Microwave Oven working and its mechanism

1. Microwave Oven

2. WHAT ARE MICROWAVES?
 Microwaves are a form of electromagnetic energy,
like light waves or radio waves.
 Its frequency range is from 300 MHz (0.3 GHz) to
300 GHz.
 Microwaves are used extensively in
communications.

3. HISTORY
 The idea of microwave oven was first conceived by
Percy L. Spencer in 1946.
 Mechanism：the principle of frictional heat
production using microwaves.
 The first home version was produced by Raytheon
Corporation in 1965.

4. ELECTROMAGNETIC SPECTRUM
 Electromagnetic radiation exists in a range of
frequencies called the electromagnetic spectrum.
 c = fl
 The frequency used in microwave oven is 2.45 GHz

6. BASIC STRUCTURE

7. HOW DOES A MICROWAVE OVEN COOK
FOOD?
 Water (H2O) is a polar molecule with 2 hydrogen
atoms being more positive than the single oxygen
atom.

8.  In liquid water, the molecules are in constant motion
and are normally randomly oriented.
 Glass, paper, ceramic, or plastic containers are
used in microwave cooking .
 Metal reflects micrwaves

9. Cooking with Microwaves
represents water molecule;
represents molecules of food.
Magnetron produces microwaves which pull the water
molecules back and forth at the rate of about 2.5 billion
times per second.
This rapid back-and-forth motion between the water
molecules creates friction, and hence heat.
And then the heat is transferred to the
molecules of food nearby.

10. WHY DO THEY HAVE TURNTABLES?
 Microwaves are reflected by the oven wall, forming
“standing waves” in the cooking chamber.

11.  In side a microwave oven, the electromagnetic
waves also form standing waves from reflections at
the walls.

12. INTERACTION OF MICROWAVES WITH METALS
 Microwaves, incident on the metal walls of the oven.
 The microwaves are perfectly reflected.

13. MAGNETRON
 Magnetron is an electronic device which generates
high energy microwaves. It is the core element in a
microwave oven.
 Working principle:
When a charge/charge particle accelerates in
space, it generates electromagnetic waves.

14. PARTS OF MAGNETRON
 Cathode
 Anode
 Permanent magnet

15. CATHODE
o Based on principle of thermionic emission.

16. ANODE
 Anode in magnetron is a copper cup like structure
which is a little bit modified to perform more
functions than a simple anode does.

17. PERMANENT MAGNET
 The purpose of the permanent magnet is to apply a
continuous magnetic field across the cathode area.

18. WORKING OF MAGNETRON

19. RESONATOR

20. OPERATION OF MICROWAVE OVEN
 In the high-voltage section of a microwave oven,
the diode and the capacitor function together to
effectively double the already-high voltage. This is
called a voltage-doubler circuit.
 Voltage-doubler circuits are fed with the stepped-up
AC voltage from the high-voltage transformer's
secondary (or output) winding.

21. THE HALF-WAVE VOLTAGE DOUBLER
 During the first positive half-cycle, which is
designated on the sine wave graph as T1 , the
voltage from the transformer increases .

22.  At time T3, the transformer secondary (output)
voltage swings into the negative half-cycle and
increases in a negative direction to a negative 2800
volts, with polarities .

23.  The transformer secondary and the charged capacitor
are now essentially two energy sources in series.
 voltage doubler is also a rectifier, the output is a DC
voltage.

24. ADVANTAGES
 Compact and Stylish
 Chick and trim design
 Child safety lock

25. HARMFUL EFFECTS
 Cancer Causing Effects
 Decrease in Nutritive Values
 Biological Effects