Mode (electromagnetism) explained

The mode of electromagnetic systems describes the field pattern of the propagating waves.^[1]

Some of the classifications of electromagnetic modes include;

• Modes in waveguides and transmission lines. These modes are analogous to the normal modes of vibration in mechanical systems.
  • Transverse modes, modes that have at least one of the electric field and magnetic field entirely in a transverse direction.
    • Transverse electromagnetic mode (TEM), as with a free space plane wave, both the electric field and magnetic field are entirely transverse.
    • Transverse electric (TE) modes, only the electric field is entirely transverse. Also notated as H modes to indicate there is a longitudinal magnetic component.
    • Transverse magnetic (TM) modes, only the magnetic field is entirely transverse. Also notated as E modes to indicate there is a longitudinal electric component.
  • Hybrid electromagnetic (HEM) modes, both the electric and magnetic fields have a component in the longitudinal direction. They can be analysed as a linear superposition of the corresponding TE and TM modes.
    • HE modes, hybrid modes in which the TE component dominates.
    • EH modes, hybrid modes in which the TM component dominates.
    • Longitudinal-section modes
      • Longitudinal-section electric (LSE) modes, hybrid modes in which the electric field in one of the transverse directions is zero
      • Longitudinal-section magnetic (LSM) modes, hybrid modes in which the magnetic field in one of the transverse directions is zero
  • The term eigenmode is used both as a synonym for mode^[2] and as the eigenfunctions in a eigenmode expansion analysis of waveguides.^[3]
    • Similarly natural modes arise in the singular expansion method of waveguide analysis and characteristic modes arise in characteristic mode analysis.^[3]
• Modes in other structures
  • Bloch modes, modes of Bloch waves; these occur in periodically repeating structures.

Mode names are sometimes prefixed with quasi-, meaning that the mode is not quite pure. For instance, quasi-TEM mode has a small component of longitudinal field.

Notes and References

1. Book: Jackson, John David . Classical electrodynamics . 1975 . Wiley . 978-0-471-43132-9 . 2d . New York.
2. Book: Rothwell . Edward J. . Electromagnetics . Cloud . Michael J. . 2001 . CRC Press . 978-0-8493-1397-4 . Electrical engineering textbook series . Boca Raton, Fla.
3. Huang . Shaode . Pan . Jin . Luo . Yuyue . 2018 . Study on the Relationships between Eigenmodes, Natural Modes, and Characteristic Modes of Perfectly Electric Conducting Bodies . International Journal of Antennas and Propagation . en . 2018 . 1–13 . 10.1155/2018/8735635 . free . 1687-5869. 10453/132538 . free .