Narrow Scanning Research Articles

Fabrication and Process Monitoring of 316L Stainless Steel by Laser Powder Bed Fusion with µ-Helix Scanning Strategy and Narrow Scanning Line Intervals

Fabrication and Process Monitoring of 316L Stainless Steel by Laser Powder Bed Fusion with µ-Helix Scanning Strategy and Narrow Scanning Line Intervals

Circularly polarized beam-scanning antenna with eliminated open-stopband

In the paper, a circularly polarized (CP) frequency beam-scanning antenna based on photonic crystal (PC) is proposed, which possesses the characteristics of eliminating open-stopband (OSB). In the microwave field, the PC is typically constructed by embedding the air or metal column into the material. However, it is difficult for the PC with perfect magnetic conductor walls to accomplish the degeneracy of eigenmodes at the Γ point. Additionally, antennas based on the PC with perfect electric conductor walls exhibit a narrow scanning angle. The proposed unit based on 1D PC possesses perfect electric and magnetic conductor walls. The unit can not only eliminate OSB but also has a wide scanning range. In addition, the unit breaks into the original symmetrical field distributions of 1D PC. Based on the perturbation theory, leaky-wave slots can be designed to generate electromagnetic waves with the CP characteristics. And a CP antenna based on the unit is designed. The antenna can achieve a 70° beam-scanning within the entire operating band (7.6–9.2 GHz), and the variation of the realized gains is below 1.0 dBi around the broadside frequency. Simultaneously, the antenna is fabricated and measured. The measured results are in accordance with the simulation, which validates the success of the design.

Time-domain slicing optical frequency domain reflectometry.

A time-domain slicing (TDS) optical frequency domain reflectometry is proposed for large strain sensing with better spatial resolution. Compared with the conventional frequency domain slicing (FDS) method, the TDS with a Burg spectrum estimation is capable of enhancing the similarity of a local spectrum under large strain and mostly suppressing the fake peaks during the strain resolving. The experimental results demonstrated that it enables measurements of strain ranging from 600 to 4200 µε with a spatial resolution of 2.4 mm and a narrow optical frequency scanning range of only 10 nm. Moreover, the measurement accuracy is improved by six times by decreasing the root mean square error (RMSE) from 8.6611 to 1.3396 µε without any hardware modification.

Reconfigurable transmissive metasurface with a combination of scissor and rotation actuators for independently controlling beam scanning and polarization conversion

Polarization conversion and beam scanning metasurfaces are commonly used to reduce polarization mismatch and direct electromagnetic waves in a specific direction to improve the strength of a wireless signal. However, identifying suitable active and mechanically reconfigurable metasurfaces for polarization conversion and beam scanning is a considerable challenge, and the reported metasurfaces have narrow scanning ranges, are expensive, and cannot be independently controlled. In this paper, we propose a reconfigurable transmissive metasurface combined with a scissor and rotation actuator for independently controlling beam scanning and polarization conversion functions. The metasurface is constructed with rotatable unit cells (UCs) that can switch the polarization state between right-handed (RHCP) and left-handed circular polarization (LHCP) by flipping the UCs to reverse their phase variation. Moreover, independent beam scanning is achieved using the scissor actuator to linearly change the distance between the UCs. Numerical and experimental results confirm that the proposed metasurface can perform beam scanning in the range of 28° for both the positive and negative regions of a radiation pattern (RHCP and LHCP beams) at an operational frequency of 10.5 GHz.

3-D ultrasonic imaging of bolt thread cracks using a linear array probe

The bolt is a widely-used standard component, and the cracking of its thread often leads to final fractures. Traditional 1-D (one-dimensional) A-scan detection and 2-D (two-dimensional) imaging methods only display the position and depth of bolt cracks, without providing information about the crack’s circumferential characteristics. While 1-D array linear scanning and 2-D array can achieve 3-D (three-dimensional) imaging in simple planar components, they have limitations when it comes to bolts. The former has a narrow scanning area, and the latter requires a long post-processing time. To overcome these limitations, the three-dimensional reconstruction algorithm (3-DR) and the half-matrix sparse total focus method (HMS-TFM) are proposed. Our approach involves adopting 360° circumferential scanning based on a 1-D linear array to achieve 3-D imaging of bolt cracks. At each scanning position, the 2-D image data are captured and are then fused to obtain the 3-D image. Different from the simple stacking of 2-D image data in linear scanning, our 3-DR algorithm reconstructs 3-D images based on discrete sampled 2-D images. To reduce the time required for 2-D imaging, the proposed HMS-TFM reduces the required data volume while maintaining acceptable image quality. Experiment results demonstrate that circumferential scanning based on the linear array can achieve 3-D imaging of bolt defects with lower time cost compared to using a matrix array for 3-D imaging. We obtained accurate circumferential quantification for radial-direction cracks with depths of 1 mm, 1.5 mm, and 2 mm with a relative error better than 6.23 %.

