--- Robin van Spaandonk <[EMAIL PROTECTED]> wrote: > In reply to Paul's message of Wed, 11 Oct 2006 > 08:11:08 -0700 > (PDT): > Hi Paul, > [snip] > >contact with his daughter. BTW, do you have a > contact > >for five nines grade iron? > [snip] > Isn't pure iron just going to convert all those > lovely microwaves > into pure heat? > Regards, > > Robin van Spaandonk
Hi Robin, Under normal usage the magnetic material absorbs most of the radiation. The radiation is typically in the hundreds of MHz (not GHz) for non-electrical materials and considerably lower in frequency for electrically conductive materials such as iron. In electrically conductive materials the free electrons act as inductance, which slows down the electrons flip rate. So in iron, depending on purity, the peak radiation frequency ranges from KHz to MHz, not hundreds of MHz let alone GHz. Even if it were microwaves (GHz), which for the most part the radiation is not, the metal would act as a high refractive index. In other words, the metal would slow down the radiation velocity. Furthermore, most of the radiation would internally reflect off the cores outer walls. Note that in microwave ovens the metal reflects the radiation-- only a small amount is absorbed. This process of slowing down the radiation and reflecting is understood when studying electrodynamics in detail. Also you can see this effect in electrodynamic computer simulations. The end result would be most of the radiation reflecting internally, which would cause heat. Here's a list of methods to decrease the magnetic materials ability to absorb the radiation in addition to increasing the potential radiation. 1. Use materials with smallest domains at operating temperatures-- amorphous and nanocrystalline cores. The smaller the domain the more potential energy. When times permit I would like to precisely demonstrate this in a step-by-step process using conventional physics. 2. The thinner the core the better! Your goal is to prevent the core from absorbing the MCE radiation. Presently I am pondering upon a design that uses long thin magnetic electrically conductive wires. The thin wire would be the core and coil. 3. High saturation materials. A fully saturated core prevents the intrinsic electron spins from absorbing the magnetocaloric energy. Of course a fully saturated core is useless, but no realistic coil can fully saturate magnetic material. The core should be close to saturation. 4. Unless you use filters you'll need to flip the process so you can collect the energy during the cores radiating cycle. You do this with a permanent magnet. Also the PM helps saturate the core, but you don't want to fully saturate it. 5. The field from your coil will oppose the PM's field. So you slowly increase your coil current to decrease the cores net applied field and then you want to drop the current or reverse the current as quickly as possible (high di/dt). High di/dt causes a higher percentage of the electron spins to flip simultaneously, which in turn greatly reduces the cores ability to absorb MCE energy, which allows more of the energy to escape the core. In short, ultra high di/dt lowers the effective permeability, which in turn prevents the core from absorbing a great deal of the MCE energy, which your circuit can then properly absorb. If the core material has low electrical resistivity then the Eddy currents will absorb the radiating energy and then with precise timing you can rob a certain percentage of the Eddy currents energy. Regards, Paul Lowrance __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com
