Re: Can household microwave be tuned to such a frequency that it resonates H2O

Greg,

You have a number of good questions.  I hope my answers make it easier for 
you to do your project.

First, a microwave oven converts low frequency AC current into DC voltage 
that is used to create very high frequency microwave energy.  The basic 
electronic principles involve heating a cathode to a very high temperature 
inside the magnetron, which is surrounded by a strong permanent magnet.  
The design of the internals of the magnetron allow a harmonic to resonate 
inside the magnetron, as the electrons interact with the magnetic field of 
the magnet, producing electromagnetic energy at 2.45 billion cycles per 
second (gigahertz).  Across the world, home microwave ovens operate at 
2.45 gigahertz, not because they interact with water best at this 
frequency, but because this frequency was allocated to industrial and 
scientific use in the 1940's when most of the long wavelength spectrum was 
allocated to communications.  At the time, it was considered 
insignificant.  Today, the communications industy would have taken that 
frequency from industrial users had not so many people around the world 
had microwave ovens in their home.  Please note that no domestic microwave 
oven operates at exactly at 2.450000 gigahertz.  In fact, they are allowed 
to operate in a narrow range or band of frequencies.  In the U.S., the 
normal allowed band is from 2.37 to 2.52 gigahertz (or pretty close to 
that - I don't remember the exact numbers).

A microwave oven will heat water just fine, as you know.  However, it will 
heat a lot of other things as well.  Other "safe" things you can heat in a 
microwave oven include fats, proteins, soft starches and anything with 
about 2% water in it or more.  Small amounts of water are much harder to 
heat in a microwave oven than are larger quantities of water.  Things that 
are not heated by microwave energy are dry salt, dry sand, polyethylene, 
polystyrene, and atmospheric pressure gases.

The frequencies that resonate with water molecules exclusively are in the 
range of thousands of gigahertz.  These are not easily produced or 
controlled, and producing much power with these frequencies is very 
difficult.  If you have access to a university library, you can 
investigate microwave absorption chromatography.  It is quite a complex 
science and does not reveal much useful data for the average scientist. 
These resonant frequencies are very close together, so once an interaction 
occurs, signal spreading results, making signal interpretation very 
difficult.

Although microwave energy is used industrially to dry many materials 
(remove water or other solvents), the potential of using it to heat only 
the water and not the surrounding matter is poor.  Remember that even if 
water is the only medium that converts microwave energy into heat, once a 
difference in temperature is created, heat will flow outward from the 
water by conduction or convection to the cooler surroundings.  That is not 
so bad when you want to make sure an object has no wet or dry spots, such 
as a sheet of wood veneer or a piece of lumber.  If a wet spot exists, the 
microwave energy will heat that spot and dry it.  Less heating and drying 
occurs in drier areas, so the entire mass gets more evenly dried.  For 
large masses of wet materials that clump, microwave energy can break the 
clumps apart by building up pressure due to vaporization inside the 
clump.  There are lots of materials that clump when wet and are very 
difficult to dry other than with microwave energy.

If you have more specific questions, I would be happy to assist you in 
designing an experiment that will help you dry materials.  I have done 
hundreds of experiments with household ovens and industrial equipment, so 
I may have already attempted what you are interested in doing.  I have 
written several articles on the interaction of matter with microwave 
energy and could send you the text of one if desired.


Good Luck!