Temperature Measurement based on Phase-OFDR with a Narrow Frequency Scanning Range

Temperature Measurement based on Phase-OFDR with a Narrow Frequency Scanning Range

Fabrication and Process Monitoring of 316L Stainless Steel by Laser Powder Bed Fusion with µ-Helix Scanning Strategy and Narrow Scanning Line Intervals

We first fabricated the single crystal of 316L stainless steel by laser powder bed fusion (L-PBF), focusing on the applicability of the µ-Helix scanning strategy with narrow pitch as a method for obtaining a single crystal. Various combinations of laser power and laser scanning speed were examined. The cubic block samples were orientated to <100> in the X-laser scanning direction, to <110> in the Y-laser scanning direction, and to <110> in the building direction, which is contrary to that obtained by the µ-Helix scanning strategy in electron beam melting (EBM), in which the X- and Y-laser scanning directions are orientated to <110>, and Z-direction is oriented to <100> direction. Also, it has been demonstrated that melt pool monitoring by on-axis and off-axis dual photodiodes can detect the nonequivalence of ±X-scanning and ±Y-scanning, which is responsible for the unexpected crystal orientation.

Multi-scale dilated dense reconstruction network for limited-angle computed tomography

Objective. Due to the incomplete projection data, the image reconstructed by limited-angle computed tomography (CT) usually suffers from significant artifacts, by which the structural details are heavily blurred. In this study, we aim to develop a novel approach to improve the limited-angle CT reconstruction performance, especially for the narrow scanning angular range. Approach. A deep learning based iterative framework for limited-angle tomography is proposed, which is named multi-scale dilated dense reconstruction network (MSDDRNet). The MSDDRNet utilizes a multi-scale dilated dense convolution neural network (MSDD-CNN) with conventional reconstruction algorithm for predicting image from incomplete projection data. The MSDD-CNN enhances the image features in the network by merging the DenseNet-Like structure, which serves to restore invisible singularities and reduce artifacts, as well as introducing constraints on the projection domain data into the iterative process to achieve better image detail recovery. Additionally, to improve the training speed of the network, we use a strategy of pre-training and model migration. Main results. Numerical experiments demonstrate that the proposed MSDDRNet performs well in terms of artifact correction, noise reduction and structure recovery compared to existing methods with limited scan angles, and we also extend the proposed method to more general scanning condition and other application such as dental CT data. Significance. The proposed method is a general framework, which can be applied to other CT problems, such as low dose CT, sparse-data CT and spectral CT.

High depth resolution wavelength scanning interferometry with narrow scanning bandwidth via sinewaves separation

Wavelength scanning interferometry (WSI) is a promising tomographic imaging technique. However, the depth resolution is fundamentally limited by a narrow wavelength scanning bandwidth, which brings challenges to the frequency extraction for depth information. In this work, we proposed a parameter estimation (PE) paradigm via sinewaves separation, which allows high depth resolution tomographic measurement with narrow-band sources. To obtain accurate depth information, a sinewaves separation model is designed to estimate the frequency of the overlapped signals and it can achieve higher depth resolution without any prior knowledge even under limited scanning bandwidth. Moreover, the estimated frequency is used for phase retrieval and the multi-layer 3D profile measurement can be further implemented. The simulation and experimental results show that the PE method can reach the same depth resolution level as discrete Fourier transform (DFT) even reducing 60% scanning bandwidth when PSNR is higher than 35 dB.

