Charge your phone while you walk: Experimental device fits in a backpack

The swaying motion of a heavy backpack can generate enough electricity to search the internet or make calls.

The swaying motion of a heavy backpack can generate enough electricity to search the internet or make calls.

Researchers have developed an energy-harvesting device that exploits the side-to-side movement of a laden backpack to generate electricity as you walk.

In its trial version, the device would be suitable for people working or trekking in remote places to power an emergency beacon or GPS – such as soldiers, scientists, emergency workers or adventurers.

The researchers from Queen’s University, Canada, experimented with seven different conditions for energy harvesting and found a load of nine kilograms generated the optimum amount of power without any extra metabolic cost (overall effort) to the wearer.

The experimental form of the backpack device that harvests energy from the side-to-side movement that occurs when walking. In real-life applications, the metal plate providing weight would be replaced by the necessities of a long-haul trek. Illustration: Queen’s University

The nine kilograms would be made up of the clothes, food, stove, fuel, sleeping bag and tent packed for a long trek.

The weight of the device – what’s known as a biomechanical energy harvester – and the backpack add another five kilos. This setup produces about .22 Watts of electricity, enough to power GPS and emergency beacons.

Adding more weight will generate more power

In their paper, the researchers Jean-Paul Martin and Qingguo Li – from the university’s Mechanical and Materials Engineering and Ingenuity Labs – calculate that adding more weight to the backpack will generate more power.

“Modelling predicts that an increase in electrical power production could be achieved by increasing the weight carried,” they write.

“If generating over (one Watt) of electrical power was desired for powering higher demand devices, such as talking or browsing the internet with a cell phone, our model indicates that over 20 kilograms of weight would need to be carried.”

Too much weight for most people, not soldiers though

For most people, that’s quite a bit of weight to carry over a long distance – and the swaying movement could prove debilitating. Also, you’d need to carry more than that to maintain phone usage because the consumption of food and fuel gradually lightens your load.

However, soldiers on long-haul missions in Iraq and Afghanistan carry at least 27 kilos and as much as 45 kilos – more than enough to keep a satellite phone charged.

On that basis, the experimental device represents a significant step in the development of biomechanical energy harvesters – gadgets carried by humans that generate electricity by harvesting energy from everyday incidental movements.

So far research has gleaned results more cute than useful.

The new device consists of a weight – a metal plate in the experiment [your necessities on the march] attached to the top part of a pendulum that swings back and forth with each footstep. The heavier the weight, the greater the momentum of the pendulum.

The bottom end of the pendulum pushes into and squeezes springs on either side of the device; these are connected to the energy-harvesting module.

The device is mounted in a frame that can be placed inside a backpack.

The advantage of this design, the researchers say, is that the user does not have to engage in any other activity to generate electricity, such as cranking a handle. They plan to improve the design to reduce weight without loss of power generation.

On a grander scale: In May, an international team of scientists demonstrated for the first time that it is possible to generate a measurable amount of electricity in a diode directly from the coldness of the universe.

The infrared semiconductor device faces the sky and uses the temperature difference between Earth and space to produce the electricity.

The idea is to solve the main problem with solar energy – the inconstant supply of sunny days – with a constant supply of coldness from space.

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