Professor M Pepper FRS on The Catt Question



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Portrait of a Drivelmaster  … A one-electron man. Can’t handle a whole row of them.Sir Michael Pepper

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From: Professor M. Pepper, FRS June 21, 1993

Ivor Catt, Esq.,
121 Westfields,
St Albans

Dear Mr Catt,

As a Trinity physicist the Master suggested that I might provide some comments on the questions raised in your recent letter to him on aspects of electromagnetic theory.

If I understand the position correctly, your question concerns the source of the charge at a metal surface which by responding to the presence of the EM wave ensures that the reflectivity of the metal surface is virtually unity, hence providing waveguide action and related applications.

If I may restate the basis of your question, what is the maximum frequency of radiation which is reflected? It is this parameter rather than light velocity which is important. The solution lies in the maximum frequency response of the electron gas, which is the plasmon frequency w p and is calculated in a straightforward way. If light frequency is greater than w p then the electron gas in the metal can no longer respond and the reflectivity tends to zero. The problem you are posing is that if the wave is guided by the metal then this implies that the charge resides on the metal surface. As the wave travels at light velocity, then charge supplied from outside the system would have to travel at light velocity as well, which is clearly impossible.

The answer is found by considering the nature of conduction in metals. Here we have a lattice of positively charged atoms surrounded by a sea of free electrons which can move in response to an electric field. This response can be very rapid and results in a polarisation of charge at the surface and through the metal. At frequencies greater than w p the electron gas cannot respond which is the reason for the transparency of metals to ultra-violet radiation. However for frequencies used in communications the electron gas can easily respond to the radiation and reflectivity is unity.

If a poor conductor is used instead of a metal, i.e. there are no freely conducting electrons, then there is no polarisation, and as you point out charge cannot enter the system, and there can be no surface field. Consequently reflection of the radiation will not occur at these low frequencies and there is no waveguide action.

I hope that these comments provide a satisfactory explanation.

Yours sincerely,

[signed] M Pepper
cc: Sir Michael Atiyah - Trinity College [Master]
........Mr. A Weir - Trinity College
........Telephone: 01223 337330




August 23, 1993 Dear Raeto West, I write with reference to your letter of August 19. Your description of the process is correct; as a TEM wave advances so charge within the conductor is polarised and the disturbance propagates at right angles to the direction of propagation of the wave .... .... Yours sincerely, M Pepper


Portrait of a Drivelmaster… A one-electron man. Can’t handle a whole row of them.

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“The point about the Catt Anomaly has, says Ivor, nothing to do with his theory. It is an anomaly between rival textbooks and professors [Pepper and McEwan]. They will answer his polite query in their condescending authoritative manner until they are told that their ‘explanation’ is the exact opposite of that taken by other authors and professors . Then they cannot be induced to communicate with one another to resolve the problem.” – Editorial, Electronics World, August 2003, p3.


As the wave travels at light velocity, then charge supplied from outside the system would have to travel at light velocity as well, which is clearly impossible. - Pepper, above.



I conclude that the 'Josephson view' remains correct, while the alternative is based on the incorrect idea that the electrons would have to travel at the speed of light if they arrived along the 'east west' axis. - Josephson




DOES flow from somewhere to the left! The charges DON'T have to travel at anywhere near the speed of light to do this! - McEwan



The flaw here is the assumption that the charges move with the wave. whereas in reality they simply come to the surface as the wave passes, and when it has gone they recede into the conductor. No individual charge moves with the velocity of the wave. The charges come to the surface to help the wave go by and then pass the task to other charges further along the line which are already there and waiting. Lago



Polonius the Scientist