Designers of rugged computer boards and chassis continue to struggle with reducing size, weight, and power, developing efficient cooling systems, and fighting tin whiskers, as a new generation of standard small-form-factor embedded computing prepares to make its debut.
BY Skyler Frink
As the modern battlefield continues to evolve, equipment has evolved with it. Rugged embedded computers are included on aircraft, vehicles, radios, sensors, unmanned aerial vehicles (UAVs), and all manner of electronics. In today’s information-laden battlefield, companies have been creating rugged embedded computers with smaller sizes, less weight, and lower power use than ever before.
Military systems designers are looking for the same things they’ve always been looking for: smaller size, lower weight, and less power consumption. The industry term for this is SWaP (size, weight, and power), and the designers of rugged embedded computers have been designing products that meet military standards while giving the best SWaP they can at the lowest possible price. SWaP is always balanced against actual performance, and each rugged embedded computer is designed to provide maximum performance for the lowest SWaP score possible.
|Convection-cooled chassis pull heat from system components and dissipate the heat directly into the atmosphere via heat fins on the exterior walls of the chassis.|
Most military systems designers have taken to looking at commercial off-the-shelf products, or COTS, to provide their rugged embedded computers. The reason is simple: COTS costs less than systems designed specifically for one task.
“Cost is always an issue in these days of budget crisis. The military is interested in COTS because it is a price-effective way to do things,” explains Jim Blazer, chief executive officer of RTD Embedded Technologies Inc. in State College, Pa. The switch to COTS is not without its own problems, however.
“While they’ve opened their arms to COTS, they haven’t really lowered their expectations,” Blazer says. “I think that’s one of the problems where the COTS products need to be made a little better and the military guys need to lower their standards a little.” Since products are not being designed with full knowledge of the product they are being designed for, but only for a set of military standards, it is more difficult to meet the exact criteria military systems designers desire. Each rugged embedded computer is expected to have low SWaP, and there are many factors that make designing them a challenge.
|The Air-Flow-Through (AFT) chassis technology utilizes environmentally sealed covers on the system modules that provide air channels over the board electronics. Air is pumped through these channels directly on the boards, providing an efficient cooling path.|
Rugged embedded computer power use produces heat that needs to be dissipated. There are many methods used for cooling, and plenty of things that complicate the cooling process.
Conduction cooling is common among lower-power rugged embedded computers. By drawing heat out through metals that connect the chips to the chassis, air runs along fins installed on the chassis which draws heat away from the computer. “Everyone would prefer to have conduction and convection cooling in all systems,” says Jason Shields, product development manager for Curtiss-Wright Controls Embedded Computing in Ashburn, Va. However, many computers use much more power than can be dissipated through passive means such as conduction and convection.
Those higher-power systems require active cooling. "A lot of the new technologies out there, liquid flow through and air flow through, have enabled us to cool very high-power systems in a very small space,” Shields says. Air- and liquid-flow-through cooling involve forcing air or liquid as close to the heat-producing cards as possible, and require complex systems that increase the size and weight of rugged embedded computers. The SWaP trade-offs for using these advanced cooling systems are obvious. By trading in a slight gain in size and weight, more powerful computers can be used to provide greater performance.
The environment also has an effect on cooling methods, says Bill Ripley, director of business development for mission and payload systems at Themis Computer in Fremont, Calif. He points out how sand in Iraq became a major problem for convection-cooled systems deployed to the Middle East. Systems shut down frequently because sand in the air flowing through the cards during convection cooling caused damage to the cards in the system. This forced many systems that used convection cooling to switch to conduction cooling instead, which allowed the actual chassis to be completely sealed while still providing proper cooling.
|A chassis that employs forced-air cooling technology is equipped with a built-in, military-grade fan assembly that pulls cooling air over the chassis heat fins.|
Power requirements in rugged embedded computing systems vary wildly depending on the system, the computer, and its packing. Rugged embedded computers can be designed to use tens of watts or hundreds of watts, but less power use is always preferred.
“General improvements in processor technology have greatly improved the ability to use less power and keep them cooler,” says Norman Lange, director of product development at Black Diamond Advanced Technology in Tempe, Ariz. New technology always is in the works, and engineers have been able to design processors that run on a fraction of the power that processors required just a few years ago. These advances in technology not only lower the power use of rugged embedded computers, but they also produce less heat.
Whether a rugged embedded computer is going into a vehicle or a radio, there always are limitations on how large the system can be. “You typically have a set amount of space for your system to reside,” explains John Wranovics, director of public relations at Curtiss-Wright Controls Embedded Computing. “Everybody wants more and more performance in smaller and smaller space.” Embedded computers are competing with critical systems on vehicles, and they need to fit into the smallest possible space to allow for more functionality. Fortunately, the continual advances of technology have made this easier and easier for companies to do.
“You can now get more and more on a smaller and smaller card,” says Jacob Sealander, embedded computing architect for Curtiss-Wright. With modern computers growing smaller and smaller, processors and memory have been shrinking in size at a steady rate, allowing computers that used to require a small room to operate to be placed in chassis that are smaller than a box of tissues. Of course, with size reductions there is always the reduction of weight.
While weight may not be as critical an issue for ground vehicles as it is for aircraft and missiles, the weight of embedded computers is particularly important for aircraft. “Every pound that you can take out of the vehicle, or system, gives you more time over the target,” says Themis’s Ripley.
