Cloak for magnetic obstacles

Fascination of technology Cloak for magnetic obstacles

2025-03-06 Source: Universität Bayreuth | Translated by AI 2 min Reading Time

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In our section "Fascination of Technology," we present impressive projects from research and development to engineers every week. Today: how researchers make objects invisible.

Like a cloak: Cloaking is a physical method that envelops an object in a kind of invisibility cloak.(Image: MehmetKemal - stock.adobe.com) — Like a cloak: Cloaking is a physical method that envelops an object in a kind of invisibility cloak.
(Image: MehmetKemal - stock.adobe.com)

Making objects invisible is no longer just a fictional concept from fantasy or sci-fi movies. At least in principle, this also works in research: manipulating objects so that they become invisible to certain waves like light or sound. Researchers in Bayreuth are extending cloaking to particle movements as well. Cloaking for particle streams in miniaturized chemical laboratories—so-called lab-on-a-chip devices—can help transport active substances precisely without exposing them to unwanted premature chemical reactions.

How cloaking works

Cloaking refers to a physical method that envelops an object in a kind of invisibility cloak, rendering it unrecognizable. Until now, cloaking has only been studied with waves, such as light or sound waves. In this process, waves are guided around an object or obstacle, similar to how water flows around a stone in a river. As a result, the waves reach their destination as if the obstacle were not there, thus making it "invisible."

Illustration from the original publication.(Image: Universität Bayreuth, DOI: https://doi.org/10.1038/s41467-025-57004-4) — Illustration from the original publication.
(Image: Universität Bayreuth, DOI: https://doi.org/10.1038/s41467-025-57004-4)

Anna Rossi, Thomas Märker, Nico Stuhlmüller, Daniel de las Heras, and Thomas Fischer from the Chair of Experimental Physics and Theoretical Physics at the University of Bayreuth (Germany) have now developed a method to realize cloaking for particle movements.

What the researchers have achieved

For this purpose, they allowed small particles, called colloids, to flow through a chessboard pattern via a magnetic field. The colloids are paramagnetic, meaning they only exhibit magnetic behavior when near a magnet or an external magnetic field. Through mathematically grounded, targeted changes to the magnetic field, areas on the chessboard were created that remained untouched by particle transport—thus becoming "invisible." These areas influenced the colloids only as they navigated around the obstacle, but not after passing it. The particles reached the destination at the same time as the particles on the unobstructed path.

We have also experimentally shown that with the correct choice of obstacle shape, the size of the obstacle doesn't matter—it can be arbitrarily large, and the particles still arrive at their target in time.

Anna Rossi

The results were developed in collaboration with the University of Kassel (Germany) and the Polish Academy of Sciences. They report their findings in Nature Communications.

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Date: 08.12.2025

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