A shirt with not a single sensor. The anatomy of a fabric that hears

A shirt with not a single sensor

In the ETH Zurich lab in Rüschlikon, two engineers pick up a single strand of glass. It is 130 micrometres thick — thinner than two sheets of paper stuck together. They weave it into an ordinary black cotton-and-polyester T-shirt. At both ends of the strand they attach two ceramic discs. Then they send sound through the glass.

This shirt has not a single sensor. No transistor, no electrode, no nanowire. And yet it knows where a finger touched it, which finger just bent, and how fast the person wearing it is breathing.

The whole secret is a piece of glass — the same material optical fibres are made of. Except that here the glass does not carry light. It carries sound. And the signal the electronics reads is not data at all — it is the sound going quiet when you touch the fabric.

The team named the idea SonoTextiles. The paper appeared in Nature Electronics in May 2025. Let us take this shirt apart layer by layer. There are four of them, and each solves a problem the previous one created.

Layer 1 — glass that carries sound

The first layer is that strand. Pure silica, SiO₂, the same as in a window pane. Optical fibres made of this material have carried the internet across oceans since the 1970s — a beam of light bounces off their walls and travels for kilometres. The authors asked a question: if glass guides light, why shouldn't it guide sound?

The answer is: it does. And remarkably well.

Glass has a Young's modulus of 72 gigapascals. In plain terms: it is stiff. And stiff materials carry sound waves fast and with little loss. Along the glass strand, an acoustic wave — specifically a Lamb wave — travels the way a pulse of light travels down an optical fibre. When something touches the strand, part of the wave's energy escapes at the contact point. The rest reaches the far end. The electronics measure exactly how much energy was lost.

And here is the first paradox. Glass is associated with brittleness, yet a strand 130 micrometres thick can be bent, tangled and woven into fabric — the authors bent it 122 degrees and nothing happened. A thick rod snaps. A thin fibre yields. That is geometry, not chemistry.

Layer 2 — a crystal that speaks and listens

At the ends of the strand sit two discs of PZT piezoceramic. The first turns current into vibration — the transmitter. The second turns vibration back into current — the receiver. Together they form a speaker and a microphone the size of a fingernail.

They operate at frequencies from 100 to 200 kilohertz. The human ear hears up to about 20 kilohertz, so this sound is inaudible. What is more, it is imperceptible. The crystal's vibrations have an amplitude on the order of nanometres — millionths of a millimetre. The wearer feels nothing.

That matters, because the piezoelectric effect has a hundred and forty-five years of history behind it. The brothers Pierre and Jacques Curie discovered it in 1880: some crystals, when squeezed, produce an electric charge. It works in reverse too — apply a voltage and the crystal twitches. In the 1950s engineers developed PZT, a lead-zirconate-titanate crystal that does it a thousand times more strongly. Today the same discs sit in a cigarette lighter, in an echosounder and in a phone's speaker. Here they play the role of the fabric's mouth and ears.

Layer 3 — fabric that has to breathe

The third layer looks the dullest: two-thirds cotton, one-third polyester. It is precisely what sets this idea apart from almost everything previously tried in wearable electronics.

Until now, 'smart textiles' relied on conductive nanomaterials: graphene nanoribbons, polypyrrole, barium titanate. The trouble is that such materials degrade quickly, can be toxic — especially to children and pregnant women — and are expensive to make. On top of that, they demand powerful electronics to process data from thousands of measurement points.

Here it is different. The sensor is the glass itself. The fabric stays breathable, flexible and light, because the only thing added to it is a thin strand. The authors verified that weaving in many strands does not spoil the material's breathability. The shirt can be washed, crumpled and worn in the heat — glass does not react to sweat or temperature.

Cost matters too. The whole set — strands, crystals, measurement electronics — fits within a few hundred dollars. Not because anyone subsidised production. Simply because every component has been commercially available for years.

The team also checked what happens when the fabric is stressed. After repeated stimuli and bending cycles, the system stayed stable — glass does not wear out the way conductive nanomaterials do. That is no technical footnote. It is exactly the threshold where wearable electronics kept stumbling: a sensor that works in the lab but dies after the first wash is useless to anyone.

Layer 4 — an address written in frequency

The fourth layer is the least visible, because it is pure mathematics. When a fabric has many strands, the signals would mix together. The authors solved it with a method mobile phones have known for decades: FDMA, frequency division.

Each strand gets its own frequency — like each radio station gets its own wave. In the 4-by-4 tactile matrix, four warp strands transmit at 100, 101, 102 and 103 kilohertz. In the glove, five fingers get 175, 177, 179, 181 and 183 kilohertz. One receiver listens to all of them at once and, by frequency, recognises which strand just lost energy.

