Advanced Characterization of a Hybrid Shielding Solution for Reducing Electromagnetic Interferences at Board Level

Abstract

The development of new advanced functionalities, miniaturization, and the aim of obtaining optimized performance in electronic devices significantly impacts their electromagnetic compatibility (EMC). As electronic components become more densely packed on a printed circuit board (PCB), unintended coupling between components can cause electromagnetic interference (EMI). These requirements result in design restrictions that make using a board level shield (BLS) essential in reducing intra-system EMI in PCB designs. This contribution focuses on studying and characterizing a BLS solution based on combining a noise suppression sheet (NSS) with an aluminum layer to reduce intra-system EMI coupling. This hybrid solution has the advantage of providing a shielding option that does not require any electronic redesign. It does not need a footprint or a ground connection as it can be affixed over the EMI source. The solution is expected to provide higher attenuation levels than using only an NSS by combining the absorbing properties of the magnetic material and the loss mechanism of the metal. In order to verify the effectiveness of the hybrid BLS proposed solution, the magnetic near-field emissions of an EMI source are analyzed in this study. The experimental measurements and simulated results demonstrate a significant increase (51.6 dB at 1 GHz) in the shielding effectiveness (SE) provided by the proposed solution compared to a conventional NSS.

1. Introduction

The ongoing trend to increase complexity, integration, and connectivity has characterized the evolution of electronic devices. This evolution has introduced important challenges in the field of electromagnetic compatibility (EMC) [1,2,3]. The miniaturization of electronic components, driven by advancements in microelectronics, has led to devices with smaller form factors. While this enhances the portability of electronic devices, it also necessitates careful design considerations to manage the proximity of components and prevent unwanted coupling [4,5]. Specifically, the process of combining multiple functions into a single integrated circuit (IC) can generate even more challenges related to EMC. High-density ICs require advanced shielding techniques to address electromagnetic considerations [6,7]. This situation is critical when the device holds a wireless communication technology since it amplifies the risk of electromagnetic interference, and there is a need for robust EMC strategies to ensure reliable operation [8,9]. To reduce electromagnetic interference (EMI), one should consider using the systems approach. This involves applying advanced grounding, optimized layout design, and filtering and shielding techniques throughout the design process [10,11].

Effective management of EMI problems requires the ability to eliminate or reduce coupling. To achieve this, the coupling may be decreased using spatial separation between the interference source and the victim circuit or their orthogonalization [12,13,14]. Nevertheless, if these methods are not feasible due to miniaturization requirements, applying an electromagnetic shield is necessary [15]. An ideal shield should be an infinitely conducting enclosure without any openings, but real enclosures require them for ventilation, controls, or cables [16].

A board level shield (BLS) is a specially designed shielded enclosure that provides localized shielding to protect electronic devices on a printed circuit board (PCB) [17]. The main purpose of the BLS is to ensure that there is no interference between its contents and other components nearby on the same PCB or in the same electronic system [17,18,19]. Given the tiny size of a typical BLS, it can be characterized by its effectiveness in reducing EMI in the (very) near field [20]. It is interesting to determine the effectiveness of a BLS in reducing near-field problems, such as undesired magnetic decoupling between two adjacent circuits [21,22,23].

The shielding cabinet (also known as a shielding can) is the most common component used for BLS. By connecting to the reference plane of the PCB, it provides five of the six walls required to form a Faraday cage [19,24]. Another widely employed option for shielding is the use of a noise suppression sheet (NSS) [25,26]. An NSS is not generally as effective as shielding cabinets in attenuating EMI, although it offers the distinct advantage of being easily applicable during the validation stage. Unlike cabinets, which require a footprint to be included on the PCB, it is unnecessary to carry out modifications to the PCB to apply an NSS [27,28]. In addition to being an advantageous solution during the validation stage, it is easy to incorporate in the production stage, and it can be implemented as a final solution for a product.

