Utilising energy from sound waves to control electronic devices

This innovation is particularly relevant for sensors monitoring critical infrastructure like bridges and buildings, or those embedded in medical devices such as hearing aids, which traditionally rely on batteries. Batteries, once depleted, contribute significantly to environmental waste, with an EU study predicting that by 2025, daily battery disposal will reach 78 million units.

The researchers have sought a patent for this novel mechanical sensor and have detailed their findings in the journal Advanced Functional Materials. Unlike conventional sensors, this device does not require an external power source but is activated by the vibrational energy from specific sound waves, as explained by Robertsson: "The sensor works purely mechanically and doesn’t require an external energy source. It simply utilises the vibrational energy contained in sound waves."

The sensor's mechanism is triggered by specific words or sounds, generating just enough electricity to activate a previously switched-off electronic device. The prototype, developed in Robertsson's lab at the Switzerland Innovation Park Zurich in Dübendorf, differentiates between the words ‘three’ and ‘four,’ with ‘four’ resonating more with the sensor due to its higher sound energy, leading to activation.

Plans are underway to evolve the sensor to recognise up to twelve different commands, such as ‘on’, ‘off’, ‘up’, and ‘down’, and to significantly reduce its size from palm-sized to thumbnail-sized. The sensor's innovative design stems from its classification as a metamaterial, relying on structure rather than material composition, thus avoiding the use of toxic heavy metals or rare earth elements found in traditional sensors. It consists of silicone and features a network of plates and connecting bars designed through computer modelling and algorithms to respond to specific sound vibrations.

The application potential of these sensors is vast, including earthquake and structural integrity monitoring, where they can detect specific sound or wave energy indicative of structural damage. Additionally, they could monitor decommissioned oil wells for gas leaks, offering a cost-effective and low-maintenance solution. In the medical field, they hold promise for powering devices like cochlear implants and measuring eye pressure, where space for battery packs is limited.

Serra-Garcia, now at AMOLF in the Netherlands, is focused on refining these sensors, aiming for a robust prototype by 2027. This development underscores a significant interest in zero-energy sensors across various industries, with potential plans for a start-up if the technology garners sufficient interest.

(Main image: The prototype of the sound sensor is relatively large. (Photograph: Astrid Robertsson / ETH Zurich))