WO1999026074A1

WO1999026074A1 - Dielectric scanning probe for paper characterization

Info

Publication number: WO1999026074A1
Application number: PCT/US1998/024656
Authority: WO
Inventors: Abe Eftekhari
Original assignee: MNEMONIC SYSTEMS INCORPORATED A Nichols Research Corporation
Priority date: 1997-11-19
Filing date: 1998-11-19
Publication date: 1999-05-27
Also published as: AU1464199A

Abstract

A method and device to verify the authenticity and genuiness of currency or other documents. An array of capacitive electrodes (130) is pressed against both sides of the document under test (100). The capacitive array is probed so data related to the impedance values are generated and stored. Those values are then correlated to values representative of genuine documents and the authenticity of the document under test is thus established. Data values that do not correlate within certain limits would point out to a counterfeit or defective document.

Description

DIELECTRIC SCANNING PROBE FOR PAPER CHARACTERIZATION

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority from provisional patent application Serial No. 60/066,167 filed November 19, 1997, entitled DIELECTRIC SCANNING PROBE FOR PAPER CHARACTERIZATION, which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to product sensors, and more particularly to a product sensor that measures dielectric values of a product to compare with known values to determine a likelihood of product origin.

2. Description of Related Art

There are a number of circumstances in which it is desirable to determine the properties of a product such as paper with some precision. Generally, in forensics science, it is desirable to be able to determine whether a sample of paper, film, printing media of various sorts and sheet media in general (hereinafter collectively paper) originate from a common source or, more specifically, whether they are genuine exemplars of what they purport to be. This approach is particularly useful in the determination of counterfeit currency. A number of techniques are well known for detecting counterfeit currency.

SUMMARY OF THE INVENTION

In this application, an electronic Counterfeit Bill Detector system utilizes the experimental finding that microstructural characteristics and morphology of laminated films, polymers and paper depend upon the manufacturing process as well as the aging and weathering history and can be used to discriminate paper from different sources.

Different paper type ages differently, and the microvoid distributions and size are the two factors which determine source, type and even the differences between the products from different batches.

Low quality paper's microstructural property is very different from well manufactured paper. The chemical components of the raw material, synthesis condition, aging, and environmental conditions are the prominent factors in durability and integrity of the paper.

While every counterfeit detection device in the market determines the integrity of image and printing on the paper, this inventive device and techniques measure a fundamental property of the paper, namely Dielectric constant. Dielectric value is an indicator of the dipole property and the amount of moisture and other materials contained inside the microscopic pores [microvoid] within the thickness of the material. While the print and images can be distorted, destroyed, or copied, the internal properties of the substrate of the printed film [e.g. paper] stays substantially unchanged. The microscopic structure of paper can not be copied and the change in the physical properties with time is very different from manufacturing lot to manufacturing lot.

Applications of this innovation find use in detection of bogus money and valuable documents, in source determinations and matching of copies, fax documents, origination of letters and documents, and even in tracing of white paper evidences to the origination point. Counterfeit detection experts, usually use different electronic devices with various degrees of sensitivities, but they all believe in a sense of "FEELING & TOUCH" of the documents, and in determination of hardness and texture of the paper by direct examination. The dielectric device's measurement and output is directly related to the properties of texture or TOUCH for the document. There is a need for an arrangement that is able to accurately identify the origin of a product, such as a form of currency.

There is a need for an arrangement that utilizes the capacitance value of a product to compare with a predetermined value of a known reference-standard to identify the likelihood that the product originated from the same source as the reference- standard. There is a need for a method that relies on the accuracy of measurements, such as capacitance, for confirming the likelihood a product such as currency originates from a authentic source.

There is also a need for an arrangement that intuitively provides a user interface for displaying the likelihood a tested product, such as currency, originates from an authentic source.

These needs are satisfied by the present invention, where a source-identifier sensor for confirming origination of a product is provided. The source-identifier comprises: an ultra-high frequency (UHF) oscillator that produces analog UHF signals which oscillate between two voltage levels; a UHF resistive/capacitive bridge or voltage divider having a pair of contacts coupled to the oscillator, wherein the product is placed between the contacts for measuring a product value; a computing unit that compares a property of the product value with a reference value associated with origination of a reference product to which the product is being compared, and identifies a correspondence between the product value and the reference value. Every product source produces a unique variation of product based on contaminants such as water and soil contained within microscopic pores of the product, and these contaminants effect the product's capacitance. The source-identifier sensor of the present invention accurately measures a test product's capacitance to determine the likelihood the product originates from the same source as a reference-standard product previously identified as originating from the source.

