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Contrary current flow within a radiator
What diametric ratio must a fractional wave length radiator be to allow contrary current flow thru it's center. ? Diameter / wavelength = 1.0, 0.5, 0.1. 0.001, 0.0001, 0.00001,...? Regards Art |
Contrary current flow within a radiator
"Art Unwin" wrote in message ... What diametric ratio must a fractional wave length radiator be to allow contrary current flow thru it's center. ? Diameter / wavelength = 1.0, 0.5, 0.1. 0.001, 0.0001, 0.00001,...? Regards Art infinite |
Contrary current flow within a radiator
"Art Unwin" wrote in message ... What diametric ratio must a fractional wave length radiator be to allow contrary current flow thru it's center. ? Diameter / wavelength = 1.0, 0.5, 0.1. 0.001, 0.0001, 0.00001,...? Regards Art Art, Did you look at my link below? What does "diametric" mean? Ansoft's (www.ansoft.com) "Maxwell" is a "Finite Element Modeling" (FEM) program which, among other things, can accurately produce a graphical representation of the current distribution in a cylindrical conductor. See examples at: http://www3.telus.net/nighttrainexpr...in%20depth.htm These graphs are reproduced from an article in the November/December issue of QEX magazine, pp20 - 29, by Rudy Severns, N6LF. 73, Frank |
Contrary current flow within a radiator
On Jan 13, 3:02*pm, "Frank" wrote:
"Art Unwin" wrote in message ... What diametric ratio must a fractional wave length radiator be to allow contrary current flow thru it's center. ? Diameter / wavelength = 1.0, * *0.5, *0.1. * * 0.001, * * *0.0001, 0.00001,...? Regards Art Art, Did you look at my link below? *What does "diametric" mean? Ansoft's (www.ansoft.com) "Maxwell" is a "Finite Element Modeling" (FEM) program which, among other things, can accurately produce a graphical representation of the current distribution in a cylindrical conductor. *See examples at:http://www3.telus.net/nighttrainexpr...in%20depth.htm These graphs are reproduced from an article in the November/December issue of QEX magazine, pp20 - 29, by Rudy Severns, N6LF. 73, Frank No, but I will now. First I will look up the word "finite" and "finite" Just now going out for dinner Re diametrics, I was referring to the ratio of diameter with respect to wavelength ( I am assuming that skin depthg is not limitless.) Best regards Art |
Contrary current flow within a radiator
"Art Unwin" wrote in message ... ( I am assuming that skin depthg is not limitless.) of course it is limitless, it is an exponential function so it never goes to zero. the so called 'skin depth' is only the point where the current has dropped to 1/e or about 37% of the surface value, still a significant current. |
Contrary current flow within a radiator
Dave wrote:
"Art Unwin" wrote in message ... ( I am assuming that skin depthg is not limitless.) of course it is limitless, it is an exponential function so it never goes to zero. the so called 'skin depth' is only the point where the current has dropped to 1/e or about 37% of the surface value, still a significant current. The plots at the link Frank provided show current going rather abruptly to zero - even negative ("contrary"?) in some cases. I wouldn't presume to know whether it is modeled correctly. ac6xg |
Contrary current flow within a radiator
On Jan 13, 5:00*pm, "Dave" wrote:
"Art Unwin" wrote in message ... ( I am assuming that skin depthg is not limitless.) of course it is limitless, it is an exponential function so it never goes to zero. *the so called 'skin depth' is only the point where the current has dropped to 1/e or about 37% of the surface value, still a significant current. Yes, skin depth is measured or referred to as 1/e which incorporates decay. I am totally unaware how" decay" comes into the picture or what happens with respect to density Now I question the term "decay" in this instance as it is the displacement field that creats resistance ala eddy current which I allude to as the levitating force on a unbound electron. At the moment I cannot see how a unbound electro within an empty shell can be absorbed by a tight matrics consisting of bound electrons or when reaching the inside of a tubular conductor fall off the inner surface! The morer I get into the radiation subject the more I begin to question things. The idea that a circulating current /field is limitless in depth blows my mind. Art |
Contrary current flow within a radiator
The plots at the link Frank provided show current going rather abruptly to zero - even negative ("contrary"?) in some cases. I wouldn't presume to know whether it is modeled correctly. ac6xg Having some expience of Ansoft's FEM modeling software I feel the results are highly credible. Also Rudy Severns publishing list is pretty impressive: http://www.snubberdesign.com/Springt...terprises.html 73, Frank (VE6CB) |
Contrary current flow within a radiator
On Jan 13, 10:19*pm, "Frank" wrote:
The plots at the link Frank provided show current going rather abruptly to zero - even negative ("contrary"?) in some cases. *I wouldn't presume to know whether it is modeled correctly. ac6xg Having some expience of Ansoft's FEM modeling software I feel the results are highly credible. *Also Rudy Severns publishing list is pretty impressive:http://www.snubberdesign.com/Springt...terprises.html 73, Frank (VE6CB) Frank, I am not saying he is not credible but he is part of the older generation and there was not enough detail supplied to determine whether I accept it on trust. When the antenna programs throw out the yagi in favor of arrays or radiators in equilibrium form should we throw it out in favor of conforming with the past? Yes,the article is in line with what the older generation has lived with but the new generation have more tools and information than the present dying generation. Problem with present day authors is up against the "publish or perish" format regure references to prior papers in quantity to provide legitamacy to any new papers, without which they will have a hard time publishing. Greasing the wheels of fellow contributers or white paper authors is much preferable to declaring those who judge are in error. Frank, a lot of the theory of antennas is either based on vanishingly thin radiators without regard to room required for eddy field and in some cases with transmission lines where it is possible to get three different current flows together with a closed circuit, yet we are now protecting the idea of non closed circuits where the current flow is on top of each other. No wonder it is said over the last 100 years that we don't fully understand radiation especially when it takes over 70 posts on how to make a cantenna from a panel of experts Best regards Art |
