Unequal Phase Research Articles

NEW DUAL-BAND BANDPASS FILTER WITH WIDE UPPER REJECTION BAND

A new circuit structure is proposed for design of dual- band bandpass fllters with a wide upper stopband. The unit cell of the circuit consists of two two-port networks in shunt connection; one is a coupled-line section of ‚/4 long followed by a transmission line segment of identical length, and the other has the same elements but cascaded in reverse order, where ‚/4 is the wavelength at arithmetic mean frequency of the two passbands. Higher-order circuits can be obtained by directly cascading two or more such cells and show improved frequency selectivity. In addition to on both sides of the passbands, transmission zeros are also created in the rejection bands. Analysis of the unit cell circuit is formulated by the transmission line theory, and design curves for one- and two-cell circuits are provided. In realization, interdigital capacitors are incorporated with the ‚/4 coupled sections for compensating the efiect of unequal modal phase velocities on the fllter performance in the rejection band. Two circuits are fabricated and measured to validate the analysis.

How does wall slippage affect hydrodynamic dispersion?

How hydrodynamic dispersion is affected by wall slip remains to be fully understood. An attempt is made in this article looking into this issue for dispersion in some elementary pressure-driven flows. Both the long-time Taylor–Aris dispersion and the early-phase convection-dominated dispersion are investigated, analytically and numerically, respectively. The mean and the variance of the residence time distribution are also examined. In the basic case where the walls of a parallel-plate channel have equal slip lengths, the slip is in general to reduce the spread of a solute cloud in a finite channel by either increasing the convection speed or decreasing the dispersivity. However, the decreasing effect of slip on dispersion can be diminished or even reversed by unequal slip lengths and/or phase exchange with the wall. The convection-dominated regime is investigated, following a recently proposed transport-based method, to determine how the mean residence time and variance of elution profiles may change with axial positions depending on the slip.

Controlling electrical power losses in transmission and distribution networks in Nigeria

Electrical power losses in Transmission and Distribution (T&D) networks in Nigeria have been examined to det-ermine the high technical and non-technical losses associated with the system, and the control measures to man-age the losses. Very long and over-aged T&D lines, unequal phase loads, inadequate reactive compensation and energy theft contributed to the high energy losses in the networks. The measures proposed to control the losses, enhance efficiency and strengthen reliability of the networks were using conductors of appropriate sizes, realig-ning the lines, introducing more substations, undertaking regular energy audit and implementing pre-paid meter-ing systems. The policies on deterring energy theft, meter tampering, fully accounting for energy generated and distributed and strategic marketing of power should be enforced. The re-branding of the Power Holding Comp-pany of Nigeria for satisfactory services would restore confidence of the customers.

Dynamic Analysis of Porous Media Considering Unequal Phase Discretization by Meshless Local Petrov-Galerkin Formulations

Dynamic Analysis of Porous Media Considering Unequal Phase Discretization by Meshless Local Petrov-Galerkin Formulations

A new directional coupler for UHF RFID reader

AbstractA conventional microstrip directional coupler has poor isolation due to its unequal phase velocity between the even and odd modes. In this article, a compact dual‐stub microstrip directional coupler for the UHF RFID reader is proposed. The operating frequency band is 902–928 MHz. It is found that the coupler can obtain a good isolation of −65 dB at 920 MHz. Modeling and simulation results are also presented which are in good agreement with measurement data. © Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1973–1975, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23495

Numerical Study of Stratified Gas-Liquid Flow

In this work the effects of empirical correlations of friction factors (wall and interfacial) on the numerical stability and parameters predictions in stratified gas-liquid pipelines flow, was studied using the two-fluid model, where unequal phase pressure effects were considered. To study the effects of such empirical correlations without taking into account the instabilities due to ill-posed initial-value problems or multiple solutions, the two-fluid model was solved using input data, which satisfies a linear stability criterion where multiple solutions do not occur. In general, we found that the empirical correlations are not important for numerical stability but do, however, affect significantly the parameters predictions.

DUAL BEAM SYNTHESIS USING ELEMENT POSITION PERTURBATIONS AND THE G3-GA ALGORITHM

The position perturbations of linear antenna elements are used for designing non-uniformly spaced reconfigurable antennas radiating with multiple pattern such that the same amplitude distribution and perturbed positions produces either a pencil or a flat topped beam, the difference being dependent upon phase distribution of the array. The perturbation method consists of inducing small perturbations in the element positions of a linear array to obtain the desired patterns and offer the flexibility of simple design and is similar to other adaptive techniques like phase only or phase/amplitude synthesis. The problem of finding the element position perturbations is treated as a non linear problem and has been solved using a the generalized generation gap steady state genetic algorithm (G3- GA) using parent centric crossover. In the G3-GA approach the population diversity versus selection pressure problem considers both the parent selection and the replacement plans of GA. The position- phase synthesis method using the G3-GA approach is compared with the G3-GA phase-only synthesis technique. It is seen that, an optimal set of element-perturbed positions in a constrained position range with uniform amplitude, unequally spaced elements with unequal phases has the potential to overcome the design challenge of phase only syntheses that uses a larger number of elements to get the same desired side lobe level. Further when the main beam is scanned it is found that the proposed method can maintain a sidelobe level .without distortion during beam steering for the angular positions studied.

