Large Deflection Angles Research Articles

Investigation of Asymmetric Flow of a Slender Body with Low-Aspect Ratio Fins Having Large Deflection Angles

Investigation of Asymmetric Flow of a Slender Body with Low-Aspect Ratio Fins Having Large Deflection Angles

Polarization Independent Dynamic Beam Steering based on Liquid Crystal Integrated Metasurface

Digital Micromirror Devices, extensively employed in projection displays offer rapid, polarization-independent beam steering. However, they are constrained by microelectromechanical system limitations, resulting in reduced resolution, limited beam steering angle and poor stability, which hinder further performance optimization. Liquid Crystal on Silicon technology, employing liquid crystal (LC) and silicon chip technology, with properties of high resolution, high contrast and good stability. Nevertheless, its polarization-dependent issues lead to complex system and low efficiency in device applications. This paper introduces a hybrid integration of metallic metasurface with nematic LC, facilitating a polarization-independent beam steering device capable of large-angle deflections. Employing principles of geometrical phase and plasmonic resonances, the metallic metasurface, coupled with an electronically controlled LC, allows for dynamic adjustment, achieving a maximum deflection of ± 27.1°. Additionally, the integration of an LC-infused dielectric grating for dynamic phase modulation and the metasurface for polarization conversion ensures uniform modulation effects across all polarizations within the device. We verify the device’s large-angle beam deflection capability and polarization insensitivity effect in simulations and propose an optimization scheme to cope with the low efficiency of individual diffraction stages.

Design and fabrication of an achromatic liquid crystal polarization grating with large deflection angle for visible wavelength

Design and fabrication of an achromatic liquid crystal polarization grating with large deflection angle for visible wavelength

Linearly polarized GaN micro-LED with adjustable directional emission integrated with a continuous metasurface

Traditional LEDs emit light that exhibits incoherence and displays a Lambertian distribution. To achieve linearly polarized (LP) light and control the emission direction, a variety of optical components are required to be stacked, which is unsuitable for compact applications and results in low deflection efficiency. Here, we propose and and numerically simulate a novel single-chip micro-resonant cavity LED (micro-RCLED) device that generates directional LP light by integrating a continuous metasurface. This device includes a bilayer grating at the GaN layer's bottom, providing high transverse electric (TE) reflectivity above 89.5% and an extinction ratio exceeds 57 dB at 500 nm. The top distributed Bragg reflector (DBR) and the bilayer grating together constitute a TE mode Fabry–Pérot resonant cavity. This not only promotes the emission of the TE wave, but also guarantees its collimation with the appropriate phase, thereby enhancing its spatial coherence. A functional metasurface above the DBR layer precisely controls the TE wave's deflection angle. It maintains a low aspect ratio while enabling efficient, large-angle deflection. The simulation results demonstrate that this device provides an effective solution for generating highly spatially coherent directional LP light, with broad potential applications in fields such as polarized light imaging and advanced 3D micro-LED display systems.

Design of an Electromagnetic Micro Mirror Driving System for LiDAR.

Electromagnetic micro mirrors are in great demand for light detection and ranging (LiDAR) applications due to their light weight and low power consumption. The driven frequency of electromagnetic micro mirrors is very important to their performance and consumption. An electromagnetic micro mirror system is proposed in this paper. The model of the system was composed of a micro mirror, an integrated piezoresistive (PR) sensor, and a driving circuit was developed. The twisting angle of the mirror edge was monitored by an integrated PR sensor, which provides frequency feedback signals, and the PR sensor has good sensitivity and linearity in testing, with a maximum of 24.45 mV/deg. Stable sinusoidal voltage excitation and frequency tracking was realized via a phase-locked loop (PLL) in the driving circuit, with a frequency error within 10 Hz. Compared with other high-cost solutions using PLL circuits, it has greater advantages in power consumption, cost, and occupied area. The mechanical and piezoresistive properties of micro mirrors were performed in ANSYS 19.2 software. The behavior-level models of devices, circuits, and systems were validated by MATLAB R2023a Simulink, which contributes to the research on the large-angle deflection and low-power-consumption drive of the electromagnetic micro mirror. The maximum optical scan angle reached 37.6° at 4 kHz in the behavior-level model of the micro mirror.

