With the advent of switching power supply technology, the presence of low frequency magnetic fields has led to an interest in evaluating these devices as new sources of electromagnetic energy exposure. A project for a major computer manufacturer was conducted to measure the magnitude of both magnetic and electric fields associated with selected switching power supply designs as they might relate to technician and design engineer exposures. These measurements made use of a displacement current type of electric field sensor and a shorted loop magnetic field sensor. The shorted loop technique made use of small clamp-on current probe to measure the induced current in the loop; the single-turn loop was used to provide for as much bandwidth as possible to capture high frequency harmonics produced by the switching process. The use of rms detection permitted a direct measurement of the magnetic field while a digital oscilloscope was used to acquire time-series samples of the field. An FFT algorithm was used to transform the observed time-domain data into the frequency domain.
