Researchers at Cornell University have proposed a method to modulate both the absorptive and refractive qualities of metamaterials in real time. Their findings present new opportunities to control — in both time and space — the propagation and scattering of waves for applications in various areas of wave physics and engineering. The theoretical work aims to expand the capabilities of metamaterials to absorb or refract electromagnetic waves. Previous research was limited to modifying either absorption or refraction, though the Monticone Research Group, headed by Francesco Monticone of the School of Electrical and Computer Engineering, has shown that if both qualities are modulated in real time, the effectiveness of the metamaterial can be greatly increased. These temporally modulated metamaterials, sometimes called “chrono-metamaterials,” could open unexplored opportunities and enable technological advances in electromagnetics and photonics. “What we demonstrate,” Monticone said, “is that if you modulate both properties in time, you manage to absorb electromagnetic waves much more efficiently than in a static structure, or in a structure in which you modulate either one of these two degrees of freedom individually. We combined these two aspects together to create a much more effective system.” The team’s findings may lead to the development of new metamaterials with wave absorption and scattering properties that far outperform what is currently available. For example, a broadband absorber has to be thicker than a certain value to be effective, but the material thickness will limit the applications of the design. The aim of the Monticone group is to open new areas of research to produce increasingly efficient practical applications. The research pushes the limits of electromagnetic wave absorption by using another degree of freedom: modulation in time. “What we are trying to do is not incremental changes to the technology,” Monticone said. “We want disruptive changes. That’s really what motivates us. So how can we make a dramatic improvement to the technology, not just an incremental improvement? To do that, very often, you have to go back to the fundamentals.” With this new theoretical underpinning in place, experimentally implementing temporal modulations of this kind will be the challenge for future research. Conducting a physical experiment would first require a mechanism to control the modulation of absorptive and refractive qualities of a material over time, which may include laser beams or microwave components. The work holds implications for many applications such as broadband radar absorption and temporal invisibility and cloaking. Applications could also extend to other areas of wave physics including acoustics and elastodynamics. “Our findings, and the exciting results by other researchers working in this area, highlight the many opportunities offered by time-varying metamaterials for both classical and quantum electromagnetics and photonics,” Monticone said. The research is supported by the U.S. Air Force Office of Scientific Research and the NSF. Additional support is provided through the Fulbright Foreign Student Program of the U.S. Department of State. The research was published in Optica (www.doi.org/10.1364/OPTICA.423089).