Efficient magnetic field measurements

Measuring magnetic fields of equipment under test at low frequencies which is received by loop antennas using an EMI receiver with small bandwidths takes much time and can even reach a week for a standard measurement. This waste in time could be avoided by applying time domain measurements. Commercial time-domain EMI (TDEMI) measurement equipment are sampling at the intermediate frequency, and are still relatively expensive. Base-band sampling using low-cost digitizers, or an oscilloscope, is proposed in this paper. The measured data is converted to the typical results in frequency domain via fast Fourier transform, while the necessary large dynamic range is achieved via oversampling. This methodology decreases the cost of the test equipment, but most of all reduces the measurement time drastically compared to the classical frequency domain measurement approach. The setup is described. Measurements with a conventional receiver parallel to the digitizer using a signal generator powering a radiating loop have been performed. Also measurements on an actual interfering source with pulsed magnetic fields are performed. It is shown that the measurement results are the same, while the measurement time has been reduced drastically.