Radiofrequency waves in magnetic and anisotropic media - Non reciprocal four ports networks

The study of radio waves in anisotropic magnetic media calls on a number of scientific themes, including..:

• microscopic properties of matter ;

• propagation phenomena ;

• microwave electronic component technologies.

As the article is primarily intended for didactic purposes, the text will focus on propagation. Nonetheless, the other fields will be mentioned without providing the detailed explanations that the reader will find in the references cited at the end of the text under the heading "Learn more".

The article is divided into two distinct sections.

The first section, mainly devoted to the properties of the plane wave animated by continuous oscillations, will first recall some important theoretical bases.

With this in mind, we introduce the concepts of rectilinear field polarization and the wave number vector associated with the complex representation of sinusoidal signals.

The description then turns to circularly polarized fields. These developments may seem lengthy, but they were nevertheless useful in avoiding certain confusions linked to the simultaneous use of vector representations and the algebraic treatment of complex quantities.

After a brief overview of ferrite magnetization processes, the text will discuss the anisotropic properties of this material exposed to the combined effects of a large-amplitude static magnetic field and a dynamic field carried by a small-amplitude radio wave.

These properties are embodied in the concept of the permeability tensor and the matrix wave equation used to study plane waves.

Solving the wave equation will show that there are strong links between circularly polarized fields and non-reciprocal propagation governed by the gyromagnetic pulsation of the medium. Numerical simulations and the analogy with the Faraday and Cotton Mouton effects observed in optics will highlight these highly instructive physical phenomena for future applications.

The second section will focus on the realization of non-reciprocal quadrupoles. Reference will be made here to the properties of transmission lines or waveguides.

The concept of memductance will enable us to adapt line theory to introduce non-reciprocal propagation phenomena acting independently on the progressive wave and the retrograde wave.

The analysis will lead to the description of some processes combining the properties of quasi-TEM and TE waves coupled with a ferrite blade immersed in guided structures.

The...