Sensor systems are the eyes of automatic sliding doors, detecting approaching pedestrians and triggering door opening. Infrared and microwave sensors use fundamentally different detection principles with distinct performance characteristics. This article compares both technologies.
1. Infrared Sensor Detection Principle
Passive infrared sensors detect changes in thermal energy radiated by approaching pedestrians against the background thermal environment. The sensor contains a pyroelectric detector that responds to changes in infrared radiation levels within its field of view. When a warm body moves across the detection zone, the sensor detects the thermal signature change and generates an activation signal. Infrared sensors are sensitive to ambient temperature and require calibration for effective operation in thermally dynamic environments.
2. Microwave Sensor Detection Principle
Microwave sensors emit continuous microwave radiation and detect Doppler shifts in reflected signals from moving objects. The sensor transmits microwaves at a specific frequency, then analyzes the frequency of reflected signals. Moving objects cause a frequency shift proportional to their velocity through the detection zone. Microwave sensors detect all moving objects regardless of thermal signature, making them effective for detecting both pedestrians and vehicles.
3. Detection Zone Coverage Patterns
Infrared sensors create zone patterns based on lens optics and detector positioning, typically providing accurate presence detection in the immediate door approach area. Microwave sensors create broader coverage patterns that can extend several meters from the door, potentially detecting passing traffic on adjacent sidewalks and triggering unwanted door openings. Sensor positioning and angle adjustment optimize coverage while minimizing false activations.
4. Environmental Performance Comparison
Infrared sensors perform reliably in stable thermal environments but may experience reduced sensitivity during extreme heat when pedestrian thermal signatures match background conditions. Microwave sensors perform reliably across temperature ranges but may false-trigger near moving air, ventilation outlets, or reflecting surfaces that create multipath interference. Combined dual-technology sensors use both technologies to improve reliability and reduce false activation rates.
5. Application Selection Guidance
For standard commercial entrances with pedestrian traffic only, infrared sensors provide adequate performance at lower cost. For applications requiring detection through glass or glazed doors, microwave sensors mounted inside the door frame can detect through transparent materials that block infrared radiation. For high-traffic commercial entrances, combined sensors provide the most reliable detection with minimal false activations.
This article compiles information from publicly available automatic door industry resources.