Single-layer Broadband Research Articles

Single layer broadband spectrally selective SiON coatings for passive radiative cooling

Single layer broadband spectrally selective SiON coatings for passive radiative cooling

A single layered broadband circularly polarized MIMO antenna based on metasurface with aperture CPW feed

ABSTRACT In this paper, a single-layered broadband circularly polarized MIMO antenna is presented for a 5 GHz wireless local area network (WLAN). The Metasurface is designed with an array of patches and these patches are excited by four uniform aperture CPW feed MIMO antennas. The stubs are added across the aperture and central patches at respective apertures are increased to achieve broad bandwidth. Truncated corner square patches are used for the metasurface to achieve circular polarization (CP). The CP MIMO antenna has achieved an impedance bandwidth of 33% (4.35 GHz-6.08 GHz), a 3 dB axial ratio (AR) bandwidth of 11.95% (5.18 GHz-5.8 GHz) and a gain of 8dBi.

Advancing broadband light structuring through single-size nanostructured all-dielectric meta-devices

Traditional optical components and most artificially engineered structures (metamaterials) used for light manipulation are usually designed for narrow bandwidth and limited functionalities. Furthermore, bulkiness and inefficiency limit their application for integrated devices. Metasurfaces, the ultracompact counterpart of bulky metamaterials, exhibit an unprecedented ability to manipulate incident electromagnetic waves at a micron scale. Metasurfaces have emerged as promising candidates for light structuring and its potential applications, ranging from high-capacity data communication to particle manipulation. Despite significant advancement in metasurfaces, realizing high-performance metadevices exhibiting a broadband light manipulation capability is still challenging due to the material's intrinsic nature and lack of a more straightforward design methodology. Here, we demonstrated a broadband single-cell driven all-dielectric metadevice platform to realize high-performance phase modulation for light structuring over the broad visible spectrum475−650nm. The building block consists of an intelligently optimized nanoantenna made of unique zinc sulfide material that employs the PB phase to realize single-layered broadband metadevices for structured light generation, ensuring a decent average transmission efficiency ηavg=79.9% over the intended band. To prove the concept, we designed numerous metadevices for structured light generation and numerically investigated each under the illumination of selected visible wavelengths. We envisioned that the presented work could accelerate real-life applications such as high-resolution color imaging, optical communication and sensing, quantum information processing, and micromanipulation.

A Single-Layered Broadband Reflectarray Employing 0.15-Wavelength Elements

A single-layered broadband reflectarray antenna employing 0.15-wavelength elements is proposed and investigated in this letter. The unit cell is constituted by a ring patch inserted with an interior concave arm and arranged in a grid size of 4.5 mm × 4.5 mm, corresponding to only 0.15 wavelength at 10 GHz. Despite such a small grid spacing, a linear phase close to 360° can still be obtained by changing the height of the embedded concave arm, without adjusting the external ring size. A planar reflectarray antenna composed of 2116 unit cells is designed, manufactured, and tested. According to the measured results, the 1 dB gain bandwidth of the reflectarray antenna is 29%, while the peak aperture efficiency is 66%. Besides, satisfactory sidelobe and cross-polarization levels are also achieved. These promising features show a good overall performance of the proposed array and also successfully demonstrate the feasibility of employing 0.15-wavelength element for wideband reflectarray designs.

Single-Layer Broadband Endfire Antenna with High-Gain and Stable Beams Based on Spoof Surface Plasmon Polaritons

Single-Layer Broadband Endfire Antenna with High-Gain and Stable Beams Based on Spoof Surface Plasmon Polaritons

Design of Coplanar Proximity Coupled Feed Hexagonal Shaped Circular Polarized Microstrip Patch Antenna

