Patent Application
20060202132
Many detection problems depend on sensing a fluorescent dye that is excited by UV light. For example, many countries utilize currency that includes fluorescent dyes to make it more difficult to counterfeit the currency. The dyes are located in a specific pattern and are viewable with the aid of a UV light. In addition, different denomination bills have different dyes and/or dye patterns to further inhibit counterfeiting by printing larger denomination bills on the paper utilized for smaller denomination bills. Vending machines often include fluorescent imaging systems for determining the authenticity of currency that has been input to the machine. Similarly banks have scanners for detecting counterfeit bills.
UV LEDs are now available, and hence, an inexpensive, compact, fluorescent detection system can, in principle, be constructed for use by the average consumer. Counterfeit detection systems based on fluorescent dye detection are not, however, readily available to the general public for two reasons. First, the use of such a detection system would require the user to carry a portable viewing system for verifying the authenticity of the currency. Since the need for such verification occurs relatively rarely, most consumers are not willing to carry a separate illumination system and scanner for this purpose.
Second, such detection schemes require the use of UV light sources. Such light sources present significant safety hazards. The intensity of UV light needed to activate the dyes is sufficient to cause damage to a user's eyes. Hence, there are significant safety and legal liability problems with any consumer device that can illuminate the user's eyes with the UV light.
The present invention includes a handheld fluorescence detector that includes a handheld data processing system and a UV light source connected to the data processing system. The UV light source illuminates an object to be scanned with light having a UV illumination wavelength. The present invention includes a safety mechanism that inhibits the light from the UV light source from reaching an eye of a person in the vicinity of the UV light source at an intensity that would damage the eye. A fluorescence detector senses fluorescent light generated by the object in response to the illumination. In one embodiment, the detector includes a photodetector that detects fluorescent light emitted from the object in response to the illumination. The data processing system receives a signal from the photodetector and displays an indication of the presence of the fluorescent light on a display. In another embodiment, the detector is a human observer and the fluorescence detector includes a transparent window in a baffle system, the transparent window allowing a user of the detector to view fluorescent light emitted from the object while blocking UV light from reaching the user at an intensity that could harm the user. In one embodiment, the safety mechanism includes a baffle that allows an object to be irradiated by the UV light while preventing a user of the detector from viewing the UV light source. The baffle may include a transparent window in the baffle that allows a user of the detector to view fluorescent light emitted from the object while blocking UV light from reaching the user at an intensity that could harm the user. In one embodiment, the system includes an object sensing mechanism that generates an object present signal if an object is positioned to be irradiated by the UV light source and an interlock that prevents the UV light source from generating UV light at an intensity that would damage a user's eye when the object present signal is not generated. In one embodiment, the safety mechanism includes an optical enclosure having a transparent surface from which the UV light is internally reflected and wherein the object to be scanned is placed adjacent to the surface such that a surface of the object is within an electric field generated by the UV light. In one embodiment of this type, the fluorescence detector views the object through the transparent surface. Embodiments in which the handheld data processing system is a cellular telephone or PDA can also be constructed. One embodiment utilizes a cellular telephone that includes first and second halves that fold together when a user thereof is not talking on the cellular telephone, an object to be scanned is passed between the first and second halves when the first and second halves are folded together.
The present invention overcomes the safety problems discussed above by providing a detection device that prevents the user from illuminating his or her eyes with UV light at an intensity that could cause damage to the eye. Refer now to
UV light source 12 is preferably an UV-emitting LED. Light source 12 preferably emits UV light in the band from 350 to 400 nm.
Detector 14 includes a filter 17 and one or more photodetectors 18 that are sensitive to light in the fluorescent emission band of interest. Since the bank note is drawn past the detector, a single detector can form a one-dimensional image of the bank note along a predetermined scan path that is determined by the dimensions of enclosure 16. If only the presence of the fluorescent dye is to be detected, a single photodiode is sufficient. If a more detailed two-dimensional image is desired, an array of photodiodes can be utilized.
Filter 17 blocks any UV light that is reflected by the object being scanned from reaching the photodetectors. In one embodiment, filter 17 is a band-pass filter having a narrow band centered at the wavelength of the fluorescent band or bands of interest. The band-pass filter embodiment provides increased signal-to-noise, since it blocks visible light that leaks into enclosure 16 from outside enclosure 16.
Filter 17 can be eliminated in embodiments in which the UV light source is pulsed on and off. If the decay time of the excited phosphor is long compared to the length of the UV light pulse, the phosphor will continue to emit light after the UV light is turned off. In such embodiments, the fluorescent light is only detected between UV pulses, and hence, the background caused by the reflection or scattering of the UV light is not significant.
To further reduce the possibility of exposing the user to UV, detection system 10 can also include a bill detection mechanism for detecting the absence of a bill in the scanning region. An interlock mechanism is then utilized to prevent UV light source 12 from generating UV light at a level that could harm a user's eyes when no bill is present. Such a bill detection system preferably utilizes the components of the bill scanning system to minimize the cost of providing this additional safety feature.
