The vision for the future soldier is to be combat effective and also highly mobile, adaptive, networked, sustainable with total battle space situation awareness and information assurance. Therefore, he is equipped with night- vision goggles, radios, smartphones, GPS, infrared sights, a laptop as well as batteries to power them. Some of the missions the soldiers perform can take weeks, rather than days, without any ability to recharge; therefore he carries many spare batteries. Sometimes soldier carry seven types of batteries weighing up to 16 pounds for a 72 hour mission.
In modern warfare, soldiers carry a 7 kg-battery for 72 h operation of GPS devices, telecommunication equipment, and other equipment. Heated clothing is used to warm the body in outdoor activities at cold temperatures, which requires a power of ~10W and about 1 kg of Lithium-ion battery for a 10 h-usage. Powered prostheses for walking consume up to 20 W with a 0.49 kg-battery, which should be charged approximately every 3 h . Such high demand of power may not be fulfilled by batteries alone.
New battery and power requirements could come from augmented reality equipment and the more sophisticated Next Generation Squad Weapon program, which will add new targeting capabilities to the soldier’s rifle but also need power that’s not there now.
Powering all of these equipments are vital for success in battlefield, however, they also add up to the weight, an infantry platoon currently carries about 700 pounds of batteries (17 pounds per soldier) for a 72-hour mission, according to the Army. In addition it is expensive, according to the U.S. Army Research Laboratory; a typical infantry battalion spends more than $150,000 on batteries alone each year, the second highest expense next to munitions. Such high demand of power may not be fulfilled by batteries alone.
Batteries are considered conventional energy sources yet suffer from several limitations, such as limited lifespan and power efficiency as well as limited energy storage capacity, which necessitates frequent recharging. One of the alternative source is solar energy which has the issues like in extreme cold when the batteries fail to hold a charge, and in heavy shade the panels don’t operate. Researchers are working to develop wearable energy-harvesting technology solutions including wearable solar panels as well as backpack and knee kinetic, energy-harvesting devices to reduce weight and the quantity of batteries soldiers required to power their devices.
Human Energy harvesting devices have also been studied as an assistant energy source for batteries or independent energy sources for the permanent use of wearable devices without restrictions associated with power consumption. Human energy can originate from a chemical or a physical energy source. Typical sources of physical energy include the thermal and kinetic energy of the human body. Wearable thermoelectric devices convert heat from the human body into electricity of several Watts continuously without affecting the human body. The human body generates kinetic energy in various forms by using muscles, such as foot strike; motions of joints such as ankle, knee, hip, arm, and elbow; and center-of-gravity (COG) motion of the upper body.
Energy harvesting is the process of collecting the wasted energy from the surrounding such as heat, sound, vibration and the other sources to generate electricity. Some of the rnergy harvesting technologies are thermoelectric, piezoelectric, electromagnetic, wireless power transfer and multi modal versions. However no other form of energy has the harvesting potential matching that of solar.
In the military field, soldiers walking for the long distances can use this energy harvester to provide consistent power sources. Waste energy from their motion will be converted to electrical energy and then used for power up the low power devices.
Soldiers Power Up with Energy-Harvesting Devices
Julianne Douglas, the Energy Harvest lead with the Army’s Communications-Electronics Research, Development and Engineering Center said in an Army release that the “added weight means soldiers can get fatigued much more easily, are more susceptible to injury and are less able to maneuver nimbly.”
So, she, along with Noel Soto, a systems engineer with the Army’s Research, Development and Engineering Command are looking at some advanced solutions to make the batteries that soldiers carry last longer. Which means soldiers will be able to haul fewer batteries to the field.
They are experimenting with wearable solar panels that can fit to the body and recharge or continuously charge batteries on the move. While it isn’t always sunny in the field, soldiers are almost always moving. So, researchers are also looking at a backpack frame that generates electricity to charge batteries from the subtle movements of the backpack frame while soldiers are on the march. They’re also working on the “kinetic knee harvester.” This device would use the motion of a soldier’s legs to build electric current while walking.
MC-10’s photovoltaic, Solar Panel Harvester cover a soldier’s backpack and helmet, are constructed from thin gallium arsenide crystals that provide flexibility to the panel’s material and allow it to conform to a soldier’s gear. Under bright sunlight conditions, with the PV panel facing the sun, the backpack panel is capable of delivering 10 watts while the helmet cover panels provides seven watts of electrical power.
