Crack detection in engineering materials has become a prominent research area due to the severe consequences of potential failures in safety-critical systems such as pipelines, railway systems, welded joints, rotating machinery elements, and load-bearing structures. Although significant advancements have been made in nondestructive testing (NDT) methods, there is currently no single method capable of simultaneously meeting the requirements of high detection sensitivity, quantitative crack characterization capability, and applicability under real service conditions. In this study, literature published from 2000 to the present is reviewed using a systematic and method-oriented approach. Unlike conventional reviews, this study classifies existing methods based on the fundamental physical principles underlying the crack detection mechanism rather than the types of sensors used. The investigated approaches are discussed under the categories of Magnetic Flux Leakage (MFL), direct current electromagnetic and motion-induced eddy current techniques, Eddy Current Testing (ECT) and ACFM methods, thermography-assisted electromagnetic approaches, weak magnetic field and Metal Magnetic Memory (MMM) techniques, magneto-optical and visual methods, hybrid EMAT-ultrasonic systems, and optical/data-driven approaches. Each method is comparatively analyzed in terms of material compatibility, sensitivity to crack type, quantitative evaluation capacity, static/dynamic or real field/load/structure applicability, and system complexity. The cross-evaluation demonstrates that high quantitative accuracy, applicability under real field conditions, and low system complexity cannot be simultaneously achieved in most methods. Consequently, crack detection is evolving as a multidisciplinary research area at the intersection of materials science, sensor physics, and data-driven modeling, necessitating the development of holistic and application-specific sensing strategies in the future.

The study of electromagnetic phenomena in the atmosphere is very interesting because it allows us to predict the dangers caused by induced currents resulting from an electrical discharge from an existing cumulonimbus cloud. Simulation of the electromagnetic properties of a possible discharge from the cumulonimbus cloud observed in Chad shows that lightning can occur with a very high magnetic field intensity and an electric current density outside safe limits. Such an electrical discharge could not occur without consequences for the surrounding electrical equipment, the habitat, and humanity.

To help address global warming, various power generation methods that do not release carbon dioxide have been established, including electrostatic power generation. A wide variety of electrostatic generators have been proposed for many centuries; however, the vibration-type electrostatic generator is currently the most commonly utilised. Electricity is generated via the movement of a charge carrier, which is charged by electrostatic induction in opposition to an injection electret (Hereafter, this will be abbreviated as IE.). The carrier is displaced from the electret using external energy forms such as waves, and the resultantly generated charge is allowed to flow. As IE and charge carrier are charged with opposite polarities, a strong Coulomb force is generated between them, which acts as a braking force against the movement of the carrier. Therefore this paper present an improved method that revealed this braking force can be eliminated by placing a counter-electret (Hereafter, this will be abbreviated as CE.)—charged with the opposite polarity—adjacent to IE.

Innovative definitions of the electric and magnetic diffusivities through conducting mediums and innovative diffusion equations of the electric charges and magnetic flux are verified in this article. Such innovations depend on the analogy of the governing laws of diffusion of the thermal, electrical, and magnetic energies and newly defined natures of the electric charges and magnetic flux as energy, or as electromagnetic waves, that have electric and magnetic potentials. The introduced diffusion equations of the electric charges and magnetic flux involve Laplacian operator and the introduced diffusivities. Both equations are applied to determine the electric and magnetic fields in conductors as the heat diffusion equation which is applied to determine the thermal field in steady and unsteady heat diffusion conditions. The use of electric networks for experimental modeling of thermal networks represents sufficient proof of similarity of the diffusion equations of both fields. By analysis of the diffusion phenomena of the three considered modes of energy transfer; the rates of flow of these energies are found to be directly proportional to the gradient of their volumetric concentration, or density, and the proportionality constants in such relations are the diffusivity of each energy. Such analysis leads also to find proportionality relations between the potentials of such energies and their volumetric concentrations. Validity of the introduced diffusion equations is verified by correspondence their solutions to the measurement results of the electric and magnetic fields in microwave ovens.

This paper investigates the ability of the depolarization degree, derived from the characteristic polarization states at the resonant frequency set, to identify corner or swept, i.e. dihedral, changes in same-class targets by a metallic wire example. A well-estimated depolarization degree requires a robust extraction of the fundamental target resonance set in two orthogonal sets of fully co-polarized and cross-polarized polarization channels, then finding the null polarization states using the Lagrangian method. Such depolarization degree per resonance mode has the potential to form a robust feature set because it is relatively less sensitive to onset ambiguity, invariant to rotation, and could create a compact, recognizable, and separable distribution in the proposed feature space. The study was limited to two targets with two swept changes of fifteen degrees within normal incidence; under a supervised learning approach, the results showed that the identification rate converging to upper-bound (100%) for a signal-to-noise ratio above 20 dB and lower-bound around (50%) below −10 dB.

