Mirror Orientation Research Articles

Metasurface loaded dual port circularly polarized dielectric resonator antenna with reduced RADAR cross section and mutual coupling features

The design of dual port radiator with a polarization diversity technique and reduced radar cross section (RCS) is described in this study. Cross slot is used to stimulate cylindrical ceramic for generating circular polarization features. Mirror orientation of aperture between port-1 and port-2 improves the isolation level by 25 dB. To suppress the antenna’s monostatic RCS, split ring resonator (SRR) based frequency selective surface is positioned between and around the dual ports. Experimental outcomes confirm the designed radiator operates from 4.11–5.24 GHz along with 3-dB axial ratio in between 4.15–4.92 GHz. The value of monostatic RCS is reduced by 15 dBsm in between the operating band. Broadsided radiation characteristics and good value of diversity parameter makes the designed radiator applicable for C-band Radar applications.

Texture Evolution and Plastic Deformation Mechanism of Cold-Drawn Co-Cr-Ni-Mo Alloy

The plastic deformation behavior and mechanisms of Co-Cr-Ni-Mo alloy were investigated. The wires were subjected to different reductions using a multi-pass drawing approach and the resulting microstructures were characterized by EBSD and TEM. It was found that the alloy cold-drawn from surface to center exhibited non-uniform radial strain, with decreasing strain from surface to center. As the strain increased, the transverse texture of the alloy evolved from the initial bimodal texture consisting of strong {100}<110> and weak {110}<001> components to bimodal texture with {110}<233> and {112}<111> components, with significant twinning and mirror orientation between twin and matrix. The longitudinal texture evolution of the alloy mainly occurred on the α-fiber line, and ultimately did not form a significant texture due to grain elongation and crystal rotation. The plastic deformation mechanism of the Co-Cr-Ni-Mo alloy was dominated by dislocation slip at lower strain levels, which gradually transitioned to a combination of dislocation slip and twinning at higher strain levels. The deformation twins were typically distributed in high-density dislocation regions, and the twin boundaries transformed into high-angle sub-grain boundaries, hindering the extension of dislocation slip and deformation twin. With the increase in strain, work hardening results in a significant increase in strength and microhardness.

The advanced motion control system in HEPS beamline

In synchrotron radiation facilities such as the High Energy Photon Source (HEPS), numerous motorized actuators are equipped on the optics devices of HEPS beamline to manipulate the orientation of crystals and mirrors, thereby altering the position and characteristics of X-rays. The motion control system (MCS) plays an important role in the optics devices of HEPS beamlines, such as monochromator, K-B mirror and sample plants. In order to acquire the specify properties of X-ray and satisfy the complex experimental requirements, MCS must have the ability to handle the complicated control demands. Therefore, HEPS has developed a standardized motion control system for synchrotron radiation applications, which is a distributed system based on EtherCAT fieldbus. The hardware of this system consists of the control unit and driver unit, which has the flexibility to suit for different applications. The software of MCS is designed under the Experimental Physics and Industrial Control System (EPICS), which is very popular in synchrotron radiation facilities all over the world. In this paper, the performance tests of IOC software were demonstrated, and a few flyscan applications were given, which include spiral scan, raster scan and position event trigger, to demonstrate the feasibility and effectiveness of this system.

Development of the mirror-image sensitivity for different object categories-Evidence from the mirror costs of object images in children and adults.

Object recognition relies on a multitude of factors, including size, orientation, and so on. Mirrored orientation, particularly due to children's mirror confusion in reading, holds special significance among various object orientations. Brain imaging studies suggest that the visual ventral and dorsal streams exhibit distinct orientation sensitivity across diverse object categories. Yet, it remains unclear whether mirror orientation sensitivity also varies among these categories during development at the behavioral level. Here, we explored the mirror sensitivity of children and adults across five distinct categories, which encompass tools that activate both the visual ventral stream for function information and the dorsal stream for manipulation information, and animals and faces that mainly activate the ventral stream. Two types of symbols, letters and Chinese characters, were also included. Mirror sensitivity was assessed through mirror costs-that is, the additional reaction time or error rate in the mirrored versus the same orientation condition when judging the identity of object pairs. The mirror costs in reaction times and error rates consistently revealed that children exhibited null mirror costs for tools, and the mirror costs for tools in adults were minimal, if any, and were smaller than those for letters and characters. The mirror costs reflected in absolute reaction time and error rate were similar across adults and children, but when the overall difference in reaction times was considered, adults showed a larger mirror cost than children. Overall, our investigation unveils categorical distinctions and development in mirror sensitivity of object recognition across the ventral and dorsal streams.

