Non-destructive PCB/IC testing
NV magnetometry images current paths to find shorts & opens without probes.
Underground mapping
Cold-atom gravimeters locate voids/tunnels for civil engineering and geology.
GPS-denied navigation (MagNav)
Airborne magnetometers track Earth-field gradients to aid navigation; requires high sample rates with good sensitivity.
Decode the spec sheet
- Noise density (η) in T/√Hz — the sensor’s noise floor per √bandwidth.
- Bandwidth (BW) wider BW captures faster changes but raises noise.
- Coherence (T2*) sets useful averaging time before drift.
- Dynamic range clipping (NV fluorescence) or phase wrapping (atoms).
SNR vs time (play with it)
Model: for white noise, SNR grows as
SNR ≈ (Signal/η) · √(T/BW).
Here η is noise density in T/√Hz, BW is measurement bandwidth (Hz), and T is your averaging/integration time (s).
The minimum detectable field at SNR≈1 is
Bmin(T,BW) = η · √(BW/T).
Sensitivity 101: why T/√Hz matters (and MagNav)
T/√Hz is a convenient way to quote a sensor’s fundamental noise. If you average for time T,
white noise falls as 1/√T. If you need higher sample rate (larger BW), noise rises as √BW.
That’s why a magnetometer with η = 1 nT/√Hz reaches ~0.32 nT in 10 Hz BW after 1 second
(1×√(10/1)), but only ~1 nT at 100 Hz BW — and much worse at 1 kHz.
MagNav implication: an aircraft moving quickly needs ≥100–1000 samples/s to resolve geologic/urban gradients without aliasing. That high BW inflates noise unless η is very low. Practically: pick a magnetometer with the lowest η you can afford and validate Bmin(T,BW) at the mission’s sample rate.
What to measure in a pilot
- In-field noise density vs temperature and vibration
- Calibration drift over hours; re-zero procedure and time
- Packaging and alignment stability (optics, vacuum)