Resonant Transmission Of Microwaves Research Articles

Frequency scanning from subwavelength aperture array.

Resonant transmission of microwaves is demonstrated through subwavelength holes on a semicircular radiator. Split ring resonators, offering a perfect control of the emitting apertures, are applied to determine the radiation direction and the resonant frequency. Full wave simulation shows that our design is capable of achieving wide angular scanning beams without causing any other main lobe, and the steerable beams could be easily controlled through tuning the excitation frequency.

Experimental Validation of Resonant Microwave Transmission Through Subwavelength Ridged Circular Apertures in Thin Conducting Screen

ABSTRACTThe resonant microwave transmission characteristics through subwavelength ridged circular apertures (SRCAs) are investigated based on experimental observations beyond the near‐field (NF) region. The measured received power levels at the far‐field (FF) region for several SRCA arrangements are also confirmed using numerically calculated FF values transformed from the scattered NF of the SRCAs. The measured enhancements in the power throughputs for the multiple SRCA arrangements clearly confirm strong mutual coupling phenomena among the SRCAs, as previously predicted theoretically. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:2497–2501, 2013

Resonant microwave transmission from a double layer of subwavelength metal square arrays: Evanescent handedness

A double layer of identical subwavelength metal patch arrays is experimentally shown to be electromagnetically chiral due to the evanescent coupling of the near fields between nonchiral layers---it exhibits ``evanescent handedness.'' Despite each layer being intrinsically isotropic in the plane with four mirror planes orthogonal to the plane of the structure, circular dichroism, leading to significant polarization rotation, is found in the resonant microwave transmission for any incident linear polarization.

Comparison of Mutual Coupling Phenomena in Subwavelength Ridged Circular Apertures and Half-Wavelength Dipole Antenna Arrays

The resonant microwave transmission characteristics of several coupled subwavelength ridged circular aperture arrangements in a thin metallic film are investigated using the three-dimensional finite-difference time-domain (3D FDTD) method. Simple equivalent circuits represented by the self and mutual conductances that have been quantitatively extracted for each resonance condition, including the mutual coupling effects, are also devised with the help of virtual magnetic current elements. Furthermore, a duality is identified between the ridged circular apertures and conventional half-wavelength dipole arrays based on comparing the respective resonance conditions.

Analytical model for the transmission of electromagnetic waves through arrays of slits in perfect conductors and lossy metal screens

This paper presents a very simple analytical model for the analysis of the resonant transmission of microwaves or millimeter waves through periodically distributed slits in a thick metal screen. The model is based on equivalent circuits consisting of transmission line elements of known characteristic admittances and propagation constants loaded by capacitors. Closed-form analytical expressions are provided for all the circuit parameters. Alternatively, the circuit parameters can be quickly computed from numerical simulations carried out at a few frequency points. The proposed analytical model accounts for all the details of the observed transmission spectrum, including conventional Fabry-Pérot (FP) resonances, which are controlled by the thickness of the screen, as well as extraordinary transmission peaks, which are related to the periodicity. The range of validity of the model as a function of dimensional parameters is discussed. The experimentally observed and numerically predicted redshift of the Fabry-Pérot transmission peaks with respect to the ideal Fabry-Pérot resonance condition is accurately accounted for by the capacitors of the model. For narrow slits, the extraordinary transmission peak is linked to the singular behavior of the capacitances at the Rayleigh-Wood anomaly frequency point. Finally, the effect of the lossy nature of the metal screens is included in the model, providing accurate predictions of the transmission losses. Additionally, for lossy screens the model adequately predicts the anomalous behavior of the above mentioned redshift when the slit width becomes comparable to the skin depth in the metal, which is in good agreement with experimental and theoretical data previously reported for a single slit.

