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Inside Science and Technology 

Troops Could Look to Their Soles For Power 

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By Dan Parsons 

As American combat gear becomes ever more sophisticated, the problem of how to power weapon sights and communication equipment has become acute.

The tactical advantages electronics provide evaporate when batteries run dry in the field. High-tech equipment, without power, becomes dead weight.

“More and more electronics give U.S. troops a distinct advantage over enemies,” said Michel Barton, CEO of STC Footwear, which has helped devise energy harvesting combat footwear. “But when he is fighting the Taliban without it, it is a one-to-one man equation.”

Advanced soldier gear and the batteries to power them add weight that can slow down and potentially injure troops in the field. The Holy Grail solution is a power source that needs no recharging, adds little weight to a soldier’s load and is virtually invisible to the wearer.

STC Footwear and Lockheed Martin Corp. have come closer than many companies looking for that elusive combination of attributes by fitting a kinetic charger into the standard-issue boots soldiers and Marines wear.

Kinetic Boot, as it is called, adds only ounces and converts energy from the wearer’s gait to energy that powers all of his or her electronic equipment.

“By design, we decided to find out how we could harvest the energy of a man walking,” Barton said. “For the end user at the end of the day, the only difference is the two or three ounces. For the wearer, there is exactly no other effort added or required.”

Every ounce of battery weight removed from the load troops carry lightens the burden on their muscles and can be replaced with water and ammunition. Kinetic Boot fits within the existing structure of a combat boot, harnessing the otherwise wasted energy generated by ordinary walking or running.

As a human walks, the foot is lifted then the sole pressed to the ground, energy is exerted through muscle contraction and expelled as heat, the way a runner burns calories while rounding the track. That heat energy is lost to the sole or the knee joint, Rebecca Schwartz, nanotechnology lead at Lockheed Martin, told National Defense. Simply walking with the Kinetic Boot captures much of the wasted heat and transforms it into energy to power wearable electronics.

“There is no change in the gait,” Schwartz said. “You create energy when you walk, but it is wasted. It’s not going to have a huge impact to the feel of the walk. In that natural step, there is energy that your leg loses when it makes contact with the ground. It is transferred to your ankle, knee, hip and spine.”

Lockheed’s boot is more efficient at harvesting kinetic energy at a smaller size and with less weight than existing kinetic energy harvesting systems, Schwartz said. Larger mechanisms generally are capable of generating more energy from motion, she said, but would not elaborate on how Kinetic Boot works specifically.

Seamless integration with existing equipment is key, Schwartz said. STC used a finished combat boot and added the necessary components to generate power.

The resultant Kinetic Boot was tested alongside several similar energy harvesting technologies at a Marine Corps experimental forward operating base at Camp Pendleton, California, in mid-May.

Other devices included Bionic Power’s PowerWalk M-Series, which is worn like an athletic leg brace over the thigh, knee and lower leg. One 1.7-pound power-generating brace is worn over each leg, according to company information. Walking at a normal pace, a wearer can generate 12 watts of electricity, which can charge four mobile devices in an hour.

InStep NanoPower fielded a device that uses liquid “microdroplets” to produce 20 watts of electricity at a normal gait when integrated with the sole of everyday footwear. Another device built by Lightning Packs harnesses the movement of a soldier’s rucksack to create energy in much the same way.

Schwartz said several Marines tried on Kinetic Boot at the event and feedback from the troops would be used to inform the design of its next iteration.

“You could feel that it was comfortable,” she said of her own experience wearing Kinetic Boot. “It’s still very much a prototype. The key is going to be the end users, if it is comfortable to them.”

Within a year, Lockheed hopes to release a finalized version of the boot that is tailor-made to accept the power-generating components, rather than having them retrofitted onto existing designs.

“The next phase will be to integrate this into a boot and then to make all the molds and components,” Barton said. “Then, with the right materials, we will be able to check the wearability when you jump out of a tank, when you cross a river.”

The most pressing engineering challenge is to eliminate the need for cords to connect the power-generating boot to a soldier’s electronics, Schwartz said. The device now requires a wire that would run either inside or along the exterior of a wearer’s pant leg.

“That was the first thing end users wanted to know — how to link it,” she said. “They said they don’t really want wires or cables around them.”
 
FTC and other fabric manufacturers are working to weave conductive materials directly into fabrics that could be used to construct soldier trousers and blouses. Electricity could flow directly through a soldier’s clothing instead of along wires that could trip them up or inhibit free movement, Barton said.

“At the macroscopic level, there is a lot happening in intelligent textiles,” he said. “There is also a lot of research on centralized energy management systems that take power from one device to the other automatically. This would eliminate the whole need for cables.”

Ultimately, the search is one for a non-volatile power source that is worn on a soldier’s person, generates energy passively, adds as little weight burden as possible and is virtually undetectable while in operation, he added.

“There are a lot of different interesting designs for what will ultimately be the best method of generating power,” Schwartz said. “From our standpoint, we are trying to come up with a design that is efficient, that is small, that adds as little weight as possible. We want it to be invisible to the wearer.”
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