EMC Question of the Week: September 22, 2025

room with large tinted windows

At 100 MHz, a tinted window (σ = 10-12 S/m, εr = 8, thickness = 3 mm) has a plane wave shielding effectiveness of approximately  

  1. 0 dB
  2. 2.2 dB
  3. 4.4 dB
  4. 6 dB

Answer

The best answer is “a.” The magnitude of the reflection coefficient off the front face is 0.48; however, the reflection coefficient off the back face has the same magnitude and is nearly 180° out of phase. A pane of glass that is thin relative to a quarter-wavelength provides virtually no attenuation. At frequencies where the glass is a quarter wavelength thick (in this case 8.8 GHz), the plane wave shielding effectiveness reaches its maximum value (4 dB). At frequencies where the glass is multiple of a half-wavelength, the shielding effectiveness is approximately 0 dB. 

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