Why isn't there a non-conducting core wire for high-frequency coil applications












5












$begingroup$


Background



The commonly known skin effect formulas are derived and only apply to solid conductors. The commonly used "skin depth" only applies in these cases. It is for this reason that in some applications tubes are used, as these are much more weight-efficient than the same diameter wire at a high-enough frequency.



At 1MHz the skin depth of copper wire is 65µm which means that only 40% of the volume of a 1mm diameter wire is carrying 95% of the current, with >35% of it in the outside 20%.



From the skin-depth formulas it is known that a lower conductivity material (e.g., aluminum) has a skin depth that is considerably larger than a higher conductivity one (e.g., copper). As the formula predicts, skin depth is inversely proportional to the square root of the conductivity. If we carry this to its logical consequences, it should be the case that for a conducting tube (which has an insulation core) skin depth should be larger than for an equivalent solid conductor.



As an alternative intuition a thin-walled insulated-core conductor would have nearly twice the surface area of a solid conductor. So it should asymptotically approach nearly half the resistance at a high enough frequency.



In effect, as can be seen in this paper from HB Dwight in 1922 (possible paywall), the increase in resistance w.r.t. frequency for a tube whose wall thickness is 20% of its diameter is more than a factor of two lower than for a solid wire.



Skin effect in tubes and wires



From the above curves it can be seen that a tube with t=200µm and d=1mm, due to the increased actual skin depth, should have less than 50% of the impedance increase than a solid d=1mm wire (do note that the curves are normalized w.r.t $ F / R_{dc} $, so interpretation is a bit tricky).



Similar effects (although not as dramatic) can be observed with individually-insulated stranded wire.



Application



In medium-frequency applications, as for example switching power supplies, it is common to use Litz Wire a multi-stranded insulated wire which reduces the losses due to skin effect but becomes less and less effective at higher frequencies (~1MHz) because of the proximity effect and the capacitive coupling of the individual strands.



Probably more gains (particularly with respect to proximity effects) could be obtained if there were multiple individual strands embedded around the periphery of a non-conducting core.



Question



Have I missed something in the theory?



If not, why isn't insulated core wire (either tubes or strands around a core) being commercially exploited for high-frequency inductor applications?



Addendum



As John Birckhead answer points out, flat wire has basically the same advantages with none of the disadvantages (e.g., fill factor). But this leads me to ask:



Why isn't insulated-core flat wire being used for these applications? It should have the same advantage of flat wire with nearly half the resistance at high enough frequencies. Are the possible gains inconsequential?










share|improve this question











$endgroup$












  • $begingroup$
    Comments are not for extended discussion; this conversation has been moved to chat. Any conclusions reached should be edited back into the question and/or any answer(s).
    $endgroup$
    – Dave Tweed
    5 hours ago












  • $begingroup$
    I'll need to read it further, but I found this set of pages on Litz wire. Just a note.
    $endgroup$
    – jonk
    4 hours ago
















5












$begingroup$


Background



The commonly known skin effect formulas are derived and only apply to solid conductors. The commonly used "skin depth" only applies in these cases. It is for this reason that in some applications tubes are used, as these are much more weight-efficient than the same diameter wire at a high-enough frequency.



At 1MHz the skin depth of copper wire is 65µm which means that only 40% of the volume of a 1mm diameter wire is carrying 95% of the current, with >35% of it in the outside 20%.



From the skin-depth formulas it is known that a lower conductivity material (e.g., aluminum) has a skin depth that is considerably larger than a higher conductivity one (e.g., copper). As the formula predicts, skin depth is inversely proportional to the square root of the conductivity. If we carry this to its logical consequences, it should be the case that for a conducting tube (which has an insulation core) skin depth should be larger than for an equivalent solid conductor.



As an alternative intuition a thin-walled insulated-core conductor would have nearly twice the surface area of a solid conductor. So it should asymptotically approach nearly half the resistance at a high enough frequency.



In effect, as can be seen in this paper from HB Dwight in 1922 (possible paywall), the increase in resistance w.r.t. frequency for a tube whose wall thickness is 20% of its diameter is more than a factor of two lower than for a solid wire.



