Transient Emission Model

[idarney]

The paper ‘Modelling the transient emission from a twin-conductor cable’ describes a test where a step pulse is applied to one end of an open-circuit cable. -  http://ietdl.org/t/ZKt6U 
The waveform of the differential-mode current delivered to the line was recorded. This was different from the waveform of a lossless line, since there were radiation losses. A circuit model was created to simulate the hardware-under-review and was subjected to transient analysis. Adjusting component values of the model enabled close correlation to be achieved between test results and model simulation. The process of creating the model provides an improved understanding of the mechanisms involved.

The ‘References’ section of the paper includes a link to the Mathcad worksheet which performs the calculations.

Comments will be welcome.

[LucMeekes]

I wonder what side-effect your first sheet (Fig2) runs on. I get this (in Mathcad 11):

The variable 'Ini' is undefined.

However, with this change it runs:

Luc

[idarney]

Reply to LucMeekes

With Mathcad15, there was no need for me to pre-define the variable Ini. So I didn’t.

Ian Darney

[AlanStevens]

"Comments will be welcome."

Not sure what sort of comments you are after, but I've looked at figure 2 in a somewhat different way.  The attached worksheet shows all the currents rather than just Ina.

(I used M15, which doesn't give the problem in the original figure 2 worksheet that Luc experienced, as it assigns initial values of zero by default)

Alan

PS I might have a look at the other figure worksheets if I get time.

[idarney]

Response to Alan Stevens

It is possible to carry out bench tests on prototype equipment using a signal generator and oscilloscope to measure the susceptibility and emission characteristics of the equipment; then to create a circuit model to replicate that behaviour. The model can subsequently be used to predict the results of formal EMC Tests. Mathcad software is uniquely capable of carrying out all the calculations and presenting the results in a form suitable for peer review. One example is provided. The technique is capable of analysing any form of EMI coupling.

It may be that some of the statements in the paper could give rise to a sceptical response.

Thank you for your example of one way to develop the Time-Step Analysis program. I now have a copy on file.

  Ian Darney

[-MFra-]

If the electric line is, for example, a coaxial cable, powered by a radiofrequency source,  it is demonstrated that there is absolutely no loss of energy for irradiation in the surrounding space.. In a two-wire line, much of the electromagnetic energy is confined between the two wires, in the surrounding space, however, the electromagnetic field is present. In the vicinity of the line is a reactive em field, while a small percentage of active power is radiated at a great distance in the surrounding space. This, I am sure that also applies to transient conditions.

Best regards

F.M.

[idarney]

Response to F M

There is always radiation, even from a co-axial cable.

There is a fair correlation between behaviour in the frequency domain and that in the time domain. However, analysis of transients in the time domain leads to an improved understanding of the mechanisms involved.

Ian Darney

[-MFra-]

My, it was a response based on intuition and not on an analytical demonstration. I'm sure that things are as you say. Thanks for your kind response.

Greetings

FM

[idarney]

I am grateful to F M for raising the point made in his previous comment.

The statement ‘There is a fair correlation between behaviour in the frequency domain and that in the time domain. However, analysis of transients in the time domain leads to an improved understanding of the mechanisms involved.’ was not based on intuition. It was based on the content of a paper available for download from the internet via the link http://ietdl.org/t/ZKt6U

This paper identifies the relationship between frequency analysis and transient analysis, and goes on to provide an improved understanding of the nature of the mechanism involved in the propagation of electromagnetic interference. It would not have been published in the Journal of Engineering by the Institute of Engineering and Technology if it had been anything other than an ‘analytical demonstration’.

The IET subjects any submitted paper to a rigorous review process before it agrees to publish that paper. Included in the review process is a check that each assertion made in the paper is supported by the analysis provided by a reference document, and that each document referred to has also been subjected to peer review.

See also  http://digital-library.theiet.org/journals/joe/author-guide  

If there are any errors or misleading statements in the paper, this is a good time to identify them.

[-MFra-]

I am very surprised reading the article indicated. They seem heresies. Has always spoken of electromagnetic energy (or active power) radiated (beyond the Fraunhofer region), never heard or read something about the emission of electric charges by an antenna.

Greetings

FM

[idarney]

It is not at all surprising that F.M. has ‘never heard or read something about the emission of electric charges by an antenna’. I have several books on Electromagnetic Theory and several books on Electromagnetic Compatibility. None of them describe the electromagnetic field in terms of moving charges. Circuit Theory makes the assumption that current flow is strictly confined to branches of the network.

Yet the theory of the half-wave dipole transmitter leads to the inevitable conclusion that it is current which is departing from the surface of the conductors and flowing into the environment.

