As the Department of Defense (DOD) continues its development and implementation of a new category of weaponry known as directed energy weapons (DEW), other nations are expected to follow suit. The design method known as transformation optics (TO), developed by Pendry, Schurig, and Smith, provides a highly useful design tool for determining the electromagnetic material properties required to redirect incoming electromagnetic radiation along a more desirable path.
This design method has proven effective in the fabrication of real-world structures using metamaterials — materials engineered to possess properties which are not found in nature. Although both powerful and elegant in its formulation, TO relies upon a purely linear formulation of the response of materials to electric and magnetic fields.
It has been known since at least 1941 that sufficiently large electric and magnetic field amplitudes induce nonlinear (i.e., second and higher order) material responses. As these high field amplitudes are naturally expected in an environment in which the concern is the countering of certain classes of DEW, such as high-power lasers and microwave devices, a question of the effectiveness of TO derived redirection structures for counter-directed energy weapon (CDEW) applications arises.
A directed energy weapon is a weapon that delivers electromagnetic energy, rather than a traditional projectile, to its target. Typical examples of directed energy weapons include high-power microwave (HPM) or high-power radio frequency (HPRF) devices, designed to induce large voltages and currents in adversary electronic systems in order to render those systems inoperative, and high-energy lasers (HEL), which ablate target material through the delivery of a focused high-intensity beam of electromagnetic radiation onto a small area of the target. These weapon systems have been active areas of Navy research since the 1960s and are the subject of ongoing development.
As research into these devices proceeds, concern has grown regarding the ability of potential adversaries to field similar weaponry, particularly within the realm of anti-satellite applications. In response to this concern, the Office of Naval Research (ONR), in conjunction with the Naval Postgraduate School (NPS), United States Naval Academy (USNA), and Naval Research Laboratory (NRL) is “investigating basic research topics in counter threats from directed energy weapons systems, such as highpower lasers or microwaves.” These research topics include:
Advanced materials including nano- and/or nonlinear materials for enhanced HEL protection of sensors, optics, airframe, etc.
Metamaterial structures for the control and mitigation of HEL and HPRF irradiation.
Techniques for HEL mitigation such as use of plasmas and obscurants.
HEL protection by degrading atmospheric transmission (e.g. thermal blooming, scattering, absorption aids, and turbulence).
Modeling and sensing of off-axis detection and source geolocation.
Novel instrumentation for detection of HEL and HPRF irradiation.
Active/passive circuit protection and limiters for HPRF
Modeling of HPRF and HEL effects to materials, electronics and sensors as applied to CDEW objectives.
One area that shows particular promise is the field of transformation optics, which uses the form invariance of Maxwell’s equations, the fundamental equations of electromagnetism, as well as the transformation properties of various electromagnetic fields and material properties under coordinate transformations, in order to determine the material properties necessary to force electromagnetic fields to behave in some desired fashion.
A design tool for directing electromagnetic radiation along a specified path, transformation optics’ potential for CDEW applications was quickly recognized. Just as quickly, the material parameters necessary to realize a working electromagnetic redirection structure (as seen below), were discovered to be unlike those found in nature. Specifically, negative electric and magnetic susceptibility values are commonly required. In addition, several applications require unrealistically diverging permittivity and permeability as an outer or inner edge of the structure is approached, as well as continuously (spatially) varying permittivity and permeability. The accompanying illustration shows both ideal and approximate material parameters required to achieve the cylindrical redirection structure, as well as the simulated performance of the same structure with ideal material parameters.
This work was done by Jacob D. Thompson for the Naval Postgraduate School. For more information, download the Technical Support Package below. NPS-0020
This Brief includes a Technical Support Package (TSP).
Nonlinear Effects in Transformation Optics-Based Metamaterial Shields for Counter Directed Energy Weapon Defense
(reference NPS-0020) is currently available for download from the TSP library.
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