Time-Frequency Multiplexing Apparatus for Downhole Resistivity

The patent segments the signal acquisition process into distinct time intervals and frequency bands using TDM and FDM schemes. Different transmitters are activated in sequential time slots and at different frequencies, allowing the system to separate multiple signals that would otherwise interfere with each other. This segmentation enables clear distinction between signals from different transmitters while reducing mutual interference.

The patent introduces windowed filters as intermediary components that selectively pass specific frequency ranges during specific time intervals. These filters act as mediators between the multiplexed signals and the receiver, isolating the desired signal from interfering signals. The windowed filters enable the system to manage complexity by providing a controlled way to separate signals without requiring complete signal isolation.

The patent implements periodic activation of transmitters in sequential time slots using TDM. Each transmitter is activated in a specific time window, creating periodic signal patterns that can be distinguished from each other. This periodic action allows low-frequency instruments to maintain clear signal separation even when mode separation is reduced, as the time-domain gating provides additional discrimination capability.

The patent changes the operational parameters by introducing time-varying excitation patterns and frequency modulation. Instead of continuous operation, the system uses pulsed excitation with varying frequencies and time windows. This parameter change creates distinct signal fingerprints for each transmitter, enabling accurate measurement even at low frequencies where mode separation is naturally reduced.