Abstract:
The present invention relates, in general, to the field of securing, prevention of fraud, or theft of products such as pharmaceuticals, cigarettes, alcohol and other high value often counterfeited products. In particular the invention teaches an apparatus and method to encode packaging of the protected goods using a near infrared luminescing compound and detecting the compound through recognition of a characteristic spectral signature of its emission.

Description:
TECHNICAL FIELD OF THE INVENTION  
       [0001]     The present invention relates, in general, to the field of securing, prevention of fraud, or theft of products such as pharmaceuticals, cigarettes, alcohol and other high value often counterfeited products. In particular the invention teaches an apparatus and method to encode packaging of the protected goods using a luminescing compound which shifts the wavelength and detecting the compound through recognition of a characteristic signature of its emission.  
       BACKGROUND OF THE INVENTION  
       [0002]     Prevention of fraud, copying, or theft of packaged goods such as pharmaceuticals, cigarettes and alcohol has been a long-standing problem in society. In addition to prevention of fraud and theft, authentification and verification is a particular problem in the case of controlled substances such as pharmaceuticals. The prior art is replete with many approaches to deter or avoid fraud, copying or theft by placing a visible and/or invisible identification mark on the goods. Prior art identification marks have been placed on the surface of the goods or in covert locations.  
         [0003]     For example, U.S. Pat. No. 4,239,261 issued to Richardson discloses a micro-marking label applied to an article. The marker or label is formed from a small, thin plate of generally clear plastic material. The area of the marker is divided into zones into which homogeneous or digital markings are placed in order to designate a specific code to identify the object. A disadvantage of this marker is that it resides on the surface of the article and so can be seen and examined. Also, the marker can be removed or covered in which case it looses its effectiveness.  
         [0004]     In many printing applications it is necessary to distinguish an original from a copy or counterfeit item. With modern copying techniques, printed material can be reproduced easily and can be virtually indistinguishable from the original. Various means and methods have been proposed for covertly marking and identifying such items. Typically, inks or paints are used that fluoresce when subjected to an ultraviolet light. For example, U.S. Pat. No. 4,736,425 issued to Jalon discloses a two-step marking method for important documents to prevent forgery and to authenticate them. However, this method is disadvantageous because the mark must be resident on the surface of the document to be effective.  
         [0005]     U.S. Pat. No. 3,614,430 issued to Berler discloses a method of electronically retrieving coded information imprinted on a substantially translucent substrate. An ink is used to code the information that fluoresces when exposed to ultraviolet light. The fluorescence is photoelectrically sensed through the translucent substrate. A reader device then interprets the coded information. A disadvantage is that the coded information is printed on the surface of the substrate.  
         [0006]     U.S. Pat. No. 5,542,971 issued to Auslander et al. discloses a bar code printed in an upper layer and lower layer. The ink used to print the lower bar code is a regular ink which absorbs in the visible range of the spectra, i.e., between 400 and 700 nanometers. The upper layer bar code is printed using an ink that is invisible to the naked eye. The invisible inks used are based on complexes of rare earth elements such as Eu, Th, Sm, Dy, Lu and various chelating agents to produce chromophore ligands that absorb in the ultraviolet and blue spectra region. The lower bar code is read by a first excitation source emitting a first wavelength and a first sensor and the upper layer bar code is read by a second sensor detecting second excitation source emitting a second wavelength.  
         [0007]     U.S. Pat. No. 6,138,913 issued to Cyr discloses an invisible indicia or encoded information imprinted on a substrate having a compound which produces a fluorescence at a wavelength greater than about 650 nm when exposed to near infrared radiation. The information is covered by a layer of material that reflects or absorbs a substantial amount of visible and UV radiation illuminating its surface.  
         [0008]     Japanese Patent No. JP-A-3-154187 (published in 1991) discloses that a cover layer, made of infrared transparent and invisible materials can be used to cover a bar code made of an infrared absorber which absorbs infrared rays within the specific wavelength range between about 700 nm and about 1500 nm. However, the bar codes can be easily located by the use of infrared scopes, and can be easily duplicated because the information contained is in the form of a bar code and not in the form of a special signature.  
