HIDDEN OBJECT DETECTION BY MAGNETOABSORPTION AND INDUCTION METHODS
Final technical rept. Jun 1965-Jun 1966
SOUTHWEST RESEARCH INST SAN ANTONIO TX INSTRUMENTATION RESEARCH DIV
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The magnetoabsorption signal is shown to be useful for detecting magnetic voids in soils caused by buried objects which are both nonmagnetic and nonconducting. The magnetoabsorption signal from the soil is obtained through the use of a specially constructed detection head, with a radiofrequency double- D coil placed inside of a low frequency magnetizing coil, and a marginal- oscillator type of detection system. The magnetoabsorption signal is separated from the direct induction signal by using a high-pass filter. The magnetoabsorption signal decreases in magnitude by a value which varies from 10 to 40 percent for objects buried with their tops at a depth of from 2.5 inches below the soil surface to just level with the surface. The percentage variation is independent of the height of the detection head above the soil. For the detection and identification of hidden discrete objects, both the magnetoabsorption and the direct induction signals are used. The induction signal is obtained through a low-pass filter while the magnetoabsorption signal comes through a high-pass filter. The Lissajous patterns, using the magnetizing frequency as a horizontal reference, and the harmonic amplitudes for both the magnetoabsorption and the induction signals, obtained from twenty-one different objects show that discrete objects can be both detected and their material makeup identified.
- Magnetic and Electric Field Detection and Detectors