Skin effect in tubes and wires



From the above curves it can be seen that a tube with t=200µm and d=1mm, due to the increased actual skin depth, should have less than 50% of the impedance increase than a solid d=1mm wire (do note that the curves are normalized w.r.t $ F / R_{dc} $, so interpretation is a bit tricky).



Similar effects (although not as dramatic) can be observed with individually-insulated stranded wire.



Application



In medium-frequency applications, as for example switching power supplies, it is common to use Litz Wire a multi-stranded insulated wire which reduces the losses due to skin effect but becomes less and less effective at higher frequencies (~1MHz) because of the proximity effect and the capacitive coupling of the individual strands.



Probably more gains (particularly with respect to proximity effects) could be obtained if there were multiple individual strands embedded around the periphery of a non-conducting core.



Question



Have I missed something in the theory?



If not, why isn't insulated core wire (either tubes or strands around a core) being commercially exploited for high-frequency inductor applications?



Addendum



As John Birckhead answer points out, flat wire has basically the same advantages with none of the disadvantages (e.g., fill factor). But this leads me to ask:



Why isn't insulated-core flat wire being used for these applications? It should have the same advantage of flat wire with nearly half the resistance at high enough frequencies. Are the possible gains inconsequential?










share|improve this question











$endgroup$












  • $begingroup$
    Comments are not for extended discussion; this conversation has been moved to chat. Any conclusions reached should be edited back into the question and/or any answer(s).
    $endgroup$
    – Dave Tweed
    5 hours ago












  • $begingroup$
    I'll need to read it further, but I found this set of pages on Litz wire. Just a note.
    $endgroup$
    – jonk
    4 hours ago














5












5








5


1



$begingroup$


Background



The commonly known skin effect formulas are derived and only apply to solid conductors. The commonly used "skin depth" only applies in these cases. It is for this reason that in some applications tubes are used, as these are much more weight-efficient than the same diameter wire at a high-enough frequency.



At 1MHz the skin depth of copper wire is 65µm which means that only 40% of the volume of a 1mm diameter wire is carrying 95% of the current, with >35% of it in the outside 20%.



From the skin-depth formulas it is known that a lower conductivity material (e.g., aluminum) has a skin depth that is considerably larger than a higher conductivity one (e.g., copper). As the formula predicts, skin depth is inversely proportional to the square root of the conductivity. If we carry this to its logical consequences, it should be the case that for a conducting tube (which has an insulation core) skin depth should be larger than for an equivalent solid conductor.



As an alternative intuition a thin-walled insulated-core conductor would have nearly twice the surface area of a solid conductor. So it should asymptotically approach nearly half the resistance at a high enough frequency.



In effect, as can be seen in this paper from HB Dwight in 1922 (possible paywall), the increase in resistance w.r.t. frequency for a tube whose wall thickness is 20% of its diameter is more than a factor of two lower than for a solid wire.



Skin effect in tubes and wires



From the above curves it can be seen that a tube with t=200µm and d=1mm, due to the increased actual skin depth, should have less than 50% of the impedance increase than a solid d=1mm wire (do note that the curves are normalized w.r.t $ F / R_{dc} $, so interpretation is a bit tricky).



Similar effects (although not as dramatic) can be observed with individually-insulated stranded wire.



Application



In medium-frequency applications, as for example switching power supplies, it is common to use Litz Wire a multi-stranded insulated wire which reduces the losses due to skin effect but becomes less and less effective at higher frequencies (~1MHz) because of the proximity effect and the capacitive coupling of the individual strands.



Probably more gains (particularly with respect to proximity effects) could be obtained if there were multiple individual strands embedded around the periphery of a non-conducting core.



Question



Have I missed something in the theory?



If not, why isn't insulated core wire (either tubes or strands around a core) being commercially exploited for high-frequency inductor applications?



Addendum



As John Birckhead answer points out, flat wire has basically the same advantages with none of the disadvantages (e.g., fill factor). But this leads me to ask:



Why isn't insulated-core flat wire being used for these applications? It should have the same advantage of flat wire with nearly half the resistance at high enough frequencies. Are the possible gains inconsequential?










share|improve this question











$endgroup$




Background



The commonly known skin effect formulas are derived and only apply to solid conductors. The commonly used "skin depth" only applies in these cases. It is for this reason that in some applications tubes are used, as these are much more weight-efficient than the same diameter wire at a high-enough frequency.



