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Technical Discussions
Ron Olson
R & D, Aviation
The Best Aviation Company In The World, USA, Joined Feb 2005, 24

Ron Olson

R & D, Aviation
The Best Aviation Company In The World,
USA,
Joined Feb 2005
24
06:12 Oct-05-2005
Conductivity and Multiple Layers

Trying to remember my physics...

Given three different conductivities:
sigma 1
sigma 2
sigma 3

Given same thickness for each layer of conductivity with no air gaps between layers
Given each layer of conductivity is directly under the other, i.e., sigma1 on top, then sigma2 below sigma1, and so on.

Is the total conductivity computed this way?

1/sigma total = 1/sigma1 + 1/sigma2 + 1/sigma3

Is this the same equation for dielectrics and capacitors in series and resistors in parallel?

Thank you.

Ed Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1300

Ed Ginzel

R & D, -
Materials Research Institute,
Joined Nov 1998
1300
03:38 Oct-07-2005
Re: Conductivity and Multiple Layers
Ron:
I think there is much more variability in layered conductivity assessment than the simple "stacking" of capacitors.
Even after you have definitely "decided" on the absolute values of the layers' component conductivities, you still have thickness effects, surface irregularity effects at the bond interfaces and the field effect of the coil used.
Possibly the most convenient method of "estimating" the expected conductivity value you will get for a multi-layer condition is by modelling. Some work has been done in this venue. A great article is to be found on www.NDT.net at
http://www.ndt.net/article/wcndt00/papers/idn228/idn228.htm

The software TEDDY that was provided for this paper is a great start on understanding the variability of results that occurs with variation in the parameters involved. The modelling programme is limited to maximum 2 layers but even then you can see that a simple addition is not the solution. in Eddy Current Testing you are using a field effect to determineconductivity. How far that field has penetrated the sample and the layer thicknesses along the way will determine the value you get. This is an indirect measurement technique.

I think TEDDY was a shareware. It has a great set of parameter options including geometry of part tested, coil parameters, liftoff, sample conductivity and permeability. As you will see from the article link, impedance plane diagrams are provided.
Regards
Ed
----------- Start Original Message -----------
: Trying to remember my physics...
: Given three different conductivities:

: sigma 1
: sigma 2
: sigma 3
: Given same thickness for each layer of conductivity with no air gaps between layers
: Given each layer of conductivity is directly under the other, i.e., sigma1 on top, then sigma2 below sigma1, and so on.
: Is the total conductivity computed this way?
: 1/sigma total = 1/sigma1 + 1/sigma2 + 1/sigma3
: Is this the same equation for dielectrics and capacitors in series and resistors in parallel?
: Thank you.
------------ End Original Message ------------

Ron Olson
R & D, Aviation
The Best Aviation Company In The World, USA, Joined Feb 2005, 24

Ron Olson

R & D, Aviation
The Best Aviation Company In The World,
USA,
Joined Feb 2005
24
03:44 Oct-07-2005
Re: Conductivity and Multiple Layers
Thank you, Mr. Ginzel.

I'll read this article soon. Looks promising. I may give my thoughts after I read the article. BTW, what does TEDDY mean? I hope the shareware is available!

I believe the equation I gave is correct - ideally. I know that I'm assuming homogeneity, perfect contacts and perfect surfaces but essentialy the equation works. Since, conductivity and resistivity are just another way of stating Ohm's Law: the current density, J, is proportional to the applied electric field, E, by the materials conductivity, o. IOW, J=oE.

I may have time to empirically prove this. Anyone else done this by experiment?

----------- Start Original Message -----------
: Ron:
: I think there is much more variability in layered conductivity assessment than the simple "stacking" of capacitors.
: Even after you have definitely "decided" on the absolute values of the layers' component conductivities, you still have thickness effects, surface irregularity effects at the bond interfaces and the field effect of the coil used.
: Possibly the most convenient method of "estimating" the expected conductivity value you will get for a multi-layer condition is by modelling. Some work has been done in this venue. A great article is to be found on www.NDT.net at
: http://www.ndt.net/article/wcndt00/papers/idn228/idn228.htm
:
: The software TEDDY that was provided for this paper is a great start on understanding the variability of results that occurs with variation in the parameters involved. The modelling programme is limited to maximum 2 layers but even then you can see that a simple addition is not the solution. in Eddy Current Testing you are using a field effect to determine conductivity. How far that field has penetrated the sample and the layer thicknesses along the way will determine the value you get. This is an indirect measurement technique.
: I think TEDDY was a shareware. It has a great set of parameter options including geometry of part tested, coil parameters, liftoff, sample conductivity and permeability. As you will see from the article link, impedance plane diagrams are provided.
: Regards
: Ed
: : Trying to remember my physics...
: : Given three different conductivities:
: : sigma 1
: : sigma 2
: : sigma 3
: : Given same thickness for each layer of conductivity with no air gaps between layers
: : Given each layer of conductivity is directly under the other, i.e., sigma1 on top, then sigma2 below sigma1, and so on.
: : Is the total conductivity computed this way?
: : 1/sigma total = 1/sigma1 + 1/sigma2 + 1/sigma3
: : Is this the same equation for dielectrics and capacitors in series and resistors in parallel?
: : Thank you.
------------ End Original Message ------------

