BIOIMPEDANCE SPOOF DETECTION

• US 20170124374A1
• Filed: 08/24/2016
• Published: 05/04/2017
• Est. Priority Date: 02/25/2014
• Status: Active Grant

• Current Assignee: HID Global Corporation (Assa Abloy AB)
• Original Assignee: HID Global Corporation (Assa Abloy AB)
• Inventors: ROWE, ROBERT K., MATTER, NATHANIEL I.
• Granted Patent: US 10,810,404 B2
• Time in Patent Office: Days
• CPC Class Codes: G06K 19/07354 by biometrically sensitive means, e.g. fingerprint sensitive fingerprint sensors in general G06V40/12; biometrically activated access control G07C9/25
• CPC Class Codes: G06V 40/1306 non-optical, e.g. ultrasonic or capacitive sensing
• CPC Class Codes: G06V 40/1329 Protecting the fingerprint sensor against damage caused by the finger
• CPC Class Codes: G06V 40/1347 Preprocessing; Feature extraction
• CPC Class Codes: G06V 40/1359 Extracting features related to ridge properties; Determining the fingerprint type, e.g. whorl or loop
• CPC Class Codes: G06V 40/1365 Matching; Classification
• CPC Class Codes: G06V 40/1394 using acquisition arrangements
• CPC Class Codes: G06V 40/40 Spoof detection, e.g. liveness detection

Abstract

Embodiments relate to bioimpedence-based spoof detection in an optical biometric reader. For example, embodiments operate in context of a biometric reader having a platen integrated with substantially transparent bioimpedance source and receiver electrodes covered by a substantially transparent protective layer. A multi-frequency input signal can be injected from the source electrode into a purported skin site (through the protective layer), so that a response signal is received by the receiver electrode. The response signal is interrogated to formulate a dispersive bioimpedance response of the purported skin site to the input signal over multiple frequencies. A biometric spoof determination can then be made according to the dispersive bioimpedance response. The spoof determination can be used for spoof detection, presence detection, and/or other functions.

Claims

1. A biometric sensor comprising:

a platen;

a source electrode and a receiver electrode disposed on the platen;

an imaging system that operates to form an image of a purported skin site through the platen using optical wavelengths; and

a controller that operates to;

inject an input signal from the source electrode into a purported skin site that is coupled with the source electrode and the receiver electrode via the protective layer, thereby causing the receiver electrode to receive a response signal, the input signal comprising a plurality of frequencies;

interrogate the response signal to formulate a dispersive bioimpedance response of the purported skin site to the input signal over the plurality of frequencies; and

determine whether the purported skin site is a live finger according to the dispersive bioimpedance response.

2. The bioimpedance sensor of claim 1, further comprising:

an insulative protective layer disposed on the platen and covering the source and receiver electrodes, wherein the skin site is coupled with the source electrode and the receiver via the protective layer.

3. The biometric sensor of claim 1, wherein the controller operates to determine whether the purported skin site is a live finger according to the dispersive bioimpedance response by:

applying the dispersive bioimpedance response to an electrical lumped-component model to determine an apparent dispersion response of the purported skin site, the electrical lumped-component model describing, as an arrangement of electrical components, at least a characteristic skin site coupled with the source electrode and the receiver electrode through the protective coating; and

computing a correspondence of the apparent dispersion response of the purported skin site to a stored dispersion model.

4. The biometric sensor of claim 3, wherein the electrical lumped-component model is a resistive-capacitive (RC) model, the arrangement of electrical components being an arrangement of at least one resistive component and at least one capacitive component.

5. The biometric sensor of claim 1, wherein the controller operates to:

interrogate the response signal to formulate a dispersive bioimpedance response of the purported skin site to the input signal over the plurality of frequencies by;

measuring a first impedance magnitude at a first frequency, a first impedance phase at the first frequency, a second impedance magnitude at a second frequency, and a second impedance phase at the second frequency; and

formulating the dispersive bioimpedance response as a function of the first impedance magnitude, the first impedance phase, the second impedance magnitude, and the second impedance phase.

