Beam Detector Polarisation Change for False Alarm Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Reflective-type beam detectors face challenges with false alarms due to reflections from metallic or glossy surfaces within the monitored volume, which can return signal levels equivalent to or higher than the reflector, making installation difficult and prone to false alarms.
Innovation Solution
The beam detector apparatus employs a first linearly polarised beam of light that is either modified into circular, elliptical, or unpolarised light upon reflection, allowing the receiver to distinguish between light from the reflector and other sources by converting it into a second linearly polarised beam with different polarisation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a reflective-type beam detector uses a projected beam of light to detect obscuration, then it can monitor large volumes, but it becomes prone to false alarms from reflections off metallic or glossy surfaces
Solution Approach 1:
The patent changes the polarisation parameter of the light beam from linear to circular polarisation. The emitter produces a circularly polarised beam that reflects off the retroreflector and returns to the receiver. This polarisation state change allows the system to distinguish between light from the retroreflector and spurious reflections from metallic or glossy surfaces, eliminating false alarms while maintaining large volume monitoring capability.
2Reliability
If the detector uses a circularly polarised beam, then it becomes immune to false alarms from spurious reflections, but the system complexity increases due to polarisation conversion components
Solution Approach 1:
The patent introduces a retroreflector as an intermediary component that performs dual functions: it returns the light beam to the receiver and simultaneously converts the linearly polarised light from the emitter into circularly polarised light. This single component eliminates the need for separate polarisation conversion elements at both transmitter and receiver, reducing overall system complexity while achieving false alarm immunity.
3Ease of operation
If the beam detector aligns automatically to the highest signal level, then installation is simplified, but it may align to spurious reflections instead of the retroreflector
Solution Approach 1:
The patent changes the polarisation parameter of the returned light beam to circular polarisation through the retroreflector. The receiver is equipped with a circularly polarising filter that only transmits circularly polarised light. This creates a unique polarisation signature that automatically identifies the correct retroreflector alignment, preventing the system from locking onto spurious reflections from metallic or glossy surfaces while maintaining ease of installation.
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
This solution enhances the detector's immunity to false alarms from reflections, making it easier to install and operate, while also improving the system's ability to differentiate between desired reflections and background light sources.
Implementation Method 1
the beam emitter apparatus is capable of creating a first linearly polarised beam of light of first linear polarisation
Implementation Method 2
modifying such light into a beam having circular polarisation, elliptical polarisation or being unpolarised
Implementation Method 3
modifying such light into a beam having circular polarisation, elliptical polarisation or being unpolarised
Implementation Method 4
reflecting said circularly polarised, elliptically polarised or unpolarised beam of light towards the beam receiver apparatus
Implementation Method 5
creating therefrom a second linearly polarised beam of light, in which the first and second linearly polarised beams of light have different polarisation
Data Source
AI summary
A beam detector apparatus (1) comprising: beam emitter apparatus (2); reflector apparatus (3), locatable across a volume to be monitored; and beam receiver apparatus (4). The beam emitter apparatus (2) is capable of creating a first linearly polarised beam of light of first linear polarisation and directing said first linearly polarised beam of light towards the reflector apparatus. The reflector apparatus (3) is capable of either: receiving the first linearly polarised beam of light and modifying such light into a beam having circular polarisation, elliptical polarisation or being unpolarised, and reflecting said circularly polarised, elliptically polarised or unpolarised beam of light towards the beam receiver apparatus; OR receiving the first linearly polarised beam of light and reflecting such light towards the beam receiver, and modifying such light into a beam having circular polarisation, elliptical polarisation or being unpolarised. The beam receiver apparatus (4) is capable of receiving said circularly polarised, elliptically polarised or unpolarised light and creating therefrom a second linearly polarised beam of light, in which the first and second linearly polarised beams of light have different polarisation.