Improved modal method of moments technique to compensate the effect of wall dimension in shielding effectiveness evaluation
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Abstract:
In the conventional modal method of moments (MoM) method, when shielding effectiveness (SE) of a rectangular enclosure is the goal, it is assumed that the incident wave is reflected from an infinite wall. This assumption makes the results inaccurate specifically at low frequencies where the wall size is not large compared to the illumination wavelength. In this study, the mentioned reflected wave is corrected by considering the reflection from a box without any aperture. To obtain the reflected wave from the box, an induced electric current on the metallic surface is assumed. Using Rao Wilton Glisson basis functions along with free space Green's function, the unknown electric currents and consequently the reflected wave are calculated. The results are compared with full wave numerical methods. A very good agreement is observed between the results and it is shown that for lower frequencies the proposed method has more accuracy rather than the modal MoM itself specifically for an enclosure with a very large aperture.Keywords:
Enclosure
Aperture (computer memory)
Reflection
Shielding effectiveness is a major problem to prevent electronic products from emission and radiation. This paper is written to present the measurement of shielding effectiveness (SE) and S 21 for such enclosure at frequencies below 1GHz. The measurement results indicate that a wire or cable penetrating into an enclosure has impact to the shielding effectiveness. The coupling between a wire penetration and a detector inside the enclosure show good agreement between experiment and simulation. The different length and direction of a wire penetration were used to interpret the theory. All results indicate the same resonant frequency approximately 707.1MHz for a 300 x 120 x 300 mm enclosure.
Enclosure
Penetration (warfare)
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This paper presents a design of band-pass shielding enclosure for two frequency bands of WLAN. The proposed design employs a compact frequency selective surface to highlight the advantages of these miniaturized structures for the selective shielding of such enclosures that are electrically small. The results indicate that the proposed shielding enclosure has high transmittance in both the pass bands for horizontal and vertical polarizations, while offers a good amount of electromagnetic shielding outside these frequency bands.
Enclosure
Frequency band
Radio spectrum
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This paper presents the shielding effectiveness (SE) study for enclosure incorporating a newly developed frequency selective surface (FSS) with consideration of the ratio of vent hole array and the oblique wave incidence. Not only is the SE at the center of the enclosure analyzed, but also the global shielding effectiveness (GSE) is evaluated as a complementary approach for more reasonable prediction. Compared to an enclosure commonly shielded by metal with the same vent hole array, the shielding effectiveness of the enclosure with the FSS shield is about 20 dB higher in the frequency range of 23 GHz - 25.5 GHz, which meet the requirements of SE >= 30 dB and BW| SE=30dB > 2 GHz. The results also show that the ratio of vent hole array to one surface of the enclosure has impact on the shielding effectiveness of enclosure. Importantly, the study indicates that FSS technology can be a promising alternative when conventional metallic shielding is limited due to ventilation requirement in the high frequency applications.
Enclosure
Shielded cable
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In order to gain shielding enclosure with better shielding effectiveness and lower expense, six riveted steel-plate enclosure models are established. The experimental results show that the shielding effectiveness for continuous wave and transient electromagnetic wave can be above 50 dB if the models are specially designed. Some valuable conclusions for engineering construction are obtained.
Enclosure
Transient (computer programming)
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Citations (0)
An analytical formulation has been developed for the shielding effectiveness of a rectangular enclosure with an aperture. Both the magnetic and electric shielding may be calculated as a function of frequency, enclosure dimensions, aperture dimensions and position within the enclosure. Theoretical values of shielding effectiveness are in good agreement with measurements. The theory has been extended to account for circular apertures, multiple apertures, and the effect of the enclosure contents.
Enclosure
Aperture (computer memory)
Position (finance)
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Citations (501)
The transmission-line modeling (TLM) numerical method is employed to investigate the high-frequency shielding effectiveness (SE) of a metallic enclosure with unconventional aperture geometries. Analytical methods can predict SE but they have two main limitations: one is they can predict the SE of enclosure with very simple aperture shapes and second is that results cannot be predicted with accuracy after the first resonance frequency of cavity. We have investigated some new geometries for apertures from 0 to 3 GHz frequency band and discovered some important characteristics of these shapes by using the TLM based simulator. A novel concept of complementary apertures is introduced which has pronounced effect on cavity resonance modes and SE of enclosure. Another useful phenomenon was also observed and that is despite of longer aperture lengths perpendicular to electrical field (E-field), some apertures have better SE than others for the same coverage area.
Enclosure
Aperture (computer memory)
Schumann resonances
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The shielding effectiveness to different sized slots in a shielding enclosure is calculated using the FDTD method. It is demonstrated that the resonance of a shielding enclosure's cavities and slots greatly influences a screened room's shielding effectiveness. Fast time-varying EMP couples more easily in a shielding cavity with slots.
Enclosure
Shielding effect
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Citations (1)
This study introduced a method for enhancing the shielding effectiveness of an enclosure with apertures using an absorber. The absorber was installed on the inner surface of the aperture of the enclosure and attenuated incident electromagnetic waves as they passed through it. Furthermore, the absorber reduced the standing waves generated inside the enclosure owing to the cavity effect, improving shielding effectiveness. A 3D numerical analysis confirmed that the proposed structure enhanced the shielding effectiveness of the enclosure.
Enclosure
Aperture (computer memory)
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The results of feature selective validation (FSV) technique are used as analysis tools to identify the influence of differences and/or imperfections in the results between measurement setup and simulation models for the evaluation of shielding effectiveness in slotted enclosures. The experiments are carried out on the enclosure placed in the gigahertz transverse electromagnetic (GTEM) cell. A new technique for the evaluation of the shielding of a slotted enclosure is proposed. The enclosure under test is equipped with a built-in, rotating, and conductive stirrer, and the shielding is measured or computed at discrete angles of the stirrer. The stirrer is used for modeling different internal arrangements of the enclosure and for an approximation of the "worst case" of the shielding performance.
Enclosure
Electromagnetic Compatibility
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Shielding effectiveness (SE) is an important measure of how well an enclosure reduces the electromagnetic (EM) field incident upon it. Commonly, when the shielding effectiveness of an enclosure is stated it is for the case when the enclosure is empty. Including contents such as printed circuit boards (PCBs) in the enclosure will affect the shielding effectiveness as the PCB absorbs EM energy. One technique of determining how much energy a PCB absorbs is to measure its absorption cross section (ACS) using a reverberation chamber (RC). The measured ACS can be used to predict the shielding effectiveness of an enclosure when the PCB is inside it using power balance techniques. In this paper the ACS of a number of PCBs are measured both individually and in closely stacked groups. This information is then used to show how the ACS can be used to calculate shielding effectiveness and the results are compared to direct measurement of the SE of the enclosure containing a PCB. Knowledge of the ACS of typical or particular PCBs could be used by engineers to estimate the real shielding effectiveness of an enclosure with contents, when designing electronic systems.
Enclosure
Electromagnetic reverberation chamber
Shielding effect
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Citations (10)