This eddy current produces a back electromotive force and blocks the penetration. The higher the frequency, the greater the rejection and shallower the penetration. Complex frequencies interact in the body causing a non-linear spread of current. A prime example of a non-linear electrical device is a diode. A diode conducts current of one polarity far greater than the opposite polarity.
Most living tissue exhibits non-linear characteristics, functioning somewhat like diodes.
Our present knowledge of electromedicine is not sufficient to determine the optimum frequency for a specific tissue response so the use of sine waves is not recommended. The length of time the pulse lasts is called the width. This is usually measured in microseconds. It may seem odd to measure a width in time intervals rather than millimeters or other measure of length, until one understands that pulse width really refers to the time the wave is active. The body responds to the peak of electrical signals and to the number of electrons in that signal.