Design, simulation, and measurement of near-zero-index shells for electromagnetic beam generation

Abstract

We present design and simulation of three-dimensional (3D) shell structures, which generate directional radiation patterns from isotropic sources thanks to their near-zero-index (NZI) characteristics, as well as realizations of these shells via low-cost 3D printing. Throughout the design process of NZI beam generators, both homogenized structures, for which near-zero relative permittivity and/or permeability values are enforced, and actual models involving periodic arrangements of dielectric rods are considered. Solutions of the electromagnetic problems are obtained by using rigorous implementations of the state-of-the-art surface-integral-equation (SIE) formulations in frequency domain. Iterative solutions of matrix equations derived from SIEs are accelerated by different forms of the multilevel fast multipole algorithm (MLFMA) and suitable preconditioners, when necessary. In the design process of NZI shells, alternative strategies are employed to obtain customized radiation patterns. In this context, various cavities with strong resonance behaviors are designed as source regions. At the same time, outer surfaces are modified to either enhance or suppress outgoing electromagnetic fields. In addition to comprehensive simulations and analyses of NZI beam generators, their capabilities are verified by measurements, specifically at 10.3 GHz, on different prototypes fabricated via 3D printing. Measurements of diverse NZI shell structures are presented to demonstrate that NZI properties can successfully be achieved by well-designed arrangements of dielectric rods with proper materials. The results demonstrate the feasibility of efficient, effective, low-cost, and reconfigurable NZI shells to generate alternative beam configurations that can be useful in a plethora of microwave applications.

Keywords:

• Zero-index materials
• beam generators
• metamaterials
• multilevel fast multipole algorithm
• 3D printing
• microwave applications

Acknowledgments

The authors would like to thank Prof. Dr. Özlem Aydın Çivi for her invaluable suggestions on the characterization and measurement stages of this study.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported in part by the Scientific and Technical Research Council of Turkey (TUBITAK) (Türkiye Bilimsel ve Teknolojik Araştirma Kurumu) [research grant number 118E243] and in part by the Turkish Academy of Sciences (TUBA) in the framework of the YSA Program. Ö. Eriş was also supported by Türk Telekom within the framework of 5G and Beyond Joint Graduate Support Programme coordinated by Information and Communication Technologies Authority.