# Helsinki physicists steer water, powder and gas through a wall-free ultrasound tube prototype

- Published: 2026-11-15 19:17 UTC
- Section: Machines & Making › Manufacturing
- Tags: ultrasonic tube, acoustic manipulation, Bessel-like acoustic fields, phased array of transducers, contactless transport of matter, containerless laboratory, University of Helsinki, additive manufacturing, steering a spark with sound
- URL: https://realtech.media/news/rt-d0178355eb2ad578c34f0792_helsinki_physicists_steer/

**A tabletop prototype with 256 ultrasonic transducers guides a continuous flow along a bendable path over about 8 cm, so the matter touches no walls.**

![Helsinki physicists steer water, powder and gas through a wall-free ultrasound tube prototype](https://realtech.media/media/2026/11/71a8124d5fe810d9.jpg)
*Earth.com*

Physicists at the University of Helsinki, together with colleagues at the Public University of Navarre in Spain and the University of Michigan, built a prototype that guides a continuous flow of matter through air inside a tube formed by ultrasound. The work, led by Ari Salmi and Dmitry Nikolaev, is published in Proceedings of the National Academy of Sciences. [1] A ring of 256 ultrasonic transducers, each about the size of a shirt button, surrounds the stream from about 5 cm away. So far the tube works over a stretch of about 8 cm.

## How the sound tube works

Acoustic manipulation uses sound waves to exert force on matter. Existing methods, such as acoustic holograms and phased arrays, move individual particles or small clusters one by one and are not suited to dispersed matter such as gases or aerosols. [1] The new method uses elongated Bessel-like acoustic fields. They create converging radial forces along a programmable path and form a conduit in mid-air without physical guiding structures. [1]

The team timed the 256 transducers so that their waves add up into a long, thin field. Its highest pressure wraps around a quiet core, like the walls of a hose, and anything that drifts is pushed back toward the center. Changing the timing bends the tube. The researchers tilted the water stream left and right and shifted its landing point by about 16 mm without losing a drop.

The ring runs at about 40,000 vibrations per second, above the range of human hearing. According to Nikolaev, the intensity at the core is comparable to a continuous roar of gunfire next to the ear.

## Solids, liquids, gases and a spark

Different forms of matter need different field configurations. A donut-shaped field with high pressure around a hollow center held a stream of water and single drops 1–2 mm across. Silica grains about the width of a human hair circled inside this field, caught in a slow swirl of air stirred by the sound, and were flung out. A field with petal-shaped lobes kept the powder on track, with only a few stray grains falling. [1]

Gases needed a third setting, with pressure focused along the axis. Carbon dioxide, nitrous oxide and mist from a household humidifier followed the field. Helium, which is lighter than air, could not be steered in these tests.

A spark from a small Tesla coil placed in the tube strayed by about 1 mm with the sound on. With the sound off it wandered up to 25 mm from side to side. The authors argue that the same pressure that steers a gas steers the heated thread of air. The team used the steered spark to weld the edges of two plastic pieces without touching them.

## Throughput and limits

Powder passed through the ring at about 4.2 g per minute, and liquid at up to 30 mL per minute. The authors name containerless laboratory operations, contamination-free delivery of reagents or energy, and additive manufacturing as areas of use. [1] Other demonstrations included the letter E written in water drops, rows of tiny wells filled with liquid or powder, and two liquid streams merged in mid-air.

The prototype is a tabletop device meant for small, delicate flows. Any turbulence in a gas stream broke the guidance, so the researchers draped fabric around the device to block drafts. Sound bouncing inside the cylinder weakened the field more than their calculations predicted, which is one reason the steering section was built as a widening cone. The code for shaping the fields is public, and the University of Helsinki has filed a patent application on the method.

## Sources

1. [Proceedings of the National Academy of Sciences](https://doi.org/10.1073/pnas.2614959123)
2. [Earth.com](https://www.earth.com/science/a-tube-made-of-tiny-speakers-is-called-the-closest-thing-to-magic-this-scientist-has-ever-seen)

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Source: RealTech, realtech.media — https://realtech.media/news/rt-d0178355eb2ad578c34f0792_helsinki_physicists_steer/