Dielectric Material Parameters Research Articles

Research on distribution of leaf water by terahertz spectrum

The influence of varied water distribution in different locations of the mesophyll and mid-vein of the same leaf on the absorption and refraction coefficient is described. And the further comparisons between green leaf and yellow leaf reveal that the complex permittivity of leaf can provide important information about the water content and can characterize the changes of the water distribution of the leaf. So our measurements tend to demonstrate that the dielectric material parameters will be employed to determine the leaf water status in plant leaves.

Traps and trapping phenomena and their implications on electrical behavior of high-k capacitor stacks

The traps and trapping phenomena and their implications on leakage currents, conduction mechanisms, and stress-induced leakage current in high-k dielectrics have been investigated. Various dielectrics (mostly multicomponent materials) have been studied to demonstrate the large diversity of phenomena that govern the electrical behavior of the structures depending on dielectric material, trap and stack parameters, and measurement conditions. The effects common for the most of high-k dielectrics and those typical for each individual structure have been discussed. The singly positively charged oxygen vacancy has been elucidated as the main electron transport site in the high-k materials. The role of the pre-existing traps for the electrical degradation of high-k stacks has been evidenced.

Calibration of a UWB Sub-Band Channel Model Using Simulated Annealing

This communication presents a calibration method of an indoor UWB sub-band deterministic channel model by means of simulated annealing. Based on the characterization of the channel at sub-bands with a subset of measurement locations, the calibration optimizes the dielectric material parameters of the environment, which improves the accuracy of the model in terms of path loss (L) and time dispersion parameters (root mean square delay spread sigma <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">tau</sub> and maximum excess delay tau <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> ) at all test locations within the test area. The performance of the calibration has been assessed by two indoor measurement campaigns, including line of sight (LOS) office and corridor and non line of sight (NLOS) corridor-office at the Antenna, Propagation and Networking Section building at Aalborg University and at the building of the Institut fur Nachrichtentechnik at Braunschweig Technical University. A reasonable performance of the calibration is noticed in improving the model accuracy within the building, requiring a few pilot measurements.

Evaluation of leaf water status by means of permittivity at terahertz frequencies

We present an electromagnetic model of plant leaves which describes their permittivity at terahertz frequencies. The complex permittivity is investigated as a function of the water content of the leaf. Our measurements on coffee leaves (Coffea arabica L.) demonstrate that the dielectric material parameters can be employed to determine the leaf water status and, therefore, to monitor drought stress in plant leaves. The electromagnetic model consists of an effective medium theory, which is implemented by a third order extension of the Landau, Lifshitz, Looyenga model. The influence of scattering becomes important at higher frequencies and is modeled by a Rayleigh roughness factor.

Millimeter-Wave Transmittance Measurements on Ferrites Near Ferromagnetic Resonance

This paper presents complex dielectric permittivity and magnetic permeability measurements of pure and diluted barium ferrites in the millimeter-wave frequency range. A broadband quasi-optical millimeter-wave spectroscopy with backward-wave oscillators as high-power tunable sources of coherent radiation has been utilized. The real and imaginary parts of the dielectric permittivity and magnetic permeability as functions of frequency are computed from the transmittance spectra. A magneto-optical approach in millimeter waves has been successfully employed for the separation of the dielectric and magnetic effects and the simultaneous determination of the magnetic and dielectric parameters of barium ferrite materials near ferromagnetic resonance.

Automatic Multimode Measurement for Microwave Ceramics

Automatic measurement system with multimode for microwave ceramic materials is developed. Based on traditional parallel-plate resonance method, the whole system is composed of a parallel-plate cavity, a vector network analyzer (VNA), an interface card for GPIB to USB, and a PC with measurement programs. Besides the fundamental mode, higher order resonant modes are also measured at the same time. Based on a platform of VEE, a set of analysis software is programmed with the functions of not only automatically calibrating and searching resonant frequencies but also automatically computing and displaying the dielectric parameters of microwave materials with high reliability and efficiency in a wide frequency range.

