EMI Shielding Effectiveness
SE = 20 × log10(Ei / Et)
Quick answer
This calculator solves SE = 20 × log10(Ei / Et) for Shielding Effectiveness. With Incident Field 12 V, Transmitted Field 26.4 V, the result is -6.848 dB. It solves in 3 directions, so you can enter the values you have and get the one you need.
Calculator
Formula
Description
Shielding effectiveness quantifies how well an enclosure or shield attenuates electromagnetic fields, expressed as the ratio of incident to transmitted field strength in decibels. A higher SE means better shielding. Shielding works through three mechanisms: reflection (impedance mismatch at the shield surface), absorption (energy converted to heat as the wave passes through the conductor), and multiple reflections (re-reflection within the shield material). At low frequencies, magnetic shielding is more difficult than electric field shielding.
Variables
- SE — Shielding effectiveness (dB)
- Ei — Incident electric field strength (V/m)
- Et — Transmitted electric field strength (V/m)
Practical Notes
Typical SE values: unshielded enclosure 0 dB, painted enclosure 0-10 dB, conductive gasket sealed metal enclosure 40-80 dB, welded enclosure 80-120+ dB. Shield effectiveness degrades at seams, joints, and apertures. Any opening larger than λ/20 significantly compromises shielding. Use conductive gaskets, finger stock, or EMI tape at enclosure seams.
Symbols and units
| Symbol | Meaning | Default unit | Accepted units |
|---|---|---|---|
| SE | Shielding Effectiveness | dB | dB |
| Ei | Incident Field | V | pV, nV, µV, mV, V, kV |
| Et | Transmitted Field | V | pV, nV, µV, mV, V, kV |
Step by step
- 1. What you know: Incident Field 12 V, Transmitted Field 26.4 V
- 2. The relation: SE = 20 × log10(Ei / Et)
- 3. Substitute: Ei = 12 V, Et = 26.4 V
- 4. Result: Shielding Effectiveness = -6.848 dB
Worked examples
Minimum range
Given: Incident Field 0.33 V, Transmitted Field 0.726 V
Result: Shielding Effectiveness = -6.848 dB
Low range
Given: Incident Field 3.3 V, Transmitted Field 7.26 V
Result: Shielding Effectiveness = -6.848 dB
Typical
Given: Incident Field 12 V, Transmitted Field 26.4 V
Result: Shielding Effectiveness = -6.848 dB
High range
Given: Incident Field 0.23 kV, Transmitted Field 0.506 kV
Result: Shielding Effectiveness = -6.848 dB
Maximum range
Given: Incident Field 2.3 kV, Transmitted Field 5.06 kV
Result: Shielding Effectiveness = -6.848 dB
Solving for each variable
Solve for Shielding Effectiveness
Incident Field 0.33 V, Transmitted Field 0.726 V → -6.848 dB
Solve for Incident Field
Shielding Effectiveness 0.3 dB, Transmitted Field 0.726 V → 0.7515 V
Solve for Transmitted Field
Shielding Effectiveness 0.3 dB, Incident Field 0.33 V → 0.3188 V
How Shielding Effectiveness changes with Incident Field
| Incident Field (input) | Shielding Effectiveness (result) |
|---|---|
| 1.2 V | -26.85 dB |
| 3 V | -18.89 dB |
| 6 V | -12.87 dB |
| 9 V | -9.347 dB |
| 12 V | -6.848 dB |
| 18 V | -3.327 dB |
| 24 V | -0.8279 dB |
| 48 V | 5.193 dB |
| 84 V | 10.05 dB |
| 120 V | 13.15 dB |
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<p><a href="https://vbatpower.com/formulas/emi-shielding/">EMI Shielding Effectiveness</a> Calculator by vbatpower.com</p>Frequently asked questions
How do you calculate EMI Shielding Effectiveness?
Use SE = 20 × log10(Ei / Et). With Incident Field 12 V, Transmitted Field 26.4 V, Shielding Effectiveness works out to -6.848 dB.
What is the formula for EMI Shielding Effectiveness?
The formula is SE = 20 × log10(Ei / Et). Shielding effectiveness quantifies how well an enclosure or shield attenuates electromagnetic fields, expressed as the ratio of incident to transmitted field strength in decibels.
How do you find Incident Field when you know the other values?
Rearrange for Incident Field: with Shielding Effectiveness 0.3 dB, Transmitted Field 0.726 V, Incident Field is 0.7515 V.
How do you find Transmitted Field when you know the other values?
Rearrange for Transmitted Field: with Shielding Effectiveness 0.3 dB, Incident Field 0.33 V, Transmitted Field is 0.3188 V.
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