At 1MHz the skin depth of copper wire is 65µm which means that only 40% of the volume of a 1mm diameter wire is carrying 95% of the current, with >35% of it in the outside 20%.



From the skin-depth formulas it is known that a lower conductivity material (e.g., aluminum) has a skin depth that is considerably larger than a higher conductivity one (e.g., copper). As the formula predicts, skin depth is inversely proportional to the square root of the conductivity. If we carry this to its logical consequences, it should be the case that for a conducting tube (which has an insulation core) skin depth should be larger than for an equivalent solid conductor.



As an alternative intuition a thin-walled insulated-core conductor would have nearly twice the surface area of a solid conductor. So it should asymptotically approach nearly half the resistance at a high enough frequency.



In effect, as can be seen in this paper from HB Dwight in 1922 (possible paywall), the increase in resistance w.r.t. frequency for a tube whose wall thickness is 20% of its diameter is more than a factor of two lower than for a solid wire.



Skin effect in tubes and wires



From the above curves it can be seen that a tube with t=200µm and d=1mm, due to the increased actual skin depth, should have less than 50% of the impedance increase than a solid d=1mm wire (do note that the curves are normalized w.r.t $ F / R_{dc} $, so interpretation is a bit tricky).



Similar effects (although not as dramatic) can be observed with individually-insulated stranded wire.



Application



In medium-frequency applications, as for example switching power supplies, it is common to use Litz Wire a multi-stranded insulated wire which reduces the losses due to skin effect but becomes less and less effective at higher frequencies (~1MHz) because of the proximity effect and the capacitive coupling of the individual strands.



Probably more gains (particularly with respect to proximity effects) could be obtained if there were multiple individual strands embedded around the periphery of a non-conducting core.



Question



Have I missed something in the theory?



If not, why isn't insulated core wire (either tubes or strands around a core) being commercially exploited for high-frequency inductor applications?



Addendum



As John Birckhead answer points out, flat wire has basically the same advantages with none of the disadvantages (e.g., fill factor). But this leads me to ask:



Why isn't insulated-core flat wire being used for these applications? It should have the same advantage of flat wire with nearly half the resistance at high enough frequencies. Are the possible gains inconsequential?







inductor high-frequency skin-effect litz-wire






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share|improve this question








edited 3 hours ago







Edgar Brown

















asked 6 hours ago









Edgar BrownEdgar Brown

5,6722731




5,6722731












  • $begingroup$
    Comments are not for extended discussion; this conversation has been moved to chat. Any conclusions reached should be edited back into the question and/or any answer(s).
    $endgroup$
    – Dave Tweed
    5 hours ago












  • $begingroup$
    I'll need to read it further, but I found this set of pages on Litz wire. Just a note.
    $endgroup$
    – jonk
    4 hours ago


















  • $begingroup$
    Comments are not for extended discussion; this conversation has been moved to chat. Any conclusions reached should be edited back into the question and/or any answer(s).
    $endgroup$
    – Dave Tweed
    5 hours ago












  • $begingroup$
    I'll need to read it further, but I found this set of pages on Litz wire. Just a note.
    $endgroup$
    – jonk
    4 hours ago
















$begingroup$
Comments are not for extended discussion; this conversation has been moved to chat. Any conclusions reached should be edited back into the question and/or any answer(s).
$endgroup$
– Dave Tweed
5 hours ago






$begingroup$
Comments are not for extended discussion; this conversation has been moved to chat. Any conclusions reached should be edited back into the question and/or any answer(s).
$endgroup$
– Dave Tweed
5 hours ago














$begingroup$
I'll need to read it further, but I found this set of pages on Litz wire. Just a note.
$endgroup$
– jonk
4 hours ago




$begingroup$
I'll need to read it further, but I found this set of pages on Litz wire. Just a note.
$endgroup$
– jonk
4 hours ago










3 Answers
3






active

oldest

votes


















3












$begingroup$

No, you are correct in the theory, but your approach leads to an unnecessary increase in volume when compared to using flat wire, which is both easier to manufacture and provides a similar advantage for skin effect and the advantage of volumetric efficiency.






