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# Skin Effect ?? How and Y?

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#### Resistance

##### Member level 4
skin effect origin

Hi,

I know wat skin effect is and its implications..

Explian me how and y it occurs using e and m feild explanations.

regards

#### jian

implications of skin effect

Hi, Resistance: I think you can look at the standard EM theory on plane wave incident into a metallic plane. You can solve the field inside the metallic plane. You will see the E and H field will be decaying exponentially when you are going into the metallic structure. Since J = sigma*E. It means that most of J is concentraing on the surface of the metallic plane. The concentration is more severe at higher frequency and it will cause more loss because the current is passing through an equivalently narrower cross-section. That is the so-called skin effect. As I mentioned, its implication is that there will be more loss at high frequency because the current is more concentrated. Regards.

V
Points: 2

#### v_c

skin effect implications

The consequence of the skin effect is that the AC resistance will be higher than the DC resistance since the current is flowing through a smaller cross-sectional area

$R = \frac{\rho L}{A}$

where $\rho$ is resistivity, $L$ is length and $A$ is cross-sectional area.

take a look at the attached picture. Refer to the following page for more information about the web page for numerical values for cables. Do a google search and you will find lots of numerical information.

More on the skin effect'' : REACTANCE AND IMPEDANCE -- INDUCTIVE

Hope you find the information helpful.

Best regards,
v_c

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#### tyassin

Hi

When a conductor conducts current it establish a magnetic field, when this is changing as in AC systems, it induces small circular currents in the center of its conductor, which oppose the original current. These small current are called "eddy currents" and they generate there own magnetig field. This can deteriorate the fields ability to efficiently change direction which it often does in RF systems. They also dissipate energy in the form of heat.

But it is the eddy currents which decrease the current density in the center of the conductor and this leads to the increasing AC resistance.

Regards

#### Resistance

##### Member level 4
hi tyassin,

Thanks a lot i think this was wat i was in the look out for..

Could we say due to lenz's law the eddy currents could be generated.. And how frequency influenves this feild formation. jus explain that too . I know inc in freq makes current flow more at the surface..

Y this is a phenomena only in conductors ??

regards..

#### ahmed osama

##### Full Member level 6
jian said:
Hi, Resistance: I think you can look at the standard EM theory on plane wave incident into a metallic plane. You can solve the field inside the metallic plane. You will see the E and H field will be decaying exponentially when you are going into the metallic structure. Since J = sigma*E. It means that most of J is concentraing on the surface of the metallic plane. The concentration is more severe at higher frequency and it will cause more loss because the current is passing through an equivalently narrower cross-section. That is the so-called skin effect. As I mentioned, its implication is that there will be more loss at high frequency because the current is more concentrated. Regards.

I Guess J = sigma*E works for DC & AC so why skin depth appears only with AC??

#### abhi_kolkata

##### Member level 5
hi,

u can look in feynman lectures in physics (vol. 1 and 2) by r.p.feynman for detailed physical origin of skin depth. another good book is elements of elecromagnetics by sadiku.

with regards
abhi

#### svarun

##### Full Member level 5
ahmed osama said:
jian said:
Hi, Resistance: I think you can look at the standard EM theory on plane wave incident into a metallic plane. You can solve the field inside the metallic plane. You will see the E and H field will be decaying exponentially when you are going into the metallic structure. Since J = sigma*E. It means that most of J is concentraing on the surface of the metallic plane. The concentration is more severe at higher frequency and it will cause more loss because the current is passing through an equivalently narrower cross-section. That is the so-called skin effect. As I mentioned, its implication is that there will be more loss at high frequency because the current is more concentrated. Regards.

I Guess J = sigma*E works for DC & AC so why skin depth appears only with AC??

The skin depth goes as inverse of frequency and it is infinite at DC. Hence at DC skin depth is not considered. At DC, current flow is volumetric while at very high frequency the skin depth is so low that current flows only in a thin sheet and so you can model it as surface current. For more on this see Rautio's paper in MTT on modelling strips at high frequency by two sheets of current.

-svarun

#### Resistance

##### Member level 4
Hi tyassin,

Please explain the relationship between eddy currents effects or (lenz law) and freq of ac..

regards.

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