Measurement of space charge density distributions and dielectric resonance enhancement of beam deflection properties of KTN crystal

In recent years, potassium tantalum niobate (KTN) electro-optical deflection devices have gained considerable attention because of their notable advantages, such as large deflection angles, low operational voltage requirements, and compact dimensions. This study uses the phase-shifted interferometric optical path to characterize the influence of direct current (DC) voltage on charge density. An interferogram is acquired using the four-step phase-shifting technique, enabling the calculation of phase delays and deducing the variation in charge density. Experimental results demonstrate that the charge density near the cathode increases with an increase in DC voltage. Subsequently, we utilize the frequency dependence of the dielectric constant of the KTN crystal on the electric field. The dielectric constant can be enhanced when the characteristic frequency of the motion of the polar nanoscale region matches the frequency of the electric field. This field-induced enhancement effect improves the beam deflection performance of the KTN crystal. Application requirements in the field of high-speed random scanning can be realized through the mechanism of the KTN crystal co-acting with DC and alternating current electric fields.

Low-frequency ultrasonic array imaging for detecting concrete structural defects in blind zones

Ultrasonic array (UA) imaging is a promising non-destructive testing (NDT) method that is extensively used for defect detection. Due to the high attenuation characteristics of ultrasonic wave propagation in concrete structures and the directivity of sensors, the total focus method (TFM) easily misses specific defects in blind zones that are far from the sensors or located at a large deflection angle. To overcome this limitation, the diffusion attenuation compensation factor and solid directivity correction factor are adopted to improve the scattered signal energy of defects that are in blind zones. On this basis, the diffusion attenuation compensation method (DACM), the solid directivity correction method (SDCM), and the diffusion attenuation compensation-based solid directivity correction method (DAC-SDCM) are proposed. These methods are applied to characterize multiple circular holes in concrete structures using the dry point contact (DPC) low-frequency UA, and the detection results are evaluated from the intensity curve and detection area of ultrasonic images. The numerical and experimental results indicate that DACM is suitable for detecting defects located at longer distances, SDCM is capable of detecting defects located at larger deflection angles, and DAC-SDCM can significantly improve the detection performance of defects that are distant and have large deflection angles. The findings demonstrate that the proposed methods can significantly improve the detection ability of defects in blind zones and broaden the application of DPC low-frequency UA in the health monitoring of concrete structures.

Mechanical azimuthal beam‐steering Fabry–Perot resonator antenna with large deflection angle

AbstractContinuous beam steering approach with minimal power consumption is highly desirable in modern antenna designs. A simple mechanical method for achieving beam steering in the Fabry–Perot resonator antenna (FPRA) is presented. It involves rotating the upper phase gradient metasurface (PGM) mechanically to change the aperture phase distribution, so the beam is continuously steered in the azimuthal plane while maintaining a large elevation angle. The proposed PGM unit cell comprises a hexagonal ring and patch printed on both sides of the substrate, along with a honeycomb lattice. A prototype antenna operating at 5.65 GHz is fabricated and measured to validate the feasibility. Measurement results show that the FPRA achieves a gain of 14.9 dBi, and can continuously steer its beam in the azimuthal plane with an elevation angle of around θ = 50°. Measured radiation patterns in eight azimuthal directions (φ = 0°, 45°, 90°, 135°, 180°, 225°, 270°, and 315°) are consistent with the simulated results. Compared with other electrical tuning methods, our design has a compact size and requires lower power for the PGM rotation.

Hydrodynamic benefits of passive flexibility in a self-propelled oscillatory ray

In the present study, numerical simulations are conducted to investigate the hydrodynamic benefits of a self-propelled oscillatory ray with passive flexibility compared to those with active flexibility. For the active flexibility case, the prescribed motion is applied to the entire surface of the ray. On the other hand, for the passive flexibility case, the motion of the leading edges is only prescribed, whereas that of the rest parts is determined by the interaction with the surrounding fluid. The cruising speed and input power of the ray with passive flexibility increase as the horizontal bending rigidity decreases, and its propulsive efficiency is maximized at a specific horizontal bending rigidity. Compared to the active flexibility case, the propulsive performance of the oscillatory ray with passive flexibility is improved by not only enhanced circulation and added-mass effects but also by the favorable repartition of the resultant force caused by a large deflection angle. Strong vortical structures induced by a large deformation over the entire region of the fin generate strong negative pressure on the forward side of the overall surface, even near the central body (i.e., increased circulation effect). Furthermore, the positive pressure on the backward side increases in the passive flexibility case due to high fin acceleration caused by more intense oscillating motions (i.e., increased added-mass effect). When the oscillating frequency and the Reynolds number vary, the performance of the ray with passive flexibility is confirmed to be higher than that with active flexibility.

