Two categories of resistivity logs are: induction and laterolog. The laterolog tools use electrodes to inject a current on the formation and to measures voltages at different points in the tool.
The induction tools use coils and magnetic fields to develop currents in the formation whose intensity is proportional to the conductivity of the formation.
The intensity of these currents is measured on receiver coils in the tool. Halliburton provides offerings of both types.