Physicists find a way around an old theory to cancel magnetic fields from a distance

Reviewed by Emily Henderson, B.Sc.October 29, 2020

A team of scientists, including two physicists from the University of Sussex, have found a way around a 178-year-old theory, which means they can effectively cancel magnetic fields from a distance. They are the first to be able to do this in a way that has practical benefits.

Hopefully the work has a wide variety of applications. For example, patients with neurological disorders such as Alzheimer’s or Parkinson’s may receive a more accurate diagnosis in the future. Thanks to the ability to cancel out “noisy” external magnetic fields, doctors using magnetic field scanners will be able to see more accurately what is happening in the brain.

The study “Adaptation of magnetic fields in inaccessible regions” is published in Physical Review Letters. It is an international collaboration between Dr Mark Bason and Jordi Prat-Camps from the University of Sussex, and Rosa Mach-Batlle and Nuria Del-Valle from the Universitat Autonoma de Barcelona and other institutions.

The “Earnshaw Theorem” of 1842 limits the ability to model magnetic fields. The team was able to calculate an innovative way to circumvent this theory in order to effectively cancel out other magnetic fields that can confuse the readings in the experiments.

In practical terms, they achieved this by creating a device consisting of a careful arrangement of electrical cables. This creates additional fields and thus counteracts the effects of the unwanted magnetic field. Scientists have struggled with this challenge for years, but now the team has found a new strategy to address these problematic fields.

Although a similar effect has been achieved at much higher frequencies, this is the first time it has been achieved at low frequencies and static fields – such as biological frequencies – which will unlock a number of useful applications.

Other possible future applications for this work include:

• Quantum technology and quantum computing, in which the “noise” of external magnetic fields can influence the experimental readings.
• Neuroimaging, in which a technique called “transcranial magnetic stimulation” activates different areas of the brain through magnetic fields. Using the techniques described in this paper, clinicians may be able to more carefully address areas of the brain that need stimulation.
• Biomedicine, to better control and manipulate magnetic nanorobots and nanoparticles that are moved inside a body by external magnetic fields. Potential applications for this development include improved drug delivery and magnetic hyperthermia therapies.

Starting with the fundamental question of whether or not it was possible to create a remote magnetic source, we devised a strategy to control magnetism remotely that we believe can have a significant impact in technologies that rely on magnetic field distribution in inaccessible regions, such as the interior of a human body. “

Dr Rosa Mach-Batlle, lead author of the study, Autonomous University of Barcelona

Dr Mark Bason of the University of Sussex’s School of Mathematical and Physical Sciences said, “We have discovered a way around Earnshaw’s theorem that many people never imagined was possible. As a physicist, it’s quite exciting.”

“But it’s not just a theoretical exercise as our research could lead to some really important applications: more accurate diagnoses for patients with motor neuron disease in the future, for example, a better understanding of dementia in the brain, or accelerating the development of quantum technology “.