6 MetroTech Center
Brooklyn, NY 11201 USA
CS/EE1012---Introduction to Computer Engineering
April 9, 2010
Professor Spencer Kuo
Tel. 718-260-3143; email: skuo@duke.poly.edu, Office: LC 118C
Microwave Oven and Plasma Display Panel
A. Microwave Oven
•
•
•
History and basic operation principle of microwave cooking
Components and description
Safety issue discussion
B. Plasma Display Panel
•
•
Structure description
Dielectric barrier discharge for plasma generation
•
Salient features
Microwave Oven
A microwave oven
A microwave oven with a metal shelf
History
 Cooking food with microwaves was discovered accidentally in the 1940s.
 Percy Spencer, a self-taught engineer, was building magnetrons for radar sets
with the company Raytheon.
 He was working on an active radar set when he noticed that a peanut
chocolate bar he had in his pocket started to melt. The radar had melted his
chocolate bar with microwaves.
 The first food to be deliberately cooked with Spencer's microwave was
popcorn, and the second was an egg, which exploded in the face of one of the
experimenters.
Principles
• A microwave heats water and other polarized molecules within the food. This is
called “dielectric heating”.
• This heating is fairly uniform, leading to food being adequately heated throughout
(except in thick objects), a feature not seen in any other heating technique.
• Electric dipoles, meaning that they have a positive charge at one end and a negative
charge at the other, rotate as they try to align themselves with the alternating electric
field of the microwaves. This molecular rotating movement is then dispersed into
heat as the rotating molecules hit other molecules and put them into random motion.
• Microwave heating is more efficient on liquid water than on frozen water (where the
molecules are not free to rotate).
• Microwave heating at 2.45 GHz is sometimes explained as a resonance of water
molecules, but this is incorrect: such resonance only occurs in water vapor at much
higher frequencies, at about 20 GHz.
• Moreover, large industrial/commercial microwave ovens operating at the common
large industrial-oven microwave heating frequency of 915 MHz, also heat water and
food perfectly well.
• A common misconception is that microwave ovens cook food from the "inside out".
In reality, microwaves are absorbed initially also in the outer layers of food, except
with penetration deeply than other methods.
• Penetration depth of microwaves dependson food composition and the frequency,
with lower microwave frequencies (longer wavelengths) penetrating better.
• Basic microwave ovens heat food quickly and efficiently, but do not brown or bake
food in the way conventional ovens do.
Components
A microwave oven consists of:
• A high voltage power source, commonly a simple transformer or an electronic
converter, which passes energy to the magnetron
• A cavity magnetron, which converts high-voltage electric energy to microwave
radiation
• A magnetron control circuit (usually with a microcontroller)
• A waveguide (to control the direction of the microwaves)
• A cooking chamber
 The cooking chamber itself is a Faraday cage enclosure which prevents the
microwaves from escaping into the environment. The oven door is usually a
glass panel for easy viewing, but has a layer of conductive mesh to maintain
the shielding.
Efficiency and Health effects of Microwave radiation
• A microwave oven converts only part of its electrical input into
microwave energy.
• A typical consumer microwave oven consumes 1100 W of
electricity in producing 700 W of microwave power, an efficiency
of 64%.
• The other 400 W are used by the cooling fan and microcontroller,
and dissipated as heat in the magnetron tube.
 The safety level of microwave leakage is 5 milliwatts of
microwave radiation per square centimeter at approximately 2
inches from the surface of the oven.
 The radiation produced by a microwave oven is non-ionizing. It
therefore does not have the cancer risks associated with ionizing
radiation such as X-rays, ultraviolet (uv) light, and high-energy
particles.
The Magnetron Tube
Structure and Operation
Basic Magnetron Structure
Basic Magnetron Operation
• HW problem:
Prepare two potatoes with about the same
weight; one is in a round shape and the other
one in elongated shape.
Use a microwave oven to cook them with the
same amount of time, but don’t over cook
them. Answer following questions:
1. Which one will be cooked more thoroughly?
2. Why?
Plasma Display Panel (PDP)
A Pixel
Process:
Gaseous discharge changes
gas to plasma.
Plasma reacts with phosphors Reaction causes each subpixel
in discharge region.
to produce red, green,
and blue light.
Plasma Display Technology
In color panels, the back of each cell is coated with a phosphor. The
ultraviolet photons emitted by the plasma excite these phosphors to give off
colored light.
The intensity of each color is controlled by varying the number and
width of voltage pulses applied to the sub-pixel during a picture
frame. This is implemented by dividing each picture frame into subframes. During a sub-frame, all cells are first addressed – those to be
lit are pre-charged to a specific address voltage – then during the
display time the sustain voltage is applied to the entire screen
lighting those which were addressed.
Each sub-frame has a weighting ranging from 1 time unit to 128
time units for a typical eight sub-frame arrangement (Time Unit
depends on size and number of pixels on the screen).
Comparison of PDP and LCD
Air Plasma Technologies
Innovation

It leads to three US and two foreign patents:
1. “Methods and Apparatus for Generating a Plasma Torch”
US 6329628 B1. Issue Date of Patent: Dec. 11, 2001.
2. “Portable Arc-seeded Microwave Plasma Torch”
US 7091441 B1. Issue Date of Patent: Aug. 15, 2006.
3. “Plasma Torch Implemented Air Purifier,”
US7621985. Issue Date of Patent: Nov. 24, 2009.
4. “Mail Decontaminator”
ROC Patent: I 288005, Date of Patent registered: 10/11/07.
5. “A Portable Arc-seeded Microwave Plasma Torch”
PCT Patent in China, ZL200580016015.6;
Issue Date of Patent: Sept. 16, 2009.
What is plasma?
• Plasma is a distinct state of matter containing a
significant number of electrically charged and
neutral particles, including electrons, ions, and
atoms/molecules.
• Plasma is referred to as the fourth state of matter,
distinct from the solid, liquid and gas states.
• Plasmas are estimated to constitute more than 99
percent of the visible universe.
Torch for Decontamination
A Portable Arc-seeded Microwave Plasma Torch (MPT)
(US Patent No.: US 7091441 B1 )
Experimental Setup for Measurements of the
Emission Spectroscopy of Torch Plasma
Emission Spectroscopy of the MPT
Oxygen triplet spectrum in the emission of the microwave plasma
torch, indicating relatively high atomic oxygen content in the
torch;
the airflow rate is 0.393 l/s and the line of sight of measurement is
at 2 cm above the surface of the waveguide.
Rel. Intensity (a. u.)
8.E+04
6.E+04
4.E+04
2.E+04
0.E+00
776
776.5
777
777.5
Wavelength (nm)
778
778.5
779
Experimental Arrangement
The plasma effluent was directed downward, toward a dry
sample placed inside a Petri dish in reference to the distance
from the circular exit of the waveguide.
Scanning electron microscopy
(SEM)
Atomic force microscopy
(AFM)
Blood Coagulator