The presence or absence of a bill in enclosure 16 can be detected by using the bill to block or reflect light. The light source and detector utilized for this measurement can be a separate light source and detector or the UV light source and fluorescence detector. To use the fluorescence detector and UV light source for this function, the fluorescence detector must be able to detect light in both the UV and fluorescent wavelength bands, and hence, a detector that lacks the band pass filter discussed above must be utilized. As noted above, such a detector can be used if the fluorescence measurements are performed by pulsing the UV light source to activate the fluorescent dye and then detecting the fluorescent light during the period in which the UV light source is off. In such systems, the presence of the bill can be detected by observing the light received by the photodetector when the UV light is on. The wall 13 of the enclosure that is opposite UV light source 12 includes a material that absorbs any UV light reaching that wall, and hence, no signal is recorded by photodetector 14 when the bill is absent. When the bill is placed in the enclosure, part of the UV light is scattered or reflected by the surface of the bill, and hence, light is detected by photodetector 14. During the bill detection phase, the pulse lengths and/or UV light intensity are maintained at a level that will not damage a person's eye.
When the bill detection system determines that a bill is in the enclosure, the UV light is switched to a high output power mode and the bill is scanned for fluorescence. However, the detection system continues to measure the UV light received during the actual UV pulses to determine if the bill is no longer present. When the bill is removed from the enclosure, the UV light again returns to its low power mode.
The bill detection system can also operate using a separate detector and/or light source. For example, light source 12 can include a second LED that emits light in a safe wavelength band. In such an embodiment, a second photodiode in photodetector 14 can be utilized to sense the presence of light in this safe wavelength band. In such an embodiment, the bill detection system is completely independent of the fluorescent scanning system, and hence, the photodiode used to detect the fluorescent light can utilize the blocking filter discussed above, and the UV LED can operate in a continuous mode during the scanning operation.
The above-described embodiments utilize a reflective geometry in which the UV light source and detector are on the same side of the bill or other object being scanned. In principle, a transmissive geometry can also be utilized if the fluorescent dye can be illuminated through the object and the fluorescent light can escape the object to be detected. Refer now to
The above-described embodiments of the present invention depend on some form of mechanical baffle to block light from the UV light source from reaching the eyes of a person in the vicinity of the detector. Such embodiments limit the object that is being scanned to objects that can pass through the enclosure. In addition, a user may be able to extract the UV light from the device by placing a highly reflective surface, such as a sheet of aluminum foil, in the device.
Refer now to
Refer now to
A portion of the fluorescent light generated by the excited dye will enter housing 52 and reach photodetector 54. Since the fluorescent light 58 is emitted in all directions, detector 54 can be positioned such that photodetector 54 can receive a portion of this light without receiving a significant amount of UV light. Hence, a filter for blocking the UV light is not needed. However, a band pass filter can be included in photodetector 54 to improve the signal-to-noise ratio of fluorescent detection system 50.
Refer now to
If the determination of the denomination depends on knowledge of the precise wavelengths emitted by the fluorescent dye in the bill, the photodetectors in detection head 61 can include one photodetector/band pass filter for each of the possible emission wavelengths. To minimize the number of photodiode/filter pairs, a manually changeable filter can be provided for each country of interest.
As noted above, the typical consumer does not want to carry a separate scanning device for detecting counterfeit money. Hence, embodiments of the present invention that are incorporated in cellular telephones or other handheld devices, such as PDAs are preferred. Such handheld devices already include a screen and firmware that is adapted for displaying both images and text. In addition, the amount of power required to operate the fluorescent detector will not represent a significant drain of the device's batteries.
So called “flip phones” are particularly attractive candidates for incorporating a fluorescent scanner according to the present invention. Such phones include two sections that fold together when the user is not using the phone for a making a call. A small force holds the two halves together when the phone is in the closed configuration. However, a bill can still be drawn between the two halves in the closed state.
Refer now to
Refer now to
Many flip phones include a second auxiliary display 116 that is adapted for displaying text information such as the date, time, and caller identification data. This display is utilized to display the results of the scan, i.e., counterfeit vs. real and the denomination of the bill.
Similarly, reflective embodiments of the present invention can be incorporated in such telephones. Refer now to
Total internal reflection embodiments such as those discussed with reference to
The above-described embodiments utilize one or more photodiodes to detect the fluorescent light that is emitted from the object being scanned in response to the irradiation of the object with the UV light. However, embodiments in which the user detects the presence of the fluorescent material by looking at the irradiated object can also be constructed. Refer now to
It should be noted that embodiments in which photodetector 304 are omitted could also be constructed. Similarly, embodiments in which wall 311 of baffle 307 is transparent to the fluorescent light while opaque to UV light can also be constructed.
Various modifications to the present invention will become apparent to those skilled in the art from the foregoing description and accompanying drawings. Accordingly, the present invention is to be limited solely by the scope of the following claims.
