Microwave ovens: how not to get a dose?

Radiation from ultra-high frequencies UHF or so-called microwave radiation has an adverse effect on the human body. To protect yourself and your loved ones from the consequences of this type of radiation use detectors of varying complexity, determining the leakage of radiation from microwave ovens, cell phones and other devices. How to identify a dangerous device

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This is what we will talk about in this article.

Author: Andrei Kashkarov

Photo. 1. Appearance of Panasonic microwave oven

Not everything that is written in the owner’s manual of a household appliance especially translator’s manuals is true. More often than not, this is the so-called half-truth: everything seems to be true on one side, but it often turns out that something is not told. The same applies to phenomena and processes that can be hazardous to human life and health or their belongings.

Not so long ago, the time has passed or maybe not yet when portable household dosimeters were very popular with the public. No, of course, not every family had a nuclear reactor in the apartment, a country house, but the food and those things that were bought from hand and in the markets, clearly required control. Every now and then the dosimeter went off scale… For the same reason nowadays people buy devices for measuring pesticide levels in various fruits of nature.

One of the sources of adverse effects on the human body is the radiation of ultrahigh frequencies UHF or so-called microwave radiation. A striking example of an electronic device with a microwave generator magnetron is a microwave oven see “microwave oven with a magnetron” . Figure. 1 .

In addition to microwave radiation, which is potentially harmful to humans and animals, a microwave oven hereafter referred to as an oven generates strong electromagnetic radiation that has a negative effect on certain objects and things – such as electromagnetic wristwatches and others .

Photo. 2. Panasonic microwave oven with lid removed

As a rule, a new oven works reliably and is not a source of harmful radiation outside its case, but it is still better not to put watches, cell phones and other items on it.

Oven that was repaired outside of the service center, in which the main generator element – magnetron – was replaced, with a damaged case or with damage to the working chamber, waveguide and other shortcomings, is potentially dangerous to health.

To identify such malicious ovens and other devices e.g., a half-beaten cell phone , use microwave radiation indicators. The simplest diagram of such an indicator is shown in Picture 3.

Photo 3. A simple microwave indicator circuit that you can assemble yourself

Note to photo 3. A wire loop is a piece of copper wire with diameter of 1…1,5 mm. Electric spot welding wire is quite suitable for this purpose. Microwave diode – diode type 2A202A, DK-V8 or similar. Tester is a milliammeter with a total deflection current of 100 µA. In our case it is better to use a dial gauge, for example, Ts4342, Ts4317 or similar. Non-polar capacitor – any capacitor, such as MBM type.

Node connection of the magnetron with the power supply contains transition capacitors, which together with chokes form a filter to protect against microwave radiation from the magnetron and waveguide to the outside.

Principle of microwave oven testing is not complicated – “loop” with a microampere meter slowly near the body of the microwave oven at a distance of 1-6 cm from it . Slow speed “scanning” is needed to fix the microwave radiation in the most dangerous zone of the furnace.

The microwave generator is not switched on continuously in the oven during cooking, but periodically. This is also noticeable visually: the light bulb inside the oven fades a little and the oven is a little noisier when the generator is turned on.

What we don’t know about the magnetron?

The most important component of the microwave oven, the magnetron, is an electric vacuum diode designed to generate microwave oscillations. When a magnetron is operating, power is released and transferred to heat, so a thermal electromagnetic field is created inside the oven. The power generated by the magnetron flows through a waveguide, a device that transmits energy to the oven’s working area, which is a rectangular chamber working chamber .

Photo 4. Close-up of a magnetron

Next to the waveguide output is a turntable on which the product to be treated is placed. All this is inside the case of the furnace.

It is important that the radiation life-threatening with direct human exposure does not escape from the furnace housing. Furnace housing is a closed metal structure, which is also a shield for microwave radiation.

