Measuring Spectral Dielectric Properties Using Gated Time Domain Transmission Measurements

A method to measure the frequency‐dependent dielectric permittivity of simple materials based on a time domain transmission technique is described. A vector network analyzer (VNA) was connected to a twin‐rod transmission line via a coaxial cable. The complex dielectric permittivity was found from the difference in phase and magnitude between a reference line surrounded by air and the same line surrounded by the substance of interest. The spectral response showed periodic variations in the dielectric permittivity as a result of multiple reflections in the experimental setup. These multiple reflections can be removed by using a time domain gate that selects only the primary transmission and filters out any subsequent reflections. It is essential that the apparatus be designed so that the first reflection is well separated from the primary transmission. This requires a long transmission line and a long coaxial cable. However, if the transmission line is too long, excessive conductive or dielectric losses make it hard to detect the primary transmission. The application of the gated time domain transmission technique to measure the frequency‐dependent dielectric permittivity of water, ethanol, sand and saturated sand is demonstrated. This method does not have the typical limitations on sample volume. In addition, it does not require the assumptions necessary in previous time domain spectroscopy methods applied to open transmission lines where a probe model is used in conjunction with simple Debye relaxation and/or inverse methods.

[1]  Yuri Feldman,et al.  Non-Debye dielectric relaxation in complex materials , 2002 .

[2]  W. J. Shuttleworth,et al.  Application of a plane-stratified emission model to predict the effects of vegetation in passive microwave radiometry , 2002 .

[3]  William James Shuttleworth,et al.  Influence of vegetation on SMOS mission retrievals , 2002 .

[4]  Qu,et al.  Multifractal phase transitions in the non-debye relaxation processes , 2000, Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics.

[5]  G. C. Topp,et al.  Impacts of the Real and Imaginary Components of Relative Permittivity on Time Domain Reflectometry Measurements in Soils , 2000 .

[6]  R. Mcfarlane,et al.  The effect of soil electrical conductivity on moisture determination using time-domain reflectometry in sandy soil , 2000 .

[7]  Dani Or,et al.  Frequency analysis of time-domain reflectometry (TDR) with application to dielectric spectroscopy of soil constituents , 1999 .

[8]  F. Francisca,et al.  Impedance Analysis of Soil Dielectric Dispersion (1 MHz–1 GHz) , 1999 .

[9]  D. Or,et al.  Temperature effects on soil bulk dielectric permittivity measured by time domain reflectometry: Experimental evidence and hypothesis development , 1999 .

[10]  D. Or,et al.  Temperature effects on soil bulk dielectric permittivity measured by time domain reflectometry: A physical model , 1999 .

[11]  Takaaki Sato,et al.  Dynamical aspects of mixing schemes in ethanol-water mixtures in terms of the excess partial molar activation free energy, enthalpy, and entropy of the dielectric relaxation process , 1999 .

[12]  K.R. Demarest,et al.  Engineering Electromagnetics , 1997, IEEE Electrical Insulation Magazine.

[13]  T. J. Heimovaara,et al.  Frequency dependent dielectric permittivity 0 to 1 Ghz: Time Domain Reflectometry measurements compared with Frequency Domain Network Analyser measurements , 1996 .

[14]  Timo J. Heimovaara,et al.  Dielectric spectroscopy by inverse modelling of time domain reflectometry wave forms. , 1996 .

[15]  Christian Mätzler,et al.  Microwave permittivity of dry sand , 1996, IEEE Trans. Geosci. Remote. Sens..

[16]  Fawwaz T. Ulaby,et al.  Dielectric properties of soils in the 0.3-1.3-GHz range , 1995, IEEE Trans. Geosci. Remote. Sens..

[17]  Timo J. Heimovaara,et al.  Frequency domain analysis of time domain reflectometry waveforms: 1. Measurement of the complex dielectric permittivity of soils , 1994 .

[18]  T. Heimovaara.  Design of Triple‐Wire Time Domain Reflectometry Probes in Practice and Theory , 1993 .

[19]  Emmanuel Ifeachor,et al.  Digital Signal Processing: A Practical Approach , 1993 .

[20]  B. Colpitts.  Temperature sensitivity of coaxial probe complex permittivity measurements: experimental approach , 1993 .

[21]  S. Zegelin,et al.  Improved field probes for soil water content and electrical conductivity measurement using time domain reflectometry , 1989 .

[22]  Fawwaz Ulaby,et al.  Microwave Dielectric Spectrum of Vegetation-Part I: Experimental Observations , 1987, IEEE Transactions on Geoscience and Remote Sensing.

[23]  Richard K. Moore,et al.  Microwave Remote Sensing, Active and Passive , 1982 .

[24]  S. Druchinin.  Applicability of mixture formulas for describing the permittivity of media with a high content of inclusions , 2000 .

[25]  V. Tikhonov,et al.  Taking into account dielectric properties of bonded water in modeling the effective permittivity of moist soils in the microwave frequency band , 1998 .