Applications, operating principal of Microwave oven - Advantages and Disadvantages

 Applications of Microwave oven - Advantages and Disadvantages

Microwave oven is one of the most widely used household appliances. The reason for its popularity is that it cooks food in an amazingly short amount of time. They are also extremely efficient in their use of electricity because they heats only the food nothing else. The microwaves in electromagnetic spectrum range from 300 MHz to 300 GHz. The wave used in microwave. Oven found in homes and resturants generally operate at frequencies of 2.45 GHz with wavelength.

The waves of frequency 2.45 GHz. Can be produced by solid state devices but they are too weak for cooking. To get high powered waves. Microwave ovens use magnetron . Magnetrons can produce continuous or pulsed microwaves upto few megawatts. The waves of frequency 2.45 GHz have an interesting property of getting observed by water, fat and sugars while they are not a absorbed by most plastic, ceramics or glass. They are reflected by metals.

Operating Principal : 

Most food, even dry foods, have water in them. The water molecule (H2O) is a polar molecule with two hydrogen atoms being more positive than single oxygen atom. The resonant frequency of water molecule is very near to 2.45 GHz. The frequency of applied microwaves being 2.45 GHz, the direction of under the influences of fast changing of electromagnetic field get increasingly agitated and begin to vibrate at atomic level. Due to fierce vibrations, they run into each other and create friction and the energy is given oft in the form of heat.

The magnetron is the heart of microwave oven. It can generate either continuous or pulsed microwaves with powers upto mega watts and frequencies between 1 to 40 GHz. The efficiency of magnetron is around 80% and life time about 5000 hours. Here electron beam under the combined effect of electric and magnetic fields are made to follow curved trajectories. The cylindrical cathode is at the axis, several millimetres away from a hollo circular anode

Inside the anode, there are several cavities which can resonate at 245 GHz. A high voltage of several KV is applied parallel to axis such that electric and magnetic fields are perpendicular to each other. The electrons ejected by the the cathode accelerate  radially at first, but due to magnetic field they start to follow cycloidal paths. Due to strong magnetic field, elelctrons connor reach to anode and they form a rotating space charge. The resonant cavities of anode interact with these electrons by either accelerating or deaccelerating there them. This leads to electron bunches which move around the cathode at microwave frequencies. Most microwaves cook the food on a rotating turnable in the chamber. Some design may have rotating reflector, acting as stirrer. Some modes may include thermometers, grills etc. The microwave oven, the air in the oven remains at room temperature. In microwave oven the heat is not migrating through conduction. Radio waves penetrate evenly through out the food. The heat is everywhere all at once all the water molecules are all excited together and heat the food "from inside out". 

Advantages :

• Cooking time is short.

• No physical change of food, cooking of food  is from inside out.

• Destruction of nutrients is less.

• There is no flame involved.

Disadvantages

• Heat force control is difficult.

• Closed container is dangerous as chances of bursting is there. 

• Surface to sating not possible. 

• Constraint with metal container.

• Water evaporation.