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(Editor’s note: This paper was presented at the Pan-European Electronics Design Conference in Vienna, Austria, in January 2025.)
Abstract
Inherent cavity resonant modes often lead to significant degradation of shielding effectiveness, responsible for unwanted electromagnetic coupling. Cavity resonant modes of the metal shielding enclosure can produce two adverse problems: the mutual coupling among different RF modules and shielding effectiveness reduction of the metal enclosure. The cabinets serve to shield certain components from electromagnetic interference (EMI). However, these cavities present some resonance peaks at 5 GHz, making it impossible to use them at higher frequencies.
By incorporating absorber sheets inside the lid of the cabinet, these resonances are attenuated or even eliminated, allowing the use of the cabinets as a protective element in PCBs at higher frequencies. In this study, it has been calculated theoretically, simulated using a commercial EM field solver, and tested in the laboratory in different cabinets to find their resonance frequencies, as well as tested incorporating a ferromagnetic material inside them to see if this can help to attenuate the effect of resonances. In addition, thermal simulations and laboratory tests have been carried out to prove that this material can have a dual function as a resonance attenuator and as an element to direct the heat flow from inside the cabinet to the outside. The calculated, simulated, and tested data in most cases differ by 1–7% error, and a significant reduction in resonances has been demonstrated. Extending the frequency range of these cavities will make a difference for IoT applications, 5G, and future functionalities that require the use of a higher frequency range.
Introduction
The technological development over the past decades has been unprecedented, starting in the 2000s with phones just capable of making calls, to the present day, with augmented reality glasses, hyper-connectivity, and high-speed devices. To achieve this development, it has been necessary to design the hardware of all operating systems to be smaller and more optimal. Consumers and the technology industry demand higher portability, faster speeds, and high-quality performance. With this challenge in mind, and assuming that designs will not only remain as they are, but will become smaller and smaller, the industry faces a major challenge of EMI.
Industry is no longer talking about eliminating electromagnetic interference effects, but rather, assuming that such problems will occur, looking for a method to mitigate their effect. Many designers are opting to include shielding cabinets, a product used to isolate components from EMI. However, this solution may not be 100% effective at certain frequencies, resulting in a resonant cavity effect and therefore not achieving the desired isolation.
To continue reading the paper, which appeared in the June 2025 Design007 Magazine, click here.