Transmission Line Theory introduces the concept of a pulse which propagates along the length of a line at a velocity comparable with the speed of light. If a step voltage is applied to the input terminals, then a step current will be created. The current and voltage propagate in synchronism. The only way this can happen is for the pulse to consist of an electric charge (or a group of charged sub-atomic particles) moving along the line at the speed of light.

Going back to the dipole model; if current is flowing radially away from the surface of the conductors of the antenna and current is due to the flow of electric charge, then it follows that the electromagnetic field radiated into the environment is due to the emission of charged sub-atomic particles.

The paper ‘Modelling the transient emission from a twin-conductor cable’ explores the ramifications of this line of reasoning.

[RichardJ]

The only way this can happen is for the pulse to consist of an electric charge (or a group of charged sub-atomic particles) moving along the line at the speed of light.

Electrons in a conductor move at a rate of mm or cm per hour. It is impossible for them to move along the wire at anything like the speed of light.

Going back to the dipole model; if current is flowing radially away from the surface of the conductors of the antenna and current is due to the flow of electric charge, then it follows that the electromagnetic field radiated into the environment is due to the emission of charged sub-atomic particles.

The emission of electrons (i.e. current) from a low voltage conductor is negligible. An electromagnetic field is just that, a field.

[AlvaroDíaz]

Richard Jackson wrote:

The only way this can happen is for the pulse to consist of an electric charge (or a group of charged sub-atomic particles) moving along the line at the speed of light.

Electrons in a conductor move at a rate of mm or cm per hour. It is impossible for them to move along the wire at anything like the speed of light.

That's absolutely true, electron's speed is about that range. So, what travel along a wire are not electrons, is the energy. That's could be confused for direct current, but is more obvious for alternate current: electrons travel to the left then to the right, and that 50 or 60 times per second. An analogous is a seism: stones from the epicenter don't hit any head, what make the travel is the "seismic wave", which transmit the energy.

The process is interpreted as even each electron move a very short distance, impact another, transmitting the energy. So, even each electron move very slow the energy "moves" very fast, a fraction of the speed of light.

For the remittance, and dissipation of energy, as Richard says, EM is just a fiel, but fields can store energy. Where is the energy of a stone up 10 meter from the sea level? In the stone not. It's cool to say that is stored in the gravitatory field, and released when the stone fails down. In a capacitor, as another example, energy was stored into the EM field. That isn't that obvious. In the past, capacitors are named as condensators (at least, in Spanish), because they "condensate" the current, and that have a very short probability of occur.

Best regards.

Alvaro.

[RichardJ]

An analogy I have heard is a very long tube full of small balls. When you push a ball in at one end, a ball falls out of the other end. So the "signal" move very fast, even though the balls don't.

In the past, capacitors are named as condensators (at least, in Spanish),

Also in English, although it's "condensers".

[AlvaroDíaz]

Thanks Richards for the analogy, very usefully. Is impressive how many people (engineers included as people too) don't know how electricity works in a wire. Actually, me have a doubt about if in a solution, where electrons don't travel, but species do, if the ions make the travel or they push others. For example, salt in water, Na+ go in one direction, Cl- in the opposite, but I believe (but not sure) that actually each one make the all travel. Have troubles also to define the intensity: is the double because there are two charge porters?

Best Regards.

Alvaro.

PD. Ahhh. Condensers. That word there are a lot of time that don't read.

[RichardJ]

The ions will eventually reach the electrodes, but not nearly as fast as a signal can travel through the solution. I don't think it's fundamentally any different to a wire, the charge carriers are just different.

Interesting question about the intensity. You do have two charge carriers in a solution, but then in a wire you have holes as well as electrons.

[AlvaroDíaz]

Richard Jackson wrote:

The ions will eventually reach the electrodes, but not nearly as fast as a signal can travel through the solution. I don't think it's fundamentally any different to a wire, the charge carriers are just different.

Hi Richard. But preciselly because the ions reach the electrodes is very different, the charge carriers must to do the entire travel. I do some few works in a salt plant, with currents of 300 A (be carefull with tools in some palces, they are take out from hands). The voltage dump is measured direct from the the cupper pool separated by 40 cm. But can't figure how to measure the time delay from starting current in one side to receive in the other. Also, don't know if that can be done in a small tube (2 m is small, for that case) and experimentally confirm that time delay.

Best regards.

Alvaro.

PD: Ahhh. Holes. That's it.

