Application Of Magnetic And Electromagnetic Methods To Metal Detection

Abstract

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