         [0009]     U.S. Pat. No. RE37491 to Itoh discloses an information storage medium including a code storage portion disposed on a base portion which contains an infrared absorber which absorbs substantially only infrared rays within a narrow wavelength band. Product verification for security purposes is made by detecting a first reflectance of a peak absorption wavelength and a second reflectance at a comparison wavelength in comparing the two. A surface layer can also be provided for concealing the code storage portion. However, the protection layer must be transparent to both visible rays and infrared rays.  
         [0010]     U.S. Pat. No. 5,083,814 issued to Guinta et al. discloses a method for applying a marking to a vehicle. The method involves a computer network of authorized dealers which are supplied with input and output devices such as computer, monitor and a hand-held marking device. Using specified locations data supplied from a central process unit, the dealer applies to the surface of the automobile a confidential and invisible registration code. A disadvantage of this method is that the mark is placed on the surface of the article and can be seen with a UV light source. Also, recognition of the spectral signature of the mark may not be remotely controlled.  
         [0011]     Therefore, there is a need for an invisible marking that can be placed within the packaging of goods which is invisible to the user but can still be tested for authenticity. There is also a need for a covered marking that is protected from being damaged, analyzed or removed but is capable of being read without being copied. There is also a need to locate and detect a marking under one or more layers of packaging or contaminants or at a relatively large distance from the packaging. Additionally there is a need to allow recognition of a signature of a product to be changed remotely through a computer network.  
       SUMMARY OF THE INVENTION  
       [0012]     In the present invention, improvements to the field of product security and prevention of fraud in respect to goods such as pharmaceuticals, cigarettes, alcohol and other highly valued products is taught. The present invention utilizes the property of luminescence of various compounds to mark products and extremely sensitive optical filters to avoid counterfeiting and generally provide an identifying signature on security tags internal to product packaging or recognizable at great distances.  
         [0013]     The following terms should be given the following meanings:  
         [0014]     “Luminescence”—The phenomenon of the emission by matter of electromagnetic radiation which for certain wavelengths or restricted regions of the spectrum is in excess of that due to the thermal radiation from the material at the same temperature.  
         [0015]     “Fluorescence”—Property of emitting radiation as the result of, and only during, the absorption of radiation from some other source.  
         [0016]     “Phosphorescence”—Emission of light which continues after the exciting mechanism has ceased.  
         [0017]     “Window of Transmissivity”—A band of radiation that will be transmitted by a group of materials making up an obscurant.  
         [0018]     “Laser”—The term laser includes illumination sources of sufficient intensity to drive the detector through the optics provided to get a result. The illumination sources can include broadband sources such as incandescent lamps and flash bulbs; for example, a zeon flash bulb. Narrow band sources are also included such as gas discharge lasers or solid state compound epitaxial lasers. Illumination sources can also include LEDs and/or arrays of LEDs. Illumination sources further include sources of selected wavelength ranges or groups of ranges.  
         [0019]     “Signature”—A parameter set.  
         [0020]     Luminescence is the property of admitting radiation as a result of excitation of a molecule by absorption of radiation and then de-excitation of that molecule or ion back to its ground electronic state. Luminescent radiation can have a longer wavelength than that of the absorbed radiation resulting in the downshift in frequency in a Stokes manner. The luminescent radiation can also have a shorter wavelength than the exciting radiation resulting in an upshift in frequency in anti-Stokes manner. For example, when irradiated with ultraviolet radiation with wavelengths between 200 and 400 nm, a known luminescent composition will emit visible light in the range of 400 to 700 nm, as disclosed in published application no. US 2005/0042428 A1, incorporated herein by reference. As another example, a known composition containing phosphor allows infrared rays in the range of 700 to 1000 nm to produce emission in the wavelength range of 800 to 1600 nm from the compound as shown in U.S. Pat. No. 5,611,958, incorporated herein by reference.  
         [0021]     Measurement of the luminescence, including spectral domain, time domain and frequency domain properties provides an identifying set of parameters which allows for comparative analysis. Such properties are material dependent and are reproducible and adjustable with the addition of dopants to the compositions which provide for patterns and sequences to the set of parameters.  