share|improve this answer









$endgroup$









  • 1




    $begingroup$
    I have never seen flat wire being used in RF applications, transformers, or inductors while Litz wire is quite common. Could you expand your answer to point to those and how it compares?
    $endgroup$
    – Edgar Brown
    5 hours ago






  • 1




    $begingroup$
    See mouser.com/pdfdocs/bourns_ic046_flatwire_inductor_appnote.pdf
    $endgroup$
    – John Birckhead
    5 hours ago










  • $begingroup$
    To your question, Litz wire also has poor volumetric efficiency for high-current applications because of the insulation and the way the wires cross each other in the coil. It is also difficult to terminate at high currents to get an even current distribution. It is useful at low currents when you are not space constrained, because flat wire is tricky to wind.
    $endgroup$
    – John Birckhead
    4 hours ago












  • $begingroup$
    If my intuition is correct, a flat wire with a non-conductive core would have less impedance at higher frequencies than a flat wire (and it should be relatively easy to construct by flattening a thin insulation-filled tube). So, although this points in the right direction and does answer the main aspect of the question, it does not fully address it. Are the gains insignificant, or the application space non-existent?
    $endgroup$
    – Edgar Brown
    4 hours ago






  • 2




    $begingroup$
    First of all, thanks for a really interesting and well-stated question, (near to my heart being a magnetics guy). It's just easier flattening the wire down to the skin depth - there would only be a marginal difference because there is insulation between two layers just as there would be insulation in your scenario in the center of the proposed conductor, and you can get the same cross section with a wider flat wire. It would be an interesting study to determine how much if any advantage is gained - it does "feel" like inter-winding capacitance might be less.
    $endgroup$
    – John Birckhead
    3 hours ago



















1












$begingroup$

Induction Heating (Industrial) commonly uses hollow copper tubing for the inductor.



When you are running 1000 kW or higher, you better believe the copper loss needs to be minimized.



Additionally, the hollow core is used for water cooling.



Sometimes the copper is called "hollow bar". It comes in rectangular or round. It is not uncommon to order a "mill run" to get the hollow bar and thickness desired.



Image from luvata dot com



enter image description here






share|improve this answer











$endgroup$













  • $begingroup$
    At what frequency is this normally operating?
    $endgroup$
    – Edgar Brown
    1 hour ago










  • $begingroup$
    @EdgarBrown . .Induction heaters are used from 50 Hz to several megahertz. Mostly below 50 kHz though.
    $endgroup$
    – Marla
    57 mins ago





















0












$begingroup$

There is indeed a variant on insulated core wire for very high frequency applications. It's called a waveguide. It's a hollow tube used for conducting RF. I am of the understanding that the signal travels in the inside of the conducting shell rather than the outside, but the idea of only needing the conducting shell as thick as the skin effect dictates is there.



Not much use for inductors though.






share|improve this answer









$endgroup$









  • 1




    $begingroup$
    A waveguide is a rather different thing. The RF is travelling in the air itself, and being "reflected" off the inside (to simplify), rather than actually travelling in the metal of the waveguide itself,
    $endgroup$
    – mbrig
    1 hour ago











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3 Answers
3






active

oldest

votes








3 Answers
3






active

oldest

votes









active

oldest

votes






active

oldest

votes









3












$begingroup$

No, you are correct in the theory, but your approach leads to an unnecessary increase in volume when compared to using flat wire, which is both easier to manufacture and provides a similar advantage for skin effect and the advantage of volumetric efficiency.






share|improve this answer









$endgroup$









  • 1




    $begingroup$
    I have never seen flat wire being used in RF applications, transformers, or inductors while Litz wire is quite common. Could you expand your answer to point to those and how it compares?
    $endgroup$
    – Edgar Brown
    5 hours ago






  • 1




    $begingroup$
    See mouser.com/pdfdocs/bourns_ic046_flatwire_inductor_appnote.pdf
    $endgroup$
    – John Birckhead
    5 hours ago










  • $begingroup$
    To your question, Litz wire also has poor volumetric efficiency for high-current applications because of the insulation and the way the wires cross each other in the coil. It is also difficult to terminate at high currents to get an even current distribution. It is useful at low currents when you are not space constrained, because flat wire is tricky to wind.
    $endgroup$
    – John Birckhead
    4 hours ago












