Electromagnetic Response Characteristics Research Articles

Propagation of ELF Electromagnetic Waves Over a Curved Stratified Ground and its Application in Geophysical Prospecting

Electromagnetic waves radiated by a vertical electric dipole related to deep resource exploration are discussed. According to the tangential components of the field are continuous on the element interface, the spherical harmonic series expression of extremely low-frequency (ELF) electromagnetic waves in the “earth -ionosphere” model is derived, in which the earth is regarded as a curved stratified ground. The Schumann resonance serves to verify the correctness and reliability of the formula and algorithm. And our method is compared with the traditional large-scale electromagnetic method. The forward response curves of the two methods are in good agreement on the ELF band. By comparison, we can find that our method performs best when the distance between the transmitting source and receiving point is greater than 500km. To estimate the effects on the electromagnetic waves associated with resource exploration, we first discussed the ability of our method to identify formations, and then discussed the electromagnetic response characteristics of the earth as two-layer and three-layer models, which are sufficient to show the basic characteristics of the electromagnetic field in the “earth-ionosphere”. The results show that, as an emerging large-scale exploration method, the wireless electromagnetic method can be well used to detect the deep underground electrical structures.

Linear-to-Circular Polarization Converters With Both E-Field and H-Field Hybrid Responses

This article presents a novel method to design a linear-to-circular polarization converter (LCPC) by using a hybrid array structure, which is composed of meander lines and the split ring resonators (SRRs). The LCPC can respond to both the $E$ -Field and $H$ -Field for the incident wave. When the meander line and the SRR are placed along two orthogonal directions, the composed unit cell would have different electromagnetic response characteristics in the two orthogonal directions. Using this method, two LCPCs working in frequency bands of 6–18 and 2–6 GHz are designed, respectively. The simulated results show that for the LCPC working in 6–18 GHz, the axial ratio (AR) is lower than 3 dB in 6.8–17.32 GHz with a maximum insertion loss (IL) of 1.25 dB. When the angle of incident wave is less than 45°, the 3 dB AR bandwidth is 7.87 GHz. For the LCPC working in 2–6 GHz, the AR of entire frequency band is all lower than 3 dB and the maximum IL is 0.82 dB when the incident angle increases to 15°. Even at incident angle of 45°, the bandwidth with the function of polarization conversion is 3.5 GHz. Experiments on the LCPC (6-18 GHz) are carried out, and the measured results are in agreement with the simulated ones, which proves that the LCPCs design method proposed in this paper is effective and reliable.

Design and Analysis of HTS Rotor-Field Coils of a 10-MW-Class HTS Generator Considering Various Electric Insulation Techniques

This paper presents the results of an electromagnetic design and numerical analysis conducted on a 10-MW-class second-generation high-temperature superconducting generator (2G HTSG) used in an offshore wind power turbine. To report the operation reliability of 10-MW-class HTSGs employed in offshore environment, various electric insulation techniques (EITs) for HTS field coils (FCs), such as no-insulation, metal insulation, and metal-insulator transition insulation, are considered in this study. Using the time-transient solver of the three-dimensional (3D) electromagnetic finite element analysis (FEA), we investigated the electromagnetic characteristics of the HTSG with the three EITs in terms of the electrical output of the HTSG and the critical current of the FCs. To analyze the charging characteristic of the HTS FCs with the three EITs in steady-state operation as well as the electrical in transient-state operation, electric equivalent circuit models are built with key parameters based on the electromagnetic FEA results. Finally, the performances of the HTS FCs are discussed and evaluated in terms of the electromagnetic response and stability characteristics.

Vehicle-Borne Transient Electromagnetic Numerical Characteristic Parameter of Water-Bearing Body behind Tunnel Linings

The water-bearing body (WBB) behind tunnel linings has been some of the main causes of damage in operational tunnels. The WBB directly affects the serviceability state of tunnel linings; thus, determining a method to detect this problem is a widely studied issue regarding tunnel maintenance. In this paper, a vehicle-borne transient electromagnetic method (VBTEM) is put forward for the first time to detect WBB behind tunnel linings, and the aim is to fully investigate the transient electromagnetic response and numerical characteristics of the WBB behind tunnel linings. Firstly, the transient electromagnetic response curves of the WBB and surrounding rock are obtained and compared in detail by using the finite element method. Then, taking the distance, thickness, radius, and resistivity of the WBB as variable parameters, the parametric sensitivity rule of the response curve of the WBB is analyzed. Finally, a dimensionless response curve is proposed, a mathematical extraction equation is established, and seven numerical characteristic parameters are proposed and extracted. Based on seven numerical characteristic parameters, the technical parameters of the VBTEM equipment are put forward. The results illustrate that the transient electromagnetic response of the WBB is obviously different from that of surrounding rock. The seven numerical characteristic parameters of the dimensionless curve of the WBB can represent the entire response curve of the WBB. The results reveal that the first time gate of the VBTEM equipment needs to be less than 0.05 μs for short-distance problem, and the time span needs to reach four time spans at least. The research results can provide valuable technical references for the application of VBTEM.

