Irradiated Images Described by Electrical Contact

This invention relates generally to devices generating images of contact (such as fingerprints), and more specifically to a device that causes a pattern of contact itself to selectively close an open circuit, where such closure of the circuit energizes an irradiated image directly in register with the contact pattern.

Devices are known in the art to capture images described by contact on a surface. A primary, although by no means exclusive, application for such imaging devices is in the area of fingerprinting, whether for security, forensics or other purposes. Other applications include analysis of surface texture for classification or testing purposes, or recording contact for archival purposes, or possibly mechanical duplication.

All of the foregoing applications involve translating the image described by contact into a reproducible record of the image. For example, in the fingerprint application, a time-honored system is to "ink" the fingers and roll them on a paper or card surface. Of course, without further scanning of the results, such systems lack the capability to generate computer-ready signals representative of the images. Without the storage and analysis capabilities of a computer, cataloging and comparison of such fingerprint images is a time-consuming and unpredictable task.

More recent devices shine light onto the fingerprint via a prism. The reflected image may be captured on photosensitive film, or received onto a photosensitive array. In the latter case, the image may then be pixelated and stored as an analog or digital signal representative of the image. These signals are now available for further processing by computers.

The prior art references cited with this disclosure demonstrate that fingerprinting is a popular application of the "reflected image" technique. The same "reflected image" technique is also known to be used to scan paper or other textile images into scanners and photocopiers.

The disadvantage with all devices employing a "reflected image" technique of recording images is that by definition they need an independent light source and optical structure (such as a prism) to create a reflected image. The same is true of "reflected image" techniques using radiation outside the visible light band of the electromagnetic spectrum. By definition, an independent radiation source and reflective/diffractive structure is still required.

Other current art devices generating images by contact use proximity sensors to detect changes in characteristics such as capacitance or magnetic flux. The disadvantages of these devices are that (1) they can be unreliable, and (2) they can be costly. They are unreliable inasmuch that in detecting variations in, say, capacitance, there is no way to know whether capacitance change is caused by contact or by some other stray source. Further, an expense must be incurred in such devices in creating sensor circuitry having fidelity and resolution comparable to the capability of capturing and resolving reflected radiation such as visible light.

There is therefore a need in the art for a device generating images described by contact, where the contact is the primary source of energy for the image itself. In this way, the extra structure required in "reflected image" techniques would be obviated. Further, it would be highly advantageous if such an inventive device did not rely on proximity sensors to detect the contact. The inventive device would then have increased predictability in performance, without requiring complex sensor circuitry to interpret the contact.

These and other objects, features and technical advantages are achieved by an invention that generates images described by contact, in which the contact itself closes an open circuit to generate radiation in a pattern in register with the contact. In this way, an irradiated image results, which corresponds directly to the contact pattern energizing the radiation.

The invention thus has immediate (although not exclusive) application to fingerprinting techniques. In a preferred embodiment enabled by an electroluminescent system without a back electrode, a fingerprint is disposed to close the open circuit by making contact and thereby serving as a "temporary" back electrode. The electroluminescent system then energizes in a pattern in register with the contact (i.e. the fingerprint) to emit a high-resolution image of visible light with high fidelity to the contact. This image may then be directed on to a photosensitive array standard in the art suitable for pixelation and conversion into an electrical signal representative of the image. This signal is available for computerized storage, analysis, processing and comparison.

Advantageously, the electroluminescent system enabling a preferred embodiment is a low cost, screen-printed polymer thick film ("PTF") lamp, which may be electrically powered at a low AC voltage (say 20-30 volts AC) at frequencies in a range of 400 Hz to 2 kHz. Such a power supply is well known in the art to be available from low voltage integrated circuit inverters (say 3-5 volts DC). The electroluminescent system will then be very safe to the touch by virtue of the very low current levels generated by such an electrical system.

Of course, it will be appreciated that the invention is in no way limited to fingerprinting applications. According to the invention, any form of electrically conductive contact will describe an irradiated image. Thus, the surface textures of many objects, animate or inanimate, may be imaged with the invention.