Kinetic energy is also captured from the backpack’s oscillation device, as the backpack is displaced vertically; a rack attached to the frame spins a pinion that, in turn, is attached to a miniature power generator. It is capable of producing 16 to 22 watts while walking, and 22 to 40 watts while running.An articulating knee device also capitalizes on this technology by recovering kinetic energy during the actions of flex and rest changing knee positions.
The backpack frame kinetic harvesters are more efficient when soldiers are going uphill, Soto said, as that’s when their rucksacks wobble the most. Soldiers are taught to tightly fasten everything down. But having a loose-fitting rucksack results in more energy-harvesting efficiency, Soto said. For that reason, soldiers preferred the kinetic knee harvesters.
The knee harvest mechanism also helps soldiers to more efficiently brake when going downhill, so they have a better-controlled descent and reduced fatigue, Soto said. And they provide similar power output — 6 watts uphill and 30 watts downhill, as compared 8 to 40 watts, depending on wobble.
Army grant for energy harvesting backpack
An Army grant of more than $344,000 has been awarded to Lei Zuo, associate professor and John R. Jones III Faculty Fellow of Mechanical Engineering, to create a backpack energy harvester. The technology, which is expected to weigh about one pound with a harvesting capacity of 5-20 watts, will lead to lighter packs for military members, decreased supply chain requirements, and fewer muscular and skeletal injuries caused by heavy packs, improving the overall health of the soldier.
“By using mechanical motion rectifier (MMR), a technology converting oscillatory vibration motion into unidirectional rotation and scaling it down, we will work to create a device that sits on the frame of a soldier’s pack and harvests energy to recharge batteries as the soldier walks,” said Zuo. “This work builds on my previous work in energy harvesting.”
In the same way that ocean waves drive the MMR as they approach and depart an ocean energy-harvesting buoy, the backpack technology works to gather power as a soldier’s pack moves up and down as the soldier walks, with the multidirectional motion of walking converted into the unidirectional rotation of a generator. “Because the generator rotates at a steady speed with higher efficiency, it provides higher energy conversion efficiency and enhanced reliability over packs with conventional rack pinion systems,” Zuo said. “More important, the MMR motion will change the dynamics of a suspended backpack and enable it to harvest more electricity with less human metabolic cost.”
Scientists have created a 31 lbs backpack which harvests energy as you walk
A backpack-like device that can harvest the side-to-side motion generated as you walk could be used to charge up electronic devices. Engineers Jean-Paul Martin and Qingguo Li of Queen’s University, Canada, designed their energy harvesting device for people who work in remote areas, without access to the electrical grid, and routinely carry heavy backpacks.
The main advantage of the researcher’s energy harvester is that it not only acts as a renewable source of power, but that it also does not require dedicated efforts — unlike, for example, hand-crank generators, which require deliberate turning. Instead, wearers of the backpack device need merely to walk around as they likely would otherwise have been doing.
Moreover, the energy harvesting came with no extra physical demands on the wearer beyond that of carrying the weight of the device itself. Furthermore, unlike solar panels, the harvester can work whatever the weather. The device can also be tuned to reduce the side-to-side swaying forces experienced by the wearer while carrying weight in their backpack by around 27 per cent. ‘This means that the sharp increases in loading an individual normally feels when carrying weight in a backpack will be reduced using our device, increasing user comfort and potentially reducing injury,’ Mr Martin told MailOnline.
As the wearer walks, the 11 lbs (5 kg) backpack’s contents — represented by a weighted plate in tests — drives an electricity-generating pendulum. With a 20 lbs (9 kg) plate, the backpack generated enough power to operate a small electronic device such as a GPS handset or an emergency beacon. Heavier carried weights can produce more power — to generate enough power for your smartphone, however, you would need to carry at least 55 lbs (25 kg).
In testing the device, the researchers experimented with seven different damping conditions for the pendulum to find the best one for energy harvesting. When the user walked with a 20 lbs (9 kg) weight standing in for their backpack’s contents, the device generated around 0.22 Watts of electricity — enough to power smaller portable electronic devices like GPS handsets or emergency beacons.
‘Modelling predicts that an increase in electrical power production could be achieved by increasing the weight carried,’ the researchers wrote. ‘If generating over 1 W of electrical power was desired for powering higher demand devices, such as talking or browsing the internet with a cellphone, our model indicates that over 20 kg (44 lbs) of weight would be need to be carried.’
Future work should consider reducing the mass of the energy harvesting backpack system to reduce carrying costs associated with walking with the device,’ the researchers wrote in their paper.