Electromagnetic Response Characteristics Research on Mine Different Geological Body

A large number of experimental research of the mine transient electromagnetic method was used to collect typical geological anomaly experience card cases in Jin Cheng mine, such as structure, mined-out area etc. In order to achieve fine detection to geologic abnormal body, some card cases were analyzed by the electromagnetic response multi-parameter curves to identify electromagnetic response characteristics of different geologic abnormal body; Another card cases were showed all kinds of the visualization figures distinguished easily to distribution and characteristics of explain geologic abnormal body, such as structure, the mine mined-out area and contains water etc. The results show that: if there was the overall relatively low potential value, high apparent resistivity value, and the potential and apparent resistivity curves appeared to jump ups and downs, it was the typical electrical identification characteristics of no water bearing structure or goaf; If there was the overall relatively high potential value, low apparent resistivity value, and potential and apparent resistivity curve was smooth attenuation, and the inversion depth was smaller than the normal strata, it was a typical electrical characteristics of water bearing structure or goaf.

A Time-Domain Thin Dielectric Sheet (TD-TDS) Integral Equation Method for Scattering Characteristics of Tunable Graphene

A time-domain thin dielectric sheet (TD-TDS) integral equation method is presented to analyze the transient scattering of thin graphene films with the electrostatic bias. In this method, the volume integral of the time-domain volume integral equation is transformed to surface integral to reduce the scale of calculation. In this method, the Rao–Wilson–Glisson basis function and the pulse functions are employed as a spatial basis function while the fourth-order Lagrangian basis functions are employed as temporal basis functions. The main advantages of the TD-TDS method are: 1) this method provides a new way for the simulation of graphene device; 2) only the surfaces of the targets need to be meshed when the targets are modeled as surfaces instead of volumes. As a result, the computational resources and time are greatly reduced; 3) broadband electromagnetic response characteristics can be obtained only after one time computation; and 4) this TD-TDS method is suitable for analyzing the dispersive dielectric material whose permittivity is a Drude model with a time convolution operation. Numerical examples are demonstrated to show the accuracy and efficiency of the TD-TDS method.

Skin Effects of Induced Eddy in Lossy Layered Stratum

The study of induced eddy skin effects plays an important role to determine the reservoir distribution. This paper calculated the apparent conductivity of loss stratum by the use of geometrical factor theory and skin effects theory. The numerical results show that the skin effect theory has higher accuracy due to the consideration of the interaction between the induced eddy currents. And it is also easy to spread in use of inhomogeneous media. These conclusions provide a theoretical basis for the analysis of electromagnetic response characteristics in lossy multilayered stratum.

Metamateriales: principales características y aplicaciones

Las propiedades electromagnéticas de todos los materiales existentes en la naturaleza pueden ser determinadas a partir dos parámetros: la permeabilidad magnética µ y la permitividad eléctrica ε. Estos dos parámetros caracterizan la respuesta del material cuando interactúa con la radiación electromagnética. En principio, no existe límite alguno para el rango de valores posibles que pueden tomar µ y ε, por lo cual podemos pensar en diseñar y construir a voluntad materiales con características de respuesta electromagnética especificas (es decir µ y ε) no encontradas en la naturaleza. Estos materiales fabricados en el laboratorio reciben el nombre genérico de metamateriales, y entre ellos se encuentran los conocidos por sus siglas en ingles LHM (Left Handed Materials), así llamados porque los vectores de campo , de las Ondas Electromagnéticas que viajan en su interior están relacionados por la regla de la mano izquierda. La característica distintiva de los LHM es que para ciertas bandas de frecuencia presentan índice de refracción negativo ( ) con modos propagativos posibles solamente si ambos parámetros µ y ε, dentro de dichas bandas de frecuencias son negativos. El propósito de este trabajo es presentar los principios y fundamentos de estos metamateriales de manera que despierte el interés de lectores no especializados. © 2016. Acad. Colomb. Cienc. Ex. Fis. Nat.<div id="spoon-plugin-kncgbdglledmjmpnikebkagnchfdehbm-2" style="display: none;"> </div>

Multi-Physical Fields Coupling Simulation and Performances Analysis of a Novel Heated-Tip Injector

A novel heated-tip multihole spark-ignition direct-injection injector was designed and manufactured to investigate its coupling mechanism of the multiphysical fields and comprehensive performances. The coupling relationship and formation among the electromagnetic, thermal, fluid flow, and spray fields was analyzed based on coupling theories. A data information interface platform was established based on the commercial software, which was used to explore how the key parameters impact the novel spark-ignition direct-injection injector. According to the relationship among the different physical fields, coupling models were established based on the finite element method, and the comprehensive performances of the spark-ignition direct-injection injector were analyzed systematically. Systematic experiments were used to validate and verify the coupling mechanism and the accuracy of the simulation model. The comparisons of the conventional spark-ignition direct-injection injector and novel heated-tip multihole injector indicated that the novel heated-tip spark-ignition direct-injection injector has the ability to heat the fuel to a high temperature in a short time. The high temperature is the key factor that changes the electromagnetic characteristics, dynamic response, cavitation structure, and spray characteristics.

