EMC / EMI Formulas
EMC and EMI formulas quantify shielding, coupling, and the emissions that determine regulatory compliance. These calculators help you predict interference and design effective mitigation. They are key to passing certification on the first attempt.
EMC / EMI Formula Calculators
- Harmonic Frequency f_n = n × f_sw Harmonic Number 0.025, Switching Frequency 100 Hz → Harmonic Frequency = 2.5 Hz
- Differential Mode Filter Inductance L = Z / (2πf) Target Impedance 1 Ω, Frequency 100 kHz → Inductance = 1.592 µH
- Common Mode Choke Impedance Z = V_noise / I_limit Noise Voltage 0.33 V, Noise Current Limit 2 mA → Required Impedance = 0.165 kΩ
- Shielding Effectiveness SE = 20 × log₁₀(E_inc / E_trans) Incident Field 0.025, Transmitted Field 0.055 → Shielding Effectiveness = -6.848 dB
- Aperture Leakage Cutoff f_c = c / (2 × slot_length) Slot Length 0.1 mm → Cutoff Frequency = 1499 GHz
- EMI Filter Insertion Loss Required IL = V_measured − V_limit Measured Emission 0.66 dB, Emission Limit 1.41 dB → Required Insertion Loss = -0.75 dB
- ESD Clamping Voltage V_clamp = V_br + I_esd × R_dyn Breakdown Voltage 0.726 V, ESD Current 2 mA, Dynamic Resistance 1 Ω → Clamping Voltage = 0.728 V
Worked result for every EMC / EMI formula
| Formula | Expression | Worked result |
|---|---|---|
| Harmonic Frequency | f_n = n × f_sw | Harmonic Number 0.025, Switching Frequency 100 Hz → Harmonic Frequency = 2.5 Hz |
| Differential Mode Filter Inductance | L = Z / (2πf) | Target Impedance 1 Ω, Frequency 100 kHz → Inductance = 1.592 µH |
| Common Mode Choke Impedance | Z = V_noise / I_limit | Noise Voltage 0.33 V, Noise Current Limit 2 mA → Required Impedance = 0.165 kΩ |
| Shielding Effectiveness | SE = 20 × log₁₀(E_inc / E_trans) | Incident Field 0.025, Transmitted Field 0.055 → Shielding Effectiveness = -6.848 dB |
| Aperture Leakage Cutoff | f_c = c / (2 × slot_length) | Slot Length 0.1 mm → Cutoff Frequency = 1499 GHz |
| EMI Filter Insertion Loss Required | IL = V_measured − V_limit | Measured Emission 0.66 dB, Emission Limit 1.41 dB → Required Insertion Loss = -0.75 dB |
| ESD Clamping Voltage | V_clamp = V_br + I_esd × R_dyn | Breakdown Voltage 0.726 V, ESD Current 2 mA, Dynamic Resistance 1 Ω → Clamping Voltage = 0.728 V |
Variables used across EMC / EMI formulas
- f_n — Frequency of the nth harmonic (Hz)
- n — Harmonic number (integer, dimensionless)
- f_sw — Fundamental switching frequency (Hz)
- L — Required filter inductance (H)
- Z — Target impedance at the noise frequency (Ω)
- f — Frequency of the noise to be filtered (Hz)
- V — Common mode noise voltage (V)
- I — Maximum allowable noise current (A)
- SE — Shielding effectiveness (dB)
- E_inc — Incident electric field strength (V/m or arbitrary units)
- E_trans — Transmitted electric field strength after shielding (same units)
- f_c — Cutoff frequency above which the slot leaks efficiently (Hz)
- slot_length — Longest dimension of the aperture (m)
- IL — Required filter insertion loss (dB)
- V_measured — Measured emission level without filtering (dBµV or dBm)
- V_limit — Regulatory emission limit at that frequency (dBµV or dBm)
- V_clamp — Peak voltage during ESD event (V)
- V_br — Breakdown or trigger voltage of the protection device (V)
- I_esd — Peak ESD current (A)
- R_dyn — Dynamic resistance of the protection device (Ω)
Questions people ask about EMC / EMI
- Differential mode inductance calculator dc — Differential Mode Filter Inductance
- Common mode current choke impedance calculator — Common Mode Choke Impedance
Related Formula Categories
Browse the full formulas index for all 32 categories.