Propagation Constant Measurements Research Articles

Propagation constant measurements of reflection-asymmetric and nonreciprocal microwave networks from S-parameters without using a reflective standard

Abstract We propose a simple method for determination of forward and backward propagation constants of nonreciprocal uniform networks or lines with asymmetric reflections. The wave cascading matrix presentation is used to diagonalize and decompose the line in terms of impedance and amplitude/phase transitions. The proposed method uses scattering parameters of the line/network connection and the thru connection, thus eliminating errors arising from fabrication tolerance and thickness of the second line. Besides, compared with conventional methods which necessitate calibration techniques such as the thru-reflect-line, our method has the advantage that it determines propagation constants without resorting the measurement of any reciprocal reflective standard. Propagation constant measurements of a reciprocal network (different-length X-band waveguide straights) and a nonreciprocal network (microwave phase shifter) were first carried out and then compared with those measured by different methods to validate and monitor the accuracy of our method.

Determining the Complex Permittivity of Building Dielectric Materials using a Propagation Constant Measurement

<p>This paper presents a technique to determine the Dielectric constant and dielectric loss of the building dielectric materials using propagation constant measurements. The material sample is loaded in an X-band (8.5GHz-12.5GHz) rectangular waveguide and its two port S-parameters are measured as a function of frequency using a Vector Network Analyzer without TRL Calibration. The results obtained from samples of dielectric materials (Air, Cellular concrete and Wood) on the X-band frequencies show the validity of the proposed technique to determine the complex permittivity of the building dielectric materials on the X-band frequencies<em>.</em></p>

A new formula for predicting the position of severe arterial stenosis

Noninvasive location of an occlusion or a severe stenosis in the arterial system is of a great interest for surgical interventions. Here, we present a new method to determine the location of arterial 99% stenosis in the arterial (sub) system. The method requires a measurement of propagation constant and the instantaneous flow rate or velocity at two sites of an arterial tree. The method was successfully tested using Womersley’s oscillatory flow theory and the data obtained by a simulation of Fluid structure interaction (FSI). The effect of noise has been investigated to simulate experimental conditions. The results demonstrate that location of 99% severe stenosis could be accurately obtained. The spatial resolution was approximately a few centimeters and the differences between exact and computed values didn’t exceed 13%. However, the identifications of stenotic sites decreased with the distance. Further investigation of the developed method in vivo and in vitro is required.

Acoustical properties of nanoporous activated carbon fibres

This work continues a series of studies on the link between the microstructure of multiscale materials and their acoustical properties [1]-[3]. Granular activated carbons are excellent low frequency sound absorbers. Two factors contribute to this. (i) They have three scales of heterogeneities: millimetric grains and micrometric and nanometric inner-grain pores. (ii) The presence of sorption in nanometric pores leads to a decrease of static bulk modulus and, consequently, of the effective low-frequency sound speed. Activated carbon felts also show promising low-frequency sound absorption but have simpler microstructure. They do not contain inner-fibre micrometric pores, but still have inner-fibre nanometric pores. This, combined with a relatively regular fibre arrangement, makes them ideal for studying the effect of sorption on their acoustical properties. In this work, parameters describing the microstructure and sorption kinetics are measured independently for several types of felts with different levels of activation. The predictions of a microstructure-based model [3] are compared with measurements of sound absorption, characteristic impedance and propagation constant. It is concluded that sound absorbers with controlled properties can be designed by varying the level of activation, fibre size and porosity.

Determining complex permittivity from propagation constant measurements with planar transmission lines

A new two-standard calibration procedure is outlined for determining the complex permittivity of materials from the propagation constant measured with planar transmission lines. Once calibrated, a closed-form expression for the material permittivity is obtained. The effects of radiation and conductor losses are accounted for in the calibration. The multiline technique, combined with a recently proposed planar transmission-line configuration, is used to determine the line propagation constant. An uncertainty analysis is presented for the proposed calibration procedure that includes the uncertainties associated with the multiline technique. This allows line dimensions and calibration standards to be selected that minimize the total measurement uncertainty. The use of air and distilled water as calibration standards gives relatively small measurement uncertainty. Permittivity measurement results for five liquids, covering a wide permittivity range, agree very closely with expected values from 0.5–5 GHz.

Accurate Complex Permittivity Inversion From Measurements of a Sample Partially Filling a Waveguide Aperture

In this paper, we propose a microwave method, which eliminates the necessity of precise knowledge of sample thickness for accurate permittivity determination of thin materials partially filling the waveguide aperture. The method utilizes propagation constant measurements at two different frequencies for this goal. To facilitate the proposed method for dispersive and nondispersive dielectric materials, we have employed a power series representation of the complex permittivity. We have validated the proposed method from permittivity measurements of prepared thin samples by different methods. We have also noted that the accuracy of the proposed method can be increased by the enhancements in the measurement accuracy of conventional methods, which require complete sample filling into the waveguide aperture.