Bionic Power’s PowerWalk M-Series
U.S. Army soldiers will test Kinetic Energy Harvester in form of a leg-mounted exoskeleton. Bionic Power, a Vancouver-based startup, has developed a knee brace Called the PowerWalk M-Series, that would capture the kinetic energy of a marching soldier and supply it to portable devices. Wearing a PowerWalk on each leg, users can apparently generate enough electricity to charge four smartphones after an hour of walking at a reasonable pace.
The PowerWalk device uses piezoelectric and triboelectric generators that harvest the kinetic energy generated by movement . It features a gearbox that mechanically converts the knee’s rotation speed into a higher speed that is more efficient for the onboard power generator to then convert to electrical power. The result is 10 to 12 watts of electricity, which is itself then converted to charge Li-ion or NiMH batteries.
“If a soldier can generate 10 (to) 12 watts of power while wearing energy harvesting devices, we can potentially reduce the soldier’s load … and the unit’s reliance on field resupply, and extend the duration and effectiveness of the mission,” states a U.S. Army engineer on the company’s website.
Bionic Power had announced earlier that it has secured contracts with the Army, the Defense Advanced Research Projects Agency, and the Canadian Department of Defense to test the PowerWalk. The contract between Bionic Power and the US Army and Marine Corps will see PowerWalk units tested in the field in early to mid-2017.
Heel-strike kinetic energy harvester
The US Army is working with Robotic Research LLC to design sensor fitted insoles that would generate electricity each time the wearer takes a step. The technology would not only power technology, but also allows commanders to track their soldiers in GPS-denied environments. Robotic Research LLC, a leading provider of autonomy and robotic technologies, was awarded a $16.5 million contract from the US Army in dec 2019 to develop the sensors using its technology called WarLoc. The insole technology was found in a patent out of the Army’s C5ISR Center, which will create electricity through the wearer’s footsteps.
Nathan Sharpes, a scientist from the U.S. Army has recently invented a shoe insole with an embedded energy-harvesting mechanism that produces energy with every step. Army scientist has developed a technique to convert movement from a heel strike into rotational movement. This rotational movement causes the interior of an electrical generator to rotate, which causes electricity to be produced. The electricity generated can be used to charge a battery.
Designed to fit within a shoe insole, the system receives pressure from a downward step or heel strike. A rack and pinion system converts the heel strike into rotational movement which ultimately produces energy. The rack and pinion gear can be in line. As the rack moves, the pinion gear rotates. When the pinion gear experiences a rotation, the coupling mechanism rotates. The rotation of the coupling mechanism causes rotation of the electrical generator such that electricity is produced. The pinion gear can have a variable gear ratio so that the gear ratio is lower at a start to overcome initial resting inertia and increases so the gear ratio is higher toward an end of the rotation to maximize speed.
Knee Joint Energy harvesting
Siti Nooraya Mohd Tawil and others from National Defence University of Malaysia developed protoype of Energy Harvesting solution from Knee-Joint Motion. The knee joint is the best part for implementing this energy harvester. The knee flexion for the normal walking gait cycle is about 60°. The motion of the knee is almost consistent based on the activities carry out by the human.
Human motion, be it tilted, inertial or relative motion of two parts, is typically rather slow in comparison to the speeds required by the capabilities of the piezoelectric transducer. Due to the low frequency human motion usually in few hertz, it has become a limitation to the piezoelectric energy harvester to perform the generation of electrical energy. This is because the piezoelectric cantilever only operates at its maximum efficiency when actuated at its resonance frequency. Range of it resonance frequency is about ten to thousands hertz.
As a solution for that problem, researcher come up with an idea of frequency up conversion. This typically implemented via impact or plucking. For this study, to provide the vibration to the piezoelectric bimorph, magnetic plucking mechanism is used. Magnetic plucking technique is the strategy to carry out the frequency up conversion. The force from the magnet acting on the bimorph will make the bimorph to bend and vibrate freely after the applied forced passes through. By using the magnetic plucking technique, high vibration frequency can be achieved.
Piezoelectric bimorph cantilevers mounted at the inner hub were connected to the rectifier circuit. Rectifier circuit is used in this study to convert the generated AC voltage from the piezoelectric bimorph to the DC voltage. Force from the magnet acting on the bimorph causing the bimorph to vibrate and then generate electricity. Two categories of magnet are used which consist of primary and secondary magnet. The primary magnet (PM) is mounted on the outer ring and the secondary magnet is fixed on the bimorphs.
The concept of piezoelectric material is converting the mechanical energy into the electrical energy. From the ambient vibration, piezoelectric material having the mechanical stress and then polarized to generate piezoelectric effect. This effect occurs in both monocrystalline material and the polycrystalline ferroelectric ceramic.
References and Resources also include: