We report herein the observed null or negative results in measuring any known finite light speed in air, of the one way near-field signal and information velocity, of the field displacement current between the poles of a total 1.5m separated poles spherical air capacitor, caused by its impulse spark discharge.
In this study, we present an analytical model for predicting the magnetic properties and optimization of thermomagnetic devices using mathematical models. The 3D analytical magnetic model is firstly validated by the dipole model and confirmed through experimentation, enabling to accurately estimate the magnetization of the used magnet. The stray field induced by the permanent magnet over the lateral surface of the rotor is computed. Then, the resultant force and torque are derived allowing to estimate the exact number of ferromagnetic active material required and their angular gap.
In order to low-frequency stabilize the electric field integral equation (EFIE) when discretized with divergence conforming B-spline based basis and testing functions in an isogeometric approach, we propose a corresponding quasi-Helmholtz preconditioner. To this end, we derive i) a loop-star decomposition for the B-spline basis in the form of sparse mapping matrices applicable to arbitrary polynomial orders of the basis as well as to open and closed geometries described by single-or multipatch parametric surfaces (as an example non-uniform rational Bsplines (NURBS) surfaces are considered). Based on the loopstar analysis, we show ii) that quasi-Helmholtz projectors can be defined efficiently. This renders the proposed low-frequency stabilization directly applicable to multiply-connected geometries without the need to search for global loops and results in betterconditioned system matrices compared to directly using the loopstar basis. Numerical results demonstrate the effectiveness of the proposed approach.
In order to accurately compute scattered and radiated fields in the presence of arbitrary excitations, a lowfrequency stable discretization of the right-hand side (RHS) of a quasi-Helmholtz preconditioned electric field integral equation (EFIE) on multiply-connected geometries is introduced, which avoids an ad-hoc extraction of the static contribution of the RHS when tested with solenoidal functions. To obtain an excitation agnostic approach, our approach generalizes a technique to multiply-connected geometries where the testing of the RHS with loop functions is replaced by a testing of the normal component of the magnetic field with a scalar function. To this end, we leverage orientable global loop functions that are formed by a chain of Rao-Wilton-Glisson (RWG) functions around the holes and handles of the geometry, for which we introduce cap surfaces that allow to uniquely define a suitable scalar function. We show that this approach works with open and closed, orientable and non-orientable geometries. The numerical results demonstrate the effectiveness of this approach.
In this paper, a new sampling scheme of the near field radiated by a planar source is proposed and assessed. More in detail, the paper shows a uniform sampling criterion that allows representing the near field over a plane with a number of measurements lower than the classical half-wavelength sampling. At first, a discretization strategy of the near field based on the warping method is recalled from the literature. The latter requires to collect a non-redundant number of field measurements that are non-uniformly arranged over the observation domain. Despite this, the warping sampling scheme works well only if the measurement plane does not overcome the source. When the observation domain is larger, it does not predict the exact positions of the field samples at the edges of the measurement plane; accordingly, in these regions it is not possible to recover the near field behavior by the collected samples. To overcome this drawback, a spatially varying oversampling is exploited. The latter is chosen in such a way that the resulting sampling becomes uniform. Such choice also ensures a growth of the sampling rate only at the edges of the observation domain permitting the retrieval of the near field by its samples. Finally, numerical simulations based on experimental data corroborate the effectiveness of the approach in recovering both the near and the far field.
This paper is a continuation on my revolutionary theory of solving the pointwise fluid flow approximation model for time-varying queues. Thus, the long-standing simulative approach has now been replaced by an exact solution by using a constant ratio 𝛽 (Ismail's ratio) , offering an exact analytical solution. The stability dynamics of the time-varying 𝑀/𝐸 𝑘 /1 queueing system are then examined numerically in relation to time, 𝛽, and the queueing parameters.
This paper details an experiment utilizing ESP8266 modules as servers to wirelessly control diverse electrical appliances in home automation. The experiment showcased the modules' capability to respond to commands via a web interface on both mobile and desktop platforms or even tablets. While most of the experiment ran smoothly, occasional freezing and connectivity disruptions were observed. The abstract encapsulates the experiment's successes, discusses encountered challenges, and outlines a forward-looking perspective, including the integration of a custom PCB for enhanced system stability.
