Electromagnetic Waves Excitation by Thin Impedance Vibrators and Narrow Slots in Electrodynamic Volumes

Linear vibrator and slot radiators, i.e., radiators of electric and magnetic type, respectively, are widely used as separate receiver and transmitter structures, elements of antenna systems, and antenna-feeder devices, including combined vibrator-slot structures. Widespread occurrence of such radiators is an objective prerequisite for theoretical analysis of their electrodynamic characteristics. During the last decades, researchers have published results which make it possible to create a modern theory of thin vibrator and narrow slot radiators. This theory combines the fundamental asymptotic methods for determining the single radiator characteristics, the hybrid analytic-numerical approaches, and the direct numerical techniques for electrodynamic analysis of such radiators. However, the electrodynamics of single linear electric and magnetic radiators is far from been completed. It may be explained by further development of modern antenna techniques and antenna-feeder devices, which can be characterized by such features as multielement structures, integration, and modification of structural units to minimize their mass and dimensions and to ensure electromagnetic compatibility of radio aids, application of metamaterials, formation of required spatial-energy, and spatial-polarization distributions of electromagnetic fields in various nondissipative and dissipative media. To solve these tasks, electric and magnetic radiators, based on various impedance structures with irregular geometric or electrophysical parameters and on combined vibrator-slot structures, should be created. This chapter presents the methodological basis for application of the generalized method of induced EMMF for the analysis of electrodynamic characteristics of the combined vibrator-slot structures. Characteristic feature of the generalization to a new class of approximating functions consists in using them as a function of the current distributions along the impedance vibrator and slot elements; these distributions are derived as the asymptotic solution of integral equations for the current (key problems) by the method of averaging. It should be noted that for simple structures similar to that considered in the model problem, the proposed approach yields an analytic solution of the electrodynamic problem. For more complex structures, the method may be used to design effective numerical-analytical algorithms for their analyses. The demonstrative simulation (the comparative analysis of all electrodynamic characteristics in the operating frequencies range) has confirmed the validity of the proposed generalized method of induced EMMF for analysis of vibrator-slot systems with rather arbitrary structure (within accepted assumptions). Here, as examples, some fragments of this comparative analysis were presented. This method retains all benefits of analytical methods as compared with direct numerical methods and allows to expand significantly the boundaries of numerical and analytical studies of practically important problems, concerning the application of single impedance vibrator, including irregular vibrator, the systems of such vibrators, and narrow slots

Advanced Electromagnetic Waves

This book endeavors to give the reader a strong base in the advanced theory of electromagnetic waves and its applications, while keeping pace with research in various other disciplines that apply electrostatics/electrodynamics theory. The treatment is highly mathematical, which tends to obscure the principles involved

Use of electrical impedance spectroscopy for online monitoring of concrete compaction

Compaction of concrete is a crucial on-site step that enables concrete to reach design strength and density. This process is generally carried out using vibrators that pack the aggregates together and expel the entrapped air from the concrete element. Proper compaction ensures that all the entrapped air escapes the concrete without causing segregation. Based on the duration of vibration concrete can be under-vibrated, well-vibrated, or over-vibrated. Under-vibrated concrete causes many durability problems, such as: honey-combing, cold joints, and subsidence cracking. On the other hand, over-vibration of concrete leads to segregation and probable failure of the concrete element. Typically, compaction is subjectively monitored by personnel on site, which is insufficient to obtain a well-vibrated concrete. This thesis investigates the use of Electrical Impedance Spectroscopy (EIS) to monitor concrete compaction during vibration. Concrete can be divided into a resistive part and a conductive part, where the first is the cement paste and water-filled voids, while the latter is the air voids as well as the aggregates. An electrode panel was designed to investigate top, middle, and bottom layers of tested concretes. This panel was fitted inside a plexiglass mould where seven samples of the same concrete mix were tested. Three vibration dura-tions were chosen to obtain under-, over-, and well-vibrated concretes. Alternating current was sent at different frequencies using an impedance analyzer, and the resistance of each layer was obtained through analyzing the measured reactance and resistance of concrete. Followingly, three cores were drilled form each hardened concrete sample and the densities of these cores were statically analyzed to check for segregation. Additionally, vertical sections were cut to visually inspect the distribution of aggregates and air voids inside the concrete. Analysis of the data showed that segregation could be detected by studying the variance of the resistance values for different layers during compaction. The top and middle layer showed a significant resistance decrease, whereas an increase was noted in the bottom layer. This change was linked to the observed segregation in the cut vertical segments, where the bottom layer had a higher amount of accumulated aggregates compared with the other two layers. Additionally, statistical analysis was carried out on the drilled cores densities, which showed a large variance in values denoting segregation. Further analysis was carried out comparing the difference between the resistance of top and bottom layers over the vibration duration. It was found that all segregated samples passed a limit of dif-ference in those EIS obtained resistances compared with the unsegregated sample