         [0022]     The present invention utilizes these principles in a security system comprised of a luminescent tagging compound with a specific spectral signature and a reader with the ability illuminate the compound and detect the signature even when very faint. The invention further teaches the ability to detect the tagging compound through several layers of packaging, contaminants or at a great distance. The invention further teaches a novel approach to a system of filters to detect the spectral, time and frequency signature of the tagging compound. Security is enhanced by the ability of the reader to be programmed through a computer network to recognize previously defined material signatures and to report test results over that computer network. Security is further enhanced by the ability of the reader to correlate the type and presence of the tagging compound to a visible bar code.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]     For a more complete understanding of the features and advantages of the present invention, reference is now made to the detailed description of the invention along with the accompanying figures in which corresponding numerals in the different figures refer to corresponding parts and in which:  
         [0024]      FIG. 1  is a graphic illustration of one embodiment of the exterior and certain mechanical features of the security tag detection apparatus.  
         [0025]      FIG. 2  is a block diagram of one embodiment of the electrical architecture of the security tag detection apparatus.  
         [0026]      FIG. 3   a  is a block diagram of an exemplary optical assembly for the laser beam delivery optics and the emission collection optics of the invention.  
         [0027]      FIG. 3   b  is a block diagram of an exemplary optical assembly for the laser beam delivery optics and the emission collection optics of the invention.  
         [0028]      FIG. 4   a  is an illustration of the temporal behavior of the driving current of the laser in an exemplary embodiment of the invention.  
         [0029]      FIG. 4   b  is an illustration of an analysis curve of an exemplary embodiment of the invention.  
         [0030]      FIG. 5  is a flow chart of one embodiment of the steps carried out by software resident in the invention to activate the security detection apparatus.  
         [0031]      FIG. 6  is a depiction of one embodiment of the steps carried out by software resident in the invention to activate the security detection apparatus.  
         [0032]      FIG. 7  is a flow chart of one embodiment of the steps carried out by software resident in the invention to activate the security detection apparatus.  
         [0033]      FIG. 8  is a flow chart of one embodiment of the steps carried out by software resident in the invention to activate the security detection apparatus.  
         [0034]      FIG. 9 s  a block diagram of the communication architecture of one embodiment of the invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0035]      FIG. 1  shows an isometric drawing of one possible embodiment of the security tag detection apparatus  100  for exciting and detecting the optical emission from an encoded package. Other configurations of the external shape of the invention are of course possible. In the preferred embodiment, the package is formed of an opaque material such as a metallic material or a plastic coated with a metallic paint.  FIG. 1  shows rotatable head  106 , package alignment receptacles  102  and indicator  104 . Rotatable head  106  pivots around a central axis which is radially oriented to the device. A plurality of package alignment receptacles  102  are distributed in rotatable head  106  and are shaped to fit a container such as a cap on a bottle. Of course, other shapes are possible and useful depending on the type of package marked. In the preferred embodiment shown in  FIG. 1  there are a plurality of package alignment receptacles in order to accommodate packages of different sizes and shapes. In this manner the same optical source and detector may be used for packages of different sizes and shapes.  
         [0036]     Package alignment receptacles  102  are positioned so that when rotatable head  106  is turned about its axis, each receptacle may be positioned over hole  105 , optical sensors  107  and physical sensors  108 . Hole  105  is a physical opening in the device allowing light to pass from the interior of the device to the exterior. In other embodiments a transparent material such as a glass, crystal or ruby window can be included to cover the hole and seal the interior of the device. Optical sensors  108  are electric photo receptors which are positioned to sense the presence of an object in the package alignment receptacle. Physical sensors  108  are mechanical switches also positioned to sense the presence of a physical object. In the preferred embodiment, the optical sensors and the physical sensors cooperate to detect the presence and position of the package to be tested and to prevent unsafe emission from escaping and ensuring that no outside light enters the device through hole  105 .  
         [0037]     In operation, a package is inserted into a chosen package alignment receptacle  102 , the package is then interrogated by a laser through hole  105 . In a preferred embodiment of the invention, if a security tagging compound is present in the package, there will be a characteristic emission of light from the compound. The characteristic emission is then analyzed by the invention for a set of recognized parameters. If no compound is present, there will be no characteristic emission. The presence or absence of emission from a security tagging compound and its potential recognition is indicated to the user through indicator  104 . In a preferred embodiment indicator  104  is a bank of light emitting diodes and LEDs of different colors.  
