Characteristic impedance is for AC signals (or high-frequency signals). Characteristic impedance is a concept in long-line transmission. During the process of signal transmission in the transmission line, at a point where the signal arrives, the transmission line and the reference plane will meet. An electric field is formed, and due to the existence of the electric field, an instantaneous small current is generated, and this small current exists at every point in the transmission line. At the same time, the signal also has a certain voltage, so that in the process of signal transmission, each point of the transmission line will be equivalent to a resistance, and this resistance is the characteristic impedance of the transmission line we mentioned.
The continuity of the characteristic impedance (ρ) basically depends on the stability of the ratio of the distribution parameters L{{0}} and C0. We all know Ohm's law: U=RI, where R is the resistance or resistance load, in ohms (Ω). Resistance is related to the resistivity (also known as conductivity) of metal materials, but in the process of high-frequency signal transmission, we also need to understand the transmission of the physical medium (such as twisted pair, coaxial wire, waveguide) that transmits high-frequency signals characteristics, which are different from low-frequency signals, this transmission characteristic is related to the conductive material of the transmission medium (such as copper or silver), conductivity (resistivity), geometry (most commonly cylindrical), distributed inductance (L0), distributed capacitance (C0), insulating material (dielectric constant), etc. are all related, but the influence of these distribution parameters and the dielectric constant of insulating material is often not considered during low-frequency signal transmission.