Topology-optimized freeform broadband optical metagrating for high-efficiency large-angle deflection

A metagrating made of periodic arrays of subwavelength inclusions has great capability for efficient manipulation of the impinging wavefront at subwavelength scale. However, it suffers from a significant practical issue in that the diffraction efficiency declines rapidly along with the increase of deflection angle, especially for broadband application scenarios. Here, we comprehensively investigated different topology optimization approaches to design the broadband optical metagrating for high-efficiency large-angle deflection, including single-wavelength optimization (SO), max-min optimization (MO), and average optimization (AO). It is demonstrated that the AO approach is more appropriate to optimize the broadband high-efficiency metagrating. Specifically, a freeform metagrating of up to about a 70° deflection angle at a central wavelength of 10.6 µm with diffraction efficiency exceeding 80% over a broad bandwidth of 4.36 µm in the infrared range is demonstrated based on the AO approach. It is also shown that, for all three optimization approaches, the quasi-catenary metagrating optimized from initial catenary structures has the evident advantage on bandwidth compared to that optimized from initial discrete structures. Our results provide insights into the inverse design of metagratings and may find potential applications in broadband achromatic metalenses and other broadband meta-devices.

License plate recognition system in unconstrained scenes via a new image correction scheme and improved CRNN

Automatic license plate recognition plays an important role in vehicle management. The performance of current license plate recognition systems is significantly affected by large-angle deflection in unconstrained scenes. For addressing this issue, this paper develops a license plate recognition system via a new image correction scheme and an improved CRNN (Convolutional Recurrent Neural Network). In which, the yolov5l is firstly introduced for license plate detection, and it is trained by transfer learning in order to address insufficient data. Then, a new license plate correction scheme and AFF-Net (Adaptive Fusion Feature Segmentation Network) is proposed and applied, which uses the segmentation result of license plate and its original image area for perspective transformation to improve the correction effect. Finally, the channel attention mechanism is added to the CRNN model for license plate recognition, so that a single grid cell of the feature network can obtain more spatial information. The recognition accuracy of the developed license plate recognition system is 98.8 % on CTPFSD (China Temporary Parking Fee System Data), which is much higher than current mainstream license plate recognition systems. More importantly, the developed license plate recognition system has been deployed in the cloud and applied in outdoor parking toll in practice.

Design of large-deflection-angle high-diffraction-efficiency high-dispersion hybrid gratings

Gratings are key components in many optical systems such as spectrometers. Improving their dispersion is very important for their applications, but improving the single-order diffraction efficiency of an ultrahigh dispersion grating is still very challenging. Here, we propose an analytical approach for the design of a new type of grating named hybrid grating, which consists of a subwavelength grating and a non-subwavelength grating. The proposed analytical approach is based on a physical model in which the non-subwavelength grating acts as an ultrathin reflection grating and the subwavelength grating acts as an antireflection coating. Using the rigorous coupled-wave analysis and the finite-difference time-domain method, we numerically demonstrate that multiple hybrid gratings designed at different wavelengths using the proposed analytical approach show a diffraction efficiency of greater than 95 % in the -1st diffraction order for TE-polarized light, an angular dispersion of greater than 0.8 mrad/nm and a deflection angle of greater than 80°. Furthermore, we numerically demonstrate that by using a combined approach to optimize the parameters of a hybrid grating, the diffraction efficiency in the -1st diffraction order for TE-polarized light can be increased to more than 97 % under the condition that the angular dispersion and the deflection angle of the hybrid grating remain unchanged. Our work provides an avenue for rapid design of gratings with high angular dispersion, large deflection angle and high diffraction efficiency.

Switchable terahertz orbital angular momentum Bessel beams based on spin-decoupled multifunctional reflective metasurfaces.

