How the microwave works: heats, cooks and defrosts

How a microwave oven works – a household electrical appliance for quickly heating and defrosting food, not all of its owners know. This often causes breakdowns and even accidents. Knowing the device of the microwave oven, the user will be warned of possible malfunctions and the dangers that await him during self-repair.

The principle of microwave exposure

The principle of operation of a microwave oven is fundamentally different from conventional ovens. Products penetrated by waves of the microwave range are heated over the entire volume, and not over the surface, as in the case of thermal exposure. That is why the heating/defrosting process is so short.

Heating of food occurs due to a physical phenomenon – electromagnetic microwave fields are converted into heat. In a microwave oven, only the product itself is heated, energy is not wasted on heating the chamber itself, which means energy is saved.

Microwave action is able to raise the temperature of the object to the value required by the user in minutes. This is especially convenient when defrosting: a huge piece of frozen meat can be reheated in minutes without changing its properties.

The heating of food is provoked by the action of high-frequency waves, their frequency is 2 MHz. These microwaves, passing inside the object, polarize water molecules. Under the influence of radiation, molecules are built along the lines of force of the electromagnetic field.

The directed movement of molecules causes an increase in the temperature of the product throughout the volume. Microwaves, penetrating into the depth of the object by 2,5-3 cm, heat up the water molecules, and the heated parts of the object transfer heat further – in this way, the entire volume is heated.

How a microwave works

Components of a microwave oven:

• Camera. Made from metal. Equipped with metalized door. Microwave radiation is concentrated here. Food is placed here to warm up. Requires care.
• Magnetron. Emitter of high-frequency microwaves.
• Transformer. Magnetron power supply.
• Communications and control system.
• Waveguide. Transmits microwaves from the emitter to the chamber.

Additional details:

• Pallet. Rotating, it contributes to the uniform heating of cooking objects.
• Fan. For ventilation of the chamber and cooling of the magnetron.

The operation of a microwave oven is reduced to the release of energy by the magnetron, which is converted into heat. The device is connected to a stabilizer transformer. Once this device was the most expensive in a microwave oven, today its cost has decreased and microwave ovens have become much more affordable.

The circuit diagram for all microwave ovens is almost the same, they only have different characteristics, capabilities and design.

What is a magnetron

Its purpose is to generate radiation of a given frequency. In fact, this is an electrovacuum diode. Its structure:

• It has an anode in the form of a cylinder. It has a round section and ten sectors with copper walls.
• In the center of the diode is the cathode. Inside it is an incandescent thread. The function of the cathode is to emit electrons.
• Along the edges of the magnetron are ring-shaped magnetic elements. Their task is to create a magnetic field in the emitter. This field is a generator of high-frequency waves.
• The voltage applied to the anode is 4 V and to the cathode filament is 000 V.

Due to the voltage difference, the cathode emits electrons, which are caught by an electric field with a high intensity. The generation frequency depends on the configuration of the resonator chambers and on the anode voltage.

Energy is removed through a loop of wire, which is connected to the cathode and output to a radiating antenna. The radiation from the antenna is directed to the waveguide, through which it passes inside the microwave oven.

In conventional microwave ovens, magnetrons with a power of 0,8 kW are used. It happens that to cook a dish, you need power less than 0,8 kW, then the device turns on for short periods of time, interspersed with pauses.

This principle of operation is known as pulse-width modulation. Since the magnetron heats up during operation, it is placed in a plate-type radiator, which is constantly blown by a fan. Overheating can cause damage. To prevent this from happening, install a special thermal fuse.

What is a thermal fuse

These devices are also known as thermal relays. They are produced for different temperature ratings.

The thermal relay consists of an aluminum housing, which is attached to the temperature control point with a flange connection, and a bimetallic plate set to a certain temperature value. When the heating exceeds the allowable threshold, the plate, bending, starts the element that opens the contacts – the power to the stove stops.

When the magnetron cools down, the bimetallic plate will take its original shape and the contacts will close – the furnace will turn on.

Description of fan operation

Operation is not possible without a fan. Its functions:

• Blowing the radiation source and other components of the electronic circuit that generate heat.
• If there is a grill, then the fan blows it too.
• In the chamber, during cooking, a lot of heat and steam is generated. Thanks to the fan, increased pressure is created, squeezing out warm air and steam through the ventilation holes.

The fan is located near the rear wall of the device. Sucking air from the room, it directs the air flow through the air ducts to the magnetron plates, and then into the chamber. The fan blades are driven by an asynchronous AC motor.

