물의 공진주파수는 ?
: What is the resonance frequency of pure water?
A: There are numerous
vibration frequencies noted in gas phase water molecules.
For the usual oxygen
isotope with hydrogen, three important resonances occur at 1.097 x 10^14, 4.784
x 10^13, and 1.013 x 10^15 Hz There are more. They are computed as three balls
connected by two springs, which can stretch or rotate in several ways.
In addition, for pure water
in the liquid state, if an East-West magnetic field is applied for a second or
so, then when it is removed, a low level magnetic field induces a small AC
voltage at about 2 kilohertz in a sense coil surrounding it. This field fades rapidly
over 2 or 3 seconds. Its frequency is proportional to the geomagnetic field
strength. In classical terms, it is described as the proton spin precession
frequency as some spun protons return to the N-S orientation. This frequency is
one of the few absolute measures of Geomagnetic (or any other) field strength.
Why are the
microwaves in a microwave oven tuned to water?
Why do Microwave Ovens
Operate at 2.45 GHz?
I get
this question all the time when we discuss dielectric loss in my classes. The
common answer I get back is that this is the frequency for the resonance of a
water molecule. It would make it the ideal frequency to run the oven so we get
the most absorption.
But not always is the obvious answer the correct
answer
After
all, is it a coincidence that 2.45 GHz is also the same frequency as 802.11ab
wifi, the same as Bluetooth, and the Nyquist for PCIe gen 2, operating at 5
Gbps?
The use of 2.45 GHz is
because this is in the center of the unlicensed ISM band
If
you use this band for communications, buyer beware. Your protocol must be
robust to interference and the FCC will not help patrol emissions in this
frequency range.
If
microwave ovens use this band so they don’t have to be certified by the FCC,
how is it related to heating water?
The
frequency of 2.45 GHz is a wavelength in air of 122 mm or 12.2 cm. When we look
at the absorption spectrum of liquid water, the frequency is usually reported
as the wavelength, instead.
This low frequency is well
below the energy of vibration bands, and is more related to the loose, rather
“fluid” lattice of the water molecules, smeared out due to fluctuating hydrogen
bonding. Here is a typical absorption curve for
liquid water
Note
that 12.2 cm, the wavelength of the microwave oven, is the black line. At 0
decC, the absorption of liquid water, the blue curve that is a measure of the
dissipation factor, is actually sitting on the tail of the peak. It’s a very
broad peak. As the water heats up, the absorption peak actually moves to higher
frequency, shorter wavelength and the absorption for water actually gets worse.
The
broad absorption by water, in the frequency range from 1 GHz to 100 GHz, is an
important issue. This says that as an interconnect polymer absorbs water from
the humidity in the air, we would expect the losses in the material to
increase. This is why the humidity sensitivity to the dielectric loss of a
laminate material is an important metric.
But
why a microwave oven works at 2.45 GHz is more about the FCC than about the
absorption resonance of water.
첫댓글 새로운 것을 배웁니다 고맙습니다