         [0038]      FIG. 2  shows a schematic block diagram of the electronic architecture of one embodiment of the apparatus  100  for exciting and detecting the optical emission from a package encoded with the security tagging compound. As shown in  FIG. 2 , security tag  40  is deployed on or in package  50 . In accordance with the disclosed invention, security tag  40  comprises a chemical compound that emits characteristically when irradiated by a laser, but is otherwise invisible to the unaided eye. The characteristic emission may be a fluorescent emission that is down-shifted in frequency from that of the laser in a Stokes manner. The characteristic emission may also be a phosphorescent emission that is up-shifted in frequency from that of the laser in an anti-Stokes manner.  
         [0039]     In a preferred embodiment, the laser radiation and the characteristic emission are in the infrared so as to be invisible to the human eye. In one embodiment the chemical tag comprises an organic dye that emits in the infrared. In an alternate embodiment, the chemical tag comprises a plastic film incorporating a rare earth ion from the list of rare earth ions including La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb or Lu.  
         [0040]     In another preferred embodiment, the laser radiation and characteristic emission are chosen so that both will penetrate layers of different materials used in packaging. For example, modem packaging routinely consists of a plastic exterior, a cardboard or paper wrapper and an interior metallic liner such as aluminum foil. Plastic such as polypropylene is generally transparent to visible, infrared and near infrared light in or around the 900 to 1000 nm wavelength. However, polypropylene is opaque to ultraviolet light. Similarly, paper or cardboard is opaque to visible and ultraviolet light. Therefore, the “window of transmissivity” for this combination of materials is in the infrared.  
         [0041]     In the preferred embodiment, the combination of laser wavelength and the emission spectra of the security tag compound are chosen to capitalize on the “window of transmissivity” provided by a combination of the polypropylene and paper packaging. In the preferred embodiment, the excitation and the response of the compound are chosen between 700 m and 1500 nm. Of course, other types and combinations of packaging materials will provide different “windows of transmissivity.” 
         [0042]     In the preferred embodiment, the compound containing at least one rare earth ion is applied to the surface of the aluminum foil in a plastic coating. In other preferred embodiments, combinations of various compounds with different fluorescent or phosphorescent emission can be combined to produce different emissions for the same excitation wavelength. In another preferred embodiment, combinations of various frequency laser emissions are employed to elicit different spectral responses from the same or different compounds in security tag  40 . It will be readily apparent to one skilled in the art that a variety of other chemicals and chemical compounds may be used to generate characteristic emission in response to laser radiation in accordance with the invention. Generally, excitation radiation and emission in the 250 nm to 2000 nm range is useful in the invention.  
         [0043]     The security tag detection apparatus comprises supporting electronic infrastructure including system controller  110 , user interface  112 , safety interlocks  114  and power supply  116 . The security tag detection apparatus  100  further comprises an excitation laser  122 , a laser driver,  120 , and laser beam delivery optics  126 . The security tag detection apparatus further comprises emission detector  130 , detector control electronics  132 , signal conditioning electronics  134  and emission collecting optics  136 .  
         [0044]     In a preferred embodiment system controller  110  is a microprocessor, microcontroller or digital computer. System controller  110  includes memory  111 . In a preferred embodiment user interface  112  is set of indicator LEDs, for example a set of four color LEDs to indicate the presence of absence of security tag  40  after measurement. As will be obvious to one skilled in the art this embodiment is a low cost interface that provides clear indication to an untrained operator. Alternatively, user interface  112  may be a digital display, for example a CRT display, a liquid crystal display or a field emission display, which would provide a more comprehensive user interface. In this embodiment with a more comprehensive user interface, a touch screen, keyboard or key pad may also be deployed. A USB, wireless, infrared, or wireline serial, parallel or other connection may also be included in user interface  112  to provide a sophisticated user interface connection for trained users or system programmers while maintaining the simpler LED interface for routine use.  
         [0045]     Safety interlocks  114  are present to ensure the safety of the operator in the presence of laser radiation. In a preferred embodiment safety interlocks  114  comprise an electronic circuit that prohibits the driving of the laser unless multiple signals are present indicating the proper placement of a package in the package alignment receptacle. In a preferred embodiment, the presence of a package in the package alignment receptacle may be detected by a mechanical switch. In an alternate embodiment, the presence of a package in the package alignment receptacle may be detected optically. In the preferred embodiment, a set of three switches and three optical sensors are placed in the alignment receptacle to assure that the package to be tested is securely seated and that the tag is properly located above hole  105 .  
         [0046]     The preferred embodiment further includes an optical sensor within the device to check background light “noise”. If the “noise” level is too high, the laser is not allowed to fire.  