Contrary current flow within a radiator
Frank, I am not saying he is not credible but he is part of the older generation and there was not enough detail supplied to determine whether I accept it on trust. When the antenna programs throw out the yagi in favor of arrays or radiators in equilibrium form should we throw it out in favor of conforming with the past? Yes,the article is in line with what the older generation has lived with but the new generation have more tools and information than the present dying generation. Problem with present day authors is up against the "publish or perish" format regure references to prior papers in quantity to provide legitamacy to any new papers, without which they will have a hard time publishing. Greasing the wheels of fellow contributers or white paper authors is much preferable to declaring those who judge are in error. Frank, a lot of the theory of antennas is either based on vanishingly thin radiators without regard to room required for eddy field and in some cases with transmission lines where it is possible to get three different current flows together with a closed circuit, yet we are now protecting the idea of non closed circuits where the current flow is on top of each other. No wonder it is said over the last 100 years that we don't fully understand radiation especially when it takes over 70 posts on how to make a cantenna from a panel of experts Best regards Art I would hardly call the tools used in this simulation "Older". Ansoft produces some of the most sophisticated, and up to date FEM software available. I have seen Ansoft's HFSS accurately model current flow through PCB vias, around an end- launch connector at 20 GHz. CST Microwave also produces high end FEM software. All the models are done in full 3 D, with actual physical dimensions. This FEM software started to apear about 10 years ago and costs in the range of $40,000 to $50,000, with a $10,000 per year maintenance fee. "Publish or perish" is usually applied to university positions. It is doubtfull that too many people are able to pubish in the Proceedings of the IEEE, or one of the IEEE Society Transactions. |
Contrary current flow within a radiator
On Jan 13, 11:23*pm, "Frank" wrote:
Frank, I am not saying he is not credible but he is part of the older generation and there was not enough detail supplied to determine whether I accept it on trust. When the antenna programs throw out the yagi in favor of arrays or radiators in equilibrium form should we throw it out in favor of conforming with the past? Yes,the article is in line with what the older generation has lived with but the new generation have more tools and information than the present dying generation. Problem with present day authors is *up against the "publish or perish" format regure references to prior papers in quantity to provide legitamacy to any new papers, without which they will have a hard time publishing. Greasing the wheels of fellow contributers or white paper authors is much preferable to declaring those who judge are in error. Frank, a lot of the theory of antennas is either based on vanishingly thin radiators without regard to room required for eddy field and in some cases with transmission lines where it is possible to get three different current flows together with a closed circuit, yet we are now protecting the idea of non closed circuits where the current flow is on top of each other. No wonder it is said over the last 100 years that we don't fully understand radiation especially when it takes over 70 posts on how to make a cantenna from a panel of experts Best regards Art I would hardly call the tools used in this simulation "Older". Ansoft produces some of the most sophisticated, and up to date FEM software available. *I have seen Ansoft's HFSS accurately model current flow through PCB vias, around an end- launch connector at 20 GHz. *CST Microwave also produces high end FEM software. *All the models are done in full 3 D, with actual physical dimensions. *This FEM software started to apear about 10 years ago and costs in the range of $40,000 to $50,000, with a $10,000 per year maintenance fee. "Publish or perish" is usually applied to university positions. It is doubtfull that too many people are able to pubish in the Proceedings of the IEEE, or one of the IEEE Society Transactions. Frank, It has not yet been proven that current does not flow thru the center of a radiator. I see it as a manufactured statement to satisfy the idea of an uncompleted circuit where the current passes over or thru and in a different direction than the same current that generates its existence ! It does all this where the books state it is a series circuit where the paths taken by the current are not identical. Why manufacture all these happenings to prove what is just a theory, while at the same time destroying the reasoning of a closed circuit without an explanation how such actions creat radiation, especially when it is admitted that radiation is not fully understood? I think the time as come to review again from the time of Maxwell and build up afresh in line with a century of findings and then re evaluate. A good start would be to evaluate why antenna programs based on Maxwells laws provide solutions based on equilibrium while discarding all other designs. Saying that it can't be! Because" "if true it would have been discovered a 100 years ago" while silently adding "all is known about antennas and the patent offices should be closed" Regards Art |
Contrary current flow within a radiator
Jim Kelley wrote:
Dave wrote: "Art Unwin" wrote in message ... ( I am assuming that skin depthg is not limitless.) of course it is limitless, it is an exponential function so it never goes to zero. the so called 'skin depth' is only the point where the current has dropped to 1/e or about 37% of the surface value, still a significant current. The plots at the link Frank provided show current going rather abruptly to zero - even negative ("contrary"?) in some cases. I wouldn't presume to know whether it is modeled correctly. Decrease of RF current with depth below the surface of a conductor is only a true exponential if the available conductor depth is infinite. In the modeled situations where there is 'competition' from a skin effect on the opposite side of the conductor, the solution is a Bessel function which does pass through zero and reverse direction at certain depths. In other words, the model is behaving as expected. Programs such as NEC and Maxwell are not released until they have gone through a very detailed process of checking and validation. The first step is to check against special cases that can be independently solved by analytical methods (in other words, pure math). The work isn't complete until all the results agree within close margins, and the reasons for any differences are fully understood. By the time we amateurs come to hear about these programs, they have already been thoroughly validated by developers and professional users. That doesn't make them immune from further criticism... but only by people who have done the work to earn that right. -- 73 from Ian GM3SEK http://www.ifwtech.co.uk/g3sek |