Further, the invention is not limited to contact generating visible light via electroluminescence. Although the preferred embodiment as described is highly advantageous, the invention in its broadest form encompasses generating irradiated imaged described by contact, where the contact itself closes an open circuit to energize radiation in register with the contact. Thus, generation of any radiation in the electromagnetic spectrum falls within the scope of the invention. For example, an infra-red image could be generated by an open circuit where heat is emitted in pattern in register with selective closure of the circuit by the contact. Clearly, yet further fidelity and resolution of images described by contact may be available through selection of the wavelength of the radiation generated by the invention, as may be compatible with the device receiving and interpreting the irradiated image.

Similarly, the use of electroluminescence in the preferred embodiment should not be considered as limiting. Clearly, using the contact to form the back electrode of an electroluminescent lamp is a highly advantageous enablement of radiation in register with contact. The invention, however, is broad in concept in that it uses the contact itself to close an open circuit to energize radiation in register with the contact. Thus, it will be appreciated that the invention is enabled by any open circuit capable of generating radiation in register with selective closure of the circuit by a pattern of contact.

It is therefore a technical advantage of the present invention to generate an irradiated image corresponding to contact, by causing the contact to close an open circuit, thereby obviating the need for additional apparatus such as an independent radiation source and reflective/diffractive structure to enable a "reflected image."

It is a further technical advantage of the invention to eliminate the unpredictability and potential manufacturing complexity of devices using "proximity sensor" structure to generate an image of contact.

A yet further technical advantage of the invention is that it can be enabled reliably and economically on a screen-printed PTF electroluminescent lamp, where the contact forms the back electrode of the lamp. Visible light in a pattern in register with the contact may then be radiated towards a photosensitive array. This array in turn may pixelate the image and prepare a computer-ready signal corresponding to the image.

The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.

For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a section view through a preferred embodiment of the present invention;

FIG. 1A is a section view through an alternative embodiment of the present invention;

FIG. 2 is an enlargement of contact as shown on FIGS. 1A and 1B.

FIG. 3 is a cutaway view of the embodiment of the invention illustrated on FIG. 1;

FIG. 4 depicts the invention in operation; and

FIGS. 5A and 5B are actual thumb print images obtained using the preferred embodiment.

As described summarily above, by the present invention is directed to an apparatus capable of emitting radiation corresponding to zones of contact on a surface, where the contact physically closes an open electrical circuit, and where the closure of the circuit energizes the radiation in a pattern in register with the contact to a high degree of fidelity and resolution. This apparatus is particularly advantageous in generating fingerprint, palm print, footprint or other skin images where the skin is electrically conductive. A preferred embodiment will be discussed with reference to generating a visible light image of a human thumb print, although as already discussed, the invention is not limited in this regard. Skin images of other anatomical regions of humans, as well as other life forms, may be generated by the invention, so long as the skin whose contact is described by the image is electrically conductive. Further, the invention is not limited to generating images of anatomical contact. It will be appreciated that the other embodiments of the invention may generate irradiated images described by contact on a contact surface by any electrically conductive zone wherein a previously open circuit is now closed by the contact. Accordingly, images corresponding to, for example, metal surface textures, or "water marks" on electrically conductive fabrics, textiles or papers may be generated by the invention with equivalent enabling effect.

The preferred embodiment will further be discussed with reference to generating visible light using an open electroluminescent system closed by contact by a thumb print on a contact surface. It will nonetheless be further appreciated, however, that the invention is not limited in this regard. Consistent with the invention, the area of contact may be described by radiation anywhere in the electromagnetic spectrum, and not just in the visible light band as enabled by the preferred embodiment discussed below. Imagery in, for example, the infra-red, ultraviolet bands is consistent with the invention where irradiated images of such emissions have useful applications.

Likewise, the use of an open electroluminescent circuit in a preferred embodiment should not be considered as limiting under the invention. Electroluminescence has useful applications in the visible light band because an open circuit can be deployed easily and economically in the form of a laminate, where the contact to be imaged can form a back electrode, thereby closing the circuit and generating light in register with the contact. It will be appreciated, however, that other forms of circuitry will be consistent with the invention where contact closes an open circuit to generate corresponding irradiated images outside of the visible light band. For example, consistent with the invention, heat could be generated in register with the passage of current through a circuit closed by contact. Accordingly, circuitry generating infra-red radiation in register with circuit-closing contact will be enabled by the invention. Thus, by selecting various radiation-generating components in the open circuit to be closed by contact, other types of circuits will enable the invention.