Ron Olson
R & D, Aviation
The Best Aviation Company In The World, USA, Joined Feb 2005, 24

Ron Olson

R & D, Aviation
The Best Aviation Company In The World,
USA,
Joined Feb 2005
24
03:48 Oct-07-2005
Re: Conductivity and Multiple Layers
"IOW, J=oE."

Yeah, I just noticed this...a good cup of joe is very conductive! :D

----------- Start Original Message -----------
: Thank you, Mr. Ginzel.
: I'll read this article soon. Looks promising. I may give my thoughts after I read the article. BTW, what does TEDDY mean? I hope the shareware is available!
: I believe the equation I gave is correct - ideally. I know that I'm assuming homogeneity, perfect contacts and perfect surfaces but essentialy the equation works. Since, conductivity and resistivity are just another way of stating Ohm's Law: the current density, J, is proportional to the applied electric field, E, by the materials conductivity, o. IOW, J=oE.
: I may have time to empirically prove this. Anyone else done this by experiment?
: : Ron:
: : I think there is much more variability in layered conductivity assessment than the simple "stacking" of capacitors.
: : Even after you have definitely "decided" on the absolute values of the layers' component conductivities, you still have thickness effects, surface irregularity effects at the bond interfaces and the field effect of the coil used.
: : Possibly the most convenient method of "estimating" the expected conductivity value you will get for a multi-layer condition is by modelling. Some work has been done in this venue. A great article is to be found on www.NDT.net at
: : http://www.ndt.net/article/wcndt00/papers/idn228/idn228.htm
: :
: : The software TEDDY that was provided for this paper is a great start on understanding the variability of results that occurs with variation in the parameters involved. The modelling programme is limited to maximum 2 layers but even then you can see that a simple addition is not the solution. in Eddy Current Testing you are using a field effect to determine conductivity. How far that field has penetrated the sample and the layer thicknesses along the way will determine the value you get. This is an indirect measurement technique.
: : I think TEDDY wasa shareware. It has a great set of parameter options including geometry of part tested, coil parameters, liftoff, sample conductivity and permeability. As you will see from the article link, impedance plane diagrams are provided.
: : Regards
: : Ed
: : : Trying to remember my physics...
: : : Given three different conductivities:
: : : sigma 1
: : : sigma 2
: : : sigma 3
: : : Given same thickness for each layer of conductivity with no air gaps between layers
: : : Given each layer of conductivity is directly under the other, i.e., sigma1 on top, then sigma2 below sigma1, and so on.
: : : Is the total conductivity computed this way?
: : : 1/sigma total = 1/sigma1 + 1/sigma2 + 1/sigma3
: : : Is this the same equation for dielectrics and capacitors in series and resistors in parallel?
: : : Thank you.
------------ End Original Message ------------

Theodoros Theodoulidis
Theodoros Theodoulidis
05:27 Oct-08-2005
Re: Conductivity and Multiple Layers
Hi, I am the author of the TEDDY-freeware. This is a simple program that can be used for calculations of coil impedance in a number of important eddy current test geometries. It uses analytical modelling and relies heavily on the well-known Dodd and Deeds models.

The software is rather old now (about 5 years) and there has not been any newer version. I intend to upgrade it (whenever I find time) for two reasons:
2) To add additional geometries. Due to the resurgence of interest in analytical models for eddy current NDE, we now have rapid and accurate models for geometries involving for example ferrite core probes, edges and cracks.

I would like to thank all the people that asked and tested the software. Their feedback will prove very helpful in the next version. Meanwhile, the old freeware version is available on request to theodoul@ieee.org.