  • $begingroup$
    If my intuition is correct, a flat wire with a non-conductive core would have less impedance at higher frequencies than a flat wire (and it should be relatively easy to construct by flattening a thin insulation-filled tube). So, although this points in the right direction and does answer the main aspect of the question, it does not fully address it. Are the gains insignificant, or the application space non-existent?
    $endgroup$
    – Edgar Brown
    4 hours ago






  • 2




    $begingroup$
    First of all, thanks for a really interesting and well-stated question, (near to my heart being a magnetics guy). It's just easier flattening the wire down to the skin depth - there would only be a marginal difference because there is insulation between two layers just as there would be insulation in your scenario in the center of the proposed conductor, and you can get the same cross section with a wider flat wire. It would be an interesting study to determine how much if any advantage is gained - it does "feel" like inter-winding capacitance might be less.
    $endgroup$
    – John Birckhead
    3 hours ago
















3












$begingroup$

No, you are correct in the theory, but your approach leads to an unnecessary increase in volume when compared to using flat wire, which is both easier to manufacture and provides a similar advantage for skin effect and the advantage of volumetric efficiency.






share|improve this answer









$endgroup$









  • 1




    $begingroup$
    I have never seen flat wire being used in RF applications, transformers, or inductors while Litz wire is quite common. Could you expand your answer to point to those and how it compares?
    $endgroup$
    – Edgar Brown
    5 hours ago






  • 1




    $begingroup$
    See mouser.com/pdfdocs/bourns_ic046_flatwire_inductor_appnote.pdf
    $endgroup$
    – John Birckhead
    5 hours ago










  • $begingroup$
    To your question, Litz wire also has poor volumetric efficiency for high-current applications because of the insulation and the way the wires cross each other in the coil. It is also difficult to terminate at high currents to get an even current distribution. It is useful at low currents when you are not space constrained, because flat wire is tricky to wind.
    $endgroup$
    – John Birckhead
    4 hours ago












  • $begingroup$
    If my intuition is correct, a flat wire with a non-conductive core would have less impedance at higher frequencies than a flat wire (and it should be relatively easy to construct by flattening a thin insulation-filled tube). So, although this points in the right direction and does answer the main aspect of the question, it does not fully address it. Are the gains insignificant, or the application space non-existent?
    $endgroup$
    – Edgar Brown
    4 hours ago






  • 2




    $begingroup$
    First of all, thanks for a really interesting and well-stated question, (near to my heart being a magnetics guy). It's just easier flattening the wire down to the skin depth - there would only be a marginal difference because there is insulation between two layers just as there would be insulation in your scenario in the center of the proposed conductor, and you can get the same cross section with a wider flat wire. It would be an interesting study to determine how much if any advantage is gained - it does "feel" like inter-winding capacitance might be less.
    $endgroup$
    – John Birckhead
    3 hours ago














3












3








3





$begingroup$

No, you are correct in the theory, but your approach leads to an unnecessary increase in volume when compared to using flat wire, which is both easier to manufacture and provides a similar advantage for skin effect and the advantage of volumetric efficiency.






share|improve this answer









$endgroup$



No, you are correct in the theory, but your approach leads to an unnecessary increase in volume when compared to using flat wire, which is both easier to manufacture and provides a similar advantage for skin effect and the advantage of volumetric efficiency.







share|improve this answer












share|improve this answer



share|improve this answer










answered 5 hours ago









John BirckheadJohn Birckhead

4,751416




4,751416








  • 1




    $begingroup$
    I have never seen flat wire being used in RF applications, transformers, or inductors while Litz wire is quite common. Could you expand your answer to point to those and how it compares?
    $endgroup$
    – Edgar Brown
    5 hours ago






  • 1




    $begingroup$
    See mouser.com/pdfdocs/bourns_ic046_flatwire_inductor_appnote.pdf
    $endgroup$
    – John Birckhead
    5 hours ago










  • $begingroup$
    To your question, Litz wire also has poor volumetric efficiency for high-current applications because of the insulation and the way the wires cross each other in the coil. It is also difficult to terminate at high currents to get an even current distribution. It is useful at low currents when you are not space constrained, because flat wire is tricky to wind.
    $endgroup$
    – John Birckhead
    4 hours ago












