Martin Dadic

Time domain analysis of mutual coupling measurements between stacked patches

The measurement of mutual coupling between stacked patch antennas was performed in presence of distant reflections. Time domain analysis and processing were used for canceling out reflection influence on the measurements. Thus, actual values of measured mutual coupling parameter are obtained. These measurements were used for verification of theoretical model and developed software, where both amplitude and phase of the coupling parameter were compared.

Wiener Filtering for Real-Time DSP Compensation of Current Transformers over a Wide Frequency Range

An efficient system for the compensation of current transformers over a wide frequency range is presented. The proposed technique is based on digital signal processing and inverse modeling using the frequency domain approach and Wiener filtering. Since the proposed technique applies finite impulse response filtering, the compensation filter is absolutely stable. The modeling error is reduced using a small time delay in the modeled inverse transfer function, which is unobservable for the human operator. The proposed algorithm is implemented in real time using a PCI eXtensions for Instrumentation system.

Stator damper winding and electromagnetic parameters of turbogenerators

The increase of the load in specific active parts of modern turbogenerators causes higher local heating, higher magnetic leakage, increased forces of the electromagnetic origin and the increased acoustic noise level. Stator damper winding is an active cage-shaped constructive element positioned at the outer stator core diameter. Its influence has been investigated using numerical methods, since classical analytic model according to the two-axis theory and Parks equations is not applicable in this particular case.

FEM analysis and design of a voltage instrument transformer for digital sampling wattmeter

A voltage instrument transformer (VIT) or a voltage divider is needed if a National Instruments PXI 4461 Dynamic Signal Analyzer is used in a digital sampling wattmeter application. They assure that the input voltage is lowered to the allowed level of the acquisition card, and VIT also gives the galvanic isolation. This paper discusses possible types of sectionalized windings of a VIT with primary and secondary interleave, which result in lower leakage inductances. On the basis of a detailed finite element method (FEM) analysis, a prototype VIT is designed and produced. The ratio error and the phase angle error are measured on the prototype using a digital calibrator, digital multimeter (DMM) and a phase-angle meter. As well, the performance of the transformer over the wider frequency bandwidth and under the harmonically rich excitation is experimentally investigated.

Electromagnetic analysis of adiabatic coaxial line with applied air gap

Microwave power standard is significantly limited by thermostat quality (± 1 mK/h), bolometer load efficiency (absorbers) and characteristics of adiabatic line due frequency bandwidth. Several years ago, air gap was applied on coaxial adiabatic line in order to drive down heat effects. In this paper, the focus will be on further analysis of coaxial line with an applied air gap. With the finite element method tool, analysis of S — parameters for different air gap dimensions and flange radius will be carried out. The paper will present simulation model and achieved results as a first step in the development of microwave power standard at the University of Zagreb.

Fully Coupled Dynamic Model of Thomson’s Levitating Ring

The complete electromagnetic-mechanical-thermal modeling approach is demonstrated on the Thomsons levitating ring experiment. This problem, but with a different set of parameters, was also described by Laithwaite and defined by Freeman and Lowther as TEAM17 problem. This paper presents its most complete solution. The factors for determining the vertical displacements and influence of the height of the ring are explained. The whole apparatus is explained in detail so that an accurate computer model can be made. The model introduced is validated against measurements and transient finite-element method (FEM) solvers. All the results prove the applicability of using steady-state FEM analysis with lumped parameter approach for a fast and effective fully coupled modeling.

Enhanced Time-stepping FEM Simulation using Digital Signal Processing

The purpose of this paper is to present a novel approach in time-domain simulations based on the time-stepping finite element method (FEM). The method uses a single time-stepping FEM simulation to determine the unit step response of the system. On the basis of this response, a digital filter with transfer function equal to that of the target system is designed. This allows excitation to be varied without need for the field analysis to be performed again. Such an approach can give substantial speed-up in electromagnetic or structural simulation. The proposed approach was validated in the simulation of a pulsed eddy-current inspection system and in the simulation of the eddy currents induced in the shield of a busbar system.

Influence of channel transfer function on LMS algorithm based nonrecursive deghosting in analog TV

Ghosts are time delayed, attenuated and distorted versions of the intended television signal. This paper treats the influence of the channel transfer function on performance of an adaptive inverse modeling method, namely the least mean squares (LMS) algorithm. The zeros in the channel transfer function correspond to poles in the inverse model. With these poles inside or outside the unit circle on the z-plane, accurate enough modeling can be achieved with left-handed and right-handed sequences, using finite impulse response (FIR) filters, large enough and modeling delay. For non-repeated poles, the level of residual ghosts is greater, but line-by-line processing can make them smaller and their level decreases when the number of taps is increased. Repeated poles cause the largest magnitudes of residual ghosts, and they cannot be suppressed more than a level even with an increased number of taps.