EMC Question of the Week: August 23, 2021
For the purposes of high-frequency EM modeling, a round wire can generally be modeled as a flat strip and flat strips can generally be modeled as round wires. To do this, how should the width of the strip, w, be related to the radius of the wire, a?
- w = a
- w = 2a
- w = 3a
- w = 4a
Answer
The best answer is “d.” This result can be found in many publications related to EM modeling and antennas including [1]. It works very well for wires or strips that are long relative to their width at frequencies where the skin depth is small relative to the conductor thickness. It can be used to calculate loop inductances, partial inductances, partial capacitances or for full-wave simulations. It is particularly convenient when modeling round cables using EM software that employs flat rectangular or triangular mesh elements. It's also useful for modeling flat ground straps with wire-grid modeling software.
This relationship does not yield equivalent resistances, but the resistance of the conductor is usually not a significant factor when modeling radiating structures. In models where the resistance of the wire is important, equivalent resistance can often be obtained by altering the conductivity of the material.
Note that this relationship is not accurate when the wire or strip are very near other conductors. In these situations, the current distribution can be altered due to the proximity effect.
[1] Antenna Theory Analysis and Design, 2nd ed. Constantine A. Balanis, John Wiley and Sons, 1997, p. 456.
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