Customized magnetic fields in inaccessible regions
A Spanish working group has found a way to generate a spatially limited magnetic field at some distance from the source. The team around Rosa Mach-Batlle from the Universitat Autònoma de Barcelona uses cylindrical arranged, current-carrying wires that form a magnetic metamaterial. The control of magnetism, which is essential to a wide variety of technologies, is compromised by the impossibility of achieving the maximum magnetic field to generate in free space. Here the researchers propose a strategy based on negative permeability is based to overcome this severe limitation. They demonstrate experimentally that an active magnetic material can emulate the field of a straight electric wire at a distance. Their strategy leads to an unprecedented focusing of magnetic fields in empty space and enables the remote erasure of magnetic sources, which opens a way to manipulate magnetic fields in inaccessible regions. PhysRevLett https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.125.177204
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Their results open a new way to control magnetic fields remotely, with potential technological applications. For example, a large number of Microrobots and functional micro- or nanoparticles moved and actuated with the help of magnetic fields. They can carry out drug transport and controlled drug release, intraocular interventions on the retina or even stem cell transplants. However, it is known that the rapid decrease in field strength with target depth in the body severely limits the clinical development of some of these devices. Another example is transcranial magnetic stimulation, which uses magnetic fields to modulate the neural activity of patients with different pathologies. Despite its success, transcranial magnetic stimulation suffers from limited focality because it is unable to stimulate specific regions. The results achieved could benefit both technologies, as they enable the precise spatial alignment of magnetic fields at the desired depth in the body.
For specific applications, however, one should consider that the area between the metamaterial and the replica would be exposed to strong magnetic fields. Another area of application is the trapping of atoms, which, depending on their state, can be trapped in magnetic field minima (low-field seeker) or maxima (high-field seeker). Since local maxima are forbidden by Earnshaw's theorem, high-field seekers are typically caught in the saddle point of a magnetic potential that fluctuates over time. However, these dynamic magnetic traps are very flat compared to traps for low-field viewfinders. By emulating a magnetic source in the distance, one could create magnetic potential landscapes with higher gradients at the desired target position, resulting in denser traps. In summary, our results show that a shell of negative permeability can emulate and cancel out magnetic sources in the distance. This ability to remotely manipulate magnetic fields will allow both the advancement of existing technologies and potentially new applications that require the adjustment of magnetic fields in inaccessible areas.