Reflection transformation calibration for mirror-assisted multi-view digital image correlation system using fluorescent speckle patterns

Mirror-assisted multi-view digital image correlation (MV-DIC) is a simple-to-implement DIC technique for panoramic kinematic field measurements of regular-sized specimens. In the practical implementation of mirror-assisted MV-DIC, accurate reflection transformation calibration of the planar mirrors is considered as a pivotal step. In this work, we propose to use fluorescent speckle patterns fabricated on the mirrors to calibrate their reflection transformation matrices, which can fully utilize the camera’s spatial resolution and simplify the calibration processes. The fluorescent speckle patterns on the mirrors do not interfere with the virtual object surfaces using a regular blue-light stereo-DIC system. However, under the illumination of ultraviolet light, the fluorescent speckle patterns can be captured and used to calibrate the position and orientation of the planar mirrors. The practicality and efficacy of the fluorescent speckle pattern-based calibration method are validated by profile measurement and translation tests, and an application in a four-point bending experiment is also demonstrated.

Multi-pitch nano-accuracy surface profiler for strongly curved X-ray mirror metrology

We present our recent research and development effort on the Multi-Pitch Nano-accuracy Surface Profiler (MPNSP). This metrology instrument is developed to characterize strongly curved X-ray mirrors proposed to achieve diffraction-limited soft X-ray focusing for scientific applications at the synchrotron beamlines. The measurement process consists of forward-and-backward scans on the test mirror surface along its tangential direction at multiple pitch angles. Our research and development in this work aim to take the challenge of measuring strongly curved X-ray mirrors with a typical total slope range ≳10 mrad, while maintaining the Root Mean Square (RMS) value of measurement repeatability and self-consistency at 50 nrad RMS level. We first introduce the mechanical design, followed by a brief review of the mathematical model and the optimization algorithm for the MPNSP technique. By detecting the rotation axis of the mirror pitch with a machine vision approach, we can determine and then reduce the vertical distance between the pitch rotation axis and the test mirror surface to a sub-mm level. In addition, we describe a practical data acquisition procedure for strongly curved X-ray mirrors with a total slope range larger than the slope measuring range of the autocollimator used in the instrument. As a result, the proposed MPNSP measurements with different mirror orientations achieve remarkable self-consistency and reproducibility of <50 nrad RMS in slope and <0.5 nm RMS in height.

Polarization dynamics of a vertical external-cavity surface-emitting laser with a saturable absorber mirror.

We investigate experimentally the polarization dynamics of a vertical external-cavity surface-emitting laser with a saturable absorber mirror in the cavity. We demonstrate that the normalized Stokes parameters and degree of polarization are functions of time reaching extreme values around the pulse peaks. Our experiments show that light is elliptically polarized, being able to have a circular right-handed or left-handed component, depending on the orientation of the saturable absorber mirror.

DRL-Based IRS-Assisted Secure Visible Light Communications

In this paper, we develop a novel Physical Layer Security (PLS) technique for a Visible Light Communication (VLC) system composed of light fixtures assisted by mirror array sheets serving as Intelligent Reflecting Surfaces (IRS). Our objective is to optimize the Secrecy Capacity (SC) by finding the optimal beamforming (BF) weights equipped at the VLC fixtures and mirror orientations at the mirror array sheet. Due to many design parameters, including the beamforming weights, the mirror orientations, and the mobility of the users, conventional optimization techniques may not be practical to optimize the SC capacity. Therefore, we proposed a Deep Reinforcement Learning (DRL) solution based on Deep Deterministic Policy Gradient (DDPG) algorithm to solve the highly complex SC problem by adjusting the BF weights and mirror orientations. The DDPG-based algorithm provides an optimized solution that can adapt to the large size of design parameters and act fast to the channel variations due to users’ mobility. Our results show that considering both mirror array sheet and BF vectors provide the highest SC for the system. Moreover, we show the effect of changing the mirror arrangements of the mirror array sheet on SC. We conclude that for a fixed mirror array sheet size, there exists a specific mirror arrangement (i.e., number of mirrors) that optimizes the SC. After this number, the performance of SC saturates. We also show the trade-off between the training complexity and SC performance considering different mirror arrangements in the mirror array sheet.

