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The titanium carbide phase was synthesized in laser melted-pool in situ as the reinforced particles of nickel based composite coating on Ti-6Al-4V alloy surface using the nickel and graphite blending powder by laser cladding. The microstructure investigation showed that the petals-shaped particles and granular particles were two main morphology of titanium carbide particles. And a few spiral-shaped titanium carbide pattern and eutectic titanium carbide appeared on the cross-sections of the coating. The spiral-shaped titanium carbide pattern composed of some slender arc-shape titanium carbide particles and the eutectic titanium carbide was fine. The morphology and distribution of the spiral-shaped titanium carbide patterns and eutectic titanium carbide confrmed that their growth mechanism was the dissolution-precipitation mechanism and was affected by the convection behavior of the laser melted pool. The spiral-shaped titanium carbide pattern would precipitate out the high-temperature melts under high-speed convection. The eutectic titanium carbide would precipitate out when the melts stopped convection or dropped to eutectic temperature.

Purpose This paper aims to explore the influence of the reinforcement included either glass beads (GBs) or carbon fiber (CF) on the reinforced polyamide 12 (PA12) composite samples prepared by selective laser sintering (SLS). Design/methodology/approach In this paper, the microstructure and mechanical properties are investigated, and the results are compared with those obtained for non-reinforced pure PA12 samples prepared by SLS. Findings The tensile fracture surface of the non-reinforced pure PA12 sample presents strong micro-deformation within the crack origination zone between the melted PA12 matrix and the un-melted PA12 particle cores. As a result, the pure PA12 sample exhibits the greatest maximum elongation. The maximum tensile strength is obtained for the CF reinforced sample because of the strengthening effect of CF and the relatively good bonding between CFs and the PA12 matrix. The minimum tensile strength is obtained for the GB reinforced PA12 sample because of the relatively weak bonding between GBs and the PA12 matrix. Originality/value These results demonstrate that the characteristics of the interfaces between the reinforcement and the PA12 matrix have an important influence on the fracture mechanisms and mechanical properties of PA12 composites fabricated by SLS.

Image structure information is a watershed that distinguishes the content of an image, so it is very important for image enhancement techniques to correct uneven intensity of low-contrast optical remote sensing images with both strong and weak structures preservation. In this paper, a novel enhancement scheme, called spatially adaptive gamma correction (SAGC), is proposed to improve the visualization of optical remote sensing images with structures especially weak structure preservation. The SAGC method includes the following four parts: Firstly, the base image with strong structures and the detail image with weak structures are obtained by the employment of the relative total variation (RTV) method. Secondly, the base image is enhanced by a proposed adaptive gamma correction method. Thirdly, an enhancement factor is proposed to correct the detail image with weak structures. Finally, the high-contrast optical remote sensing image is obtained by the enhanced base image with the combination of the corrected detail image. Both quantitative and qualitative results on real low-contrast optical remote sensing images demonstrate that the proposed image enhancement scheme outperforms the state-of-the-arts in terms of brightness improvement, contrast enhancement, and detail preservation.

A new wideband circularly polarized antenna using metasurface superstrate for C-band satellite communication application is proposed in this letter. The proposed antenna consists of a planar slot coupling antenna with an array of metallic rectangular patches that can be viewed as a polarization-dependent metasurface superstrate. The metasurface is utilized to adjust axial ratio (AR) for wideband circular polarization. Furthermore, the proposed antenna has a compact structure with a low profile of 0.07λ 0 ( λ 0 stands for the free-space wavelength at 5.25 GHz) and ground size of 34.5×28 mm 2 . Measured results show that the -10-dB impedance bandwidth for the proposed antenna is 33.7% from 4.2 to 5.9 GHz, and 3-dB AR bandwidth is 16.5% from 4.9 to 5.9 GHz with an average gain of 5.8 dBi. The simulated and measured results are in good agreement to verify the good performance of the proposed antenna.

