Smartphone Verification of Luminescent Security Features
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Solution Overview
Problem
Luminescent-based security features are difficult to verify using inexpensive and widely available devices like smartphones due to issues with excitation source emissions matching expected emissions and short decay times of phosphors, making them unsuitable for easy verification under everyday conditions with high security requirements.
Innovation Solution
A method using a specific phosphor with a decay time in the ms range, configured to be excited by a smartphone's flash LED, allowing reliable detection of decaying luminescence signals after excitation, and an app-based system for image acquisition and processing to verify the security feature's presence and properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a smartphone flash LED is used as the excitation source for verifying phosphor-based security features, then the device becomes portable and widely accessible, but the excitation source emits the same wavelengths as the security feature, precluding reliable verification
Solution Approach 1:
The patent extracts and removes the problematic emission wavelengths from the excitation source by using a filter that blocks the specific wavelengths emitted by the security feature phosphor. This allows the smartphone flash to be used as excitation source while preventing the interfering emissions from reaching the camera sensor, thereby resolving the contradiction between portability and verification reliability.
Solution Approach 2:
The patent introduces an intermediary component - a wavelength-selective filter - between the excitation source (smartphone flash) and the detection system (camera). This filter mediates the interaction by allowing excitation wavelengths to pass through while blocking the emission wavelengths of the security feature, enabling reliable verification using a portable device.
2Adaptability or versatility
If phosphors with very short decay times (nanosecond to microsecond range) are used in security features, then the security feature can be excited by smartphone flash, but the emissions subside before the camera can capture the image
Solution Approach 1:
The patent changes the temporal parameter of the phosphor emission by selecting phosphors with longer decay times (microsecond to millisecond range) instead of the conventional nanosecond to microsecond range phosphors. This parameter change allows the emission to persist long enough to be captured by the smartphone camera, resolving the contradiction between smartphone compatibility and emission detectability.
3Ease of manufacture
If conventional phosphors commonly found in flash LEDs are used in security features, then manufacturing is simplified, but verification becomes impossible because the excitation source exhibits the same emissions expected from the security feature
Solution Approach 1:
The patent applies local quality by selecting phosphors with specific spectral characteristics (different emission wavelengths) for the security feature compared to those in the flash LED. This creates a local distinction in the spectral domain, allowing the security feature to be differentiated from the excitation source emissions through wavelength-selective filtering and detection.
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
Enables secure verification of luminescent security features using a smartphone, ensuring the authenticity and integrity of documents by distinguishing the phosphor's decay time and spectral distribution, reducing the need for specialized equipment and minimizing false rejections.
Implementation Method 1
The phosphor can be excited to luminescence by electromagnetic radiation of a predetermined wavelength, whereupon it emits radiation. The emission of the phosphor has a decay time in the millisecond range.
Implementation Method 2
The emission can be detected by means of an image capture unit of a smartphone
Data Source
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AI summary
The invention relates to a method for the verification of a luminescent-material-based security feature, which contains a luminescent material in which an emission can be stimulated, by means of a smartphone. In a first step, an emission of the luminescent material of the security feature can be stimulated by means of an illumination unit of the smartphone. After the completion of the stimulation, the emission is detected during a predetermined fall time, via receiving a series of images or a video capture with an image-capturing unit of the smartphone. Finally, the image series or video capture is evaluated using a data processing unit of the smartphone, wherein the emission detected during the fall time is compared with stored reference data in order to verify the authenticity of the security feature.