Electromagnetic oscillations at frequencies 2375, 2450 MHz – in very old models, and up to 10-12 GHz in modern furnaces are used for domestic heat treatment in the microwave wave range. In Table. 1 gives information about the depth of electromagnetic wave penetration with energy loss into some of the dielectrics.

Table 1. Depth of electromagnetic wave penetration in lossy dielectric at 20-25ºC

Dielectrics	Depth of penetration, cm at emission frequency:
433 MHz	915 MHz	2375 MHz
Barium titanate	11.3	3.5	0.6
Methyl alcohol	33.0	7.8	1.4
Water	70.5	23.4	3.5
Glass	4600	2180	840
Meat	5.1-10.7	2.8-6.2	1.6-3.1
Vegetables	8.1-9.1	5.0-6.3	2.6-3.0
Fish	5.0-6.2	3.4-3.8	1.2-2.0

Modern magnetrons sealless autocathode magnetrons type mi and similar provide “instantaneous” from the first pulse readiness for operation at full power, without requiring energy to heat the cathode, thereby significantly increasing the reliability of the magnetron.

The use of a flameless magnetron simplified the electrical circuit of the furnace, eliminating dozens of radio components. Due to this fact there is no need in a transformer, control device and voltage regulator in a chain of magnetron filament since there is no filament itself , setting and blocking generators, it was possible to reduce the weight and size of the furnace, to reduce the cost of the product, simultaneously increasing its operational reliability.

Possible faults of magnetrons:

• The anode of the magnetron is made in the form of a copper cylinder. Operating voltage of a magnetron anode depending on the type varies from 3800 to 4000 V. Capacities from 500 to 1200 watts. The magnetron is attached directly to the waveguide Fig. 3 . In ovens where the manufacturer has a magnetron with a short waveguide, you may observe such a defect as a breakdown of the mica seal. This occurs as a result of contamination of the gasket

• in case of breakdown of the gasket the magnetron cap melts it happens with magnetrons of 2M-218H(R , OM7S(20 , 2M213-09F, 2M-219H(B , 2M226-09F type and constructively similar . It the cap can be replaced with a similar cap from another magnetron

• As with any lamp, it can lose its emission, which significantly reduces the energy output and increases the cooking time. Usually the average lifetime of a magnetron e.g. 2M213-xx has a limit of 15,000 h. Its efficiency is 75-80%, which is an effective indicator for magnetrons of microwave oscillators

• Breakdown of transient capacitors can be detected by means of a tester in resistance measurement mode. The breakdown occurs on the case of a magnetron. Fix the problem by replacing the entire assembly.

Separately, magnetron can only be tested by generating all voltages necessary for its operation.

Picture 5. Microwave oven power supply

The second most important element in a microwave oven after the magnetron is the power supply photo 5 . All safe operation of the furnace depends on its reliability.

A great tool for microwave oven repair and diagnostics, particularly for diagnosing magnetrons, are current clamp meters, such as the ECT-650 “Escort”.

They allow you to measure the current consumption of the furnace, the current of the high-voltage winding of the transformer. Rated current consumption of the furnace is 4.5 to 6 A, the current of the high voltage transformer winding is 0.3 to 0.5 A.

Large deviations from these values especially in the direction of increasing individual parameters indicate a local malfunction of the magnetron.

At the same time, underestimation of all parameters can be explained by bad contacts, starting from the mains socket and finishing with the switching elements relays, electric micro-switches, contacts .

To make sure that the magnetron is in good condition and that the microwave emission inside the furnace body is sufficient, it is checked with a detector.

Microwave radiation detectors

Picture 6 shows an industrial microwave radiation detector, which can be purchased at electrical stores.

Fig. 6. Microwave radiation detector

This device registers not only microwave pulses, which can be checked by bringing the device directly to the walls of the oven during operation. It will also be useful for searching for “bugs” working at ultrahigh frequencies, searching for cellular phones and checking their work. Such an industrial tester costs less than 500 Dollars.