Theodoros Theodoulidis
University of West Macedonia
Greece

----------- Start Original Message -----------
: Thank you, Mr. Ginzel.
: I'll read this article soon. Looks promising. I may give my thoughts after I read the article. BTW, what does TEDDY mean? I hope the shareware is available!
: I believe the equation I gave is correct - ideally. I know that I'm assuming homogeneity, perfect contacts and perfect surfaces but essentialy the equation works. Since, conductivity and resistivity are just another way of stating Ohm's Law: the current density, J, is proportional to the applied electric field, E, by the materials conductivity, o. IOW, J=oE.
: I may have time to empirically prove this. Anyone else done this by experiment?
: : Ron:
: : I think there is much more variability in layered conductivity assessment than the simple "stacking" of capacitors.
: : Even after you have definitely "decided" on the absolute values of the layers' component conductivities, you still have thickness effects, surface irregularity effects at the bond interfaces and the field effectof the coil used.
: : Possibly the most convenient method of "estimating" the expected conductivity value you will get for a multi-layer condition is by modelling. Some work has been done in this venue. A great article is to be found on www.NDT.net at
: : http://www.ndt.net/article/wcndt00/papers/idn228/idn228.htm
: :
: : The software TEDDY that was provided for this paper is a great start on understanding the variability of results that occurs with variation in the parameters involved. The modelling programme is limited to maximum 2 layers but even then you can see that a simple addition is not the solution. in Eddy Current Testing you are using a field effect to determine conductivity. How far that field has penetrated the sample and the layer thicknesses along the way will determine the value you get. This is an indirect measurement technique.
: : I think TEDDY was a shareware. It has a great set of parameter options including geometry of part tested, coil parameters, liftoff, sample conductivity and permeability. As you will see from the article link, impedance plane diagrams are provided.
: : Regards
: : Ed
: : : Trying to remember my physics...
: : : Given three different conductivities:
: : : sigma 1
: : : sigma 2
: : : sigma 3
: : : Given same thickness for each layer of conductivity with no air gaps between layers
: : : Given each layer of conductivity is directly under the other, i.e., sigma1 on top, then sigma2 below sigma1, and so on.
: : : Is the total conductivity computed this way?
: : : 1/sigma total = 1/sigma1 + 1/sigma2 + 1/sigma3
: : : Is this the same equation for dielectrics and capacitors in series and resistors in parallel?
: : : Thank you.
------------ End Original Message ------------

Ilayaraja
Ilayaraja
00:43 Oct-27-2006
Re: Conductivity and Multiple Layers
i require teddy software pls mail me the web add

----------- Start Original Message -----------
: Hi, I am the author of the TEDDY-freeware. This is a simple program that can be used for calculations of coil impedance in a number of important eddy current test geometries. It uses analytical modelling and relies heavily on the well-known Dodd and Deeds models.
: The software is rather old now (about 5 years) and there has not been any newer version. I intend to upgrade it (whenever I find time) for two reasons:
: 2) To add additional geometries. Due to the resurgence of interest in analytical models for eddy current NDE, we now have rapid and accurate models for geometries involving for example ferrite core probes, edges and cracks.
: I would like to thank all the people that asked and tested the software. Their feedback will prove very helpful in the next version. Meanwhile, the old freeware version is available on request to theodoul@ieee.org.
: Theodoros Theodoulidis
: University of West Macedonia
: Greece
:
: : Thank you, Mr. Ginzel.
: : I'll read this article soon. Looks promising. I may give my thoughts after I read the article. BTW, what does TEDDY mean? I hope the shareware is available!
: : I believe the equation I gave is correct - ideally. I know that I'm assuming homogeneity, perfect contacts and perfect surfaces but essentialy the equation works. Since, conductivity and resistivity are just another way of stating Ohm's Law: the current density, J, is proportional to the applied electric field, E, by the materials conductivity, o. IOW, J=oE.
: : I may have time to empirically prove this. Anyone else done this by experiment?
: : : Ron:
: : : I think there is much more variability in layered conductivity assessment than the simple "stacking" of capacitors.
: : : Even after you have definitely "decided" on the absolute values of the layers' component conductivities, you still have thickness effects, surface irregularity effects at the bond interfaces and the field effect of the coil used.
: : : Possibly the most convenient method of "estimating" the expected conductivity value you will get for a multi-layer condition is by modelling. Some work has been done in this venue. A great article is to be found on www.NDT.net at
: : : http://www.ndt.net/article/wcndt00/papers/idn228/idn228.htm
: : :
: : : The software TEDDY that was provided for this paper is a great start on understanding the variability of results that occurs with variation in the parameters involved. The modelling programme is limited to maximum 2 layers but even then you can see that a simple addition is not the solution. in Eddy Current Testing you are using a field effect to determine conductivity. How far that field has penetrated the sample and the layer thicknesses along the way will determine the value you get. This is an indirect measurement technique.
: : : I think TEDDY was a shareware. It has a great set of parameter options including geometry of part tested, coil parameters, liftoff, sample conductivity and permeability. As you will see from the article link, impedance plane diagrams are provided.
: : : Regards
: : : Ed
: : : : Trying to remember my physics...
: : : : Given three different conductivities:
: : : : sigma 1
: : : : sigma 2
: : : : sigma 3
: : : : Given same thickness for each layer of conductivity with no air gaps between layers
: : : : Given each layer of conductivity is directly under the other, i.e., sigma1 on top, then sigma2 below sigma1, and so on.
: : : : Is the total conductivity computed this way?
: : : : 1/sigma total = 1/sigma1 + 1/sigma2 + 1/sigma3
: : : : Is this the same equation for dielectrics and capacitors in series and resistors in parallel?
: : : : Thank you.
------------ End Original Message ------------

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