Because of its direct link to self-fields such as described in the EM self-field theory, I want to talk about how antennas can be designed to emit zero nett radiation. Although antennas were shown by Hertz in 1888 to 'always' emit radiation he used only one antenna, a wire halfwave dipole with a gap at its centre; if we use two antennas working in sych with each other we can in fact design the system to emit ZERO NETT RADIATION. We are assuming here that there are two antennas (they are in fact magnetic loop antennas designed to operate at half-wavelength. i'll walk you through it verbally for a start and if I can I'll try to find out how to insert maths equation (help required mr moderator-how can I show Maxwell's eqns?);(adsbygoogle = window.adsbygoogle || []).push({});

Assume that the fields are NOT point-charge to point-charge. This is a classical concept that was born out of the experiments of Coulomb, Faraday and others around 175 odd years ago. The form of the inverse square followed Newton's gravitional law, and the experiments in electricity and magnetism are MACROSCOPIC; but we are interested in atoms say (to begin with). Looking at OTHER ways that people have dealt with such issues, and if you've done a masters thesis in axisymmetric antenna structures, you tend to learn a lot of good real world maths including some of the older techniques, Von Hippel, "dielectrics and waves" Wiley, 3rd printing, 1962, uses a rotating vector. He solves the problem of far-field radiation from a dipole antenna. In my phd (bioelectromagnetics), I studied this in regards a similar problem where it was desired to obtain ZERO RADIATION in the far-field. The way to do this is by adjusting components so that the RADIATION IN is equal to the RADIATION OUT (remember we are treating the field as ubiquitous and infinite, which turns out to be incorrect, but for this case there's heaps of energy residing IN the field, stored in the infinite field).

So we CAN in fact have zero radiation antennas; this leads to a realisation of exactly what is an 'imaginary' field and what it means physically. the antenna structure needs to be a cross dipole where there is a phase difference of pi/2 (or "j" between the ttwo dipoles. This is NOT an electric dipole but a ring dipole, a magnetic dipole. and so we have two toriods which have to 'access' each other, so most conveniently we have a solid sphere of metal in which two oscillating fields are established (no mean feat, but nice theoretically)-so much for lecture 1!! see you tomorrow

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# A Zero Radiation Antenna

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