Abstract.
Metamaterials with a negative refractive
index contain, generally, two types of elements: long conductors (wires) and inductive–capacitive
resonators (miniature split rings). The system of ring resonators causes a
delay of propagation of electromagnetic waves in the metamaterial. This is due
to the phase shift in the high frequency region of the amplitude-frequency characteristic
(AFC) of the resonators. We used half-wave vibrators in our metamaterial
samples instead of ring resonators. The
measurements were carried out in a free-space using standard horn antennas in
the frequency range 8 – 12 GHz. It
has been shown experimentally that the vibrator array used in the metamaterial
sample has a wide bandgap (9,3 – 11,0 GHz) located below the resonance frequency
of individual vibrators (11,0 GHz). Consequently,
for the investigated samples in the low-frequency region of the forbidden band
for vibrators, the condition l/λ<0.5, where l is the
length of the vibrator, and λ is the wavelength of the
electromagnetic radiation, is valid. From the theory of vibrator antenna
arrays, the characteristics of which have been studied and described in detail in
numerous monographs, it is known that in this case a parallel resonance is
observed. The phase shift will be the same as for ring resonators in the
high-frequency region of the AFC, and at these frequencies, the signal delay
will lead to the negative value of the effective magnetic permeability. Angular
dependence measurements of the electromagnetic waves transmission through the
prism of the metamaterial with vibrators showed that negative refraction is
observed at frequencies of 9,2 – 9,5 GHz, which corresponds to the
low-frequency region of the frequency response of the vibrator array. Effective
value of the refractive index for the studied metamaterial was n = - 1,37±0,06.
Keywords:
metamaterials, electromagnetic crystal,
negative refraction, vibrator.
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