first electrode positioned at a chosen distance from said one current supply electrode for said at least one frequency,
measuring a complex voltage between the first electrode and a second electrode, wherein the second electrode is positioned at a larger distance from said one first current supply electrode than said first electrode for said at least one frequency,
calculating immittance for the two skin layers based on said voltage measurements, and using said immittance as a basis for comparing with corresponding, known characteristics of skin of a live or a dead finger.
2. Method according to claim 1 , wherein said comparison of electrical characteristics comprises comparing dispersion of resistivity for at least one skin layer.
3. Method according to claim 1 , wherein said comparing of electrical characteristics comprises comparing dispersion of permittivity for at least one skin layer.
4. Method according to claim 1 , wherein said comparing of electrical characteristics comprises comparing resistivity for at least one skin layer.
5. Method according to claim 1 , wherein said comparing of electrical characteristics comprises comparing relative permittivity for at least one skin layer.
6. Method according to claim 1 wherein the distance between said one current supply electrode and said first electrode is less than 1 mm.