Field Theory ECX6241

Field Theory ECX6241Cooking with Electromagnetic wavesM.P.U.Isuranga ( 311088643 )What is Electromagnetic WaveAn electromagnetic wave consists of combination of a transverse electric field and a transverse magnetic field perpendicular to each other.

+-Arrows show field vectorsEM wave propagation in spaceElectromagnetic SpectrumElectromagnetic radiation exists in a range of frequencies called the electromagnetic spectrum. Each frequency has a specific wavelength and as the frequency decreases, the actual length of the wave gets longer. Mainly for the food Processing we use Microwaves.

Properties of MicrowavesGeneralElectromagnetic waves of radiant energyWavelength: 0.025-0.75(m)Frequency: 20,000-400(MHz)Specific to Food Applications:Frequency Approved for Food Application: 2450MHz & 915MHzReflected by metals, pass through the air, absorbed by several food constituentsAbsorbed material heated up to the extent of absorption. Microwave loses heat in the process.Loss factor and loss tangent used to define the loss of Microwave energy. Materials that are highly absorbent of microwaves are called highly loss materials.

Conventional and Electromagnetic HeatingConventionalA direct flame, heated air, etc. used in the conventional heating.Food molecules largely react from the surface inwards, producing a heating gradient.This can lead to difference in the burning of food surface and interiors.MicrowaveMicrowaves penetrate up to a few centimeters of the food which heats the food uniformly.Heat is passed in from surface by conduction but is generated quickly and uniformly throughout the mass. Hence the moisture is boiled away internally.Microwave heating thus leads to no crusting and surface browning.This is a limitation when a crust on the surface is desired. For ex, bread baking.In such a case, the microwave heating is accompanied by or followed or preceded by a conventional heating methods.

History Invented accidentally by Dr. Percy LeBaron Spencer While testing a magnetron during work, he discovered the candy bar in his pocket meltedExperimented with other food products (popcorn and eggs), and realized microwaves can cook foods quickly At 1947, 1st commercial microwave oven produced (called Radarange) where its Mostly used in restaurants, railroad cars, ocean liners and militaryImprovement and refinements made by 1967, 1st domestic microwave oven produced

Mechanism of Microwave HeatingThe microwaves that penetrate the food have an electric field that oscillates 2.45 billion times a second, a frequency that is well absorbed by polar liquid molecules such as water, sugars, fats and other food molecules.This leads to intermolecular friction, which in turn causes heating.As different components of food have different heating factors, it takes simultaneous conduction(solids) and convection(liquids) to equalize the distribution.The conduction and convection are the secondary effects while intermolecular frictional heat is the primary effect.

Microwave Generators and EquipmentMost commonly used microwave generator is Magnetron. It is a kind of electron tube within a magnetic field which propagates high frequency radiant energy.

Electrons from a hot filament would travel radially to the outside ring if it were not for the magnetic field. The magnetic force deflects them as shown and they tend to sweep around the circle. In doing so, they pump the natural frequency of the cavities. The currents around the resonant cavities cause them to radiate electromagnetic energy at that resonant frequency.

Health HazardsIt is known that microwave radiation can heat body tissue the same way it heats food. Exposure to high levels of microwaves can cause a painful burn Eg. the lens of the eye exposure to high levels of microwaves can cause cataracts. Microwave oven used low level of microwaves, within the region of non-ionizing radiationStill uncertain in the effects of humans from long term exposure to low level of microwaves Best to stay a way (an arms length) in reducing exposure to microwaves

The End.