Additive manufacturing paves new ways to the efficient exploration of the third space dimension, providing advantages over conventional planar architectures. In particular, volumetric electromagnetic antennas can demonstrate superior characteristics, outperforming their planar counterparts. Here a new approach to the fabrication of electromagnetic devices is developed and applied to antennas, implemented on curved surfaces. Highly directive and broadband antennas are 3D‐printed on hemispherical supports. The antenna skeleton and the support are simultaneously printed with different polymer materials – PLA mixed with graphene flakes and pure PLA, respectively. Weakly DC‐conductive graphene PLA‐based skeleton is post‐processed and high‐quality conductive copper layer is selectively electrochemically deposited on it. The antenna devices are found to demonstrate radiation performance, similar to that achievable with conventional fabrication approaches. However, additive manufacturing of RF antennas provides superior capabilities of constructing tailor‐made devices with properties, pre‐defined by non‐standardized end users.

The interaction between electromagnetic waves and objects is strongly affected by the shape and material composition of the latter. Artificially created materials, formed by a subwavelength structuring of their unit cells, namely metamaterials, can exhibit peculiar responses to electromagnetic radiation and provide additional powerful degrees of freedom to the scatterer design. In particular, negative material susceptibilities give rise to strong resonant interactions with deeply subwavelength particles. While the negative electrical permittivity of natural noble metals manifests itself in localized plasmon resonant oscillations, negative magnetic permeability materials are rare in nature. Here, the concept of artificial magnon resonance in subwavelength objects with effective negative permeability, designed via the metamaterial approach, is demonstrated. Strong localized oscillations of the magnetic fields within an array of split ring resonators, forming a sphere, hybridize in a collective mode of the structure. As a result, a high scattering cross section, exceeding that of a steel sphere with the same radius by four orders of magnitude, was demonstrated. Scatterers, based on tunable resonances within artificially created materials, can find use in a broad range of electromagnetic applications, including wireless communications, radars, RFID, internet of things hardware, and many others.

Suppression of backscattered electromagnetic waves by carefully designed structures is highly demanded in a range of applications, some of which are radar invisibility, antenna isolation, and many others. Salisbury screens, composed of a mirror with an additional layer on top, are traditionally used for these purposes. Here, we report on the design and experimental demonstration of a reciprocal screen, which demonstrates asymmetric reflection properties when illuminated from opposite directions. The structure utilizes near-field magneto-electric coupling between subwavelength split ring resonators and wires, forming a metasurface. While the reciprocal structure demonstrates perfect symmetry in transmission, strong backscattered asymmetry is shown to be controllable by carefully choosing the Ohmic losses, which are implemented with lumped resistors soldered into the resonators. Depending on the load, the meta-screen demonstrates switching properties that vary between fully symmetric and completely asymmetric reflection between the forward and backward directions of incident illumination. The frequency selective surface acts as a Huygens element when illuminated from one side and as a perfect mirror when illuminated from the other. The ability to tailor the asymmetric reflectance of electromagnetic metasurfaces by controlling Ohmic losses allows employing additional degrees of freedom in designing of radomes and other antenna devices. Furthermore, the concept could be extended to optical frequencies, where resistive losses can be controlled via direct carrier injection into semiconductor devices.

No abstract

No abstract