A consideration on error of Poynting vector estimation with near-magnetic-field measurement

Progress of clock frequency of digital equipments causes serious undesired emission from a printedcircuit board(PCB). Since a trial-and-error at later procedure spends cost and time, design criterion for low-emission PCB is desired. To establish the design criterion, it is necessary to understand mechanism of emission. For this purpose, many investigations on near-field measurement for estimating current distribution, predicting far-field pattern, and improving measurement accuracy are reported. However, some index denoting propagation of emission is required because near-electric or magnetic-field pattern do not always state a mechanism of propagation for undesired emission. We have proposed a method to estimate the Poynting vector from near-magnetic-field measurement [1]. Since the Poynting vector indicates direction of propagation for electromagnetic wave, it is useful to understand a mechanism of emission. We have confirmed that the proposed method has capability to visualize energy flow experimentally [2]. However, an estimation error was not discussed in the previous work. In this report, we discuss on error of the proposed method. We measured magnetic-field generated from a transmission line to estimate the Poynting vector. The obtained value is compared to the theoretical value, which is calculated analytically by using vector potential.