THz Security Element With Periodic Slits
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Solution Overview
Problem
Existing security elements for valuable documents, such as banknotes, that interact with THz radiation either have visible recesses or are thick, making them undesirable for widespread use due to increased document thickness and visibility issues.
Innovation Solution
A security element with a lattice structure formed by a metal layer that is opaque to THz radiation, featuring longitudinal slots transparent to THz radiation, arranged periodically or quasi-periodically with specific dimensions and orientations, allowing for machine authenticity checks while remaining imperceptible to the naked eye.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If metallic relief structures with embossing depth between 40 μm and 100 μm are used for THz interaction, then machine authenticity check capability is improved, but document thickness increases significantly
Solution Approach 1:
The patent changes the embossing depth parameter from 40-100 μm to 1-20 μm, and modifies the structure from sawtooth gratings to conductive elements with specific geometries (circles, squares, triangles, polygons) arranged in periodic patterns. This parameter change maintains THz radiation interaction capability while significantly reducing document thickness
Solution Approach 2:
The patent applies different geometric shapes and arrangements of conductive elements in different regions of the security feature, creating local variations in THz interaction while maintaining overall thinness. The conductive elements are strategically positioned and sized to provide authentication capability without increasing thickness
2Reliability
If metallic structures with two- to six-fold symmetry are used for THz interaction, then machine inspection capability is improved, but the structures become visible to the naked eye requiring cover layers
Solution Approach 1:
The patent modifies the geometric parameters of the conductive elements (size, shape, spacing) to fall within ranges that interact with THz radiation while remaining below the resolution threshold of human vision. The periodic arrangements and symmetry patterns are optimized for machine detection at THz frequencies without creating visible patterns
Solution Approach 2:
The patent uses dielectric materials as intermediaries between the conductive elements and the external environment. These dielectric layers with specific permittivity values enable THz radiation to interact with the conductive elements while preventing direct visual observation of the metallic structures, eliminating the need for additional cover layers
3Use of energy by moving object
If hole structures with large demetallized areas are used for THz radiation interaction, then THz transmission is improved, but the structures become clearly visible to the naked eye
Solution Approach 1:
The patent changes the size parameters of the conductive elements and the spacing between them to specific ranges that allow sufficient THz radiation transmission while keeping the individual features and gaps below the visual detection threshold. The geometric parameters are optimized to balance transmission efficiency with invisibility
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 solution enables easy machine detection using THz radiation while maintaining a thin, visually imperceptible design, balancing production ease with security effectiveness and aesthetic appeal.
Implementation Method 1
a layer which is opaque to radiation in the THz spectral range, in particular a metal layer
Implementation Method 2
in the layer adjacent longitudinal slots which are transparent to radiation in the THz spectral range are formed
Data Source
Figure 1a~1b
Figure 2a
Figure 2b
AI summary
The invention relates to a security element for the production of value documents, such as banknotes, checks, or the like, having a grid structure which cannot be discerned by the naked eye and which is formed by a layer (4) that is opaque to THz radiation, wherein: the layer (4) that is opaque to THz radiation has a layer thickness between 10 nm and 1 μm; longitudinal slits (5) are formed in the layer (4) that is opaque to THz radiation, which are transparent to THz radiation and lie adjacent to one another; the layer (4) that is opaque to THz radiation is embedded in a dielectric material (8) that is transparent to THz radiation; the longitudinal slits (5) are arranged periodically adjacent to one another with a period between 10 μm and 100 μm; and the width of the longitudinal slits (5) is not greater than 1/5 to 1/10 of the period.