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

DRS \\ 7jun02 2 techieDetail16.ppt Starting from first principles, connect an AC signal generator to 2 parallel 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 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 contours (shown in dashed red)representing lines of constant signal amplitude. Starting from first principles, connect an AC signal generator to 2 parallel 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 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 contours (shown in dashed red) representing lines of constant signal amplitude. TruePrint RF Imaging Technology Conductive plates Equipotential contours

DRS \\ 7jun02 3 techieDetail16.ppt 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 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 sensors, essentially very small antennas, placed in the electric field region will acquire voltages that represent the shape of the corrugated conductive surface. TruePrint RF Imaging Technology Corrugated Conductive plate Shaped Equipotential contours Antenna array An E-field sensor array can measure that shape

DRS \\ 7jun02 4 techieDetail16.ppt l Now lets examine the structure of the skin to see how to apply this RF imaging mechanism l Dry dead skin cells have low electrical conductivity. This region behaves as a dielectric l The boundary region where the live cells begin turning into keratinized skin is moist and electrically conductive. Dead dry skin Live skin The Structure of the Skin Air

DRS \\ 7jun02 5 techieDetail16.ppt 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 Technology Ridges and valleys on finger surface Semiconductor Part of a finger Conductive layer just beneath surface of skin Finger drive

DRS \\ 7jun02 6 techieDetail16.ppt finger RF Field (between finger and chip) mimics shape of conductive (live) skin layer Conductive layer just beneath surface of skin TruePrint RF Imaging Technology

DRS \\ 7jun02 7 techieDetail16.ppt Sensors near ridges measure higher signals Sensors near valleys measure lower signals TruePrint RF Imaging Technology

DRS \\ 7jun02 8 techieDetail16.ppt 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 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.

DRS \\ 7jun02 9 techieDetail16.ppt 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 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.

DRS \\ 7jun02 10 techieDetail16.ppt Advantages of TruePrint Technology over standard DC capacitive sensing TruePrint imaging does not depend upon air in the valleys If the valleys are worn away, filled with oil or dirt, or if they are smashed flat, the sensor still images If the valleys are worn away, filled with oil or dirt, or if they are smashed flat, the sensor still images Even very dry skin can be imaged successfully Even very dry skin can be imaged successfully TruePrint technology uses coherent planar field structures between the finger and the sensor Minimizes crosstalk between sensors, 250 sensors per inch in TruePrint technology generates a real 250 ppi information content. Most other sensors lose information due to crosstalk. Minimizes crosstalk between sensors, 250 sensors per inch in TruePrint technology generates a real 250 ppi information content. Most other sensors lose information due to crosstalk. The sensing fields penetrate thick and callused skin The sensing fields penetrate thick and callused skin The sensors can work through thicker protective coatings The sensors can work through thicker protective coatings TruePrint technology is very flexible and can be automatically adjusted to adapt to a wide range of different skin types and environments.

DRS \\ 7jun02 11 techieDetail16.ppt Dynamic optimization -- How it works Uses the flexibility of the TruePrint technology to adapt to the persons current skin condition The system takes several image frames in sequence each one better optimized than the previous each one better optimized than the previous Process continues until the image is good enough to accept or reject confidently

DRS \\ 7jun02 12 techieDetail16.ppt In Slow Motion... Dynamic optimization Example of a typical dry finger This example took 4 frames Executed in about ½ second on a PC Increase drive signal Increase amplifier gain Adjust A/D references

DRS \\ 7jun02 13 techieDetail16.ppt For more information … Back to Beginning Click here to learn about fingerprint Matching methods Click here to learn how very small fingerprint sensors work