Shielding Effectiveness Of Enclosure Research Articles

An Analytical Evaluation of the Shielding Effectiveness of Enclosures Containing Complex Apertures

Analytical methods are significantly useful tools for engineers in computational modeling. These methods provide fast simulations, while preserving physical meaning. In this paper, a full analytical formulation is developed based on the circuit approach, also known as Intermediate Level Circuit Model (ILCM), to evaluate the shielding effectiveness (SE) of metallic structures. The proposal focuses on rectangular enclosures containing apertures of complex geometrical shape, illuminated by an external plane wave. The enclosure is taken as a short-circuited waveguide. The aperture is treated as a transmission line with an intrinsic impedance that depends on the aperture polarizability, according to Bethe’s theory of small holes. The formulation easily takes into account high-order resonant modes and different apertures, such as circular, elliptical, round-ended and cross-shaped apertures. The ILCM technique reveals good agreement with a numerical full-wave method for various configurations of enclosures, covering a large range of frequencies from 0.5 GHz to 2.5 GHz, thus offering perspectives for parametric and/or optimization SE studies.

Analytical Model for Evaluating Shielding Effectiveness of an Enclosure Populated With Conducting Plates

An analytical model is proposed for evaluating shielding effectiveness (SE) of a rectangular enclosure populated with conducting plates. The conducting plates are considered as capacitive diaphragms that fill the width of the enclosure, and SE is calculated using the equivalent circuit of the enclosure. The letter presents an improved approach to evaluating enclosures populated with printed circuit boards (PCBs) or plates coated with a composite or radar-absorbing material. The evaluation of the model error was performed when the plate height changed. Both this model and finite element method were used to calculate the SE for enclosures populated with conducting plates, PCBs and the plate coated with a magnetic composite material. The results obtained in the range up to 1 GHz are in good agreement.

Study the Effect of Different Parameters and Improving the Shielding Effectiveness of a Metallic Enclosure with Extra Wall

This paper propose a new method for improving shielding effectiveness (SE) of a rectangular enclosure with multiple circular apertures. In this method in order to compensate the effects of the apertures on (SE) parameter, we use two metallic walls each containing apertures instead of the one wall. By using two walls for shielding an enclosure, the shielding effectiveness of the enclosure will improve. The numerical simulation uses a symmetric condensed node of TLM – TD (Transmission line Modeling Method – Time Domain) and subsequent Fourier Transform and the result was verified by HFSS and CST software. We obtain the shielding effectiveness response to an electric field impulsive excitation. It is shown that field polarization and enclosure direction has a noticeable effect on SE that should be considered in SE calculations. The effect of different parameters and improving the shielding effectiveness of a metallic enclosure with extra wall is studied. An optimization of the influence of the place of apertures in the walls and the diameter of circles on two walls is presented.

Method for Shielding Effectiveness of Enclosure with Apertures Including High-order Mode

Method for Shielding Effectiveness of Enclosure with Apertures Including High-order Mode

An Efficient Approach for Analyzing Shielding Effectiveness of Enclosure With Connected Accessory Based on Equivalent Dipole Modeling

The analysis of the enclosure's shielding effectiveness (SE) is an important work in the electronic device's electromagnetic compatibility problem. Almost all devices cannot work without connected accessory including cables and electronic connectors. Except for apertures and seams on the enclosure, the connected accessory is also a leakage path for electromagnetic power. For the SE problem of enclosure with connected accessory, a hybrid numerical analysis method of the partial element equivalent circuit (PEEC) and the method of moment (MoM) are proposed. PEEC is used to model the connected accessory. Based on energy conservation, the cable-connector is replaced by an equivalent dipole that has similar electromagnetic radiation properties. The equivalent dipole is added to the model of enclosure, which is analyzed by the MoM. Two experiments are presented to verify the proposed hybrid approach. The test results are in good agreement with the simulated results. This hybrid method not only could be used to calculate the SE of the cable-enclosure system, but also has the potentiality to apply to the signal integrity of printed circuit boards in enclosures.

Magnetic Shielding Effectiveness of Enclosures in Near Field at Low Frequency for Automotive Applications

In this paper, a modeling methodology is presented in order to calculate the magnetic shielding effectiveness at low frequency in the near field of enclosures with a slot. The so-called hybrid approach combining analytical and numerical methods is developed and validated experimentally. The application concerns an enclosure with a slot for electric and hybrid vehicles. The developed technique allows finding the order of magnitude of radiated fields for electromagnetic compatibility design in a very short time.