Molecular and experimental study on hydrogen sulfide formation mechanism during Chang 7 type-II oil shale kerogen pyrolysis

Hydrogen sulfide is a volatile toxic gas associated with oil and gas production, causing corrosion to surface equipment such as wellbores and doing harm to the environment. This study aims to investigate the formation mechanism of hydrogen sulfide during the pyrolysis process of Chang 7 type-II oil shale kerogen. XPS spectra are obtained with the usage of Kratos Analytical Axis UltraDLD to analyze the occurrence forms of hybrid atoms. S 2p XPS spectrum and its fitted curves are gained from full spectrum wide spectrum scanning and narrow spectrum scanning of the sulfur element. The pyrolysis characteristics and processes of kerogen with three initial structures under different temperatures are implemented with ReaxFF. The results of the hydrogen sulfide formation pathway are tracked. The sulfur element in Chang 7 II kerogen is mainly in the form of organic sulfur, with a molar ratio of 77.74%. The kerogen initial structure with fewer CC bonds containing more H atoms has a higher oil yield. The desulfurization rate sharply increases with the increase in pyrolysis temperature. Hydrogen sulfide production is affected by sulfur-containing functional groups (aliphatic sulfur, aromatic sulfur, sulfoxide, sulfone). Hydrogen sulfide formation paths mainly include capturing H radicals through HS radicals and capturing H radicals through high sulfur to form -SH2-.

Fabrication of high sensitivity and fast response IR photodetector based on VO2 nanocrystalline thin films prepared on the silicon substrate

On Si substrates, vanadium dioxide nanocrystalline thin films (VO2 NC-TH) were prepared using the radio frequency magnetron sputtering (RF) method. The very small particles reference film was a very thin surface that appeared smooth like a coated Si wafer with the same spherical particle prominent and irregularly distributed in a thin film, according to XRD patterns with narrow peaks intensity and field emission scanning electron microscopy (FESEM) images. The current-voltage characteristic of metal-semiconductor-metal (M-S-M) VO2 NC-TH infrared photodetectors (IR-PD) in the dark and irradiated with 850 nm light and intensity was (0.17) mW/cm2. IR-PD exhibits 603, 3567, 10081, and 17751 sensitivity at 2, 3, 4, and 5 bise voltage, with increasing bias voltage increasing quantum efficiency, responsivity, and detectivity. The responsitivity and detectivity under 2, 3, 4, and 5 V bias are (0.24, 1.58, 7.92, and 14.76) A/W and (0.176, 1.03, 3.81 and 6.98) x 1012 Jones, respectively.

Fabrication of GaN nanocrystalline thin films Schottky metal-semiconductor-metal ultraviolet photodetectors

Gallium nitride nanocrystalline thin films (GaN NCTH) were prepared on Si substrates using the radio frequency magnetron sputtering (RF) method. XRD patterns with narrow peaks intensity and field emission scanning electron microscopy (FESEM) images exhibits of the GaN nanoparticles have covered surfaces of the substrate with a regular distribution smooth and an average particles size proximately between are 10–20 nm. AFM indicates a smooth surface and RMS is 1.38 nm of GaN NCTH and the optical band gap was calculated to be 3.38 eV. The current-voltage characteristic of metal-semiconductor-metal (M-S-M) GaN ultraviolet photodetectors (UV-PD) in the dark and irradiated with 370 nm light and intensity was (1.4) mW/cm2 evaluated under bias voltages of −1 to 5 V. The average rise time speed of the photodetector is about 22 ms when current increases from 10 % to 90 % of its value of saturation, while the average fall time is 17 ms when current decreases from 90 % to 10 % of its value of saturation. UV-PD displays 19–261 sensitivity at a different voltage bias; internal photodetector gain between the low value is 1.19 at 8 V and 1.59 at 2 V.

A wide‐angle scanning Luneburg lens antenna

The Luneburg lens is an effective way to implement multibeam antennas. However, the existing planar Luneburg lens configuration usually can only provide a relatively narrow scanning range. To deal with this problem, a Luneburg lens consisting of one dielectric cylinder and nine dielectric rings is proposed. It can be easily fabricated using low cost ABS material through 3D printing technology. The lens is placed between two metal plates which have an additional flare structure to enhance the antenna gain. To effectively excite the lens for multibeam applications, 9 magneto electric dipoles are utilized. For validation, a wide-angle scanning planar Luneburg lens antenna operating at 35 GHz was designed, fabricated and measured. A good agreement between simulation and measurement can be observed. At the center frequency, a wide scanning coverage of 172° can be obtained with a gain variation less than 1.6 dB.

