Congratulations to third year PGR James Capers, whose paper ‘Designing the collective non-local responses of metasurfaces’ was published in Communications Physics last month.
James describes the significance of the findings:
Recently, there has been growing interest in how metamaterials can be designed to perform a specific function. The ability to perform specific input field to output field transformations is key to a wide variety of applications from medical imaging to metasurface holograms to bespoke antenna for the next generation of 6G communications. Arbitrarily manipulation of waves can be achieved using metasurfaces, 2D materials structured at the sub-wavelength scale. Currently, the two main methods of metasurface design are genetic algorithms and the Gerchberg-Saxton algorithm. Genetic algorithms are numerically demanding and can produce results that are difficult to interpret and the Gerchberg-Saxton algorithm neglects coupling between neighbouring elements of the metasurface, which can be key to optimal performance.
In this paper, we present two main contributions. Firstly, we derive a simple, numerically efficient and versatile method to design metasurfaces comprised of discrete scattering elements. As an example, we apply our method to engineer several features of antenna radiation, increasing the efficiency and re-shaping the radiation pattern. Secondly, we develop a framework to analyse the scattering from disordered systems by looking at the “eigen-polarizabilties” of the system, allowing for the identification of which interactions within the system are key to performance.
Please see below for the paper’s abstract:
The ability to design the electromagnetic properties of materials to achieve any given wave scattering effect is key to many technologies, from communications to cloaking and biological imaging.
Currently, common design methods either neglect degrees of freedom or are difficult to interpret. Here, we derive a simple and efficient method for designing wave–shaping materials composed of dipole scatterers, taking into account multiple scattering effects and both magnetic and electric polarizabilities. As an application of our theory, we design aperiodic metasurfaces that re-structure the radiation from a dipole emitter: (i) modifying of the near-field to provide a 4-fold enhancement in power emission; (ii) re-shaping the far-field radiation pattern to exhibit chosen directivity; and (iii) the design of a discrete Luneburg–like lens. Additionally, we develop a clear physical interpretation of the optimised structure, by extracting eigen-polarizabilities of the system, finding that a large eigen-polarizability corresponds to a large collective response of the scatterers.