A calibration-independent microwave method for position-insensitive and nonsingular dielectric measurements of solid materials

Calibration-independent microwave methods have successfully been used to determine the complex permittivity, ε, of dielectric materials by eliminating the necessity of the calibration before measurements. However, there are three main problems of these methods. These are: (a) they suffer from thickness uncertainty in the second sample for methods which utilize propagation constant measurements, (b) they require precise or exact shifting distance of the sample within its cell location (a waveguide or coaxial-line section) and (c) they may produce some singularity points in the measured ε. In this paper, we propose a new calibration- independent method which simultaneously eliminates all these drawbacks while extracting the nonsingular complex permittivity of solid materials. We use the uncalibrated scattering parameter measurements of the cell with the dielectric sample located arbitrarily and of extra cells attached to the same cell to achieve this goal. In addition, in the literature, there is a need for a technique which auto-monitors the accurateness of calibration-independent measurements, which are used for the extraction of electrical properties of materials. In this paper, we also propose a simple self-checking technique, which is independent of electrical properties and thickness of materials and the location of materials inside the measurement cell. Therefore, this technique gives information about the performance of measurements before extracting electrical properties of materials. We validate the proposed method by measurements of the ε of polyvinyl-chloride (PVC) and Plexiglas samples at X-band (8.2–12.4 GHz)

THICKNESS-INDEPENDENT COMPLEX PERMITTIVITY DETERMINATION OF PARTIALLY FILLED THIN DIELECTRIC MATERIALS INTO RECTANGULAR WAVEGUIDES

A microwave method has been proposed for accurate complex permittivity measurement of thin dielectric materials partially fllling the waveguide. The method employs propagation constant measurements at two locations of the sample inside its holder. It increases the accuracy of permittivity measurements of similar methods in the literature since it utilizes the measurements of the distances between the inner waveguide walls and sample lateral surfaces instead of directly measuring the sample thickness. It has been validated by comparing the measured complex permittivity of a thin Plexiglas sample by the proposed method with that of the method in the literature.

Simulation and measurement of effective propagation constant of cut-wire array

The wave propagation inside a periodic cut-wire array is investigated. The effective propagation constant is extracted from numerical simulation and measurement. Both the plasmonic cutoff behaviour and the cut-wire resonance are presented and analysed.

Calibration for time domain propagation constant measurements on power cables

A method has been developed for characterizing the wave propagation properties of medium voltage (MV) power cables. It delivers the complex propagation constant of lossy cable transmission lines as a function of frequency. The technique is based on time domain measurements and frequency domain analysis of short pulse propagation. Particular attention is paid to the calibration, as samples with arbitrary characteristic impedances can cause multiple reflections in the test setup. The influence of numerical artefacts is also investigated. The developed technique is demonstrated on MV crosslinked polyethylene (XLPE) cables. The results are verified by comparison with frequency domain measurements of the cable S-parameters.

Measurement of propagation constant in waveguides with wideband coherent terahertz spectroscopy

A quasi-optical technique for characterizing micromachined waveguides is demonstrated with wideband time-resolved terahertz spectroscopy. A transfer-function representation is adopted for the description of the relation between the signals in the input and output port of the waveguides. The time-domain responses were discretized, and the waveguide transfer function was obtained through a parametric approach in the z domain after describing the system with an autoregressive with exogenous input model. The a priori assumption of the number of modes propagating in the structure was inferred from comparisons of the theoretical with the measured characteristic impedance as well as with parsimony arguments. Measurements for a precision WR-8 waveguide-adjustable short as well as for G-band reduced-height micromachined waveguides are presented.

Permittivity characterization of low-k thin films from transmission-line measurements

Developed a broad-band technique for measuring the relative permittivity of low-k thin films using microstrip transmission-line measurements. From measurements of the complex microstrip propagation constant and the characteristic impedance, we determined the relative permittivity of thin films incorporated in microstrip lines. We present measurement results to 40 GHz for both an oxide and a bisbenzocyclobutene low-k thin film and show a variability of permittivity of approximately /spl plusmn/5% over the entire frequency range.

Characterisation and modelling of coplanar transmission lines on SiC substrates

The paper investigates the characteristics of microwave transmission in coplanar waveguides (CPWs) fabricated on various silicon carbide substrates. Propagation constant and characteristic impedance measurements were performed at frequencies from 0.1 to 10 GHz. Different propagation modes are observed as a function of frequency and substrate resistivity. In the case of the low-loss structure, a quasi-TEM equivalent circuit model was developed from the available process parameters, taking into account the effects of electromagnetic fields in CPW structures.