According to one aspect of the present invention, a method of measuring a property of a product to determine a likelihood the product originates from a source which produced a reference-standard product is provided. The method comprises: supplying an ultra-high frequency (UHF) analog signal across a pair of contacts of a resistive/capacitive bridge, wherein the product is disposed between the contacts; determining a magnitude of capacitive displacement current through the product by measuring an attenuation ratio of current sensed at each of the pair of contacts; and comparing the magnitude of capacitive displacement current with a reference magnitude associated with the reference standard product to determine if the magnitude of capacitive displacement current is within a predetermined error range associated with the reference magnitude so as to indicate the product originates from the source which produced the reference standard product.

Another aspect of the present invention provides a graphical user interface for providing an indication of product origin, comprising: a value portion that displays measured values of an attenuation ratio of displacement current sampled across a test product; a code portion that displays a code corresponding to a reference product associated with reference values to which the measured values are compared; and an outcome portion that displays a result of a comparison between the measured values and the reference values. The present invention relies on measurement of the capacitive displacement current through an unknown sample placed in a test fixture. The instrument scans the face of the sample and a numerical normalized value of dielectric constant for each point is determined and a statistic such as an average calculated. The data will be stored in the memory of the instrument and the operator can enter a code related to the specific document. The instrument will then display a message stating if the document is a counterfeit or a real one. A correlation coefficient, a number between 0 and 1, will also be displayed on the panel as a measure of confidence in the determination of genuineness; the number one being 100% correlation, and zero no correlation.

Additional objects, advantages and novel features of the invention will be set forth in, or apparent from the following detailed description of the preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference is made to the attached drawings, wherein elements having the same reference numeral designations represent like elements throughout and wherein:

Figure 1 is a perspective view of an exemplary assembly for measuring properties of paper.

Figure 2 is a plan view of an exemplary arrangement of probes for sampling properties of paper. Figure 3 is a side view of an exemplary assembly for measuring properties of paper. Figure 4 is a side view of an exemplary disk with preferred measurements utilized in the assembly of Figure 3.

Figure 5 is a schematic diagram of electronic circuitry used with the assembly of Figures 1 and 3. Figure 6 is a schematic diagram of an exemplary bridge assembly shown in

Figure 5.

Figure 7 is an exemplary graphical user interface for use in measuring properties of paper in accordance with the invention.

Figures 8 and 9 show results achieved using the techniques and apparatus of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The electronic Counterfeit Bill Detector system employs the physical principle of measurement of the dielectric properties at multiple points on paper sample being tested. The supporting electronics for the measurement apparatus consists of an Ultra High

Frequency (UHF) oscillator, amplifier and power divider feeding 8 UHF resistive/capacitive bridges or dividers [Figure 1]. Coaxial cables provide the connection between the above components and eight spring loaded contacts (pogos) within a shielded sample holder [Figure 2]. A radio frequency detector connected to each divider or bridge measures the attenuation ratio at each sampling point and converts the UHF to direct current (dc).

An Analog to Digital Conversion card samples each of the eight rectified bridge dc output levels and also samples two reference levels from similar bridges made with fixed reference capacitors. The fixed reference values are representative of the valid sample attenuation range. The fixed reference values may be different for different types of samples. The attenuation measurements of samples falling within an acceptable range shall be considered as valid samples.

Figure 1 is a perspective view of an exemplary assembly for measuring properties of paper. A paper sample, such as a sheet of currency is placed in the sample area 100 of base 110. The lid 120 is lowered bringing individual contacts 130 to bear against the currency located in the sample area. Figure 2 is a plan view of an exemplary arrangement of probes for sampling properties of paper. As shown in both Figures 1 and 2, a plurality of probes 130 are brought to bear upon a paper sample, for example, a unit of currency, for measuring the paper^'s property. Figure 3 is a side view of an exemplary assembly for measuring properties of paper. A copper clad printed circuit board 300 serves as a ground plane and a plurality of lower contacts 310 support a sheet of currency. Upper contacts 320 are spring loaded so that top contact 320 presses against the paper located between lower contact 310 and upper contact 320. When pressure is applied, the spring applies force against the paper between the two contacts keeping it substantially flat. Each of the upper contacts 320 is mounted to a post 330 which floats in a hole through the Bakelite™ sheet 340 and is held in place by a retainer on the upper side of the Bakelite™ sheet and by the spring and disk on the lower side of the sheet. Each of the posts 330 is connected by a connector 350. such as a BNC connector for the application of RF energy over conductor 355 to post 330.