Contrary current flow within a radiator
On Jan 14, 2:46*am, Ian White GM3SEK wrote:
Jim Kelley wrote: Dave wrote: *"Art Unwin" wrote in message ... ( I am assuming that skin depthg is not limitless.) *of course it is limitless, it is an exponential function so it never goes to zero. *the so called 'skin depth' is only the point where the current has dropped to 1/e or about 37% of the surface value, still a significant current. The plots at the link Frank provided show current going rather abruptly to zero - even negative ("contrary"?) in some cases. *I wouldn't presume to know whether it is modeled correctly. Decrease of RF current with depth below the surface of a conductor is only a true exponential if the available conductor depth is infinite. In the modeled situations where there is 'competition' from a skin effect on the opposite side of the conductor, the solution is a Bessel function which does pass through zero and reverse direction at certain depths. In other words, the model is behaving as expected. Programs such as NEC and Maxwell are not released until they have gone through a very detailed process of checking and validation. The first step is to check against *special cases that can be independently solved by analytical methods (in other words, pure math). The work isn't complete until all the results agree within close margins, and the reasons for any differences are fully understood. By the time we amateurs come to hear about these programs, they have already been thoroughly validated by developers and professional users. That doesn't make them immune from further criticism... but only by people who have done the work to earn that right. -- 73 from Ian GM3SEKhttp://www.ifwtech.co.uk/g3sek So the developers know why the programs in the final analysis gyrate towards radiators and arrays in equilibrium? Do you know what that reason is? Present thinking, I thought, suggest that the skin depth is quite thin when used for non destructive testing of materials. Is that also known by the developers? If the providing current is on the surface of a radiator then why does the resulting eddy current penetrate to the limits? Seems a sort of scrambled assumptions at play here! |
Contrary current flow within a radiator
What diametric ratio must a fractional wave length radiator be to
allow contrary current flow thru it's center. ? Diameter / wavelength = 1.0, 0.5, 0.1. 0.001, 0.0001, 0.00001,...? Regards Art That depends on your return on investment in cost and labor, and the application. Since the skin effect applies, thankfully, the flow through the center is less of an issue. Should we use tubular elements? Or as some have done, use Silver or Copper plated steel wire or rod? At some frequencies, this is profitable. Why should we "allow contrary current flow through it's center." as opposed to promoting the skin effect, since current flow through the center does not radiate? Like eddy currents in a transformer are just loss. |
Contrary current flow within a radiator
On Jan 14, 10:13*am, Art Unwin wrote:
So the developers know why the programs in the final analysis * gyrate towards radiators and arrays in equilibrium? I don't see how they could, being you won't describe how the word "equilibrium" applies in such a case. Do you know what that reason is? Being I have never seen an antenna modeling program gyrate, whether towards or away from a radiator or array, I sure don't. |
Contrary current flow within a radiator
Frank, I am not saying he is not credible but he is part of the older generation and there was not enough detail supplied to determine whether I accept it on trust. When the antenna programs throw out the yagi in favor of arrays or radiators in equilibrium form should we throw it out in favor of conforming with the past? Yes,the article is in line with what the older generation has lived with but the new generation have more tools and information than the present dying generation. Problem with present day authors is up against the "publish or perish" format regure references to prior papers in quantity to provide legitamacy to any new papers, without which they will have a hard time publishing. Greasing the wheels of fellow contributers or white paper authors is much preferable to declaring those who judge are in error. Frank, a lot of the theory of antennas is either based on vanishingly thin radiators without regard to room required for eddy field and in some cases with transmission lines where it is possible to get three different current flows together with a closed circuit, yet we are now protecting the idea of non closed circuits where the current flow is on top of each other. No wonder it is said over the last 100 years that we don't fully understand radiation especially when it takes over 70 posts on how to make a cantenna from a panel of experts Best regards Art This is so amusing. Those who don't appreciate knowledge thus far, probably don't know it. Those who are desperately hoping for a revolution might just have a ulterior motive or agenda. It is interesting to note though, that it takes a lot of PhD's to design something so that impoverished people (often children) can have a bowl of rice every day to build the technology. Also, the environmental disaster that is created by throwing away "gadgets" every 6 months to implement the latest technology. I wonder if the Liberal academic establishment is in touch with the environmental disaster they are creating so that we can all be enslaved to the global neural network. The cantenna posts are amusing, in that no one even brought up the transition from the connector to the resistor element, or adequate thermal conductivity between the oil and the outside air. The biggest problems revolves around these issues. Starting with how long must the transition be to allow adequate oil convection flow. The answer to all this can be found with the high power Bird loads that have a smaller oil area but use large radiating fins, or better yet, A chip resistor array directly mounted to a large fin area. |
Contrary current flow within a radiator
On Jan 14, 10:39*am, "JB" wrote:
What diametric ratio must a fractional wave length radiator be to allow contrary current flow thru it's center. ? Diameter / wavelength = 1.0, * *0.5, *0.1. * * 0.001, * * *0.0001, 0.00001,...? Regards Art That depends on your return on investment in cost and labor, and the application. *Since the skin effect applies, thankfully, the flow through the center is less of an issue. Should we use tubular elements? Or as some have done, use Silver or Copper plated steel wire or rod? *At some frequencies, this is profitable. Why should we "allow contrary current flow through it's center." as opposed to promoting the skin effect, since current flow through the center does not radiate? *Like eddy currents in a transformer are just loss. Right JB. If it didn't flow thru the center one could assume that it would radiate. Thus keeping the current flow on the outside allows us to use micro length antennas since radiation occurs all the time. Whow If one sees the current flowing thru the center where the losses are small then one can deduce that radiation is conmensurate to length up to a maximum of one wavelength. By golly isn't that the same solution that the books advocate without the invention of a circuit that flows when the circuit is abruptly terminated. Newton's laws advocate equilibrium as an absolute. Maxwell followed this absolute when formulating his laws. Application of Gaussian law of statics by using the eddict of equilibrium confirms the laws of Maxwell. Antenna programs that are allowed to follow the edicts of Maxwells laws again substantiate the edict of equilibrium. So with all of the above I am inclined to trust such computor programs but NOT the atributions supplied to explain the conditions that theories atribute to the explanation of why agreement is shown with respect to equilibrium plus the mathematics involved in all the above cases. I do not know of any other accepted circuit in physics where a circuit is abruptly terminate and still meet the requirement of equilibrium. When it is broadly agreed that radiation is not fully understood when following existing explanations I am inclined to question the theories Note Antenna programs with optimizer allows the user to initially insert a design for a particular requirement and the program will make corrections to that design by the application of Maxwells laws to achieve the required object by a solution that is in equilibrium. Programs WITHOUT an optimizer provides an answer based only on the metrics inserted and without correction I.E insert a planar design and the results arrived at reflects the input only and not the array that completely follows Maxwell which provides for superior results which never is a planar design Best regards Art Unwin....KB9MZ.... xg (uk) Now to shovel the snow wbhere it is very, very cold. |
Contrary current flow within a radiator
"JB" wrote in message ... Frank, I am not saying he is not credible but he is part of the older generation and there was not enough detail supplied to determine whether I accept it on trust. When the antenna programs throw out the yagi in favor of arrays or radiators in equilibrium form should we throw it out in favor of conforming with the past? Yes,the article is in line with what the older generation has lived with but the new generation have more tools and information than the present dying generation. Problem with present day authors is up against the "publish or perish" format regure references to prior papers in quantity to provide legitamacy to any new papers, without which they will have a hard time publishing. Greasing the wheels of fellow contributers or white paper authors is much preferable to declaring those who judge are in error. Frank, a lot of the theory of antennas is either based on vanishingly thin radiators without regard to room required for eddy field and in some cases with transmission lines where it is possible to get three different current flows together with a closed circuit, yet we are now protecting the idea of non closed circuits where the current flow is on top of each other. No wonder it is said over the last 100 years that we don't fully understand radiation especially when it takes over 70 posts on how to make a cantenna from a panel of experts Best regards Art This is so amusing. Those who don't appreciate knowledge thus far, probably don't know it. Those who are desperately hoping for a revolution might just have a ulterior motive or agenda. It is interesting to note though, that it takes a lot of PhD's to design something so that impoverished people (often children) can have a bowl of rice every day to build the technology. Also, the environmental disaster that is created by throwing away "gadgets" every 6 months to implement the latest technology. I wonder if the Liberal academic establishment is in touch with the environmental disaster they are creating so that we can all be enslaved to the global neural network. The cantenna posts are amusing, in that no one even brought up the transition from the connector to the resistor element, or adequate thermal conductivity between the oil and the outside air. The biggest problems revolves around these issues. Starting with how long must the transition be to allow adequate oil convection flow. The answer to all this can be found with the high power Bird loads that have a smaller oil area but use large radiating fins, or better yet, A chip resistor array directly mounted to a large fin area. ------------- What is truly saddening to me is the amount of philosphy/religion that creeps into these so called scientific discussions. No wonder antenna modeling is still mostly an art form and not a science. Ed, N2ECW |
Contrary current flow within a radiator
Art Unwin wrote:
So the developers know why the programs in the final analysis gyrate towards radiators and arrays in equilibrium? Do you know what that reason is? Present thinking, I thought, suggest that the skin depth is quite thin when used for non destructive testing of materials. Is that also known by the developers? If the providing current is on the surface of a radiator then why does the resulting eddy current penetrate to the limits? Seems a sort of scrambled assumptions at play here! Well, at least the last sentence was correct. -- 73 from Ian GM3SEK http://www.ifwtech.co.uk/g3sek |
Contrary current flow within a radiator
Ian White GM3SEK wrote:
Jim Kelley wrote: Dave wrote: "Art Unwin" wrote in message ... ( I am assuming that skin depthg is not limitless.) of course it is limitless, it is an exponential function so it never goes to zero. the so called 'skin depth' is only the point where the current has dropped to 1/e or about 37% of the surface value, still a significant current. The plots at the link Frank provided show current going rather abruptly to zero - even negative ("contrary"?) in some cases. I wouldn't presume to know whether it is modeled correctly. Decrease of RF current with depth below the surface of a conductor is only a true exponential if the available conductor depth is infinite. In the modeled situations where there is 'competition' from a skin effect on the opposite side of the conductor, the solution is a Bessel function which does pass through zero and reverse direction at certain depths. In other words, the model is behaving as expected. Programs such as NEC and Maxwell are not released until they have gone through a very detailed process of checking and validation. The first step is to check against special cases that can be independently solved by analytical methods (in other words, pure math). The work isn't complete until all the results agree within close margins, and the reasons for any differences are fully understood. By the time we amateurs come to hear about these programs, they have already been thoroughly validated by developers and professional users. That doesn't make them immune from further criticism... but only by people who have done the work to earn that right. Hi Ian, Please know that my comment was never intended as a slight of anyone's work. I simply don't presume to know anything about it other than to observe that the citation appears to contradict the assertion that skin depth is limitless and exponential in real conductors. 73, ac6xg |
Contrary current flow within a radiator
JB wrote:
It is interesting to note though, that it takes a lot of PhD's to design something so that impoverished people (often children) can have a bowl of rice every day to build the technology. Also, the environmental disaster that is created by throwing away "gadgets" every 6 months to implement the latest technology. I wonder if the Liberal academic establishment is in touch with the environmental disaster they are creating so that we can all be enslaved to the global neural network. Respectfully JB, is this liberals created the disposable society rant something you can lay hands or links to citations for, or is it just truthiness? - 73 de Mike N3LI - |
Contrary current flow within a radiator
Ed Cregger wrote:
What is truly saddening to me is the amount of philosphy/religion that creeps into these so called scientific discussions. No wonder antenna modeling is still mostly an art form and not a science. So right, Ed. Last time I checked, antennas did not have either a liberal or conservative bias. - 73 de Mike N3LI - |
Contrary current flow within a radiator
I don't want to add ammunition to support Art's gibberish, but it's
interesting and not widely known that current *does* flow in the opposite direction to the main flow, at certain depths in a homogeneous conductor. In a solid conductor, the current density does, of course, decrease exponentially with depth. The depth at which it's decayed to 1/e (about 37%) of the surface density is the "skin depth". This is why a hollow tube is just as good a conductor as a solid one, providing only that the tube wall is at least several skin depths thick. But the *phase* of the current changes with depth, too, quite dramatically. As you go each skin depth deeper below the surface, the phase becomes one radian (about 57 degrees) more lagging. So at pi skin depths below the surface, the current is completely out of phase with the surface current, i.e., it's flowing in the opposite direction. Of course, the current density at this point is very small, only 1/e^pi ~ 4% of the surface density, so only a small fraction of the total current flows completely backward. (Good thing!) At two pi skin depths, the current is again in phase with the surface current, but its magnitude is only 1/e^(2*pi) ~ 1/500 of the surface density. And so forth. This isn't of much immediate practical use, and it's certainly not offered as supporting in any way Art's fanciful theories (whatever they might be). But it is an interesting fact. Roy Lewallen, W7EL |
Contrary current flow within a radiator
"Jim Kelley" wrote in message ... Dave wrote: "Art Unwin" wrote in message ... ( I am assuming that skin depthg is not limitless.) of course it is limitless, it is an exponential function so it never goes to zero. the so called 'skin depth' is only the point where the current has dropped to 1/e or about 37% of the surface value, still a significant current. The plots at the link Frank provided show current going rather abruptly to zero - even negative ("contrary"?) in some cases. I wouldn't presume to know whether it is modeled correctly. ac6xg the 'contrary' current makes sense because of 2 different effects. the main one is the phase delay of propagation through the conductor. the velocity of propagation of the wave within the wire is MUCH slower than through space outside the wire. this produces a phase delay such that when you take a snapshot, as those plots most likely are, you can get opposing currents. if you were to take a time average or peak value you would get the plain exponential as predicted by the simple equations that are normally taught. The other confounding factor on those examples is the discontinuity between the copper and steel, again the velocity changes across that boundary shifting the phase in a step. |
Contrary current flow within a radiator
Jim Kelley wrote:
Hi Ian, Please know that my comment was never intended as a slight of anyone's work. I simply don't presume to know anything about it other than to observe that the citation appears to contradict the assertion that skin depth is limitless and exponential in real conductors. 73, ac6xg that's because the usual discussion of "skin depth" is cribbed from a physics textbook, where the (not always explicitly said) assumption is "in an infinite uniform plane of infinite depth with no other magnetic fields" In that restricted (but useful) case, you can model the current (for the purposes of things like resistivity) as if it were uniform from the surface to the skin depth. In cases where the thickness of the conductor is "large" relative to the skin depth, the error in using the rectangular layer of current assumption is "small". In cases where this assumption isn't valid (or, if you need higher precision), then a more complete analytical formulation is needed. If the conductor happens to be circular, then Bessel functions are surely involved (differential equations in circular things almost always involve Bessel functions and/or Hankel transforms). Since most of us don't do Bessel functions in our heads, we use tables or lookups. There's two sets of tables and graphs for round conductors: one is for solid conductors; the other is for tubular conductors. Different boundary conditions on solving the differential equations, so different analytical solutions. A 1998 paper by Gaba and Abou-Dakka gives all the equations and background, and adds the details needed for stranded wires and cables made of multiple substances (e.g. ACSR power lines). There's also some analytical solutions for square and rectangular cross sections, but they're pretty ugly, compared to the round conductors. once you start talking multiple materials and dielectrics, it becomes easier to do FEM (following the dictum of my father's differential equations professor: useful differential equations should be solved numerically, because the analytical solution is often harder and more computation than the numerical one). (another good example of this is calculating the field between two spherical electrodes) |