This paper presents a broadband-multiband circularly polarized hexagonal patch antenna. The structure is fed by a unique coplanar hexagonal gap coupled proximity coupled feed with parasitic elements. The antenna is designed using a 14.2×14.2 mm2 FR4 substrate. By introducing hexagonal slot and I slot in the patch, the structure behaves as a multiband antenna with resonating frequencies at 2.76, 5.66 and 11.52 GHz. with 0.2837, 0.4525 and 0.3356 GHz respective bandwidths. By inserting I-shaped slots and rectangular slots in patch and also, I-shaped slots in the ground, the circular polarization is achieved in the L band and C band. The proposed structure was fabricated and tested. The simulated results of the magnitude of S11, radiation patterns and realized gains show good agreement with tested results.
 HIGHLIGHTS
 
 Proposed antenna is single layer broadband multiband circularly polarized hexagonal patch antenna
 A unique feed technique coplanar hexagonal gap coupled proximity coupled feed with parasitic elements is used
 The size of the antenna is compact 14.2×14.2 mm2 and resonating frequencies at 2.76, 5.66 and 11. 52 GHz. with 0.2837GHz/28.37%, 0.4525GHz/ 45.23% and 0.3356GHz/33.56%, respective bandwidths and efficiency
 The antenna is used for WiFi/WiMax application as well as terrestrial communication applications near the costal region or a high humidity environment
 
 GRAPHICAL ABSTRACT

Design of Single-Layer Broadband Omnidirectional Metasurface Antenna Under Single Mode Resonance

A single-layer broadband vertically polarized (VP) omnidirectional metasurface antenna is proposed in this communication. To guide the optimization and design of the antenna, characteristic mode (CM) analysis (CMA) is performed to investigate the intrinsic modal behaviors of the metasurface. A mode with VP omnidirectional radiation is first identified by analyzing an array of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4 \times 4$ </tex-math></inline-formula> squared patches. To excite this mode, a complex feeding network is required, which leads to gain loss and increased structural complexity. Furthermore, the mode currents change with the frequency. Consequently, this mode cannot be excited efficiently in a wide bandwidth using a fixed feeding structure. To solve these problems, the modal current is analyzed at different frequencies. The sizes of the four corner patches and the other four edge patches are adjusted to optimize the modal behaviors. After optimization, the mode becomes much more desirable and can be efficiently excited in a wide bandwidth using a single probe. Therefore, the proposed antenna can be designed on a single-layer substrate and excited by a simple feeding structure with broadband characteristics. To verify the design, the proposed metasurface antenna is simulated, fabricated, and evaluated. The results show that the proposed metasurface antenna can achieve a broad bandwidth of 64.2%.

Broadband circular polarized reflectarray based on multi‐resonance unit

In this paper, a broadband circular polarized (CP) reflectarray using a linear polarized (LP) feed is proposed. First, a single-layer broadband dual-line polarized reflectarray unit is designed. This unit converts the LP incident waves into CP reflected waves by providing a phase difference of 90° in the orthogonal direction components of the incident waves. Based on the units proposed, a 109-element reflectarray was designed and fabricated. The measured results indicate that the reflectarray has a 1-dB gain bandwidth of 9.15 to 12.79 GHz, or equivalent to a bandwidth of 33.2%. Its 3-dB axial ratio (AR) bandwidth for CP operation is 37% (9.06-13.19 GHz). The reflectarray antenna has a peak gain of 23.53 dBi and its highest aperture efficiency is 64.1% achieved at 10 GHz.

Broadband achromatic metasurfaces for sub-diffraction focusing in the visible.

Conventional achromatic optical systems are matured to achieve effective chromatic aberration correction and diffraction-limited resolution by the multiple bulky lenses. The emergence of the super-oscillation phenomenon provides an effective method for non-invasive far-field super-resolution imaging. Nevertheless, most super-oscillatory lenses are significantly restricted by the chromatic aberration due to the reliance on delicate interference; on the other hand, most achromatic lenses cannot break the diffraction limit. In this article, a single-layer broadband achromatic metasurface comprising sub-wavelength anisotropic nanostructures has been proposed to achieve sub-diffraction focusing with a focal length of f=60 µm and a diameter of 20 µm in the visible ranging from 400 nm to 700 nm, which are capable of generating sub-diffraction focal spots under the left-handed circularly polarized incident light with arbitrary wavelength in the working bandwidth at the same focal plane. This method may find promising potentials in various applications such as super-resolution color imaging, light field cameras, and machine vision.

