Security Element with Dual IR Absorbers for Harvesting Attack Detection
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Solution Overview
Problem
Current security elements with IR absorbers on valuable documents, such as banknotes, are vulnerable to harvesting attacks where the absorbers can be transferred and reused, making it difficult to distinguish authentic from counterfeit documents without specialized IR sensors, especially when absorbers' spectra overlap.
Innovation Solution
A security element design featuring two IR absorbers with spectrally overlapping absorption spectra, where the second absorber is applied on top of the first, ensuring distinct spectral profiles to allow for reliable detection using cosine similarity and opacity criteria, enabling authentication without specialized sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single IR absorber is used on the substrate body, then the security element can be machine-readable, but it becomes vulnerable to harvesting attacks where the absorber can be transferred and reused
Solution Approach 1:
The security element is segmented into two functionally distinct IR absorbers: a first IR absorber applied to the substrate body and a second IR absorber applied to the film element. This segmentation ensures that when a harvesting attack occurs and the film element is transferred, the second IR absorber moves with it while the first IR absorber remains on the original substrate, creating a detectable spectral mismatch that prevents successful counterfeiting.
2Measurement precision
If two IR absorbers with spectrally overlapping absorption spectra are used, then reliable detection is enabled through spectral differentiation, but the detection complexity increases
Solution Approach 1:
The patent utilizes changes in spectral parameters by selecting two IR absorbers with different absorption maxima (λ1 and λ2) and different remission curves R1(λ) and R2(λ). The first absorber typically has an absorption maximum in the range of 900-1100 nm while the second has an absorption maximum in the range of 700-900 nm. This parameter differentiation allows standard IR sensors to distinguish between the two absorbers and detect harvesting attacks without requiring complex specialized sensing equipment.
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 design allows for stable and reliable detection of authentic documents by ensuring the combination spectrum differs sufficiently from individual absorber spectra, preventing counterfeiting and enhancing security without requiring advanced IR sensors.
Implementation Method 1
a first IR absorber which, as viewed towards the front side, is located below the film element and which has a first, spectrally dependent remission curve R1(λ), a first spectrum which is complementary to the remission curve R1(λ) and is thus defined by 1 - R1(λ), and an IR absorption maximum A1max at a wavelength λ1
Implementation Method 2
a second IR absorber which is applied to the film element or embedded in the film element, is located at least partially above the first IR absorber as viewed towards the front side, and which has a second, spectrally dependent remission curve R2(λ), a second spectrum, which is complementary to the remission curve R2(λ) and is thus defined by 1 - R2(λ) and has an absorption maximum A2max at a wavelength λ2
Data Source
Figure 1~2
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Figure 5~6
AI summary
The invention relates to a security document, such as a banknote. It comprises a substrate body (2) on the front (3) of which a foil element (8) is arranged, a first IR absorber (6) which is located below the foil element (8) and which has a first reflection profile R1(λ), a first spectrum complementary to R1(λ), and an IR absorption maximum at a wavelength λ1, and a second IR absorber (10) which is applied to or embedded in the foil element (8), is located at least partially above the first IR absorber (6), and which has a second reflection profile R2(λ), a second spectrum complementary to R2(λ), and an absorption maximum at a wavelength λ2. The first IR absorber (6) has a remission R1(λ1) of 30% to 80% at wavelength λ1.The second IR absorber (10) has an opacity O2(λ2) of 1.1 to 10 at wavelength λ2, and the first spectrum differs from the second spectrum in such a way that there is a cosine similarity between the two spectra in the range of 0.1 to 0.9.