Optical Chopper PIR Sensing for Stationary Occupant Detection
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Solution Overview
Problem
Conventional passive infrared (PIR) sensors are unable to detect stationary objects and distinguish between human and non-human occupants effectively.
Innovation Solution
A chopped PIR (C-PIR) sensor is developed, incorporating a semi-transparent optical chopper and a Fresnel lens, which intermittently shutters infrared radiation to create relative motion, enabling detection of both stationary and moving objects by generating a measurable voltage difference between occupied and unoccupied scenarios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional PIR sensors are used, then moving object detection is achieved, but stationary object detection is not possible
Solution Approach 1:
The patent applies the dynamics principle by introducing a moving chopper that periodically interrupts infrared radiation from stationary objects. This creates artificial temporal variations in the radiation signal, allowing the pyroelectric sensor to detect stationary objects that would otherwise produce no signal. The chopper's motion transforms a static radiation field into a dynamic signal suitable for pyroelectric detection.
Solution Approach 2:
The patent implements periodic action through the oscillating chopper that rhythmically blocks and unblocks infrared radiation paths. This periodic interruption creates a modulated signal at the sensor, enabling detection of both stationary and moving objects. The periodic chopping frequency is optimized to match the pyroelectric sensor's response characteristics.
2Adaptability or versatility
If conventional PIR sensors are used, then detection capability is limited, but device complexity remains low
Solution Approach 1:
The patent introduces a chopper as an intermediary component between the infrared radiation source and the pyroelectric sensor. This mediator periodically interrupts the radiation, creating detectable signal variations. The chopper acts as a temporal modulator that enables the sensor to distinguish between ambient radiation and occupant radiation, significantly enhancing detection capability.
Solution Approach 2:
The patent achieves multi-functionality by designing a sensor system that can detect both stationary and moving objects, distinguish human occupants from non-human objects, and provide wide-area coverage. The combination of chopper, Fresnel lens, and pyroelectric sensor creates a universal occupancy detection system applicable to various HVAC and lighting control scenarios.
3Measurement precision
If thermopile sensors are used, then both moving and stationary object detection is achieved, but manufacturing cost and device footprint increase
Solution Approach 1:
The patent uses dynamics to enable a low-cost pyroelectric sensor to achieve thermopile-like stationary object detection capability. By introducing temporal variation through the moving chopper, the system creates signal variations that allow detection of stationary objects without requiring the larger, more expensive thermopile sensor array.
Solution Approach 2:
The chopper serves as a cost-effective intermediary that enables pyroelectric sensors to detect stationary objects. This approach avoids the need for expensive thermopile sensors while achieving similar detection capabilities through temporal modulation of the infrared signal.
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 C-PIR sensor achieves accurate detection of stationary occupants up to 4 meters and moving occupants up to 8 meters with 100% accuracy, maintaining a wide viewing angle of 110°, while distinguishing between human and non-human occupants.
Implementation Method 1
the sensing principle of such devices is based on the pyroelectric effect, which relates to the ability of certain materials to generate a temporary voltage as they are heated or cooled
Implementation Method 2
a semi-transparent infrared chopper that is adapted to periodically shutter radiation incident on the sensing element. The chopper is adapted to move (e.g., oscillate) back and forth in front of the sensor during operation of the sensor to create relative motion between the sensing element and a target object
Implementation Method 3
a Fresnel lens disposed over a surface of the sensing element
Data Source
AI summary
A chopped PIR (C-PIR) sensor is capable of detecting both stationary and moving objects with a high degree of accuracy using a narrow infrared semi-transparent chopper to temporally shutter incident radiation received by pyroelectric sensing elements. Demonstrating a field of view of 110° (horizontal) and 90° (vertical), the C-PIR sensor can detect stationary objects located within 4 m of the sensor, and moving objects located within 8 m of the sensor with 100% accuracy.