July 18, the Air Force Office of Scientific Research in Arlington, Va., hosted a presentation by noted directed energy researcher Dr. Edl Schamiloglu, Professor of Electrical and Computer Engineering at the University of New Mexico in Albuquerque.
Schamiloglu’s presentation was part of a continuing series of events planned throughout the year as part of AFOSR’s 60th anniversary celebration.
Schamiloglu was the eleventh guest speaker in this series, and his presentation, Directed Energy Microwave Research: Virtual Prototyping and the Paradigm Shift, was an informative and entertaining overview of high power microwave research.
Having been studied for more than 40 years, high power microwave research is a relatively new field, originally beginning with researchers in the United States and the former Soviet Union who dominated the effort. Today, dozens of countries are actively pursuing programs in developing such sources. Early developments in the field were motivated by researchers developing sources with ever-greater output power levels and longer pulse durations (greater energy).
But interestingly, the period from the 1970s to the mid-1990s, which was dominated by the pursuit for greater and greater power levels, ran headlong into the phenomenon of pulse shortening, which was recognized as a fundamental barrier to this approach. In effect, pulse shortening is an operational barrier which severely limits HPM output pulse length and thus the amount of energy radiated. It was this limit on radiated HPM energy that forced researchers to regroup and to pursue other avenues of approach. Or as Schamiloglu described it, “moving away from the ‘flamethrower’ mentality,” and realizing that HPM power alone might not be sufficient, and that the emphasis should be on the establishment of a higher repetition (cycle) rate for these sources, and to possibly tailor HPM waveforms to optimize their effects. To do this, the community would have to focus on developing broadband HPM amplifiers to generate a desirable waveform at low power, and then amplify that signal to a much higher power. In addition, to make HPM viable from a practical application standpoint, advances in compact pulsed power were necessary so these newer models could leave the laboratory and fit on mobile platforms.
Which brings us to why the Department of Defense and the Air Force would be interested in directed energy microwaves in the first place. Several very good reasons: speed of light, all-weather electronic attack of enemy systems; area coverage of multiple targets; surgical strike; minimal collateral damage: simplified pointing and tracking; and extended operational time with low operating costs.
These significant advantages led AFOSR to fund what can be described as a paradigm shift in the HPM community at the University of New Mexico in 1994. It was at this time that virtual prototyping – the use of sophisticated particle-in-cell codes – was recognized as a critical tool for HPM source researchers. PIC codes revolutionized the field. Developed by plasma physicists, these three dimensional finite-difference-time-domain fully electromagnetic field solvers incorporate relativistic dynamics. The result: virtual prototyping, which led to a concentration on effects-driven HPM source research, the pursuit of which is greatly enhanced by the innovative use of metamaterials in confining, controlling and radiating intense microwave pulses.
In his concluding remarks, Schamiloglu noted that AFOSR investment has been key to supporting the transition to virtual prototyping that has resulted in more efficient and cost effective HPM source design and that this investment has led the way to more compact sources of pulsed power to drive HPM sources, and that continued AFOSR investment is paving the way to effects-driven HPM source research, which will lead to novel amplifiers.
AFOSR continues to expand the horizon of scientific knowledge through its leadership and management of the Air Force’s basic research program. As a vital component of the Air Force Research Laboratory, AFOSR’s mission is to discover, shape and champion basic science that profoundly impacts the future Air Force.