Optical Smoke Detector with Angular Filtering for Compact PCB Layout
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Solution Overview
Problem
Existing photoelectric smoke detectors face issues with optical sensitivity, electromagnetic interference, and space/cost considerations, particularly in integrating additional components like carbon monoxide sensors, due to the need for large chambers and PTH components.
Innovation Solution
A smoke detector design using SMT components with an optical element comprising a convex objective lens and prisms that selectively filters and redirects scattered light from predefined angles, minimizing electromagnetic susceptibility and optimizing PCB space for additional sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a large chamber is used to prevent light reflections and improve detection accuracy, then optical sensitivity is improved, but the device size and PCB space increase
Solution Approach 1:
The patent repositions the light source vertically above the photodetector rather than horizontally adjacent, utilizing the vertical dimension to create separation. This dimensional change allows the light source to be positioned out of the direct light path while maintaining effective scattering detection, thereby reducing the horizontal space required on the PCB while preserving optical sensitivity.
Solution Approach 2:
The patent divides the optical path into distinct segments: the light source projects light upward into a scattering volume, scattered light travels horizontally to the optical element, and the optical element redirects it to the photodetector. This segmentation allows each component to be optimized independently and reduces the overall space requirement by eliminating the need for a large continuous chamber.
2Object-affected harmful factors
If PTH components are used for mounting light source and photodetector, then electromagnetic interference is reduced, but manufacturing complexity and cost increase
Solution Approach 1:
The patent replaces the mechanical PTH mounting system with an optical isolation approach using a vertical light path and optical elements. This substitution eliminates the need for PTH holes while maintaining electromagnetic isolation, as the optical design inherently separates the light source from the photodetector's electrical signals, enabling the use of simpler SMT components.
Solution Approach 2:
The patent introduces an optical element (lens or prism) as an intermediary between the light source and photodetector. This intermediary redirects scattered light at specific angles to reach the photodetector while blocking direct light paths, thereby maintaining detection accuracy without requiring PTH mounting structures for electromagnetic isolation.
3Area of stationary object
If the light source is positioned close to the photodetector to save space, then PCB space is reduced, but direct light reflections increase causing false detections
Solution Approach 1:
The patent positions the light source in the vertical dimension (above the PCB) rather than horizontally adjacent to the photodetector. This dimensional separation allows the light source to be physically close in terms of PCB footprint while maintaining sufficient optical path separation to prevent direct light reflections from reaching the photodetector.
Solution Approach 2:
The patent applies directional selectivity to the optical system, where the optical element is designed to accept light from specific angular ranges (scattered light paths) while rejecting light from other directions (direct reflection paths). This local quality control at the optical element level allows compact positioning while eliminating harmful direct light reflections.
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 design enhances optical sensitivity, reduces electromagnetic interference, and allows for miniaturization, enabling integration of additional components like CO sensors while maintaining cost-effectiveness.
Implementation Method 1
detecting when a certain amount of light that is scattered from smoke particles arises
Implementation Method 2
an optical element (207) comprising: a first light-receiving surface (210) in the form of an objective lens configured to receive light scattered by the smoke particles; the optical element (207), upon receiving the scattered light, configured to redirect required scattered light onto the photodetector (208)
Implementation Method 3
a photodetector (208) configured to detect scattered light
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A smoke detector of the type that depends on the scattering of light by smoke particles comprising a chamber (301) configured to receive smoke particles from an environment in which the smoke detector is required to detect smoke, a source of light (202) configured to project light therefrom such that light that is received by the chamber is scattered by the smoke particles, an optical element (207) configured to receive light as has been scattered by the smoke particles, and, a photodetector (208) configured to detect at least some of the received scattered light, the smoke detector characterized in that upon receiving the scattered light, the optical element (207) is configured to selectively differentiate between required scattered light that is derived from a subset of predefined directions with respect to the angle of incidence upon the optical element and scattered light that is derived from other directions in order to thereby filter out the light that is not required and thereby redirect the required scattered light onto the photodetector (208).