The objective of this study is to analyze the effectiveness of a hybrid BLS that combines a conductive metal layer with a magnetic absorber material. The metal layer reduces interferences via eddy currents induced on the metal while also providing attenuation through the reflection mechanism. The magnetic material produces attenuation mainly through the losses determined by its magnetic properties [29]. The use of magnetic materials also prevents the appearance of eddy currents generated in the metal layer, which could cause unwanted interference through the re-radiation mechanism. Applying the hybrid BLS should result in higher attenuation than an NSS [30]. Moreover, the hybrid BLS does not require the inclusion of a footprint in the PCB. The hybrid BLS can be conveniently affixed over the EMI source, whether it be an IC or a certain area of the PCB that causes EMI problems [31]. In order to assess the effectiveness of reducing magnetic near-field interferences, a thorough analysis of the hybrid BLS is conducted and compared with an NSS and a shielding cabinet.

The IEEE Standard P2716 [17], “Guide for the Characterization of the Effectiveness of Printed Circuit Board Level Shielding”, is the first standard document that considers the specific topic of determining the shielding effectiveness (SE) of a BLS using standardized and non-standardized procedures. It provides comprehensive guidelines and outlines standardized measurement techniques, such as the SAE ARP6248 [32], which employs a stripline measuring method, and the reverberation method [33,34,35]. One of the alternative techniques proposed involves using a stripline within a BLS as an EMI source and another stripline outside the BLS as an external antenna [36]. This technique helps to determine the onboard coupling between the external and internal antennas when the BLS is applied [17,18]. Meanwhile, the standard IEC 62333-2 outlines methods for characterizing an NSS. Specifically, it describes how to determine the decoupling ratio parameter that specifies the reduction in coupling when a noise suppression sheet is applied [28,37].

The method of measurement developed in this study combines the use of stripline antennas proposed in the IEEE Standard P2716 and the decoupling procedure described in the IEC 62333-2. A PCB that contains a microstrip line serves as a reference source of EMI. This microstrip line can be shielded using a BLS. The emissions in a specific area outside the BLS are determined with a magnetic near-field probe (H-NFP) [22]. This technique allows us to measure the magnetic field (H-field) in a particular region close to the BLS to determine the field that can be coupled to a nearby element. The advantages of using this measurement procedure are the possibility of measuring other BLSs besides an NSS and improving the dynamic range in the measurement. This last issue may not be critical when measuring the NSS, but it might be problematic when characterizing conductive shielding, as it typically provides a higher value of SE.

The measuring procedure is carried out both experimentally and through a simulated finite element method (FEM) model that replicates the experimental setup. This is an essential issue because when the results of a simulation match the experimental results, it makes it possible to explore variations in the initial validated scenario that would be difficult to measure experimentally.

This manuscript is structured into six sections that present a comprehensive analysis of the proposed hybrid BLS. Section 2 outlines the main parameters of the materials that constitute the hybrid BLS. In Section 3, the experimental measurement setup used for the magnetic near-field measurement is featured. Section 4 defines the FEM simulation model that is developed to determine the magnetic near-field emissions. Subsequently, in Section 5, the results obtained from the experimental measurement setup and simulations are reported. This section also presents a comparative analysis of the performance of the hybrid BLS with other alternatives, such as an NSS and a shielding cabinet. Finally, in Section 6, the main conclusions of this research are summarized.

2. Shielding Material Characterization

2.1. Hybrid BLS Solution

In order to improve the shielding of a specific part of a PCB, the most common technique used is a conductive shielding cabinet. Metal materials are effective at providing significant SE levels when applied properly. However, the NSS is becoming more popular in solving complex EMI problems. This is because it offers a lightweight solution with high flexibility. The main advantage of NSSs is that they can be adapted to achieve complex shapes and are easily assembled with adhesive onto a specific component or surface without adding a footprint in the PCB [25].

