A soldier typically-equipped for battle can lug around 70kg of equipment, according to the Ministry of Defence. Much of this is taken up by heavy battery packs used to charge the radio, night vision goggles, satnav and so on. Such bulk weighs the solider down, increases fatigue, reduces motor efficiency and simply creates a bigger target for the enemy.
It’s small wonder then that the British Armed Forces are looking to technology to lighten the load.
Nanotechnology can potentially provide the answers. There are three principle methods for generating electricity at the nanoscale; converting energy from the body (kinetic), the sun (solar) and transferring heat from a fire when cooking (thermal).
Luckily for the soldier, all three can potentially be applied to military equipment, says Professor Rob Dorey of Cranfield University, who holds the chair in nanomaterials at the postgraduate-only university.
“A thermoelectric device is able to convert heat to electricity, so you can generate power from an engine or body heat, solar heating, or even from a fire,” says Prof Dorey. “The nice thing about this technology is that a temperature difference is required, so it will work in both hot and cold environments.”
A soldier could start cranking a dynamo at the end of a long yomp, but that’s not practicable, he says. “The key to successful energy harvesting is that the presence of the harvester is not noticed and that it is not a conscious decision to use it.”
How it works
Thermoelectric devices generate a tiny electrical charge by conducting electrons or protons, creating a difference in the concentration of ‘charge carriers’ at opposite ends of a material (see diagram).
The electrical current produced by this concentration gradient is very small, but multiply it enough times and the thermoelectric (TE) device can produce meaningful amounts of energy. Conceivably, TE devices embedded inside backpacks and ancillary equipment which experience temperature changes can generate small, continuous charges that are stored in a slimline battery for deployment at camp.
This could be coupled to piezo-electric harvesters, which scavenge kinetic energy. Piezoelectricity is the charge that accumulates in certain solid materials in response to applied mechanical stress; therefore, ideal for a physical combat environment. Finally, Prof Dorey likens the solar thermoelectric device to a much smaller version of a gadget familiar to some mobile phone owners, the ‘Solar Thief’. This is a fold-out plastic device using photovoltaic panels and ‘joule thieves’ to convert solar energy to charge, primarily, mobile phones.
Like the Solar Thief, most nano-energy harvesting came to the defence sector from civilian applications.
European Thermodynamics Ltd in Leicestershire is working with Cranfield University to develop more practical applications of TE devices and piezo-harvesters. European Thermodynamics (ETL) specialises in designing and making thermal management devices – mainly for “keeping cool”, says the company’s Mark Robins. “Our core business in the past has been in telecommunications, where our devices are used to keep battery arrays at certain optimum temperatures. We’ve not tapped defence yet, but we have our eye on these applications.”
Interestingly, most TE applications are engineered to convert electrical energy from heat. But ETL took flipped this principle, to extract heat energy for cooling. Another everyday use of this technique is mini-refrigerator for office desktops.
Smart ink bridges the materials gap
Cranfield is now working with ETL and other organisations on special ink. “Nano-thermoelectric ink can allow integration of thermoelectrics with a range of objects,” says Dorey. “The beauty is that the particles are only 30nm. Because they’re so tiny it allows us to process materials at very low temperatures and for integrating the material with polymers, ceramics and metals, which can be hard to blend.”
This material compatibility allows a wider range of applications. For example, experts at defence group BAE Systems are exploring the use of nanotechnology to investigate corrosion on aluminium airframes.
What about combat apparel? “It will be five to 10 years before TE devices can be incorporated properly into clothing,” says Dorey.
Even so, a British company has taken a different route to solving the same challenge of reducing battlefield weight. Intelligent Textiles has patented several techniques for weaving complex conductive fabrics. The military application is brilliantly simple; remove cables and battery mass by weaving these items into the integral clothing fabric.
“One of the problems with conventional cables is that breakages can be catastrophic,” Asha Thompson, director of Intelligent Textiles, told the BBC in April. “Here we build-in redundancy, so that if the fabric gets cut, damaged or torn, we still have a way of re-routing the data.”
The company has received £234,000 from the Centre for Defence Enterprise, a gateway for funding in science and engineering where the invention has a defence application. The CDE also wants to find solutions for reducing the physical and the “cognitive” burden placed on soldiers.