DRS \\ 7jun02 1 techieDetail16.ppt TruePrint Technology The Fundamentals.

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TruePrint™ TechnologyTruePrint™ Technology

The FundamentalsThe Fundamentals

TruePrint™ TechnologyTruePrint™ Technology

The FundamentalsThe Fundamentals

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techieDetail16.ppt

Starting from first principles, connect an AC signal generator to 2 parallel Starting from first principles, connect an AC signal generator to 2 parallel conductive plates, generating an electric field between the plates. The conductive plates, generating an electric field between the plates. The wavelength will be much larger than all dimensions of the plates, so the field will wavelength will be much larger than all dimensions of the plates, so the field will be purely electric with no magnetic component, and no electromagnetic effects. be purely electric with no magnetic component, and no electromagnetic effects. The system can be treated as a quasi-static electric field with the equipotential The system can be treated as a quasi-static electric field with the equipotential contours (shown in dashed red)contours (shown in dashed red) representing lines of constant signal amplitude.representing lines of constant signal amplitude.

TruePrint RF Imaging TechnologyTruePrint RF Imaging Technology

Conductive plates

Equipotential contours

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If we now corrugate one of the conductive surfaces, the RF electric field will If we now corrugate one of the conductive surfaces, the RF electric field will follow the shape of the conductive boundary. As illustrated here, the follow the shape of the conductive boundary. As illustrated here, the equipotential contours within the field will take on shapes that are an attenuated equipotential contours within the field will take on shapes that are an attenuated form of the shape of the conductive plate. A planar array of RF electric field form of the shape of the conductive plate. A planar array of RF electric field sensors, essentially very small antennas, placed in the electric field region will sensors, essentially very small antennas, placed in the electric field region will acquire voltages that represent the shape of the corrugated conductive surface.acquire voltages that represent the shape of the corrugated conductive surface.

TruePrint RF Imaging TechnologyTruePrint RF Imaging Technology

Corrugated Conductive plate

Shaped Equipotential contours

Antenna arrayAn E-field sensor array can measure that shape

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Now let’s examine the structure of the skin to see how to apply this RF imaging mechanism

Dry dead skin cells have low electrical conductivity. This region behaves as a dielectric

The boundary region where the live cells begin turning into keratinized skin is moist and electrically conductive.

Deaddryskin

Liveskin

The Structure of the SkinThe Structure of the Skin

Air

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Applying the principle to fingerprint imaging.An signal generator on chip applies a small RF signal between the finger and the adjacent semiconductor. The signal is coupled into the live conductive layer of the skin by a conductive surface (called the finger drive ring) positioned around the outside of the active imaging region of the sensor.

TruePrint RF Imaging TechnologyTruePrint RF Imaging Technology

Ridges and valleys on finger surface

Semiconductor

Part of a finger

Conductive layer just beneath surface of skin

Finger drive

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RF Field (between fingerfinger and chip) mimics shape of

conductive (live) skin layer

Conductive layer just beneath surface of skin

TruePrint RF Imaging TechnologyTruePrint RF Imaging Technology

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Sensors near ridges measure higher signals

Sensors near valleys measure lower signals

TruePrint RF Imaging TechnologyTruePrint RF Imaging Technology

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Cross section of antenna array reading finger skin.

Cross section of finger skin

Live skin cell layer

surface of the skin

Pixel antennae array

Excitation signal reference plane

Backup

Semiconductor substrate

Outer dead skin layer(dielectric)

TruePrint RF Imaging TechnologyTruePrint RF Imaging Technology

Excitation Generator Hi input impedance

sense amps

The pixel antennas have characteristic impedances in the teraohm range. Therefore ultra high input-impedance sense amps are used under pixel to read the antennas’ voltages and drive the switched data busses.

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Classic capacitive fingerprint sensor - cross section of sensor array reading finger skin.

Cross section of finger skin

Air gaps at valleys

Outer dead skin layer(dielectric)

Live skin cell layer

Currently active pixel sensor plate

surface of the skin

Pixel sensor plate array

Semiconductor substrate

Electric field geometry

c

DC Capacitive OverviewDC Capacitive Overview

For comparison purposes, this diagram shows the pixel structure and electric field geometry for a typical DC capacitive fingerprint sensor. In one mode of operation, a fixed charge is placed on the active pixel plate and the voltage generated is measured. Note that this is a capacitive fringing field, so the field geometry is hemispherical and it is confined to a region very close to the sensor surface.

Capacitive sensors measure the difference in permittivity between the ridge surface skin and the air in the valleys.

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Advantages of TruePrint Technology Advantages of TruePrint Technology over standard DC capacitive sensingover standard DC capacitive sensing

TruePrint imaging does not depend upon air in the valleysTruePrint imaging does not depend upon air in the valleys

If the valleys are worn away, filled with oil or dirt, or if If the valleys are worn away, filled with oil or dirt, or if they are smashed flat, the sensor still imagesthey are smashed flat, the sensor still images

Even very dry skin can be imaged successfullyEven very dry skin can be imaged successfully

TruePrint technology uses coherent planar field structures TruePrint technology uses coherent planar field structures between the finger and the sensorbetween the finger and the sensor

Minimizes crosstalk between sensors, 250 sensors per Minimizes crosstalk between sensors, 250 sensors per inch in TruePrint technology generates a real 250 ppi inch in TruePrint technology generates a real 250 ppi information content. Most other sensors lose information content. Most other sensors lose information due to crosstalk. information due to crosstalk.

The sensing fields penetrate thick and callused skinThe sensing fields penetrate thick and callused skin

The sensors can work through thicker protective The sensors can work through thicker protective coatingscoatings

TruePrint technology is very flexible and can be TruePrint technology is very flexible and can be automatically adjusted to adapt to a wide range of different automatically adjusted to adapt to a wide range of different skin types and environments.skin types and environments.

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Dynamic optimization™ -- Dynamic optimization™ -- How it worksHow it works

Uses the flexibility of the TruePrint technology to Uses the flexibility of the TruePrint technology to adapt to the person’s current skin conditionadapt to the person’s current skin condition

The system takes several image frames in The system takes several image frames in sequence sequence each one better optimized than the previouseach one better optimized than the previous

Process continues until the image is good Process continues until the image is good enough to accept or reject confidentlyenough to accept or reject confidently

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In Slow Motion . . .

Dynamic optimizationDynamic optimization Example of a typical dry fingerExample of a typical dry finger

This example took This example took 4 frames4 frames

Executed in about Executed in about ½ second on a PC½ second on a PC

Increase drive signal

Increase amplifier gain

Adjust A/D references

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For more information …For more information …

Back to Beginning

Click here to learn about fingerprint

Matching methods

Click here to learn how very small

fingerprint sensors work