Читать книгу Introduction To Modern Planar Transmission Lines - Anand K. Verma - Страница 26

The above brief review omitted developments in the electromagnetic properties of the material medium. A few important developments could be summarized. In 1837, Faraday introduced the concept of the dielectric constant of a material. In 1838, he introduced the concept of electric polarization in dielectrics under the influence of the external electric field. Soon after the discovery of the electron in 1897 by J.J. Thomson, the models around electrons were developed to describe the electromagnetic properties of a material. Around 1898, John Gaston Leathem obtained an important relation , connecting the displacement of charges in a material with polarization. Kelvin, in the year 1850, developed the concept of magnetic permeability and susceptibility with separate concepts of , , and to characterize a magnetic material. In 1900, Drude developed the electrical conduction model, now known as the Drude model, after electron theory. Subsequently, the model was extended to the dielectric medium by Lorentz in 1905. The model called the Drude‐Lorentz model explains the dispersive property of dielectrics. In the year 1912, Debye developed the concept of dipole moment and obtained equations relating it to the dielectric constant. These models laid the foundation to study of the electric and magnetic properties of natural and engineered materials under the influence of external fields [B.4, B.6, B.7, B.12]