New invention could get rid of millions of batteries, scientists say


A new sensor has the potential to get rid of millions of batteries, its creators say.

At the moment, sensors are used across the world in a variety of critical contexts: those that monitor buildings for dangerous sounds, for instance, or others that help people who are deaf. But they require constant power, and tend to rely on batteries that have to be regularly changed and generate vast amounts of rubbish.

One EU study has suggested that by 2025, 78 million batteries will be binned each day. Every one of those batteries relies on materials that can be difficult to gather and unsustainable to get rid of.

Now researchers say they have built a mechanical sensor that requires no power at all, and could help prevent some of that battery waste.

The sensor works purely by mechanics, its creators say. “It simply utilises the vibrational energy contained in sound waves,” said Johan Robertson, from ETH Zurich, one of the leaders of the new work.

It is able to respond to a particular sound: a certain word being spoken, or a particular noise being generated. Only that specific set of sound waves will cause the sensor to vibrate, which generates an electrical pulse that switches on an electronic device, showing that the sensor has been triggered.

The mechanical system is even able to distinguish between words. It can tell the difference between “three” and “four” purely by the sound energy, its creators say.

They want to be able to create even more complex abilities in the future. That could include the option to distinguish between as many as 12 different words – they could be commands such as “on” and “off”, which could prove useful for controlling machines.

The breakthrough in the study is creating what is known as a “metamaterial”: one that gets its properties not from the material itself, but the structure they are arranged into. In fact, the materials in the sensor are relatively simple – made purely of silicone – and so could be more sustainable.

The sensors could be used for monitoring earthquakes or buildings, for instance, listening for when a building cracks in a way that might be dangerous. It could also be used for oil wells, being used to listen out for escaping gas that might pose a danger.

Researchers also suggest the system could be useful for health devices. At the moment, cochlear implants for instance require changing batteries multiple times each day, which could be avoided – or it could lead to entirely new sensors that might be smaller since they do not need a battery, such as systems to measure eye pressure.

The development of the sensor is described in a new paper, ‘In-Sensor Passive Speech Classification with Phononic Metamaterials’, published in the journal Advanced Functional Materials.