Calculate Emi

EMI Shielding Effectiveness Calculator

Calculation Results:

Shielding Effectiveness (SE): 0 dB

Power Reduction: 0%

function calculateEMIShielding() { var p1 = document.getElementById("incidentPower").value; var p2 = document.getElementById("transmittedPower").value; var resultDiv = document.getElementById("emiResultBox"); var dbSpan = document.getElementById("dbValue"); var attenP = document.getElementById("attenuationLevel"); var redSpan = document.getElementById("reductionPercent"); if (p1 && p2 && parseFloat(p1) > 0 && parseFloat(p2) > 0) { var incident = parseFloat(p1); var transmitted = parseFloat(p2); // Formula for EMI Shielding Effectiveness in dB: SE = 10 * log10(Pi / Pt) var se = 10 * Math.log10(incident / transmitted); var reduction = ((incident – transmitted) / incident) * 100; dbSpan.innerHTML = se.toFixed(2); redSpan.innerHTML = reduction.toFixed(4); var quality = ""; if (se < 10) quality = "Poor Shielding (Minimal attenuation)"; else if (se < 30) quality = "Fair Shielding (Standard commercial)"; else if (se < 60) quality = "Good Shielding (Industrial grade)"; else if (se < 90) quality = "Excellent Shielding (Military/High-spec)"; else quality = "Exceptional Shielding (Scientific grade)"; attenP.innerHTML = "Performance: " + quality; resultDiv.style.display = "block"; } else { alert("Please enter valid positive power values for both fields."); } }

Understanding EMI Shielding Effectiveness

Electromagnetic Interference (EMI) Shielding Effectiveness (SE) is a critical metric used in electronics and telecommunications to measure the ability of a material or enclosure to block electromagnetic fields. Unlike financial calculations, EMI math focuses on signal attenuation and power ratios.

How to Calculate EMI Attenuation

The shielding effectiveness is typically expressed in decibels (dB). It represents the ratio between the power of the electromagnetic wave before it hits the shield (Incident Power) and the power that passes through the shield (Transmitted Power).

Formula: SE (dB) = 10 × log₁₀(P_incident / P_transmitted)

Realistic Example Calculation

If an electronic device is placed inside a protective casing, and we measure the external signal at 50 Watts (Incident) but only 0.05 Watts (Transmitted) reaches the interior, the calculation would be:

• Ratio: 50 / 0.05 = 1,000
• Log₁₀(1000): 3
• SE: 10 × 3 = 30 dB

A 30 dB result indicates that the power has been reduced by 99.9%. In high-precision aerospace or military applications, shielding goals often exceed 80 dB to ensure total signal isolation.

Factors Affecting Shielding Results

Several physical properties determine how effectively a material blocks EMI:

• Material Conductivity: Metals like copper and aluminum provide high reflection loss.
• Permeability: Magnetic materials help in absorbing low-frequency magnetic fields.
• Thickness: While it affects absorption loss, the "Skin Effect" often means that very thin coatings are sufficient for high frequencies.
• Frequency: EMI shielding performance varies significantly depending on whether you are blocking GHz-range cellular signals or low-frequency hum.