Contrary current flow within a radiator
Roy Lewallen wrote:
I don't want to add ammunition to support Art's gibberish, but it's interesting and not widely known that current *does* flow in the opposite direction to the main flow, at certain depths in a homogeneous conductor. In a solid conductor, the current density does, of course, decrease exponentially with depth. The depth at which it's decayed to 1/e (about 37%) of the surface density is the "skin depth". This is why a hollow tube is just as good a conductor as a solid one, providing only that the tube wall is at least several skin depths thick. But the *phase* of the current changes with depth, too, quite dramatically. As you go each skin depth deeper below the surface, the phase becomes one radian (about 57 degrees) more lagging. So at pi skin depths below the surface, the current is completely out of phase with the surface current, i.e., it's flowing in the opposite direction. Of course, the current density at this point is very small, only 1/e^pi ~ 4% of the surface density, so only a small fraction of the total current flows completely backward. (Good thing!) At two pi skin depths, the current is again in phase with the surface current, but its magnitude is only 1/e^(2*pi) ~ 1/500 of the surface density. And so forth. This isn't of much immediate practical use, and it's certainly not offered as supporting in any way Art's fanciful theories (whatever they might be). But it is an interesting fact. I wonder if one could set up some sort of interesting demonstration of this. If you could, for instance, have a 1 foot diameter conductor with skin depth of an inch or so, and some (probably not feasible) way to indicate current flow. (yes, in order for this to happen it has to be AC, etc.) |
Contrary current flow within a radiator
On Jan 14, 3:49*pm, Roy Lewallen wrote:
I don't want to add ammunition to support Art's gibberish, but it's interesting and not widely known that current *does* flow in the opposite direction to the main flow, at certain depths in a homogeneous conductor. In a solid conductor, the current density does, of course, decrease exponentially with depth. The depth at which it's decayed to 1/e (about 37%) of the surface density is the "skin depth". This is why a hollow tube is just as good a conductor as a solid one, providing only that the tube wall is at least several skin depths thick. But the *phase* of the current changes with depth, too, quite dramatically. As you go each skin depth deeper below the surface, the phase becomes one radian (about 57 degrees) more lagging. So at pi skin depths below the surface, the current is completely out of phase with the surface current, i.e., it's flowing in the opposite direction. Of course, the current density at this point is very small, only 1/e^pi ~ 4% of the surface density, so only a small fraction of the total current flows completely backward. (Good thing!) At two pi skin depths, the current is again in phase with the surface current, but its magnitude is only 1/e^(2*pi) ~ 1/500 of the surface density. And so forth. This isn't of much immediate practical use, and it's certainly not offered as supporting in any way Art's fanciful theories (whatever they might be). But it is an interesting fact. Roy Lewallen, W7EL Exactly. And every phase change support current /charge flow in the opposite direction in accordance with Newtons laws. Use a vector drawing to prove it for yourself ! Or provide same as proof of my errors. While you are at it do the same for a full wave radiator which IS in equilibrium per Maxwells law when the inner vector is now non existant since radiation occurs on the surface at all times in accordance with the "tank circuit" abilities And where the center path is only resistive in the case of a fractional wave antenna. This is very, very basic physics to which I know no challedge in the physics world. For you it is no difference when you were affiliated with QST and supported the commercial publishing of rediculas specifications to oppose change. Sooner or later you will again have to change your tune to one that does not include opposition to the truth. The book that Richard is quoting is available on the web for $1.99 which will allow you to confront all the authors of their "rediculus" errors at the same time together with all the Universities that use the book as part of their physics curriculum I await your appearance on CNN where it will undoubtably push aside the viewing of the president Cecil, This is how you defrock the self perceived pompous expert. He ofcourse does make errors which he will not own up to. Art Unwin......KB9MZ....(xg) |
Contrary current flow within a radiator
Jim Kelley wrote:
Decrease of RF current with depth below the surface of a conductor is only a true exponential if the available conductor depth is infinite. In the modeled situations where there is 'competition' from a skin effect on the opposite side of the conductor, the solution is a Bessel function which does pass through zero and reverse direction at certain depths. In other words, the model is behaving as expected. Programs such as NEC and Maxwell are not released until they have gone through a very detailed process of checking and validation. The first step is to check against special cases that can be independently solved by analytical methods (in other words, pure math). The work isn't complete until all the results agree within close margins, and the reasons for any differences are fully understood. By the time we amateurs come to hear about these programs, they have already been thoroughly validated by developers and professional users. That doesn't make them immune from further criticism... but only by people who have done the work to earn that right. Hi Ian, Please know that my comment was never intended as a slight of anyone's work. I didn't think that for a moment, Jim. I simply don't presume to know anything about it other than to observe that the citation appears to contradict the assertion that skin depth is limitless and exponential in real conductors. As noted above, that commonly-held assertion is only true for conductors of limitless depth. -- 73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