  • $begingroup$
    If my intuition is correct, a flat wire with a non-conductive core would have less impedance at higher frequencies than a flat wire (and it should be relatively easy to construct by flattening a thin insulation-filled tube). So, although this points in the right direction and does answer the main aspect of the question, it does not fully address it. Are the gains insignificant, or the application space non-existent?
    $endgroup$
    – Edgar Brown
    4 hours ago






  • 2




    $begingroup$
    First of all, thanks for a really interesting and well-stated question, (near to my heart being a magnetics guy). It's just easier flattening the wire down to the skin depth - there would only be a marginal difference because there is insulation between two layers just as there would be insulation in your scenario in the center of the proposed conductor, and you can get the same cross section with a wider flat wire. It would be an interesting study to determine how much if any advantage is gained - it does "feel" like inter-winding capacitance might be less.
    $endgroup$
    – John Birckhead
    3 hours ago














  • 1




    $begingroup$
    I have never seen flat wire being used in RF applications, transformers, or inductors while Litz wire is quite common. Could you expand your answer to point to those and how it compares?
    $endgroup$
    – Edgar Brown
    5 hours ago






  • 1




    $begingroup$
    See mouser.com/pdfdocs/bourns_ic046_flatwire_inductor_appnote.pdf
    $endgroup$
    – John Birckhead
    5 hours ago










  • $begingroup$
    To your question, Litz wire also has poor volumetric efficiency for high-current applications because of the insulation and the way the wires cross each other in the coil. It is also difficult to terminate at high currents to get an even current distribution. It is useful at low currents when you are not space constrained, because flat wire is tricky to wind.
    $endgroup$
    – John Birckhead
    4 hours ago












  • $begingroup$
    If my intuition is correct, a flat wire with a non-conductive core would have less impedance at higher frequencies than a flat wire (and it should be relatively easy to construct by flattening a thin insulation-filled tube). So, although this points in the right direction and does answer the main aspect of the question, it does not fully address it. Are the gains insignificant, or the application space non-existent?
    $endgroup$
    – Edgar Brown
    4 hours ago






  • 2




    $begingroup$
    First of all, thanks for a really interesting and well-stated question, (near to my heart being a magnetics guy). It's just easier flattening the wire down to the skin depth - there would only be a marginal difference because there is insulation between two layers just as there would be insulation in your scenario in the center of the proposed conductor, and you can get the same cross section with a wider flat wire. It would be an interesting study to determine how much if any advantage is gained - it does "feel" like inter-winding capacitance might be less.
    $endgroup$
    – John Birckhead
    3 hours ago








1




1




$begingroup$
I have never seen flat wire being used in RF applications, transformers, or inductors while Litz wire is quite common. Could you expand your answer to point to those and how it compares?
$endgroup$
– Edgar Brown
5 hours ago




$begingroup$
I have never seen flat wire being used in RF applications, transformers, or inductors while Litz wire is quite common. Could you expand your answer to point to those and how it compares?
$endgroup$
– Edgar Brown
5 hours ago




1




1




$begingroup$
See mouser.com/pdfdocs/bourns_ic046_flatwire_inductor_appnote.pdf
$endgroup$
– John Birckhead
5 hours ago




$begingroup$
See mouser.com/pdfdocs/bourns_ic046_flatwire_inductor_appnote.pdf
$endgroup$
– John Birckhead
5 hours ago












$begingroup$
To your question, Litz wire also has poor volumetric efficiency for high-current applications because of the insulation and the way the wires cross each other in the coil. It is also difficult to terminate at high currents to get an even current distribution. It is useful at low currents when you are not space constrained, because flat wire is tricky to wind.
$endgroup$
– John Birckhead
4 hours ago






$begingroup$
To your question, Litz wire also has poor volumetric efficiency for high-current applications because of the insulation and the way the wires cross each other in the coil. It is also difficult to terminate at high currents to get an even current distribution. It is useful at low currents when you are not space constrained, because flat wire is tricky to wind.
$endgroup$
– John Birckhead
4 hours ago