Design and Calibration of Plane Mirror Setups for Mobile Robots with a 2D-Lidar.

Lidar sensors are widely used for environmental perception on autonomous robot vehicles (ARV). The field of view (FOV) of Lidar sensors can be reshaped by positioning plane mirrors in their vicinity. Mirror setups can especially improve the FOV for ground detection of ARVs with 2D-Lidar sensors. This paper presents an overview of several geometric designs and their strengths for certain vehicle types. Additionally, a new and easy-to-implement calibration procedure for setups of 2D-Lidar sensors with mirrors is presented to determine precise mirror orientations and positions, using a single flat calibration object with a pre-aligned simple fiducial marker. Measurement data from a prototype vehicle with a 2D-Lidar with a 2 m range using this new calibration procedure are presented. We show that the calibrated mirror orientations are accurate to less than 0.6° in this short range, which is a significant improvement over the orientation angles taken directly from the CAD. The accuracy of the point cloud data improved, and no significant decrease in distance noise was introduced. We deduced general guidelines for successful calibration setups using our method. In conclusion, a 2D-Lidar sensor and two plane mirrors calibrated with this method are a cost-effective and accurate way for robot engineers to improve the environmental perception of ARVs.

Capacity Maximization for Reconfigurable Intelligent Surface-Aided MISO Visible Light Communications

This paper investigates the employment of reconfigurable intelligent surfaces (RISs) to improve the asymptotic capacity of the multiple-input single-output (MISO) visible light communication (VLC) system in the case of high signal-to-noise (SNR). For the RIS-aided MISO-VLC system based on mirror array, we regard the high-SNR asymptotic capacity with the input subject to peak-intensity constraints as a goal and formulate an asymptotic capacity maximization problem to find the optimal orientations of mirrors. As for the non-convex optimization problem, we convert it into a quadratic programming (QP) problem with hemispherical constraints and prove that it can be solved by computing the maximum eigenvalue of an equivalent matrix. Simulation results indicate that the asymptotic capacity is able to be improved significantly by adopting RIS in MISO-VLC systems. Meanwhile, we observe that the proper deployment scheme of RIS is able to enhance the degree of improvement through several simulations.

Asymmetric Patch Element Reflectarray with Dual Linear and Dual Circular Polarization

A reflectarray antenna consisting of asymmetrical patch elements is proposed, which is capable of producing dual linear and dual circular polarized operation at 26 GHz frequency. The main purpose of this design is to support four different polarizations using the same patch element. The proposed reflectarray has a single layer configuration with a linearly polarized feed and circular ring slots in the ground plane. Asymmetric patch element is designed from a square patch element by tilting its one vertical side to some optimized inclination. A wide reflection phase range of 600° is obtained with the asymmetric patch element during unit cell measurements. A 332 element circular aperture reflectarray is designed with the proposed configuration and experimentally validated with a linearly polarized prime feed configuration. Two different orientations of mirror and non-mirror asymmetric patch elements on the surface of reflectarray are analyzed. Dual linear polarization is obtained with the mirror orientation of the asymmetric patch elements on the surface of reflectarray. Alternatively, asymmetric patch elements without mirror orientation are demonstrated to produce dual circular polarization with the same linearly polarized feed. A maximum measured gain of 24.4 dB and 26.1 dB is achieved for dual linear and dual circular polarization, respectively. Their respective measured efficiencies are 28% and 41.3%, which are supported by a maximum −3 dB gain bandwidth of 13.8% and 11.5%. The circular polarization operation of the reflectarray is also supported by a 6 dB axial ratio bandwidth of 9.2%. The proposed asymmetric patch reflectarray antenna with polarization diversity, wide bandwidth and high gain is suitable to be used in many high frequency applications of 5G communication.

