A Helsinki team used 256 speakers to build a pipe made of sound that guides liquids, gases, powders and even an electric discharge, and can be steered while material is flowing.

The problem with pipes is their walls. Anything corrosive attacks them, anything sticky coats them, and anything that must stay uncontaminated picks up whatever the last substance left behind. A great deal of industrial engineering is dedicated to managing the consequences of transported matter touching its container.

Researchers at the University of Helsinki have built something that does not have that problem, because it does not have a container. Writing in the Proceedings of the National Academy of Sciences, they describe an ultrasonic field that holds and guides matter in midair, and demonstrate a stream of liquid flowing horizontally through it without contact with any solid surface.

“Of all the experimental setups I have seen, I would say this is the closest thing to magic,” said Ari Salmi, Professor of Electronics at Helsinki, who led the development of the tube.

Two hundred and fifty-six speakers

The device uses 256 speakers emitting ultrasound at about 40 kilohertz, arranged in a cylinder. The stream runs roughly five centimetres from the speakers. The prototype section is eight centimetres long and draws about 50 watts.

The underlying physics is acoustic radiation pressure. Sound is a travelling pattern of pressure, and where many sources interfere, the pressure field develops a stable three-dimensional structure with regions of high and low intensity. Objects and fluids in such a field experience forces pushing them toward particular positions, and with enough intensity those forces can exceed gravity. Acoustic levitation of small objects has been demonstrated for decades; what is new here is shaping the field into an extended channel that matter flows along rather than a point it sits at.

Forty kilohertz is a practical choice rather than an arbitrary one: it is above human hearing, and it is the frequency at which inexpensive piezoelectric transducers are mass-produced for distance sensors. The wavelength at that frequency in air is a little under a centimetre, which sets the scale of the structures the field can form.

Steerable, and not fussy about what it carries

The tube handles gas, powders, plasma and liquids, and its shape is set by how the speakers are driven rather than by anything physical.

“By changing how the speakers are controlled, we can reshape and turn the tube as needed,” said Dmitry Nikolaev, a postdoctoral researcher who led the project team. “Transporting a solid substance, for example, requires a different field configuration than transporting a liquid or a gas.”

The direction can be changed while material is flowing through, which is the difference between a clever demonstration and something that could be controlled. The team also showed liquid dispensed with single-drop precision, and guided an electric discharge along a chosen route — a plasma is a gas of charged particles and responds to pressure fields much as a neutral gas does, so steering a spark follows from the same mechanism.

The applications the researchers name follow directly from the absence of walls: transporting corrosive or sticky substances, and handling materials that must not be contaminated.

The noise

The intensity required is considerable, and the team is direct about it.

“At the core of the device, the intensity of the ultrasound is comparable to a continuous roar of gunfire,” Nikolaev said. “Even right here next to it, the sound could be compared to a jet engine if you were standing right beside it. But it is too high-pitched for the human ear.”

Inaudibility is not the same as harmlessness, and this is the practical question the release leaves open. Airborne ultrasound at high intensity is not a settled non-issue: exposure limits exist for it, and sound that cannot be heard cannot be judged by the person standing next to it. A device operating at jet-engine intensities would need shielding or distance in any real installation, and the release says nothing about either.

There is also the matter of efficiency. Fifty watts for eight centimetres is not much in absolute terms, but it is continuous power to move material a short distance, where a pipe needs none. The case for the technology rests on the applications where a wall is the problem, not on competing with plumbing generally.

From cleaning pipes to removing them

The idea has an origin story of the kind that sounds invented and generally is not. The team had been working on something almost opposite.

“We had been developing a device that cleaned the inner surfaces of pipes with ultrasound,” Salmi said. “At a lunch with a colleague, we discussed that it would be handy if a pipe had no surface for dirt to stick to.”

Getting from that remark to a working device took about four years, and the release describes the process as trial and error: searching for speaker settings that would produce a stable channel rather than calculating them from first principles. With 256 independently driven sources the parameter space is large, and the field that results from a given set of phases is not something intuition predicts well.

One module at a time

The eight-centimetre prototype is a single module, and the team’s answer to the obvious limitation is that modules could be connected in a row to make a tube of whatever length is needed.

That is plausible and unproven. Each module would need its field to match its neighbours’ at the join closely enough that material passes through without being thrown out, and the alignment tolerance for that is not reported. A chain of modules also multiplies the power draw and the acoustic output, both of which are already the system’s awkward features.

The work was done with colleagues at the Public University of Navarre and the University of Michigan, whom the release does not name individually. It does not state the study’s funding sources.

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Notes

1. Proceedings of the National Academy of Sciences, 2026. DOI: 10.1073/pnas.2614959123.
2. University of Helsinki. “Ultrasound creates a tube that guides matter through the air.” EurekAlert!, 19 October 2026. https://www.eurekalert.org/news-releases/1148281.