Self-dressing Fano interference controlled by various crystal phase transition

We study the self-dressing Fano interference controlled by different phase transitions of rare-earth-doped ions. The self-dressing Fano interference originates from Pr3+: Y2SiO5, Eu3+/Pr3+: YPO4, and Eu3+: BiPO4 at different laser power and time-gate. We explore that the self-dressed Fano exhibits photon dressing and crystal field splitting in Pr3+: Y2SiO5 and Eu3+/Pr3+: YPO4, respectively. We report that Pr3+: Y2SiO5 depict the strongest narrow single Fano, results from the narrow scanning spectrum range (3 nm) and single-level photon dressing only; however, Eu3+: BiPO4 exhibit the most prominent broad multi-level Fano among other three atomic-like mediums, due to coexisting photon-phonon dressing and a large range of spectrum scanning wavelength (40 nm). For the first time, we observe the smooth evolution of Fano interferences from self-dressing Fluorescence (FL) Fano to hybrid (FL + SFWM) Fano and to self-dressing spontaneous four-wave mixing (SFWM) in different samples of Eu3+: BiPO4 by changing the time-gate. We disclose that the Eu3+: BiPO4 sample (6:1) exhibits strong Fano interference in contrast with samples (7:1) and (1:1) owing to more sample phonon dressing in the (6:1) sample. Further, we compare the self-dressing Fano with the external-dressing Fano and notice that the Fano switch in self-dressing Fano results from the different Eu3+: BiPO4 samples transitions owing to distinct samples different detunings. However, the Fano switch in external-dressing Fano is obtained by changing the time-gate, owing to the cross and self-Kerr nonlinear phase difference. We further declare the strongest self-dressing FL Fano interference compared to the external-dressing FL Fano interference due to the double cascade dressing.

Characterizing the Chemical Structure of Ti3C2Tx MXene by Angle-Resolved XPS Combined with Argon Ion Etching.

Angle-resolved XPS combined with argon ion etching was used to characterize the surface functional groups and the chemical structure of Ti3C2Tx MXene. Survey scanning obtained on the sample surface showed that the sample mainly contains C, O, Ti and F elements, and a little Al element. Analyzing the angle-resolved narrow scanning of these elements indicated that a layer of C and O atoms was adsorbed on the top surface of the sample, and there were many O or F related Ti bonds except Ti–C bond. XPS results obtained after argon ion etching indicated staggered distribution between C–Ti–C bond and O–Ti–C, F–Ti bond. It is confirmed that Ti atoms and C atoms were at the center layer of Ti3C2Tx MXene, while O atoms and F atoms were located at both the upper and lower surface of Ti3C2 layer acting as surface functional groups. The surface functional groups on the Ti3C2 layer were determined to include O2−, OH−, F− and O−–F−, among which F atoms could also desorb from Ti3C2Tx MXene easily. The schematic atomic structure of Ti3C2Tx MXene was derived from the analysis of XPS results, being consistent with theoretical chemical structure and other experimental reports. The results showed that angle-resolved XPS combing with argon ion etching is a good way to analysis 2D thin layer materials.

High Depth Resolution Wavelength Scanning Interferometry with Narrow Scanning Bandwidth Via Sinewaves Separation

High Depth Resolution Wavelength Scanning Interferometry with Narrow Scanning Bandwidth Via Sinewaves Separation

The depression behavior and mechanism of tragacanth gum on chalcopyrite during Cu-Mo flotation separation

In this work, tragacanth gum (TG), a nontoxic and environmental friendly organic polymer, was used to replace the traditional inorganic depressants of chalcopyrite during the flotation separation of copper-molybdenum sulfides. The single mineral flotation and artificial mixed minerals flotation experiments were conducted to investigate the effect of TG on flotation separation behaviour of molybdenite and chalcopyrite. The TG’s adsorption mechanism on molybdenite and chalcopyrite was investigated by X-ray photoelectron spectroscopy (XPS) and Time-of-flight secondary ion mass spectrometry (ToF-SIMS). The flotation experiment results showed that at pH 3–8, TG had a significant selective depressive effect on chalcopyrite flotation and it was enhanced with increasing TG concentration, but hardly affected the molybdenite flotation. XPS analysis showed that TG was chemically adsorbed on both molybdenite and chalcopyrite surfaces and ToF-SIMS results demonstrated that the interaction of TG and chalcopyrite was stronger than that of TG and molybdenite. Further, XPS narrow scanning analysis suggested that TG might chemisorb onto chalcopyrite via chemical bond between the carboxyl groups and Fe sites on bulk chalcopyrite surface as well as the hydrogen bond between the hydroxyl groups and surface Fe oxides/hydroxides. The strong TG adsorption on chalcopyrite hindered the subsequent adsorption of PBX on chalcopyrite surface, thus chalcopyrite was significantly depressed and Cu-Mo flotation separation was achieved.

