6 MetroTech CenterBrooklyn, NY 11201 USA

CS/EE1012---Introduction to Computer EngineeringApril 15, 2011

Professor Spencer KuoTel. 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 shelfHistory

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 hischocolate bar with microwaves.

The first food to be deliberately cooked with Spencer's microwave waspopcorn, and the second was an egg, which exploded in the face of one of theexperimenters.

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 andfood 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 depends on 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.

ComponentsA 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 intomicrowave energy.

• A typical consumer microwave oven consumes 1100 W of electricity in producing 700 W of microwave power, an efficiencyof 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 TubeStructure 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 Plasma reacts with phosphors Reaction causes each subpixelgas to plasma. 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 sub-frames. 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 screenlighting 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

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.

Blood Coagulator(US Patent No.: US7777151)

Hole in an ear Saphenous Vein