A versatile measurement system for the determination of dielectric parameters of various materials

In this paper, a versatile method for the determination of the complex permittivity of materials from measured scattering parameters is presented. The measurement set-up consists of a waveguide applicator for housing the material sample. The considered frequency range is 2–3 GHz. The complex scattering parameters are measured by a vector network analyser. The algorithm for computing the complex permittivity from the measured scattering parameters is shown in detail and an error estimation is performed. Depending on the waveguide layout liquid, granular and solid materials can be measured. To measure granular and liquid samples two dielectric walls inside the waveguide are used to house the samples. The dielectric parameters of different soils as well as of some liquids are determined with consideration of their moisture content and temperature. In contrast to several other techniques, this measurement set-up is also suited for high loss materials. The set-up has also been successfully used for measurements of anisotropic materials.

Calibration methods for microwave free space measurements

Abstract. In this article calibration methods for the precise, contact-less measurement of the permittivity, permeability or humidity of materials are presented. The free space measurement system principally consists of a pair of focusing horn-lens antennas connected to the ports of a vector network analyzer. Based on the measured scattering parameters, the dielectric material parameters are calculable. Due to systematic errors as e.g. transmission losses of the cables or mismatches of the antennas, a calibration of the measurement setup is necessary. For this purpose calibration methods with calibration standards of equal mechanical lengths are presented. They have the advantage, that the measurement setup can be kept in a fixed position, for example no displacement of the antennas is needed. The presented self-calibration methods have in common that the calibration structures consist of a so-called obstacle network which can be partly unknown. The obstacle can either be realized as a transmissive or a reflective network depending on the chosen method. An increase of the frequency bandwidth is achievable with the reflective realization. The theory of the calibration methods and some experimental results will be presented.

Implementing Profile Permittivity Reconstruction Technique for Dielectric Tube in a Rectangular Waveguide

In this article a new approach for accurate prediction of scattering parameters of lossy dielectric materials is suggested. It is based on reconstructing complex permittivity profile of the test cell placed within rectangular waveguide and numerical determination of proper scattering parameters using algorithm Kao or its modification. Both propagating and evanescent modes excited in the test cell consisting of the dielectric tube filled with lossy materials are investigated to validate resonance and non-resonance phenomena. Comparison with earlier reported results shows a good agreement. The advantage of this method is the simplicity of its realization and accuracy in prediction of scattering parameters measured in practice.

A simple apparatus for complex measurements of piezoelectric and ferroelectric materials

Abstract A relatively simple universal apparatus consisting of standard instruments for the measurement of elastic, piezoelectric and dielectric material parameters was realized. The accuracy is satisfactory for practical use and the frequency range is from DC to about 10 kHz. The measurements can be fully automated and results processed by modern computer methods.

Investigation of Permittivity Dispersion in the Infralow-Frequency Band by Time-Domain Dielectric Spectroscopy

The transient-current method of time-domain dielectric spectroscopy, used to investigate the dispersion of the dielectric parameters of materials in the 10–4–1 Hz frequency band, and apparatus based on it, are considered. A program is developed for the mathematical processing of the results of an experiment using the numerical Fourier transformation method employing cubic splines for approximation, interpolation and extrapolation of data. The frequency spectra of Δe' and Δe'' of certain solid materials are presented.

Fluid dielectrics measurement technique using a waveguide slot bridge

An experimental method is suggested that supposes the study of characteristics of slot bridge (SB) cells in the multimode operating regime. It is based on the preliminary numerical investigation of the resonant scattering characteristics of SB, i.e., the solution of the boundary value problem (BVP). The configuration of an experimental SB cell is computed according to the required frequency band and preliminary information about dielectric parameters of the materials chosen for tests. Etalon scattering characteristics of an SB cell are computed by software development on the basis of a rigorous solution of the BVP, providing numerical data with required accuracy. ©1999 John Wiley & Sons, Inc. Microwave Opt Technol Lett 21: 455–458, 1999.

Coaxial Waveguide Slot Bridge Cell for Liquid Substances Study

The experimental method suggested suppose the studying of energy characteristics of slot bridge (SB) cells in the multi mode operating regime based on the preliminary numerical investigation of scattering resonant characteristics of SB (solution of boundary value problem and investigation of eigen frequencies and relevant field modes). The configuration of experimental model of SB cell is computed accordingly to required frequency band and preliminary information about dielectric parameters of materials chosen for tests. Ethanol scattering characteristics of SB cell are computed by software, developed on the base of rigorous solution of the boundary value problem, providing numerical data with any required accuracy.