Weight also is a major factor in embedded computers that soldiers and Marines need to carry into battle. “If we can build systems into a smaller form factor than what they have now that’s a tremendous weight savings for them,” Ripley explains. To allow for lower weight, smaller chassis often are necessary for power and performance. When weight is important, extra functionality is put aside to make the system more lightweight.
Rugged embedded computers need to survive in the harsh environments of the battlefield; temperatures below freezing or near-boiling; intense vibrations caused by engines, gunfire, and the environment itself; and electromagnetic interference caused by other devices—and they need to function the entire time.
“How rigid your board is affects vibration standards; you need to have a balance between a board that’s rigid enough to not break every component off of the board but not so soft the components won’t receive stress fractures from high-frequency vibrations,” says Curtiss-Wright’s Shields.
Helicopters produce a lot of low-frequency vibrations that max out at the rev-rate of the rotor, while jets engines produce high-frequency vibrations due to their high-speed oscillations. Even weapon vibrations from high-caliber gun firing from helicopters or jets is far from uncommon. Boards and their components need different rigidity based on what vehicle they will be placed in and which weapons they will be operating near.
The reason rugged embedded computers are made the way they are is to be sure they will always work. When in battle, a minor mistake can cost lives, and that means rugged embedded computers can’t afford to fail. “They need to work all the time. Everything plays into that,” says RTD Embedded Technologies’ Blazer. Computer failure is not an option for critical systems in an airplane or helicopter.
There are steps taken to mitigate system failures if they occur, however. “If you have a safety-critical system in a box, oftentimes they’ll put two or three identical systems in the aircraft and they will physically separate these things. If one fails, the other will take over,” says Themis’ Ripley. Redundant systems prevent one attack from destroying all the critical systems in one vehicle.
There are times when electronics with sensitive information fall into the wrong hands. Security is a growing concern for the developers of rugged embedded computers. “We’re seeing requirements for encryption on-drive like AES-256, and we see requirements for being able to do some of the certified purge cycles,” says Ripley. Recent events, such as the UAV that was brought down over Iran, have helped highlight the importance of security and anti-tamper technologies.
Deleting decryption keys can render a memory disk drive useless. While not preferable when compared to a full wipe, deleting an entire drive’s worth of information, especially when there is a terabyte’s worth of data saved on one drive, takes much longer than deleting a few keys. Most rugged embedded computers that are expected to have secure information feature encryption and the ability to wipe the drive thoroughly.
|A VITA-74 chassis compared to a 20 dollar bill.|
There’s a lot more to making rugged embedded computers than putting all the components into a chassis and calling it a day. Each component of a rugged embedded computer needs to be connected and the board needs to be laid out in the most efficient manner possible. “As memory buses and memory gets larger and larger, it gets challenging to correctly lay out all the traces associated with the memory on the plate,” says Themis’ Ripley. Much analysis needs to be done to ensure traces are where they need to be, he says. As the components in systems get better and better, it becomes difficult to let them all operate at maximum efficiency while still meeting all the military standards involved in making a rugged embedded computer. That’s also assuming the system is even capable of being created with current technology.
There is another problem with designing COTS rugged embedded computers, says Black Diamond’s Lange. “It’s almost never that I get a requirement that is perfect,” he says. “There are always trades to be made, and how you balance those is critical.” A perfect solution is often not possible, so military systems designers need to compromise in order to get a system that best meets the requirements.
Rugged embedded computers have been in use for many years, and they continue to shrink in size while offering more functionality with less weight. New standards, and new problems, have been propping up along the way.
VITA-74—a proposed new standard that may be seeing ratification in early 2012—could lead to small-form-factor circuit boards the sizes of credit cards that fit in enclosures the sizes of Rubik’s Cubes. “We’re taking orders for VITA 74 systems now,” says Ripley, whose company is leading development of VITA-74.
The VITA small-form-factor initiative, which seeks to create standard boards and enclosures smaller than the 3U form factor, consists of VITA-73, VITA-74, and VITA-75, led respectively by PCI Systems in Sunnyvale, Calif.; Themis; and Curtiss-Wright Controls Embedded Computing.
|This photo shows cards that are compatible with a VITA-74 chassis.|
Not everything is looking good for the future of rugged embedded computers, as the threat of tin whiskers grows ever closer. In 2016, it is expected that lead will no longer be allowed in the solder that holds rugged embedded computers together. Currently, a tin-lead mixture is used, as pure tin grows tiny metallic “whiskers” that can short out systems. These tin whiskers are currently a serious problem that has yet to be solved in a way that does not involve mixing lead.
Tin whiskers are not a new problem for the designers of rugged embedded computers. “It’s taken satellites out of the air, it’s ruined nuclear reactors,” says Douglas H. Patterson, vice president of the Military and Aerospace Business Sector of Aitech Defense Systems Inc. in Chatsworth, Calif.
The industry hopes to find a solution to the problem, and many companies are working together to combat the threat tin whiskers pose to rugged embedded com-puters. Committees have been formed by businesses in the industry, and the University of Maryland’s Center for Advanced Life Cycle Engineering is looking for solutions to the tin whisker problem. “You don’t want to have your weapon go down because of tin whiskers,” Patterson says.
There are currently ways of mitigating tin whiskers, but there is not yet a solution that completely prevents their formation.
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01273 570 220
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Avalue Technology Inc.
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Black Diamond Advanced Technologies
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Curtiss-Wright Controls Embedded Computing
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Elma Electronic Inc.
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General Electric Intelligent Platforms
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49 621 4 32 14 - 0
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Mercury Computer Systems
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RTD Embedded Technologies Inc.
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Themis Computer Inc.