Single-layered meta-reflectarray for polarization retention and spin-encrypted phase-encoding.

Broadband communication with high data rates is a dire need for state-of-the-art wireless technologies. For achieving efficient wireless communication (particularly in an indoor environment), the electromagnetic (EM) waves should maintain their state of polarization despite encountering multiple reflections. Metasurfaces provide a unique platform to design subwavelength-featured meta-reflectarrays which enable the desired retention of the polarization state of an EM wave upon reflection. We present a single-layered broadband meta-reflectarray, simultaneously breaking n-fold (n > 2) rotational and mirror symmetry, which exhibits an unprecedented control over the phase, amplitude, and polarization of a reflected EM wave. This unique control enables the retention of polarization state and recording of spin-encrypted information for the reflected EM waves. Such novel multifunctional meta-reflectarray can be crucial to building an indoor setup for high data rate wireless communications. Meanwhile, the meta-array's ability to encode phase information provides an extra degree of freedom to structure and control (via incident spin) the reflected EM beam in the desired way. For the proof of concept, we have experimentally demonstrated a spin-encrypted holographic display which reconstructs the recorded holographic image at an image plane for the left circularly polarized (LCP) illumination and exhibits circular dichroism for the right circularly polarized (RCP) incident waves. The proposed meta-array can find applications in 5G indoor wireless communication, chiral sensing, spin-selective imaging, holography, and encryption.

Broadband and wide angle quarter-wave plate based on single-layered anisotropic terahertz metasurface

Broadband control of polarization state is essential for terahertz applications ranging from non-destructive testing to imaging in medicine and wireless communications. We present a single-layered terahertz anisotropic metasurface quarter-wave plate consisting of hybrid metallic wire grating arrays, which enables broadband linear to pure circular polarization conversion with an ellipticity over 0.99 and 43% bandwidth of the central wavelength. The broadband effect is robust across a wide range of incident angles. Interestingly, angle-tunable arbitrary polarization states are implemented by changing the angle of incidence at other frequencies. Such single-layered broadband quarter-wave plate provides a route to develop broadband polarization conversion components, facilitating compact applications of terahertz technologies.

Design of a single-layer broadband reflectarray using circular microstrip patch loaded with two unequal slots

A linearly polarized single-layer single-resonator reflectarray, which is designed using a simple circular patch loaded with two unequal rectangular slots, is investigated for the first time. For the proposed design, the linearity and sensitivity of the phase curve (S-curve) can be easily optimized by adjusting the ratio of the two unequal slots changeable according to a simple design equation. Here, the patch radius serves as a phase-shifting geometrical parameter and it is able to achieve a wide phase range of more than 458° with low phase sensitivity and a low reflection loss of less than 0.5 dB. With the use of the optimized phase curve, an offset-fed 13 × 13 full-fledged reflectarray with a square aperture is designed, fabricated and measured. Measurement results show that a −1-dB gain bandwidth of 11.8% and an antenna gain of 23.4 dBi are realizable at the center frequency of 9.3 GHz. Also, the proposed reflectarray has an aperture efficiency of 42% and a radiation efficiency of 98%. The proposed reflectarray has a simple structure and it is able to achieve smooth phase curve, low cross-polarized radiation field and low sidelobes.

