5 research outputs found
Gain and loss enhancement in active and passive particulate composite materials
Two active dielectric materials may be blended together to realize a
homogenized composite material (HCM) which exhibits more gain than either
component material. Likewise, two dissipative dielectric materials may be
blended together to realize an HCM which exhibits more loss than either
component material. Sufficient conditions for such gain/loss enhancement were
established using the Bruggeman homogenization formalism. Gain/loss enhancement
arises when (i) the imaginary parts of the relative permittivities of both
component materials are similar in magnitude and (ii) the real parts of the
relative permittivities of both component materials are dissimilar in
magnitude
Can mixing materials make electromagnetic signals travel faster
Suppose that a composite is constructed from two phases and that we propagate an electromagnetic signal through it. The velocity of the signal in the composite depends on the microstructure. What microstructures are associated with the maximum and minimum speeds of the electromagnetic signal? Here we show that the group velocity of a pulse can be higher in the composite than in either of the two phases. We derive sharp bounds for the relative increase and decrease in the group velocity of the electromagnetic signal in the composite and give the associated optimal microstructures. We also find that a pulse in a composite can have substantially smaller dispersion and, at the same time, substantially larger group velocity than pulses traveling in the pure phases