Time Domain Reflectometry Waveforms Research Articles

Frequency domain analysis of time domain reflectometry waveforms: 2. A four‐component complex dielectric mixing model for soils

Although time domain reflectometry (TDR) is becoming accepted as an important tool for the measurement of soil water content and bulk soil electrical conductivity, a major part of the method is based on empirical relationships. An improved understanding of dielectric measurements on soils may give more insight into soil properties other than soil water content and bulk soil electrical conductivity. Frequency domain analysis of TDR waveforms enables the measurement of the frequency dependent complex dielectric permittivity of soils. The frequency dependent complex dielectric permittivity of soils can be described with a four‐component complex dielectric mixing model based on the volumetric mixing of the refractive indices of the soil components. The four soil components in the model are air, solids, bound water, and free water. Results indicate that the apparent dielectric permittivity obtained from the travel time of the TDR pulse in the soil is the dielectric permittivity at the highest measurement frequency of the cable tester, probe, and soil system. The model based on the volumetric mixing of real permittivities underestimates the measurements in situations with high values of the imaginary part of the dielectric permittivity. Because the model based on the mixing of the complex dielectric permittivities can describe the data, we conclude that the apparent dielectric permittivity is influenced by the imaginary parts in the dielectric, permittivities of the soil components. Combination of the four‐component complex dielectric mixing model with the complex dielectric permittivity obtained from the frequency domain analysis of TDR waveforms gives a tool for modeling the bulk soil electrical conductivity by separating the conductivity of the soil water into a bound water conductivity and a free water conductivity.

An enhanced time-domain approach for dielectric characterization using stripline geometry

A time-domain approach for dielectric characterization using a stripline geometry is presented. The technique uses both time domain reflectometry (TDR) and time domain transmission (TDT) measurements for determining an optimum frequency-dependent lossy transmission line model for the stripline under test. The optimization is done in the time domain by comparing the experimental TDR and TDT response waveforms with the simulated ones using a nonlinear least squares fit. The material properties such as the complex permittivity of the dielectric material are determined from the optimum lossy transmission line model. The authors present both simulated and experimental results.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A thick-film coplanar probe for time domain measurements

The design, fabrication, and characterization of coplanar probes are presented. The probes are designed to work as launchers/adapters for performing wideband microwave measurements on planar geometry lines. The probes are made in the form of tapered coplanar lines, fabricated on alumina, teflon, and teflon-ceramic composite substrates. The time-domain reflectometry (TDR) technique was used to characterize the probes. Equivalent networks for the probes are developed using the modified transient circuit analysis program (MTCAP) by fitting a simulated TDR response to the measured TDR waveform and using a circuit simulation program (e.g. SPICE) to analyze the obtained equivalent network. The equivalent network of the probe thus obtained can then be used to de-embed the probe's contribution to a wideband microwave measurement, and thereby reducing measurement errors. >

Wide-band characterization of multilayer thick film structures using a time-domain technique

A technique for modeling multilayer thick-film structures using time-domain measurements is presented. A multilayer inductor, formed by stacking spiral coils vertically with intervening dielectric layers, is used to demonstrate the technique. The component under test is placed at the end of a reference line, and a time-domain reflectometry (TDR) waveform is acquired. This TDR waveform is used to develop an equivalent network for the multilayer thick-film structure. The equivalent network model is then analyzed using conventional circuit analysis techniques to characterize the various electrical parameters (or properties) of the structure. >

Conductivity limitations in single-reflection time-domain reflectometry

Numerical modelling of single-reflection time-domain reflectometry (TDR) is presented to demonstrate the limitations imposed by finite conductivity values upon recovering dielectric permittivity from the TDR reflected waveform. The results show conductivity to cause false dispersions resulting from the incomplete decay of the TDR waveform. The results are applicable to polar liquids and wet soils and suggest that conductivity should be less than about 0.01 S m-1 when relaxation frequencies exist above about 1 GHz.