Electromagnetic Resistivity Test Mean?
An electromagnetic resistivity test is conducted to measure ground conductivity by electromagnetic induction. An alternating current (AC) of known frequency and magnitude is passed through the transmitting coil creating a primary magnetic field in the soil around the coil. The eddy currents generated induce a secondary current in underground conductors creating a secondary magnetic field picked up by the receiving coil that can be distinguished from the primary field by a phase lag.
The ratio of the magnitude of both these currents gives an indication of the electromagnetic conductivity in the area.
Trenchlesspedia Explains Electromagnetic Resistivity Test
An electromagnetic resistivity test can be carried out without the problem of direct electrical coupling and can provide faster data acquisition. 3D electromagnetic resistivity surveys can be used to produce high resolution images of subsurface zones and geologic features. Low frequency systems can find large cavities such as mines and caves.
Intermediate frequency systems can locate discrete features such as sinkholes and mines. High frequency systems can detect small targets, such as artifacts and waste drums.