What is Skin depth: Definition and 21 Discussions

Skin effect is the tendency of an alternating electric current (AC) to become distributed within a conductor such that the current density is largest near the surface of the conductor and decreases exponentially with greater depths in the conductor. The electric current flows mainly at the "skin" of the conductor, between the outer surface and a level called the skin depth. Skin depth depends on the frequency of the alternating current; as frequency increases, current flow moves to the surface, resulting in less skin depth. Skin effect reduces the effective cross-section of the conductor and thus increases its effective resistance. Skin effect is caused by opposing eddy currents induced by the changing magnetic field resulting from the alternating current. At 60 Hz in copper, the skin depth is about 8.5 mm. At high frequencies the skin depth becomes much smaller.
Increased AC resistance caused by the skin effect can be mitigated by using specially woven litz wire. Because the interior of a large conductor carries so little of the current, tubular conductors such as pipe can be used to save weight and cost. The skin effect has practical consequences in the analysis and design of radio-frequency and microwave circuits, transmission lines (or waveguides), and antennas. It is also important at mains frequencies (50–60 Hz) in AC electrical power transmission and distribution systems. It is one of the reasons for preferring high-voltage direct current for long distance power transmission.
The effect was first described in a paper by Horace Lamb in 1883 for the case of spherical conductors, and was generalised to conductors of any shape by Oliver Heaviside in 1885.

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  1. T

    Skin depth of multilayered (2-layer) wire

    Homework Statement:: Not a specific question, more just a conceptual clarification for a project. But generally: What is an equation for the effective skin depth of a multilayered (in this case only 2 layers) wire, as a function of the resistivities and relative permeabilities of both of the...
  2. iVenky

    I Is London depth in superconductors analogous to skin depth?

    London penetration depth that's defined for superconductors has a similar equation to skin depth in conductors derived from maxwell's equations. Are they equivalent?
  3. C

    Is the skin depth of tarnished silver any different than untarnished?

    That's it, just the question. I am figuring that the tarnish is an irrelevance as it does not participate either magnetically or electrically, so any RF current passing through the [still metallic] silver top layer, albeit with tarnish over the top, will pass through the same thickness of...
  4. C

    I What is meant by "low frequencies"? (EM skin depth question)

    I'm studying conductors, where complex wave number ##K=k+iα## and complex index of refraction ##N=n+iκ## is introduced. My textbook(Fowles Optics) says that for "very low frequencies", skin depth δ is equal to ##δ=\frac{1}{α}=\sqrt{\frac{λ_0}{cπσμ_0}}##. What is "very low frequency"? How much...
  5. I

    A Penetration Depth of General Complex Conductivity

    Hi all, I'm working through chapter 2 of Michael Tinkham's Introduction to Superconductivity. On page 40, he asserts that the skin-depth for a general complex conductivity is (In Gaussian units) $$\delta = \frac{c}{\sqrt{2\pi\omega\left(|\sigma| + \sigma_2\right)}}$$ where $$\sigma = \sigma_1...
  6. mertcan

    The Logic Behind Equating Differential Operators to Numbers in Electromagnetism

    hi, nowadays I try to get involved electromagnetic waves equations, and I came across that $$ \nabla $$ is treated like $$ ik $$ and $$ \frac {\partial } {\partial t} $$ is treated like $$ -iw $$ And if you look at the part painted with orange in my attachment, afterwards you can see that $$...
  7. T

    EM wave shielding & skin depth

    If I use 10mm (thickness) of a metal for the sides of a Faraday cage, with a 5mm skin depth at the frequency to be shielded, & increase the v/m of the EM wave to be blocked gradually, will there be a stage where the skin depth will increase to 6mm, or is 5mm the maximum limit?
  8. W

    Skin depth: Same for current as for incoming EM wave?

    For a good conductor, an incoming plane electromagnetic wave will be attenuated exponentially as it penetrates a distance ##z## into the conductor, ##|\vec{E}(z)| = |\vec{E_0}|e^{-z/ \delta}##. ##\delta## is called the "skin depth". The current generated by this incoming electromagnetic wave is...
  9. G

    Does AC current pass through perfectly shielded box?

