Specifications

Ver SG 9/200 15 Sharp Electronics Corporation
The purpose of the oven door is to provide an access to the cavity and also to confine the
microwave energy. A proper fitting door is essential to completely confine the energy
and, it, as well as the door flange, should be wiped clean regularly to insure good contact
of the door and the door flange. Considerable ingenuity has gone into microwave oven
door design because it is such a critical feature of the oven. A quarter wave slot or
“choke” seal around the perimeter of the door acts to choke off or cancel out microwave
emissions at this point.
Oven controls consist mainly of a touch pad, microcomputer, function display, interlock
switches and primary (cook) relay. The microcomputer is very accurate so that heating
cycles can be set with a high degree of accuracy. The microcomputer is important
because all microwave cooking is gauged by time, not temperature and time.
A few extra seconds of cook time in some cases can mean the difference between success
and failure. An audio signal usually indicates when the set time has elapsed and the oven
has turned itself off. The oven may also be turned off simply opening the door. To
protect the user from unnecessary exposure to microwave energy is a requirement of all
microwave ovens, and any one of the three interlocks operate when the door is opened,
which could turn off the oven.
The Heart of a Microwave Oven
Magnetron & associated parts:
1. Temperature fuse to protect the magnetron against excessive heat.
2. Fan motor to force cool air in the magnetron
3. Fan duct to direct air stream from the motor.
The magnetron cross-section shows a common twelve-cavity design. Each cavity is
resonant at the fundamental frequency of oscillation. As the cathode is heated in a hard
vacuum, electrons are “boiled off” accelerated towards the anode by a high voltage
(typically -4000 volts) and rotated in a helical path by the magnetic focusing field. As
electrons boil off, they rotate in clouds, tangential to the cavities, stimulating the build-up
of microwave energy in these cavities. As the rotating electrons interact with the fields in
the cavities, they get more strongly focused until “spokes” of electrons are formed, much
like the spokes of a rotating wheel. When the spokes of electrons, or space charge, rotate
synchronously with the microwave fields of the cavities, the maximum energy is coupled
from the electrons to the oscillations. Straps connect alternate cavities so that all cavities
resonate in unison, energy flows up the antenna, and is fed into the cooking cavity.