Depth of penetration

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

1. Centurion university of technology and management Project on - Depth of penetration Submitted by Name- amit kumar banra Reg no- 130301EER037 Branch - EEE

2. 1 Introduction 2 Depth of penetration Eddy current v/s current density Eddy current depth of penetration Eddy current how it penetrates Equation to calculate standard depth penetration Example copper how it penetrates problems 1 / 2 Numerical 1 / 2 10 conclusion contents

3. The  intensity  of  eddy  currents  decreases  exponentially  with  depth  in  a  material.    The  intensity  at  any  given  depth   isaffected  by  the  same  variables  that  influence  the  surface  intensity  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. introduction

4. STANDERD DEPTH OF PENETRTION Three  of  these  variables  ( conductivity ,  relative  magnetic  permeability,  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  logarithms).    The  standard  depth  of  penetration   isexpressed by the following formula

5. Penetration depth . electromagnetic radiation is incident on the surface of a material, it may be (partly) reflected from that surface and there will be a field containing energy transmitted into the material. This electromagnetic field interacts with the atoms and electrons inside the material. Depending on the nature of the material, the electromagnetic field might travel very far into the material, or may 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)  = 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 .

18. THANK YOU SUBMIT TE D TO – ARINDAM BHATTACHARJEE