Vortex rings are pretty cool, and electromagnetism even cooler. Now, a team of physicists have found a way to combine the two phenomena, creating the electromagnetic vortex cannon.
In fluids (which includes gases) vortex rings can be created thanks to frictional forces as a jet moves through the fluid at higher velocities than the surrounding fluid. Vortex cannons can be used to create these instantaneous pressure differences, which result in a vortex ring, though they occur plenty enough in nature too.
“A velocity gradient forms and causes the inner layers to roll around the outer layers forming a ring-shaped vortex,” a paper on the topic explains. “This process acts in tenths of a second, so the ring is emitted impulsively into the air domain. Due to its own momentum, thermal buoyancy and to the inertia of the rotating fluid, the vortex ring rises upwards in the atmosphere. As the ring ascends, it slows and cools down due to diffusion and heat-transfer processes with the surrounding air.”
They are pretty cool to gawp at, but don’t get too close if you are, for example, a jellyfish.
While fun, it could use a little electromagnetism. In 1996, physicists R. W. Hellwarth and P. Nouchi proposed a solution to Maxwell’s equations in which “focused doughnut pulses” or just “flying doughnuts” could be created, and propagated through free space.
Though interesting, with potential uses in communication and wireless technology, electromagnetic vortexes – or donuts to the hungry – had never been observed until now. And when they were observed, like their non-electromagnetic counterparts, they were surprisingly robust.
“Here, we report that microwave toroidal pulses can be launched by a transient finite-aperture broadband horn antenna emitter, as an electromagnetic counterpart of ‘air vortex cannon’,” an international team explained in their recent study. “Applying this effective generator, we experimentally map the toroidal pulses’ topological skyrmionic textures in free space and demonstrate their resilient propagation dynamics, i.e., how that, during propagation, the pulses evolve toward stronger space-time nonseparability and closer proximity to the canonical Hellwarth–Nouchi toroidal pulses”.
The process, though a little more complicated by the addition of electromagnetism, is somewhat similar to creating vortex rings.
“The principle involves utilizing ultra-wideband, radially polarized, conical coaxial horn antennas to create a rotating electromagnetic wave structure,” the team explained in a statement. “When the antenna emits, it generates an instantaneous pressure difference that forms these vortex rings, which maintain their shape and energy over long distances. The uniqueness of this method lies in its ability to produce electromagnetic pulses with complex topological features, such as skyrmions, that showcase remarkable resilience and self-healing properties during propagation.”
Sometimes things scientists do are just cool for cool’s sake, with little obvious application, but not here. The spectra and polarization characteristics of the vortex rings mean that they could be used to carry more information than can be carried by traditional waves, according to the team, potentially making them ideal for the next generation of communication networks, as well as offering new ways to transmit and encode data.
“Furthermore, their ability to maintain structural integrity even in the presence of environmental disturbances positions them as valuable tools in remote sensing and target detection,” the team adds. “By analyzing the unique patterns of these vortex pulses, we can develop more precise and reliable methods for detecting and locating objects, whether in defense systems or space exploration.”
More will surely follow, but for now rejoice that we finally have the long-awaited electromagnetic vortex cannon.
The study is published in Applied Physics Reviews.
