Author: Dale McGeehon Source: MDA (
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by Dale McGeehon/techapps@nttc.edu
A new technology created by an MDA-funded company could prevent high-energy transmissions or electromagnetic pulses (EMP) from destroying communications equipment on military and civilian airplanes and ships.
MDA's interest in AAC's plasma limiter technology stems from needs related to military X-band radar systems like the one shown here.
Accurate Automation Corp. (AAC; Chattanooga, TN)—the developer of the radio-frequency (RF) mitigation device, called a plasma limiter—received a $750,000 Phase II SBIR contract from MDA in 2005. The agency's interest stemmed from a desire to eliminate the possibility that powerful U.S. military X-band radar systems, which guide land-based missiles, could damage friendly communications systems.
AAC's plasma limiter responds to potentially crippling high-energy transmissions and EMPs at a much greater speed than some competing devices, and can handle a higher power load than others, said Bob Pap, company president.
Conventional plasma limiters—such as solid-state devices—are fast to turn on (in less than 1 picosecond) but have a low power-handling capability (less than 100 kilowatts). Or others—such as those employing conventional gas discharge tubes—have slow turn-on times (greater than 100 nanoseconds) but can handle a high peak power (greater than 1 megawatt).
AAC's plasma limiter provides the best of both worlds. Its response time is less than 10 nanoseconds, and it can handle greater than 1 megawatt of peak power, Pap said.
Stronger protection by a new type of plasma limiter has been needed because RF sources have become more powerful, and smaller-scale EMP effects can be created using nonnuclear devices with batteries or reactive chemicals. Attacks using these weapons could stop radar and battlefield communications—as well as cell phone towers, television towers, and Internet networks—from working. Lightning strikes also could render similar structures temporarily useless.
A single EMP attack could instantaneously degrade or shut down a large part of the electric power grid in the geographic area of EMP exposure, said Dr. William Graham, chairman of the Commission to Assess the Threat to the United States from Electromagnetic Pulse Attack, before a House of Representatives subcommittee in 2009. Because some of the critical components of the electrical power infrastructure, such as large high-voltage transformers, are no longer made in the United States, loss of these components could leave significant parts of the electrical infrastructure out of service for months or a year, he testified.
High-powered microwaves (HPM) are another form of electromagnetic energy that can melt circuitry or cause equipment to fail, although the HPM range is shorter than the range of an EMP. A military helicopter flying in New York in 2001 while performing a radar test involving HPM weapons generated an energy pulse that reportedly disrupted for two weeks the GPS technology being used to land commercial aircraft at an airport in Albany, according to a 2008 Congressional Research Service report.
AAC's plasma limiters are made with carbon nanotubes, some of the smallest and strongest structures known to man—structures that have unique electrical properties. The nanotubes allow the plasma limiter to absorb the pulse and then reflect it.
"If you hit me with a pulse, you're not going to like me with what I do back at you," Pap said. "It's like putting a mirror in a laser."
The plasma limiter typically resides between an antenna and the circulator in a system, such as in a radar. Because it is a passive device, it does not require a power supply.
While robust and fast, the plasma limiters are difficult to manufacture quickly in large quantities, Pap said. The nanotubes are made in a vacuum, and their assembly is complicated, requiring a long period of time to get started. If a component in the assembly line needs replacing, requiring the manufacturing process to stop, it is expensive to get the production line moving again. Despite the inherent start-up problems, AAC does have a plan to make the manufacturing process smoother, and the company is working to execute that plan.
AAC is looking for corporate partners to help it win contracts with prime manufacturers. Although it is not actively seeking financial assistance from investors or venture capitalists, if any investment company wanted to discuss options, AAC is willing to talk, Pap said.
Meanwhile, AAC is working with Lockheed Martin to put the plasma limiters onto Navy vessels. To leverage its success, the company hopes to sell the technology to radar and electronic warfare systems. "It's not just applicable to Navy ships," Pap said.