To improve the wear resistance of gray cast iron and the quality of the laser cladding coating, a composite coating was designed and produced using Cu-Ti-Ni blending powder on the surface of gray cast iron by fiber laser cladding system. The phase constituents and microstructure of the composite coating were investigated using X-ray diffraction (XRD) and scanning electron micrograph (SEM). Microhardness and wear resistance of the coatings were evaluated. The experimental results indicated that TiC reinforced composite coating was produced and the matrix of the laser cladding zone composed of alloy γ-Fe, acicular martensite, and α-Cu. Microscale TiC particles were synthesized in the laser melted pool using the graphite phase of the substrate and the titanium atom of the blending powder. The surface properties of gray cast iron was improved by TiC reinforced comppsite coating. The microhardness of the laser cladding zone was approximately 2 to 3 times that of the substrate and the wear resistance of the coating was significantly improved. The wear mechanism of the coating was adhesive wear and abrasive wear because the matrix was soft alloy γ-Fe and α-Cu. The coating could significantly improve the performance of grey cast iron under severe service conditions.

Here we investigate the arbitrary conversion of transmitted linear polarized light from 0° to 90° based on all-dielectric metasurfaces. The simulation results show that proposed polarization converter can obtain transmitted light with desired polarization angle.

In the present study, Fe–Cr–Ni alloy coatings were produced by laser cladding using the blending powder of Cr and Ni on the surface of T10 steel. The composition of phase and microstructure were analyzed by scanning electron microscope (SEM) and x-ray diffraction (XRD). The microhardness and corrosion resistance were investigated. The Fe–Cr–Ni cladding coatings composed of austenites and a few eutectic ferrites. And the content of eutectic ferrite in the grain boundary decreased with the decreasing Cr/Ni ratio of the blending powder. The Creq/Nieq ratio and the ferrite number (FN) of the coatings confirm that the solidification process was the AF mode for the Fe–Cr–Ni cladding coatings. The average microhardness value of Fe–Cr–Ni coatings was about 380HV0.2 and the Cr/Ni ratio of the blending powder was not an obvious effect. The corrosion resistance of Fe–Cr–Ni alloy coatings which was significantly superior to T10 steel decreased with the decreasing Cr/Ni ratio of the blending powder. This research exhibits that the Fe–Cr–Ni coatings and laser cladding processing have a potential engineering application value on hypereutectoid carbon steel.

We propose two categories of broadband, high-efficiency reflective wave plates operating in the infrared region. The first one is a half-wave plate (HWP) composed of single L-shaped antennas, and the second one is a quarter-wave plate (QWP) composed of double L-shaped antennas. In contrast to the conventional wave plate, the proposed QWP is a simple combination of two HWPs. We theoretically analyze the feasibility of the design and simulate the conversion efficiency. The proposed HWP and QWP are highly efficient with bandwidths of 1670–2791 nm and 1592–3867 nm, respectively. The novel design may be beneficial for the implementation of polarization conversion devices.

In this paper, a novel polarization-reconfigurable converter (PRC) is proposed based on a multilayer frequency-selective surface (MFSS). First, the MFSS is designed using the square patches and the grid lines array to determine the operational frequency and bandwidth, and then the corners of the square patches are truncated to produce the phase difference of 90 $^{\circ} $ between the two orthogonal linear components for circular polarization performance. To analyze and synthesize the PRC array, the operational mechanism is described in detail. The relation of the polarization states as a function of the rotating angle of the PRC array is summarized from the principle of operation. Therefore, the results show that the linear polarization (LP) from an incident wave can be reconfigured to LP, right- and left-hand circular polarizations by rotating the free-standing converter screen. The cell periods along $x$ - and $y$ -directions are the same, and their total height is 6 mm. The fractional bandwidth of axial ratio (AR) less than 3 dB is more than 15% with respect to the center operating frequency of 10 GHz at normal incidence. Simultaneously, the AR characteristics of different incidence angles for oblique incidence with TE and TM polarizations show that the proposed PRC has good polarization and angle stabilities. Moreover, the general design procedure and method is presented. Finally, a circularly shaped PRC array using the proposed PRC element based on the MFSS design is fabricated and measured. The agreement between the simulated and measured results is excellent.

A multilayer frequency selective surface (FSS) with subwavelength fractal elements based on the antenna-filter- antenna (AFA) concept is proposed in this paper. The upper fractal patches are inductive and non-resonant, and the fractal slots on the ground provide a capacitance. The thin substrate is equivalent to a transformer and some resonant modes are produced. Multiple transmission poles are obtained by cascading multilayer two-dimensional periodic structure array of the fractal patches and slots on the ground. The cell periods along $x$ and $y$ directions are the same and the total height is 8 mm, and the fractional bandwidth reaches 30% at normal incidence. To analyze and understand the operating mechanism of the FSS, the equivalent circuit model (ECM) is proposed to analyze the transmission and reflection characteristics. The results of the synthesis from ECM agree well with the results of full-wave simulation. The multilayer AFA-FSS has been manufactured and measured to verify the effectiveness and correctness of the design and synthesis. The simulated results are in good agreement with the tested ones.

