example the resonant network device 120 can be a single turn coil with a one inch cross section wrapped around a ferrite core or any other suitable device of any suitable shape size and configuration can be used the ringing signal generated by the resonant network device includes information of interest because it is modulated by changes in either the capacitor inductor or both which thus act as the sensors for example the frequency of the ringing is determined by the shifts in the l c circuit 39 s value of capacitance and or inductance note this frequency is chosen so as not to be at the same frequency of the input charging frequency which is typically 300 khz so as to not confuse data interpretation by way of example the capacitor of the l c circuit may be configured as a capacitive pressure sensor in which distance between plates of the capacitor is reduced as pressure is increased and vice versa likewise inductive displacement sensors may be used where inductance changes with motion of a permeable core in accordance with changes in pressure in a volume or strains in a structure the intensity of the signal 39 s energy is such that much energy can be transmitted through the ground itself the interaction of the signal with the surrounding formation can yield important information about the formation itself indeed the signal can be received by separate above ground surface antennas away from the well site and the signal interpreted by various methods shifts in the signal 39 s frequency attenuation delays and echo effects may give valuable underground information.