The bifacial silicon solar cell subjected to a magnetic field, is illuminated by the back side by a monochromatic light in frequency modulation, with high absorption, At minority carriers diffusion coefficient resonance frequency, a graphical study of the expressions of recombination velocity on the rear side is carried out. The optimum thickness of the base of the bifacial solar cell is deduced for each resonance frequency.

In this paper, an inequality satisfied by the vacuum energy density of the universe is derived using an indirect and heuristic procedure. The derivation is based on a proposed thought experiment, according to which an electron is accelerated to a constant and relativistic speed at a distance L from a perfectly conducting plane. The charge of the electron is represented by a spherical charge distribution located within the Compton wavelength of the electron. Subsequently, the electron is incident on the perfect conductor giving rise to transition radiation. The energy associated with the transition radiation depends on the parameter L. It is shown that an inequality satisfied by the vacuum energy density will emerge when the length L is pushed to cosmological dimensions and the product of the radiated energy and the time duration of emission are constrained by Heisenberg's uncertainty principle. The inequality derived is given by 9 3

In further discussion on the Maxwell-Lorentz equations in Dirac’s symmetrisation, I introduce the concept of magnetic monopole as an “act of electric current” in the 2nd equation (i.e. the analog of the “act of movement” in Classical Mechanics), I postulate a “magnetic displacement current” and a “magnetomotive force” in the 3rd and 4th equations, respectively (i.e. the analogs of the “electric displacement current” and of the “electromotive force” in the 4th and 3rd equations, respectively). As a consequence, I propose a generalised vision of the Electromagnetism in which inhomogeneous, microscopic, and relativistically linked equations describe the static and the oscillatory phenomena. Then, in the frame of Relativity, I propose analog microscopic equations to study the Gravitation and the Space-Time in terms of static and oscillatory phenomena: the static equations show the sources of newly defined vector fields (the generalised mass density as the source of the generalised mass field, the generalised time density as the source of the generalised space field, respectively), whereas the oscillatory equations describe the propagation of the gravitational waves and of the spatiotemporal waves, respectively. In other words, I propose to unify Electromagnetism, Gravitation, and Space-Time in terms of microscopic Maxwell-Lorentz-like equations in Dirac’s symmetrisation, where the unifying trait is c. Finally, using the concepts of the proposed generalised Electromagnetism, I discuss the conservation in Electromagnetism and the interaction between matter and electromagnetic waves.

A composite accelerating cavity utilizing a resonant, periodic structure with a dielectric sphere located at a spherical conducting cavity center is presented. The resonator design is of the whispering gallery type to take advantage of the excellent electromagnetic field confinement offered by this geometry. The maximum electromagnetic fields of this structure exceed by several orders of magnitude the values reached in resonant cavities of typical linear accelerators. And the skin current losses are reduced without engaging superconductivity and cryogenic systems for this new construction. Especially because all field components at the metallic wall are either zero or very small in this proposed spherical cavity, one can expect the cavity to be less prone to electrical breakdowns than the traditional cavity. In this paper, the new type of accelerating structure was analyzed and calculated. The results are in very well agreement with the corresponding values simulated by CST. And for the existing ultra-low loss dielectrics, Q can be three orders of magnitude better than obtained in existing cylindrical cavities.

Curved coils constructed by flexible printed circuit board (PCB) or hand-wound Litz-wire have been steadily becoming popular due to its applicable potential on devices that have a curved body. Inductive Power Transfer (IPT) systems based on curved coils and flexible ferrite sheets may provide more flexible charging solutions for various electronic devices such as rice cookers and robot vacuum cleaners. Power repeaters are also used in IPT systems to extend wireless charging range by guiding magnetic fields to the receiving coil. The interaction of these three topics could be inspiring. In this paper, two adjustable power repeaters are applied to an IPT charging system with various curved receiving coils designed for vacuum cleaners. Two power repeaters share the identical structure as the Tx coil and could be rotated to mirror symmetrically. The input and output power are calculated by analyzing the equivalent circuit model. The self-inductance, mutual inductance, and coupling coefficient of the proposed system are obtained via finite element method simulation with variable rotating angles. Three typical IPT designs have also been simulated in ANSYS Maxwell and compared with the proposed magnetic design. The comparison indicates the enhancing feature of the passive power repeaters on coupling performance and the ability to guide the magnetic flux for better magnetic field coupling. Furthermore, two types of co-simulations defined by the power source via Simplorer are conducted to explore how much power could be transferred. The tuned system is shown to be able to provide about 32 W under 100 kHz operating frequency for charging the battery of a robot vacuum cleaner. The results from theoretical calculation and simulation align well with each other.