B-DOT AND D-DOT FIELD SENSORS

A B-dot sensor measures the time derivative of a magnetic flux density (dB/dt) and is typically constructed as a specialised conductive loop. A D-dot sensor measures the time derivative of an electric displacement field (dD/dt) and is typically constructed as an asymptotic conical dipole. Both are passive analog sensors used to characterise fast-changing electromagnetic environments.

Standard field probes are designed to measure the rms value of the field, not the real time-domain waveform. They often struggle with ultra-fast, high-intensity transient signals due to bandwidth limitations and saturation risks. Derivative sensors (B-dot and D-dot) offer sub-nanosecond rise times, exceptionally high upper cutoff frequencies, and the ability to withstand extreme field strengths without signal distortion.

Yes. Because B-dot and D-dot sensors output a voltage proportional to the rate of change of the field, the raw signal must be integrated over time to reconstruct the actual magnetic (H) or electric (E) field waveform. This is typically achieved using a dedicated passive or active hardware integrator, or by numerical integration after signal acquisition.

These high-precision sensors are critical for demanding applications involving high-voltage pulsed power. Common use cases include NEMP and EMP testing, lightning strike simulation and measurement, HPM (High-Power Microwave) characterisation, advanced EMC immunity testing, particle accelerator diagnostics, and any EM study where the shape of the field matters (not only the rms value).

Sensor selection requires a trade-off between sensitivity and bandwidth. A larger sensor provides higher voltage output (better for lower-intensity fields) but has a lower upper-frequency limit. A smaller sensor offers higher bandwidth, essential for measuring ultra-fast rise times.

Unlike electronic probes, these passive sensors do not drift over time. As long as the mechanical geometry remains unchanged (no dents or structural damage), the sensitivity factor remains valid. We recommend a simple TDR test to check electrical continuity and a visual inspection to confirm integrity.

Montena’s sensors naturally handle high-intensity transient signals without saturation issues. Precise geometry and high-quality materials ensure stable sensitivity and predictable frequency response. Combined with appropriate baluns and fibre optic links, they operate with excellent immunity to electromagnetic interference and complete galvanic isolation.