A detailed investigation of the electromagnetic field distributions in high frequency printed circuits and high-speed interconnects is very useful for physical understanding, studies of electromagnetic coupling effects for EMC and EMI and for optimization of electromagnetic circuit designs. The aim of this paper is to show how to measure the electric field distributions in electromagnetic circuits. An electromagnetic analysis for microstrip-line circuits is carried out by using a finite-difference time domain technique and its measurement is carried out by using a small probe antenna. The measurement results are in fairly good agreement with those of the numerical analysis using the FDTD method. Thus, the measurement system offers a valid means for predictions in the theoretical analysis of more complicated discontinuity problems.

A method is described for approximately estimating the surface specific-absorption-rate (SAR) in an anatomically realistic model of the human head for microwave exposure using the external magnetic near-field. The finite-difference time-domain (FD-TD) technique is used to compute the electromagnetic fields in the head model for 750-MHz and 1.5-GHz far-field exposures with the 1991 ANSI specified safety level. The spatial pattern tracking between the one-gram averaged surface-SAR and external magnetic near-field is demonstrated on the horizontal cross sectional perimeter of the head model. The regression coefficients between them are also obtained on the fifty-five horizontal cross sectional perimeters, which could give an approximate value of the surface-SAR in an acutual head, if the external magnetic near-field would be measured. This is validated by the theoretical results in a semi-infinite homogeneous flat model for normal incidence microwave exposure.