For a small-sized shielding enclosure, an infinitesimal monopole antenna is installed inside an enclosure to measure the quality factor and the shielding effectiveness. The characteristic of the monopole antenna, however, affects the measurement of the quality factor and the shielding effectiveness. This article proposes a new measurement method that does not require any antenna installation inside the enclosure. Instead, the proposed method utilizes an aperture on the enclosure surface. A theoretical model is derived for the enclosure response, which represents a response of the enclosure when a pulse signal is incident to the enclosure in the nested reverberation chamber. The response model is used to measure the quality factor and the shielding effectiveness, respectively. The enclosure response affected by an aperture on the enclosure surface is measured, and the measured response is then used to calculate the quality factor by comparing it with the response model. The response model also is used to measure the shielding effectiveness. The enclosure responses are measured with two aperture conditions, respectively, and the shielding effectiveness is calculated using the measured responses. The proposed method is advantageous in that the quality factor and the shielding effectiveness of a small-size enclosure can be accurately measured without being affected by the quality factor of the monopole antenna.

An electromagnetic field penetrating through an aperture or slot of a metallic enclosure generates many standing-waves due to the resonance inside the metallic enclosure, which results in reduced shielding performance. This paper examines the effect of absorbent material (absorber) to improve shielding effectiveness (SE) of large metallic rooms with apertures or slots. First, a theoretical formulation to extract the Q-factor of an absorber with any shape is proposed. Using this, the contribution of the absorber to the SE improvement of a shielded room with different sized circular apertures was investigated. Second, the resonant mode density inside the shielded room was classified into non-resonant, under-moded, and over-moded states with an increase in frequency, and the effect of the absorber in each frequency range was examined. The analysis was conducted through numerical simulation using a commercial full-wave simulator and experimental measurement using a fabricated actual shielded room and commercial absorbers. The accuracy of the analysis results was verified through the comparison of simulated and measured results. The analysis results ensured that the absorber was not effective in improving the SE in the non-resonant state of the metallic room. It was also confirmed that the absorber was effective in improving the SE in the over-moded state of the metallic room where a severe standing-wave occurs. In addition, the SE improvement level differed depending on the location of the absorber in the room.

In this paper, electromagnetic wave analysis was performed efficiently in a large structure using the theoretical method. While taking into consideration the important assumptions of the employed theoretical method, we created an environment for measurement and simulation. A shield room with an aperture was selected as the target structure, and a measurement system based on frequency domain was constructed and used. Using the simulation tool, Wireless Insite, electromagnetic wave analysis was performed by modeling the measurement environment. To verify the efficiency and accuracy of the theoretical method, the results of the actual measurement, the commercially available simulation tool, and the theoretical method were compared. These results showed that the theoretical method can be more efficiently interpreted than the commercially available simulation tool in an electrically large structure.

Generally, various technologies, including waveguide below cutoff (WBC), gasket sealing, and bonding, are employed in metallic enclosures to achieve the high electromagnetic shielding performance required for EMP protection and EMC countermeasures in shielding structures or facilities. While the shielding structure or facility is properly constructed and maintained according to design specifications, its electromagnetic shielding performance can remain at the required level, effectively protecting internal electrical and electronic equipment from external electromagnetic interference. However, unintended apertures often occur during the construction or maintenance of shielding facilities, compromising their shielding performance. Therefore, it is crucial to develop technologies that prevent shielding effectiveness degradation caused by both intentional and unintentional apertures. This paper proposes a structure incorporating a composite absorber (made of dielectric and magnetic absorber) within a double metal panel of enclosure featuring an aperture, aimed at maintaining and improving the facility’s shielding performance. The effectiveness of the proposed structure was validated through numerical simulation.

For low-frequency magnetic field shielding measurement of large shielded rooms, the standard methods, such as IEEE-Std-299 and MIL-Std-188-125-1, are commonly used. In this letter, three types of loop antennas are analyzed to reduce the SE variation that occurs when using the standard measurement method based on the unit test area. Simulation shows that the rhombic and long rectangular loops can reduce the SE difference due to slot position compared to a conventional circular loop. Finally, a shielded room and loop antennas are fabricated and their effects verified through experiments.