Dielectric constant measurement technique for a dielectric strip using a rectangular waveguide

A dielectric constant measurement technique for dielectric strips is presented in this paper. In the measurement, the strip is placed parallel to the broad walls of a rectangular waveguide, and it is found that the measured reflection coefficient is insensitive to the position of the strip when it is placed around the middle of the waveguide cross section. The new sample placement scheme becomes very convenient, especially when a large number of strips have to be measured. To develop the forward scattering formulation, the reflection coefficient of the strip placed in the waveguide is evaluated using the method of moments. With this forward model, a genetic algorithm is developed to retrieve the dielectric constant of the strip from the measured reflection coefficient. The validity of the calculated reflection coefficient is verified by measuring a Teflon strip in a WR187 waveguide, and the dielectric constant of the Teflon is successfully retrieved from the measurement. For the measurement of many strips, a special sample holder is made to ensure insensitivity of the measured reflection coefficient to the position of the strip.     

A novel numerical technique for dielectric measurement of generallylossy dielectrics

A method for determining the dielectric properties of infinite half-space of generally lossy dielectric materials is described. This method utilizes the measurement of the admittance of a rectangular waveguide radiating into such dielectrics. It is shown that the real part of the admittance is relatively insensitive to the variations of the imaginary part of the dielectric constant. A numerical procedure is initiated which provides a simple and fast-converging approach for calculating the dielectric properties. This numerical procedure lends itself to implementation by personal computers. The theoretical formulation for the expression of the admittance of an open-ended waveguide and the numerical procedure are discussed in detail. Results of several measurements of freespace and lossy dielectric samples (rubber with carbon black) to verify the theory and the numerical scheme are given. The results give good agreement with other measurement schemes. Comments on the accuracy of the results are also provided     

A grounded coplanar waveguide technique for microwave measurement of complex permittivity and permeability

We present a method for extracting the complex permittivity and permeability of dielectric/magnetic thin films in a grounded coplanar waveguide configuration. The technique is applicable for extraction of these material parameters for lossy and lossless materials over a broad frequency range with high accuracy. For validation, we extracted complex permittivity and permeability, using the scattering parameters obtained from the full-wave electromagnetic simulation for two test cases over a frequency range of 5 to 15 GHz. Accuracy for both dielectric as well as magnetic materials is within 2% error.     

Improvement of open resonator technique for dielectric measurement at millimetre wavelengths

An open resonator system is designed and constructed for the accurate measurement of complex permittivity at Ka band. It is solved successfully for the first time in how to achieve the consistency of cavity lengths corresponding to different resonant frequencies over a broad band and how to determine the proper permittivity from multiple transcendental equation roots of one sample. Many kinds of samples such as fused quartz, Teflon, quartz ceramic, MgF₂ and MgAl₂O₄ are measured and the results are in good agreement with published data. The systematic error analysis shows that the relative standard deviation of the measurement system is less than 0.172% for permittivity and 18.35% for loss tangent. The software developed to control the system improves the measurement efficiency greatly.     

Guided-wave technique for the measurement of dielectric thin-film materials' thermal properties

A pump-and-probe setup that uses a totally reflecting prism coupler is presented. Its electromagnetic and thermal models are described. To our knowledge, the first results are given concerning the measurement of thermal properties of thin films.     

Microwave tomography for compact-support dielectric objects

A technique for imaging compact-support dielectric objects from microwave backscattering data is proposed. It is based on a linear data model, which permits the evaluation of the object spectrum on a band-pass region, and the application of the Projected Landweber method for spectrum extrapolation. The performance of the resulting algorithm is then investigated as a function of the relaxation parameter and the possible preconditioning strategy. Several experimental results are shown both for noiseless and noisy cases. This algorithm is shown to be an additional possibility to be taken into consideration, alongside the classical linear algorithms and the fully nonlinear ones. The experimental results show that the solutions are far better than the ones obtained by linear methods, yet require far fewer computations than the nonlinear approaches. © 1998 John Wiley & Sons, Inc. Int J Imaging Syst Technol, 9, 14–23, 1998     

Coupled electromagnetic wave propagation in a cylindrical dielectric waveguide filled with Kerr medium: nonlinear effects

Propagation of the coupled electromagnetic wave, which is a superposition of TE and TM waves, in a dielectric circular cylindrical waveguide filled with non-linear inhomogeneous medium is studied (if the permittivity is linear, the coupled wave does not exist). Non-linear coupled TE–TM wave is characterized by two (independent) frequencies and two (coupled) propagation constants (PCs). The physical problem is reduced to a non-linear two-parameter transmission eigenvalue problem for Maxwell’s equations. The system of dispersion equations with respect to PCs is derived and solved numerically. Two types of coupled PCs and coupled guided modes are found: non-linear solutions of the first type become solutions of the corresponding linear problems as the nonlinearity coefficient tends to zero; solutions of the second type seem to be ’purely’ non-linear as they stay away from any linear solutions as coefficient of the nonlinearity tends to zero. Coupled PCs and coupled eigenmodes are calculated and plotted.     

Tightly focused epimicroscope technique for submicrometer-resolved highly sensitive refractive index measurement of an optical waveguide

We introduce a very sensitive new configuration, to the best of our knowledge, in an optical microscope system that utilizes two detectors: one is to measure the power of a low reflected signal from a sample, and the other is only to monitor the confocal geometry of the system. With this new configuration, we could effectively remove measurement noise associated with small perturbation in measurement conditions such as surface curvature, tilt, and vibration in a microscope system. We have obtained a high-resolution relative index precision of 9x10(-5) by employing this novel technique with two detectors.     

