Leonardo Sandrolini

Modelling the electrical properties of concrete for shielding effectiveness prediction

Concrete is a porous, heterogeneous material whose abundant use in numerous applications demands a detailed understanding of its electrical properties. Besides experimental measurements, material theoretical models can be useful to investigate its behaviour with respect to frequency, moisture content or other factors. These models can be used in electromagnetic compatibility (EMC) to predict the shielding effectiveness of a concrete structure against external electromagnetic waves. This paper presents the development of a dispersive material model for concrete out of experimental measurement data to take account of the frequency dependence of concretes electrical properties. The model is implemented into a numerical simulator and compared with the classical transmission-line approach in shielding effectiveness calculations of simple concrete walls of different moisture content. The comparative results show good agreement in all cases; a possible relation between shielding effectiveness and the electrical properties of concrete and the limits of the proposed model are discussed.

Modelling shielding properties of concrete

Concrete is a porous, heterogeneous material whose abundant use in numerous applications demands a detailed understanding of its properties. Besides experimental measurements, mathematical models can be useful to investigate its behaviour with respect to frequency, moisture content or other agents. These models can be used in EMC to predict the shielding effectiveness of a concrete structure against external electromagnetic waves. This paper presents a comparison between an analytical approach that relies on measurements, and numerical simulations that make use of dispersion models. The comparative results demonstrate that the analytical approach, which is more computationally efficient than numerical solvers, can be used to predict the shielding effectiveness of concrete structures

Estimation of Stray Current From a DC-Electrified Railway and Impressed Potential on a Buried Pipe

DC-electrified traction systems are a potential source of stray current that may corrode internal and external structures and installations. The stray current intensity depends on several factors (traction current, rail insulation, concrete mat and piers resistance), that are accounted for in the proposed model. The case of a viaduct and a victim-buried pipeline is considered in detail, and the estimated impressed voltage on the pipe is compared successfully with experimental results.

Transform method for calculating low-frequency shielding effectiveness of planar linear multilayered shields

A two-dimensional analytical solution for quasistatic magnetic field shielding with planar infinite multilayered shields is presented. The magnetic field source is a system of long straight wires parallel to the shield, carrying sinusoidal currents. The analysis assumes that material media can be considered linear under the applied source fields. The spatial Fourier cosine and sine transforms are applied to the analytical expressions of the magnetic field intensity and flux density is obtained by solving the diffusion equation in each layer. Using transfer relations for every layer in terms of transformed variables allows one to obtain the shielded field, and thus the shielding effectiveness, with no need to determine the integration functions explicitly. The results obtained with both this approach and a finite-element computer code are in good agreement. The method seems to be also suited for the analysis of problems with more complex geometries and source distributions.

Equivalent circuit characterization of resonant magnetic coupling for wireless transmission of electrical energy

This paper provides the accurate characterization of a wireless power transfer system consisting of two resonant air-core coils mutually coupled in free space. The lumped-circuit parameters of the equivalent circuit are determined with analytical formulas taken from the literature and validated by comparison with numerical simulations with a finite-element computer code and with experiments. The parameters are determined taking as input only the geometry of the system (coil size and mutual distance, conductor radius, and turn distance) and the frequency. Once the lumped-circuit parameters are known with good accuracy, the assessment of the power transfer system can be carried out by evaluating the current and voltage gains and efficiency for different system geometries, operating frequencies and load conditions. The Scilab programming environment was used to perform all the calculations. The characterization presented in this paper can then be considered as an effective tool in designing an efficient wireless power system. Copyright

Shielding effectiveness of concrete buildings

The prediction of the shielding effectiveness of concrete structures is a fundamental aspect of the architectural design phase of purpose built control centres. These buildings designed with a functional requirement to house sensitive control equipment; malfunction of such equipment may lead to loss of life and impact on revenue service. In this paper, a simple analytical approach is proposed to influence the design of buildings such that the structure provides adequate attenuation to hostile electromagnetic ambient and potential electromagnetic pulses. Comparison with numerical methods is provided. The effect of moisture content on the shielding effectiveness of a concrete wall is outlined.

Shielding properties of conductive concrete against transient electromagnetic disturbances

This paper studies the shielding properties of conductive concrete, when exposed to a transient electromagnetic pulse in the form of a uniform plane wave. The conductive concrete under investigation is a cementious composite having a low volume concentration of steel fibres included in the cement mix. It is shown that the real and imaginary parts of the complex relative permittivity and the conductivity of the conductive concrete are higher than those obtained from an undoped concrete up to approximately 2 GHz. However, it is equally shown for the case investigated that the increases in the real part of the complex relative permittivity and in the conductivity do not translate into significant increases in the ability of conductive concrete to attenuate electromagnetic disturbances.

Experimental verification of predicted electromagnetic fields radiated by straight interconnect cables carrying high-frequency currents

This paper provides an experimental verification of analytical expressions for predicting radiated electromagnetic fields from straight interconnect cables carrying high-frequency currents. These analytical expressions are derived through two different models. The former model is based on the assumption that a radiating two-wire transmission line can be considered as two Hertzian dipoles, while in the latter one each radiating wire is treated as a chain of short radiating dipoles. The radiated field is calculated and measured at selected locations and the results are compared in order to verify the agreement among them. Different configurations (two parallel cables at various distances from a conducting ground plane) are considered.

Evaluation of Stray Current From a DC-Electrified Railway With Integrated Electric–Electromechanical Modeling and Traffic Simulation

Leakage currents from a dc-electrified railway requires careful consideration throughout the life time of the railway. The design objective is to minimize the current leakage from the railway return path (the running rails for a dc-electrified railway, with possibly additional conductors in parallel for ac-electrified systems). For this objective to be met, the design needs to account for foreseeable misuse during the construction phase (i.e., the lack of independence between the earthing system and the stray current collection system, due to space and construction exigencies in a viaduct) and degradation of insulation due to ageing and poor maintenance. Perhaps, more importantly, other influences, such as the train characteristics, time tabling, headway, multiple train movement, etc., need consideration to determine the worst case leakage current and, thus, the ability to define appropriate mitigations with respect to stray current management. In this paper, we describe the implementation of an integrated model for the assessment of stray current for a dc-electrified railway, in which these factors are considered. We provide an analysis of the stray current magnitude under worst case train operating conditions (i.e., multiple trains with a 90-s headway accelerating) and highlight factors that determine the efficiency of the stray current collection system. The integrated model presented enables a detailed assessment of all factors impacting the stray current magnitude, as well as an assessment of the overall performance of the stray current collection system.

ANALYTICAL CALCULATION OF THE INDUCTANCE OF PLANAR ZIG-ZAG SPIRAL INDUCTORS

An analytical procedure for the calculation of the inductance of planar zig-zag spiral inductors is proposed. The procedure is based on the partial inductance concept and models the inductor as a series of a number of parts. The self-inductance of each individual part, which has the shape of a parallelogram, and the mutual inductance between any two parts of the inductor are determined. The inductance of a planar zig-zag spiral inductor can thus be obtained for any width, length and angle of the saw-tooth conflguration. The procedure is validated with experimental measurements; the agreement between estimated and measured inductances is very good.