Pulsed Excitation Document Verification Residual Fluorescence
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Solution Overview
Problem
Existing methods for detecting counterfeit documents of value, particularly banknotes, often misclassify genuine documents with weak phosphorescence signals as counterfeit due to residual fluorescence from UV lamp afterglow, leading to incorrect sorting out of genuine documents.
Innovation Solution
A method involving pulsed excitation light with periodic switching, where the first luminescence intensity is recorded during illumination and the second luminescence intensity during darkness, with the latter corrected by scaling the former to account for residual fluorescence, allowing for accurate comparison against a threshold to determine phosphorescence authenticity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a high threshold value is set for phosphorescence signal detection, then counterfeit documents with residual fluorescence are correctly rejected, but genuine documents with weak phosphorescence signals are also rejected
Solution Approach 1:
The patent extracts and removes the harmful residual fluorescence signal from the phosphorescence measurement by detecting it separately during the illumination phase and subtracting it from the dark phase measurement. This isolation of the interfering signal allows for accurate phosphorescence detection without requiring a high threshold that would reject genuine documents.
Solution Approach 2:
The patent performs preliminary detection of the residual fluorescence signal during the illumination phase before the phosphorescence measurement is taken. By measuring and storing this residual signal in advance, the system can subsequently subtract it from the dark phase signal to obtain the true phosphorescence intensity, enabling accurate detection of genuine documents with weak signals.
2Device complexity
If the UV lamp afterglow is not compensated, then the phosphorescence measurement is simplified, but residual fluorescence falsifies the phosphorescence signal
Solution Approach 1:
The patent implements a feedback mechanism where the residual fluorescence signal detected during illumination is fed back and subtracted from the dark phase measurement. This closed-loop approach automatically compensates for the UV lamp afterglow effect, maintaining measurement precision without requiring complex hardware modifications or manual calibration.
Solution Approach 2:
The patent introduces an intermediary calculation step that computes the residual fluorescence contribution based on the illumination phase signal and uses this intermediary value to correct the dark phase measurement. This mathematical intermediary allows the system to separate the overlapping fluorescence and phosphorescence signals without additional physical components.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively distinguishes genuine from counterfeit documents by accurately assessing phosphorescence signals, reducing false positives and ensuring genuine documents with weak signals are not misclassified, even when heavily soiled.
Implementation Method 1
The term luminescence is understood as a generic term for the radiation emitted back by the document of value after optical excitation. Both fluorescence intensity and phosphorescence intensity can therefore contribute to the luminescence intensity.
Implementation Method 2
Both fluorescence intensity and phosphorescence intensity can therefore contribute to the luminescence intensity.
Implementation Method 3
A first luminescence intensity is detected from the document of value or from a portion of the document of value within a first time interval in which the light source is switched on, and a second luminescence intensity is detected within a second time interval in which the light source is switched off.
Data Source
Figure 1a~1c
Figure 2a~2b
Figure 3a~3c
AI summary
The method involves illuminating value document with clocked excitation light of a light source. The excitation is switched ON and OFF between predetermined time interval. The luminescence intensity of value document within the bright phase of excitation light is detected. The luminescence intensity of value document within the dark phase of excitation light is detected. Both the luminescence intensities are compared to determine corrected luminescence intensity of phosphorescence areas (A,P) of value document. An independent claim is included for apparatus for checking value document.