    Hello. I've recently have a lot of question of building Faraday cage for our high voltage gas discharge lab. I think this question is a kind of fundamental question for such a job. Let's say I would make perfect Faraday cage with perfect shielding or have metal plate of infinity transverse...
  10. G

    Understanding Skin Depth in DC and AC Fields: Confusion and Clarification

    Hello. The skin depth is nothing but measure of penetration depth of EM Wave when it is incident on the conductor. It is well known that the skin depth is decreased when the EM wave frequency increases. But thinking about DC field. We know that when DC is applied to metal (metal is installed...
  11. beowulf.geata

    Current density and skin depth

    Homework Statement A thin metallic strip on a circuit board has length L, width a and thickness t, with L>>a>> t. Derive an expression for the resistance between the ends of the strip at frequency f, assuming that the skin depth is small compared with the thickness t. Homework Equations The...
  12. R

    Voltage on a conductor due to skin depth

    As we know due to skin depth effect the Alternating Current flows at a depth from the conductor surface (which means there is no voltage on the surface of the conductor, it is only at a depth from the surface). Then how is it possible for voltage to get appeared across some other conductor...
  13. H_man

    In acoustics is there something analogous to skin depth in EM?

    Hi all The reflection and transmission of a pressure wave at a boundary depends on the relative impedance of the two media. I'm pretty new to acoustics but the textbook I've been looking at doesn't seem to specify that the such calculations are only valid when the medium is at least a few...
  14. Z

    Skin depth of a good conductor

    Homework Statement for my assignment given i was told to derive the equation of the skin depth of a good conductor and i derived it as d=sqrt(2/\mu\omega\sigma) then i was told to calculate d where i was given w=10^15 and sigma=10^7 and this gave me a d of d=1.26E-8 which i guess is...
  15. F

    Skin depth of zero thickness in DC circuits

    Hello Forum, the formula for skin depth is both inversely proportional to conductivity and frequency omega. There seem to be 3 cases when the skin depth of a metal is exactly (or tends to) zero: 1) if an EM wave of frequency f (any frequency) is incident on a perfect metal wall (infinite...
  16. P

    Skin Depth Confusion: Investigating Different Equations for Paul

    Dear all I am slightly confused over the equations for skin depth. My university notes give me the equations: \delta = tan-1 (tan\delta) = \frac{\sigma}{\omega \epsilon} (loss tangent) where \delta is skin depth and \sigma is conductivity. I am also given the equation: \delta =...
  17. B

    Importance of skin depth in radio communications

    Homework Statement 'Briefly explain the importance of skin depth in the context of radio communications.' Homework Equations The Attempt at a Solution A guess would be that, the frequencies of the radio transmissions should be kept small so that the signal has a large skin depth...
  18. T

    Skin Depth Q: Cellphone Rings in Cavity

    I placed a cellphone in 2 half-spheres that i closed afterwards to create a metal cavity (aliminium 1mm) and called it (with another cellphone). The phone rang even if it wasn't supposed to considering the skin effect (wavelenght were about 0,04m and i couldn't see any holes). Anyone has a clue why?
  19. P

    Solving Skin Depth for Copper at 1.0 GHz

    hi there, I am stuck on this question can some give me a hint on how to solve the question: the question is: Calculate the skin depth for copper at 1.0 GHz . σ = 5.8x10^7 S/m, εr=1, μr=1. the formula i think that i need to use is tan δ = σ / (ω)(ε0)(εr) ω = 2nf = 2 x n x 1 x 10^9...
  20. D

    Solving Skin Depth Challenges in Electromagnetics

    hi all i run into some contradictions while studing electromagnetics. you know skin depth decreases when frequency increases.It ans that waves of higher frequencies have lower skin depth. ok and every one of us knows that X-ray have higher frequencies than other waves for example radio...