The object has three layers. Two are concentric spheres with an interior “spiral-cylinder” made of a ferromagnetic mu-metal, funneling magnetic field lines from one side of the cylinder to the other so that it is undetectable while in transit. In the words of the author of the study, “this device can transmit the magnetic field from one point in space to another point, through a path that is magnetically invisible.”
From the paper: “Constructing an artificial gravitational wormhole connecting two distant regions in the universe is an apparently unrealizable challenge. Large amounts of negative gravitational energy would be required, which makes impossible its realization with present technology…In this work we construct an actual 3D wormhole for magnetostatic fields. It will allow the passage of magnetic field between distant regions while the region of propagation remains magnetically invisible.”
In the short term, the ability to “cloak” a magnetic field might be able to help build MRI scanners. It also has applications in the real world study of invisibility cloaks.