A New Methodology to Predict the Magnetic Shielding Effectiveness of Enclosures at Low Frequency in the Near Field

In this paper, a methodology to calculate the shielding effectiveness of enclosures with slots at low frequency in the near magnetic field is presented. This modeling technique is based on the magnetic moments and the transmission line approach and makes specific assumptions. It is applied to a slot of small size relative to the dimensions of the enclosure. The slot is electrically short. This technique is validated in the case of a real enclosure with numerical simulations and experimental data. This method is dedicated to the case of mechatronics boxes using in electric and hybrid vehicles, it allows obtaining the results with sufficient accuracy precision for dimensioning a magnetic shielding in a short time.

Numerical calculation of shielding effectiveness of enclosure with apertures based on EM field coupling with wire structures

Shielding effectiveness of a protective metal enclosure with apertures and receiving antenna placed inside is numerically considered. The purpose of the antenna, here considered as a dipole, is to detect the electromagnetic (EM) field level within the enclosure and to transfer this information via a coaxial cable to a network analyzer. This follows the experimental procedure used to measure the shielding effectiveness of enclosure. A numerical model, based on the Transmission-Line Matrix (TLM) method enhanced with so-called wire node, is used to simulate this dipole antenna/cable arrangement in order to investigate how much it disturbs the level of shielding effectiveness due to their two-way coupling with EM field inside the enclosure. The numerical model, whose accuracy is proved by comparison with experimental results available in the literature, is used to consider the influence of radius and length of the dipole-receiving antenna and the impact of cable presence on the distribution of EM field inside the enclosure and shift of resonant frequencies for normal and oblique incidence.

Validation of a measurement method for magnetic shielding effectiveness of a wire mesh enclosure with comparison to an analytical model

Abstract. This paper deals with the validation of a measurement method for determining the magnetic shielding effectiveness of a wire mesh enclosure in the frequency range from 10 kHz to 150 kHz. The comparison with an analytical model (parallel-plate-shield, see Kaden, 1959) for magnetic shielding effectiveness of wire mesh is also part of this contribution. To measure the shielding effectiveness of an enclosure in general, two steps are necessary: 1. Reference measurement of the incident electro-magnetic field. 2. Measurement of the incident electro-magnetic field in the enclosure by same conditions. This method presented in the contribution uses a Helmholtz coil as magnetic field source, controlled by a signal generator and an amplifier in voltage mode. At first, a field meter was used to measure the frequency dependent magnetic field in the center of the Helmholtz coil. The magnetic field strength was also analytically calculated and compared to the measurement results. The next step was to measure the induction voltage caused by the magnetic field with a magnetic field probe, which was later used for the measurements of the shielding effectiveness either. A signal amplifier was needed to raise the signal-to-noise-ratio (SNR). The gain of the signal amplifier was also determined and measured. Two positions of the enclosure in the Helmholtz coil were considered, horizontal and vertical. The vertical position of the enclosure approaches the analytical model of Kaden (1959) closely and the results show a good match with the analytical model.

Study on the Shielding Effectiveness of a Metallic Rectangular Enclosure with Four Square Apertures having Different Position Arrays

In this paper, electric field shielding effectiveness (SE) of rectangular enclosure with four apertures illuminated by vertical polarization plane wave has been studied by using modal method of moment technique. Electric field SE of enclosure with four square apertures has been calculated at three different points on the same plane inside enclosure. The numerical results of the proposed technique are in very good agreement with data available in the literature and experimental results. It is shown that apertures’ position and aperture’ number have noticeable effect on the electric field SE.

TLM modelling of receiving dipole antenna impact on shielding effectiveness of enclosure

Impact of receiving dipole antenna on shielding effectiveness of metallic enclosure is numerically considered in this paper. Transmission line matrix (TLM) method enhanced with compact wire model is used to efficiently describe the dipole antenna presence and its coupling with electromagnetic field inside enclosure. By using the presented numerical model, influence of receiving antenna on enclosure shielding effectiveness is demonstrated on several examples through comparison with the numerical and analytical approaches in which the antenna presence is neglected.

