1. Microwaves Dr inż. ZDZISŁAW PÓLKOWSKI Polkowice, 2015 University of Pitesti Dolnośląska Wyższa Szkoła Przedsiębiorczości i Techniki w Polkowicach Ion Paul Mihai

2. TOPICS MENU What are microwaves Satellites and microwaves Microwave Frequency Band The Reflex Klystron Microwaves Properties Microwave Oven A Brief History of the Microwave Oven

3. What are microwaves Microwaves are a type of electromagnetic radiation, as are radio waves, ultraviolet radiation, X-rays and gamma-rays. Microwaves have a range of applications, including communications, radar and, perhaps best known by most people, cooking. Electromagnetic radiation is transmitted in waves or particles at different wavelengths and frequencies. This broad range of wavelengths is known as the electromagnetic spectrum (EM spectrum). The spectrum is generally divided into seven regions in order of decreasing wavelength and increasing energy and frequency. The common designations are radio waves, microwaves, infrared (IR), visible light, ultraviolet (UV), X-rays and gamma-rays. Microwaves have frequencies ranging from about 3 billion cycles per second, or 3 gigahertz (GHz), up to about 30 trillion hertz (terahertz or THz) and wavelengths of about 30 centimeters (12 inches) to 3 millimeters (0.12 inches), although these values are not definitive. This region is further divided into a number of bands, designated as L, S, C, X and K. http://www.livescience.com/50259-microwaves.html

4. http://www.wisegeek.org/what-is-microwave-radiation.htm Below you can see the diagram of Electromagnetic Spectrum:

5. Satellites and microwaves Earth satellites relaying microwave signals from the ground have increased the distance that can be covered in one hop. Microwave repeaters in a satellite in a stationary orbit 22,300 miles (35,880 kilometers) above Earth can reach one-third of Earth's surface. More than one-half of the long-distance phone calls made in the United States are routed through satellites via microwaves. http://www.scienceclarified.com/Ma-Mu/Microwave-Communication.html www.pinterest.com Communication Tower from Berlin, Germany.

6. Microwave Frequency Band http://www.google.com/patents/EP2422550A1?cl=en

7. The Reflex Klystron Another tube based on velocity modulation, and used to generate microwave energy, is the REFLEX KLYSTRON. The reflex klystron contains a REFLECTOR PLATE, referred to as the REPELLER, instead of the output cavity used in other types of klystrons. The electron beam is modulated as it was in the other types of klystrons by passing it through an oscillating resonant cavity, but here the similarity ends. The feedback required to maintain oscillations within the cavity is obtained by reversing the beam and sending it back through the cavity. The electrons in the beam are velocity-modulated before the beam passes through the cavity the second time and will give up the energy required to maintain oscillations. The electron beam is turned around by a negatively charged electrode that repels the beam. This negative element is the repeller mentioned earlier. This type of klystron oscillator is called a reflex klystron because of the reflex action of the electron beam. http://www.tpub.com/neets/book11/45d.htm

8. Below is the diagram of Reflex Klystron: http://www.daenotes.com/electronics/microwave-radar/microwave-tube-devices

9. Microwaves Properties Microwaves are sometimes considered to be very short radio waves (highfrequency and high-energy radio waves). Some important properties of microwaves are: They are reflected by metal surfaces. They heat materials if they can make atoms or molecules in the material vibrate. The amount of heating depends on the intensity of the microwave radiation, and the time that the material is exposed to the radiation. They pass through glass and plastics. They pass through the atmosphere. They pass through the ionosphere without being reflected. They are absorbed by water molecules, how well depends on the frequency (energy) of the microwaves. Transmission is affected by wave effects such as reflection, refraction, diffraction and interference. http://revisionworld.com/gcse-revision/physics/electromagnetic-radiation/radio-waves-microwaves

10. Microwaves Application Microwaves have a lot of application.Below we have some application: Telecom Point-to-point communication, Satellite, Cellular access technologies Space Sensing/Spectroscopy, Communication, Radio astronomy MedTech Diagnostics, imaging, and treatment applications. Defense Radar, Communication Security Car avoidance radar, Traffic surveillance, Air traffic security “cameras” Navigation, Positioning & Measurement GPS Food Heating & detection of foreign bodies in food New and novel application areas are constantly being added. http://www.microwaveroad.se/microwaves-and-application-areas.html

11. http://www.dotfive.eu/index.php?id=18 I chose this image as a example for microwaves application:

12. Microwave Oven A Microwave Oven consists in: a high voltage transformer, an electron tube called magnetron, a wave guide fan and an oven chamber. The transformer passes electric energy to the magnetron and the magnetron converts this electric energy into microwave radiation. The microwaves are reflected in the oven chamber and are absorbed by food http://www.slideshare.net/fascinating/microwaves-presentation http://ffden-2.phys.uaf.edu/104_spring2004.web.dir/arts_mcnulty/howmicrowaveovenswork.htm

13. A Brief History of the Microwave Oven Like many of today's great inventions, the microwave oven was a by- product of another technology. It was during a radar-related research project around 1946 that Dr. Percy Spencer, a self-taught engineer with the Raytheon Corporation, noticed something very unusual. He was testing a new vacuum tube called a magnetron (we are searching for a picture of an actual 1946 magnetron), when he discovered that the candy bar in his pocket had melted. This intrigued Dr. Spencer, so he tried another experiment. This time he placed some popcorn kernels near the tube and, perhaps standing a little farther away, he watched with an inventive sparkle in his eye as the popcorn sputtered, cracked and popped all over his lab. http://www.smecc.org/microwave_oven.htm http://ethw.org/Microwave_Ovens

14. The next morning, Scientist Spencer decided Microwave Oven Inventor Percy Spencerto put the magnetron tube near an egg. Spencer was joined by a curious colleague, and they both watched as the egg began to tremor and quake. The rapid temperature rise within the egg was causing tremendous internal pressure. Evidently the curious colleague moved in for a closer look just as the egg exploded and splattered hot yoke all over his amazed face. The face of Spencer lit up with a logical scientific conclusion: the melted candy bar, the popcorn, and now the exploding egg, were all attributable to exposure to low-density microwave energy. Thus, if an egg can be cooked that quickly, why not other foods? Experimentation began... Dr. Spencer fashioned a metal box with an opening into which he fed microwave power. The energy entering the box was unable to escape, thereby creating a higher density electromagnetic field. When food was placed in the box and microwave energy fed in, the temperature of the food rose very rapidly. Dr. Spencer had invented what was to revolutionize cooking, and form the basis of a multimillion dollar industry, the microwave oven. http://www.smecc.org/microwave_oven.htm