Select material, thickness and frequency to instantly calculate skin depth, absorption loss, reflection loss and total SE (dB). Compare materials with the full frequency-spectrum chart.
The foundation of shielding is the skin depth (δ). It defines the distance over which the electric field of an electromagnetic wave decays to about 37% (1/e) of its surface value inside a conductive material. It depends on the material's resistivity (ρ) and magnetic permeability (μ), and the angular frequency (ω) of the wave.
$$\delta = \sqrt{\dfrac{2\rho}{\omega\mu}}$$Where:
δ = Skin depth (m)
ρ = Electrical resistivity (Ω·m)
ω = Angular frequency = $2\pi f$ (rad/s)
μ = Magnetic permeability = μrμ0 (H/m)
A smaller δ means the wave is absorbed in a thinner layer, leading to higher absorption loss for a given material thickness.
The total Shielding Effectiveness (SE) is the sum of Absorption Loss (A) and Reflection Loss (R). Absorption is directly proportional to thickness (t) and inversely proportional to skin depth. Reflection is a surface phenomenon based on the impedance mismatch between free space and the shield material.
$$A = 8.686\,\dfrac{t}{\delta}\quad \text{(dB)}$$ $$R = 168 - 10\log\!\left(\dfrac{f\mu_r}{\sigma_r}\right)\quad \text{(dB)}$$ $$SE = A + R \quad \text{(dB)}$$Where:
t = Shield thickness (m)
f = Frequency (Hz)
μr = Relative permeability
σr = Relative conductivity (relative to copper)
The constant 8.686 comes from converting Nepers to decibels (20 log(e) ≈ 8.686). The constant 168 in the reflection formula is derived from the properties of free space and copper.
Medical Device Shielding: MRI machines generate intense magnetic fields at specific radio frequencies. The shielded room, or "Faraday cage," uses layers of copper or aluminum to contain these signals, preventing interference with other hospital equipment and protecting patient data. The thickness and material are chosen based on the precise frequency used.
Consumer Electronics: The inside of your smartphone or laptop is a maze of small metal shields (often thin nickel-plated steel cans). These protect sensitive components like the processor and radio chips from interfering with each other, ensuring your Bluetooth, Wi-Fi, and cellular signals remain clear and your device passes electromagnetic compatibility (EMC) regulations.
Aerospace & Defense: Aircraft and military vehicles use shielding to protect onboard digital systems from both internal noise and external threats like electromagnetic pulses (EMP). Here, materials like aluminum are favored for their good shielding-to-weight ratio, which is critical for flight.
Industrial Automation: In factories, variable-frequency drives (VFDs) that control motors emit strong electromagnetic interference (EMI). Metal enclosures with proper gasketing and thickness are calculated to shield this noise, preventing malfunctions in nearby robotic arms or sensor systems.
First, there is the common assumption that "a higher Shielding Effectiveness (SE) is always better." While high SE is ideal, it involves trade-offs with cost, weight, and manufacturability. For instance, if a device requires 40dB of SE but you design for 80dB, costs can skyrocket due to the need for materials like Mu-metal. It's crucial to use tools to check the SE across your target frequency band and adopt an approach of selecting materials and thicknesses that are adequate and necessary.
Next is the tendency to think that "material property values are always constant." The conductivity and permeability used in simulators are values for ideal purity and annealing states. Actual materials like extruded aluminum or steel sheets vary due to alloy composition and processing history. For example, the conductivity of A5052 aluminum alloy is about half that of pure aluminum. In real-world design, you must account for measured values from datasheets and incorporate safety margins.
Finally, "calculations that ignore the effects of seams and apertures" are the biggest pitfall. Tools calculate the performance of a uniform flat plate, but actual enclosures have gaps, screw holes, and display windows. Electromagnetic waves leak easily from these points. Even if a flat plate has an SE of 100dB, a 1mm slit can dramatically reduce the overall SE. Treat simulation results as the "potential capability of that material." In a real product, designing for shielding continuity (using gaskets, etc.) is where the real work lies.
The core calculation of this tool is based on understanding the phenomenon of "wave attenuation within a conductor." This is a central concept in electromagnetics, directly linked to loss calculations for waveguides and coaxial cables in wireless communication, and even to the principle of eddy current testing used in non-destructive inspection (detecting flaws near conductive surfaces).
It is also deeply related to transmission line theory. The reflection loss at a shield surface arises from the mismatch between the characteristic impedance of air (approximately 377Ω) and the surface impedance of the metal. This concept of "impedance matching" is common to antenna design and techniques for reducing reflection noise in high-speed signal lines (SI: Signal Integrity) on circuit boards. For example, providing a ground plane can itself be considered a form of shielding.
Furthermore, applications in materials engineering and thermal engineering are noteworthy. The conductivity appearing in the skin depth formula varies with material purity and heat treatment, and permeability is a key property of magnetic materials. Also, the conversion of electromagnetic wave energy into heat via absorption loss is the very principle behind induction heating (IH) cookers and high-frequency metal heating. Conversely, in the thermal design of electronic devices, you may sometimes need to consider this heat generation.
The next step is understanding the "multiple reflection correction term." The approximate formula $SE \approx A + R$ used here is valid when the absorption loss A is sufficiently large (e.g., when the plate thickness is more than three times the skin depth). For thin shields, waves reflect internally multiple times, requiring calculation with the correction term $B$ added: $SE = A + R + B$. You can observe this effect by making the plate thickness extremely thin in the tool and watching the graph change.
Mathematically, the essence lies in deriving the wave equation from Maxwell's equations and following its solution (attenuating wave) inside a conductor. The skin depth $\delta$ is derived as the distance at which the electric field amplitude decays to $1/e$. The tricky part here is handling complex numbers ($j$). Becoming comfortable with Euler's formula $e^{j\theta} = \cos\theta + j\sin\theta$ and understanding the phase changes of waves will give you a comprehensive view of electromagnetics.
As a next topic closer to practical work, consider evaluating "composite materials and layered shields." For example, laminating a magnetic material (high permeability) with a good conductor (high conductivity) can yield high SE across a broad frequency band. Also, learning how to evaluate materials other than homogeneous metal plates—such as conductive pastes, meshes, and conductive plastics—can significantly expand your design freedom.