The proposed hybrid BLS solution consists of an NSS combined with an attached aluminum metal layer, as shown in Figure 1. It consists of an adhesive non-conductive layer for fixing the hybrid BLS to the EMI source. This is followed by a layer of magnetic absorber material (t = 1.0 mm), an adhesive layer (t = 0.1 mm), and an aluminum foil layer (t = 0.04 mm) [31].

This hybrid solution has the advantage of not requiring any redesign of the electronics as it can be affixed to the EMI source in a customized shape and size. Unlike shielding cabinets, it does not cause cavity resonance problems as it does not form a complete Faraday cage. Adding the metal layer is expected to obtain higher attenuation than using just an NSS. The attenuation of the EMI in the hybrid BLS is determined by the interaction of its constituent materials. The magnetic material primarily causes attenuation through the losses determined by its magnetic properties, mainly defined by its permeability [38]. On the other hand, the metal layer can reduce interferences through eddy currents induced on the surface and provide attenuation through the reflection mechanism. The use of magnetic material in the hybrid structure further prevents the occurrence of undesired interference through the re-radiation mechanism caused by eddy currents generated in the surface and the capacitive coupling produced, as shown in Figure 2a,b [31]. Thereby, this structure may extend the working bandwidth of these materials and obtain a more significant attenuation than each of these materials could provide individually.

2.2. Magnetic Material Characterization

Magnetic absorbing materials are metamaterials that convert electromagnetic interference into heat, which ultimately reduces the strength of the magnetic field. These materials are effective in reducing EMI depending on factors such as frequency, thickness, and dimensions. [29,39]. The selected magnetic absorber material, to be combined with a conductive layer, contains iron particles homogeneously distributed throughout a polymer matrix. In the presence of an H-field, the iron particles present in the polymer matrix are magnetized and absorb the magnetic energy. If the size of particles and spatial periods is significantly smaller than the wavelength of the electromagnetic field produced by the EMI source, then the material can be considered homogeneous [28,29].

To comprehend the mechanism by which a magnetic material can reduce EMI, it is essential to consider its permeability (μ) [40,41]. The complex relative permeability of a material can be partitioned into real and imaginary components, which are dependent on the frequency, as shown in Figure 3. The selected magnetic absorber material included in the hybrid BLS proposed has a thickness of t = 1.0 mm and an initial permeability of µ_i = 100.

Another intrinsic material property worth mentioning is the electrical permittivity (Ɛ_r). This is an essential material property that shows how a material can resist the formation of electric fields when an external field is applied. It has two components: the real part (Ɛ_r′) shows how a material can store electrical energy, while the imaginary part (Ɛ_r″) represents dielectric losses due to energy dissipation in the material. Figure 4 shows the permittivity components of the selected material, measured using a parallel conducting plates fixture, connected to a material analyzer equipment. As expected, the magnetic properties are more relevant in this kind of material.

2.3. Conductive Material Characterization

Aluminum and copper materials are usually used as shielding solutions because they are highly conductive. These materials generally are used to manufacture components such as shielding tapes or textiles. Although copper may be preferred for its superior electrical conductivity, aluminum might be selected for being lightweight and cost-effective. Additionally, aluminum has better corrosion resistance than copper due to the protective oxide layer it forms.

In order to observe the performance of aluminum material compared to copper material in the frequency range of interest, aluminum and copper layers with a thickness of t = 0.04 mm are compared in terms of SE. This characterization is carried out by following the ASTM D4935-18 standard [42]. It defines the test method for measuring the electromagnetic shielding effectiveness of planar materials [16]. The method lies in measuring the insertion loss (IL) that results when introducing test samples in a coaxial two-conductor transmission line holder, supporting the transverse EM (TEM) propagation mode. This test method is effective in determining the SE of conductive materials in a narrow frequency range from 30 MHz to 1.5 GHz. The holder is connected to a vector network analyzer (VNA) equipment that is used to determine the IL parameter, as shown in Figure 5. The procedure requires two types of specimens that must have the same thickness in order to take SE measurements: the reference and the load specimens. The difference between the measurements of the load and the reference specimens provides the measurement of the SE.

