Volume specific characterization of human skin by electrical immitance

• US 20070043301A1
• Filed: 05/14/2003
• Published: 02/22/2007
• Est. Priority Date: 05/14/2002
• Status: Active Grant

• Current Assignee: IDEX Biometrics ASA
• Original Assignee: Idex ASA
• Inventors: Grimnes, Sverre, Martinsen, Ørjan
• Granted Patent: US 7,856,262 B2
• Time in Patent Office: Days
• US Class Current: 600/547
• CPC Class Codes: A61B 5/0531 Measuring skin impedance
• CPC Class Codes: A61B 5/442 Evaluating skin mechanical properties, e.g. elasticity, hardness, texture, wrinkle assessment
• CPC Class Codes: A61B 5/6826 Finger
• CPC Class Codes: A61B 5/6838 Clamps or clips
• CPC Class Codes: G06V 40/45 Detection of the body part being alive

Abstract

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.

Claims

1. Sensor assembly for measuring characteristics of a surface, preferably skin, comprising a first pair of current supply electrodes coupled to a current source for providing an electrical current to the skin, at least two pickup electrodes at chosen positions relative to the current supply electrodes and an instrument coupled to a first of said at least one of said pickup electrodes and a first of said current supply electrodes for measuring the voltage between said first pickup electrode and said first current supply electrode, wherein said instrument also is coupled to a second of said pickup electrodes and being adapted to measure the voltage between said first and second pickup electrodes, said first pickup electrode being positioned at a distance from said first current supply electrodes being less than the distance between said first current supply electrode and said second pickup electrodes, said distance being less than 1 mm.

2. Sensor assembly according to claim 1, wherein the supplied current is oscillating within a chosen frequency range.

3. Sensor assembly according to claim 2, wherein the frequency is in the range of 10-1000 kHz, preferably approximately 100 kHz.

4. Sensor assembly according to claim 1, wherein the contact surfaces of the pickup electrodes are comparable to the stratum corneum thickness.

5. Method for measuring the electrical characteristics of two outer parts of the skin, i.e. the stratum corneum and the viable skin, comprising the steps of:

applying a current or voltage to the skin between two current supply electrodes,

measuring the voltage between a first of said supply electrodes and a first pickup electrode positioned at a chosen distance from said first supply electrode,

measuring the voltage between the first pickup electrode and a second pickup electrode, said second pickup electrode being positioned at a larger distance from the first supply electrode than the first electrode,

comparing the voltages measured at the two electrodes for providing the permittivity and/or resistivity of at least one of the skin layers.

6. Method for inspecting whether an object consists of living skin, e.g. human skin, comprising the following steps:

measuring electrical characteristics of two outer layers of the skin i.e. stratum corneum and living skin,

comparing the measured electrical characteristics for a living, or possibly a dead, finger, wherein the measurements of electrical characteristics in the two slin layers is characterized in

applying a alternating current or voltage with at leas tone frequency to the slin between two current supply electrodes,

for the applied frequencies measuring the 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 current supply electrode,

for said applied frequencies measuring the complex voltage between the first and a second electrode, wherein the second electrode is positioned at a larger distance from said first current supply electrode than said first electrode,

calculating immitance for the two slin layers based on said voltage measurements, and use of this as a basis for comparing with corresponding, known characteristics of a live, or possibly a dead, finger.

7. Method according to claim 6, wherein said comparison of electrical characteristics comprises comparing dispersion of resistivity for at least one skin layer.

8. Method according to claim 6, wherein said comparing of electrical characteristics comprises comparing dispersion of permittivity for at least one skin layer

9. Method according to claim 6, wherein said comparing of electrical characteristics comprises comparing resistivity for at least one skin layer.

10. Method according to claim 6, wherein said comparing of electrical characteristics comprises comparing relative permittivity for at least one skin layer.

11. Method according to claim 6 wherein the distance between said first current supply electrode and said first electrode is less than 1 mm.