CONTENTS Introduction Discovery Frequency range Microwave source Uses Frequency Bands Health Effects
INTRODUCTIONMicrowaves are electromagnetic waves with wavelengthsranging from 1 mm to 1 m, or frequencies between300 MHz and 300 GHz. As a consequence, practicalmicrowave technique tends to move away from the discreteresistors, capacitors, and inductors used with lowerfrequency radio waves. Instead, distributed circuit elementsand transmission-line theory are more useful methods fordesign, analysis. The term microwave generally refers to thealternating current.Electromagnetic waves longer (lower frequency) thanmicrowaves are called "radio waves". Electromagneticradiation with shorter wavelengths may be called"millimeter waves", or t-rays
DISCOVERY The existence of electromagnetic waves, of whichmicrowaves are part of the frequency spectrum, waspredicted by James Clerk Maxwell in 1864 from hisequations . Heinrich Hertz was the first to demonstratethe existence of electromagnetic waves by building anapparatus that produced and detected microwaves in theUHF region. J. C. Bose publicly demonstrated radiocontrol of a bell using millimeter wavelengths, andconducted research into the propagation of microwaves.
FREQUENCY RANGES The microwave range includes ultra-high frequency (UHF) (0.3–3 GHz), super high frequency (SHF) (3– 30 GHz), and extremely high frequency (EHF) (30– 300 GHz) signals. Above 300 GHz, the absorption of electromagnetic radiation by Earths atmosphere is so great that it is effectively opaque, until the atmosphere becomes transparent again in the so-called infrared and optical window frequency ranges.
MICROWAVE SOURCE Vacuum tube based devices operate on the ballisticmotion of electrons in a vacuum under the influence ofcontrolling electric or magnetic fields, and include themagnetron, klystron, travelling wave tube (TWT), andgyrotron. These devices work in the density modulatedmode, rather than the current modulated mode. Thismeans that they work on the basis of clumps of electronsflying ballistically through them, rather than using acontinuous stream.A maser is a device similar to a laser, except that itworks at microwave frequencies.Solid-state sources include the field-effect transistor, atleast at lower frequencies, tunnel diodes and Gunndiodes.
USES COMMUNICATION REMOTE SENSING NAVIGATION POWER
COMMUNICATION Microwaves are used for communication, as theyare easier to control because small antennas coulddirect these waves very easily. These waves can cover long distances very easily,about 4 miles. Before the invention of optical fibers, microwaveswere used for communication., as they travel withspeed of light. Microwaves helps in wireless LAN protocolHelps in MAN Cable TV and internet access on coaxial as wellas broadcast televisions uses microwave of lowerfrequencies
Mobile phones network and GSM also usesmicrowaves of lower frequencies Microwave radio is used for broadcast andtelecommunication due to its high frequencies. Microwaves are used in television news totransmit the signal from a remote location to atelevision stations. Used for communication satellites. They are used for those areas where cables wirecould not be used
REMOTE SENSING Radar uses microwave radiation to detect the range, speed, and other characteristics of remote objects. Now radar is widely used for applications such as air traffic control, navigation of ships, and speed limit enforcement. A Gunn diode oscillator and waveguide are used as a motion detector for automatic door openers. Most radio astronomy uses microwaves
NAVIGATION Global Navigation Satellite Systems (GNSS) including the American Global Positioning System (GPS) and the Russian ГЛОбальная НАвигационная Спутниковая Система (GLONASS) broadcast navigational signals in various bands between about is 1.2 GHz and 1.6 GHz.
POWER A microwave oven passes (non-ionizing)microwave radiation (at a frequency near 2.45GHz) through food, causing dielectric heatingby absorption of energy in the water, fats andsugar contained in the food. Microwave heating is used in industrialprocesses for drying and curing products. Many semiconductor processing techniquesuse microwaves to generate plasma.
Microwaves can be used to transmit power overlong distances. NASA worked in the 1970s and early1980s to research the possibilities of using Solarpower satellite (SPS) systems with large solar arraysthat would beam power down to the Earths surfacevia microwaves.