3503 リアクトルコアの磁場と構造の連成解析による最適防振設計(OS3-8 設計と最適化VIII)

This paper proposes optimal vibration-proof design of reactor core based on coupled analysis of magnetics and harmonic response. A reactor is a part of the in-vehicle DC-DC converter to boost the electric voltage, and it is composed of cores, coils, and so on. Because of electromagnetic and harmonic response characteristics of the reactor, the reactor core vibrates when the reactor core is in use, and as a result, noises are generated. To reduce these noises, a topology optimization method for reactor core design is proposed in this paper. Here, the main difficulty is to compute the electromagnetic force appropriately. Roughly speaking, standard topology optimization methods, such as density based methods, are not suitable to compute the electromagnetic force because grayscale elements smear out the structural boundary in which the electromagnetic force is imposed. Therefore, in this paper, boundary tracking type level-set based topology optimization is used where grayscale elements can be suppressed completely. Thanks to this grayscale-free topology optimization, the coupled analysis of magnetics and harmonic response is successfully performed, and as a result, topology optimization of the reactor core for reducing the noises is realized. The usefulness of the proposed method is confirmed using some numerical examples.

Parameter Response Numerical Simulation of Resistivity LWD Instrument Based on Hp-FEM

Numerical simulation of electrical logging is important to the electrical logging instrument design and logging data interpretation and application. In this paper, we combine the hp finite element method (hp-FEM) analysis software HERMES and VC++ development platform as a tool to direct reflect the instrument drilling detection and distribution of induced electric field in the formation and it's boundary, and the instrument parameter response by changing spacing, transmitting frequency and excitation current intensity have been studied based on self-adaptive hp-FEM algorithm. Because the performance of resistivity LWD instrument have decided by design parameters, thus study the electromagnetic response characteristics of resistivity LWD instrument has important significance to guide the high precision resistivity LWD instrument develop and improve the security of logging operation.

The Transient Electromagnetic Response Characteristics of Unfavorable Geological Bodies in Tunnels

A numerical model of Transient Electromagnetic Methods, which used to detect geological conditions in tunnels, was created by ANSYS finite element software, and the transient electromagnetic response characteristics of typical unfavorable geological bodies were discussed. The results indicate that the apparent resistivity isoline almost outputs in straight structure, and augments equably with the depth increasing when no unfavorable geological body is in front of the tunnel workface. The apparent resistivity isoline obviously reduces when water-rich karst cave, fault, or fracture exist in the front of the tunnel workface, where water-rich karst cave exists, the apparent resistivity isoline becomes close together, and there is to be an ordered pyramid resistivity-reduced area which can be an evidence of rich water fault. However, it will increase when dry fault or karst cave exist, and the high resistivity area corresponding to dry cave shows some triangles, but this phenomena is hard identified, which need detail analyses according to hydrogeologic data.

The Electromagnetic Response of Multiple Cylindrically Curved Thin Screens Excited by a Line Electric Current Source

A generalized mathematical procedure is presented for investigating the electromagnetic response characteristics of multiple cylindrically curved thin screens excited by a line electric current source, and the mathematical treatment is based on the direct integral equation technique combined with Galerkin's procedure. Both the near- and the far-zone field solutions to such a multiple coupling system are obtained in an analytical form, and the induced electric currents on the curved thin screens are expanded in terms of a series of Chebyshev polynomials of the first kind. Furthermore, parametric studies are performed to show the variation of the penetrated near-zone and scattered far-zone fields of some typical cylindrically curved thin screens.

INDUCED CURRENT DISTRIBUTION IN A CONDUCTIVE TWO‐LAYER SPHERICAL BODY

Under complex geologic situations the analysis of induced current distribution, rather than of the scattered field, may provide a useful physical insight into the electromagnetic response characteristics of a conducting ore body. Influence of a conducting cover and inhomogeneity in the conductivity on the currents induced in aspherical conductor excited by a uniform alternating magnetic field has, therefore, been investigated. The analysis shows (a) reduction of the current‐density amplitudes in the core by the cover, (b) occurrence of current‐density maxima inside the conducting system for some characteristic frequencies, (c) enhancement of the in‐phase component in some cases, and (d) reduction of current‐density in the shell with increase in the core conductivity and significant influence of the inhomogeneity in conductivity at low frequencies. Since there is a direct correspondence between the electromagnetic response of a target and the currents induced in it, these results are expected to aid in the interpretation of data over ore deposits having a halo‐zone of disseminated mineralization.

Turam response of a permeable inhomogeneous cylindrical conductor surrounded by a thin shell

Electromagnetic response characteristics of an inhomogeneous permeable cylinder surrounded by a thin insulated concentric dissipative shell is obtained in presence of a line-source of current. The 3-layer boundary value problem is solved by assuming the thickness of the shell to be much smaller than the skin-depth in the shell. Numerically computed results are presented in the form of argand diagrams to examine the influence of the shell parameters (conductivity and its proximity with the core) and magnetic contrast. The multi-frequency response of the system is also given which resolves the two conducting layers and analyzes the frequency dependence of screening behavior of the shell.