Click here to purchase the entire book in PDF format. Electrical field coupling Electrical field coupling is determined by the capacitance between the source and the receiver or their transmission media. Once upon a time, we looked at the construction of a capacitor as being two metal plates side by side but not touching each other. If we push electrons into one of the plates, we'll repel electrons out of the other plate and we appear to have ``current'' flowing through the capacitor. The higher the rate of change of the current flowing in and out of the plate, the easier it is to move current in and out of the other plate. Consider that if we take any two pieces of metal and place them side by side without touching, we're going to create a capacitor. This is true of two wires side by side inside a mic cable, or two wires resting next to each other on the floor or so on. If we send a high frequency through one of the wires, and we have some small capacitance between that wire and the ``receiver'' wire, we'll get some signal appearing on the latter. The level of this noise is proportional to: The area that the source and receiver share (how big the plates are, or in this case, how long the wires are side by side) The frequency of the noise The amplitude of the noise voltage (note that this is ``voltage'') The permittivity of the medium (dielectric) between the two The level of the noise is inversely proportional to the square of the distance between the sender and the receiver (or in some cases their connected wires)