$begingroup$
If my intuition is correct, a flat wire with a non-conductive core would have less impedance at higher frequencies than a flat wire (and it should be relatively easy to construct by flattening a thin insulation-filled tube). So, although this points in the right direction and does answer the main aspect of the question, it does not fully address it. Are the gains insignificant, or the application space non-existent?
$endgroup$
– Edgar Brown
4 hours ago




$begingroup$
If my intuition is correct, a flat wire with a non-conductive core would have less impedance at higher frequencies than a flat wire (and it should be relatively easy to construct by flattening a thin insulation-filled tube). So, although this points in the right direction and does answer the main aspect of the question, it does not fully address it. Are the gains insignificant, or the application space non-existent?
$endgroup$
– Edgar Brown
4 hours ago




2




2




$begingroup$
First of all, thanks for a really interesting and well-stated question, (near to my heart being a magnetics guy). It's just easier flattening the wire down to the skin depth - there would only be a marginal difference because there is insulation between two layers just as there would be insulation in your scenario in the center of the proposed conductor, and you can get the same cross section with a wider flat wire. It would be an interesting study to determine how much if any advantage is gained - it does "feel" like inter-winding capacitance might be less.
$endgroup$
– John Birckhead
3 hours ago




$begingroup$
First of all, thanks for a really interesting and well-stated question, (near to my heart being a magnetics guy). It's just easier flattening the wire down to the skin depth - there would only be a marginal difference because there is insulation between two layers just as there would be insulation in your scenario in the center of the proposed conductor, and you can get the same cross section with a wider flat wire. It would be an interesting study to determine how much if any advantage is gained - it does "feel" like inter-winding capacitance might be less.
$endgroup$
– John Birckhead
3 hours ago













1












$begingroup$

Induction Heating (Industrial) commonly uses hollow copper tubing for the inductor.



When you are running 1000 kW or higher, you better believe the copper loss needs to be minimized.



Additionally, the hollow core is used for water cooling.



Sometimes the copper is called "hollow bar". It comes in rectangular or round. It is not uncommon to order a "mill run" to get the hollow bar and thickness desired.



Image from luvata dot com



enter image description here






share|improve this answer











$endgroup$













  • $begingroup$
    At what frequency is this normally operating?
    $endgroup$
    – Edgar Brown
    1 hour ago










  • $begingroup$
    @EdgarBrown . .Induction heaters are used from 50 Hz to several megahertz. Mostly below 50 kHz though.
    $endgroup$
    – Marla
    57 mins ago


















1












$begingroup$

Induction Heating (Industrial) commonly uses hollow copper tubing for the inductor.



When you are running 1000 kW or higher, you better believe the copper loss needs to be minimized.



Additionally, the hollow core is used for water cooling.



Sometimes the copper is called "hollow bar". It comes in rectangular or round. It is not uncommon to order a "mill run" to get the hollow bar and thickness desired.



Image from luvata dot com



enter image description here






share|improve this answer











$endgroup$













  • $begingroup$
    At what frequency is this normally operating?
    $endgroup$
    – Edgar Brown
    1 hour ago










  • $begingroup$
    @EdgarBrown . .Induction heaters are used from 50 Hz to several megahertz. Mostly below 50 kHz though.
    $endgroup$
    – Marla
    57 mins ago
















1












1








1





$begingroup$

Induction Heating (Industrial) commonly uses hollow copper tubing for the inductor.



When you are running 1000 kW or higher, you better believe the copper loss needs to be minimized.



Additionally, the hollow core is used for water cooling.



Sometimes the copper is called "hollow bar". It comes in rectangular or round. It is not uncommon to order a "mill run" to get the hollow bar and thickness desired.



Image from luvata dot com



enter image description here






share|improve this answer











$endgroup$



Induction Heating (Industrial) commonly uses hollow copper tubing for the inductor.



When you are running 1000 kW or higher, you better believe the copper loss needs to be minimized.



Additionally, the hollow core is used for water cooling.



Sometimes the copper is called "hollow bar". It comes in rectangular or round. It is not uncommon to order a "mill run" to get the hollow bar and thickness desired.



