EMC Question of the Week: September 3, 2018

Current distribution in round wire illustrating skin effect and skin depth

Due to the skin effect, at high frequencies the resistance of conductors in a transmission line

  1. increases with increasing frequency
  2. decreases with increasing frequency
  3. exhibits a "sweet spot" where the resistance is zero
  4. is equal to the characteristic impedance of the transmission line

Answer

The correct answer is "a". The skin depth decreases with increasing frequency causing the current to be constrained to a smaller cross-sectional area of the conductors. This results in higher resistance. At frequencies where the skin depth is small relative to the conductor dimensions, the resistance will increase proportional to the square root of the frequency. 

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