Estimation of spatial distribution of electromagnetic noise radiated from PCB

This study aims to clarify the frequency characteristics of the spatial distribution of electromagnetic noise inside a distance of 3 m around a printed circuit board (PCB) by simulation and experiment. It is also shows that the finite difference time domain method (FDTD method) is a useful tool to estimate the frequency characteristic of the spatial distribution for the electric and magnetic field around the PCB. By comparison between the electric and magnetic near field spectrum above the printed line by simulation, these spectra are shown to have differences in the resonance frequency: when the characteristics of the electric and magnetic field strength at 60 ns after the excitation is calculated, the electric field is decreased, the magnetic field is not decreased, as the distance from PCB is farther. From the characteristics of particular frequencies, the electric field spectrum at 3 MHz, i.e, clock pulse, is decreased, whereas the magnetic field is not decreased. The electric and magnetic field strength at the resonance frequency, 417 MHz, is decreased in inverse proportional to the square of the distance. It is also clear that the low frequency magnetic field strength may be superior to higher frequency.