The SE measurement can be expressed as the difference between the IL expressed in dB of the load (IL_dB,l) and reference specimens (IL_dB,r), as follows:

$$S{E}_{dB}=I{L}_{dB,l}-I{L}_{dB,r}.$$

(1)

Figure 6 shows the SE of the two shielding metal layers measured according to the ASTM D4935-18 standard. Given that the behavior of both materials is identical across the entire bandwidth, aluminum is validated as the material to incorporate into the final hybrid BLS.

3. Experimental Measurement Procedure

In this study, a novel method of measurement is proposed that utilizes the stripline antennas, as suggested in the IEEE P2716, in conjunction with the decoupling procedure, as described in IEC 62333-2. According to the fundamental diagram of an EMC problem, the microstrip line serves as the source of EMI, while the H-NFP is the victim element. The EMI source is implemented by a PCB that holds a microstrip line, which acts as a reference emission level. The H-NFP is used to measure the H-field emissions in a particular region close to the EMI source. Specifically, the location of the H-NFP is adjusted to the center of the microstrip line, which was found to be the area of maximum emission. As the H-NFP introduces approximately 30 dB of attenuation, obtaining measurements of maximum emissions is crucial in order to have a significant dynamic range in the experimental measurement setup. The distance between the H-NFP and the microstrip line must be as close as possible without touching the NSS or hybrid BLS under test. Considering this statement and the thickness of the hybrid BLS, the distance is fixed at 1.4 mm. By applying different BLSs, emissions are measured and compared with the reference measurement without using any BLS. Thereby, it is possible to quantify the SE provided by the BLS applied to the EMI source.

The developed method significantly enhances the dynamic range of the measurement setup. Using a microstrip line as an EMI source instead of an H-NFP significantly improves the dynamic range of the measurement since, generally, an H-NFP can introduce about 30 dB of attenuation [22]. Thus, the results are significantly attenuated if two H-NPFs are used both as a source and receiver (as defined by the IEC 62333-2). When measuring the NSS, the issue mentioned in the text might not be critical. However, it could be problematic while characterizing conductive shielding as it usually provides a higher value of SE. The proposed method has an added advantage over the IEC 62333-2 as it allows us to measure other BLSs apart from the NSS.

The EMI source consists of a PCB that includes a 50 Ω microstrip line, as shown in Figure 7. On the bottom side of the PCB, a ground plane with a 0.035 mm thickness is added, and two SMA connectors are attached, one at each end of the strip conductor. The SMA connectors are located on the bottom layer and connected to both ends of the microstrip line through two vias. One SMA connector is connected to a signal generator equipment (SG), while the other one is connected to a matched 50 Ω load. The SG is configured to power the EMI source with a parametric signal ranging from 100 MHz to 1 GHz.

The H-NFP is placed at a right angle with the EMI source and connected to spectrum analyzer (SA) equipment to measure the emissions, as shown in Figure 8.

The XF-R 3-1 from Langer EMV GmbH is the H-NFP selected since it is able to measure the emissions in a specific area. The XF-R 3-1 is specifically designed to directly and accurately measure H-fields on a particular component or assembly, with high resolution. Figure 9 depicts the H-field correction factor of the XF-R 3-1 probe in terms of (dBµA/m)/dBµV. It is used for the transformation of voltage measurements obtained through the SA into magnetic field results. A significant advantage of the proposed measurement setup is that it makes it possible to compare the experimental results with those obtained from the simulation model.

Therefore, given the H-NFP response and the measurements obtained with the SA, (2) and (3) are used to determine the experimental results in H-field units (dBA/m):

$$H\left[dB\frac{\mu A}{m}\right]=U_{out}\left[dB\mu V\right]+K_H\left[dB\frac{\mu A}{m}\right]$$

(2)

$$H\left[dB\frac{A}{m}\right]=H\left[dB\frac{\mu A}{m}\right]-120$$

(3)

where $U_{out}$ represents the voltage that the H-NFP provides to the SA and $K_H$ correction factor represented in Figure 9.

