As an increasing number of C4ISR systems migrate to tactical ground vehicles, the U.S. military has been putting a greater emphasis on resilient vehicle electronicsvetronics. In recent years, defense contractors have been seeing this increased concern take the form of customer demands for increased levels of protection against vibrations and electromagnetic interference (EMI), which are regulated by MIL-STD 810F and MIL-STD 461 standards, respectively.
The U.S. Army, for example, has gotten stricter on vibrations for commercial off-the-shelf (COTS) tech adapted to military use, argues Jim Shaw, EVP of Engineering at the Crystal Group, which develops ruggedized servers. "It used to be, 'Do the best you could.' And because of the price, they were willing to accept whatever you had. But I see them getting more selective," he says.
In fact, while both vetronics and avionics must meet equally stringent EMI requirements, military customers are far more concerned about the vibrations in ground platforms. "A wheeled vehicle is significantly more difficult because it's low frequency, high amplitude, so it's essentially a rough ride," he says, adding that the solder joints found in COTS equipment "don't like to flex or be strained."
The Crystal Group's aluminum chassis servers have circuit boards treated with special adhesives, and, according to Shaw, can withstand 4.43 Gs. The company is trying to get them on the Joint Light Tactical Vehicle, the servers already integrated on other ground platforms. For example, the RS255 two-rack unit is employed on the Warfighter Information Network-Tactical vehicle, and the single-rack RS112 1U server is used in the Army's PROPHET Prophet signals intelligence program.
Mounted on Humvees, MRAPs and MATVs, and deployed in Afghanistan, PROPHET Prophet systems allow the tactical commanders to detect, process, analyze and exploit enemy battlefield communications. "Our computers are being used to process and store that data," Shaw says.
As for EMI, increased customer attention is partly a function of the greater number of computers in vehicles and the need to prevent systems from stepping over each other's signals.
"You can have over 20 systems on an MRAP," says Russ Nieves, director of International Sales for Acromag, which develops embedded computers. "Typically, there's maybe7seven or 8eight different controllers on those systems within the MRAP. So each one of those is a standalone computer system that has functionality … If any of those systems puts out errant noise, it could disrupt the performance of any of those others."
In November, Acromag introduced its ARCX-4000, a hardened small-form computer with an Intel fourth-generation Core i7 processor, to support a variety of applications – from sensor storage to vehicular guidance systems. According to Nieves, "Fundamentally, what we're doing is taking a desktop computer … ," Nieves says, "and we've shrunk it down as small as we possibly can to do a couple of things: Oone is to make it lightweight; two is to make it as power-friendly as possible."
The ARCX-4000 comes in two sizes (5.5x8.5x4 inches and 8.5x8.5x4 inches), weighs 6-8 lbs. and consumes 40-54 watts. Its ferrite cage keeps electronic noise from getting in or leaking out. Nieves says Acromag is talking with BAE, Northrop Grumman and DRS for integration on a variety of platforms, including ground vehicles.
There are four forms of EMI. There's the system that radiates its own emissions and can pick up interference from other systems – both of which can be countered by building a Faraday cage out of conductive material. Then there are emissions coming off from the connecting power line and that can cut both ways, which can be mitigated by power filters.
In October 2013, the Crystal Group developed RS114PS18, a carbon fiber server 20- to 40-percent lighter than a standard one-rack unit. Made for drones, the 12-pound lbs server has also been on manned aircraft and ground vehicles, especially in transit case form. But in designing the RS114PS18, the company has had to reengineer re-engineer its Faraday cage to contain emissions without the benefit of aluminum shielding, Shaw says.
A final driver for more stringent EMI standards is the increase of plug-and-play Ethernet-based systems in vehicles, says Carmen Brokke, electrical engineering supervisor at Curtiss-Wright Defense Solutions. In such a scenario, EMI can lead to the degradation of Ethernet packets.
In December, Curtiss-Wright Defense Solutions went public with its Parvus DuraNET 20-12 6-port 10/100 Ethernet switch, which has round Quadrax-style contacts with four pins in a "star configuration" that create two differential signaling pairs for Ethernet. "With differential signaling, we have two wires that send complementary signals, so any noise is induced in both wires and is canceled out at the receiver," Brokke explains.
He declined to name which platforms host the switch.