How energy harvesting can replace batteries and cables

How energy harvesting can replace batteries and cables

Renewable energy is not just about wind turbines, tidal barrages, and micro-generation systems on homes and businesses; another option for eliminating batteries and power cables in smaller devices is to harvest ‘free’ energy from the operating environment. Jon Severn reports on how technological developments are presenting new opportunities for low-powered applications such as wireless sensors.

Renewable energy is a wide-ranging subject, with both large-scale and micro-generation schemes in operation and under continuous development. But there are also millions of battery-powered applications that could benefit from an alternative to conventional or even next-generation batteries. Interestingly, many of these applications require such low levels of power that they are viable candidates for various forms of energy harvesting.

For example, self-winding mechanical wrist watches have been manufactured for over 80 years, and kinematic powered quartz watches have been on the market for around 20 years. Other electrical and electronic technologies offer additional possibilities, as illustrated by passive RFID (radio frequency identification) tags. These can harvest sufficient energy from the RF reader/writer to power an integrated circuit and transmit data to the reader and/or decode and record data on the internal memory. Furthermore, devices using micro-electro-mechanical system (MEMS) technology only require tiny amounts of energy, hence many academic groups are investigating ways to harvest sufficient energy from the environment to provide the necessary power.

One option is to harvest energy from the electromagnetic waves that surround us as a result of radio and television broadcasts, mobile telephone communications, and the electromagnetic fields created by electric currents passing through conductors. This can be made to work provided a large enough collection area can be used and the RF power is sufficiently high – which usually implies that the source and receiver have to be close together.

More promising results have come from teams investigating ways to harvest energy from vibrations. Southampton University in the UK has been at the forefront of this field of research through its membership of the multi-million euro EU-funded Vibes (Vibration energy scavenging) project; in 2004 a company called Perpetuum Limited was spun off to commercialise the technology.

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