The device is powered by a 6F22 “Krona” battery with the voltage of 9 V. Standby current consumption of the device is within 1 µA, so the battery lasts a long time. On the top of the housing there is an indicator LED.

It will light up when microwave radiation is present in the detector area shown by an arrow on the case . The device does not measure the power of the radiation, but registers its presence.

With such a detector can be checked not only the working chamber of microwave ovens and the presence of malicious radiation outside of their casing, but the presence of cell phone radiation. To make it simple.

It is necessary to bring the detector to a possible source of radiation, for example to the body of a cell phone at a distance of 2-10 cm. When a cell phone is active: when there is an incoming and outgoing call, unauthorized “communication” of a cell phone with the base station, when a cell phone is registered in the network for example, when turning on the cell phone and in other cases – the indicator of the detector will show the presence of microwave radiation.

This illustrative lesson would be useful to use at the physics lessons in schools so that people understand how harmful or useful it is to constantly carry a cell phone close to your own body on the chest, on the belt, in the pocket, especially the breast .

the results of harmful microwave radiation especially with constant exposure , probably better commented by scientists and medical professionals. I can only add from myself that microwave radiation is like an atom, which can be peaceful and not so peaceful. This should be clearly understood when operating a seemingly harmless cell phone or microwave.

As a microwave radiation detector, you can also use another industrial device, designed for motorists, which is called a “spark indicator”. Such devices are available for sale, one of which is shown in Fig. 7.

Fig. 7. A picture view of the microwave radiation detector – a spark indicator

The device is designed to test the high voltage ignition circuits of cars. Inside the housing is a radiation detector the same loop as in the diagram in Fig. 5, only in miniature , which responds, as practice has shown, not only to the high pulse voltage in the car ignition, but also to microwave radiation from microwave ovens and cellular phones.

Microwave radiation is also indicated by the red LED installed at the “high voltage” arrow.

On the remote wires, the indicator light is powered by any power source with a constant voltage of 8-15 V, including a Krona-type battery or a car battery.

The feature is that it has adjustable sensitivity adjustment knob is placed on the top of the housing . Such a device costs about 300 Dollars. Having it, you do not have to worry about other microwave radiation detectors.

Safety Precautions for Microwave Oven Repair and Maintenance

Failure to follow these rules can lead to electrocution, injury and failure of quite expensive components.

The most dangerous of all those available in the household environment for humans is alternating current with a frequency of 50 Hz, as well as microwave radiation.

Microwave oven connected to 220 V mains live can be repaired and tested only in those cases when it is impossible to perform work in the unplugged appliance setting, adjustment, measurement of modes, search for bad contacts in the form of “cold soldering” and in similar cases .

Care must be taken to avoid exposure to hazardous voltages.

Beware of being burned by the heated elements.

In all cases of work with the furnace switched on, it is necessary to use insulated tools. Work with one hand, wearing long sleeves or gloves.

Do not touch the oven case or other grounded objects central heating pipes, water pipes with the other hand at this time. Wires on measuring instruments must terminate with feelers and must be well insulated.

These are general electrical safety rules.

Warning, dangerous:

• Soldering elements of the furnace that are energized

• Repair a plugged-in oven in a damp area or on a cement or other electrically conductive floor

• is not allowed to be near the machine by persons who are not repairing it

• As with any microwave radiation source, magnetron radiation can cause eye damage or skin burns if directly exposed. Microwave radiation is not visible to the human eye

• Be especially careful when replacing a magnetron. Do not leave installation debris in the waveguide

• Before replacing, always cut the capacitor in the magnetron power circuit with a piece of insulated wire the bypass resistor sometimes fails .

In addition, when operating the oven, do not:

• Turn the oven on when the door or grid is open it will not turn on by itself, since there is protection, but this point is relevant for those who neglect this protection by turning it off

• Do not make holes in the body housewives who dream of hanging the oven on the wall, like a breadbox, give up such thoughts .