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Magnetic Invisibility: Scientists Create Bilayer Cloak That Makes Objects Disappear from Magnetometers

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  Published in Science and Technology on Friday, December 19th 2025 at 14:50 GMT by Interesting Engineering

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Magnetic Invisibility: A New Cloaking Concept That Makes Objects “Disappear” From Magnetometers

Scientists have long dreamed of cloaking objects from light, turning them into invisible “ghosts” that can slip through the world without disturbing their surroundings. A recent breakthrough announced on Interesting Engineering shows that the same idea can be applied to magnetism. By carefully shaping the flow of magnetic fields, a team of researchers has created a cloak that renders an object invisible to magnetometers and other magnetic‑sensing devices. The new design, described in a paper published in Scientific Reports, promises applications ranging from improved magnetic shielding in medical imaging to covert magnetic detection systems.

How Magnetic Cloaking Works

Unlike light, magnetism is a static phenomenon governed by the distribution of magnetic permeability (µ) in space. A static magnetic field can be distorted by materials that either attract or repel the field lines. The trick to a magnetic cloak is to guide the field lines around an object so that they re‑merge on the other side, leaving the exterior field unchanged. In other words, the cloak must cancel the disturbance an object would normally cause in a magnetic field.

The concept borrows heavily from transformation optics, a mathematical framework that has been used to design invisibility cloaks for light. By re‑mapping coordinates, one can dictate how the electromagnetic properties of a material must vary to guide waves (or, in the static case, field lines) along a desired path. For magnetic fields, the equations simplify: one must engineer a shell of material with a specific radial distribution of permeability that satisfies Laplace’s equation for static fields.

The New Design: An Isotropic, Bilayer Cloak

Previous magnetic cloaks relied on highly anisotropic metamaterials—engineered composites whose magnetic response depends on direction. While effective, such structures are difficult and expensive to fabricate, especially for practical sizes. The new design circumvents this issue by using an isotropic bilayer of commercially available high‑permeability metal (nearly 1000 µ₀, where µ₀ is the permeability of free space) and a thin layer of a material with almost zero permeability (a diamagnetic alloy). The two layers are arranged concentrically: the inner high‑µ shell surrounds the object, and the outer diamagnetic shell encases the inner layer.

Because both layers are isotropic, the cloak can be produced with simple manufacturing processes such as extrusion or rolling. The key is choosing the ratio of inner to outer shell thicknesses to satisfy a boundary‑matching condition derived from the transformation‑optics equations. The research team verified this by numerically solving the magnetostatic equations for a cylindrical geometry and then fabricating a prototype.

Experimental Verification

The prototype was a 2‑cm‑diameter cylinder containing a small permanent magnet. The cloak was tested inside a uniform external magnetic field produced by a pair of Helmholtz coils. When the cloak was removed, a standard Hall‑effect sensor placed near the cylinder detected a clear disturbance—an elevated magnetic field due to the magnet’s presence. With the cloak in place, the sensor’s reading returned to that of the undisturbed field, confirming that the magnet’s influence had been cancelled.

To demonstrate robustness, the researchers performed measurements at different orientations and field strengths. The cloak preserved the external field for angles up to 90° and for field strengths ranging from 10 mT to 200 mT. In all cases, the magnetic field inside the cloaked region remained suppressed to less than 5 % of the background value, meaning that the magnet could be shielded from external sensors.

Why Is This Important?

1. Medical Imaging and MRI
   Magnetic resonance imaging (MRI) machines rely on highly uniform magnetic fields. Any ferromagnetic object in the field can distort the image and even damage the equipment. A lightweight, low‑cost magnetic cloak could enable the safe placement of sensitive electronic components near the imaging area, reducing shielding costs and improving patient safety.

2. Quantum Computing
   Superconducting qubits, the building blocks of many quantum computers, are extremely sensitive to stray magnetic fields. Magnetic cloaks could be used to isolate qubits from ambient magnetic noise, potentially improving coherence times and device reliability.

3. Stealth and Sensor Evasion
   In security and defense, magnetic cloaks could hide objects from magnetic anomaly detectors used in mines, submarines, or anti‑radar systems. Conversely, cloaks could protect valuable equipment from unwanted magnetic interference in hostile environments.

4. Fundamental Research
   The new design demonstrates that static magnetic cloaking can be achieved with readily available materials. This paves the way for exploring more complex field manipulation techniques, such as magnetic “lenses” or “waveguides” that could shape static fields for novel device architectures.

Next Steps and Challenges

While the prototype proved the concept, scaling the cloak to larger sizes or more complex shapes remains a challenge. The bilayer design is inherently cylindrical; extending it to arbitrary geometries would require advanced fabrication techniques or the development of graded permeability materials. Moreover, the cloak is effective only within a specific range of magnetic field strengths; at very high fields, the permeability of the materials may saturate, reducing performance.

The research team is already investigating a tripartite cloak that incorporates a superconducting core to achieve perfect shielding at low frequencies. They are also exploring active cloaking—using electronic circuits to dynamically adjust the cloak’s response in real time.

Conclusion

The magnetic invisibility cloak described in this new research represents a significant leap forward in controlling static magnetic fields. By harnessing a simple bilayer of isotropic materials, the scientists have turned a complex, physics‑heavy concept into a practical, manufacturable device. As the technology matures, we can expect magnetic cloaks to appear in a range of high‑tech applications, from safer MRI environments to quieter, more reliable quantum computers, and even covert military sensors. The day when magnets can be made truly invisible may be closer than we thought.