BREAKING THE SYMMETRY: HOW NON-COAXIAL FRESNEL LENS DESIGNS ENABLE UNIFORM PIR DETECTION
In most passive infrared (PIR) motion detection systems, the Fresnel lens has long been treated as a static, well-understood component. It focuses infrared radiation onto a pyroelectric sensor, forming discrete sensing zones to detect motion as a person or object crosses them. Traditional designs favor coaxial symmetry, where all segments focus IR light toward a single focal point along the lens’s central axis.
Field Performance – Beyond Simulation
Simulation is essential, but field validation is the final test of design quality. In multiple commercial installations, non-coaxial Fresnel lenses have demonstrated:
Improved detection coverage at wide angles, especially in room corners and aisle edges.
Lower detection latency, as uniform IR delivery leads to faster signal rise time in peripheral motion.
Reduced false negatives, particularly in low-motion scenarios like seated humans or slow walkers.
We also conducted controlled indoor lab tests comparing two lens types under identical conditions. A test subject walked in a circle 3 meters from the ceiling-mounted PIR sensor. The results were telling:
| Metric | Coaxial Lens | Non-Coaxial Lens |
|---|---|---|
| Average signal strength (edge) | 0.42 V | 0.68 V |
| Missed detections (per 20 laps) | 4 | 0 |
| Signal variance across zones | ±45% | ±12% |
This confirmed what simulation suggested: non-coaxial designs maintain usable signal levels across the entire sensing field, not just in the center.
Design Challenges and Solutions
Designing non-coaxial Fresnel lenses introduces additional complexities not seen in traditional coaxial configurations:
Tooling difficulty: Asymmetric grooves require more precise mold design and multi-angle polishing during manufacture.
Injection molding constraints: Small-angle features are sensitive to shrinkage and flash.
Zemax optimization is time-intensive: More parameters, more iterations.
To overcome these challenges, Aubor has developed:
Custom hybrid diamond turning + CNC tooling processes for asymmetric groove profiles.
Modular simulation frameworks to test multiple non-coaxial models in parallel.
Proprietary "groove deviation indexing" methods that speed up the lens profile generation and polishing simulation.
We also collaborate with customers to define detection priority zones, allowing targeted energy optimization. For example, in a retail store sensor, the front entry area may require higher sensitivity, while side zones are tuned to minimize aisle cross-traffic false triggers.
Applications of Non-Coaxial Fresnel Lenses
Non-coaxial Fresnel lens designs are particularly suitable for applications requiring:
Wide-angle uniform detection, such as ceiling-mounted room sensors
Direction-aware PIR algorithms, where signal symmetry affects classification
AI-enhanced motion learning, where consistent signal quality across all angles improves model training
Robotic navigation, where the sensor must detect humans or objects from oblique side approaches
As systems increasingly rely on smart PIR modules for presence detection, occupancy classification, and movement pattern learning, signal consistency across all angles becomes critical.
About Aubor Optical
Aubor Optical is a precision optics manufacturer specializing in infrared Fresnel lenses, freeform polymer optics, and lens-module co-design. Our services include:
Zemax-based non-imaging lens simulation
In-house tooling for non-coaxial Fresnel grooves using diamond turning and CNC hybrid methods
Full production chain from prototyping to scalable molding
Custom material selection and IR transmission testing for 8 to 14 μm range
With a dedicated R&D team and experience serving clients in security, smart home, robotics, and industrial automation, we are committed to solving motion sensing challenges through optical innovation.
At Aubor, we believe the future of motion detection is uniform, and we are building the optics to make that future possible.