         [0047]     Power supply  116  supplies electrical power to active components requiring voltage bias or drive current, including, in a preferred embodiment, system controller  110 , user interface  112 , safety interlocks  114 , laser driver  122 , detector  130 , detector control electronics  132  and signal conditioning electronics  134 . In alternate embodiments of the invention, laser beam delivery optics  126 , or emission collection optics  136  may also require power in order, for example, to actively scan security tag  40  to record spatially encoded, or patterned information. In a preferred embodiment, power supply  116  may be an ac-dc power supply providing multiple output voltages and currents. Alternatively, for portable applications, power supply  116  may comprise a battery power supply or an inductively coupled power transmission system.  
         [0048]     System controller  110  is functionally connected to laser driver  122  which is in turn functionally connected to laser  120 . In operation, if safety interlocks  114  indicate the presence of a package in package alignment receptacle  102 , then system controller  110  commands laser driver  122  to fire laser  120 .  
         [0049]     In a preferred embodiment, laser  120  is a semiconductor laser emitting in the near infrared portion of the spectrum, for example, from 800 nm to 1100 nm in accordance with the spectral response of the chemical compound in the security tag. It will be readily apparent to one skilled in the art that InP semiconductor lasers or GaAs semiconductor lasers, or other compound epitaxy may be used for the semiconductor laser. While a diode laser is preferred because of cost, size and power requirements, other lasers such as gas discharge lasers or solid state lasers may also be used in the invention. In an alternate embodiment, more than one laser of different spectral emission can be combined to elicit different responses from the security tag.  
         [0050]     Referring to  FIG. 2 , laser beam delivery optics are positioned to accept the laser beam and direct the beam to security tag  40 . In a preferred embodiment, laser beam delivery optics comprise at least one lens and one dichroic mirror in order to focus the laser beam and thereby enhance the emission from security tag  40 .  
         [0051]     Emission collecting optics  136  are positioned to accept the characteristic emission from security tag  40  and direct it onto detector  130 . In a preferred embodiment, emission collecting optics  136  comprise at least one lens in order to focus the characteristic emission and thereby enhance the detected signal from detector  130 . Detector  130  detects the characteristic emission and converts the optical signal to an electric signal. In preferred embodiment, the detector is a photomultiplier tube (PMT). In an alternate embodiment, the detector is a solid state semiconductor detector, for example, an avalanche photodiode (APD). In an alternate embodiment, an array of detectors may be used in order to detect the image of a spatially encoded pattern of characteristic emission.  
         [0052]     Referring again to  FIG. 2 , the electrical output of detector  130  may be further optimized using various techniques. For example, system controller  110  may adjust the response or the gain of detector  130  via detector control electronics  132 . Detector control electronics  132  in an alternate embodiment includes circuitry to minimize overload recovery time by disabling accelerating voltage on the first several dynodes of the PMT during firing of the laser.  
         [0053]     Another optimization technique entails conditioning the detected signal using signal conditioning electronics  134 . In order to meet the Nyquist criterion, an anti-aliasing filter acts as a low pass filter to the incoming waveform. The filter of the preferred embodiment filters the waveform at half the sampling frequency or less. In this way, the high frequencies resulting from the PMT are filtered out to prevent false readings and reduce noise. Signal conditioning electronics may further include analog to digital conversion (ADC) and may include a digital signal processor (DSP) such as the TMS 320 from Texas Instruments. The output of the signal conditioning electronics  134  is sent to system controller  110 . Further conditioning electronics may include high speed charge sensitive amplifiers for photon counting provided for the photomultiplier tube. In the preferred embodiment the amplifiers have a signal to noise ratio of about 100 dB.  
         [0054]      FIG. 3   a  shows a block diagram of an exemplary optical assembly for the laser beam delivery optics  126  and emission collecting optics  136 , including security tag  40 , laser  120 , and detector  130 . Further, shown in  FIG. 3   a  are laser collimator lens  312 , focusing lens  314 , coupling lens  316 , excitation filter  322 , emission filter  326 , and dichroic mirror  324 .  
