Application Of Magnetic And Electromagnetic Methods To Metal Detection

Magnetic and electromagnetic methods are routinely used to search for buried metal targets on<br>environmental sites. The methods are used to explore directly for buried tanks, buried pipe lines,<br>and individual or caches of buried steel drums. In addition trenches that contain hazardous waste<br>may also contain enough metallic debris to be detected with these methods.<br>Surveys are often performed with both methods to collect four different but complimentary<br>measurements. The two magnetic measurements are total intensity of the magnetic field and<br>vertical gradient of the magnetic field. The two electromagnetic measurements are quadrature<br>component (apparent conductivity) and in-phase component (metal detection). Electromagnetic<br>measurements are sensitive to all types of metal whereas magnetic measurements only detect<br>ferromagnetic metals. The Geonics EM-31 D terrain conductivity meter is a popular instrument for<br>environmental surveys. The instrument will simultaneously measure apparent conductivity and<br>presence of buried metal. The depth of investigation with electromagnetic methods is in part<br>controlled by instrument design. Therefore, this paper presents findings on detection of buried<br>metal that are specific to the Geonics EM-31 D instrument.