Frederick J. Young

Ferromagnetic Shielding Related to the Physical Properties of Iron

The reasons why a nonlinear mathematical treatment of the shielding effectiveness of iron is required are discussed. A brief traveling wave solution is given to the EMP shielding problem when iron material is used. It is estimated that a one mil thick HIPERNOM sheet can provide shielding against a 104 volts/meter EMP of 13 microseconds duration. It is shown that iron shields more effectively than copper. The shielding efficiency of several commercial grades of iron is measured in the frequency range of 30 Hertz to 57 Kilohertz. Various physical factors influencing shielding effectiveness in this frequency range are discussed.

Flux Distribution in a Linear Magnetic Shield

The two-dimensional flux distribution in a magnetic shield of constant permeability and conductivity is presented in a series of magnetic vector-potential contour plots. The plots show the leakage-flux tubes in the shield and in the shielded region. Three- dimensionless parameters representing the shielding 1) thickness, 2) skin depth, and 3) permeability are introduced as the flux-distribution variables. The induced eddy currents cause the resulting fields in the shield to be elliptically polarized and to break into a characteristic cell structure which increases in complexity with rising frequency.

The Shielding of Electromagnetic Pulses by Use of Magnetic Materials

An experimental verification of previous theoretical work on the diffusion of saturated regions in magnetic materials has been accomplished. The diffusion times for the saturated region in Hipernom® tubes have been measured for various exciting magnetic fields and pulse durations. The calculated and experimentally obtained diffusion times are in excellent agreement. Exciting pulse currents up to several thousand amperes have been impressed on the test samples which varied in thickness from 5 to 18 mils. Saturation diffusion times for a 6 mil tube varied from 6 to 0.3 ? sec. depending on the impressed magnetic field amplitude as predicted by the theory. Prior to punch through of the saturated region, little or no magnetic field leakage was detected in the interior of the test samples.