EMC & Product Safety Testing Blog/

Helmholtz Coils

Helmholtz Coils

A simple design for a pair of one-meter coils consists of ten turns each of #10 AWG copper wire housed in wooden boxes. Combined coil resistance is 1Ω.

Per IEC 61000-4-8 Power Frequency Magnetic Field Immunity Testing;

H=1.22 (N/D) * I A/m
For the GME coils; H=12.2 * I A/m,
When the coils are connected to the power resistor, the system impedance is 4 Ω


Magnetic Field (A/m) Coil Current (I) Coil Voltage (V)
3 0.25 1
10 0.8 3.3
30 2.5 10
100 8.2 33


diagram of Helmholtz Coils

The Helmholtz coils can also be used for magnetic field immunity testing from 30 Hz to 150 kHz. (Dotted Lines)

A signal generator is connected to a power amplifier, and the output of the amplifier is connected to the coils.

A spectrum analyzer is connected to a loop antenna that is placed in the coils. The signal generator is swept over the frequency range and the field is verified on
the spectrum analyzer display.

Reference: MIL-STD-461 RS101