Electromagnetic probe for measuring properties of a subsurface formation

A system for measuring electromagnetic properties of a subsurface formation, comprising:

• a logging tool and a probe coupled to the tool by a deployment arrangement, wherein the probe comprises:
• a) a pad having a first face adapted for engagement with a borehole wall;
• b) at least one pair of transmitting antennas;
• c) at least two pairs of receiving antennas, wherein the at least one pair of transmitting antennas and the at least two pairs of receiving antennas are mounted in the first face of the pad, and each of the at least two pairs of receiving antennas comprises a first receiving antenna and a second receiving antenna, and each of the first receiving antennas is distributed on one side of the at least one pair of transmitting antennas and each of the second receiving antennas is distributed on an opposite side of the at least one pair of transmitting antennas;
• and,
• d) an electronic arrangement comprising at least one transmitter module arranged to excite the transmitting antennas by applying an excitation signal modulated by at least a first frequency and a second frequency, and at least one receiver module coupled to at least one receiving antenna of the receiving antennas and arranged to determine an attenuation and a phase shift of each reception signal provided by each receiving antenna relatively to the excitation signal;
• wherein the electronic arrangement further comprises a high frequency source and the transmitter module comprises a first low frequency source for the first frequency, a first modulator, a 90 degree phase-shifter, a second low frequency source for the second frequency, a second modulator, a splitter, a first amplifier and a switch, wherein the high frequency source is coupled to the second modulator via the 90 degree phase-shifter, the first low frequency source is coupled to the first modulator, the second low frequency source is coupled to the second modulator, the first modulator and the second modulator are coupled to the splitter, the splitter is coupled to the amplifier, and the amplifier is coupled to the switch, such that in operation the first modulator provides an in-phase signal IIS modulated with the first frequency and the second modulator provides a quadrature signal QIS that is a 90 degree phase-shifted signal modulated with the second frequency, and the IIS and QIS signals are summed in the splitter and amplified by the amplifier to produce the excitation signal which is applied through the switch to the transmitting antennas.