In this study, switchable terahertz (THz) multi-orbital angular momentum (OAM) Bessel beams (BBs) were developed based on a spin-decoupled reflective multifunctional metasurface (MTS). Switchability was achieved by switching the feed between left-hand circular polarization (LCP), right-hand circular polarization (RCP), and linear polarization (LP) incidences. A switchable physical model was established for calculating the beam direction, OAM mode, polarization, and non-diffractive distance of the outgoing BBs. As an example, a spin-decoupled MTS was designed to generate dual BBs under LCP incidence, which was subsequently switched to RCP or LP for switchability. The outgoing BBs could be switched among three types of beams: Type-1 under LCP incidence (LCP, θL = 40°, φL = 0°, lL = 1, dL = 18 cm) and (RCP, θR = -40°, φR = 0°, lR = -1, dR = 20 cm); Type-2 under RCP incidence (RCP, θR = 40°, φR = 0°, lR = 1, dR = 18 cm) and (LCP, θL = -19°, φL = 0°, lL = 3, dL = 16.4 cm); and Type-3 under LP incidence (LP, θ = 40°, φ = 0°, l = 1, d = 18 cm), (RCP, θR = -40°, φR = 0°, lR = -1, dR = 20 cm) and (LCP, θL = -19°, φL = 0°, lL = 3, dL = 16.4 cm). Compared with previous MTSs, the proposed spin-decoupled MTS has the advantages of switchability among BBs, high non-diffractive distance/aperture size ratio of 15, large beam deflection angle of up to 40°, and high BB conversion efficiency of up to 96%. The simulated results were consistent with those calculated using the physical model, thus validating the physical model. The designed switchable BBs have potential THz near-field applications, such as high-capacity near-field wireless communications, wireless power transfer, high-resolution imaging, non-destructive testing, and speed detection of high-speed rotating objects.

The non-plane initiation and propagation mechanism of multiple hydraulic fractures in tight reservoirs considering stress shadow effects

Multi-cluster fracturing in horizontal wells is an important stimulation technology for unconventional tight reservoirs. The interference among multiple simultaneously growing hydraulic fractures results in a non-uniform fluid distribution into fractures and non-planar fracture geometries. In this paper, the competition mechanism between perforations under the stress shadow, the formation mechanism of complex non-plane fractures near the wellbore, and the initiation and propagation mechanism of multiple hydraulic fractures are investigated by using the 3D lattice method. Also, the effects of fracture geometry, fracture spacing and rock mechanics parameters on the stress interaction among fractures are analyzed by the dislocation theory. The results showed the complexity of fracture initiation near the wellbore and the low efficiency of the perforation initiation in the case of spiral perforation, due to a strong interaction between perforations. However, these initial micro-cracks will eventually coalesce to be a macroscopical fracture which perpendicular to the direction of minimum principal stress. The study indicated that stress interaction and fracture propagation is significantly affected by inclined well orientation. The hydraulic fracture is more likely to deflect and propagate non-uniformly with the increasing width of hydraulic fracture, the decreasing spacing between perforation clusters and the increasing rock modulus. When the horizontal principal stress difference is small, it is obvious to cause a large deflection angle and sometimes furcation of fractures. This study can provide a theoretical basis and technical guidance for hydraulic fracturing design in tight reservoirs.

Fully Analytical Design of Dual-Wire PCB Metagratings for Beam Steering and Splitting

The printed circuit board (PCB) type metagrating (MG), a periodic microstrip planar structure with discrete distribution of polarization currents, can realize high-angle wavefront shaping with near-unity efficiency for potential application in high beam-steering antennas or reflectors. For large angle deflection, only a small number of meta-atoms are required in the metagrating’s period. As such, here we focus on a reflective PCB MG in the presence of only two meta-atoms, whose complex load impedance densities is explicitly derived from fully analytical expressions. The passive and lossless conditional equations as well as the equations for the power ratio control of the diffraction modes are given, which allows avoiding numerical optimization procedure. Three practical prototypes, including anomalous reflector and beam splitters are designed, simulated and measured. The measurement results agree well with the simulation results and are consistent with the theoretical predictions.

Improving the Electro-Optical Deflection Performance of KTN Crystals Based on the Temperature Compensation Effect

The laser deflector is a crucial device used to change the direction of light beam propagation in various fields, including lithography, lidar, and scanning. In this paper, we conduct a systematic study of two KTa(1–x)NbxO3 (KTN) crystals that use different physical deflection mechanisms. We analyze their dielectric properties, entropy, domain structure, and deflection performance. We also address the drawback of the small deflection angle of the compositional gradient KTN deflector crystal by proposing a new temperature-compensated temperature control strategy to improve its deflection performance. The gradient temperature control mechanism maximizes the dielectric constant in different regions of the KTN crystals, leading to a threefold (10.67 mrad) increase in deflection angle compared to conventional uniform temperature control equipment. This optimized temperature control mechanism can significantly enhance the practical application of KTN crystals, providing a new avenue for achieving a large deflection angle beam deflector.

