Transparent Elevation Sensor for Intrusion Detection
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Solution Overview
Problem
Existing infrared intrusion detection systems are vulnerable to sabotage through sprays that are opaque in the mid-infrared range but transparent in the visual and near-infrared ranges, making them difficult to detect using current technologies.
Innovation Solution
A sensor arrangement featuring transparent elevations with carefully chosen angles for total reflection, where incident rays are reflected in the absence of a liquid but transmitted when a liquid is present, utilizing a light source and detector to differentiate between these conditions, and optionally incorporating tetrahedron-shaped elevations and capillary-enhancing facets to improve liquid detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a light source and detector are used to monitor transmission through the entrance window, then the system can detect opaque materials, but it cannot detect transparent sprays that are opaque only in the mid-infrared range
Solution Approach 1:
The patent changes the wavelength parameter of the detection light from near-infrared to visible light range. This parameter change enables the detection system to detect sprays that are transparent in near-infrared but opaque or scattering in visible light, thereby resolving the limitation of detecting only mid-infrared opaque materials
Solution Approach 2:
The patent introduces a diffraction grating as an intermediary optical element between the light source and detector. This grating creates multiple diffraction orders that can be selectively focused onto the detector, enabling the system to detect subtle changes in light transmission caused by transparent spray layers that would otherwise be undetectable
2Reliability
If an optical diffraction grating structure is used to focus diffraction rays onto the light sensor, then spray detection becomes possible, but the structure becomes difficult to manufacture in low-cost plastic material and highly sensitive to dust and greasy atmosphere
Solution Approach 1:
The patent replaces complex precision-manufactured diffraction gratings with simpler optical elements that can be easily fabricated in low-cost plastic materials. The design accepts that these simpler elements may have shorter operational lifetimes or require more frequent replacement, but significantly reduces manufacturing costs and complexity
Solution Approach 2:
The patent segments the optical detection function into separate components: a light source, a simpler optical element (such as a prism or lens array instead of a precision grating), and a detector. This segmentation allows each component to be optimized independently, with the optical element being manufacturable in inexpensive materials while maintaining adequate detection performance
3Reliability
If the entrance window is illuminated with near infrared light emitter, then reflection detection is possible, but the system cannot detect sprays that are transparent in the near infrared range and the technique only works with plan windows
Solution Approach 1:
The patent changes the illumination wavelength from near-infrared to visible light range. This parameter change has two effects: it enables detection of sprays that are transparent in near-infrared (since many spray materials scatter or absorb visible light), and it allows the use of visible light optics that can be focused into compact arrangements suitable for curved or non-plan window surfaces
Solution Approach 2:
The patent transitions from a single-point reflection detection approach to a distributed array of detection points across the window surface. By using an array of light sources and detectors or a scanning mechanism, the system can accommodate curved and non-plan window geometries, adding spatial dimensionality to the detection capability
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
Effectively detects liquid coverage on infrared intrusion detection systems, including transparent sprays, by leveraging total reflection principles and capillary effects, providing a reliable and cost-effective solution to sabotage attempts.
Implementation Method 1
A first facets of the transparent elevation defines a first angle with the surface. This first angle is larger than an angle at which a total (internal) reflection occurs at an interface of the first transparent material and air and is at the same time smaller at an angle at which a total reflection occurs at an interface of the first transparent material and the liquid
Implementation Method 2
optionally incorporating tetrahedron-shaped elevations and capillary-enhancing facets to improve liquid detection
Data Source
AI summary
A sensor arrangement includes at least one transparent elevation, which is formed on the surface. The transparent elevation is made of a first transparent material. At least one first facet of the transparent elevation defines a first angle with the surface. This first angle is larger than an angle at which a total-reflection occurs at an interface of the first transparent material and air and is at the same time smaller than an angle at which a total reflection occurs at an interface of the first transparent material and the liquid. A light source is arranged for emitting an incident ray into a first direction passing through the surface into the transparent elevation such that in a presence of a liquid at the first facet, an incident ray is transmitted through the first facet. In an absence of a liquid, the incident ray is reflected due to a total reflection at the facets. A light detector is provided for detecting the reflected ray.