Tech Briefs

AFRL scientists earn a patent for an airframe-integrated energy storage technology concept.

The Air Force (AF) is evolving from a Cold War-era force with a large, containment- focused infrastructure to a smaller, more responsive and affordable Air and Space Expeditionary Force. In support of this transformation, AFRL is developing affordable, sustainable, and scalable force applications, including directed energy weapons, kinetic energy weapons, electromagnetic guns and launchers, and high-power microwaves.

Capacitors are an essential component in all of these systems because of their ability to store prime electrical energy and expel it in short, fast energy pulses. If they were to be made using conventional technology, however, the capacitors required to support such advanced systems would be bulky and could weigh thousands of pounds. Consequently, AFRL researchers are exploring ways to integrate load-bearing capacitor fibers into air vehicle structures to reduce airframe weight, free up valuable space, and offer fuel cost savings.

ImageThree AFRL scientists, Mr. William Baron, Dr. Maxwell Blair, and Mrs. Sandra Fries-Carr, recently received a patent entitled "Airframe Structure- Integrated Capacitor" (see inset). The term "structural capacitance" implies that in addition to carrying load, the aircraft or spacecraft structure maintains a capacitive charge that permits energy storage and power conditioning for use in a variety of applications, both pulsed and continuous. The specific objectives of the scientists' work effort were to identify a plausible design concept, conduct experimental trials, and characterize the concept's structural and electrical efficiency.

In selecting from available capacitor types, the team considered only those configurations capable of carrying normal, shear, and bending loads. Two common capacitors— parallel plate and cylindrical—met this requirement. While evaluating parallel plate capacitors, the researchers considered laminated structural systems constructed from metal and dielectric material; they envisioned bonding sheets of aluminum to the chosen dielectric material. Commercially available, structural precedents such as Arall™ use this procedure. Although not designed for electrical purposes, Arall is a structurally durable material constructed from impregnated aramid fibers and bonded with aluminum sheets into a laminate. Technicians apply this design approach to the structural capacitor application by laminating a good dielectric with a conductive lamina. Because the parallel plate capacitor concept is quite efficient, the team members initially believed it had significant potential. However, they later abandoned the concept because of associated developmental challenges, including the control of dielectric layer properties, damage tolerance, and repair issues.