A signal processing technique for measurement of multimode waveguide signals: An application to monitoring of reaction bonding in silicon nitride

A system that uses ultrasonic techniques to monitor the reaction bonding of silicon nitride is described. Reaction bonding of silicon nitride takes place in a nitrogen atmosphere at temperatures up to 1400°C. As with many sensors used in hostile environments, it is difficult to design the ultrasonic sensor in a way that provides optimal clarity of the signal. The sensing system must be designed within the physical limitations on access to the furnace. Ultrasonic probes that accommodate limited access to the silicon nitride sample have been designed and ultrasonic signals acquired during processing, albeit with significant noise and complexity in the signal. Signal processing techniques are used which make it possible to measure changes in phase velocity and attenuation during reaction bonding. Because of variability in the measured velocity and attenuation, the method of signal processing presented is applicable to those cases where it is not possible to redesign the probe for optimal clarity of the ultrasonic signal. This technique demonstrates the potential to perform measurements using signals that would have been considered intractable in the past. Data obtained from ultrasonic monitoring are suitable for use as input to a manufacturing process control feedback loop.     

The open resonator with a longitudinally placed dielectric film in measurement technique

The case when a thin dielectric film is placed longitudinally in an open resonator is considered. When measuring the parameters of the film this arrangement enables one to increase the volume of material introduced into the field without any appreciable distortion of the field of the open resonator and also increases the deviations of the measured parameters.Translated from Izmeritel'naya Tekhnika, No. 10, pp. 50–51, October, 1993.We wish to thank V. N. Apletalin for his help with the experiment.     

Wave propagation in a bifurcated impedance-lined cylindrical waveguide

The radiation of a cylindrical-surface-wave mode which propagates towards the mouth of a semi- infinite cylindrical waveguide which supports surface waves is considered. This semi-infinite cylindrical waveguide is symmetrically located inside an infinite cylindrical waveguide whose surfaces are lined with an absorbent material. The whole system constitutes a new bifurcated cylindrical-waveguide boundary-value problem that has application in acoustics and electromagnetism. The mathematical model results in a scalar Wiener–Hopf problem which can be rigorously solved to give a closed-form solution.     

A multi-section technique for the electroabsorption measurements in waveguide semiconductor electroabsorption modulators

A technique for measuring the optical absorption spectra of waveguides, semiconductors and electroabsorption modulators is described. The technique uses a multi-sectioned optical waveguide that has electrically isolated longitudinal sections and has a p-i-n cross-section structure. Light generated in forward biased sections is used to probe the optical absorption in sections that can be reverse biased. The technique is applied to a p-i-n electroabsorption device that was designed to operate over a broadband of optical communication wavelengths. It has an active region consisting of multiple-width InGaAs-InAlGaAs quantum wells. For this device, a band edge shift of 40 meV is obtained at an applied field of 105 kV cm^-1, and figures of merit Deltaalpha, Deltaalpha/F and Deltaalpha/alpha₀ were also determined as a function of wavelength and applied field, where alpha₀ is the absorption coefficient change due to electroabsorption, Deltaalpha static absorption coefficient of the wells at zero bias field and F the applied reverse bias field.     

Polarization properties of a four-layer dielectric waveguide

A new integrated-optics polarizer system is analyzed. Calculations are made and experiments carried out to demonstrate the performance of this system. Pis’ma Zh. Tekh. Fiz. 24, 35–39 (March 26, 1998)     

A simple technique for installing strain gauges on cylindrical surfaces

In this paper a simple technique for the installation of strain gauges on circular and conical cylindrical surfaces has been described. This technique may be adopted in an experimental stress analysis laboratory where sophisticated equipment is not available.     

Analysis of mode scattering from an abruptly ended dielectric slab waveguide by an accelerated iteration technique

A new modification of the integral equation method using an iteration technique with "accelerating" parameters is presented to solve the problem of guided-mode scattering from an abruptly ended asymmetrical slab waveguide. The optimal choice of the parameters is shown to be closely connected with the variational principle. The electric-field distribution at the terminal plane, the reflection coefficient of the guided mode, and the far-field radiation pattern are computed. Numerical results are presented for several cases of abruptly ended waveguides, including the systems with constant and variable profiles of the refractive indices. The phenomenon of the radiation pattern rotation is examined in detail.     

A differential-equation method for the computation of the electromagnetic scattering by an inhomogeneity in a cylindrical waveguide

Summary In this paper an exact method is described for computing numerically the scattering by an inhomogeneity in a cylindrical waveguide. The Generalized Telegraphist's Equations are used to transform the electromagnetic-field equations into a system of ordinary differential equations. The latter system behaves numerically unstable. A method is given to cope with this difficulty. Numerical results are presented for two- and three-dimensional obstacles in a waveguide of rectangular cross-section and they are compared with those obtained by other methods. Our method requires, in general, a relatively small amount of computation time and storage capacity. Another advantage of the method is its flexibility.     

A general advancing front technique for filling space with arbitrary objects

An advancing front space‐filling technique for arbitrary objects has been developed. The input required consists of the specification of the desired mean point distance in space and an initial triangulation of the surface. One object at a time is removed from the active front, and, if possible, surrounded by admissible new objects. This operation is repeated until no active objects are left. Two techniques to obtain maximum packing are discussed: closest object placement (during generation) and move/enlarge (after generation). Different deposition or layering patterns can be achieved by selecting the order in which objects are eliminated from the active front. Timings show that for simple objects like spheres the scheme is considerably faster than volume mesh generators based on the advancing front technique, making it possible to generate large (> 10⁶) yet optimal clouds of points in a matter of minutes on a PC. For more general objects, the performance may degrade depending on the complexity of the penetration checks. Several examples are included that demonstrate the capabilities of the technique. Copyright © 2004 John Wiley & Sons, Ltd.