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Fig. 1. (a) The multisection transmission line model of the time domain reflectometry (TDR) measurement system, in which each uniform section is characterized by the geometric impedance (Zp), resistance loss factor (
R), complex dielectric permittivity (
r*), and waveguide length (L). The transmission line is driven by a source voltage (Vs) with a source impedance (Zs) and terminated in a load (ZL). The input impedance (Zin) is defined as the ratio of line voltage (V) to the line current (I). (b) The associated direct current circuit model, in which Rs is the inner resistance (equal to the source impedance Zs), Rcable is the cable resistance, R is sample resistance, vs is the source voltage (in time domain), and v
is the TDR steady-state voltage. (c) A typical TDR waveform showing definition of reflection coefficient (
), where t0 is the roundtrip travel time in the probe section, and tcable is the roundtrip travel time in the cable section.
