Patent ID: 7683625

Claim:
A submersible electromagnetic (EM) field generator for seafloor electromagnetic surveying, comprising: an AC to DC converter operable to generate first and second DC outputs from an AC input as positive and negative DC signals on the first and second DC outputs; a switching module operable to generate a tristate waveform driving signal of a desired functional form by selective switching of the first and second DC outputs, the switching module comprising a first switch pair and a second switch pair, each connected in series between the first and second DC outputs, first and second waveform output electrodes being provided at connection points between each switch pair; an antenna formed by first and second antenna electrodes connected to the first and second waveform output electrodes respectively, wherein the antenna electrodes are spaced apart along the length of the antenna and separated from each other by seawater when submerged, wherein said selective switching of the first and second DC outputs switches the DC outputs to the antenna to pass a current through the seawater between the antenna electrodes in order to generate an EM field in response to the waveform driving signal that follows the desired functional form defined by said selective switching; and a controller that is operable to control selective switching of the switching module so as to generate the tristate waveform driving signal.