Bye-bye battery

Is the battery going to be replaced by devices that harvest their own energy?

A pacemaker that doesn’t need batteries? That would be a godsend for heart patients. Nima Tolou, university lecturer in precision and microsystems engineering at TU Delft, is looking into it.

Text: Anouschka Busch, image: James Cavallini/HH, Towfiqu/Getty Images, TU Delft

Tick. Tick. Tick. Pacemakers emit an electric signal to the heart about once every second. Contract. Contract. Contract. Of course, there’s no way a battery can sustain that forever. After six or seven years, pacemakers need replacing. That’s a burden for heart patients, who then need to have another operation. That’s why Nima Tolou, university lecturer in precision and microsystems engineering at TU Delft and engineer of the year in 2018, wants to develop a new kind of pacemaker. It won’t run on batteries but will be driven by the beating of the heart. If he succeeds in doing that, then the pacemakers of the future won’t need to be replaced anymore.

The principle works

It may sound peculiar. A pacemaker enables the heart to beat, so how can that same beating heart provide the pacemaker with energy? And yet that will be possible if the pacemaker gets a makeover. Right now it gets its electrical energy from built-in batteries. If Tolou’s makeover succeeds, it will become a device that harvests its own energy. In which case the pacemaker will no longer have a battery but parts that absorb (‘harvest’) the movements of the beating heart and then convert them into an electrical signal that allows the heart to beat again.

This kind of a pacemaker doesn’t exist yet. But Tolou has shown that the principle works with his start-up Kinergizer. He developed an energy harvester that somewhat resembles the batteries you use in flashlights. But it’s completely different on the inside. It has a flexible plate that captures and reinforces vibrations in the environment. That causes a magnet slide back and forth in a coil, which instigates the flow of an electrical current. It’s the same principle as charging a flashlight by briefly shaking it. But in this case, thanks to the flexible plate you don’t have to shake it really hard. A small vibration is enough to get the magnet to move.

Energy from motion

This energy harvester can generate several milliwatts of energy. That’s not much: you need at least a thousand times more than that to charge a smartphone. But it’s enough to enable a sensor to operate. And they’re becoming increasingly prevalent (see also the box ‘The Internet of Things’). It’s not the first attempt to create a device that harvests energy from motion. Previous energy harvesters turned out to have little use in practice, however. ‘They do well in a laboratory setting, where the vibrations have a constant frequency,’ says Tolou. ‘But in the real world vibrations are never constant.’

Take railways, one of the places where energy harvesters are being tested. Sensors there continuously measure whether everything is running smoothly. Are the tracks okay, the points, the train wheels and other parts? An energy harvester can provide these sensors with electricity by making smart use of the vibrations produced by trains. But they’re never the same. ‘Some trains go slowly,’ Tolou says, ‘and others go fast. The circumstances on railway tracks are always different. The number of passengers changes, as does the temperature. As a result, the vibrations are always different.’ Existing energy harvesters, which only resonate in a fixed frequency, are unable to deal with that. Tolou’s harvester reacts to all kinds of vibrations and has to be able to handle them all well.

Medical applications

In his research at the university, Tolou focuses on medical applications, such as the pacemaker. In that case, the energy harvester can’t be too large: at most it will be the size of a two-cent coin. And instead of a magnet that slides back and forth it will be equipped with piezoelectric crystals. That material generates energy when something presses against it. But the micro-harvester hasn’t been made yet. Developing that kind of device for medical purposes will still require a great deal of research and testing. ‘It will take at least ten years before we have a battery-free pacemaker,’ Tolou estimates. But after that many other applications will follow rapidly. In the medical world, but also beyond it. ‘By that time, sensors will most likely have become so much more energy efficient that the micro-harvester can be used in all kinds of areas.’

The Internet of Things

There are conceivable applications for energy harvesters outside of the medical world as well. Take ‘The Internet of Things’. Those are devices that you wouldn’t immediately think would forward or exchange data via the internat. A thermostat in your home that you operate remotely, for example, or watches that measure your heartbeat and keep track of the distance you’ve covered. That happens through billions of sensors and other small devices that all require power. It’s impossible to wire them all up. Energy harvesters that get their energy from their environment, for example through vibrations, may well be the solution one day.

Inspired by a watch

Nima Tolou got the idea for his energy harvester when he was working on a new movement for watches. Movements usually consist of about thirty parts. With a team from manufacturer Zenith and fourteen researchers and students, Tolou reduced that to a single flexible plate. The same plate that can also be used as an energy harvester in railway sensors, for example. This kind of elastic mechanism was not the obvious choice for a watch. To ensure that a timepiece is accurate, you have to make sure that it has a highly regular heartbeat. Elastic mechanisms inherently generate irregular vibrations. Tolou’s team managed to control the flexible time mechanism so well that the irregularities cancel each other out exactly. The result: the most accurate mechanical watch every produced.