MICROWAVES Dobrica Adrian Dr inż. ZDZISŁAW PÓLKOWSKI University of Pitesti Dolnośląska Wyższa Szkoła Przedsiębiorczości i Techniki w Polkowicach Dobrica Adrian Dr inż. ZDZISŁAW PÓLKOWSKI Polkowice, 2015

TOPICS MENU Definition Mobile Phone Charging Using Microwaves Microwave oven Microwave frequency measurement Effects on health

Definition Microwaves are a form of electromagnetic radiation with wavelengths ranging from as long as one meter to as short as one millimeter; with frequencies between 300 MHz (100 cm) and 300 GHz (0.1 cm). This broad definition includes both UHF and EHF (millimeter waves), and various sources use different boundaries. In all cases, microwave includes the entire SHF band (3 to 30 GHz, or 10 to 1 cm) at minimum, with RF engineering often restricting the range between 1 and 100 GHz (300 and 3 mm). http://en.wikipedia.org/wiki/Microwave

The term microwave refers to electromagnetic energy having a frequency higher than 1gigahertz (billions of cycles per second), corresponding to wavelength shorter than 30 centimeters. Microwaves are high frequency radio waves (radiofrequency fields) and, like visible radiation (light), are part of the electromagnetic spectrum. Microwaves are used primarily for TV broadcasting, radar for air and sea navigational aids, and telecommunications including mobile phones. They are also used in industry for processing materials, in medicine for diathermy treatment and in kitchens for cooking food,mobile phone charging using microwaves. http://searchnetworking.techtarget.com/definition/microwave

Mobile Phone Charging Using Microwaves http://www.slideshare.net/NaveenKumar765/wireless-charging-of-mobile-phones-using-microwaves-29663792

Advantages & Disadvantages Only one microwave transmitter can serve to all the service providers in that area. The need of different types of chargers by different manufacturers is totally eliminated. Mobile get charged as we make call even during long journey. Disadvantages Wireless transmission of the energy causes some drastic effects to human body, because of its radiation Practical possibilities are not yet applicable as there is no much advancement in this field. Process is of high cost http://www.slideshare.net/NaveenKumar765/wireless-charging-of-mobile-phones-using-microwaves-29663792

Transmitting station with the microwave transmitter Block diagram Transmitting station with the microwave transmitter sensor Rectenna RF cable circulator waveguide Slotted waveguide Antenna mobile signal http://www.slideshare.net/NaveenKumar765/wireless-charging-of-mobile-phones-using-microwaves-29663792

MICROWAVE OVEN www.dreamstime.com

ARE MICROWAVE OVENS SAFE? When used according to manufacturers' instructions, microwave ovens are safe and convenient for heating and cooking a variety of foods. However, several precautions need to be taken, specifically with regards to potential exposure to microwaves, thermal burns and food handling. http://www.who.int/peh-emf/publications/facts/info_microwaves/en/

HOW DO MICROWAVE OVENS WORK? Domestic microwave ovens operate at a frequency of 2450 MHz with a power usually ranging from 500 to 1100 watts. Microwaves are produced by an electronic tube called a magnetron. Once the oven is switched on, the microwaves are dispersed in the oven cavity and reflected by a stirrer fan so the microwaves are propagated in all directions. They are reflected by the metal sides of the oven cavity and absorbed by the food. Uniformity of heating in the food is usually assisted by having the food on a rotating turntable in the oven. Water molecules vibrate when they absorb microwave energy, and the friction between the molecules results in heating which cooks the food.  http://www.who.int/peh-emf/publications/facts/info_microwaves/en/

Oven manufacturers do not recommend operating an empty oven Oven manufacturers do not recommend operating an empty oven. In the absence of food, the microwave energy can reflect back into the magnetron and may damage it.  Microwave oven users should carefully read and comply with the manufacturer’s instructions because new ovens vary widely in design and performance. While most modern ovens can tolerate some food packaging made of metal, oven manufacturers generally recommend not placing metal in the oven, particularly not close to the walls, as this could cause electrical arcing and damage the oven walls. Also, because metal reflects microwaves, food wrapped in metal foil will not be cooked, while food not in metal wrap may receive more energy than intended, causing uneven cooking. http://www.who.int/peh-emf/publications/facts/info_microwaves/en/

General information Microwave technology is extensively used for point-to-point telecommunications (i.e. non-broadcast uses).Microwaves are especially suitable for this use since they are more easily focused into narrower beams than radio waves, allowing frequency reuse; their comparatively higher frequencies allow broad bandwidth and high data transmission rates, and antenna sizes are smaller than at lower frequencies because antenna size is inversely proportional to transmitted frequency. Microwaves are used in spacecraft communication, and much of the world's data, TV, and telephone communications are transmitted long distances by microwaves between ground stations and communications satellites. Microwaves are also employed in microwave ovens and in radar technology. http://en.wikipedia.org/wiki/Microwave

Microwave signals propagate in straight lines and are affected very little by the troposphere. They are not refracted or reflected by ionized regions in the upper atmosphere. Microwave beams do not readily diffract around barriers such as hills, mountains, and large human-made structures. Some attenuation occurs when microwave energy passes through trees and frame houses. Radio-frequency (RF) energy at longer wavelengths is affected to a lesser degree by such obstacles. www.studyblue.com http://searchnetworking.techtarget.com/definition/microwave

Microwave frequency measurement Microwave frequency can be measured by either electronic or mechanical techniques. Frequency counters or high frequency heterodyne  systems can be used.Here the unknown frequency is compared with harmonics of a known lower frequency by use of a low frequency generator, a harmonic generator and a mixer. Accuracy of the measurement is limited by the accuracy and stability of the reference source. Mechanical methods require a tunable resonator such as an absorption wavemeter, which has a known relation between a physical dimension and frequency. http://en.wikipedia.org/wiki/Microwave

Effects on health Microwaves do not contain sufficient energy to chemically change substances by ionization, and so are an example of non-ionizing radiation.The word "radiation" refers to energy radiating from a source and not to radioactivity. It has not been shown conclusively that microwaves (or other non-ionizing electromagnetic radiation) have significant adverse biological effects at low levels. Some, but not all, studies suggest that long-term exposure may have a carcinogenic effect.This is separate from the risks associated with very high-intensity exposure, which can cause heating and burns like any heat source, and not a unique property of microwaves specifically. http://en.wikipedia.org/wiki/Microwave

When injury from exposure to microwaves occurs, it usually results from dielectric heating induced in the body. Exposure to microwave radiation can produce cataracts by this mechanism, because the microwave heating denatures proteins in the crystalline lens of the eye (in the same way that heat turns egg whites white and opaque). The lens and cornea of the eye are especially vulnerable because they contain no blood vessels that can carry away heat. Exposure to heavy doses of microwave radiation (as from an oven that has been tampered with to allow operation even with the door open) can produce heat damage in other tissues as well, up to and including serious burns that may not be immediately evident because of the tendency for microwaves to heat deeper tissues with higher moisture content. http://en.wikipedia.org/wiki/Microwave