Electronic – Skin effect for pulse current


I've just bought some 6mm^2 copper wire for my project where I will have large pulse currents – ~500A peak (driving very large Xenon flash bulbs, 1000J pulse in 2ms).

But I know that skin effect make it useless to use thick wires on high frequency, but does it apply to sharp fronts? Is that correct that having multiple non-isolated wires make it even worse? (mine cable have about 20 tiny 'wires')

Best Answer

You should use the finest magnet wire with many multiple strands or LITZ WIRE to improve L/R time constant and peak current for lowest loss cable. Your discharge rise time will then drop to xx picoseconds. But for conductor pairs use twisted pair Litz wire to reduce CM emissions.

Otherwise, you can jam many radios/mobiles with high rep rates of > 1pps affecting AGC. !!

In most conductors R(f) rises fast and L(f) drops slow from skin effect. This R effect increases more with iron content since it is from Eddy Currents. In DSL and cable modem skin effects change Zo, phase shift and group delay.... Tony

ref wiki

Although the geometry is different, a twisted pair used in telephone lines is similarly affected: at higher frequencies the inductance decreases by more than 20% as can be seen in the following table.

Characteristics of telephone cable as a function of frequency
Representative parameter data for 24 gauge PIC telephone cable at 21 °C (70 °F).

   (Hz) R (Ω/km)    L (mH/km)   G (μS/km) C (nF/km)
     1    172.24    0.6129      0.000      51.57
    1k    172.28    0.6125      0.072      51.57
   10k    172.70    0.6099      0.531      51.57
  100k    191.63    0.5807      3.327      51.57
    1M    463.59    0.5062     29.111      51.57
    2M    643.14    0.4862     53.205      51.57
    5M    999.41    0.4675    118.074      51.57

The spectrum of your pulse is not at all like a square wave, since it is not repetitive over a small interval. It is a continuous spectrum rolling off similar to The null of 2nd harmonics of the equivalent pulse of a "square" wave and then rolling off above the 0.35Tr rise time. So resonant frequency and group delay calculations of pulses is very poor and affected by skin effects, even in controlled impedances, making Baseband communication much worse than the discrete equalized channel's of a modem for thruput in bps/Hz .....Tony

However hollow copper tubing with interior flash gold plating works wonders in microwave as does ENIG on stripline and gold-plated aluminum cases for RF circuits and enclosures for microwave. I saw this in '77.

Here is a different skin effect from UV on dielectrics (human skin) and how Sodium Bicarbonate helps prevent cancer. ( also reduce causes/reactions of itching). https://www.cancertutor.com/simoncini/. :):)