This article advances the existing theoretical analysis of pulsed electric field (PEF) treatment, an application of pulsed power technology. PEF treatment has attracted significant attention due to its potential to be used for non-thermal biological sterilization and inactivation of microorganisms, bio-extraction, and for the possible role that it may play in the treatment of tumors and cancers such as in electrochemotherapy. However, the bioelectric effects of impulsive electric fields on different biological matter are not yet completely understood. Further advances in this direction would aid in the optimization of the necessary pulse waveforms to achieve the desired PEF effects in, for example, various biomedical and food processing industries. In this work, the commonly used multi-shell model of microorganisms utilized for the analysis of cell transmembrane potentials (TMPs) has been generalized to include an arbitrary number of layers. Analysis has been conducted on the novel mathematical model, which demonstrated the ability to estimate TMPs and relaxation times for an n-shell topology using a meshfree approach. This allows for complex many-shelled cell models to be analyzed, free from the limitations of spatial or temporal discretization, i.e., those present when using finite-element or finite-volume based methods. Using this model, the effects that the pulse rise-time and pulse duration have on the developed TMPs in a single 6-layer Saccharomyces cerevisiae yeast, and under the microsecond-PEF regime, have been investigated. It has been found that the pulse rise-time has a far lesser effect on the PEF action compared to the modulation of the pulse duration, supporting past experimental observations. The role of the electrical conductivity of the extracellular medium (and considering induced changes in the cell components) has additionally been studied, under low (σ = 1 mS/m), medium (σ = 50 mS/m), and high (σ = 100 mS/m) conductivity values. Estimations provided by this model may support the optimization of pulse waveforms for current and future PEF applications, and for the analysis of complex multilayered cell structures under pulsed electrical stress.
This paper proposes a novel human-aware energy beamforming (BF) method for safe and secure microwave wireless power transfer (MWPT). The proposed method first estimates an equivalent channel between a transmitting array antenna and a human body from continuous-wave pilot signals Doppler-shifted by human vital activities by utilizing the MWPT system as a quasi-monostatic multiple-input multiple-output (or single-output) radar. This allows the online estimation of the radio frequency (RF) exposure power without prior human geometry information. Then, the closed-form optimum BF weight can be derived to maximize the figure of merit (FoM), defined as the ratio of the received power to exposure power in the form of a generalized Rayleigh quotient. This simultaneously facilitates the suppression of RF exposure and enhancement of transfer efficiency. Comprehensive experiments were conducted to evaluate the proposed BF performance using our multi-antenna testbed with proven applicability to various human-sensing experiments. The indoor experiment proved that the proposed method performs null steering auto-tuned to human positions within a distance of up to 3 m and to the physical characteristics of six subjects, even under realistic conditions with multipath fading and array error. It achieved the highest FoM of 21.65 dB among conventional BF methods for a typical case. This was an improvement of 7.10 dB when compared with the result of maximum ratio transmission BF, which maximizes the transfer efficiency. This study demonstrates the possibility of coexistence of humanity and MWPT technology for its future social implementation.
An electromagnetic (EM) metasurface is a passive device capable of manipulating the reflected signal of a radar in both spatial and frequency domains. This paper presents a novel analytical design of EM scattering center model guided passive synthetic aperture radar (SAR) deception based on diverse frequency time-modulation. The objective of this design is to disguise real target as an intended deceptive target and conceal its original EM characteristics. To achieve this, we first extract the scattering center model of an intended deceptive target and express its SAR image analytically. The SAR image is determined by the number, amplitude and position of scattering center. Subsequently, we derive the SAR image of a metasurface modulated on fast and slow time scales with diverse frequencies, establishing the relation between modulation parameters and the resulting SAR image properties. By comparing and aligning the SAR images between scattering center model and the modulated metasurface with predetermined similarity threshold, we successfully accomplish scattering center model guided SAR deception. The simulated results demonstrate that the SAR image similarities of both scattering center model and modulated metasurface exceed 0.9, indicating the effectiveness of this method as an electronic countermeasure.
This article describes the computational analysis of Radio Frequency-Electromagnetic Field (RF-EMF) exposure of Uterus-Fetus Units (UFUs) embedded inside the body of a 26 year old human female. Realistic UFU models are obtained from ultrasound images acquired for different fetuses and at specific development stages (7 weeks, 9 weeks and 11 weeks old), for which a deep-learning based segmentation method is developed. Each UFU model is then inserted into a computational electromagnetic model of a 26 year old female. The Specific Absorption Rate (SAR) of the fetus at commonly used wireless communication frequencies is estimated using a commercially available numerical electromagnetic solver. The Inverted F antenna (IFA), which is a commonly used mobile phone antenna was used as the excitation source. Fetus SAR values are reported for different combinations of excitation frequencies, phone positions and UFU ages. It was found that the fetus SAR for all the cases is well below the maximum allowable exposure limit of 80 mW/kg, as prescribed by ICNIRP. Furthermore, we replace the embryo with uterus tissues and calculate the SAR in the uterus tissues (i.e. uterus tissues with same volume and shape, and at the same location as that of UFU). The uterus SAR values were found to be only marginally different from that of fetus SAR.
