Sensors that monitor infrastructure, corresponding to bridges or buildings, or are utilized in medical devices, corresponding to prostheses for the deaf, require a continuing supply of power. The energy for this normally comes from batteries, that are replaced as soon as they’re empty. This creates an enormous waste problem. An EU study forecasts that in 2025, 78 million batteries will find yourself within the rubbish each day.
A brand new variety of mechanical sensor, developed by researchers led by Marc Serra-​Garcia and ETH geophysics professor Johan Robertsson, could now provide a treatment. Its creators have already applied for a patent for his or her invention and have now presented the principle within the journal Advanced Functional Materials.
Certain sound waves cause the sensor to vibrate
“The sensor works purely mechanically and doesn’t require an external energy source. It simply utilises the vibrational energy contained in sound waves,” Robertsson says.
At any time when a certain word is spoken or a selected tone or noise is generated, the sound waves emitted — and only these — cause the sensor to vibrate. This energy is then sufficient to generate a tiny electrical pulse that switches on an electronic device that has been switched off.
The prototype that the researchers developed in Robertsson’s lab on the Switzerland Innovation Park Zurich in Dübendorf has already been patented. It might distinguish between the spoken words “three” and “4.” Since the word “4” has more sound energy that resonates with the sensor in comparison with the word “three,” it causes the sensor to vibrate, whereas “three” doesn’t. Which means the word “4” could turn on a tool or trigger further processes. Nothing would occur with “three.”
Newer variants of the sensor should give you the chance to tell apart between as much as twelve different words, corresponding to standard machine commands like “on,” “off,” “up” and “down.” In comparison with the palm-​sized prototype, the brand new versions are also much smaller — concerning the size of a thumbnail — and the researchers are aiming to miniaturise them further.
Metamaterial without problematic substances
The sensor is what’s referred to as a metamaterial: it is not the fabric used that offers the sensor its special properties, but relatively the structure. “Our sensor consists purely of silicone and accommodates neither toxic heavy metals nor any rare earths, as conventional electronic sensors do,” Serra-​Garcia says.
The sensor comprises dozens of an identical or similarly structured plates which might be connected to one another via tiny bars. These connecting bars act like springs. The researchers used computer modelling and algorithms to develop the special design of those microstructured plates and work out attach them to one another. It’s the springs that determine whether or not a selected sound source sets the sensor in motion.
Monitoring infrastructure
Potential use cases for these battery-​free sensors include earthquake or constructing monitoring. They might, for instance, register when a constructing develops a crack that has the appropriate sound or wave energy.
There may be also interest in battery-​free sensors for monitoring decommissioned oil wells. Gas can escape from leaks in boreholes, producing a characteristic hissing sound. Such a mechanical sensor could detect this hissing and trigger an alarm without continuously consuming electricity — making it far cheaper and requiring much less maintenance.
Sensor for medical implants
Serra-​Garcia also sees applications in medical devices, corresponding to cochlear implants. These prostheses for the deaf require a everlasting power supply for signal processing from batteries. Their power supply is situated behind the ear, where there isn’t a room for giant battery packs. Which means the wearers of such devices must replace the batteries every twelve hours. The novel sensors may be used for the continual measurement of eye pressure. “There’s not enough space in the attention for a sensor with a battery,” he says.
“There’s an important deal of interest in zero-​energy sensors in industry, too,” Serra-​Garcia adds. He not works at ETH but at AMOLF, a public research institute within the Netherlands, where he and his team are refining the mechanical sensors. Their aim is to launch a solid prototype by 2027. “If we have not managed to draw anyone’s interest by then, we’d found our own start-​up.”