         [0055]     Laser collimator lens  312  acts to collect and collimate the laser radiation emitted from laser  120 . In a preferred embodiment laser collimator is an aspheric lens that compensates the astigmatism of the diode laser beam. Bandpass excitation filter  322  allows only a limited band of illumination wavelengths to illuminate the security tag. In the preferred embodiment the bandpass filter is a long pass filter with a rejection ratio close to 10,000:1. Dichroic mirror  324  reflects the laser beam radiation toward security tag  40 . The dichroic mirror should have a rejection ratio of about between 5:1 and 100:1. In other embodiments the dichroic mirror may be replaced with a partially silvered mirror. Focusing lens  314  is a focusing lens to concentrate the laser radiation and thereby boost the characteristic signal level emitted from the security tag. In the preferred embodiment the focal point of the lens is at the surface of the security tag. The surface of the security tag may be several layers beneath the surface of the product. The characteristic emission from security tag  40  is collimated by focusing lens  314 , and is transmitted through the dichroic mirror. Emission filter  326  further rejects radiation that is not in the spectral band of the characteristic emission. In the preferred embodiment the rejection ratio of the emission filter is close to 10,000:1. Lens  326  focuses the characteristic emission onto detector  130 . In the preferred embodiment the characteristic emission is chosen to order to match the preferred collection aperture of detector  130 .  
         [0056]     In the preferred embodiment, security tag  40  is placed under covering layer  42  and covering layer  41 . Covering layer  42  is typically polypropylene plastic. Covering layer  41  is typically of compressed cardboard. In the preferred embodiment, security tag  40  comprises a thin layer of aluminum foil on which is deposited a chemical layer producing a characteristic emission desired. In other embodiments the covering layers can consist of contaminants such as dirt, dust or ice. The combination of collimator lens  312  focusing lens  314  coupling lens  316 , bandpass excitation filter  322 , emission filter  326 , dichroic mirror  324  and signal conditioning electronics as described result in a signal to noise ratio before signal processing of between about 50 db and about 130 db.  
         [0057]     It should be noted that the exact arrangement of the optical assembly may be modified to achieve the same functionality. For example, laser collimator lens  312 , focusing lens  314 , and coupling lens  316 , may each comprise multiple optical elements for enhanced performance. Similarly, the position of bandpass excitation filter  322  may be shifted relative to the laser collimator lens  312  if desired. The position of emission filter  326  may be shifted relative to coupling lens  316  if desired.  
         [0058]     In an alternate embodiment, the dichroic filter of the optical assembly may be mechanically pivoted and driven to scan the laser beam spatially in order to acquire a characteristic response in a spatial pattern from a patterned security tag. Alternatively, focusing lens  314  and coupling lens  316  may together image the characteristic emission onto a detector array in order to acquire spatial pattern information.  
         [0059]     Referring now to  FIG. 3   b  an alternate embodiment of an exemplary optical system for the laser beam delivery objects  126  and the emission collecting optics  136  is shown in a block diagram. In this block diagram dichroic mirror  324  serves to direct delivery of the excitation from laser  120  toward security tag  40 . In this embodiment distance “d” between focusing lens  314  and security tag  40  can be a great distance depending on the characteristics of the medium separating the two. For example, in one preferred embodiment where the medium separating dichroic mirror  324  and security tag  40  is dry air distance “d” can be up to about 5,000 feet. In another example where the separating medium is wet air such as encountered during rainy conditions, the distance “d” can be up to about 1,000 feet. It will be recognized by those skilled in the art that the distance is dependent on the signal ratio of the laser excitation to the returning emission from the security tag.  
         [0060]      FIG. 4   a  shows the temporal character of the input current driving the laser radiation of the preferred embodiment of the tagging compound in time traces. Trace  410  is a square wave that approximates the temporal behavior of the input current to the laser. Input current rises quickly starting at time t=t 1 , to a constant value and abruptly falls at time t=t 2 . It will be understood by those skilled in the art that the input current can be repeated in a train of such pulses in order to repeat the measurement process and thereby acquire sufficient signal to overcome noise.  
         [0061]     The time trace shown in  FIG. 4   b  at  430  is the output voltage of the PMT according to the characteristic emission of the security tag. There are four distinct stages to the time trace. The initial level of the background voltage of the PMT is small but non-zero at t=0 to t=t 1  shown as approximately a 1 . At t=t 1 , there is a rapid linear rise from signal level a 1  to signal level b 1  caused by the onset of illumination after the laser fires. The signal continues to grow, characterized by an exponential with a time constant T 1  ending in a signal level c 1  at t=t 2 . At time t=t 2 , the end of the laser radiation pulse, to t=t 3 , a linear decay lowers the signal level to b 2.  The signal then takes on an exponential decay with a time constant T 2  ending at a final level a 2  at t=t 3 . In this example, t 3 ≅5T 1 , where T 1  is a time constant related to the compound in the security tag.  