Single-Layer Dual-Band Wide Band-Ratio Reflectarray With Orthogonal Linear Polarization

In this letter, a single-layer broadband wide band-ratio (ratio of f higher to f lower ) reflectarray that can achieve different linear polarizations at the X-band and the K-band is designed. Its elements consist of a split square loop with two square shaped phase delay lines (outer structure) and a phoenix square loop (inner structure) operating at the X-band and the K-band, respectively. The ingeniousness of the design is that the outer structure and the inner structure can achieve a 0° - 360° phase shift by adjusting the phase shift lines and the side length of the inner square ring, respectively. At the same time, they do not affect each other in space. Different polarizations corresponding to the two structures are orthogonal to each other, so their electrical performances do not affect each other. To verify our design concept, the reflectarray is fabricated and measured in a microwave anechoic chamber. The simulated and measured results are in good agreement. The measured gains are 23.6 dBi at 10 GHz (f lower ) with aperture efficiency of 48%, and 30.6 dBi at 22 GHz(f higher ) with aperture efficiency of 43%. The 1-dB gain bandwidths are 20% (9.1 GHz-11.1 GHz) at the X-band and 19% (19.8 GHz-23.9 GHz) at the K-band. The band-ratio of the reflectarray is 2.2. A single-layer dual-band wide band-ratio reflectarray with dual-linear polarization is confirmed.

Broadband, dual‐band reflectarray with dual orthogonal polarisation for single and multi‐beam patterns

Two single-layered broadband dual-band dual orthogonal polarisation reflectarrays are designed and developed in the X- and Ku-bands. The well-known holographic technique is employed such that one antenna generates a single radiation beam in two bands and another generates a five-beam pattern in two bands simultaneously. For both antennas, a subwavelength Jerusalem-Shaped unit cell is employed to independently realise two impedance distributions for each band and, consequently, not only broaden the operational bandwidths for both bands, but also limit the mutual coupling between two sets of impedances. As a typical case, an X/Ku band 20 cm × 20 cm five-beam dual-band reflectarray with dual linear polarisation is designed and fabricated for the experimental verification. The measurement results show that the fabricated antenna has 21% 1-dB gain bandwidth (from 8.5 to 10.5 GHz) with vertical polarisation and has 8.8% 1-dB gain bandwidth (from 14.65 to 16 GHz) with horizontal polarisation. Furthermore, the maximum measured aperture efficiencies in the X- and Ku-bands are 57 and 69%, respectively.

Tunable broadband metamaterial absorber with single-layered graphene arrays of rings and discs in terahertz range

A tunable single-layered broadband metamaterial graphene absorber in the THz range is investigated in this paper. The absorber is made up of the ring and disc of the graphene, a metallic ground plane bottom layer and a polyimide spacer layer. The simulated results show that the relative bandwidth of 90% absorbance is 81.44% from 1.15 to 2.73 THz under the normal incident angle. In addition, the absorber is insensitive to the polarization and has a wide range of the incidence for the TE mode and TM mode. Moreover, the absorbance of the absorber can be flexibly changed from 0 to 1 by controlling the Fermi energy from 0 to 1.0 eV.

Comment on “Broadband ultrathin low-profile metamaterial microwave absorber”

In a recently published report, Sood et al. (Appl Phys A 122.4:1–7, 2016) proposed a single-layer broadband ultrathin low-profile metamaterial absorber (ULMA) to realize the broadband absorption with the wide angle of incidence. The proposed ULMA has three absorption peaks at 8.25 GHz, 11.72 GHz and 14.37 GHz with the absorption of 99.72%, 99.64% and 99.26%, respectively. However, we found that the cross-polarization reflection component is ignored by Sood et al. [1]. It is found that there are only two absorption peaks at 7.904 GHz and 14.768 GHz with real absorption rates of 2.56% and 7.90%, respectively. Obviously, the authors mistakenly regard a polarization converter as an absorber.

Broadband Achromatic Metasurface-Refractive Optics.