Turning now to FIG. 1, a general arrangement of the preferred embodiment includes human thumb 10 making thumb print contact on a contact surface 101 on electroluminescent system 100. Thumb 10 also concurrently makes electrical contact with contact plate 120, contact plate 120 being isolated electrically from electroluminescent system 100.

With further reference to FIG. 1, electroluminescent system 100 comprises substrate 105 on which translucent electrode layer 104 is deposited. In a preferred embodiment, substrate 105 may be any suitable material allowing the passage of visible light, such as polyester, polycarbonate, vinyl or elastomer.

In a preferred embodiment, the active ingredient doped into translucent electrode layer 104 is Indium-Tin-Oxide ("ITO"), although any other functionally equivalent transparent metal oxide dopant known in the art may be used, such as, for example, Tantalum-Oxide. In another embodiment (not illustrated) substrate 105 and translucent layer 104 may be combined using a pre-sputtered ITO polyester sheet. Translucent electrode layer 104 also includes bus bar 106 connected to power source 110. Although shown in section on FIG. 1, it will be appreciated that bus bar 106 is continuous within translucent electrode layer 104 so as to energize the planar area of the layer. In a preferred embodiment, bus bar 106 is screen printed on to a substrate 105, using a silver polymer thick film (PTF) ink, prior to screen printing of translucent electrode layer on to substrate 105. It will be appreciated, however, that bus bar 106 is not limited in this way, and may also be, for example, a thin copper strip adhered to substrate 105 prior to depositing translucent electrode layer 104. Of course, if pre-sputtered ITO polyester sheet is used to combine substrate 105 and translucent electrode layer 104 (not illustrated), then bus bar 106 may be eliminated.

Continuing to refer to FIG. 1, contact surface 101 is on top of envelope layer 107. Envelope layer is an electrically conductive layer protecting electroluminescent system 100. Advantageously, envelope layer 107 is a hard wearing material so as to give contact surface 101 a long life. Examples of materials suitable for envelope layer 107 when the invention is practiced in accordance with screen printing techniques as described further below are epoxies, polyurethanes, acrylics and other similar hard wearing materials.

Envelope layer 107 and translucent electrode layer 104 are separated by dielectric layer 102 and luminescent layer 103. In a preferred embodiment, the layer sequence is as shown in FIG. 1, where luminescent layer 103 is closer to substrate 105 than dielectric layer 102. The invention would still be enabling if luminescent layer 103 and dielectric layer 102 were reversed. Light irradiated from luminescent layer 103 would then have to pass through dielectric layer 102 to reach substrate 105, however, possibly with disadvantageous effects such as energy loss, diffusion or diffraction. Accordingly, a preferred embodiment arranges the layers as shown in FIG. 1.

In a preferred embodiment, the active ingredient in dielectric layer 102 is Barium-Titanate and in luminescent layer 103 is encapsulated Phosphor. Inks doped with these ingredients are screen printed down on top of each other before envelope layer 107 is screen printed down to seal the system. Note that for optimum results, luminescent layer 103 should be deposited extremely evenly to generate a constant and predictable light emission by contact at any point on contact surface 101.

FIG. 1A depicts an alternative embodiment in which envelope layer 107 on FIG. 1 is omitted, its function replaced by a hard wearing dielectric layer 102A. In FIG. 1A, therefore, contact surface 101A is on dielectric layer 102A. Dielectric layer 102A on FIG. 1A is advantageously comprised of Barium-Titanate doped into a screen printed layer of epoxy, the epoxy selected as the binder for hard-wearing and environmental-resisting life. The advantage of the embodiment according to FIG. 1A, of course, is that it has less components and so is therefore more economical to manufacture. The disadvantage compared to the embodiment of FIG. 1, however, is that as dielectric layer 102A wears from use, the layer itself deteriorates. Ultimately, as wear continues, this may directly affect the luminescent fidelity of the inventive apparatus in describing contact on contact surface 101A. To prepare and prolong the life of the system depicted on FIG. 1A, therefore, additional catalytic cross-linking of the system is highly advantageous, using chemical or ultra-violet treatment techniques known in the art.

Returning now to FIG. 1, it will be seen that electroluminescent system 100 is incomplete inasmuch that it lacks a back electrode. Further, when power source 110 is coupled between bus bar 106 and contact plate 120 as shown in FIG. 1, an open circuit results, stretching from contact surface 101, through electroluminescent system 100, and round to contact plate 120 via power source 110.