Integrated multi-objective optimisation of the support structure of heliostats in concentrated solar power plants using a genetic algorithm

The optimisation of the support structure of heliostats in concentrating solar power plants is a fundamental task aimed at attempting to reduce the high levelised cost of energy (LCOE) of current configurations. In this work, an integrated multi-objective optimisation framework is presented, which relies on the combination of a lean and fast structural model with a genetic algorithm to simultaneously minimise both the overall mass of the support structure and the mean angle of rotation of the mirror surface, which directly affects the optical efficiency of the component. A particular feature of the proposed framework is that it represents an integrated solution, i.e., it allows to simultaneously optimise the main components of the heliostat support structure, i.e., the pedestal, the truss and the back support structure, assuming they are off-the-shelf components easily available on the market. The optimisation problem is set up selecting as design variables (i) the number of elements in the back support structure and (ii) the relevant characteristics of all the components considered, i.e., section shape and dimensions, according to the components commercial datasheets. At each iteration of the optimisation process, the structural model is fed with the current design variables values and, according to some computed aerodynamic loads, it allows evaluating the displacement and rotation of the points of interest within the mirror surface. An aerodynamic model present in the literature based on experimental wind tunnel tests is used to estimate the wind forces acting on the heliostat as a function both of the mirror inclination angle with respect to the ground and of the wind direction with respect to the mirror orientation. In this work, the proposed methodology is demonstrated on a realistic case study and the results commented in detail, highlighting possible future developments and the limitations of the framework.

High-accuracy electrohydraulic control system for the position and orientation of the primary mirror for a large telescope

High-accuracy electrohydraulic control system for the position and orientation of the primary mirror for a large telescope

A Mirror-Based Active Vision System for Underwater Robots: From the Design to Active Object Tracking Application.

A mirror-based active system capable of changing the view’s direction of a pre-existing fixed camera is presented. The aim of this research work is to extend the perceptual tracking capabilities of an underwater robot without altering its structure. The ability to control the view’s direction allows the robot to explore its entire surroundings without any actual displacement, which can be useful for more effective motion planning and for different navigation strategies, such as object tracking and/or obstacle evasion, which are of great importance for natural preservation in environments as complex and fragile as coral reefs. Active vision systems based on mirrors had been used mainly in terrestrial platforms to capture the motion of fast projectiles using high-speed cameras of considerable size and weight, but they had not been used on underwater platforms. In this sense, our approach incorporates a lightweight design adapted to an underwater robot using affordable and easy-access technology (i.e., 3D printing). Our active system consists of two arranged mirrors, one of which remains static in front of the robot’s camera, while the orientation of the second mirror is controlled by two servomotors. Object tracking is performed by using only the pixels contained on the homography of a defined area in the active mirror. HSV color space is used to reduce lighting change effects. Since color and geometry information of the tracking object are previously known, a window filter is applied over the H-channel for color blobs detection, then, noise is filtered and the object’s centroid is estimated. If the object is lost, a Kalman filter is applied to predict its position. Finally, with this information, an image PD controller computes the servomotor articular values. We have carried out experiments in real environments, testing our active vision system in an object-tracking application where an artificial object is manually displaced on the periphery of the robot and the mirror system is automatically reconfigured to keep such object focused by the camera, having satisfactory results in real time for detecting objects of low complexity and in poor lighting conditions.

Cryogenic suspension design for a kilometer-scale gravitational-wave detector

We report the mirror suspension design for large-scale cryogenic gravitational wave telescope, KAGRA, during bKAGRA phase 1. Mirror thermal noise is one of the fundamental noises for room-temperature gravitational-wave detectors such as Advanced LIGO and Advanced Virgo. Thus, reduction of thermal noise is required for further improvement of their sensitivity. One effective approach for reducing thermal noise is to cool the mirrors. There are many technical challenges that must be overcome to cool the mirrors, such as cryocooler induced vibrations, thermal drift in suspensions, and reduction in duty cycling due to the increased number of potential failure mechanisms. Our mirror suspension has a black coating that makes radiative cooling more efficient. For conduction cooling, we developed ultra high purity aluminum heat links, which yield high thermal conductivity while keeping the spring constant sufficiently small. A unique inclination adjustment system, called moving mass, is used for aligning the mirror orientation in pitch. Photo-reflective displacement sensors, which have a large range, are installed for damping control on marionette recoil mass and intermediate recoil mass. Samarium cobalt magnets are used for coil-magnet actuators to prevent significant change of magnetism between room temperature and cryogenic temperature. In this paper, the design of our first cryogenic payload and its performance during bKAGRA phase 1 are discussed.