Contrary current flow within a radiator
On Jan 14, 4:18*pm, Jim Lux wrote:
Roy Lewallen wrote: I don't want to add ammunition to support Art's gibberish, but it's interesting and not widely known that current *does* flow in the opposite direction to the main flow, at certain depths in a homogeneous conductor. In a solid conductor, the current density does, of course, decrease exponentially with depth. The depth at which it's decayed to 1/e (about 37%) of the surface density is the "skin depth". This is why a hollow tube is just as good a conductor as a solid one, providing only that the tube wall is at least several skin depths thick. But the *phase* of the current changes with depth, too, quite dramatically. As you go each skin depth deeper below the surface, the phase becomes one radian (about 57 degrees) more lagging. So at pi skin depths below the surface, the current is completely out of phase with the surface current, i.e., it's flowing in the opposite direction. Of course, the current density at this point is very small, only 1/e^pi ~ 4% of the surface density, so only a small fraction of the total current flows completely backward. (Good thing!) At two pi skin depths, the current is again in phase with the surface current, but its magnitude is only 1/e^(2*pi) ~ 1/500 of the surface density. And so forth. This isn't of much immediate practical use, and it's certainly not offered as supporting in any way Art's fanciful theories (whatever they might be). But it is an interesting fact. I wonder if one could set up some sort of interesting demonstration of this. *If you could, for instance, have a 1 foot diameter conductor with skin depth of an inch or so, and some (probably not feasible) way to indicate current flow. *(yes, in order for this to happen it has to be AC, etc.) Why not insert a wafer of the same material parallel to the axis and apply a non destuctive test on the material as a whole. When the wafer is withdrawn would it not be possible to observe the actual effective skin depth. Of course, the slot for the wafer must not enter the radial surface of the radiator other wise circular flow would be interupted thus destroying the datum apearance. Obviously I have not utelised a non destructive test first hand. From my point of view as long as there is an eddy current on the surface to eject a resting particle there is not the requirement for endles depth and decay would be the condition of the particle alone and not that of the conductor. The particle still has nuclear content when it emerges from the Sun's arbritary field which is obviously subject to decay Regards Art |
Contrary current flow within a radiator
On Wed, 14 Jan 2009 16:29:33 -0500, Michael Coslo
wrote: Ed Cregger wrote: What is truly saddening to me is the amount of philosphy/religion that creeps into these so called scientific discussions. No wonder antenna modeling is still mostly an art form and not a science. So right, Ed. Last time I checked, antennas did not have either a liberal or conservative bias. *** observing nothing technically redeeming in this thread *** Hi Mike, Circular polarity is not political? You can have a left hand screw or a right hand screw. *** Fulfilling the entertainment mandate of RRAA for 14 years *** 73's Richard Clark, KB7QHC |
Contrary current flow within a radiator
On Jan 14, 12:07*am, Art Unwin wrote:
It has not yet been proven that current does not flow thru the center of a radiator. Assuming that significant r-f current exists at the center of a radiating conductor, where does it go when it reaches the end of that conductor? RF |
Contrary current flow within a radiator
Richard Fry wrote:
On Jan 14, 12:07 am, Art Unwin wrote: It has not yet been proven that current does not flow thru the center of a radiator. Assuming that significant r-f current exists at the center of a radiating conductor, where does it go when it reaches the end of that conductor? RF It doesn't "go" anywhere. As the conductor (and it's return path; ground or whatever) is resonant, the generator sees it as a resistor. The current is "absorbed" by this "load". But instead of pure heat, an electromagnetic field ensues. Nothing goes anywhere. |
Contrary current flow within a radiator
Richard Clark wrote:
On Wed, 14 Jan 2009 16:29:33 -0500, Michael Coslo wrote: Ed Cregger wrote: What is truly saddening to me is the amount of philosphy/religion that creeps into these so called scientific discussions. No wonder antenna modeling is still mostly an art form and not a science. So right, Ed. Last time I checked, antennas did not have either a liberal or conservative bias. *** observing nothing technically redeeming in this thread *** We need a new Punchinello, don't you think? - 73 de Mike N3LI - |
Contrary current flow within a radiator
On Thu, 15 Jan 2009 09:45:05 -0500, Michael Coslo
wrote: *** observing nothing technically redeeming in this thread *** We need a new Punchinello, don't you think? Hi Mike, Too true, instead we have a Howdy Dodat. 73's Richard Clark, KB7QHC |
Contrary current flow within a radiator
On Jan 15, 7:35*am, Dave wrote:
Richard Fry wrote: On Jan 14, 12:07 am, Art Unwin wrote: It has not yet been proven that current does not flow thru the center of a radiator. Assuming that significant r-f current exists at the center of a radiating conductor, where does it go when it reaches the end of that conductor? RF It doesn't "go" anywhere. *As the conductor (and it's return path; ground or whatever) is resonant, the generator sees it as a resistor. The current is "absorbed" by this "load". *But instead of pure heat, an electromagnetic field ensues. *Nothing goes anywhere. Methinks you are playing games, current doesn't move but charges do Very devious Art |
Contrary current flow within a radiator
Richard Fry wrote:
On Jan 14, 12:07 am, Art Unwin wrote: It has not yet been proven that current does not flow thru the center of a radiator. Assuming that significant r-f current exists at the center of a radiating conductor, where does it go when it reaches the end of that conductor? Ahh.. the famous "boundary condition".. Say you've got a big bar 100 feet long and a foot in diameter, and you've induced a rf current along it by some means. All those equations with the Bessel functions tell you the magnitude and phase of the current in some infinitely thin slice in the middle. But, at the end, those equations don't hold. Essentially, the "reverse current" flows radially across the end and forms part of the "forward current" on the surface. I doubt there is a good analytical solution of this. There's probably some decent approximations (within 5% or something), but anyone who really cares is going to do a FEM analysis of some sort and solve the problem numerically. RF |
Contrary current flow within a radiator
On Jan 15, 3:48*pm, Jim Lux wrote:
Richard Fry wrote: On Jan 14, 12:07 am, Art Unwin wrote: It has not yet been proven that current does not flow thru the center of a radiator. Assuming that significant r-f current exists at the center of a radiating conductor, where does it go when it reaches the end of that conductor? Ahh.. the famous "boundary condition".. Say you've got a big bar 100 feet long and a foot in diameter, and you've induced a rf current along it by some means. *All those equations * with the Bessel functions tell you the magnitude and phase of the current in some infinitely thin slice in the middle. But, at the end, those equations don't hold. *Essentially, the "reverse current" flows radially across the end and forms part of the "forward current" on the surface. I doubt there is a good analytical solution of this. *There's probably some decent approximations (within 5% or something), but anyone who really cares is going to do a FEM analysis of some sort and solve the problem numerically. RF Hmmmm I think anybody with a education could apply vectors to a full wave RESONANT radiator with charge and applied current such that Newton's laws can be shown as being satisfied Why would anybody shy away from that since we know that there is no current/ charge flow on the inside so the vectors will balance. Is there any disagreement with that aproach. If so why? It WILL show agreement with the groups aproach with respect to zero current / charge flow in the center of a radiator which should make you all feel good. Art Art |
Contrary current flow within a radiator
Art wrote:
"Frank, It has not yet been proven that current does not flow through the center of the radiator." It definitely has been proven that significant current does not ordinarily flow through the center of a radiating conductor. Skin effect is an accepted and observed phenomenon. An RF conductor has a radial E-field, its lines terminating on its surface. Also, the current carrying conductor has has an H-field whose lines encircle it. The E-field lines are not exactly perpendicular to to the conductor`s surface but inclined at a slight angle to it. The surfaces of equal phase are cupped inward slightly on the forward side as if the wave were dragging its feet along the conductor`s surface. The H lines are parallel to the conductor`s surface. Direction of propagation of the energy is at right angles to both the E and H fields, but not quite parallel to the conductor`s surface. It is inclined slightly toward the inside of the conductor. Direction of propagation can be indicated by a vector P. P can be resolved into two components, PL and PR . PL represents the longitudinal component of vector P. PR represents the small amount of energy which is being drained away from the transmitted signal and dissipated as heat in the conductor. Radial E lines of force tilted forward in propagation along the conductor are slowed and short-circuited by the conducting material through which they are moving. This current flowing through the resistance of the conductor causes I squared R losses. It also gives rise to a magnetic field within the conductor which opposes the external H field. The result of the above is that the density of the current is quite high at the copnductor`s surface, diminishing as we look inward toward the center. The relative phase of the current, in addition, is not the same at all depths; because of the slow velocity of propagation of the wave within the conductor, the phase of the current is progressively delayed as we examine it at greater depths. At some depth, the phase of the current may be 180 degrees behind that of the surface current, which means that it is flowing in the opposite direction! The integral of the current density, integrated over the entire cross-sectional area of the conductor, will of course be equal to the current in the conductor as would be read by an ammeter. Not all conductors are solid copper or aluminum. Seawater has been thoroughly inveatigated in regard to communication with submarines. Actual RF currents at all depths have been calculated and measured. Best regards, Richard Harrison, KB5WZI |
Contrary current flow within a radiator
Dave wrote:
Richard Fry wrote: On Jan 14, 12:07 am, Art Unwin wrote: It has not yet been proven that current does not flow thru the center of a radiator. Assuming that significant r-f current exists at the center of a radiating conductor, where does it go when it reaches the end of that conductor? RF It doesn't "go" anywhere. As the conductor (and it's return path; ground or whatever) is resonant, the generator sees it as a resistor. The current is "absorbed" by this "load". But instead of pure heat, an electromagnetic field ensues. Yes, it's like asking where does the current go in a real big capacitor. Charge flows onto and off of the conductors, and since they're physically large, time is required for the change in field to propagate from one end to the other. We calculate the current flowing along antenna elements. But we can also calculate a current flowing through the aether based on the same principles. Perhaps knowing the magnitude of the field traveling the element would be at least as useful as knowing the magnitude of the current. The two are after all inextricably liked. Nothing goes anywhere. Indeed. I like it. It's leads me postulate further that nothing goes everywhere; anything goes nowhere; everything goes anywhere; anything goes everywhere; nothing goes nowhere; or perhaps even that everything goes nowhere. ac6xg |
Contrary current flow within a radiator
On Thu, 15 Jan 2009 14:53:32 -0800 (PST), Art Unwin
wrote: I think anybody with a education could apply vectors to a full wave RESONANT radiator with charge and applied current such that Newton's laws can be shown as being satisfied Education? Vectors? Laws? This is tales from the crypt of dead white scientists. I already showed two ways to DO IT - who needs to go to a library? Only gurus and those who dress like them. 73's Richard Clark, KB7QHC |
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