         [0062]     In the preferred embodiment, the increase of the PMT voltage during the period t 1 &gt;t&gt;t 2  is described by the equation: 
 
 V   PMT   =K 1 −K   1   e   (1−t/T     1     1)   +a   1  
 
 Similarly, the decrease of the PMT Voltage during the period t 2 &gt;t&gt;t 3  is controlled by the equation: 
 
 V   PMT   =K   1   e   −t/T     2     −a   1  
 
         [0063]     Where K 1  is a material constant. In the preferred embodiment, in order to determine the signature of the security tag  40 , the values of a 1 , b 1 , c 1 , T 1 , K 1 , a 2 , b 2 , and T 2  are repeatedly measured for a train of 16 pulses over a space of about 0.5 seconds. During the period between t=0 and t=t 1 , 20 readings are taken at equal time increments before the laser pulse begins. 160 readings are taken between t=t 1  and t=t 2  at equal time intervals during the period that the laser pulse is active. 40 equally timed readings are taken between t=t 2  and t=t 3  during the period that the laser pulse is deactivated, resulting in  220  readings for each pulse. Each similarly timed reading is summed for each of the 16 pulses and a regression analysis is used to determine the best value for each reading. After completion of a regression analysis, values of a 1 , b 1 , c 1 , T 2 , K 1 , a 2 , b 2 , and T 2  are determined from the best values of the data. These values form the signature of the tagging compound of the security tag. In an alternate embodiment, any single value or subset of values from the group of a 1 , b 1 , c 1 , T 1 , K 1 , a 2 , b 2 , and T 2  can be used as the signature of the compound.  
         [0064]     Memory  111 , contained in the controller, possesses a lookup table of predetermined values of the spectral signature for one or more formulations of tagging compounds. The values derived from the data are compared to the values in the lookup table within a precision of some multiplier of the standard deviation of each average. In the preferred embodiment, the multiplier is 3. As will be apparent to those of skill in the art, since the standard deviation varies with background noise, a dynamic threshold is established which reduces or eliminates false readings. If the values meet the prescribed criteria, a “match” is declared by the processor and appropriate signals are sent to report the condition to the interface.  
         [0065]      FIG. 5  shows a cross-sectional view of an example of a packaging application and a chemical security tag. This packaging application is typical of bulk packaging of pharmaceutical pills as delivered to pharmacies from manufacturers. Container  510  is closed with plastic cap  512  which typically supports a cardboard liner  514 . The package typically includes a hermetic seal  516  comprising foil or polymer bonded to the top of container  510 . In a preferred embodiment, hermetic seal  516  comprises the marking surface  520  for security tag  40 . Incident laser radiation  530  propagates through plastic cap  512  to excite the tagging compound printed on or included within hermetic seal  516 . The characteristic emission  540  propagates back through cardboard liner  514  and plastic cap  512  following the same “light cone” where it is measured by detector  130 .  
         [0066]      FIGS. 6, 7  and  8  show flow charts illustrating a method of security tag detection in accordance with another aspect of the invention. In  FIG. 6  is the overall algorithm for security tag detection programmed into and running in the system controller comprising a Main Loop  610  and a Measure Loop  620 .  FIG. 7  shows detailed steps comprising Main Loop  610  and in  FIG. 8  shows detailed steps comprising Measure Loop  620 .  
         [0067]     Referring now to  FIG. 7 , Main Loop  610  comprises Measure Key Status step  710 , Interlock Key Status step  720  and Light Sensors Dark Status step  730 . If Measure Key Status Step  710  results in a “no” response, then logic loops waiting for a “yes” response. If step  710  results in a “yes” response then logic proceeds to step  720 . If Interlock Key Status Step  720  result in a “no” response, then logic proceeds to Debounce step  740 . Those skilled in the art will recognize that Debounce step  740  allows the measurement electronics and line voltages to “settle” before proceeding. If step  720  results in a “yes” response then logic proceeds to step  730 . If Light Sensors Dark Status step  730  results in a “no” response, then logic proceeds to Debounce step  740 . Light Sensors Dark Status step  730  results in a “yes” response, then the logic proceeds from Main Loop  610  to Measure Loop  620 .  