Time domain dielectric spectroscopy: An advanced measuring system

The new time domain measurement system for dielectric measurements is described. The current model is comprised of an IBM PC-AT/486, ‘‘TDM-2,’’ a new time domain measurement system, a set of thermostabilized sample holders, and operation and analysis software. This system is designed for use in the measurement of dielectric parameters of liquid and solid materials over the frequency range 100 kHz–10 GHz. Software consists of programs of registration, accumulation and data collection, Fourier analysis, time domain treatment, analysis software: fast and reliable nonlinear curve fitting programs to determine spectroscopic parameters and correlation analysis in time domain. The system utilizes the difference method of measurement with the registration of primary signals with multiwindow nonuniform sampling. Such a system permits the overlap of a frequency range of five orders in a single measurement.

Determination of electrodynamical parameters of dielectric pipe-shaped materials using millimeter wave cavity

Employment ofE0np modes of cylindrical cavity resonator for measurement of electrodynamical parameters of dielectric pipe-shaped materials in millimeter wavelength band is suggested. Dielectric permittivity ɛ and conductivity σ of a sample can be found by measuring the frequency shift and theQ-factor change of the resonator.

Measurement of dielectric parameters of wall materialsat 60 GHz band

A method for determining the dielectric parameters of light internal wall materials at millimetre-wave frequencies is presented. The method is based on transmission coefficient measurement of a wall sample consisting of two slabs, the distance of which is variable. The dielectric parameters of the slabs can be determined by finding the parameter values which yield the minimum difference between measured and calculated transmission coefficient values. The results for plasterboard and chipboard walls are in line with the results given previously in the literature.

Measuring the permittivity and permeability of a sample at K/sub /spl alpha// band using a partially filled waveguide

A novel method of measuring the relative complex permittivity (/spl epsi/=/spl epsi/'-j/spl epsi/'') and relative complex permeability (/spl mu/=/spl mu/'-j/spl mu/'') of a material at K/sub /spl alpha// Band (26.5-40 GHz) using a partially filled waveguide (PFW) (rectangular) and a vector network analyzer (VNA) is presented. The method is based on 1) placing a material sample of length L/spl tilde/, width /spl alpha//spl tilde/ (waveguide width), and height d/spl tilde//spl les/b/spl tilde/ (b/spl tilde/ is the waveguide height) in a rectangular waveguide, 2) measuring the S-parameters of the sample using the VNA, and 3) inferring the /spl epsi/', /spl epsi/'', /spl mu/', and /spl mu/'' parameters by comparing the experimental S-parameters with numerically generated S-parameters. The paper presents a method of moments analysis and also a variational formulation of the scattering that occurs from a finite length sample that partially fills a waveguide. Formulas to calculate the complex Poynting power and energy in the waveguide are derived to check the degree to which the numerical solutions obey the conservation of complex power. Numerical methods to extract the material parameters from the S-parameter data are proposed. The experimental PFW S-parameters of a radar absorbing material are measured and its dielectric material parameters are inferred.

Dielectric materials for gyrotron output windows

The dielectric parameters of materials for gyrotron output windows measured in the range 65–300 GHz are given. The special attention is paid to the spread of values of the refractive index and loss tangent of dielectrics produced by different firms. The refractive index and loss tangent are measured for sapphire at the cryogenic temperatures and for boron nitride and silica glass at the temperatures 300–1000K.

A method of moments solution of a cylindrical cavity placed between two coaxial transmission lines

The author presents a method for analyzing a dielectric-filled cylindrical cavity separating two coaxial transmission lines. The analysis is based on the method of moments and the equivalence principle taking into account higher order modes excited at the junctions between the cavity and the two transmission lines. Expressions relating the cavity's scattering parameters to the structure dimensions and the dielectric parameters are derived and implemented numerically. Numerical simulation results as well as experimental results are presented. The method was also applied to the measurement of the dielectric parameters of certain dielectric materials. >

An accurate measurement technique for line properties, junction effects, and dielectric and magnetic material parameters

Transmission/reflection coefficients of unknown transmission lines are analyzed. The characteristic impedance, the propagation constant, and the parameters of the junctions at the connections with the measurement setup can be calculated if the coefficients of three different lengths of the line being investigated are measured. Therefore it is called the L/sup 3/ method (line/line/line). Transmission data suffice for the determination of only the propagation constant. They are used in the case of material parameter measurements with loaded lines. Dielectric and magnetic properties of the filling material are calculated using the set of transverse resonance equations.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>