4. Simulation Model Definition

The FEM simulation is created using the software Ansys Electromagnetics Suite 2022 R1 HFSS 3D’s electronics simulation platform (Ansys Electronics Desktop). The experimental measurement setup has been replicated to assess the distribution of near H-fields when different BLSs are applied to the EMI source. In the model, the SG equipment used for powering the EMI source PCB is implemented as a lumped port that is connected to one end of a microstrip line. This port emulates the signal emitted by the SG equipment and sets the power and frequency to the same values used for the experimental measurements. The other end of the microstrip line is matched with a 50 Ω load, replicating the experimental model. The following scenarios are assessed to evaluate the performance of the hybrid BLS:

• Reference measurement: H-field without applying any shielding component;
• H-field when only the NSS is applied;
• H-field when the hybrid BLS is applied;
• H-field when a 30 mm × 30 mm shielding cabinet is applied.

Note that the NSS has been modeled from the relative permeability and permittivity defined in Section 2. The hybrid BLS also utilizes the same model as the NSS and adds an aluminum layer defined by the electrical conductivity parameter (3.6 × 10⁷ S/m).

These scenarios make it possible to assess the performance of the hybrid BLS in comparison to the reference level. Additionally, the hybrid BLS can be compared with the NSS without the inclusion of the aluminum layer. Finally, the effectiveness of the hybrid BLS can be evaluated by comparing it with a shielding cabinet, which is one of the most widely used and effective solutions.

4.1. Near-Field Distribution Simulation

The results obtained from the simulation model are verified by comparing them with those obtained from the experimental setup. This is carried out by analyzing the H-field parameter measured at the selected distance from the EMI source. The simulation environment provides the resulting measurement by maintaining the same position of H-NFP as in the experimental setup. It is important to note that when the results of a simulation match those of an experiment, it becomes possible to explore different variations in the initial validated scenario that may be difficult to measure experimentally. Once the simulation model is verified, the near-field distribution generated by the EMI source can be analyzed to observe the considered scenarios. The initial size of the NSS and hybrid BLS sheets is chosen to be 60 × 60 mm to measure only the H-field produced by the microstrip line. The near-field distribution is also studied by applying the hybrid BLS with different sample dimensions on the EMI source. The obtained results provide insights to optimize the size of the hybrid BLS. Consequently, scenario 3 is modified by testing shorter (30 mm × 30 mm) and larger (100 mm × 100 mm) dimensions of the hybrid BLS.

The scenarios defined to study the near-field distribution generated by the EMI source are shown in Figure 10. Figure 10a shows the reference scenario 1 without applying any shielding. Scenario 2 is represented in Figure 10b, where the 60 mm × 60 mm NSS is applied to the EMI source. In Figure 10c, the hybrid BLS with dimensions of 60 mm × 60 mm is used (scenario 3). Figure 10d represents scenario 4, where a shielding cabinet is connected to the ground plane of the EMI source. Additionally, the models of Figure 10e,f show the hybrid BLS with shorter and larger dimensions, respectively.

4.2. Frequency Response Simulation

The use of filtering and shielding techniques is effective in reducing EMI, although it is essential to ensure that they do not affect the intended working signals. Thereby, the transmission attenuation ratio [29] for scenarios 1, 2, and 3 proposed is simulated and analyzed through the S21 parameter. A signal is injected into the microstrip line, covering a frequency range up to 1.0 GHz, that is received at its other end. Scenario 1 is expected to have a flat response of around 0 dB. On the other hand, the NSS and the hybrid BLS are expected to have a response similar to a low-pass filter. The most noteworthy result from this measurement is the point at which the hybrid BLS can start affecting the signals present in the area it covers.