According to the present invention, and as shown on FIG. 1, thumb 10 completes the open circuit, by concurrently touching contact plate 120 and making thumb print contact with contact surface 101. It will be appreciated that contact plate 120 is but one choice of enabling electrical contact with thumb 10, and other methods (such as a wire attached by an electrode) would have an equivalent enabling effect.

Of particular inventive significance, however, is that thumb 10 makes thumb print contact with contact surface 101. As enlarged on FIG. 2, thumb 10 makes selective zones of contact C in a pattern described by ridges 201 touching contact surface 101, while valleys 202 remain clear. The open circuit described above with respect to FIG. 1 is thus selectively closed in a pattern in register with zones of contact C. This circuit in turn causes electroluminescent system 100 to energize in a pattern in register with zones of contact C, so that luminescent layer irradiates a visible light image with high fidelity and resolution to zones of contact C. In the embodiment of the invention shown on FIG. 1, this irradiated image is projected downwards through substrate 105.

FIG. 1 also shows photosensitive array 150 immediately below substrate 105. Photosensitive array 150 may then pixelate the irradiated image described by zones of contact C on FIG. 2 into electrical signals representative of the image. These signals may be processed further according to the application for the inventive apparatus.

Referring back to discussion at the beginning of this section, therefore, it will be seen that thumb 10 on FIG. 1 may be substituted for other electrically conductive structures whose surface texture can be described by an irradiated image via contact with contact surface 101. Moreover, although FIG. 1 has described an electroluminescent system generating a visible light image describing zones of contact C on the contact surface 101, a broader aspect of the invention is that irradiated images are generated by selectively completing an open electric circuit in register with the contact. Thus, as described earlier, other forms of radiation generated via selective closure of other types of open circuit fall within the scope of the invention.

FIG. 3 illustrates the invention in cutaway view. As suggested earlier, a preferred embodiment of the invention deploys electroluminescent system 100 (as shown on FIG. 1) by successively screen printing layers according to the described laminate. Advantageously, screen printing techniques such as described and enabled in great detail in commonly-assigned, co-pending U.S. patent application "ELECTROLUMINESCENT SYSTEM IN MONOLITHIC STRUCTURE," Ser. No. 08/656,435, filed May 30, 1996, the disclosure of which application is fully incorporated herein by reference, will be used to enable the present invention. Specifically, materials, quantities and techniques disclosed in the above-referenced co-pending application using a vinyl resin carrier in gel form will enable a hard-wearing electroluminescent laminate suitable for the thumb print application described herein.

FIG. 4 illustrates the irradiated image R of the invention described by thumb print contact of thumb 10 on contact surface 101. In FIG. 4, image R is passing through to photosensitive array 150 as described above with reference to FIG. 1.

FIGS. 5A and 5B are representations of thumb print images irradiated in accordance with the preferred embodiment as described herein, as captured by a digital camera. The high degree of fidelity and resolution will be appreciated.

With reference to the preferred embodiment, application-specific adjustment of layer thickness of the electroluminescent system may be necessary, in combination with corresponding adjustment of power source parameters and dopant concentrations, in order to maximize fidelity, contrast and resolution. For example, in the thumb print generator described herein using an electroluminescent system detailed in above-referenced co-pending U.S. application "ELECTROLUMINESCENT SYSTEM IN MONOLITHIC STRUCTURE," power source 110 on FIG. 1 should generate at least 20 volts AC at approximately 1.5 kHz. Note, however, that a voltage in excess of 50 volts AC may generate an electrical sensation to an adult human user, albeit harmless at the levels of current generated by the apparatus. Power source requirements will also vary with the physical size of the irradiated image expected to described by contact. For example, in the arrangement described above, experimentation has shown 20 volts AC at 1.5 kHz generates a satisfactory image for a human fingerprint or thumb print, while 30 volts AC at 2 kHz is needed for a satisfactory palm print image.

Note that from an applications standpoint, integrated circuit chip-based inverter modules convert low direct current voltages (3 volts to 5 volts) to the suggested alternating current voltages and frequencies described. The low currents generated by these modules are ideal for PTF electroluminescent systems and are very safe for human use.

Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.