Conventional magnetically coupled resonant wireless power transfer systems are faced with resonant frequency splitting phenomena and impedance mismatch when a receiving coil is placed at misaligned position. These problems can be avoided by using uniform magnetic field distribution at receiving plane. In this paper, a novel 3D transmitting coil structure with improved uniform magnetic field distribution is proposed based on a developed optimization method. The goal is to maximize the average magnetic field strength and uniform magnetic field section of the receiving plane. Hence, figures of merit (FoM1 and FoM2) are introduced and defined as product of average magnetic field strength and length or surface along which uniform magnetic field is generated, respectively. The validity of the optimization method is verified through laboratory measurements performed on the fabricated coils driven by signal generator at operating frequency of 150 kHz. Depending on the allowed ripple value and predefined coil proportions, the proposed transmitting coil structure gives the uniform magnetic field distribution across 50% to 90% of the receiving plane.
This article is a result of measuring the dielectric constant of a dielectric used in studying the influence of dielectrics on the antennae reflection coefficients. A paper having a density of 0.797 g/cm3, moisture content of 0% and temperature of 210C, is used as a dielectric. Although the literature provides a lot of data on the dielectric properties of wood and paper, without direct measurement of the dielectric constant it is impossible to know its amount for the dielectric used in the defined frequency range. Dielectric constant measurements are performed in the frequency range from 100 Hz to 100 kHz, while the frequency range of its impact on the aperture antenna reflection coefficients is up to 2 GHz. The frequency range from 100 KHz to 10 GHz is interpolated and fitted by using measurements and available literature data and by respecting physical influences and phenomena and functional changes of the dielectric constant of paper within the given range
This study presents an optimisation of antenna arrays on the spherical surface with new elementary antenna distribution using the particle swarm optimisation method. Many distributions of antenna elements on the sphere are known and processed, like icosahedral, spiral, Leopardi and so on, but neither of them is optimal. In this study, optimisation of the antenna array includes radiation pattern optimisation in order to achieve a radiation pattern with a narrow main lobe and very low side lobes. Although distribution of antenna elements is not uniform, optimisation is performed for two planes using the average fitness function. Different applications of antenna arrays require different parameters and different optimisation/process control procedures, too. Spherical antenna arrays with optimised placement of elements are capable of producing a desired radiation pattern, providing electronic scan coverage over the entire sphere and satisfying requirements for many applications in different branches of communications. An antenna array analysed in this study is a spherical array with very low grating lobes and a very narrow main lobe, and it could be used in hemispherical scan coverage.
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