Page 339 - Maxwell House

FEED LINE BASICS 319

Figure 6.6.10 a) Coaxial to TM01-mode transition, b) Rotary joint, c) Schematic drawing
of rotary joint

2. According to the Lorentz’s equation introduced in Chapter 1, the E-field nudges the
positively charged particles in the direction of the field. Evidently, the negatively charged
particles move and accelerate in the opposite direction. If such interaction between the
fields and particles lasts long enough (in term of speed of light), the kinetic energy of
particles and their speed can be substantially increased. It’s imperative that the accelerated
particles do not collide with gas molecules on their journey through the accelerator, so the
particle beam is contained in an ultrahigh vacuum inside a metal pipe that is a natural WC.
To maintain the particle acceleration, we must create in such tube the longitudinal force
continuously pushing particle forwards. TM01-mode with its z-component meets this
requirement perfectly well. We stop here since more detail discussion of power transfer
efficiency during the accelerating process, and accelerator structure itself is far beyond the
scope of this book.
3. One of the WC application is the industrial microwave material processing. The idea is
trivial: a wide range of materials are more or less conductive. Then according to Ohms law,
the E-field exerts the conductivity current and heats a material the same way as our home
microwave oven warms up food. One of such “oven” for fruit drying is demonstrated in
17
Figure 6.6.11a . Figure 6.6.11b illustrates the basic schematic of the heating process. Wet
material is put on a conveyor belt that transports it inside the microwave heater. At room
temperature and 1 atmosphere pressure, 1 kilowatt of microwave energy will evaporate
approximately ~1.13 kg of water in 1 hour. As such, water vaporizes, and the dry material
leaves the heater. TM01-mode in WC is one of the best candidates for such applications
because it has the longitudinal component of E-field continuously heating material on its
way inside the “oven.” The significant advantage of microwave heating is that the EM
waves penetrate deeply into material drying it from inside out. Conventional processing is
opposite and dries first the material surface and only then heats interior typically quite slow
due to the commonly low thermal conductivity of materials. If so, the surface temperature
could reach the burning level while its interior is still unheated. Microwave heating
overcomes those time and temperature limitations even when the materials are relatively
thick.

17 Public Domain Image, source: http://spanish.alibaba.com/product-gs/fruit-juice-industrial-microwave-
tunnel-dryer-with-panasonic-magnetron-60300592430.html