Here lies the cleverest number in the whole paper. A traditional sensor matrix of size n by n needs n² sensors. This technology needs only 2·(n+1). For a 4-by-4 grid that is ten sensors instead of sixteen. At a 10-by-10 grid the gap becomes crushing: twenty-two instead of a hundred. Each additional strand grows linearly, not quadratically. That means fewer wires, less electronics and lower cost — exactly where wearable electronics has been choking.

From breath to the alphabet of fingers

What does all of this deliver in practice?

A 4-by-4 tactile matrix — sixteen points — fits on a 10-by-10-millimetre square, the size of a fingernail. Touching a single point damps the signal by 19 to 22 decibels and the electronics return the coordinates without error. A finger pressing from zero to 14.7 newtons lowers the signal amplitude from 65 to 6.7 millivolts.

The glove recognises gestures from zero to five. Bending the index finger from zero to 85 degrees almost completely blocks the wave — a loss of 18.8 decibels. The authors write openly about the prospect of translating sign language into speech.

And then breathing. A shirt with a strand woven into the abdominal region tracks inhalation and exhalation. Inhaling produces a loss of 14.4 decibels. In a 40-second test the subject breathed normally — 18.5 breaths per minute — then sped up to 46.5, simulating tachypnoea. The fabric told the two states apart. The signal amplitude dropped from 30 to 18 millivolts. For an asthmatic or a post-operative patient, that is the difference between a peaceful night and a call to the ambulance.

Then there are the muscles. When you flex a biceps, the muscle swells and presses the fabric harder against the skin — the signal loses 25.6 decibels. When the muscle relaxes, the loss disappears. In cyclic movement the amplitude ripples with the contractions to within 25 decibels. It is a free feedback signal for a physiotherapist: a stroke patient bends their fingers correctly, or only pretends to exercise.

The authors list a whole set of recipients in the paper: post-stroke rehabilitation, tracking the progress of arthritis, gestures that control a computer without touch, gaming, robotics, teleoperation. And for blind people, the fabric could one day describe through touch what cannot be seen.

Others are already doing it. Just not here

The idea does not start in a vacuum. In 2022, Wei Yan's team published in Nature an acoustic fabric from a single fibre — but based on a complex synthesis of nano-piezocomposites that cannot be cheaply replicated. Google has been developing Project Jacquard since 2015: Levi's jackets with a woven conductive thread that recognises swipe gestures on the sleeve. Except that these solutions either sit in the lab or rely on expensive functional materials that wear away in the wash.

SonoTextiles sidesteps both problems at once. It uses glass and ceramics that industry has been mass-producing for decades, and instead of another sensor at every point — one frequency per strand. This is not yet a product. The electronics — signal generator, processing, wireless transmission — still sit on the bench, wired up. But this is exactly the moment when technologies lift off from the lab bench: the hard scientific problem is solved, and only miniaturisation engineering remains.

The market is waiting. Poland has the thread

The market for smart textiles and wearable health monitoring is growing by over ten percent a year, and the breathing-and-heart monitoring segment alone is worth tens of billions of dollars. Poland does not have to chase it empty-handed. It has exactly the building blocks SonoTextiles is made of.

First — the fibre. Corning, one of the world's largest optical-fibre makers, has a factory in Mszczonów. Poland ranks among Europe's leading producers of optical fibre, and it is literally the same material: silica glass fibre. Second — the fabric. Łódź and its surroundings are a historic textile region, and LPP of Gdańsk is Poland's largest clothing company. Third — acoustics and electronics: the faculties at AGH and Gdańsk University of Technology, plus the Institute of Electronic Materials Technology in Warsaw, have been working on piezoceramics for years.

There is also a ready market trail. Poznań's StethoMe built an electronic stethoscope that listens to the lungs at home and sends the results to a doctor — exactly the same idea, acoustics in the service of health, just in different packaging. What is missing is the link that connects these skills: a team that would build its own version of the hearing shirt from Polish fibre, Polish fabric and Polish piezoceramics. The funding path exists: NCBR and the Foundation for Polish Science finance research into materials and electronics, and PARP's Ścieżka SMART programme subsidises implementations that connect the laboratory to the factory.

The stakes are not abstract. Today the kit costs a few hundred dollars because it is made of laboratory parts. In mass production the price would drop by an order of magnitude. The race is about who first stuffs power, processing and wireless transmission into a garment that can be washed like an ordinary T-shirt. Whoever does it is not selling a shirt. They are selling a category.

Sources

Wang Y., Sun C., Ahmed D., A smart acoustic textile for health monitoring, Nature Electronics 8, 485–495 (2025). DOI: 10.1038/s41928-025-01386-2

Yan W. et al., Single fibre enables acoustic fabrics via nanometre-scale vibrations, Nature 603, 616–623 (2022). DOI: 10.1038/s41586-022-04476-9

Libanori A., Chen G., Zhao X., Zhou Y., Chen J., Smart textiles for personalized healthcare, Nature Electronics 5, 142–156 (2022). DOI: 10.1038/s41928-022-00723-z