Evaluation of high frequency vibrator response

Accurate analysis of the motion of a commercial high frequency hydraulic vibrator commonly used for near-surface applications demonstrated that the rigid body assumption of the weighted-sum approximation is not valid throughout the vibrator's operational frequencies. This study reveals significant response variability across the baseplate, which is dependent on accelerometer position with respect to radial position and internal baseplate structure. Consequently, the baseplate cannot be considered a point source of propagation, which complicates optimizing source operations to increase data fidelity. In an effort to optimize the source signature approximation to increase data fidelity, simultaneous acquisition of baseplate acceleration and pressure beneath the baseplate provided a means to directly compare the response of strategically placed accelerometers to the true ground force. This study concludes that the most representative approximation occurs when multiple accelerometers are positioned on the baseplate to average the baseplate motion. In addition, this study found that the IVI Minivib I is incapable of providing measurable seismic energy at frequencies over 200 Hz due to opposing baseplate and reaction mass phase. Based on this observation, it is clear the design of the baseplate needs to be modified by adding extra weight and rigidity to the driven structure. Increasing rigidity of the baseplate will reduce source generated harmonic distortion caused by baseplate flexure resulting in a more uniform response across the baseplate and a more accurate ground force approximation. Additionally, the opposing phase relationship between the baseplate and the reaction mass could be remediated by increasing the baseplate weight resulting in an increase in energy above 200 Hz

Vibroacoustics of the piano soundboard: Reduced models, mobility synthesis, and acoustical radiation regime

In string musical instruments, the sound is radiated by the soundboard, subject to the strings excitation. This vibration of this rather complex structure is described here with models which need only a small number of parameters. Predictions of the models are compared with results of experiments that have been presented in Ege et al. [Vibroacoustics of the piano soundboard: (Non)linearity and modal properties in the low- and mid- frequency ranges, Journal of Sound and Vibration 332 (5) (2013) 1288-1305]. The apparent modal density of the soundboard of an upright piano in playing condition, as seen from various points of the structure, exhibits two well-separated regimes, below and above a frequency flim that is determined by the wood characteristics and by the distance between ribs. Above flim, most modes appear to be localised, presumably due to the irregularity of the spacing and height of the ribs. The low-frequency regime is predicted by a model which consists of coupled sub-structures: the two ribbed areas split by the main bridge and, in most cases, one or two so-called cut-off corners. In order to assess the dynamical properties of each of the subplates (considered here as homogeneous plates), we propose a derivation of the (low-frequency) modal density of an orthotropic homogeneous plate which accounts for the boundary conditions on an arbitrary geometry. Above flim, the soundboard, as seen from a given excitation point, is modelled as a set of three structural wave-guides, namely the three inter-rib spacings surrounding the excitation point. Based on these low- and high-frequency models, computations of the point-mobility and of the apparent modal densities seen at several excitation points match published measurements. The dispersion curve of the wave-guide model displays an acoustical radiation scheme which differs significantly from that of a thin homogeneous plate. It appears that piano dimensioning is such that the subsonic regime of acoustical radiation extends over a much wider frequency range than it would be for a homogeneous plate with the same low-frequency vibration. One problem in piano manufacturing is examined in relationship with the possible radiation schemes induced by the models.Comment: Research highlights: - Synthetic modelling of a piano soundboard overa broad-frequency-range (several kHz). - Quantitative agreement between predicted and measured apparent local modal density. -Modal density of a plate with non-special orthotropy and arbitrary contour. -Similar characteristic impedance between comparable pianos, over several kHz. -Extension of the subsonic regime of acoustical radiation over a wide frequency range. Journal of Sound and Vibration (2013) http://dx.doi.org/10.1016/j.jsv.2013.03.01

Формування електромагнітних полів комбінованими вібраторно-щілинними випромінюючими структурами в електродинамічних об’ємах з імпедансними границями

