Eric Yeatman, Professor of Microengineering, has invented a series of devices to harvest energy to power small-scale electronics.

Why do this?

There is a growing trend in society for using wireless sensors to capture all sorts of data – from wearable sensors for health and fitness to environmental sensors for pollution monitoring. The question is how to power them all – you don’t want to have to be regularly replacing thousands of batteries. We began to look into ways to make these sensors energy self-sufficient. We chose to work with motion because it is ubiquitous, even if just as vibrations from passing vehicles for example.

How does your device harvest this energy?

We are using the piezoelectric effect – which is seen in a special class of materials that generate charge when put under mechanical strain. Our recent design has a piezoelectric beam with a magnet on its end. Another magnet is attached to a rotating inertial mass. As the device moves, the rotating mass plucks at the piezoelectric beam, which generates a current as it bends.

What is the main challenge?

You don’t always make energy when you need it, and vice-versa, so balancing generation and consumption can be a challenge. You need something like an energy dam: something that will gather energy as it is harvested and release it as a steady stream. Because we’re working at a small scale we can use a simple rechargeable battery for this. How do you see your device being used? An initial use for this would be wearable sensors or wristwatches – they move a lot making them ideal for energy harvesting. Eventually, we would like to see them used in medical implants such as pacemakers.

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