Passive Infrared Detector With Segmented Optical Fields
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Solution Overview
Problem
Passive infrared detectors face significant challenges in outdoor environments due to high levels of thermal interference and false alarms caused by wind, rain, temperature variations, and animal movements, which overwhelm the desired signal, leading to unreliable motion detection.
Innovation Solution
The implementation of a passive infrared detector design featuring multiple sub-detectors with non-overlapping, angled fields-of-view and advanced signal processing circuitry that distinguishes between desired and undesired signals by analyzing time relationships and spatial separations of detection zones, reducing false alarms and enhancing signal processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If multiple optical segments are used to expand the field-of-view coverage, then the detection coverage area is improved, but the thermal interference from multiple zones simultaneously reaches the sensor causing false alarms
Solution Approach 1:
The detector is divided into multiple independent sub-detectors, each with its own optical segment and sensor. Each sub-detector views a distinct non-overlapping sub-field-of-view, physically separating the detection zones so that thermal interference from one zone cannot affect other zones, thereby eliminating false alarms while maintaining wide coverage
Solution Approach 2:
The patent extracts the sensor from the common optical path and assigns dedicated sensors to each optical segment. This extraction prevents thermal radiation from any single optical segment or external source from simultaneously reaching multiple sensors, isolating each detection zone's thermal signature to its corresponding sub-detector only
2Device complexity
If a single sensor is used with multiple optical segments, then the device complexity is reduced, but the signal-to-noise ratio deteriorates due to simultaneous thermal interference from all zones
Solution Approach 1:
The detector is divided into multiple independent sub-detectors, each with its own optical segment and sensor. Each sub-detector views a distinct non-overlapping sub-field-of-view, physically separating the detection zones so that thermal interference from one zone cannot affect other zones, thereby eliminating false alarms while maintaining wide coverage
Solution Approach 2:
The patent extracts the sensor from the common optical path and assigns dedicated sensors to each optical segment. This extraction prevents thermal radiation from any single optical segment or external source from simultaneously reaching multiple sensors, isolating each detection zone's thermal signature to its corresponding sub-detector only
3Measurement precision
If lens segments are used to focus IR energy, then the detection sensitivity is improved, but the lens itself cannot prevent insects and spurious matter from entering the detector
Solution Approach 1:
The optical segments serve dual functions: they focus infrared energy onto the sensors for detection while simultaneously acting as protective windows that prevent insects and spurious matter from entering the detector housing, eliminating the need for separate protective structures
Solution Approach 2:
The optical segments serve dual functions: they focus infrared energy onto the sensors for detection while simultaneously acting as protective windows that prevent insects and spurious matter from entering the detector housing, eliminating the need for separate protective structures
4Adaptability or versatility
If mirror segments are used instead of lenses, then the window function is separated allowing dedicated IR transparent window, but the structural complexity increases
Solution Approach 1:
The optical segments serve dual functions: they focus infrared energy onto the sensors for detection while simultaneously acting as protective windows that prevent insects and spurious matter from entering the detector housing, eliminating the need for separate protective structures
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 design significantly improves the signal-to-noise ratio and reduces false alarms by isolating desired motion signals from thermal interference, providing more reliable motion detection in harsh outdoor conditions.
Implementation Method 1
Each of the plurality of optical segments is arranged to focus IR energy emanating from a pre-defined detection zone onto an infrared sensor such as a pyroelectric sensor
Implementation Method 2
The lens assembly includes multiple Fresnel lens segments arranged in three rows, which are positioned in front of the sensor and serve as a detector window
Implementation Method 3
In such detectors, incoming infrared radiation enters the detector through a wide IR transparent window in the detector housing and is reflected by the mirror segments to focus onto a pyroelectric sensor
Data Source
AI summary
A passive infra-red detector including at least three sub-detectors, each sub-detector being operative to receive infra-red radiation from a corresponding one of at least three sub fields-of-view, each sub field-of-view being exclusively defined by an optical element which does not define any other sub field of view, the sub fields-of-view being angled with respect to each other, adjacent ones of the sub fields-of-view being separated by a gap of no more than 30 degrees and at least one of the sub fields-of-view having at least one of the following characteristics: extending over no more then 45 degrees in azimuth; and including not more than three azimuthally distributed detection zones, and signal processing circuitry, operative to receive output signals from the sub detectors and to provide a motion detection output.