         [0068]     Referring now to  FIG. 8 , Measure Loop  620  comprises Check PMT Background Light step  810 , Set PMT Gain step  820 , Check PMT Background Light step  830 , Measure Security Tag step  840 , Calculate Algorithm Step  850  and Indicate Output step  860 .  
         [0069]     Even in total darkness a small anode voltage from the PMT is typically present. In order to set a base line for gain calculation, at step  810  the system controller checks the anode voltage from the PMT.  
         [0070]     At PMT gain step  820  the system controller uses the value of PMT voltage derived at step  810  to set the gain of the PMT. In a preferred embodiment, a useful gain control algorithm is utilized to compensate for a temporal hysteresis of the PMT. In this algorithm, the gain is ramped up from the minimum value until optimal signal level is reached. This counterintuitive approach yields a faster acquisition than dithering the gain around the midpoint value.  
         [0071]     Once the gain is set, measure loop  620  moves to step  830  where the background light of the PMT is again checked. If the PMT output voltage reading from the PMT at step  830  exceeds that determined in step  810  the system controller returns to step  810  in order to assure that the proper gain is set.  
         [0072]     Proceeding to step  840 , the system controller transmits appropriate signals to activate the laser and monitor the PMT voltage to gather useful data concerning the signature of the security tag. At step  850  the data is averaged and the calculations for the required coefficients are made. Once calculations for the coefficients are complete comparison is made with the table stored in memory which contains parameters of measured information for one or more types of security tags.  
         [0073]     Moving to step  860 , if the comparison step results in a “match” this condition is reported at step  860 . Similarly if the condition results in a “mismatch” the condition is also reported. The program then exits to main loop  610  to await another test.  
         [0074]     The data table stored in memory may contain numerous sets of parameters characterizing the signature of many different types of materials. One skilled in the art will recognize that multiple tests can be run on the same security tag and the results compared with the sets of parameters in the table. In one preferred embodiment of the invention, more than one type of compound is used so that varied security tags can be created. The ability to have different security tags recognized by the invention allows indexing of security tags for different products or for different users.  
         [0075]     The data loaded into memory  111  can be uploaded from many sources. Referring to  FIG. 9 , a network architecture  900  is shown including system controller  110  and memory  111 . In  FIG. 9  system controller  110  is connected to a communications module  112 . In the preferred embodiment communications module  112  is a protocol manager capable of supporting an address and receiving and transferring data via TCP/IP protocol. Communications module  112  is further connected to wireless communications controller  925 , internet  910  and ethernet  915 . In turn ethernet  915  is connected to various network nodes  920 . Using this architecture, data tables can be uploaded from any number of sources to memory  111  through communications module  112 . Additionally, test responses can be downloaded indicating the results of test from one or more groups of tests procedures carried out by the invention. As a result, additional security is provided because the spectral signature of the security tag can be changed without the knowledge or cooperation of the person conducting the test.  
         [0076]     Additionally, wireless communications controller  925  can include a position tracking sensor so that the physical location of the device can be monitored. In one embodiment, the position tracking sensor includes a GPS location device. In other preferred embodiments, the location device includes a dedicated cell phone and use of caller ID information. Moreover, if the device is used on a portable platform, the location can be used to determine the signature that is expected by the system controller to determine a “match”. For example, a first type of pharmaceuticals may be present for a first security tag at a first location and a second type of pharmaceuticals at a second location with a second different security tag. The memory contains a first predetermined signature and a second predetermined signature correlated to different locations. Without reference to or knowledge of the user, GPS data is used by the system controller to choose the correct predetermined signature for each location and recognize the first and second security tags as genuine even though they have different signatures.  
         [0077]     In another preferred embodiment, the signature of the security tag can be correlated to an external marking on the package. For example, a bar code is programmed to include information related to the presence or absence and type of compound used in the security tag. In use, the bar code is read by a conventional bar code scanner and the security tag is read by the apparatus, and the results are compared by system controller  110 . Security is increased because a counterfeiter cannot consistently detect the correlation of the presence and type of the compound (or absence of the compound) to the bar code and so cannot duplicate the combination.  
         [0078]     While this invention has been described in reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications and combinations of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to the description. It is therefore intended that the appended claims encompass any such modifications or embodiments.