Experimental and Numerical Modeling and Analysis of a Multi-Layer Composite Cavity

Modeling of a large cavity containing multiple layers inside the structure has been studied using equivalent impedance approximations along with simplified single ray tracing analysis. This investigation examines the modeling of the effects of radiating with a source enclosed in a large vacant cavity relative to a short wavelength. The intent is to provide predictions for the E-field levels if a transmitter either deliberately or unintentionally is activated when in operational use. During this investigation, the modeling effort requires the development and completion of a three step process. First, the heritage geometric reduction and approximation is investigated. Within this step particular emphasis involves an approach that is an application of Poynting's Theorem. This work was first performed at Goddard Space Flight Center in 1998. A commercial Computational ElectroMagnetic (CEM) software tool, via a technique such as a Physical Optics or Moment Method, is used to model a previously developed experimental model that was modified with thin aluminum sheets. A characterization of the losses associated with the inner blanketing layers is provided. Another emphasis of the first step also validates the modeling technique with a metal shell with experimental results to evaluate the attenuation of the inner blanket layers and is compared to the heritage method as well as the CEM model. Second, the heritage and CEM method are used to characterize the shielding effectiveness of a hollow vacant graphite epoxy composite cavity. The modeling analyses are also compared to the experimental results as a validation process. Lastly, a generic multi-layer payload fairing (hollow cone connected to a hollow cylinder) with a radiating source to determine the resonant effects within the fairing as another approximation baseline that is extended from the two prior validation steps for the modeling technique. The modeling results are used to improve the estimate of the overall shielding performance of the cavity and the respective attenuation or losses associated with the respective layers. This work has been ongoing at Kennedy Space Center since 2005.