5. Results and Discussion

This section focuses on the analysis of the hybrid BLS to reduce near-field EMI problems. The results obtained from the experimental measurement setup and those provided by the simulation model are compared through the near H-field parameter. There are two main purposes for this comparison. The first purpose is to analyze the accuracy of the reference measurement (scenario 1) in order to ensure that the simulation model has been designed properly. The second purpose is to validate the model of the magnetic absorber material that has been created using the permeability and permittivity parameters. This second point is crucial in evaluating the performance of the hybrid BLS since the magnetic material defined is one of its layers. Figure 11 shows the results obtained for the first three scenarios described in Section 4. It represents the experimental (solid traces) and computed (dotted traces) H-field provided by the EMI source and measured at the same specific position.

Based on the obtained results, it has been confirmed that both the simulation model and the magnetic material are accurately designed. The black traces in the graph represent the reference measurement for scenario 1. The experimental measurement shows a mean H-field of −4.7 ± 0.6 dBA/m, whereas the simulated measurement is −4.6 ± 0.6 dBA/m. Therefore, it can be concluded that there is a strong correlation between the experimental and simulated measurement setups.

Scenario 2, which represents the use of the NSS, validates that this material has been adequately modeled since the simulated and experimental result trends are very similar. The model is observed to be more precise in the high-frequency region, with the largest disparity observed in the lowest frequency studied (4.58 dB at 100 MHz). When the NSS is applied to the EMI source, it reduces the H-field measured to −23.1 dBA/m at 100 MHz and −10.4 dBA/m at 1.0 GHz, according to the experimental results. The maximum SE provided by this solution is observed in lower frequencies since the H-field measurement decreases with increasing frequency. The experimental data show that the SE provided by the NSS is −17.8 dB at 100 MHz.

According to the experimental results, the modeled hybrid BLS has a significant match. The maximum error observed is 1.9 dB at 400 MHz and 800 MHz. In the rest of the frequency range studied, the difference is less than 0.5 dB. Comparing the H-field attenuation generated by applying the hybrid BLS with that obtained using only magnetic material, it is evident that the former is more effective. At 100 MHz and 1 GHz, the H-field is reduced to −60 dBA/m, resulting in an SE of 37.5 dB and 51.6, respectively. These results demonstrate that the hybrid structure can provide a significant SE value.

The scope of this analysis is limited to the frequencies specified by the simulation model, owing to the measurement of permeability and permittivity data up to 1.0 GHz. The trend of the NSS reveals that the higher the frequency, the slower the SE is reduced. Conversely, the trend of the hybrid BLS suggests a more substantial attenuation of SE in the higher frequency range compared to the characterized region.

5.1. Near-Field Distribution Results

The simulation model allows for an analysis of performance regarding the distribution of the H-field. This analysis considers the scenarios outlined in Section 4. Figure 12 illustrates the strength of the H-field on the Y-Z plane, which is the plane perpendicular to the PCB substrate. This H-field is generated by the EMI source at 500 MHz. In scenario 1, the H-field is distributed over the microstrip line, as shown in Figure 12a. As explained above, the maximum H-field is concentrated in the center of the microstrip line. However, it does not generate an H-field in the area under the PCB because it is blocked by the ground reference plane included under the stripline. In scenario 2, the introduction of the NSS causes a slight attenuation of the H-field, as shown in Figure 12b. This result is in line with the findings presented in Figure 11. In scenario 3, the H-field is significantly attenuated when the hybrid BLS is attached to the EMI source, as demonstrated in Figure 12c. This situation is similar to the one presented in Figure 12d when the shielding cabinet is applied (scenario 4). Note that in this case, a significant part of the field is enclosed inside the cabinet area. As expected from the results shown in Figure 11, the attenuation provided by the hybrid BLS is notable and may be comparable with the cabinet’s effectiveness. Moreover, the hybrid BLS has an advantage over a shielding cabinet as it can be easily attached to the source of interference without requiring the electronics to be redesigned by introducing a footprint.

