Researchers Produce Synthetic Hall Effect for Unidirectional Radio Transmission

Researchers from the University of Illinois at Urbana-Champaign have reproduced one of the most well-known electromagnetic effects in physics, the Hall effect, using radio waves (photons) at place of an electric current (electrons). Their technique could be used to create advanced communication systems that drink signal transmission in one direction while absorbing signals going in the opposite direction.

The Hall effect, discovered in 1879 by Edwin Hall, is due to the interaction of charged particles and electromagnetic fields. In an electric field, the negatively charged particles (electrons) undergo a force opposite the direction of the field. In a magnetic field, moving electrons undergo a force in the direction perpendicular to both their motion and the magnetic field. These two forces combine in the Hall effect, where perpendicular electric and magnetic fields combine to generate an electric current. Since the light is not charged, normal electric and magnetic fields can not be used to generate a similar "light flow". However, in a recent article published in Letters of physical examinationresearchers have done exactly that with the help of what they call "synthetic electric and magnetic fields".

The research group of principal investigator Gaurav Bahl worked on several methods to improve radio and optical data transmission as well as fiber optic communication. Earlier this year, the group exploited an interaction between light and sound waves to prevent the scattering of light from material defects and published its findings in Optica. In 2018, Christopher Peterson, a member of the team, was the lead author of an article in Science Advances that explained a technology that promised to halve the bandwidth needed for communications by enabling an antenna to send and receive signals on the same frequency simultaneously via a process called non-reciprocal coupling.

In the present study, Peterson provided another promising method for controlling data transmission using a principle similar to the Hall effect. Instead of an electric current, the team has generated a "stream of light" by creating synthetic electric and magnetic fields, which affect light in the same way that normal fields affect electrons. Unlike conventional electric and magnetic fields, these synthetic fields are created by varying the structure by which light propagates both in space and in time.

"Although radio waves do not carry a charge and therefore do not suffer from electric or magnetic field forces, physicists have known for many years that equivalent forces can be produced by confining light in structures varying in intensity. space or in time, "said Peterson. "The rate of change of the structure over time is actually proportional to the electric field, and the rate of change of space is proportional to the magnetic field.While these synthetic fields were previously considered separately, we have shown that their combination affects the photons in the same way that it affects the electrons ".

By creating a circuit specifically designed to enhance the interaction between these synthetic fields and radio waves, the team leveraged the Hall Effect principle to boost radio signals in one direction, increasing their power while stopping and absorbing the signals transmitted in the other. direction. Their experiments have shown that with the right combination of synthetic fields, signals can be transmitted through the circuit more than 1000 times more efficiently in one direction than in the opposite direction. Their research could be used to create new devices to protect radio wave sources from potentially damaging interference or to ensure the accuracy of sensitive quantum measurements. The team is also working on experiments that extend the concept to other types of waves, including light and mechanical vibrations, to establish a new class of devices based on Hall effect application outside its original domain.