How does the door work

Thanks to the interlock, which is triggered when the door is opened, users are protected from exposure. The device of the door is quite complicated – the safety of the owner depends on the serviceability of its operation. The design of the door provides protection measures:

• Tight fit to the body. A stove with large gaps cannot be used. The radiation is capable of leaving the chamber through the slits. The metal body of the appliance and the special groove in the door must be separated by a gap, the width of which is equal to ¼ of the microwave length. In such a gap, a standing-type electromagnetic wave is formed, which has zero amplitude at the place where the door adjoins the body, which is why it does not go beyond the chamber. This method of protection – from waves using the waves themselves – is called a microwave choke.
• There is a high-frequency damper around the perimeter of the door that reduces radiation to a safe level.
• When casting the door body, various additives are used, thanks to which the metal absorbs radiation better. They do not provide 100% absorption, but weakened waves definitely do not pose a danger to humans.
• To prevent the stove from turning on when the door is open, the appliance has a system of switches that control its position. As a rule, there are three switches – to turn off the magnetron, to turn on the backlight and to send a signal to the control unit. The setting and location of the microswitches prevents them from being activated when the door is open.

Protection system

Any microwave oven is a source of powerful radiation that can cause great damage to the human body and all living things. To protect others from exposure, the device is shielded with a metal case through which high-frequency radiation cannot pass.

The door is equipped with transparent glass so that the user can observe the processes of heating, cooking, defrosting. The glass is also shielded – it has a fine-mesh metal mesh that prevents the penetration of microwaves.

Control unit design

The tasks of the control unit – the “brain” of the microwave oven:

• Maintain the set power.
• Turn off the oven at the end of the process.

In early versions, the control was carried out by two mechanical switches: one set the power, the other the time. Today, devices are equipped with electronic and microprocessor control units that control, in addition to the two named, a variety of functions – important and unimportant. For example:

• built-in clock;
• sound signal about the end of the process;
• power display;
• cooking dishes according to special programs, “sewn” in the unit’s memory.

Types of microwaves

Consider the main types of stoves that you can buy.

with grill

These devices have a heating element – heating element or quartz. The first is placed in different places of the camera and in different positions, it is quite reliable and inexpensive. Quartz is installed only at the top. It is more powerful than the heater, but it costs more.

In ovens with a grill, you can easily cook barbecue or bake chicken with a crispy crust.

An example of a microwave oven with a grill is the LG MH6022D. This model is equipped with a 600W quartz grill and has a mechanical control. Its characteristics:

with convection

It will be useful for those who love to bake. Thanks to convection, you can cook food with warm air. This allows you to get delicious homemade cakes. The heated air, circulating around the cooked dish, evenly bakes it.

The device operates in a combined mode – microwave plus convection. This mode allows you to cook dishes faster than in a conventional oven, which means that more vitamins are stored. The oven, equipped with a grill and convection at the same time, replaces the stove and oven. Here you can cook everything – from compote to barbecue.

A striking example of a microwave with a grill and convection is the Samsung MC28H5013AW. Its characteristics:

With inverter

In traditional devices, the power is regulated by switching the radiation – on / off. Because of this, the food often turns out to be overdried. Thanks to the inverter control, the power is regulated smoothly. Built-in inverters allow you to save the texture and usefulness of the cooked products.

Such models, having recently appeared on the market of microwave ovens, have already become popular.

An example of an inverter model is Panasonic NN-GD371M. Options:

Small microwave ovens

Mini microwaves are usually designed for reheating and defrosting only. These are budget models without grill and convection. They are small in size and power. They don’t have a turntable.

They are chosen for cramped kitchens. They do not prepare pickles – they only heat and defrost food.

An example of an inexpensive but durable model is the Daewoo KOR-5A0. Its characteristics:

Uniform distribution of microwaves

A major drawback of conventional microwave ovens is the uneven distribution of microwaves. Result: food is too hot in one place, barely warm in another. The reason for this phenomenon is the concentration of microwaves in one area. To eliminate this shortcoming, instead of one emitter, manufacturers install three at once.

One of the most popular technologies today is I-wave. In devices with such a solution, the waves propagate in a spiral.

An example of such a device is the LG MS2043HS. Characteristics:

Useful Tips

• For networks with frequent voltage drops, a voltage stabilization device is required. If the voltage jumps in the network, the LCD screen with touch control will be the first to fail.
• Do not forget to buy a care product in a specialized store.
• Check the warranty card. The store where the goods are bought must cooperate with a specific service center – from the manufacturer.
• The pallet is usually made of glass. Check it for chips and other defects.
• Be sure to inspect the product and check the packaging.

What precautions are important to know

1. You can not cook food in metal utensils. Firstly, the waves do not pass through the metal, and secondly, metal objects placed in the stove can lead to breakage of the stove.
2. Do not heat liquid foods in a closed container. You can not cook bird eggs in the shell – a mini-explosion can occur. This also applies to sausages in plastic wrap.
3. Be careful when heating water – it can be hotter than boiling point. Such water can instantly boil when moving. This is particularly the case with water placed in smooth-walled containers. From dishes with a narrow neck, water can simply pour out and burn your hands.
4. Do not put dishes with a metal coating. A thin layer of metal heated by eddy currents can cause cracking of dishes.

Often, when choosing a microwave oven, the consumer pays attention only to the brand, design and cost. As a result, a thing is purchased that does not meet the needs and expectations of the consumer.

Knowing the device and the principle of operation of the microwave oven, you will not only easily buy the right model, but also protect yourself from harmful effects.