Figure 4 is a side view of an exemplary disk with preferred measurements utilized in the assembly of Figure 3 for the upper and lower contacts.

Figure 5 is a schematic diagram of electronic circuitry used with the assembly of Figures 1 and 3. A voltage controlled oscillator, 500, is tunable by the application of an adjustable D.C. voltage from D.C. tune level 510. The VCO has a +9 dbm output into a 50 ohm load. That output is fed to amplifier 515 which provides amplification in a frequency range of 2 to 2,000 MHz. In the example shown, it provides a gain of approximately +10 dbm. The output of amplifier 515 is applied to splitter 520 where the incoming signal is divided into two components, each going to a respective amplifier 525. Amplifiers 525 have band passes in the range of 10 through 1,000 MHz and provide approximately +13 dbm gain. The output of amplifiers 525 are applied to respective splitters 530 which split the signal into six substantially equal components for application to the circuitry shown in Figure 6 (540). Each of splitter 520, amplifiers 525, and splitters 530 have input and output impedances, in this example, in the 50 ohm range.

Turning to Figure 6, the ten outputs from splitters 530 are applied as inputs 610 shown at the left extreme of Figure 6. Each input 610 is fed through a resistor 620. Four of the inputs in each of the upper and lower banks of inputs from the respective splitters is applied to a contact probe 130 which is identical with the upper contact 320 shown in Figure 3. A sample of paper is inserted between the contact probes 130 (320) and 310. The RF applied to input 610 goes through resistor 620 and is applied across the sample by contact probes 320 and 310. The amount of capacitance between those probes is effected by the dielectric of the paper inserted between the contacts. As a result, there is a voltage drop which is a function of the amount of capacitance across contacts 320 and 310, with the sample in place. As a result, the amount of signal applied to an output 630 is a function of the relative impedance of resistor 620 and the capacitive reactance across the contacts 310 and 320. A separate calibration channel 640 is utilized with standard capacitors 650 for each of the banks of probes. The standard capacitors 650, in combination with the resistor 620 for that channel provide a known voltage drop against which the outputs of the other capacitive probes can be referenced.

Returning to Figure 5, the output signal level which comes off the bridge arrangement shown in Figure 6 is detected by RF detectors 550. RF detectors 550 are passed to a multiplex sampler 570 over a PC (personal computer) board interface 560 for sampling and for analog-to-digital conversion in ADC 580 within a PC 590. The sample data are then stored and displayed as discussed more hereinafter.

In operation, the properties of the paper are measured by placing a sample in the measuring assembly, closing the lid, applying some pressure to ensure that the probes 130 are snug against the sample, measuring the voltage output from the bridge arrangement resulting from the application of the RF energy across the sample and then sampling and storing the values for later interpretation.

Figure 7 shows exemplary graphical user interface for use in measuring properties of paper. In the examples shown, the eight values resulting from an eight point measurement of dielectric constant are displayed together with an average. Code 105 shown is an index that the database uses for different documents for correlation purposes. The 100 series of codes are reserved for American (USA) denominations, i.e. 105 for $5 currency. The instrument correlates the measured points versus the values in a database developed using known good currency. A correlation co-efficient will be calculated and displayed and, in some implementations, the instrument will determine if the document is a real or a counterfeit document based on the correlation co-efficient value.

The data illustrated in Figures 8 and 9 show the comparison in normalized dielectric constant between the genuine denomination and counterfeit money. For both cases, the error bar is equal to twice the related standard deviation. The difference in dielectric for both figures is higher than two standard deviations. When calibrating the instrument, an ultra pure sheet of Teflon ™ is preferably utilized which has a known dielectric constant and which enables variations in instrumentation error to be normalized and removed from the calculations. Thus, using the apparatus and techniques shown and described, highly reliable detection of counterfeit currency can occur. In addition, paper samples from a variety of forensic applications can be compared to determine whether or not they originate from the same source, or alternatively, from a genuine source.

Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation.

Claims

WHAT IS CLAIMED IS:

1. A source-identifier sensor for confirming origination of a product, comprising: an ultra-high frequency (UHF) source that produces analog UHF signals; a UHF measuring circuit having at least one pair of contacts coupled to the source, wherein the product is placed between the contacts for measuring a product value associated with a product property; and a processing unit that compares the product value with a reference value range associated with reference products to which said product is being compared, and determines if said product value falls within said reference value range.

2. The source-identifier sensor of claim 1 wherein the property compared is magnitude of dielectric constant measured by said UHF measuring circuit.

3. The source-identifier sensor of claim 1 wherein the property being compared is related to one of dipole property and amount of moisture or materials contained within microscopic pores of said product.

4. The source-identifier sensor of claim 1 wherein the bridge has a plurality of pairs of contacts for measuring product values taken at locations on said product, wherein said computing unit compares said product values to a plurality of reference values of said reference product at locations corresponding to those measured by said source-identifier.

5. The source-identifier sensor of claim 1 wherein the product comprises a sheet of material.

6. The source-identifier sensor of claim 5 wherein the sheet of material is selected from the group consisting of film, laminated films, polymers, printing media and paper.

7. The source-identifier sensor of claim 5 wherein the sheet of material is a form of currency.

8. The source-identifier sensor of claim 1 further comprising: an amplifier, coupled to said oscillator, for amplifying an analog signal supplied by the oscillator; a power divider, coupled to the amplifier, for splitting the output of said amplifier and applying respective outputs to a respective pair of contacts, with each contact of a pair of contacts placed on opposite sides of said product and a plurality of detectors each measuring a product value at particular locations across said product.

9. A method of measuring a property of a product to determine a likelihood that a product originates from an authorized source, comprising: applying an ultra-high frequency (UHF) analog signal across at least one pair of contacts with said product disposed between said at least one pair of contacts; determining a magnitude of capacitive displacement current through said product; and comparing said magnitude of capacitive displacement current with a reference magnitude range associated with products known to originate from an authorized source to determine if said magnitude of capacitive displacement current is within said range so as to indicate said product originates from an authorized source.

10. The method of claim 9 further comprising calibrating a pair of contacts by measuring a calibration magnitude of displacement current across separate calibration capacitance and using said calibration magnitude as a reference for determining said magnitude of capacitive displacement current.

11. The method of claim 10, wherein said reference magnitude range associated with said standard-reference product is based on a standard deviation.

12. The method of claim 11 in which the method further comprises using an error value equal to approximately twice the standard deviation when determining if said magnitude of capacitive displacement current is within a predetermined error range.

13. The method of claim 9, wherein the measurement of displacement current is used to determine a dielectric value associated with said product.

14. The method of claim 13 further comprising scanning a plurality of points across a surface of the product, normalizing a value of dielectric constant at each point, and storing normalized values in memory for comparison to a user selected standard dielectric value.

15. The method of claim 13 further comprising displaying a measure of confidence based on a correlation coefficient calculated between the dielectric values of a sample being measured and dielectric values from samples known to originate from an authorized source.

16. A graphical user interface for providing an indication of product origin, comprising: a value portion that displays measured values of an attenuation ratio of displacement current sampled across a test product; a code portion that displays a code corresponding to a reference product associated with reference values to which said measured values are compared; and an outcome portion that displays a result of a comparison between the measured values and the reference values.

17. The graphical user interface of claim 14, wherein the result displayed by the outcome portion is achieved by determining if said comparison is within a predetermined error range.

18. The graphical user interface of claim 14, wherein the result displayed by the outcome portion is achieved by determining if a plurality of comparisons corresponding to a plurality of locations on said test product are within a predetermined error range to confirm said test product originates from a source producing the reference product.

19. A method of detecting counterfeit documents or currency, comprising the steps of: a. measuring a dielectric constant of paper on which a document or an item of currency is printed; and b. comparing said dielectric constant with dielectric constants of genuine documents or currency.