Electromagnetic induction (EM) methods are used in many
different types of geological and environmental
applications. As the equipment generally is lightweight and
portable, large areas can be mapped rapidly and accurately.
EM methods have proven to be quite reliable for the
detection and mapping of buried structures such as building
foundations, as well as for the detection of highly
conductive metallic objects like steel drums, tanks,
metallic utilities and other nondescript buried ferrous
metallic objects. EM methods can provide high quality
information about soil types and variations as well as the
presence of sinkholes, karst terrain or bedrock formations
when interpreted correctly.
The Electromagnetic conductivity instrument operates by
creating an alternating primary magnetic field at the
transmitting coil. This primary field is produced by
alternating current in the transmitting coil at an audio
frequency. An electromagnetic field induced in the earth by
the primary field causes secondary loops of electrical
current to flow in the subsurface. This process is known as
electromagnetic induction.
An alternating secondary magnetic field results from this
current flow in the earth .The receiving coil responds to an
electromotive force generated by the resultant of the
primary and secondary fields. Buried metal objects (e.g.
drums, pipelines, etc.) produce characteristic anomalies
which result from the geometrical relation between the
object and the instrument coils along with the very high
conductivity of the metal.
