Design of a Perfect Absorber for Normal Incident Waves Using Dirac Cone Metasurface with Anchor Shaped Unit Cells

2018 ◽  
Author(s):  
Subaru Morita ◽  
Atsushi Sanada
Keyword(s):  
Perfect Absorber ◽  
Dirac Cone ◽  
Unit Cells ◽  
Incident Waves

scholarly journals Graphene Hypersurface for Manipulation of THz Waves

2020 ◽  
Vol 1009 ◽  
pp. 63-68
Author(s):  
Sasmita Dash ◽  
Christos Liaskos ◽  
Ian F. Akyildiz ◽  
Andreas Pitsillides
Keyword(s):  
Active Control ◽  
Ground Plane ◽  
Perfect Absorption ◽  
Reflection And Transmission ◽  
Phase Gradient ◽  
At Resonance ◽  
Anomalous Reflection ◽  
Unit Cells ◽  
Incident Waves ◽  
Thz Waves

In this work, we investigated graphene hypersurface (HSF) for the manipulation of THz waves. The graphene HSF structure is consists of a periodic array of graphene unit cells deposited on silicon substrate and terminated by a metallic ground plane. The performance of the proposed HSF is numerically analyzed. Electromagnetic parameters of HSF such as permeability, permittivity, and impedance are studied. The proposed graphene HSF has active control over absorption, reflection, and transmission of THz waves. The graphene HSF provides perfect absorption, zero reflection and zero transmission at resonance. Moreover, the graphene HSF structure has the advantage of anomalous reflection and frequency reconfiguration. Incident waves can be reflected in the desired direction, depending on the phase gradient of the HSF and the perfect absorption is maintained at all reconfigurable frequencies upon reconfiguration. The results reveal the effectiveness of the graphene HSF for the manipulation of THz waves.

scholarly journals Hemispherical acoustic Luneburg lens with the acoustic Goos–Hänchen shift and Fresnel filtering effect

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Choon Mahn Park ◽  
Geo-Su Yim ◽  
Kyuman Cho ◽  
Sang Hun Lee
Keyword(s):  
Acoustic Waves ◽  
Total Internal Reflection ◽  
Incident Angle ◽  
Plane Waves ◽  
Homogeneous Medium ◽  
Surface Boundary ◽  
Unit Cells ◽  
Luneburg Lens ◽  
Filtering Effect ◽  
Incident Waves

Abstract A two-dimensional (2D) slice of a 3D hemispherical acoustic Luneburg lens using a quasi-conformal transformation and face-centred-orifice-cubic (FCOC) unit cells is designed and fabricated. With the system, the focusing characteristics of acoustic waves with frequencies that satisfy the homogeneous medium condition of the metamaterial are observed, such as focusing of acoustic plane waves at the antipodal point on the transformed surface of the opposite side for the incident direction and focus spreading due to total internal reflection at the focus point. The attenuation losses of the system are measured and compared with those of an untransformed system with respect to frequency. The value of the acoustic Goos–Hänchen shift is determined by comparing the experimental and theoretical and simulated values of the focus points with respect to the incident angle. The effect of acoustic Fresnel filtering due to the angular distribution of the incident waves at the flat surface boundary is verified by comparing the results of the experiment and a simulation.

scholarly journals An ultra-thin double-functional metasurface patch antenna for UHF RFID applications

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Mohsen Koohestani ◽  
Alireza Ghaneizadeh
Keyword(s):  
Patch Antenna ◽  
Equivalent Circuit Model ◽  
Unit Cell ◽  
Perfect Absorber ◽  
Uhf Rfid ◽  
Compact Structure ◽  
Incident Waves ◽  
Metallic Sheet ◽  
Rfid Applications ◽  
Rfid Readers

AbstractAn ultra-thin double-functional metasurface patch antenna (MPA) was proposed, where it can operate not only in the antenna mode but also can simultaneously act as perfect absorber for normal incident waves, suitable for RFID applications in the 868 MHz band. The MPA structure consists of a typical coaxially-fed patch antenna merged, for the first time, with a metasurface absorber acting as artificial ground. A methodology for the unit-cell design of the metasurface is proposed followed by an equivalent circuit model analysis, which makes it possible to transform a low-loss ($$tan\delta =0.0015$$ t a n δ = 0.0015 ) unit-cell with highly-reflective characteristics to a perfect absorber for normal incident waves. It is based on modifying the critical external coupling by properly introducing slits on the unit-cell, allowing to design an ultra-thin ($$\lambda _0/225$$ λ 0 / 225 at 868 MHz) and a very compact structure in comparison to previously developed designs. For validation purposes, the MPA was fabricated and its performances in both functional modes were characterized numerically and experimentally. It is demonstrated that merging the absorber with the patch not only allows obtaining a well-matched ($$|S_{11}|<-30$$ | S 11 | < - 30  dB) antenna with an enhanced gain (by 175.6% compared to a typical patch) at the desired frequency but also leads to an overall thickness of only 2.5 mm ($$\lambda _0/138.1$$ λ 0 / 138.1 at 868 MHz). With an absorber size limited to the MPA dimensions, a reasonable 1.3 dB reduction in powers reflected by the MPA was achieved compared to a similar size metallic sheet. Whilst having the lowest profile among the so far reported RFID readers, the proposed MPA can be conveniently fitted for example within the required volume of smart shelf RFID readers or used in portable RFID readers while being capable of mitigating multipath reflection issues and incorrect reading of RFID.

