# Analysis of Shielding Effectiveness of a Cavity with Internal Dielectric Plate and Apertures
## 1 Introduction  
Electromagnetic interference suppression techniques include shielding, filtering, grounding, and bonding. Shielding is the most concise and effective method for electromagnetically compatible structural design [1]. Shielding cavities are often added to electronic devices to avoid mutual electromagnetic radiation interference between electronic devices that can interrupt the circuit system and affect the power output accuracy [2]. A shielding cavity protects the interior from external electric or magnetic fields [3]. Shielding effectiveness (SE) is an important parameter for evaluating shielding performance [4]. SE is an indicator that quantifies the ability of a shielding body to block or reduce the transmission of electromagnetic energy, representing the ratio of the electromagnetic field intensity before and after shielding.  
The design and implementation of cavity shielding involve engineering issues, including material selection, structural design, size optimization, and installation methods. In terms of material selection, conductive metals with excellent performance such as aluminum, copper, and steel are commonly used to provide good shielding. The structural design considers the enclosure, sealing, and stability of the cavity to effectively block the propagation of electromagnetic waves. In addition, the size and shape of the cavity shielding must be optimized for the best shielding performance. Cavity shielding is widely used as an EMI control technique.  
Scholars have conducted extensive research on the electromagnetic shielding of perforated shielding cavities. Commonly used methods for determining the shielding effectiveness of perforated metal cavities include the equivalent circuit method (Robinson) [5], method of moments (MOM) [6], transmission line matrix method (TLM) [7], finite element method (FEM) [8], and finite-difference time-domain method (FDTD) [9]. The equivalent circuit method proposed in [5] effectively simplifies the calculation of field problems and significantly reduces the resources and time required to calculate the shielding effectiveness of a perforated single-layer shielding cavity. However, this method does not consider the energy coupled outward through the aperture after an electromagnetic wave is reflected inside the cavity, resulting in significant errors when calculating the shielding effectiveness of the cavity. The authors of [10] explored the shielding effectiveness of empty cavities; however, in practical applications, most shielding bodies aim to protect internal circuit boards and other electrical and electronic components from electromagnetic interference. Scholars have proposed different analytical methods to address cavity shielding effectiveness [11; 12; 13; 14; 15; 16; 17; 18; 19; 20]. Studying the shielding effectiveness of metal cavities with internal circuit boards and other components is of practical value.  
This study determines the shielding effectiveness of perforated cavities by considering different spatial and aperture configurations of the shielding body. We apply transmission line theory, [PERSON]'s algorithm, and electromagnetic topology theory to construct the BLT equation to calculate the shielding effectiveness of a single-layer shielding cavity irradiated by a plane wave. By placing a dielectric plate inside the shielding cavity, the effect of apertures on the internal dielectric plate of a single-layer perforated shielding cavity is investigated, including the relationship between the aperture size, location, and quantity, as well as the shielding effectiveness of the cavity and the impact of different aperture configurations on the internal dielectric plate. The accuracy and effectiveness of the model were verified by comparing the results obtained from transmission line theory, BLT equation calculations, and HFSS software simulations (2022 R1). The approach enables efficient electromagnetic shielding and protects electronic equipment and personnel from electromagnetic interference.