The hybrid BLS and the shielding cabinet test results revealed that some of the H-field is re-radiated from the component edges. To further investigate this situation, scenario 3 has been modified by varying the dimensions of the hybrid BLS sheet. The simulation results for the two sheet dimensions, 30 mm × 30 mm and 100 mm × 100 mm, defined in Section 4, are shown in Figure 13. When the hybrid BLS sheet is reduced, the results are similar to those shown in Figure 12. It can be observed that the near H-field distribution of the hybrid BLS, which has the same dimensions as the shielding cabinet, also significantly attenuates the emissions generated by the EMI source. However, it should be noted that the stray field generated in the edges of the hybrid BLS of size 30 × 30 mm has increased compared to the 60 × 60 mm sheet. Moreover, as seen in Figure 13a, the edge of the sheet is closer to the microstrip line, and the re-radiated H-field is affecting it, which may lead to undesired couplings. If the hybrid BLS sheet is extended to overlap the EMI source PCB, the re-radiated H-field will be generated at the edge of the PCB instead of the sheet’s edge. Additionally, the H-field will be re-radiated only toward the area located under the PCB, as the hybrid BLS protects the area situated over the PCB. Specifically, in this case, due to the proximity of the aluminum layer of the hybrid BLS and the copper ground plane of the PCB, a capacitive undesired effect occurs, which results in re-radiation. The re-radiating effect is produced when a discontinuity between both parallel conductive planes is produced. Therefore, it is essential to properly select the dimensions of the hybrid BLS to avoid the edge re-radiating effect that may affect the area or component that wants to be shielded.

5.2. Frequency Response Analysis

Figure 14 shows the outcome of the frequency response analysis of the transmission attenuation ratio. This is carried out by placing a BLS on the microstrip line of the EMI source PCB. As anticipated, scenario 1 (red trace) indicates a constant response across the entire frequency range studied. This is because when no BLS is applied to the microstrip line, it is expected to have an even response of approximately 0 dB. The NSS and hybrid BLS act as a low-pass filter. As a result, scenario 2 (black trace) demonstrates that the transmitted signal becomes attenuated beyond 200 MHz. The worst attenuation result is produced at 1.0 GHz, and the value is 0.8 dB. The hybrid BLS, whose dimensions are the defined by scenario 3 (orange trace), becomes attenuated from 110 MHz and experiences the maximum attenuation at 1.0 GHz, which corresponds to 2.4 dB.

If the criterion selected to determine the cutoff frequency is an attenuation of −3.0 dB, it can be confirmed that for the hybrid BLS, this value is reached at a frequency higher than the one studied. This indicates that this solution can be deemed optimal at least up to 1.0 GHz since it does not affect the desired signal.

6. Conclusions

The hybrid BLS solution based on combining an NSS with an aluminum layer to reduce intra-system EMI coupling was presented. The main layers contained in the hybrid BLS were described and characterized. This proposed shield was analyzed in terms of its ability to reduce intra-system EMI coupling. The hybrid BLS was modeled and evaluated through a simulation model that emulates the experimental measurement technique employed to determine the near H-field emissions. Based on the obtained results, it was confirmed that both the simulation model and the magnetic material were accurately designed.

The hybrid BLS presented a significant attenuation of the near H-field (up to 51.6 dB at 1 GHz) when applied to the EMI source. Hence, it is verified that the SE is more than that provided using the NSS. The near H-field distribution diagrams reveal that the attenuation provided by the hybrid BLS is notable and may be comparable with the shielding cabinet’s effectiveness. Additionally, the re-radiation caused by the use of the hybrid BLS was studied, concluding that it is essential to select the dimensions of the hybrid BLS to avoid the edge re-radiating effect affecting the area that needs to be shielded or other near elements.

Consequently, the hybrid BLS represents an interesting solution since it is able to yield similar results to the shielding cabinet in the frequency range studied. Moreover, the hybrid BLS has an advantage over a shielding cabinet as it can be easily attached to the source of interference without requiring the electronics to be redesigned by introducing a footprint.