Originally posted by lamare
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There's an interesting article by John Pendry on manipulation of the near field with meta-materials. excerpt:
"A loop of wire has a magnetic response to an external magnetic
field because of the currents induced. Unfortunately the phase of the
currents is such that only a diamagnetic response is seen. To create
the more interesting responses which produce negative values of m
we must change the phase of the induced current which we do by
arranging that the conductors are part of a resonant system. One of
the first such systems devised [5] was the so called ‘Swiss roll’
structure (or ‘jelly roll’ depending on which side of the Atlantic you
do your cookery). Figure 4 shows a schematic of this magnetic
metamaterial which consists of an insulated metal sheet wound
around a cylinder. The inductance of the coil and the capacitance
between the inner and outer turns produce a resonance so that the
response to a magnetic field is strongly paramagnetic just below the
resonant frequency, m >> 0 , and above the resonant frequency
m << 0 . On resonance the permeability is purely imaginary taking a
large positive value dictated by the losses in the system, and the
rolls behave like magnetic wires."
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