Re: Detecting Microwave oven leakages

Greetings:

Reference: Howard W. Sams & Co.,
Reference Data For Radio Engineers, 5th Edition,
International Telephone and Telegraph Corp., 1969

Leakage from a microwave oven is a relative term. There are no perfect seals for an
oven door that must be often open and closed. Thus, all microwave ovens leak some
amount of radiation, the issue is how much do they radiate. For microwave radiation
the referenced book states: " It is believed that exposure to a power density of
10 milliwatts per square centimeter should not be allowed for more than 1 hour, and
that 1 milliwatt per square centimeter is safe indefinitely." There has been
considerable debate over the years about what is a safe level of microwave radiation
and to be safe most equipment is designed to maintain less that 0.1 milliwatts
(100 microwatts) per square centimeter a few meters from the oven. Microwave ovens
generate between 500 watts and one thousand watts of microwave power at a frequency
of 2400 megahertz (MHz or 2400 million cycles per second) corresponding to a
wavelength of 12.5 cm (4.9 inches)in air. A hole less that one tenth of a wavelength
is considered to be a good shield. Thus the wire mesh in the oven windows have holes
less that one tenth of a wavelength in size. My microwave oven has one millimeter
diameter holes in the mesh, 1/125 of a wavelength in diameter.

Cell phones operate at wavelengths about twice as long as the wavelengths used for
microwave ovens and so the oven shielding should be more effective for cell phone
radiation because leakage is determined by the size of a leaking hole (s) relative
to a wavelength. For a given size hole, the longer the wavelength the lower the
level of leakage. However, cell phones have very sensitive receivers and can detect
less than one billionth (1/1,000,000,000) of a watt of microwave energy.

Even for an oven operating at a safe level of leakage, a cell phone could detect
the cellular transmitter from inside an oven. The question then becomes, how far
is the cellular transmitter from the oven. If the distance is great the cell
phone might not detect the signal suggesting the oven is safe and if the transmitter
is near by the cellphone could receive a strong level of signal which could indicate
that the oven is bad. In either case this is not a measure of the level of oven
leakage, but of transmitter distance and receiver sensitivity. The building walls
may also reduce the signal level which would give a false indication. The only
accurate method for measuring oven leakage is to measure the actual power density
leaking from the microwave oven with a calibrated receiver and antenna located at a standard
distance from the oven (usually one meter).

Personally,while I have found my ovens to be operating at
a safe level, for the sake of prudence, I have asked my wife and children to not look closeup through
the oven door, for I know that there will be leakage there. Just as there are
X-rays leaking close up to a television picture tube, another location prudence
says to stay a few meters away from.

Best regards, Your (very cautious) Mad Scientist
Adrian Popa