Lung impedance measurements are/are not more useful than simpler measurements of lung function in animal models of pulmonary disease

The following letters are in response to Point:Counterpoint: “Lung impedance measurements are/are not more useful than simpler measurements of lung function in animal models of pulmonary disease” that appears in this issue. To the Editor : Mitzner argues that constant phase modeling is not more

Numerical Analysis of Sound Pressure Fields Focused by Phase Continuous Fresnel Lens Using Finite Difference Time Domain Method

A convex lens using room temperature vulcanization (RTV) silicone rubber, whose acoustic impedance matches well with that of water, is a typical acoustic lens. However, some considerations are required to reduce the thickness of the lens because attenuation is very large in the RTV silicone rubber. Therefore, we have proposed a phase continuous Fresnel lens, which has some devices to keep the phase continuous in the entire lens aperture without an unequal phase on the exit side. This lens is fabricated by removing its thickness in a staircase shape in which the difference between each step is an integer multiple of wavelength. In this study, the sound fields focused by the phase continuous Fresnel lens are analyzed using a finite difference time domain (FDTD) method. Using a two-dimensional (2-D) FDTD method, we surveyed the sound pressure field of the focal region by changing the burst pulse length, angle of incidence, and frequency. Results show that the lens gain of the phase continuous Fresnel lens is greater than that of the convex lens, that focusing characteristics depend on the burst pulse length of sound source signal, and also that focal points strongly depend on frequency. In another analysis using a three-dimensional FDTD method, we found that the main lobe is the same as that indicated by 2-D analysis results and that the level outer of the main lobe is lower than that in the 2-D analysis results.

Effect of hydrogen addition on the route preference in natural gas flow in regular, horizontal T-junctions

During the transport of natural gas through pipelines small amounts of condensate can be formed due to temperature and pressure changes. If this natural gas/condensate flow arrives at a regular, sharp-edged T-junction in the pipeline system an interesting phenomenon may be observed i.e. unequal phase splitting of gas and condensate. In this paper its has been shown that the addition of hydrogen into a natural gas stream results in a different splitting behaviour in comparison with the natural gas flow without hydrogen addition.

A four-frame phase shift method insensitive to phase shifter nonlinearity

A four-frame phase shift method and an associated algorithm using unequal phase steps are presented. The unique advantage of this method is that it becomes insensitive to phase shifter nonlinearity because of the performance of a special procedure, in which the phase shifts are shared out between the reference beam and the object beam. By this means, any phase shifter can work as long as one phase shift is accurately known. On the basis of the technique, a simple calibration method for the linear phase shifter is suggested. The influences of phase shifter miscalibration, detector nonlinearity and random noise on the algorithm are investigated, and the optimal phase shifts are given.

Tilt-shift error detection in phase-shifting interferometry

Temporal phase shifting in automatic interferogram analysis offers very high accuracy of phase retrieval providing that several experimental conditions are met. The paper is focused on the calibration error of unequal phase changes across the interferogram field, i.e., tilt-shift error. For its detection the lattice-site representation of phase shift angles is proposed. The error can be readily discerned using (N+1) algorithms with the last frame overlapping the first one. Four and five frame algorithms are considered. The influence of experimental parameters on the error detection sensitivity is discussed. Numerical studies are complemented by experimental results.

Frequency dependence of elliptical particle motion of acoustic waves transmitted into the seabed from a point source in water

When perpendicular components of the particle velocity of a continuous acoustic wave have unequal amplitude and phase, the displacement traces an elliptical path. This is caused by inhomogeneous waves and/or losses in the medium. For spherical waves radiating from a point source in water and transmitted into the seabed, the orientation of the elliptical orbit varies with receiver location and frequency, and the ellipse major axis is not always parallel to the direction of propagation suggested by Snell’s law. If not accounted for, this could bias estimates of sediment sound speed derived from particle velocity measurements. This presentation describes a simple orbit model based on numerical evaluation of integrals for the transmitted field over the entire wavenumber range. The model provides rapid simulation of results for different experimental geometries and source frequencies. The model is validated using an established full-field model and compared with experimental data. [Work supported in part by ONR Code 32.]

Simultaneous digital correction of amplitude and phase errors of retrieved wave-front in phase-shifting interferometry with arbitrary phase shift errors

Both the amplitude error and phase error retrieved in the recording plane in phase-shifting interferometry (PSI) have effects on the reconstructed wave-front in original object plane placed a distance away. We have proposed a simple and effective algorithm, which can simultaneously correct both kinds of wave errors caused by arbitrary and unequal phase shift errors in PSI for an off-lying object and then greatly improve the reconstructed object wave-front by digital image processing based on the statistic nature of diffraction field. The principles are explained, and a series of computer simulations are made to verify its feasibility.