Periodic Leaky-Wave Antennas Based on Microstrip-Fed Slot Array With Different Profile Modulations for Suppressing Open Stopband and n = −2 Space Harmonic

This article proposes a periodic leaky-wave antenna that is based on a microstrip-fed periodically modulated transverse-slot array in the ground plane. The profile of the transverse-slot array is periodically modulated to introduce a fast space harmonic ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$n = -1$ </tex-math></inline-formula> ) that generates a narrow beam scanning in the backward and the forward quadrants. Different profile modulations are studied for suppressing the open stopband and the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$n = -2$ </tex-math></inline-formula> space harmonic. If the slot profile is designed to have the impedance matched at the broadside frequency, the leaky-wave antenna has the open stopband suppressed and allows continuous scanning of the main beam through the broadside from the backward endfire to the forward direction. However, it cannot avoid the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$n = -2$ </tex-math></inline-formula> space harmonic, which causes another stopband that limits the scanning range in the forward quadrant. If the slot profile is modulated with a profile such that the aperture illumination excludes the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$n = -2$ </tex-math></inline-formula> space harmonic, the leaky-wave antenna avoids the stopband and grating lobe caused by the harmonic and thereby has the scanning range in the forward quadrant enlarged, but its open stopband cannot be suppressed simultaneously. Prototypes with the two profile modulations are fabricated and measured for validation.

Phase interpolation Fourier transform beamforming for spatial division applications

The spatial division represents an efficient approach to increasing data throughput in wireless networks. It can be implemented by spanning the channel in spatial domain with orthogonal beams generated by a Fourier transform (FT) beamforming network and using each beam to simultaneously convey an independent data stream from the base station (BS) to several users. This study presents a feasibility study of a simplified BS front-end architecture based on a spatial discrete FT beamforming network, with the number of the output ports being lower than the number of the elements in the antenna array. It is shown that connecting each output port of the FT network via power dividers to several array elements, thus implementing a `sample-and-hold' phase interpolation, preserves the orthogonality, gain and beam-width in a narrow scanning sector. Therefore, in applications where few orthogonal beams are required to span a narrow spatial sector, the proposed approach can offer a reduction of the hardware complexity. The simulated radiation patterns for a phase interpolation Fourier beamforming network are demonstrated. The measured antenna radiation patterns are reported for the architecture implemented with a Fourier Rotman lens and Wilkinson power dividers feeding a microstrip antenna array, which confirm the simulated trends.

A Rapid and Low-Cost Pathogen Detection Platform by Using a Molecular Agglutination Assay.

Rapid and low-cost pathogen diagnostic approaches are critical for clinical decision-making procedures. Cultivating bacteria often takes days to identify pathogens and provide antimicrobial susceptibilities. The delay in diagnosis may result in compromised treatment and inappropriate antibiotic use. Over the past decades, molecular-based techniques have significantly shortened pathogen identification turnaround time with high accuracy. However, these assays often use complex fluorescent labeling and nucleic acid amplification processes, which limit their use in resource-limited settings. In this work, we demonstrate a wash-free molecular agglutination assay with a straightforward mixing and incubation step that significantly simplifies procedures of molecular testing. By targeting the 16S rRNA gene of pathogens, we perform a rapid pathogen identification within 30 min on a dark-field imaging microfluidic cytometry platform. The dark-field images with low background noise can be obtained using a narrow beam scanning technique with off-the-shelf complementary metal oxide semiconductor (CMOS) imagers such as smartphone cameras. We utilize a machine learning algorithm to deconvolute topological features of agglutinated clusters and thus quantify the abundance of bacteria. Consequently, we unambiguously distinguish Escherichia coli positive from other E. coli negative among 50 clinical urinary tract infection samples with 96% sensitivity and 100% specificity. Furthermore, we also apply this quantitative detection approach to achieve rapid antimicrobial susceptibility testing within 3 h. This work exhibits easy-to-use protocols, high sensitivity, and short turnaround time for point-of-care testing uses.