scholarly journals Design of Low RCS Circularly Polarized Patch Antenna Array Using Metasurface for CNSS Adaptive Antenna Applications

Materials ◽  
2019 ◽  
Vol 12 (12) ◽  
pp. 1898 ◽  
Author(s):  
Jianxing Li ◽  
Tayyab A. Khan ◽  
Juan Chen ◽  
Muhammad U. Raza ◽  
Anxue Zhang
Keyword(s):  
Antenna Array ◽  
Patch Antenna ◽  
Satellite System ◽  
Adaptive Antenna ◽  
Antenna Element ◽  
Magnetic Conductor ◽  
Circularly Polarized ◽  
Measurement Results ◽  
Unit Cells ◽  
Incident Waves

A low radar cross section (RCS) circularly polarized patch antenna array operating at the downlink S-band (2492 ± 5 MHz) of the Chinese Compass Navigation Satellite System (CNSS) is proposed. The low RCS is achieved by replacing the conventional metallic ground with an artificial magnetic conductor (AMC)-based metasurface. Two different AMC unit cells are designed having a phase difference within 180 ± 37° and combined in a chessboard-like configuration to realize the AMC-based metasurface. Furthermore, the AMC-based metasurface is utilized as the ground of the CNSS array for wideband RCS reduction. A wideband RCS reduction from 6 GHz to 17 GHz is achieved due to the wideband diffusion property of the AMC unit cells. The maximum RCS reduction is more than 14 dB at 13.3 GHz irrespective of the polarization direction of the incident waves. Moreover, the circular polarization (CP) performance is realized by embedding a circular slot on the patch radiator of the antenna element. The radiation characteristics of the CNSS array are hardly impacted by the inclusion of the metasurface-based ground. The proposed CNSS array has been fabricated and measured. The measurement results are in reasonable agreement with the simulations. The proposed CNSS array can be a good candidate for CNSS adaptive antenna applications where low RCS is simultaneously demanded.

scholarly journals Single-Beam 1-Bit Reflective Metasurface Using Pre-Phased Unit Cells for Normally Incident Plane Waves

2020 ◽  
Author(s):  
Jiexi Yin ◽  
Qun Lou ◽  
Qi Wu ◽  
Haiming Wang ◽  
Zhining Chen ◽  
...  
Keyword(s):  
Phase Difference ◽  
Phase Distribution ◽  
Plane Waves ◽  
Inherent Limitation ◽  
Single Beam ◽  
Incident Plane ◽  
Unit Cells ◽  
Layer Stacking ◽  
Incident Waves ◽  
Beam Patterns

<p>A single-beam pre-phased 1-bit reflective metasurface is proposed to achieve single-beam patterns under normally incident plane waves. Theoretical analysis and numerical simulations are presented to show that, under normally incident waves, single-beam patterns can be achieved by introducing a fixed pre-phase distribution with two values in the 1-bit metasurface. Compared with conventional 1-bit reflective metasurfaces, the proposed scheme alleviates the inherent limitation of single-beam patterns on 1-bit reflective metasurfaces under normally incident plane waves. To verify the proposed scheme, a 1-bit unit cell is designed with a 180º ± 25º phase difference between the two states for frequencies ranging from 34.3 to 49.9 GHz, and a layer-stacking method is proposed to achieve two pre-phases with a 90-degree phase difference. As an example, three 1-bit reflective metasurfaces comprising 20×20 unit cells with single beams pointing separately at 0, 15 and 30 degrees are designed and measured over frequencies of 37.0 to 41.0 GHz; the measured sidelobe levels are less than -7.8 dB. Simulated and measured results show that the proposed pre-phased 1-bit metasurface can achieve single-beam patterns under normally incident plane waves.</p>

scholarly journals Single-Beam 1-Bit Reflective Metasurface Using Pre-Phased Unit Cells for Normally Incident Plane Waves

2020 ◽  
Author(s):  
Jiexi Yin ◽  
Qun Lou ◽  
Qi Wu ◽  
Haiming Wang ◽  
Zhining Chen ◽  
...  
Keyword(s):  
Phase Difference ◽  
Phase Distribution ◽  
Plane Waves ◽  
Inherent Limitation ◽  
Single Beam ◽  
Incident Plane ◽  
Unit Cells ◽  
Layer Stacking ◽  
Incident Waves ◽  
Beam Patterns