Existing methods of correcting for chromatic aberrations in optical systems are limited to two approaches: varying the material dispersion in refractive lenses or incorporating grating dispersion via diffractive optical elements. Recently, single-layer broadband achromatic metasurface lenses have been demonstrated but are limited to diameters on the order of 100 μm due to thelarge requiredgroup delays. Here, we circumvent this limitation and design a metacorrector bycombininga tunable phase and artificial dispersion to correct spherical and chromatic aberrations in a large spherical plano-convex lens. The tunability results from a variationin light confinement in sub-wavelength waveguides by locally tailoring the effective refractive index. The effectiveness of this approach is further validated by designing a metacorrector, which greatly increases the bandwidth of a state-of-the-art immersion objective (composed of 14 lenses and 7 types of glasses) from violet to near-infrared wavelengths. This concept of hybrid metasurface-refractive optics combines the advantages of both technologies in terms of size, scalability, complexity, and functionality.

Investigation of Magnetic and Microwave Absorption Properties of Ba(1−2x)LaxNaxFe10CoTiO19 Hexaferrites in 18.0–26.5 GHz Band

A series of Ba(1−2x)LaxNaxFe10CoTiO19 hexaferrite samples with x = 0.00–0.25 (step size 0.05) were prepared by using conventional solid-state reaction technique. The magnetic properties of the hexaferrites have been investigated at room temperature by employing a vibrating sample magnetometer. There is an overall decrease in saturation magnetization from 70.64 to 57.83 emu/g with an increase in doping concentration from x = 0.00–0.25. The microwave measurements were done utilizing vector network analyzer in the k-band (18.0–26.5 GHz) frequency range. The electromagnetic measurements revealed that the gross tangent loss is maximum for x = 0.10 sample. The microwave absorption measurements show that sample x = 0.10 with 1.4 mm thickness exhibits a reflection loss of − 26.59 dB (99.78% signal absorption) and 7.65 GHz bandwidth. Thus, it is considered for thin single-layer broadband microwave absorber applications in 18.0–26.5 GHz frequency range.

An ultra-broadband terahertz metamaterial absorber based on split rings array and island-shape structures

An ultra-broadband absorber is achieved by constructing novel island-shape structures on a single-layered broadband absorber. The single-layered absorber contains four same sized metallic split rings with different heights of the base. Its absorption goes beyond 98% from 1.82 THz to 3.70 THz and the full width at half maximum (FWHM) is 102.3% (from 1.47 THz to 4.55 THz), much better than these achieved by assembling multiple nested resonators. Then, by stacking novel island-shape structures over the single-layered absorber, we can excite 1-order magnetic response to precisely add a new peak near the broadband and enhance the bandwidth. The multi-layered absorber covers a bandwidth of 3.51 THz (the absorption over 90% from 1.23 THz to 4.74 THz) and the FWHM is up to 139.7%, far larger than previous reported results. It also performs well at considerably large oblique incident angles. Moreover, the island-shape structures have the potential to be applied in some other single-layered absorbers to widen their bandwidth.

Broadband polarization-independent wide-angle and reconfigurable phase transition hybrid metamaterial absorber

We report the simulation, fabrication, and experimental characterization of a single-layer broadband, polarization-insensitive and wide-angle near perfect metamaterial absorber (MA) in the microwave regime. The topology of the resonators is chosen in such a way that is capable of supporting simultaneously multiple plasmon resonances at adjacent frequencies, which lead to a broadband operation of the MA. Absorption larger than 80% at normal incidence covering a broad frequency range (between 7.4 GHz and 10.4 GHz) is demonstrated experimentally and through numerical simulations. Furthermore, the performance of the metamaterial absorber is kept constant up to an incident angle of 30°, for both TE and TM-polarizations. In addition, a hybrid model of the MA is proposed and implemented numerically in order to dynamically tune the absorption window. The hybrid MA is controlled by incorporating vanadium dioxide (VO2) temperature-driven metal-insulator phase transition material, which enables the transition from broadband (80% absorption and 3 GHz bandwidth) to narrowband (80% absorption and 0.7 GHz bandwidth) absorption window. Our proposed single-layer MA offers substantial advantages due to its low-cost and simplicity of fabrication. The results are very promising, suggesting a potential use of the MA in wide variety of applications including solar energy harvesting, biosensing, imaging, and stealth technology.