Anisotropic permittivity and attenuation extraction from propagation constant measurements using an anisotropic full-wave Green's function solver for coplanar ferroelectric thin-film devices

In this paper, a full-wave spectral-domain integral-equation technique is used to study double substrate layer coplanar devices with the ferroelectric thin film adjacent to the conductor guiding interfacial surface. The Green's function is used in the anisotropic situation for anisotropic permittivities. In examining specific laboratory data, going from an unbiased static electric field to the biased case, the permittivity tensor is allowed to go from a unity tensor to a uniaxial one. Consistent with this permittivity tensor behavior, the attenuation trend with frequency and its amplitude is also found.

Complex permittivity determination from propagation constant measurements

The authors present a new transmission line method for measuring the complex permittivity of dielectric materials using propagation constant measurements. In contrast to previous methods, a network analyzer calibration is unnecessary since calibrated scattering parameters are not required. They use measurements in X-band waveguide to show that this technique compares well with the transmission/reflection and cylindrical cavity methods.

Characterization of broad-band transmission for coplanar waveguides on CMOS silicon substrates

This paper presents characteristics of microwave transmission in coplanar waveguides (CPW's) on silicon (Si) substrates fabricated through commercial CMOS foundries. Due to the CMOS fabrication, the metal strips of the CPW are encapsulated in thin films of Si dioxide. Many test sets were fabricated with different line dimensions, all on p-type substrates with resistivities in the range from 0.4 /spl Omega//spl middot/cm to 12.5 /spl Omega//spl middot/cm. Propagation constant and characteristic impedance measurements were performed at frequencies from 0.1 to 40 GHz, using a vector-network analyzer and the through-reflect-line (TRL) deembedding technique. A quasi-TEM equivalent circuit model was developed from the available process parameters, which accounts for the effects of the electromagnetic fields in the CPW structure over a broad frequency range. The analysis was based on the conformal mapping of the CPW multilayer dielectric cross section to obtain accurate circuit representation for the effects of the transverse fields.

Direct measurement of propagation constant in optical waveguides by heterodyne scattering detection (HSD) method

A new measurement method for the propagation constant of optical waveguides, which can measure the phase difference of two distant points nondestructively, was proposed and demonstrated. A super-fine fiber probe for the photon STM is used to pick up the scattered light from an optical waveguide, and the collected light is detected using a heterodyne technique. The phase difference between two points is measured from the phase change of the electrical signal of heterodyne detection as the fiber probe traces the waveguide pattern. The phase difference between 100 /spl mu/m distant points in a three-dimensional ARROW was successfully measured and the error was evaluated to be 0.25% by comparison with the theoretical value.

Impulse measurements of impedance and propagation constant compared to rigid-frame and dual-wave predictions for foam

Acoustic impulse techniques are used to obtain measurements of propagation constant in three different foams and to determine both the characteristic impedance and the normal impedance at the surface of a hard-backed layer over the frequency range from 200 Hz to 10 kHz. A comparison is made of existing rigid-frame and dual-wave models of sound propagation in porous media, and predictions from both models are compared with experimental measurements. Both models give good agreement with the lower flow resistivity foam measurements, however, the dual-wave model better predicts the overall results for a foam with a flow resistivity of 25100 N s m−4, implying the need of the slow wave mode. The position of the maxima in the layer impedance results are particularly sensitive to the correct choice of tortuosity. An emphasis is placed on how the two models compare as the frame material becomes rigid and these ideas are used to consider the implication of a previous claim about the existence of a slow wave in foams.

Impedance and complex propagation constant measurements at W-band on planar circuits

The voltage standing wave on a coplanar waveguide (CPW) is measured at W-band (75–110 GHz) using an array of bismuth microbolometers placed over the CPW. From this information, the impedance at the end of the line can be determined in addition to the complex propagation constant of the CPW. This measurement technique should also be applicable for other planar transmission lines and be extendable above 110 GHz. This work represents the highest frequency, direct measurement of a VSW on a CPW made to date.

Measurement of the characteristic impedance and propagation constant of materials having high flow resistivity

A technique for the measurement of characteristic acoustical impedance and propagation constant of porous materials is presented. Samples are mounted in an impedance tube and both the surface impedance and a transfer function along the sample length are determined; characteristic impedance and propagation constant may be calculated using these quantities. For this implementation, a classical standing wave procedure is used for the determination of surface impedance. Measurements are obtained for frequencies between 100 and 4000 Hz. A special procedure that makes use of extension tubes, between sample and the fixed part of the impedance tube, is used to achieve the low-frequency results. The new technique yields results that are comparable in accuracy to the ‘‘two-cavity’’ technique described by Utsuno et al. [J. Acoust. Soc. Am. 86, 637–643 (1989)] for samples of low flow resistivity (17.2 and 43.6 cgs-rayl cm−1 ), but substantially better for a sample of higher flow resistivity (380 cgs-rayl cm−1 ).