are valid for an xor logical function the driving inputs and resultant outputs waveforms are shown in fig4 b signal 410 is the lower therapeutic frequency signal 420 is the higher pwm frequency whose duty cycle is varied under programmatic control and is xor 39 d with signal 410 to create the resulting bipolar output signal 430 and 440 waveform 440 includes scalar components 444 and 445 which occur when an inductive load is driven and signal 410 switches its input polarity causing a reversal in the stored energy in the driven inductor fig5 presents the preferred embodiment of the present invention in the present invention microcontroller 3 is capable of generating a variable duty cycle higher frequency pulse width modulation pwm square wave 12 which is xor modulated with the lower therapeutic frequency square wave 11 using a half h bridge 5 which consists of 2 n channel semiconductors and 2 p channel semiconductors arranged so that the current across a connected load 6 can be switched in polarity alternatively a full h bridge can be used requiring four controlling outputs from microcontroller 3 all frequencies are derived from a quartz crystal timing element 4 with a fundamental frequency which deviates less than 1 from a fibonacci number in the preferred embodiment the crystal frequency selected is 24 000 000 hz which is.