Analytic and numerical modeling of normal penetration of early-time (E1) high altitude electromagnetic pulse (HEMP) into dispersive underground multilayer structures

In this paper, penetration phenomenon of an early-time (E1) high altitude electromagnetic pulse (HEMP) into dispersive underground multilayer structures is analyzed using electromagnetic modeling of wave propagation in frequency dependent lossy media. The electromagnetic pulse is dealt with in the power spectrum ranging from 100 kHz to the 100MHz band, considering the fact that the power spectrum of the E1 HEMP rapidly decreases 30 dB below its maximum value beyond the 100MHz band. In addition, the propagation channel consisting of several dielectric materials is modeled with the dispersive relative permittivity of each medium. Based on source and channel models, the propagation phenomenon is analyzed in the frequency and time domains. The attenuation levels at a 100m underground point are observed to be about 15 and 20 dB at 100 kHz and 1MHz, respectively, and the peak level of the penetrating electric field is found 5.6 kV/m. To ensure the causality of the result, we utilize the Hilbert transform.