Image from luvata dot com



enter image description here







share|improve this answer














share|improve this answer



share|improve this answer








edited 51 mins ago

























answered 2 hours ago









MarlaMarla

3,89311226




3,89311226












  • $begingroup$
    At what frequency is this normally operating?
    $endgroup$
    – Edgar Brown
    1 hour ago










  • $begingroup$
    @EdgarBrown . .Induction heaters are used from 50 Hz to several megahertz. Mostly below 50 kHz though.
    $endgroup$
    – Marla
    57 mins ago




















  • $begingroup$
    At what frequency is this normally operating?
    $endgroup$
    – Edgar Brown
    1 hour ago










  • $begingroup$
    @EdgarBrown . .Induction heaters are used from 50 Hz to several megahertz. Mostly below 50 kHz though.
    $endgroup$
    – Marla
    57 mins ago


















$begingroup$
At what frequency is this normally operating?
$endgroup$
– Edgar Brown
1 hour ago




$begingroup$
At what frequency is this normally operating?
$endgroup$
– Edgar Brown
1 hour ago












$begingroup$
@EdgarBrown . .Induction heaters are used from 50 Hz to several megahertz. Mostly below 50 kHz though.
$endgroup$
– Marla
57 mins ago






$begingroup$
@EdgarBrown . .Induction heaters are used from 50 Hz to several megahertz. Mostly below 50 kHz though.
$endgroup$
– Marla
57 mins ago













0












$begingroup$

There is indeed a variant on insulated core wire for very high frequency applications. It's called a waveguide. It's a hollow tube used for conducting RF. I am of the understanding that the signal travels in the inside of the conducting shell rather than the outside, but the idea of only needing the conducting shell as thick as the skin effect dictates is there.



Not much use for inductors though.






share|improve this answer









$endgroup$









  • 1




    $begingroup$
    A waveguide is a rather different thing. The RF is travelling in the air itself, and being "reflected" off the inside (to simplify), rather than actually travelling in the metal of the waveguide itself,
    $endgroup$
    – mbrig
    1 hour ago
















0












$begingroup$

There is indeed a variant on insulated core wire for very high frequency applications. It's called a waveguide. It's a hollow tube used for conducting RF. I am of the understanding that the signal travels in the inside of the conducting shell rather than the outside, but the idea of only needing the conducting shell as thick as the skin effect dictates is there.



Not much use for inductors though.






share|improve this answer









$endgroup$









  • 1




    $begingroup$
    A waveguide is a rather different thing. The RF is travelling in the air itself, and being "reflected" off the inside (to simplify), rather than actually travelling in the metal of the waveguide itself,
    $endgroup$
    – mbrig
    1 hour ago














0












0








0





$begingroup$

There is indeed a variant on insulated core wire for very high frequency applications. It's called a waveguide. It's a hollow tube used for conducting RF. I am of the understanding that the signal travels in the inside of the conducting shell rather than the outside, but the idea of only needing the conducting shell as thick as the skin effect dictates is there.



Not much use for inductors though.






share|improve this answer









$endgroup$



There is indeed a variant on insulated core wire for very high frequency applications. It's called a waveguide. It's a hollow tube used for conducting RF. I am of the understanding that the signal travels in the inside of the conducting shell rather than the outside, but the idea of only needing the conducting shell as thick as the skin effect dictates is there.



Not much use for inductors though.







share|improve this answer












share|improve this answer



share|improve this answer










answered 3 hours ago









elchambroelchambro

1112




1112








  • 1




    $begingroup$
    A waveguide is a rather different thing. The RF is travelling in the air itself, and being "reflected" off the inside (to simplify), rather than actually travelling in the metal of the waveguide itself,
    $endgroup$
    – mbrig
    1 hour ago














  • 1




    $begingroup$
    A waveguide is a rather different thing. The RF is travelling in the air itself, and being "reflected" off the inside (to simplify), rather than actually travelling in the metal of the waveguide itself,
    $endgroup$
    – mbrig
    1 hour ago








1




1




$begingroup$
A waveguide is a rather different thing. The RF is travelling in the air itself, and being "reflected" off the inside (to simplify), rather than actually travelling in the metal of the waveguide itself,
$endgroup$
– mbrig
1 hour ago




$begingroup$
A waveguide is a rather different thing. The RF is travelling in the air itself, and being "reflected" off the inside (to simplify), rather than actually travelling in the metal of the waveguide itself,
$endgroup$
– mbrig
1 hour ago


















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