Дисертацію присвячено розвитку теорії комбінованих вібраторно-щілинних випромінюючих структур, що містять лінійні імпедансні вібраторні і щілинні випромінювачі в електродинамічних об’ємах з імпедансними границями, включаючи багатоелементні системи. Розвинуто числово-аналітичні методи розв’язання інтегро-диференціальних рівнянь для електричних і магнітних струмів у вібраторних і щілинних елементах комбінованих структур, побудовано високоефективні за точністю й швидкістю розрахунків математичні моделі, методи й алгоритми. Запропоновано новий метод імпедансного синтезу антенних решіток. Виявлено нові фізичні закономірності у формуванні електромагнітного поля вібраторно-щілинними структурами у хвилевідних трактах, на сферичних поверхнях, хвилевідних зчленуваннях з імпедансними поверхнями (включаючи покриття з метаматеріалу) і діелектричними вставками, багаточастотними випромінювачами. Визначено умови реалізації випромінювачів з необхідними електродинамічними характеристиками. Отримані результати є основою для розробки і створення нової елементної бази радіоелектронних засобів метрового і мікрохвильового діапазонів, яка дозволяє значно розширити їх функціональні можливості, сприятиме вирішенню проблем забезпечення електромагнітної сумісності, завадозахищеності, селекції сигналів, мініатюризації.Berdnik S.L. Formation of electromagnetic fields by combined vibrator-slot radiating structures in electrodynamic volumes with impedance boundaries. – Manuscript of qualifying scientific work. Thesis for a Doctor degree in physical and mathematical sciences: Speciality 01.04.03 – radiophysics (Physical and mathematical sciences). – V.N. Karazin Kharkiv National University, Ministry of Education and Science of Ukraine, Kharkiv, 2021. The dissertation is devoted to the development of the theory of combined vibrator-slot radiating structures, creation of physically correct mathematical models, and improvement of numerical-analytical methods for solving corresponding boundary value problems of electrodynamics, which allow a theoretical analysis of physical properties of excitation fields (the radiation, scattering) and functional characteristics of combined vibrator-slot structures containing impedance vibrators and slot radiators, as well as their multi-element systems located in different electrodynamic volumes with impedance boundaries (including coating of metamaterial) and filled with material

Multiband Asymmetric Biconical Dipole Antenna with Distributed Surface Impedance and Arbitrary Excitation

A numerical-analytical solution of a problem concerning the current distribution and input characteristics of asymmetric biconical dipole with distributed surface impedance and arbitrary excitation and derived in the thin-wire approximation. Solution correctness is confirmed by satisfactory agreement of numerical and experimental results from literary sources. Numerical results are given for the input characteristics of the dipole in the case of its asymmetric excitation by a point source

Seismic Technology Adapted to Analyzing and Developing Geothermal Systems Below Surface-Exposed High-Velocity Rocks - Final Report

The objective of our research was to develop and demonstrate seismic data acquisition and data processing technologies that allow geothermal prospects below high-velocity rock outcrops to be evaluated. To do this, we acquired a 3-component seismic test line across an area of exposed high-velocity rocks in Brewster County, Texas, where there is high heat flow and surface conditions mimic those found at numerous geothermal prospects. Seismic contractors have not succeeded in creating good-quality seismic data in this area for companies who have acquired data for oil and gas exploitation purposes. Our test profile traversed an area where high-velocity rocks and low-velocity sediment were exposed on the surface in alternating patterns that repeated along the test line. We verified that these surface conditions cause non-ending reverberations of Love waves, Rayleigh waves, and shallow critical refractions to travel across the earth surface between the boundaries of the fast-velocity and slow-velocity material exposed on the surface. These reverberating surface waves form the high level of noise in this area that does not allow reflections from deep interfaces to be seen and utilized. Our data acquisition method of deploying a box array of closely spaced geophones allowed us to recognize and evaluate these surface-wave noise modes regardless of the azimuth direction to the surface anomaly that backscattered the waves and caused them to return to the test-line profile. With this knowledge of the surface-wave noise, we were able to process these test-line data to create P-P and SH-SH images that were superior to those produced by a skilled seismic data processing contractor. Compared to the P-P data acquired along the test line, the SH-SH data provided a better detection of faults and could be used to trace these faults upward to the boundaries of exposed surface rocks. We expanded our comparison of the relative value of S-wave and P-wave seismic data for geothermal applications by inserting into this report a small part of the interpretation we have done with 3C3D data across Wister geothermal field in the Imperial Valley of California. This interpretation shows that P-SV data reveal faults (and by inference, also fractures) that cannot be easily, or confidently, seen with P-P data, and that the combination of P-P and P-SV data allows VP/VS velocity ratios to be estimated across a targeted reservoir interval to show where an interval has more sandstone (the preferred reservoir facies). The conclusion reached from this investigation is that S-wave seismic technology can be invaluable to geothermal operators. Thus we developed a strong interest in understanding the direct-S modes produced by vertical-force sources, particularly vertical vibrators, because if it can be demonstrated that direct-S modes produced by vertical-force sources can be used as effectively as the direct-S modes produced by horizontal-force sources, geothermal operators can acquire direct-S data across many more prospect areas than can be done with horizontal-force sources, which presently are limited to horizontal vibrators. We include some of our preliminary work in evaluating direct-S modes produced by vertical-force sources.Bureau of Economic Geolog

Lead zirconate titanate/poly(vinylidene fluoride-trifluoroethylene) 1-3 composites for ultrasonic transducer applications

Author name used in this publication: Helen Lai Wah ChanVersion of RecordPublishe