Voltage scanning and technical upgrades at the Collinear Resonance Ionization Spectroscopy experiment

To optimize the performance of the Collinear Resonance Ionization Spectroscopy (CRIS) experiment at CERN-ISOLDE, technical upgrades are continuously introduced, aiming to enhance its sensitivity, precision, stability, and efficiency. Recently, a voltage-scanning setup was developed and commissioned at CRIS, which improved the scanning speed by a factor of three as compared to the current laser-frequency scanning approach. This leads to faster measurements of the hyperfine structure for systems with high yields (more than a few thousand ions per second). Additionally, several beamline sections have been redesigned and manufactured, including a new field-ionization unit, an electrostatic bend with a larger deflection angle, and improved ion optics. The beamline upgrades are expected to yield an improvement of at least a factor of 5 in the signal-to-noise ratio by avoiding the use of high-power lasers (which yield non-resonantly produced ions) and providing time-of-flight separation between the resonant ions and the collisional background.

Design and optimization of a compact quasi-isochronous 180-deg transport arc with suppressed CSR-induced emittance growth

Preserving the beam quality of a high-brightness electron beam is a noteworthy issue when delivering the electron bunch through a beam transfer line. In a beam transfer line with a large deflection angle, e.g., a 180-deg transport arc comprised of a large amount of dipoles, emission of coherent synchrotron radiation (CSR) can lead to transverse emittance dilution. In addition, the longitudinal dispersion may cause undesirable bunch length variation. Both effects can degrade beam quality. Nevertheless, design and optimization of a 180-deg transport arc that can be well applied to practical applications is a challenging problem, considering the practical nonlinear effects of a real lattice and the contributions of transient CSR at the dipole edges and CSR in the subsequent drifts. In this study, we present the design and optimization of a compact 180-deg transport arc comprised of multi-triple-bend achromat (TBA) cells, aiming at suppressing the CSR-induced emittance growth and avoiding bunch length variation simultaneously. The TBA cells and optics along the arc are adjusted to suppress the CSR-induced emittance growth and bunch length variation cell by cell, after which a multi-objective optimization of the arc is conducted. Practical considerations including lattice nonlinear effects and a full one-dimensional CSR model (including transient CSR and CSR in drifts) are taken into account.

A Novel Point Target Attitude Compensation Method Using Electromagnetic Reflectance Theory

During the process of the airborne synthetic aperture radar (SAR) system platform in space, platform attitude deflection is inevitable. However, large attitude deflection angles are unacceptable for polarimetric calibration using point targets, especially the dihedral, which is very sensitive to the pointing angle of the radar. To mitigate the impact of attitude angles on calibration accuracy, attitude compensation of the corner reflector is necessary during the calibration process. The conventional approach to attitude compensation typically maps the three-dimensional attitude angle information to the one-dimensional polarimetric orientation angle (POA) information. However, the reduction of dimension inevitably results in information loss, leading to errors that affect calibration performance when the attitude angle is large. In order to ensure the accuracy of point target calibration, this paper proposes a novel point target compensation method based on the reflection theory of electromagnetic waves. This method is based on three-dimensional attitude angle information and has higher reliability than the POA method. Finally, this paper calculates the distance between the scattering matrices obtained after compensation based on the proposed method and the POA method to obtain the difference in the performance of the two methods. Through a simulation, this paper finds that when the attitude angle is small, the results of the two schemes are approximately the same, but as the attitude angle increases, the error between the two gradually increases. This suggests that the proposed method has greater advantages in the case of attitude deflection. Furthermore, the proposed method does not require additional information supplementation compared with the equivalent POA method, making it highly practical.

Rotational Doppler Velocimetry of a Surface at Larger Tilt Angles

Here, we experimentally demonstrate a straightforward-to-implement scheme that enables the rotating velocimetry of a noncooperative target at large deflection angles. This scheme is based upon the combination of digital modal decomposition with the rotational Doppler effect of orbital angular momentum (OAM)-carried light modes. To achieve this, we first theoretically analyzed the tilt effect of a rotating surface on the OAM complex spectra and rotational Doppler spectrum. Our findings validate that the tilted surface causes not only the broadening of OAM power and phase spectra, but also the broadening of the scattered Doppler spectrum. Furthermore, we introduce a compensation phase for tilted OAM light that effectively suppresses the sidebands of the OAM power spectrum, thereby restraining the sideband amplitudes of the Doppler spectrum. As a consequence, the rotating velocimetry can be extended to cover larger tilt angles (as large as 70 degrees) than those of existing systems. Our outcomes have the advantages of providing, in addition to profound insight into the interaction between OAM-carrying light and object motion, potential opportunities for noncontact optical metrology and the telemetry of angular speeds, particularly in meteorological applications.