Numerical simulations of gyromagnetic media

• Main Author: Lee, Shu Hui
• Other Authors: Chong Yidong
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2021
• Subjects: Science::Physics; Engineering::General
• Online Access: https://hdl.handle.net/10356/148393
• Institution: Nanyang Technological University

The theory and applications of magneto-optic media are discussed. The dispersion of electromagnetic waves through a gyromagnetic medium is simulated and compared with analytical solutions. A literature review on the role of inverse design methods in various fields, as well as on nonreciprocal microwave devices, is conducted in this study. While the adjoint method has been studied extensively as an effective tool for microwave applications, exploration has been scarce on the effectiveness of coupling both gyromagnetic and dielectric media with the adjoint method in designing a nonreciprocal device. In this report, gyromagnetic and dielectric media are both combined in inverse design simulations of a T-junction for the first time to investigate the efficacy of inverse design in producing nonreciprocal devices. Three different geometric permutations – a pure dielectric, a dielectric-gyromagnetic (in which the dielectric medium faces the input port), and a gyromagnetic-dielectric (where the gyromagnetic medium is in closer proximity to the input port) scatterer – are simulated and analyzed. Inverse design is conducted on the dielectric segments of these scatterers, composed of pixels with refractive indices 1.44 and 3, to maximize nonreciprocal transmission of the guided transverse electric (TE) mode through a planar T-junction via the adjoint solver in FDTD simulations. This design is achieved under the formulation of an objective function with user-tuned hyperparameters. Filtering with morphology operators is also used to improve the potential of final designs for future fabrication. The results indicate the potential for further exploration of the gyromagnetic-dielectric hybrid structures in nonreciprocal microwave applications.