From the electromagnetic viewpoint, the wide variety of non-magnetic materials can be entirely characterized by a physical quantity known as complex dielectric permittivity, in which the imaginary part is related to the electrical conductivity. The aim of this contribution is to present an experimental technique using standard measurement equipments commonly encountered in didactic laboratories, based on the time domain reflectometry, to measure the dielectric permittivity of materials in the RF spectrum, helping students to perceive the connection between theory and practice. First of all, the general theory of the complex dielectric permittivity is presented and typical dependence of the permittivity versus frequency are briefly discussed and illustrated. Next, we discuss the standard permittivity measurement technique based on the RC circuit, in which the capacitor is filled with the material medium to be characterized. Finally, the time domain reflectometry technique is presented in the context of permittivity determination, and for didactic purposes, water and the material known as FR-4, used in printed circuit boards, are experimentally characterized.
dielectric permittivity; time domain reflectometry; water
