Field notes
No camera, no transponder: detecting vehicles with passive magnetometry
By Ross Day2 min read
No camera. No transponder. Just two pads at the curb.
That's how NextMAG detects a real vehicle in real time, using nothing but the magnetic disturbance the vehicle itself creates as it passes.
Why cameras and transponders leave gaps
Most detection systems either need line of sight (cameras, LiDAR) or cooperative equipment on the target (ADS-B for aircraft, RFID for freight). Both leave gaps. Cameras fail in low visibility. Transponders can be turned off.
A passive magnetic sensor has neither problem.
How passive magnetometry works
NextMAG is passive magnetometry. The vehicle's own metal disturbs the local field. Two pads at the curb do the rest — presence, direction, class, speed — without emitting anything and without asking permission.
A car or truck carries a lot of steel, and steel bends the Earth's magnetic field around it. A magnetometer at the curb sees a steady field until a vehicle passes, then a disturbance that rises and falls with it. Two pads a known distance apart see that disturbance at slightly different times, which gives direction and speed.
Passive is the point. The sensor only listens. It sends nothing out, so there is no signal to find, and nothing has to be installed on the vehicle. It captures no images either, so there are no faces or license plates to store.
The unit that does this is NextMAG Rugged. It is part of the NextMAG line we build with Nextage LLC; NextMAG itself is a research-grade 3-axis magnetometer with GPS-disciplined timing and 2.7 nT resolution at 1 Hz. Our browser-based Passive Magnetic Sensing platform has a live demo you can open right now.
Where it fits
Applications we're already talking about:
- Airport ground-vehicle tracking in low-vis conditions where cameras and radar have blind spots
- Traffic engineering (counts, speed studies) without pole cameras or embedded loops
- Fleet operations: know when a truck actually arrives at your yard, not when someone remembers to log it
- Rail crossing pre-warning
- Site security where active RF would give away position
None of them needs a camera on a pole or a tag on the vehicle.
What's the passive-sensing gap you're solving for right now?