Estimation Of Shielding Effectiveness Research Articles

A hybrid method for shielding effectiveness estimation of a perforated enclosure against planewave excitation

ABSTRACTThis paper develops a hybrid model based on the combination of full-wave simulation method and circuit model analytic algorithm, which can predict the shielding effectiveness of a perforated rectangular enclosure irradiated by a planewave with arbitrary incident and polarization direction. In order to take the effect of the electromagnetic losses of the aperture into account, the full-wave simulation method is adopted to calculate the coupling voltage of the aperture. The circular aperture or rectangular aperture with arbitrary length–width ratio can be positioned anywhere in the front panel of the enclosure. Taking the effect of the thickness into account, we establish the equivalent circuit model of the perforated enclosure with aperture coupling voltage as an equivalent voltage source. Then, the TEmn and TMmn modes of the coupling electric field at arbitrary observation point within the enclosure are calculated based on waveguide theory. Simulation results of the hybrid model are in good agreement with those of transmission line matrix method within the frequency range of 0–3 GHz. Solution times using the hybrid model are far less than those required by pure numerical methods.

Using Aperture Impedance for Shielding Effectiveness Estimation of a Metallic Enclosure With Multiple Apertures on Different Walls Considering Higher Order Modes

In this paper, our previously published analytical method for calculation of shielding effectiveness ( SE ) of a metallic enclosure with a centered aperture is extended to generalize the method for a much wider range of applications. The new extended analytic formulation considers an enclosure with centered and off-centered apertures on different enclosure walls and the monitoring point can be anywhere inside the enclosure. In addition, the incident field angle and the polarization angle are arbitrary and higher order modes are considered. An analytic discussion and an experimental setup are proposed for the validation of the new method. The proposed measurement setup can lead to a new SE measurement method for enclosures with arbitrary position apertures. In this measurement method, there is no need for antennas, reverberation chambers, etc. Another advantage of the proposed method is introducing a new figure of merit for shield evaluation. This new figure of merit is S11 of a two port microstrip line which is placed over the apertures.

Shielding Effectiveness Estimation by using Monopole-receiving Antenna and Comparison with Dipole Antenna

Abstract In this paper, a numerical analysis of shielding properties of a protective metal enclosure has been performed by simulating a receiving antenna placed inside. Here, the main focus is put on the monopole antenna type. This antenna type is used in an experimental set-up to measure the shielding effectiveness (SE) of the enclosure as often as some other antennas such as dipole. Numerical model, based on the Transmission-Line Matrix (TLM) method, is applied to numerically investigate an impact this antenna might have on a detected level of electromagnetic (EM) field when it is used in the SE measurements. As in experiments, the estimation of SE of an enclosure in the numerical model is performed based on the current induced on the antenna, directly provided by a compact TLM wire model. The model accuracy is verified through a comparison with the experimental results from the literature. The analysis includes the monopole antenna with different radii and lengths, in order to consider changes in the resonant frequencies and the SE level of enclosure. Finally, the enclosure with either the monopole or the dipole is simulated in order to compare their influence on EM field distribution inside the enclosure.

Electromagnetic topology based fast algorithm for shielding effectiveness estimation of multiple enclosures with apertures

Shielding effectiveness (SE) estimation for an enclosure with apertures has been an attractive issue in electromagnetic compatibility (EMC) research area. Though many fast algorithms are developed for SE calculation, they mainly focus on the case of single cavity. Moreover, most of these methods neglect the wave coupling through apertures from enclosure to outside. A fast algorithm based on electromagnetic topology is proposed for calculating the SE of cascading multiple enclosures with apertures. In this algorithm, the wave coupling through apertures in both directions is taken into consideration. Firstly, the equivalent circuital model of cascading double enclosures and its signal flow graph of electromagnetic topology are given, followed by the derivation of scattering matrix of apertures node. Then propagation relationships at tube level and reflection relationships at node level are derived. As a result, the general BLT (Baum-Liu-Tesche) equation for voltage calculation at each node is established. Two major categories of cascading three enclosures with apertures are investigated. For serially cascading three enclosures, the general BLT equations are extended on the basis of BLT equations for cascading double enclosures, since the structures are a simple extension of them. For hybrid serially-parallelly cascading three enclosures, the common walls between the main enclosure and two sub-enclosures are considered as a topological node represented by a three-port network, whose scattering matrix is derived according to the definition of scattering parameters. Consequently, the general BLT equations for hybrid serially-parallelly cascading three enclosures are developed. Compared to the algorithms presented in the relevant literature, the topology-based algorithm proposed in this paper can not only calculate the shielding effectiveness for cascading multiple enclosures, but also lead to more accurate results in that the impedance of apertures is obtained through using diaphragms model. In order to validate the proposed method, a cascading double enclosures from a literature is chosen as an example. Calculated SE results are in good agreement with those in the literature. Then, three enclosures with different configurations and dimensions are also designed to validate the proposed method. Results from the proposed method are compared with those from the finite difference time domain (FDTD) method, and they are found to be in good agreement with each other. Experimental results also demonstrate the validation of the proposed method. Especially, the proposed method takes far less time to calculate SE than for FDTD method.

Coupling Between Multipath Environments Through a Large Aperture

A key issue in measuring the shielding of buildings against wireless communications signals is presented. We use a mode-stirred reverberation chamber (RC) to emulate the EM coupling through windows or doors. This is achieved experimentally by leaving the RC door open. The room hosting the RC is identified as an external semi-reverberant space, and thus used to generate the stochastic field exciting the internal RC through the door opening. Two methods for the transmission parameter measurement and shielding effectiveness estimation are compared: the first one consists in moving receiving antenna within a volume, the second one makes use of a rotating stirrer. The comparison confirms the interchangeability of the two techniques provided a proper averaging factor is introduced. This argument supports a quasi-ergodic hypothesis in imperfect and semi-open reverberating environments. The measured aperture SE is compared to a theoretical value given by an ideal reverberating environment.

孔缝箱体屏蔽效能电磁拓扑分析模型

孔缝箱体屏蔽效能电磁拓扑分析模型

Combined model for shielding effectiveness estimation of a metallic enclosure with apertures

This study presents an approach which combines an analytical model developed by Robinson et al. and a model which analyses the shielding effectiveness (SE) of enclosure loss with an off-centre aperture. It is based on the analytical model of transmission lines theory and aims at predicting the SE of a metallic enclosure with apertures. The combined model is more general than other analytical methods and proposes to consider the enclosure with numerous small apertures and the incident wave with varied angles of polarisation. It is therefore far quicker to calculate the SE with the combined model which on the other hand enables the impact of design parameters to be investigated. This investigation is often difficult via numerical methods because they require high computational times and memory in order to model a problem with sufficient details. This combined model is validated by comparing the SE predictions with full-field simulations using the finite-difference time-domain technique, CST Microwave Studio simulation tools and experimental investigations of the SE in a semi-anechoic chamber.