This is ths ppt of electromagnetic theory,given as an assingement in centurion university,jatni.

1. Submitted by
Name-amit kumar banra
Reg no-130301EER037

2. 1 Introduction
2 Depth of penetration
3 Eddy current v/s current density
4 Eddy current depth of penetration
5 Eddy current how it penetrates
6 Equation to calculate standard depth
penetration
7 Example copper how it penetrates
8 problems 1 / 2
9 Numerical 1 / 2
10 conclusion
CONTENTS

3. The intensity of eddy currents decreases exp
onentially with depth in a material. The inte
nsity at any given depth isaffected by the sa
me variables that influence the surface inten
sity of eddy currents, although not always in
the samemanner or by the same amount. To put
it another way, the depth of penetration of a
specific intensity of eddy current sis affected by
the variables, as indicated in Table 4-
4. Generally, any parameter that increases the
depth of penetrationwould provide an equivalent
eddy current response at a greater depth in a
test part.

4. STANDERD DEPTH OF PENETRTION
Three of these variables (conductivity, relative magnetic permea
bility, and frequency) are used to define the standarddepth of
penetration. Standard depth of penetration is the depth below the
surface of the inspection article at which
themagnetic field strength, or the intensity of the induced eddy
currents, is reduced to 36.8 percent of the value at thesurface.
(0.368 = 1/e, where e = 2.71828, the base of natural logarit
hms). The standard depth of penetration isexpressed by the
following formula

5. Penetration depth
.electromagneticradiation is incident onthe surface of a material, it may be
(partly) reflected from that surface and there will bea field containing energy
transmitted into the material. This electromagnetic field interacts with the atoms
and electrons inside the material. Depending onthe nature of the material, the
electromagnetic field might travel very far into the material, ormay die out very
quickly. For a given material, penetration depth will generally be a function of
wavelength

6. EDDY CURRENT vs CURRENT DENSITY
Eddy current density does not remain constant across the depth of a material. The
density is greatest at the surface and decreases exponentially with depth (the "skin
effect"). The standard depth of penetration equation (shown to the right) is used to
explain the penetration capability of eddy current testing, which decreases with
increasing frequency, conductivity, or permeability

7. EDDY CURRENT DEPTH OF PENETRATION

8. Eddy current how it penetrates
The depth that eddy currents penetrate into a material is
affected by the frequency of the excitation current and the
electrical conductivity and magnetic permeability of the
specimen. The depth of penetration decreases with
increasing frequency and increasing conductivity and
magnetic permeability. The depth at which eddy current
density has decreased to 1/e, or about 37% of the surface
density, is called the standard depth of penetration (d). The
word 'standard' denotes plane wave electromagnetic field
excitation within the test sample (conditions which are
rarely achieved in practice). Although eddy currents
penetrate deeper than one standard depth of penetration,
they decrease rapidly with depth. At two standard depths of
penetration (2d), eddy current density has decreased to 1/e
squared or 13.5% of the surface density. At three depths (3d),
the eddy current density is down to only 5% of the surface
density.

9. Eddy current penetratration
Since the sensitivity of an eddy current inspection depends on
the eddy current density at the defect location, it is important
to know the strength of the eddy currents at this location.
When attempting to locate flaws, a frequency is often
selected which places the expected flaw depth within one
standard depth of penetration. This helps to assure that the
strength of the eddy currents will be sufficient to produce a
flaw indication. Alternately, when using eddy currents to
measure the electrical conductivity of a material, the
frequency is often set so that it produces three standard
depths of penetration within the material. This helps to assure
that the eddy currents will be so weak at the back side of the
material that changes in the material thickness will not affect
the eddy current measurements.

10. Equation to calculate standard depth penetration
Where
δ = Standard Depth of Penetration (mm)
π = 3.14
f = Test Frequency (Hz)
µ = Magnetic Permeability (H/mm)
0 = Electrical Conductivity (% IACS)

11. Example of the material copper

12. questions
Q.1.What is the standard depth of penetration when performing an
eddy current inspection on a piece of 304 Corrosion Resistant Steel?
The material has a relative permeability of 1.05 and a conductivity
of 2.5% IACS. The frequency used to drive the eddy current probe is
50 kHz
Q.2. Determine the frequency needed to achieve a depth of
penetration of 2mm in 7075-T76 aluminum plate
-

13. soloutions
Question 1.

14. soloutions
Question 2.

15. NUMERICALS 1

16. Numericals 2

17. conclusion
“I would like to thank all of my friends and “EMT sir, MR
ARINDAM BHATTACHARJEE..for giving me this opportunity for
presenting a ppt on such a wonderfull topic,as In the class I didn’t
understand too much about this topic but when I was given the topic
“depth of penetration” as my topic of presentation I came to know
many things about this chapter,by researching it on google,books
etc!
And at last not the least, I thank you for taking out time to read out
my ppt.