Basic Wireless Communication for Microcontrollers
Chapter 1 - Electricity and Magnetism
Impedance of Free Space
There is a quantitiy, eta, called the impedance of free space, which is defined by Eta=sqrt(Uo/Epislon_o). It's units are ohms, just as if it were an impedance in a circuit. It turns out that, for EM plane waves in free space (which we will discuss in the next section), it determines the ratio of the E field strength to B field strength.