A three-dimensional plot shows how the microwave frequency (x axis) generated by a new NIST oscillator varies with changes in the current (yaxis). The height of each peak represents the power of the signal produced at specific frequencies.
MICROWAVE FREQUENCY BANDS The microwave spectrum is usually defined as electromagnetic energy ranging from approximately 1 GHz to 1000 GHz in frequency, but older usage includes lower frequencies. Most common applications are within the 1 to 40 GHz range. Microwave frequency bands, as defined by the Radio Society of Great Britain (RSGB), are shown
Microwave frequency bandsDesignation Frequency range L band 1 to 2 GHz S band 2 to 4 GHz C band 4 to 8 GHz X band 8 to 12 GHz Ku band 12 to 18 GHz K band 18 to 26.5 GHz Ka band 26.5 to 40 GHz Q band 30 to 50 GHz U band 40 to 60 GHz V band 50 to 75 GHz E band 60 to 90 GHz
W band 75 to 110 GHz F band 90 to 140 GHz D band 110 to 170 GHz (Hot)
Health effects Health effects of environmental electromagnetic fields . Antibody responses of mice exposed to low-power microwaves . Cancer morbidity in subjects occupationally exposed to high frequency electromagnetic radiation. Accelerated development of spontaneous skin cancer in mice exposed to 2350 MHz microwave radiation. It is powerful and effects human skin very badly.
CONTENTS INTRODUCTION PRINCIPLE INVENTION HOW IT WORKS EFFECTS OF MICROWAVE OVEN
INTRODUCTION A microwave oven, is a kitchen appliance that can come in many different sizes and styles employing microwave radiation primarily to cook or heat food. This is accomplished by using microwaves, almost always emitted from a magnetron, to excite water (primarily) and other polarized molecules within the food to be heated. This excitation is fairly uniform, leading to food being heated everywhere all at once
PRINCIPLE Microwave oven works by passing non-ionizing microwave radiation,usually at a frequency of 2.45 GHz (a wavelength of 12.24 cm), through thefood. Microwave radiation is between common radio and infraredfrequencies. Water, fat, and other substances in the food absorb energyfrom the microwaves in a process called dielectric heating. Many molecules(such as those of water) are electric dipoles, meaning that they have apositive charge at one end and a negative charge at the other, and thereforerotate as they try to align themselves with the alternating electric field of themicrowaves. This molecular movement creates heat as the rotatingmolecules hit other molecules and put them into motion. Microwaveheating is most efficient on liquid water, and much less so on fats andsugars (which have less molecular dipole moment), and frozen water (wherethe molecules are not free to rotate). Microwave heating is sometimesexplained as a rotational resonance of water molecules, but this is incorrect:such resonance only occurs in water vapor at much higher frequencies, atabout 20 gigahertz.
INVENTIONCooking food with microwaves was discovered byPERCY SPENCER while building magnetrons for radarsets. He was working on an active radar set when henoticed that a peanut chocolate bar he had in his pocketstarted to melt. The radar had melted his chocolate barwith microwave. Then he cooked popcorns and food inmicrowave . Spencer created a high densityelectromagnetic field by feeding microwave power into ametal box which it had no way to escape. When foodwas placed in the box with the microwave energy, thetemperature of the food rose rapidly.
WORKING Every microwave oven contains a magnetron, atube in which electrons are affected by magnetic andelectric fields in such a way to produce microwavelength radiation. This microwave radiationinteracts with the molecules in the food. All waveenergy changes polarity from positive to negativewith each cycle of the wave and this cause the polarmolecules to rotate at the same frequency millions oftimes a second. All this agitation creates a molecularfriction within the food and at last this heats up thefood.
HARMFUL EFFECTS CANCER CAUSING EFFECTS DECREASE IN NUTRITIVE VALUES BIOLOGICAL EFFECTS
CANCER CAUSING EFFECTS CANCEROUS CELLS IN BLOOD TUMORS CREATION OF AGENTS ELEMENTAL FOOD UNSAFE FOR BABY’S MILK
DECREASE IN NUTRITIVE VALUESDECREASE IN SOME TERMS OFFOOD ENERGY CONTENTS NUCLEOPROTIENS