Resonant transmission of microwaves through a hexagonal array of holes in a thin metal layer

Resonant transmission of microwaves through a hexagonal array of holes in a very thin aluminium layer is studied. The array of holes, with diameter much less than the incident wavelength, leads to a strong transmission peak at a frequency just lower than the diffraction limit of the array. The results are well-modelled using a finite element package. The effect of metal depth on transmission intensity and the maximum efficiency of the hole array is also explored. Further experimental data are presented for the transmission of microwaves as a function of angle of incidence. It is shown that strong transmission occurs at frequencies just lower than the diffraction edges of the array. Incidentally, it is also shown that less than 0.01% of normally incident microwave radiation is transmitted through a continuous metal layer of thickness only 40% of the skin depth.

Slow waves caused by cuts perpendicular to a single subwavelength slit in metal

Resonant transmission of microwaves through a subwavelength slit in a thick metal plate, into which subwavelength cuts have been made, is explored. Two orientations of the cuts, parallel and perpendicular to the long axis of the slit, are examined. The results show that the slits act as though filled with a medium with anisotropic effective relative permeability which at low mode numbers has the two values ∼(1, 9.1), increasing to ∼(1, 14.4) for higher mode numbers.

Resonant transmission of microwaves through a finite length subwavelength metallic slit

The resonant transmission of microwaves polarized perpendicular to a single subwavelength slit of finite length is presented in detail. It is shown that the resonant frequency rises monotonically as slit length is reduced. Increasing confinement of the resonant fields within the slit is shown to cause the frequency rise. Angle dependence of the transmission is also presented. The results show clearly Fabry-Perot-like standing waves in the direction of propagation with waveguide mode behaviour in the orthogonal direction.

Remarkable Zeroth-Order Resonant Transmission of Microwaves through a Single Subwavelength Metal Slit

A slit in a thick metal plate that is extremely subwavelength will not transmit microwaves polarized parallel to it. It is shown here that cuts perpendicular to the slit allow parallel polarized radiation to resonantly transmit. Furthermore, a zero-order mode may be excited within the slit, the frequency of which, to first order, is independent of the plate depth. Remarkably, for this novel type of resonance, the field in the slit oscillates with a constant phase and little amplitude variation throughout the plate depth, while the resonant wavelength tends to infinity as the slit width approaches zero.

Resonant transmission of microwaves through subwavelength fractal slits in a metallic plate

We demonstrate through both experiment and theory that in the microwave regime one can have high transmittance through narrow fractal-patterned slits in thick metallic plates, whereby the aperture is subwavelength in all cross sectional dimensions. In contrast to the recently discovered extraordinary transmissions via surface plasmon excitations and Fabry-Perot-like resonances, the transmission in the present case is independent of the incident angle, plate thickness, or array periodicity. We show the physics to be governed by the transversal shape resonance localized in the metallic fractal slots. In particular, for the lowest transmission mode the EM field experiences no phase change when transmitting through the metallic plate. Simulation demonstrates the viability of the observed phenomenon as a subwavelength $k=0$ waveguide mode, where $k$ is the axial wave number.

Resonant transmission of microwaves through a narrow metallic slit.

Strong resonant transmission of microwave radiation through a very narrow (much less than the radiation wavelength) metallic slit is recorded. The results show that a set of resonant self-coupled surface plasmons are excited within the small gap, giving a Fabry-Pérot-like behavior in accord with analytical results published earlier [Y. Takakura, Phys. Rev. Lett. 86, 5601 (2001)]. The metallic slit, formed by two thick metal plates spaced apart by tens of microns, is inserted in a wavelength-sized aperture. On resonance the transmissivity through the metal slit is more than 2 orders of magnitude greater than the radiation impinging on the slit area.

Enhanced transmission of precessing magnetization energy through metal-metalloid foils at x-band FMR

Greatly enhanced resonant microwave transmissions have been found to take place in Fe 78Si 10B 12 metal-metalloid foils at FMR. Removing the rough surface layers of the specimen by polishing with an alumina suspension has an outstanding effect on enhancing and sharpening the resonant microwave transmission peak.