The age of energy harvesters – the Hindu BusinessLine

Nothing in this world (except perhaps Wordsworth’s butterfly) is truly still. Everything is, if not in motion, at least trembling or vibrating. Ocean waves, spinning vehicles, and branches swaying in the wind are more visible, but even bridges shake when vehicles pass over them and buildings are built to move a bit, to let a gust blow, or absorb an earthquake wave.

Each movement is an opportunity to capture energy, if only a little. This thinking has led to more research in an area commonly known as “energy harvesting”.

In today’s world of IoT or the Internet of Things, where every device is wirelessly connected to the others, it is necessary to provide local power. There are (are going to be) billions of sensors everywhere. Thousands can be found, for example, under the soil of an agricultural field. Inside aircraft engines, dozens of sensors send information about the health of a component. Underwater sensors detect enemy submarines.

All of this needs energy. Imagine powering billions of sensors with batteries that need to be replaced every few years. Nightmare! The only way is then self-powered sensors.

The recovery of the energy of the movements is seen as the solution.

Interesting products are under development. For example, shoes that generate electricity when you walk. The Defense Research and Development Organization is working on a device that a soldier can carry in a backpack to generate power as they walk.

At IIT Madras, Shaik Faruque Ali, Associate Professor, Department of Applied Mechanics, is working on a project, funded by the Department of Science and Technology, to produce ‘energy harvesting trees’ – their leaves produce electricity as they tremble in the wind. He is also working on a project to manufacture portable devices that generate electricity from the movements of the wearer.

How is electricity produced from movements? There is the good old electromagnetic method – the way most electricity is produced today, by moving a coil in a magnetic field. The more magnetic lines the coil cuts, the more electricity passes through the coil.

So if you place a coil suspended like a pendulum in a magnetic field in your car, you have an on-board generator.

The other way to collect movements (or vibrations) is to use the “piezoelectric effect”. Piezoelectric materials spit out an electrical charge when compressed (subjected to mechanical stress). This is a reversible property, which means that if electricity passes through a piezoelectric material, it will vibrate.

Another trick is to combine electromagnetic and piezoelectric principles to produce hybrid devices. Electromagnetic devices operate at low frequencies of motion, while piezo operates only at high frequencies. IIT Madras has developed and placed such materials on the buses that run on campus, on an experimental basis.

Ali says India is not lagging behind other countries in theoretical research in this area, but it apparently lags behind in its application, as only some sensor companies have tapped into the technology.

EnOcean GmbH from Germany, for example, proclaims: “We get energy for our wireless sensors from the immediate environment – from motion, light and temperature. The British company Perpetuum (recently acquired by the Japanese company Hitachi Rail) specializes in monitoring railway bogies using sensors powered by the vibrations of the bogies.

Well, if the science is so well known, what ever stopped “energy scavengers” from becoming ubiquitous? Ali points out that there are still problems to be solved (they will be). One problem, for example, is that devices generate very low power (from mic to milliwatt). To generate more, says Ali, you can harvest energy from multiple sources and connect them to form a network.

Which brings the discussion to the next challenge. Today, devices can be manufactured for a particular application, which will then operate under that specific movement. But harvesting more energy requires devices that can harness multiple types of motion – devices need to be given more versatility. It is currently an area of ​​research.

The economic value of the power harvested may not be great. But energy harvesters are what would make the deployment of IoT possible.

The future is on the move.

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