We present the results of a study of the design and effectiveness of Faraday cages against a high-altitude electromagnetic pulse (HEMP) created by an exoatmospheric nuclear explosion. Faraday cages are metallic enclosures used to shield the interior region from electromagnetic (EM) radiation. They are used in a wide array of applications from shielding computers and sensors from EM interference to hardening electrical power substations against electromagnetic attacks and geomagnetic disturbances and serve a crucial role in digital/information security. While they are effective for low frequency electromagnetic radiation, their shielding effectiveness is degraded at high frequencies, especially in unique geometries. Often these cages are made from a metallic mesh or perforated metal plates. We challenge the common belief that a Faraday cage will be effective if the hole size is of the order of the wavelength of the electromagnetic radiation or smaller using electromagnetic simulations for cage designs with varying hole size and spacing. The simulations are performed with Ansys HFSS, an industry-leading commercial computational electromagnetic solver. We find that up to 2% of the electromagnetic field is present in the interior of a Faraday cage with a holes 500 times smaller than the wavelength of the electromagnetic radiation. While acceptable for most purposes, this would not be effective in protecting sensitive electronics against a HEMP which can result in fields over 50 kV/m. We evaluate the designs’ ability to attenuate the EM pulses and aim to optimize Faraday Cage design to contain the least amount of material while also effectively shielding broad-band pulses – especially those present in EMP attacks (i.e., in the MHz/GHz range). We also evaluate the transmission of electromagnetic energy into the enclosure due to external power wires and other electronic cabling.

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