HEMP Field Penetration into an Ideal Shelter without a Floor through a Lossy Earth

EMP hardening of existing ground based facilities by shielding the facility principally from above has been investigated. This study supports the following conclusions: 1) Wall extensions provide an added measure of protection for EMP hardening. 2) The soils with high conductivity shield best. 3) The angle of arrival of the EMP is relatively unimportant. 4) Finite length shelters (all real shelters) can allow significant energy to penetrate, and 5) Finite length shelters allow large magnetic fields to penetrate the shelter although the coupling mechanism (dH/dt, the time rate of change in the magnetic field) is considerably reduced (factor of u 50).