[-MFra-]

Hi Ian Darney,

To support your argument, it would be enough, an analytical demonstration. Two, so to speak, calculations with Ohm's law, do not meet me at all. It has been known for some centuries that a very short voltage pulse which propagates, with a certain speed less than c, in an open two-wire electric line, undergoes multiple reflections before its energy is dissipated (Joule effect) into the environment. To avoid the reflections one must ensure that there is matching, ie, the line must have a load with an impedance equal to its characteristic impedance (c.c.). So in case of matching, all of the pulse energy is dissipated (Joule effect) in the resistive component of the load and there isn't reflection. If the line load is an antenna with inpedance adapted to that of the line, all the energy is radiated in the space in form of electromagnetic waves. We can also see this phenomenon from the corpuscular point of view. Namely the antenna releases into the surrounding space a flow of low-energy photons each photon has an energy given by the well-known relationship,E=hf  , where h is the Planck constant and f is the radiation frequency.

Only in the case in which the line is subjected to a constant (in time) voltage , then you have the corona effect, which is also very well known.

Best regards

F. M.

[AlvaroDíaz]

Ian Darney wrote:

I am grateful to F M for raising the point made in his previous comment.

The statement ‘There is a fair correlation between behaviour in the frequency domain and that in the time domain. However, analysis of transients in the time domain leads to an improved understanding of the mechanisms involved.’ was not based on intuition. It was based on the content of a paper available for download from the internet via the link http://ietdl.org/t/ZKt6U

Hi Darney, F.M. Actually, I'm not very sure what's the mean of a frequency analysis of a transient. For me it is more intuitive to make the analysis of transients in time domain.

Transient implies a linear system. Nonlinear don't have "transients", have a complicated response, but not what implies a transient. Transient are the solutions to the non - homogeneous equation(s). Also, called particular solution. Transient must to have limit for t->infinity equal to zero. If not, the system was unstable and go to broken. Stationary solution, the solution for the long place time, is the solution for the homogeneous equations, without external exitations. For stationary solutions is where the freq domain analysis take sense. But the transient response can be anything (any "particular" thing), just because in brief go down. If transients are some big, then the system can be broken too. The study of transient responses are useful for starting (or stopping) procedures, and for preserve the system from damage. Direct start, star-delta start, freq variator start for motors are examples of that. And always, the transient is analyzed in the time domain.

The stationary solution can be analyzed in the freq domain because came from the lineal algebra theory (with the entire pack of tools), unlike the transient, which came from ... nowhere. Eventually, from try and error procedure (literal).

So, going back: transient implies linearity. And that's sometimes are hard to prove. Assuming proved that the transmission line is lineal (obtained with some assumptions), you next study the answer of the system to a pulse and to a step. Why? Just because lineal systems are perfect determined by the answer to two signals. And those two are specially easy to apply and understand.

So, going back again: the use of Ohm law, for example, is just an assumption of the linearity of the system. Actually, Ohm law isn't a "true law". It is just a good rule that holds a lot of times for a lot of materials and big ranges of potentials and currents.

All that as comments from the initial " Comments will be welcome ".

Best regards.

Alvaro.

[idarney]

Response to comments by Richard Jackson & Alvaro Diaz on 13 June:

It is agreed that electrons move along the conductors at a snails pace when a DC voltage is applied, and vibrate when an AC voltage is applied. Since power and signals propagate at near-light velocity, the current carriers must be sub-atomic particles. The name given to these by the scientific community is ‘photons’.

If one end of a co-axial cable is open-circuit and the other is connected to a battery via a switch, the line behaves as a capacitor. When the switch is closed, a step current flows from the positive terminal of the battery into the send conductor. This current has two components; a ‘displacement current’ and a ‘conduction current’. Displacement current is a flow of photons from the send conductor to the return conductor (during the first traverse of the step current). Conduction current is a flow of photons along the send conductor and back via the return conductor.

Response to comments by F.M. on 13 June:

Thank you for your supportive comment and for the statement that ‘the antenna releases into the surrounding space a flow of low-energy photons’.

The line load of an antenna is the radiation resistance. That is, the antenna delivers current into the environment. Since current is the rate of change of charge, it is charge which emanates from the conductor. Since the entities which are released are photons, it follows that each photon must carry a charge. From an engineering point of view, it does not matter what the magnitude of that charge is, since the basic parameter used to measure the magnitude of the transmitted radiation is current.

Response to final comment by Alvaro Diaz on 13 June:

I agree that it is more intuitive (and more practical) to carry out the analyses of transients in the time domain. One such analysis is described in the paper   http://ietdl.org/t/ZKt6U

For a lossless line, the parameters which characterise the response in the time-domain are the time T, the time taken for a pulse to travel from one end of the line to the other and Ro, the characteristic resistance. The loop inductance La can be derived, using La =  T*Ro , and the capacitance between the conductors, Ca , would be Ca = T / Ro.   

With analyses in the frequency-domain, the parameters La and Ca would be used.

[-MFra-]

Thank you so much Ian Darney,

for your light description.

