Soldier on

Soldiers could one day power electronic devices such as personal radios using just their own movements on the battlefield.

The technology is being developed through a two-year government-sponsored programme that aims to create kinetic-energy harvesting systems that can be worn by army personnel.

Principal investigator Prof Andrew Bell, director of the Institute for Materials Research at Leeds University, said soldiers using this technology will not have to carry extra supplies of batteries.

These batteries, which range from AA 1.5V to 200W lithium-ion batteries, are used to power equipment such as torches, GPS and night-vision goggles.

'Soldiers in the field in Afghanistan and previously Iraq can carry packs of up to 75kg in weight when they're on patrol,' he said. 'A significant proportion of that weight can be from batteries so the military is looking for solutions to reduce the reliance on them.'

Bell and his researchers believe piezoelectric material, which converts movement into electrical energy, may be the answer. His group aims to make a wearable device that does not restrict a soldier's movement on the battlefield.

'What this project needs to deliver is not only devices that can harvest the energy, but they must do it with minimal impact to the soldier and possibly positive impact,' he added.

Bell and his team have suggested a device that would sit around the knee and extract energy as a soldier stretches his leg forward and cushion his knee as the leg returns. Bell said electrical engineers working on the project will optimise the electronics so that they take energy out of the device's transducer during the part of the walking cycle when the leg extends.

'We need to take energy out of the device at the right part of the cycle so the soldier doesn't feel it,' he explained.

The electricity generated would be distributed through wires weaved across a soldier's uniform and used to charge up the batteries that power its devices.

Bell said such a power distribution system could be avoided if the piezoelectrics were self-contained in the electronic devices. His group aims to develop a personal radio that demonstrates this possibility.

'The innards of the radio will move up and down as the soldier walks,' he said. 'Kinetic energy can be harvested from that.'

A significant part of the project will focus on the type of piezoelectric material used. Bell explained his group is not likely to use PZT, the most popular piezoelectric in the world, and will instead look for newer, more energy-dense materials on the market.

The group is considering single crystal piezoelectric material. 'They have the potential to be 10 times better at energy conversion compared with PZT,' he said.

Bell said the strength of the material and its flexibility will also be a concern — especially for applications such as the knee-worn device. He added that it is possible to create a composite made of the fibres of the piezoelectric material so that the piezoelectrics could be worn around a soldier's knee like an elastic bandage.

'That's one concept we hope to model and explore a little bit experimentally,' he added.

Bell's group hopes to demonstrate its kinetic-energy harvesting personal radio within two years. 'We will also have identified other areas of the soldier's body where we can apply novel transducers,' he said, 'and have some mock-ups of these transducers for the knee and the soldier straps of the backpack.'

Siobhan Wagner