output is applied to the load 40 and rectifier multiplier capacitors 26 and 29 the arrangement of outputs can be used to create either a unipolar or bipolar charge with respect to ground the ground shield is used prevent transient capacitive coupling between primary and secondary the circuit is phased by controlling the applied frequency of the gate drive pulses to 9 10 11 and 12 relative to the resonant frequency of the secondary f u00bd p l 2 c 2 1 2 in our topology when the drive and secondary resonant frequencies are within 10 and when the coupling is gt 0 6 the secondary circuit back emf or induced flux reduces the current in the primary which in turn reduces the current to be switched in some cases the current to be switched can be arranged to be zero the reduction in current past the peak of the waveform is shown in fig5 the current is turned off before the peak in the secondary waveform in the half h circuit of fig2 we can eliminate half the components of the full h bridge because the magnetic fields are reset to zero and then inverted by the secondary parallel resonant circuit a challenge of our topology is that the secondary must carry an rms current v 2l 2 c 2 1 2 which increases the amount of wire which must be used on the secondary to reduce losses such wire is inexpensive and easy to wind the simplest transformer geometry for the loosely coupled resonant transformer topology consists of solenoidal coils such as are shown in fig3 the wire is wound in a spiral on a circular form as shown in a plan view in fig3 the coupling is equal to the area ratio of the inner over the.