I would not look like an irreverent and stubborn man,  but the antenna resistance is considered a lumped resistor, and is the load of the line. Shouldn't it be confused with the free space  radiation resistance, which is equal to approximately 377 Ohm, regardless of the type of antenna!

When you apply an electromotive force at the terminals of a power line, in the surrounding space and between the two conductors  propagates, at a speed close to that of light, (dependent on the properties of the medium), an electromagnetic field (a field that consists of two orthogonal vectors (Electric field intensity vector E,  and a Magnetic field intensity vector H, both satisfying the Maxwell equations) lying on a transverse plane to the line. Then there are the reflections, if there is no matching.

With best regards

FM

[LucMeekes]

As far as I remember from school:

Photons are energy packets, they carry energy, not current; they have no rest mass.

Electrons (and holes) are particles in the sense that they have a rest mass; they carry current.

It is electrons that stay in the antenna, and do not normally get out.

Photons will leave (and enter) an antenna, they are the particles that carry (electromagnetic) energy.

Luc

[-MFra-]

Nowadays, we could consider the electron, as well as being the quantum of electric charge, ... a lump of quarks, with a  spin .... been part of  a cloud, imprisoned in the lattice of the copper wire, and that in it flows ....

A Small Sample of Maxwell's equations, which, you certainly know very well...and correct me if I'm wrong somewhere ..

Greetings

FM

[RichardJ]

It is agreed that electrons move along the conductors at a snails pace when a DC voltage is applied, and vibrate when an AC voltage is applied. Since power and signals propagate at near-light velocity, the current carriers must be sub-atomic particles. The name given to these by the scientific community is ‘photons’.

The current carriers are electrons (or if you prefer, holes, i.e. the absence of an electron)

Since the entities which are released are photons, it follows that each photon must carry a charge.

Photons do not have a charge.

This is physics 101.

[AlvaroDíaz]

Ian Darney wrote:

Response to comments by Richard Jackson & Alvaro Diaz on 13 June:

It is agreed that electrons move along the conductors at a snails pace when a DC voltage is applied, and vibrate when an AC voltage is applied. Since power and signals propagate at near-light velocity, the current carriers must be sub-atomic particles. The name given to these by the scientific community is ‘photons’. 

Hi Ian. As LucMeekes points, and Richard too, photons don't carry charge nor current. What charge photons is the EM field. Gluons, bosons (including High's boson) are field porters. If photons scape to the sourronder, the EM field decreases. So? Because EM field gives the force to move electrons, less force implies less electrons moving, less current. Coaxial is the protection to enclose the EM field (and they porters, the photons) in the cilinder, providing a Faraday jail to the photons, not to electrons.

Best regards.

Alvaro.

[-MFra-]

Hi AD,

about the transients in simple linear electronic systems, you can find many examples created by me in the pages illustrated below:

Best regards

FM

[AlvaroDíaz]

Cia Francesco. Sure, they are very good works, What I try to say is that in the introduction appoint to the time analysis of the transients as new method as the opposite to the more usual and intuitive freq analysis, and I point to that isn't for me.

Best regards.

Alvaro.

[-MFra-]

Hi AD,

relatively to transients in the antennas (in particular the Hertzian dipole),I can point you  two articles not very recent, in fact they were written the second half of the last century, and that is:

1) "Emerging Technology for Broad-Band and Transient Analysis and Synthesis of Antennas and Scatterers" - Carl E. Baum - Proceedings of the IEEE, Vol. 64, NO. 11, November 1976

2) "Transient Fields of Linear Antenna Arrays"  - K. J. Langenberg , Applied Physics 20,101-118 (1979)

With best regards

FM

[idarney]

In response to comments by F.M., Richard Jackson, Alvaro Diaz and Luc Meekes:- 

If a thing looks like a cat, feels like a cat, sounds like a cat, and acts like a cat, it is a cat.

One of the strands of reasoning leading to the deduction that the electromagnetic field is due to the flow of charged sub-atomic particles is available at  www.designemc.info/PTC/RadiationResistor.pdf

I agree that these particles are not electrons, and am willing to take advice on what name to assign to them. It does not really matter what that name is. I am an Electronic Engineer who is concerned about EMC. By visualising the field as a flow of charged particles, I have gained a better understanding of the mechanisms involved in the propagation of EMI as well as the ability to simulate those mechanisms using the mathematics of Circuit Theory. It may be that other designers can utilise the same technique.

The paper http://ietdl.org/t/ZKt6U  is worth another read.

Ian Darney

[AlvaroDíaz]

Ian Darney wrote:

... By visualising the field as a flow of charged particles, ...

Remember what happen to charged particles in mouvement, and how much energy must to emmit. That kind of fields violetes the energy conservaton principle.

Alvaro.