<p>A single-beam pre-phased 1-bit reflective metasurface is proposed to achieve single-beam patterns under normally incident plane waves. Theoretical analysis and numerical simulations are presented to show that, under normally incident waves, single-beam patterns can be achieved by introducing a fixed pre-phase distribution with two values in the 1-bit metasurface. Compared with conventional 1-bit reflective metasurfaces, the proposed scheme alleviates the inherent limitation of single-beam patterns on 1-bit reflective metasurfaces under normally incident plane waves. To verify the proposed scheme, a 1-bit unit cell is designed with a 180º ± 25º phase difference between the two states for frequencies ranging from 34.3 to 49.9 GHz, and a layer-stacking method is proposed to achieve two pre-phases with a 90-degree phase difference. As an example, three 1-bit reflective metasurfaces comprising 20×20 unit cells with single beams pointing separately at 0, 15 and 30 degrees are designed and measured over frequencies of 37.0 to 41.0 GHz; the measured sidelobe levels are less than -7.8 dB. Simulated and measured results show that the proposed pre-phased 1-bit metasurface can achieve single-beam patterns under normally incident plane waves.</p>

Measurement and Reduction of Radiation Damage in Frozen Hydrated Crystalline Specimens

1978 ◽  
Vol 36 (3) ◽  
pp. 70-77 ◽  
Author(s):  
R.M. Glaeser ◽  
S.B. Hayward
Keyword(s):  
Diffraction Pattern ◽  
Structural Information ◽  
Structural Disorder ◽  
Structural Features ◽  
Biological Macromolecules ◽  
Diffraction Intensity ◽  
Object Structure ◽  
Specimen Material ◽  
Unit Cells ◽  
Identical Unit

Highly ordered or crystalline biological macromolecules become severely damaged and structurally disordered after a brief electron exposure. Evidence that damage and structural disorder are occurring is clearly given by the fading and eventual disappearance of the specimen's electron diffraction pattern. The fading and disappearance of sharp diffraction spots implies a corresponding disappearance of periodic structural features in the specimen. By the same token, there is a oneto- one correspondence between the disappearance of the crystalline diffraction pattern and the disappearance of reproducible structural information that can be observed in the images of identical unit cells of the object structure. The electron exposures that result in a significant decrease in the diffraction intensity will depend somewhat upon the resolution (Bragg spacing) involved, and can vary considerably with the chemical makeup and composition of the specimen material.

Electron microscopy of niobium and tantalum hydrides

1978 ◽  
Vol 36 (1) ◽  
pp. 644-645
Author(s):  
T. Schober
Keyword(s):  
Electron Microscopy ◽  
Heat Storage ◽  
Measurement Techniques ◽  
Metal Hydrides ◽  
Detailed Understanding ◽  
Storage Devices ◽  
Unit Cells ◽  
Endothermic Reactions ◽  
Hydrogen Reactions ◽  
New Phase

Nb, Ta and V are prototype substances for the study of the endothermic reactions of H with metals. Such metal-hydrogen reactions have gained increased importance due to the application of metal-hydrides in hydrogen- und heat storage devices. Electron microscopy and diffraction were demonstrated to be excellent methods in the study of hydride morphologies and structures (1). - Figures 1 and 2 show the NbH and TaH phase diagrams (2,3,4). EM techniques have contributed substantially to the elucidation of the structures and domain configurations of phases β, ζ and ε (1,4). Precision length measurement techniques of distances in reciprocal space (5) recently led to a detailed understanding of the distortions of the unit cells of phases ζ and ε (4). In the same work (4) the existence of the new phase η was shown. It is stable near -68 °C. The sequence of transitions is thus below 70 %.

Crystal Structure Analysis of Cu-Zr Alloys by Convergent Beam Diffraction

1981 ◽  
Vol 39 ◽  
pp. 354-355
Author(s):  
A. F. Marshall ◽  
J. W. Steeds ◽  
D. Bouchet ◽  
S. L. Shinde ◽  
R. G. Walmsley
Keyword(s):  
Crystal Structure ◽  
Point Group ◽  
Intermetallic Phase ◽  
Three Dimensional ◽  
Crystal Structure Analysis ◽  
Ion Milling ◽  
Composition And Structure ◽  
Unit Cells ◽  
Sputter Deposited ◽  
Convergent Beam

Convergent beam electron diffraction is a powerful technique for determining the crystal structure of a material in TEM. In this paper we have applied it to the study of the intermetallic phases in the Cu-rich end of the Cu-Zr system. These phases are highly ordered. Their composition and structure has been previously studied by microprobe and x-ray diffraction with sometimes conflicting results.The crystalline phases were obtained by annealing amorphous sputter-deposited Cu-Zr. Specimens were thinned for TEM by ion milling and observed in a Philips EM 400. Due to the large unit cells involved, a small convergence angle of diffraction was used; however, the three-dimensional lattice and symmetry information of convergent beam microdiffraction patterns is still present. The results are as follows:1) 21 at% Zr in Cu: annealed at 500°C for 5 hours. An intermetallic phase, Cu3.6Zr (21.7% Zr), space group P6/m has been proposed near this composition (2). The major phase of our annealed material was hexagonal with a point group determined as 6/m.

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