We propose a machine learning (ML) modeling methodology to predict the propagation mode number of electromagnetic (EM) fields inside a metallic rectangular waveguide based on the field configuration in the waveguide cross-section, in the presence of noise. We consider the Transverse Electric (TEmn) modes and assume m and n in the range of 0 to 2 inside the waveguides, where the magnitude and phase of the noiseless field configurations are obtained from the analytical solution of the electric vector field E. We generate training/testing datasets that includes 64,000 plots of the magnitude and phase of E over the waveguide cross-section, spanning various TE modes in the frequency range of 13-17 GHz. Our methodology for training and evaluation is based on the classification model, and relies primarily on Stochastic Gradient Descent (SGD) and k-Nearest Neighbors. For real-world scenarios which include noise, we introduce two random distributions in the datasets; specifically, the exponential and the Gaussian distributions are added onto the computed E-fields to further challenge the ML model. We discuss the limitations of the proposed ML modeling approach and the challenges in finding the optimal ML model for these types of problems. The proposed methodology may be generalized to predict both the TE and Transverse Magnetic (TMmn) mode numbers with a wide ranges of m and n, as well as for other types of waveguides; e.g., circular, elliptical, etc.
The visual human perception of electromagnetic waves is limited to the so-called visible spectrum. Artificial extension of the human vision, e.g., via infrared cameras, is possible. Due to the expected low resolution at large wavelengths, however, this is rarely done in the low GHz regime. We investigate the quality of images obtained by simply turning a directive antenna across a scene. The procedure is straight forward and can be compared to how the lens in the human eye creates an image on the retina. Simulation data of an exemplary domestic indoor scenario illustrates how mono-frequency vision of WiFi signals might look like.
Conventional non-convex phase retrieval algorithms struggle with local minima and false solutions, in particular in the presence of noise. These issues are overcome with a linearized phase retrieval algorithm for multi-probe nearfield measurements without global reference signal. We present measurement results to verify that this algorithm works well with noisy real-world measurement data, given a suitably designed probe array and sufficient oversampling.
We present an adaptive cross approximation (ACA) strategy for the magnetic field integral equation (MFIE), where an application of the standard ACA strategy can suffer from early convergence, in particular, due to block-structured interaction matrices associated with well-separated source and test domains. Our scheme relies on a combination of three pivoting strategies, where the active strategy is determined by a convergence criterion that extends the standard criterion with a mean-based random sampling criterion; the random samples give rise to one of the pivoting strategies, while the other two are based on (standard) partial pivoting and fill-distance pivoting. In contrast to other techniques, the purely algebraic nature as well as the quasilinear complexity of the ACA for electrically small problems are maintained. Numerical results show the effectiveness of our approach.
In this article, a full-domain harmonic potential balance (HPB) model, which is free of subdomain division and cumbersome geometric transformations, is presented for 2-D magnetic field analysis of electrical machines. The key contribution is the proposed HPB equation, by which the harmonic distribution of magnetic vector potential in electrical machine is solved. To achieve this result, the singularity functions are applied to realize a global modeling. Then the full-domain magnetic vector potential distribution equation, which implies the boundary conditions, is established. For radial-flux electrical machines with 2-D annular domain, the logarithm-translation mapping is applied to transform the shape of domain into strip. The image domain extension is proposed to construct symmetry and periodicity for harmonic modeling. The HPB equation is then derived by 2-D convolution theorem and regularized by symmetry analysis. A case study is performed by examining the magnetostatic field distribution of a 6-slot/4-pole permanent magnet machine, and comparing results from finite element analysis validate the HPB model. In light of its accuracy and simplicity, HPB model could be a promising analytical modeling method for electrical machines.
The four-port couplers are the fundamental building blocks of large-scale passive beam-forming network design. They find application in the design of antenna feed networks, power combiners and dividers, balanced mixers and amplifiers. Conventional branch-line couplers (BLCs) were designed for quadrature-phase imbalance using four quarter-wavelength transmission lines (TLs). On the other hand, conventional rat-race couplers (RRCs) are designed for in-phased/out-of-phased imbalance using six identical quarter-wavelength TLs. To obtain a non-quadrature phase-shift, external phase shifters are required. Recently, BLCs with inherent non-quadrature phase imbalance properties have received attention among microwave researchers. There are several types of implementation such as lumped, distributed, and mixed with different topologies, that have been proposed by several researchers. It is quite challenging for young researchers to extract all possible design data from the design equations and simulate them to understand their figure of merits. This motivates the author to provide solutions for non-quadrature unequal power division BLCs.