A new single-layer microstrip dual-resonance conformal loop (DRCL) element is proposed to design a printed beam deflector array for broadband application. By utilizing variable parameters of the DRCL element, a nearly progressive phase-shift ranging more than 550 $^{\circ}$ is achieved for deflecting wave within a wide band. It is important that a small DRCL element can be flexibly used to generate a 360 $^{\circ}$ phase shift, which decreases the cell period between the neighboring elements. The DRCL is less sensitive to the variation of incidence angles for both TE and TM polarizations. An X-band plane wave beam deflector array is designed, fabricated and measured. The results show a significant improvement in gain-bandwidth performance of the deflector array using the new structure element. The 1 dB gain-bandwidth of 20% can be achieved. The measured results agree well with the simulation results.

In this letter, a two-dimensional multifunctional cylindrical electromagnetic concentrator (CEMC) with arbitrary geometries is proposed using transformation optics (TO) and the concept of complementary media. The CEMC not only can concentrate the electromagnetic waves and power, but also can make objects around the concentrator invisible. In addition, the concentrator can produce an illusion effect. An example of a circular CEMC is designed and studied by full-wave simulations. Furthermore, the simplified constitutive parameters of a CEMC are proposed and simulated. With the reduced parameters, the CEMC can be constructed from 10 concentric layers that have equal thickness at different regions, and the required metamaterials in each layer are homogeneous.

A low profile chip-package stacked-patch antenna is proposed by using low temperature cofired ceramic (LTCC) technology. The proposed antenna employs a stacked-patch to achieve two operating frequency bands and enhance the bandwidth. The height of the antenna is decreased to 4.09 mm (aboutλ/25 at 2.45 GHz) due to the shorted pin. The package is mounted on a 44 × 44 mm2ground plane to miniaturize the volume of the system. The design parameters of the antenna and the effect of the antenna on chip-package cavity are carefully analyzed. The designed antenna operates at a center frequency of 2.45 GHz and its impedance bandwidth(S11< -10 dB)is 200 MHz, resulting from two neighboring resonant frequencies at 2.41 and 2.51 GHz, respectively. The average gain across the frequency band is about 5.28 dBi.

In this paper, a new multi-functional reflective polarization converter (RPC) is proposed based on an anisotropic metasurface. The metasurface is composed of the periodic array of square patches with truncated corners and a solid ground plane. The RPC is designed based on a single-layer anisotropic metasurface. The reflected magnitude and phase of the anisotropic metasurface are different in two orthogonal directions. Therefore, The incident linear polarization can be converted to the orthogonal linear polarization, right- or left-hand circular polarizations reflected wave in the different frequency bands. The simulated results agree well with theoretical design.

A new polarization diversity converter (PDC) is presented in this paper based on a multilayer frequency selective surface (MFSS). The MFSS consists of three-layer square patches with truncated corners and two-layer grid lines. The converter is considered as a free-rotating screen. The polarization of the transmitted wave can be reconfigured to linear polarization or circular polarization by rotating the different angles of PDC. The simulated fractional bandwidth of the 3dB axial ratio reaches 15% with respect to 10GHz frequency band. The measured results show the good performance of PDC, which is important for communication and remote sensing applications.

In this paper, a novel multilayer frequency selective surface (FSS) with fractal structures is designed using subwavelength element based on the antenna-filter-antenna (AFA) concept. The upper fractal patches are inductive and non-resonant, and the fractal slots on the ground provide a capacitance. The thin substrate is equivalent to a transformer and a resonant frequency is formed. The cell periods along x and y directions are the same and the total height is the 8mm (λ / 3.75 at center operating frequency 10 GHz). Moreover, the fractional bandwidth reaches 30%. To well analyze and understand the operating mechanism of the FSS, the equivalent circuit model is proposed to analyze the transmission and reflection characteristics. The results of the simulation agree well with the results of the synthesis.