A Novel and Efficient Technique for Improving Shielding Effectiveness of a Rectangular Enclosure using Optimized Aperture Load

An efficient and practical method to enhance the shielding effectiveness of a rectangular enclosure with aperture against electromagnetic interferences is presented. In this paper an extra aperture as a matched load instead of a shorted waveguide has been proposed. Transmission line matrix method was used for simulation the rectangular enclosure under electromagnetic plane waves and the result was verified by analytical method and CST software. A complete range of simulations were performed to find the optimum size for second aperture. The proposed method resulted in a very good improving of shielding effectiveness of enclosure especially in resonant frequency.DOI: http://dx.doi.org/10.5755/j01.eee.18.10.3071

An improved model of Robinson equivalent circuit analytical model

The Robinson equivalent circuit analytical model can be used only in calculating shielding effectiveness of enclosure with the same multi-holes in one wall, but cannot be used in different multi-holes in two walls. According to the practical requirement, this article uses Konefal’s and Farhana’s characteristic impedance of apertures to improve the equivalent circuit analytical model in different multi-holes in two walls. The improved equivalent circuit analytical model is more useful than Robinson equivalent circuit analytical model. In the article, all kinds of enclosures are simulated by TLM (Transmission-Line Matrix method) to prove that this improved model is feasible in multimode.

Time-Domain Investigation on Cable-Induced Transient Coupling Into Metallic Enclosures

A hybrid time-domain method is proposed for characterizing electromagnetic interference (EMI) signals coupled into some composite structures with metallic enclosures, braided shielded cable, printed circuit boards, and even lumped active devices. In order to rapidly capture the induced interior EMI, the finite-difference time-domain, modified node analysis, and multiconductor transmission lines methods are combined together and implemented successfully. Numerical investigation is carried out to demonstrate the frequency-dependent transfer impedance of the coaxial cable, the induced voltage at the place of active loaded element in the transmission line network, and the enclosure shielding effectiveness of these composite enclosures. The captured transient response information is useful for further designing electromagnetic protection of the inner circuits against the impact of voltage or current surge caused by nonintentional as well as intentional electromagnetic interference.

Accurate Analysis of Reverberation Field Penetration Into an Equipment-Level Enclosure

The paper focuses on the reverberation chamber method for the shielding properties evaluation of equipment-level enclosures. The enclosure under test is numerically modeled by an in-house finite-difference time-domain code that is able to predict the field inside the enclosure and the voltage captured by the probe placed inside it. The chamber fields have been modeled by applying the plane-wave superposition. The code is validated by measurements in our reverberation chamber. Subsequently, the effect of probe positioning and length on the induced voltage is analyzed. Finally, the enclosure shielding effectiveness is evaluated by applying two different definitions, and a statistical analysis is carried out, thus allowing an estimation of the measurement uncertainty.

On the Shielding Effectiveness of Enclosures

This paper deals with new definitions of shielding effectiveness, in particular for high-frequency and transient electromagnetic fields. They are practicable and supposed to better characterize the shielding ability than the commonly used definitions. From the ratio of the time-averaged input power of the unshielded load to that one of the shielded load, in the limiting case of a vanishing load the electromagnetic shielding effectiveness is derived. This is a simple combination of the commonly used and easily measurable electric and magnetic shielding effectiveness. A similar procedure is then employed for the transient case, where in the limiting case of a vanishing load the ratio of the absorbed energies turn into the transient shielding effectiveness. Numerical results are shown for closed as well as for nonclosed cylindrical shields.

Low-Frequency Shielding Effectiveness of Nonuniform Enclosures

This paper presents a quasi-static approximate solution to the magnetic shielding of several nonuniform enclosures using the integral form of Maxwell's equations and insight gained from other approaches. The solution is called quasi-static as the assumptions made are from physical arguments based on low-frequency cases where the enclosure size is much less than a wavelength. The integral form of Maxwell's equations is used to obtain a first order correction to the static solution to obtain induced currents in the time-varying case. A cylindrical shell immersed in an axial magnetic field is used to illustrate the method, which is then extended to derive a formula for a similarly excited rectangular enclosure. These shields are seen to behave like a low-pass filter. Although the enclosure dimensions are small compared to the wavelength, the skin depth effects in the walls cannot be neglected even for relatively thin material as usually encountered in an enclosure. These skin effects are included in the analysis and experimental checks performed on a variety of enclosure sizes and materials, excited by a Helmholtz coil show agreement within two decibels over the 4-octave frequency range examined. No one can say whether this method offers a better solution to the shielding problem, as all solutions are approximate, but the author attempts to present an alternative formulation that aids in understanding the physical processes involved in the shielding effectiveness of an enclosure and fills some of the gaps between the plane-wave analysis and circuit approaches presently used.