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Electromagnetism 1 ISBN: 0 906340 10 1 Comments on Introduction Since the book was written in 1994, much more evidence has come to light about the worldwide lack of grasp of the Transverse Electromagnetic (TEM) Wave. Added to this, the reader will not have access to sensible discussion of the subject. This is proven by the lack of riposte to my assertions at the following www addresses, which are the first three Google hits when searching for “TEM Wave”; The Transverse
Electromagnetic Wave; a lost concept. This means that the only source for a reliable and clear description of the nature of a TEM wave is this author Ivor Catt. Since it is the basis of my (And Heaviside’s) approach to electromagnetic theory, I have to go to a great deal of effort to explain the TEM Wave. It is probably safest to give more than one approach. When giving private seminars, I would illustrate the TEM wave by telling the students to imagine that the ceiling was one conductor and the floor the other. I would walk across the room with my eyes shut and arms outstretched. The right arm was vertical to represent the electric field, and the left arm was horizontal to illustrate the magnetic field. I would then try to move forward at the speed of light in the third dimension, guided by the two conducting plates. Thus, I would stay on the ground, but advance from one end of the room to the other. Since the TEM Wave travels at the speed of light for the dielectric, I would be blind to what was ahead of me and also to what was behind me. If a Concorde airliner is advancing towards your back, the first you know of it is when it hits you. This helps to illustrate the TEM Wave. The only thing that a TEM Wave can “see” is the space immediately ahead of it. For TEM Wave travelling through vacuum, each square of this space has an aspect ratio of 377 ohms. One portion of a TEM wave does not know whether there is another portion ahead of it or behind it. Each wafer of what Heaviside called energy current is blind to possible portions ahead and behind it. In principle, the wafer of energy current has approaching zero thickness. However, this doews not mean that it does not exist. At a point in a brick, the brick material has zero mass. However, the brick exists. We integrate the brick’s density over area to get from zero mass to finite mass. Similarly with the TEM Wave of energy current, although each portion is elsewhere to every other, has finite total energy. (There is no instantaneous action at a distance, so in the language of Minkowski, each wafer of energy current is “elsewhere” to every other waver; is a separate universe.) Heaviside called the TEM Wave a slab of energy current. This is more convenient terminology than “wafer”, so I will use it. If the two conductors guiding the TEM Wave are flat, then the E field and H field make a Cartesian grid. A good way to deal with edge effects is the have two more or less flat plates close to each other but forming two concentric cylinders, with the TEM Wave travelling between them down the outer tube. If the two plates are close compared with the radii, we then get a rectilinear field pattern. Twisted pair. In Figure 2, we have a cross section of a twisted pair. The lines represent the E field. The lines representing the H field should have been drawn at right angles to the E lines (looping round one or other conductor), thus forming an array of curvilinear squares. Figure 5 shows another way of representing a TEM Wave. When giving private seminars, c represented my nose, E my vertical right arm, and H my horizontal left arm. Ivor Catt 9june03 |
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A much more difficult
discussion. Measuring a TEM Wave |
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