THz Security Element with Inverted Grating Structures
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Solution Overview
Problem
Existing security elements for documents of value, such as banknotes and passports, face challenges in industrial production due to the difficulty in creating narrow slits in metal films, which are required for THz-effective lattice structures, making series production inefficient and prone to reproduction.
Innovation Solution
A security element with a grid structure formed by a metal layer in a dielectric, featuring transparent longitudinal slots for THz radiation, embedded in a second layer with an inverted line grating structure that fills the gaps, allowing for easy machine detection using THz radiation while remaining imperceptible to the naked eye, and can be combined with overt security features.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If narrow slits are created in metal films using additional etching steps or laser demetallization, then THz-effective lattice structures are achieved, but production complexity and difficulty increase significantly
Solution Approach 1:
The patent divides the metal layer into periodic strip structures with narrow gaps, creating a lattice pattern that is effective for THz radiation. This segmentation is achieved through a single-step photolithography and metal deposition process, avoiding the need for additional etching steps. The periodic structure with controlled gap widths (1-10 μm) between metal strips provides the necessary THz detection capability while simplifying manufacturing.
Solution Approach 2:
The patent performs the lattice structure formation as a preliminary step during the initial metal layer deposition, before any subsequent processing. By patterning the metal layer and depositing it in a single step alongside the dielectric layer formation, the narrow gaps are created beforehand without requiring additional demetallization or etching operations, thus reducing production complexity.
2Reliability
If narrow slits with width of about 1 μm are realized, then THz radiation transparency is improved, but industrial production becomes challenging
Solution Approach 1:
The patent replaces mechanical etching or laser demetallization processes with a photolithography-based metal deposition approach. By using photoresist patterning followed by metal evaporation or sputtering, narrow gaps of 1-10 μm are achieved through standard semiconductor fabrication techniques that are well-suited for industrial production, rather than through challenging mechanical or thermal removal processes.
Solution Approach 2:
The patent optimizes the gap width parameter to be between 1-10 μm, which balances THz radiation transmission requirements with manufacturability. This parameter range is achievable through standard photolithography resolution and metal deposition control, making the structure suitable for industrial production while maintaining effective THz detection properties.
3Reliability
If a single metal layer with narrow slits is used, then THz detection capability is achieved, but production effort increases due to additional processing steps
Solution Approach 1:
The patent combines the formation of the dielectric layer and the metal lattice structure into a single integrated processing step. The metal layer is deposited directly onto the dielectric substrate in one operation, merging what would otherwise be separate fabrication steps. This integration maintains the THz detection capability while significantly reducing production effort and improving series production efficiency.
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 enhances the security element's properties in the THz range, simplifies series production, and provides a covert security feature that can be easily authenticated using THz radiation, while maintaining a visually imperceptible design, thus addressing the challenges of reproduction and production effort.
Implementation Method 1
The first layer (60) has a first line lattice structure (8), which cannot be seen with the naked eye, and which consists of parallel longitudinal slots (20)... The longitudinal slots (20) are arranged adjacently and periodically or quasi-periodically
Implementation Method 2
A second line lattice structure (14) is formed in a second layer (12)... This is inverted to the first line lattice structure (8) and offset by half a period... the second line lattice structure (14) forms longitudinal webs (22), which, when viewed from above, exactly fill the gaps left by the first longitudinal slots (20) in the first layer (10)
Data Source
Figure 1~2B
Figure 2C~2D
Figure 3A~3C
AI summary
The invention relates to a security element for producing security documents, such as bank notes, checks or the like, wherein a first layer is arranged in a first plane (10) in a dielectric (6) which is transparent to THz radiation, said first layer being formed from a layer material which is opaque to THz radiation and forming a first periodic or quasi-periodic line lattice structure (8) consisting of parallel longitudinal slots (20) which produce gaps in the first layer and being invisible to the naked eye, wherein a width of the longitudinal slots (20) is not greater than 1/5 of the period (p), preferably not greater than 1/10 of the period (p), wherein a second layer is arranged in a second plane (12) in the dielectric (10), which second plane is parallel to the first plane (10), said second layer also being formed from a layer material which is opaque to THz radiation and forming a second line lattice structure (14), which is inverse to the first line lattice structure (8).