Security Document Refractive Surface Structure Noise Suppression
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Solution Overview
Problem
Security documents with diffractive surface reliefs face challenges in reading out information due to low angular and wavelength selectivity, leading to diffuse scattering of reconstruction light, making it difficult to distinguish the signal from noise.
Innovation Solution
Incorporating a noise suppression structure that includes a volume hologram and a reflection or absorption element to enhance the signal-to-noise ratio by directing and filtering the reconstruction light, allowing for improved visibility of the information stored in the diffractive surface structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a diffractive surface relief is used as a security element, then the security document gains anti-falsification capability, but the reconstruction light is diffusely scattered making information difficult to read out
Solution Approach 1:
A transparent channel is introduced as an intermediary optical path between the diffractive surface relief and the observer. This channel guides the diffracted reconstruction light directly to the viewer while blocking the diffusely scattered light from opaque layers, thereby resolving the contradiction between maintaining security features and enabling readable information output.
Solution Approach 2:
The patent applies different optical properties to different regions: the transparent channel provides high transmittance for the signal path, while surrounding opaque layers provide scattering that becomes visible only outside the channel. This local differentiation allows the system to simultaneously maintain security integrity and provide readable information through spatial separation of optical functions.
2Reliability
If opaque layers are used in the security document, then security and durability are improved, but transmitted reconstruction light is diffusely scattered creating noise
Solution Approach 1:
The transparent channel extracts the useful signal (diffracted reconstruction light) from the noisy environment created by opaque layers. By creating a dedicated light path that bypasses the scattering regions, the channel separates the signal transmission function from the security/protection function performed by opaque layers, thereby maintaining both security and information quality.
3Use of energy by moving object
If the diffractive surface relief is made more prominent to improve diffraction efficiency, then more light is diffracted, but angular selectivity decreases further
Solution Approach 1:
The transparent channel acts as an angular-selective intermediary that compensates for the reduced selectivity of prominent diffractive structures. By providing a defined geometric path for light transmission, the channel restores angular discrimination capability even when the diffractive relief has low inherent selectivity, allowing prominent features to be used without sacrificing adaptability.
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
The combination of a volume hologram and reflection or absorption elements improves the signal-to-noise ratio, enabling clearer reconstruction of the information stored in the diffractive surface structure, making it more difficult to counterfeit and enhancing the readability of the security document.
Implementation Method 1
the noise suppression structure comprises a volume hologram which diffracts and/or reflects at least one diffraction order of the transmitted reconstruction light
Implementation Method 2
the noise suppression structure comprises a reflection element, which supports a directed reflection of at least part of the reconstruction light transmitted through the diffractive surface structure
Implementation Method 3
the noise suppression structure additionally comprises an absorption element which at least partially absorbs the reconstruction light transmitted through the diffractive surface structure
Implementation Method 4
a diffractive surface structure (4) is introduced into the diffraction layer (2)... about 4% of the incident light is reflectively diffracted by the diffractive surface relief
Data Source
Figure 1~3
Figure 4~6
Figure 7a~7c
AI summary
The invention relates to a security document (1) comprising at least one security feature and to a method for the production thereof. The invention also relates to, in particular, a security document (1) with at least one security element, comprising a document body with at least one diffraction layer (2) that comprises on a top side, a diffraction surface structure (4) that is embodied as an optically thin projection hologram as the at least one security element. In the document body, at least one suppression structure is formed or arranged behind the diffraction surface structure when viewed from the top side (6) of the at least one diffraction layer (2), in order to minimise an oriented reflection of a reconstruction light (9, 10) back through the top side of the diffraction layer (2), transmitted by the diffraction structure (4) and appearing on the top side (6) of the diffraction layer (2) for reading out the diffraction surface structure (4).