Comfortable gateway to the kQ theory invited

This paper stimulates undergraduates and young engineers working in the field of power transfer by offering a quite simple problem on a resistive two-port system. A black box having input and output ports is excited by a DC voltage source, and loaded with a resistor. Starting with its voltage and current relations, we derive elegant formulas on kQ and the maximum power transfer efficiency in terms of four resistance parameters. To help understand these results, we show a convenient piecewise approximation, a look-up table of numerical examples, and a graphical approach for an intuitive comprehension. This is an easy-to-enter gateway to the basic concept of kQ and an effective bridge to practical power transfer engineering as well.