Determination of Depth of Shallowly Buried Objects by Electromagnetic Induction

A method of determining the depth of a shallowly buried metallic object by using its electromagnetic response is investigated. The method consists in relating the distance of the object from the sensor to the ratio of voltages induced in two coils by the object when it is subjected to a pulsed magnetic field. While the theory is developed for a spherical object, experimental data for both spheres and spheroids are used to evaluate the technique. It is shown that over the range of depths for which the signal-to-noise ratio is large enough, the error in determining a sphere's depth should not exceed approximately 10 cm.