With regard to electrical characteristic of a cable, necessary parameter changes at low frequency and high frequency.
When it is looked at from cable side,
Cable Length / Transmitted Electromagnetic Wavelength << 1: Low Freuquency Cable Length / Transmitted Electromagnetic Wavelength >> 1: High FreuquencyNever forget this, as it is not determined by extent of frequency. In case signal waveform is other than sine wave, it is compared with the highest frequency component (spectrum) wavelength.
Wavelength of electromagnetic wave is given by following equation.
λ = Vp / f hereby, λ = wavelength of electromagnetic wave (m) Vp = phase velocity of electromagnetic wave (m/s) f = frequency of electromagnetic wave (Hz)Phase velocity of high frequency is calculated by following equation.
Vp = c * Vr hereby, c = light velocity in vacuum (299,792,458 m/s) Vr = velocity ratio of cable (0 < Vr <= 1) = 1 / sqrt(εs) εs = (equivalent) relative permittivity of cable dielectric (1 <= εs)Relative permittivity of polyethylene is about 2.3, therefore velocity ratio of polyethylene insulated coaxial cable at high frequency is about 0.66. Velocity ratio at low frequency range becomes smaller than that at high frequency range.
Electrical characteristic at low frequency is called primary parameters in transmission line theory and that at high frequency is called secondary parameters.
As far as energy transmission is concerned, above characteristic factors are enough, however, there are cases that the following characteristic must be considered depending on applications.
Shielding effectiveness involves all of different physical mechanism countermeasure against Conductive Coupling (Common Impedance Coupling), Electromagnetic Coupling (Mutual Inductance Couplig), Capacitive Coupling (Mutual Capacitance Coupling) and Electromagnetic Wave Coupling (Radiation Field Coupling), therefore special care is required. Namely, this word itself is obscure.