Vibrating kettles - power stations of the future

A team at Bristol University hopes to harvest kinetic energy from vibrating household appliances and vehicles in order to use it as a clean source of commercial electricity within five years.

The concept known as 'energy harvesting' has been around for more than a decade, and commercial devices already exist in specialised areas. For example, vibrations from industrial pumps are currently employed to power sensors that monitor the pumps' operational condition.

At the moment, devices can only make use of vibrations within a narrow range of frequencies or number of vibrations per second. They use a spring with a mass on the end and employ a process called resonance to amplify small vibrations, which enables energy to be extracted.

"Even just a few milliwatts can power small electronic devices like a heart rate monitor or an engine temperature sensor, but it can also be used to recharge power-hungry devices like MP3 players or mobile phones," said Dr Stephen Barrow, who is leading the project.

But the current problem is that, if such vibration levels are too low, too little electricity is produced to make the device usable. This situation generates problems in applications such as transport, where the frequency of vibrations changes constantly.

As a result, the Bristol University team is developing a new kind of device based on a non-linear spring and mass. The new type of spring enables the appliance to resonate over a much wider range of frequencies than a conventional one, which should broaden the number of applications in which it can be used.

The amount of energy produced is similar in scale to a battery, but is more environmentally friendly in that devices do not run the risk of leaking polluting chemicals on disposal. They also do not need to be regularly replaced.

"There's a huge amount of free, clean energy out there in the form of vibrations that just can't be tapped at the moment. Wider-frequency energy harvesters could make a valuable contribution to meeting energy needs more efficiently and sustainably," said Burrow.

Such devices are particularly suited to applications where hard wiring is impractical, vulnerable to damage or difficult to get at for maintenance purposes.

They are also expected to be used in wireless monitoring and diagnostic sensors that generate data on the amount of stress that engine components and structural elements in buildings are subject to.

The appliances could likewise be used to monitor break temperatures in railway rolling stock or patients' heart rate, body temperature and blood pressure.

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