6. The biometric sensor of claim 5, wherein formulating the dispersive bioimpedance response comprises computing a resistive dispersion over the plurality of frequencies and a capacitive dispersion over the plurality of frequencies as a function of the first impedance magnitude, the first impedance phase, the second impedance magnitude, and the second impedance phase.

7. The biometric sensor of claim 1, wherein the controller operates to inject the input signal as a single-frequency sinusoid driven at a first of the plurality of frequencies for a first timeframe and driven at a second of the plurality of frequencies signal for a second timeframe.

8. The biometric sensor of claim 1, wherein the input signal comprises, superimposed, the plurality of frequencies.

9. The biometric sensor of claim 8, wherein the controller operates to interrogate the response signal to formulate the dispersive bioimpedance response of the purported skin site to the input signal over the plurality of frequencies by:

sampling time-domain information from the response signal;

computing frequency-domain information for the response signal as a function of transforming the time-domain information; and

formulating the dispersive bioimpedance response over the plurality of frequencies according to the frequency-domain information.

10. The biometric sensor of claim 8, wherein the controller operates to:

interrogate the response signal to formulate the dispersive bioimpedance response of the purported skin site to the input signal over the plurality of frequencies by sampling the response signal to formulate the dispersive bioimpedance response as a time-domain response; and

determine whether the purported skin site is a live finger according to the dispersive bioimpedance response by computing a correspondence of the dispersive bioimpedance response to a stored time-domain dispersion model.

11. The biometric sensor of claim 10, wherein the controller operates to determine whether the purported skin site is a live finger according to the dispersive bioimpedance response by calibrating out an impedance contribution from the source electrode and the receiver electrode prior to computing the correspondence of the dispersive bioimpedance response to the stored time-domain dispersion model.

12. The biometric sensor of claim 8, wherein the input signal is one of a step signal, and impulse signal, or a broad-spectrum periodic signal.

13. The biometric sensor of claim 1, wherein the input signal is a voltage signal or a current signal, and the response signal is a voltage signal or a current signal.

14. The biometric sensor of claim 2, wherein the platen, the source electrode, the receiver electrode, and the protective layer are substantially transparent to the imaging system.

15. The biometric sensor of claim 14, further comprising:

a plurality of electrical traces that electrically couple the controller to the source electrode and the receiver electrode,

the plurality of electrical traces being substantially transparent to the imaging system, and

the plurality of electrical traces, the source electrode, and the receiver electrode all being disposed on a single layer of the platen below the protective layer.

16. The biometric sensor of claim 2, further comprising:

an array of electrodes, each selectively activatable as either a source or a receiver,

wherein the controller further operates to;

detect that the purported skin site is coupled with at least a first of the array of electrodes and a second of the array of electrodes through the protective layer;

in response to the detecting, selectively activate the first of the array of electrodes as the source electrode and selectively activate the second of the array of electrodes as the receiver electrode.

17. The biometric sensor of claim 1, further comprising:

a plurality of source and receiver electrodes,

wherein the controller further operates to interrogate multiple pairs of the source and receiver electrodes to output two-axis locating feedback for the purported skin site.

18. The biometric sensor of claim 1, further comprising:

a guard band that is disposed on the platen between the source and receiver electrodes and operates to sink current that flows between the source and receiver electrodes without passing through the purported skin site.

19. The biometric sensor of claim 2, further comprising:

a conductor patterned on the platen below the protective layer, the conductor being substantially transparent to the imaging system; and

a tamper detection circuit that operates to detect disruption of the transparent conductor.

20. The biometric sensor of claim 1, wherein the controller further operates to:

output a presence detection indication when the controller determines the purported skin site is a live finger according to the dispersive bioimpedance response.

21. The biometric sensor of claim 1, wherein the imaging system operates to form a direct image of the purported skin through the platen under multispectral illumination.

22. The biometric sensor of claim 2, further comprising:

a guard band that is disposed on the platen between the source and receiver electrodes and operates to sink current that flows along the protective layer without passing through the purported skin site.