Millimeter-wave extraordinary transmission: connection to metamaterials and technological applications
Fecha
2006Autor
Director
Versión
Acceso abierto / Sarbide irekia
Tipo
Tesis doctoral / Doktoretza tesia
Impacto
|
nodoi-noplumx
|
Resumen
The phenomenon of Enhanced Transmission also happens in the millimeter
wave range, as it happened in optical frequencies. This experimental fact
shows that this is a phenomenon mostly linked to the periodic structure
regardless of the model used to describe the metal.
The number of illuminated holes is a key parameter to observe the Enhanced
Transmission band. Measurements in Fresnel zone sh ...
[++]
The phenomenon of Enhanced Transmission also happens in the millimeter
wave range, as it happened in optical frequencies. This experimental fact
shows that this is a phenomenon mostly linked to the periodic structure
regardless of the model used to describe the metal.
The number of illuminated holes is a key parameter to observe the Enhanced
Transmission band. Measurements in Fresnel zone show a weak band, and
with the farfield illumination a good level is obtained.
It has been shown that ET is mainly governed by one of the transversal
periodicities, the one in the direction of the electric field (under normal
incidence).
The presence of dielectrics can produce a great field confinement and
therefore a more efficient illumination of holes.
Enhancement of transmission through a narrow slot on a metallic plane
achieved by corrugating the metallic plane has been experimentally proven in
the range of microwaves and millimeter waves. This result links the
enhancement to the geometry of the metallic substrate rather than to the
metallic model.
It has been checked the ability to produce a strong beaming at broadside in
the configuration of corrugations drilled on the output face.
Several low-profile and all-metallic antenna prototypes have been designed
and measured in the microwave range. The feeding is made by means of a
waveguide. By changing the central (ideally) infinite slit to a finite slot several
improvements can be done, fundamentally the thickness of the antenna can be
reduced and a dual-band operation can be achieved. A great variety of
farfield characteristics can be obtained by changing the number of
corrugations.
High gain antennas can be attained by using annular corrugations, the socalled
Bull’s-Eye antenna. Further improvements deal with the insertion of
dielectric inside the corrugations and with changes in the shape of the corrugations, for example sinusoidal profile.
An artificial waveguide defined by introducing a set of parallel electric and
magnetic conductors can be employed to analyze the diffraction problem of
an incident plane wave normally to a sub-wavelength hole array. Evanescent
higher order modes play a key role in the ET effect.
Even more unexpected results appear if a periodic structure is made by
stacking several of such plates: a left-handed metamaterial can be achieved by
the periodic stacking of sub-wavelength hole array plates to form a photonic
band-gap structure.
The stack period with LH behavior can be made much smaller than the
operating wavelength, and therefore it can be safely stated that the structure
works in that dimension as an effective metamaterial.
Simulation and experimental results presented show that left-handed
propagation effects appearing in the band where EOT happens can be
allowed or inhibited by a proper engineering of the band gap position of the
photonic crystal made of stacked subwavelength hole-arrays.
In the transition from LH to RH behavior a nearly zero slope band is
observed, which can evidence a frozen mode propagation regime inside the
structure.
A simplified model based on inverse line equivalent circuit has been exposed
to explain the LH and RH behavior.
The stacked hole array structure can be engineered to construct prisms with
anomalous behavior. Other geometries such as parabolic lenses can also be
achieved.
It has been seen that surfaces made by the periodical arrangement of Split-
Ring Resonators (SRRs) and its complementary particle (CSRRs) illuminated
by a plane wave show a high variety of cross-polarization effects. The
analytical discussion based on the homogenization principle has been
compared with the experimental results. It is able to catch the qualitative
features in the response of the screens. The complementarity in the response
of SRRs and CSRRs has been checked. Applications of the studied devices to frequency selective surfaces, polarizers and polarization converters can be
envisaged.
The existence of electroinductive waves (EIWs) in chains of electrically
coupled CSRRs has been demonstrated both theoretically and experimentally.
The duality between EIWs and previously reported MIWs has been discussed,
and the ability of long CSRR chains to transport electromagnetic energy along
many periods has been shown.
A practical transducer between electromagnetic and EIWs in planar
technology has been proposed and analyzed.
Regarding practical applications, EIWs can be an alternative to MIWs for the
guidance of electromagnetic energy, as well as for the design of couplers,
delay lines and other planar devices, when electric couplings rather than
magnetic couplings are imposed, or simply desired for the design.
Taking as a basis the resonators used to implement an EI waveguide, a further
step has been given in the design of a UWB filter in microstrip technology.
This filter can be improved by inserting CSRRs to reject the higher
frequencies.
A final word fundamentally related to the ET results presented here: The
reported results have been achieved for the millimetre range, but similar
results are expected to happen at optical frequencies since extraordinary
transmission has been shown at optical frequencies and the kind of structure
presented here will present low losses in higher frequency regime. The control
of the EOT-LHM could lead to a new class of practical devices both in the
microwave and in the optical range. [--]
Materias
Extraordinary transmission,
Metamaterials,
Millimeter-wave frequencies
Departamento
Universidad Pública de Navarra. Departamento de Ingeniería Eléctrica y Electrónica /
Nafarroako Unibertsitate Publikoa. Ingeniaritza Elektrikoa eta Elektronikoa Saila