A system for unobtrusive measurement of surface currents

The authors demonstrate an approach that is an effective, noninvasive means of measuring surface current distributions. Some guidelines for making the measurements are given, and results from an actual measurement are presented. For example, it is shown that the magnetic field components have better measurement characteristics than the electric field components. The number of spatial samples per wavelength can be estimated from the spatial sharpness of the current distribution. The size of the measurement window, which is directly proportional to the measurement distance, must be sufficiently large to capture the majority of the spatial field distribution and to prevent the edges of the window from interfering with the results. In addition, the extraction of sub-wavelength features or sharp edges requires the measurement plane to be close to the surface current, a high SNR, close spacing of measurement samples, and a small field probe.