"For metals, the attenuation of microwave radiation arises from the
creation of currents resulting from charge carriers being displaced
by the electric field. These conductance electrons are extremely
mobile and unlike water molecules can be completely polarized
in 10^-18 s. In our microwave cavity, the time required for the
applied electric field to be reversed is far longer than this, in fact
by many orders of magnitude. If the metal particles are large, or
form continuous strips, then large potential differences can result,
which can produce dramatic discharges if they are large enough
to break down the electric resistance of the medium separating
the large metal particles. Interestingly, and most appropriate for
our new assay platform described here, small metal particles do
not generate sufficiently large potential differences for this “arcing”
phenomenon to occur.
Source: Article Microwave-Accelerated Metal-Enhanced Fluorescence: Platform ...
Dear Arti,
The metal particles has large density of free electrons embeded in a see of fixed positive ion cores of the metal atoms. This is well known about the charge picture in metals. The free electrons can drift under the influence of an external electric field including the electric field of the an applied electromagnatic wave.
Assume that the electric field is E and the mobility of the electrons is mu then the the drift velocity vd will be = mu E,
If the length of the particle along the electric filed is L, then the time T required to move the electron from one end to the other end can be expressed by T= L/ mu E,
Under high electric field the drift velocity saturates to a maximum value vs
of about 10^7 cm/s. Assuming the length of the particle 1 nanometer,
Then T for the specimen of i nanometer = 10^-14 seconds.
Assuming a micrwave frequency of 10 GHz, then the cycle time Tcycle= 1/ 10^10= 10 ^-10 seconds.. If the particles are 100 nanometers it will take only 10^-12 seconds to to be polarized, which is still hundered time smaller than the cycle time which means the electrons in the paricle will accumulate one end leaving their positive core ions uncompnsated which means that an electric dipole is formed. This electric dipole has external electric filed when it is high enough it can cause breakdown in the surrounding environment. This breakdown is associated with emission of light.
Best wishes
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