Metamaterials Could Produce Flying Doughnuts

Textbook electromagnetic waves are typically transverse, which means their electric and magnetic fields point perpendicularly to the direction of wave propagation. However, certain electromagnetic waveforms have longitudinal field components that are parallel to the propagation direction. One example is the flying electromagnetic doughnut, whose fields wrap around in a torus pattern. Such pulses could potentially transfer information, accelerate particles, or perform spectroscopy, but so far they have never been observed. A new scheme by Nikolay Zheludev from the University of Southampton, UK, and colleagues shows how flying doughnuts might be generated using a metamaterial based on a circular array of resonators.