Mixed-Signal, RF & Microwave Seminar
Surface Waves, Line Waves, and Chiral Modes for One-Directional Propagation in Electromagnetic and Acoustic Systems
We will discuss propagation of surface waves on electromagnetic metasurfaces, including the recently developed concept known as "line waves" which are the one-dimensional analog of surface waves, confined to the interface between two complementary two-dimensional impedance surfaces. They support one-way propagation of two orthogonal modes, and they do not require any external magnetic field. They link time inversion to spatial inversion, thus forming a kind of chiral mode, and they have the unique property of a field singularity at the interface, which is not present in higher dimensional interface modes. We will then examine the relationship between photonic topological insulators and chiral modes. These new material systems promise one-way propagation without scattering due to unique band structure properties. In electromagnetic systems, this sometimes requires classical time reversal symmetry breaking features, such as magnetic materials or time modulation. However, static and nonmagnetic photonic topological insulators have been demonstrated by taking advantage of certain geometrical tricks. These materials and methods for evaluating them will be illustrated through several examples. Analogous mechanical structures can be useful for acoustic isolation. By extending the concept to phononic systems using anisotropic materials, one-way thermal transport may be possible.