Generalized phase-shifting interferometry with arbitrary unknown phase steps for diffraction objects.

A general method of extracting the arbitrary unknown and unequal phase steps in phase-shift interferometry from interferograms recorded on the diffraction field of an object and then reconstructing the object wave front digitally with our derived formulas is proposed. The phase steps are first calculated based on the statistical nature of the diffraction field and are further improved by an iterative approach. This method is simple, highly accurate, and usable for any frame number N (N > or = 3) and for both smooth and diffusing objects, as is verified by a series of computer simulations.

Analysis of Two-Phase Homogeneous Bubbly Flows Including Friction and Mass Addition

The present work is a theoretical investigation of two-phase bubbly flows. The main objective is to get a better insight of the basic phenomena associated with such flows through nozzles via physical modeling and mathematical formulation. Introducing Mach number into the flow equations, we find novel, closed-form analytical solutions and expressions for homogeneous bubbly flows including the influence of wall friction and mass addition. The expressions obtained demonstrate an analogy to those of classical, single-phase gas flows. The study deals with homogeneous flows, however, its approach and results can also be applied to investigate flows with unequal phase velocities, to study instability phenomena, as well as to design and analyze water jet propulsion systems.

Phase-shift extraction and wave-front reconstruction in phase-shifting interferometry with arbitrary phase steps.

A new approach to reconstructing the object wave front in phase-shifting interferometry with arbitrary unknown phase steps is proposed. With this method the actual phase steps are first determined from measured intensities with an algorithm based on the statistic property of the object phase distribution in the recording plane. Then the original object field is calculated digitally with a derived formula. This method is simple, accurate, and capable of retrieving the original object field, including its amplitude and phase distributions simultaneously, with arbitrary and unequal phase steps in a three- or four-frame method. The effectiveness and correctness of this approach are verified by a series of computer simulations for both smooth and diffusing surfaces.

Incoherent scatter radar plasma density measurements at Jicamarca using a transverse-mode differential-phase method

The 50 MHz Jicamarca incoherent scatter radar can be used to make very high precision F‐region plasma drift measurements with less than a m/s uncertainty and 5 min/15 km time/height resolutions. In such measurements the transmitting antenna beam is pointed perpendicular to the geomagnetic field [e.g., Kudeki et al., 1999] and backscattered fields consist of magneto‐ionic O‐ and X‐components with unequal phase retardations. Detecting the fields with an orthogonal pair of linear‐polarized antennas and fitting the average power and differential‐phase of the antenna outputs to an appropriate data model we have succeeded in making F‐region electron density measurements with data collected during Jicamarca drifts experiments. This procedure provides Jicamarca with a new capability for simultaneous drifts and density measurements at F‐region heights.

Synthesis of uniform amplitude unequally spaced antenna arrays using the differential evolution algorithm

A computationally efficient global optimization method, the differential evolution algorithm (DEA), is proposed for the synthesis of uniform amplitude arrays of two classes, i.e., unequally spaced arrays with equal phases and unequal phases. Phase-only synthesis and the synthesis of uniformly exited unequally spaced arrays (position only synthesis) are compared and it is seen that, by using the unequal spacing, the number of array elements can be significantly reduced for attaining reduced sidelobe levels. From the DEA-based synthesis of unequally spaced arrays with uniform amplitudes and unequal phases, it is found that a tradeoff exists between the size of the unequally spaced arrays and the range of phases for the same radiation characteristics. The proposed synthesis technique using uniform amplitudes, unequal spacing, and unequal phases (position-phase synthesis) not only decreases the size of the array for the same sidelobe level compared to both the phase-only synthesis and position-only synthesis but also retains their advantages.

Filter banks for less ringing artifacts

In image compression using a filter bank, blocking can be reduced by overlapping the basis functions in the lapped orthogonal transform or the lapped biorthogonal transform, whereas ringing can be conspicuous. In this paper, two methods are proposed to suppress ringing while blocking is reduced. One of them uses an unequal length linear phase biorthogonal filter bank. This is an extension of the unequal length orthogonal transform to the biorthogonal type and a generalization of the filter length in the lapped biorthogonal transform. This filter bank can be realized with a lattice structure. By reducing the length of the high-frequency filter on the synthesis side, ringing is compressed to the edge so that it is less visible. Another method introduces the peak-to-peak ratio into the performance criterion of the filter bank design. In this method, ringing can be suppressed by restricting the impulse response of the filter. By means of these methods, ringing can be reduced while coding performance is retained in comparison with the conventional equal length filter banks. © 2002 Scripta Technica, Electron Comm Jpn Pt 3, 85(6): 1–10, 2002