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Normalized magnetic field distributions from FEM simulations of HMSs with varying transverse dimension, w and thickness, L. A magnetic line source is excited at a distance of λ 30 from the HMS. In all cases, ε = 1 x
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We demonstrate highly directive and transversely confined emissions from hyperbolic metasurfaces (HMSs) to free-space. The generation of such beams is attributed to the narrow hyperbolic isofrequency contour, such that only propagating waves with their wavevectors near normal incidence can transmit through the medium. The directions of transmitted...
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... system configuration is the same as that in the previous analysis, except for the finite transverse dimension of the HMS along the x-direction. Figure 3 shows normalized magnetic field distributions for different transverse dimensions, w and thicknesses, L of the HMS. When the HMS is finite, corner diffractions from both ends along the transverse direction of the HMS turn to be an important factor. ...
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... one can expect that the emitted field approaches the infinite HMS case when the transverse dimension is increased. It is found that when λ > w 3 , the corner diffractions only provide negligible contributions to the emitted beam, and the transmitted wave changes to be highly directive and transversely confined, as shown in figure 3(b). Although the generation of nondiffracting beams prefers thin HMSs, the practical realization of the device depends on the current fabrication technology. ...
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... it is essential to investi- gate the effect of HMS's thickness on the generated beams. Figure 3(c) shows that the transverse field confinement degrades slightly when the thickness of the HMS is increased from λ 100 to λ 40, and the loss is increased accordingly to maintain such a confinement, following our previous analysis. In practical applications, it is often desirable to generate non- diffracting beams only towards a single direction. ...
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Citations
... One type of metamaterials is the hyperbolic metamaterial which is known as an anisotropic media which have hyperbolic dispersion (Poddubny et al. 2013). The permittivity of the hyperbolic material is definined as a tensor, as presented in Eq. 3 where the permittivity of the structure is either ε || > 0 and ⊥ < 0 or ε || < 0 and ⊥ > 0 (Zhao 2015). ...
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... In this work, we propose a PIN diode-based reconfigurable metasurface for realization of dual operations when the diode is in different bias states. Specifically, when the PIN diode is forward biased, at the frequency of interest, the metasurface acquires the properties of epsilon-negative (ENG) materials which forbid wave propagation and reflect all incident waves with appropriate polarization; when the diode is in its reverse-biased state, the metasurface obtains properties of mu-near-zero (MNZ) materials which direct wave propagation [29][30][31][32]. Based on these two controllable functions of the proposed metasurface, we then further design a feeding dipole radiator to realize a compact beam switching antenna, and its radiation patterns can be electrically controlled by the applied bias voltage across the PIN diode. ...
... When the diodes are reverse biased, the upshift of the resonant frequency results in a positive ε x while μ y still remains near zero, creating a MNZ metasurface at the same frequencies around 2.45 GHz. Although observed from the transmission and reflection coefficients that the metasurface is still highly reflective for plane waves, the MNZ metasurface is capable of altering wave vectors of near fields and acting as a wave director, according to our previous analysis [29][30][31][32]. Thus, a reconfigurable PIN diode-based metasurface is realized to achieve dual functionality of a wave reflector and a wave director depending on the applied bias voltage. ...
... In addition, it can be observed that the metasurface antenna has good impedance matching for both diode states. The difference in antenna gains in Figure 4(b) is due to the fact that the efficiency of the metasurface behaving as a wave reflector is higher than that as a wave director [29][30][31][32]. The calculated three-dimensional (3-D) radiation patterns (gain) from CST simulations and the comparison between simulated and measured radiation patterns are shown in Figures 5 and 6, respectively. ...
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... As obtained, the properties of these metasurfaces are described in terms of effective permittivity and permeability [2,3], electric and magnetic surface susceptibilities [4,5], and surface reactance (impedance) [6][7][8]. In addition, due to the planar and thin configuration, they can realize anisotropic and extreme constitutive parameters governed by the orientation of their unit cell structures [9,10]. More recently, the strong interaction between EM waves and the metasurface has been a topic of considerable interest. ...
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... 9 The recent development of metasurfaces 10 has brought wide interests in their applications in antenna designs lately. [11][12][13][14][15][16] In this paper, based on our previous investigations on the generation of nondiffracting beams from HMSs, 17 we propose a two-layer-stacked antenna design using HMS for the 2.4 GHz frequency band, and demonstrate through numerical simulations and experiments that high antenna gain and wide bandwidth can be achieved. In contrast to the previous metasurface-antennas in which the metasurfaces act as impedance matching structures or parasitic radiating elements to enhance the antenna bandwidth, 11,12 the operation of our HMS design relies on altering wave vectors' directions; 17 comparing with metasurface-based leaky-wave antennas, 13-16 our proposed HMS antenna offers a smaller overall thickness and higher tolerance in fabrication. ...
... Following, 17 the electric field at any location (x, y) can be approximated as ...
... The transverse dimension of both HMSs is 3λ, which is large enough to avoid corner diffractions. 17 more spatially confined (or directive) for the CLSRR-HMS, which is due to the fact that the effective thickness of the CLSRR-HMS is much smaller than that of the DSRR-HMS. In addition, the CLSRR-HMS is less lossy observed from the imaginary part of the extracted permeability, owing to its simpler composition with less metallic part. ...
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