High power characterisation of the ECRH transmission lines and power deposition calculations in the TJ-II stellarator

Abstract In the TJ-II stellarator, the last mirror of both ECRH transmission lines is an in-vessel steerable phase correcting mirror that distorts the power distribution of the reflected beam whenever the mirror orientation angles deviate from the design position. Beam distortions cannot be measured due to space restrictions when accessing the inner part of the device, particularly if we have in mind the wide range of orientation angles needed to carry out ECRH and ECCD experiments, for which such experimental characterisation should be performed. Instead, a set of full wave electromagnetic simulations allows us to estimate the power distribution of the beam coupled to the plasma and how this distribution changes when the in-vessel mirror is steered. High power characterisation of the transmission lines is first accomplished and documented in order to determine the beam power distribution before entering the vessel. For the perpendicular injection case, the additional contribution to the beam distortion produced by its passage through the structure supporting the window is calculated. Leaving aside the power losses due to beam trimming (7% and 10% for the first and second line respectively), the added distortion produced by the window housing is of minor importance compared to the effect of the internal mirror. The impact of beam distortion on the width of the power deposition profiles for several launching directions is addressed using the ray/beam tracing code TRUBA. Results show that the beam waist in the plasma appears smaller and ahead of the position predicted by quasi optical theory, leading to beam widening in the magnetic axis where the resonant layer is located. Despite the evident distortion, power deposition profiles calculated with beam tracing, refined with a Gabor expansion of the wave field distribution in case of strongly oblique incidence, do not differ much from the predictions of the standard ray tracing calculation.

A Whole-Body Sensory-Motor Gradient is Revealed in the Medial Wall of the Parietal Lobe.

In 1954, Penfield and Jasper's findings based on electric stimulation of epileptic patients led them to hypothesize that a sensory representation of the body should be found in the precuneus. They termed this representation the "supplementary sensory" area and emphasized that the exact form of this homunculus could not be specified on the basis of their results. In the decades that followed, their prediction was neglected. The precuneus was found to be involved in numerous motor, cognitive and visual processes, but no work was done on its somatotopic organization. Here, we used a periodic experimental design in which 16 human subjects (eight women) moved 20 body parts to investigate the possible body part topography of the precuneus. We found an anterior-to-posterior, dorsal-to-ventral, toes-to-tongue gradient in a mirror orientation to the SMA. When inspecting body-part-specific functional connectivity, we found differential connectivity patterns for the different body parts to the primary and secondary motor areas and parietal and visual areas, and a shared connectivity to the extrastriate body area, another topographically organized area. We suggest that a whole-body gradient can be found in the precuneus and is connected to multiple brain areas with different connectivity for different body parts. Its exact role and relations to the other known functions of the precuneus such as self-processing, motor imagery, reaching, visuomotor and other body-mind functions should be investigated.SIGNIFICANCE STATEMENT Using fMRI, as well as sensitive spectral analysis, we found a new homunculus in the precuneus: an anterior-to-posterior, dorsal-to-ventral, toes-to-tongue somatotopic gradient in a mirror orientation to the SMA. When inspecting body-part-specific functional connectivity, we found differential connectivity patterns for the different body parts to the primary and secondary motor areas, parietal and visual areas, and a shared connectivity to the extrastriate body area, another topographically organized area. We suggest that a whole-body gradient can be found in the precuneus and is connected to multiple brain areas in a body-part-specific manner.

Automated method to differentiate between native and mirror protein models obtained from contact maps.

Mirror protein structures are often considered as artifacts in modeling protein structures. However, they may soon become a new branch of biochemistry. Moreover, methods of protein structure reconstruction, based on their residue-residue contact maps, need methodology to differentiate between models of native and mirror orientation, especially regarding the reconstructed backbones. We analyzed 130 500 structural protein models obtained from contact maps of 1 305 SCOP domains belonging to all 7 structural classes. On average, the same numbers of native and mirror models were obtained among 100 models generated for each domain. Since their structural features are often not sufficient for differentiating between the two types of model orientations, we proposed to apply various energy terms (ETs) from PyRosetta to separate native and mirror models. To automate the procedure for differentiating these models, the k-means clustering algorithm was applied. Using total energy did not allow to obtain appropriate clusters–the accuracy of the clustering for class A (all helices) was no more than 0.52. Therefore, we tested a series of different k-means clusterings based on various combinations of ETs. Finally, applying two most differentiating ETs for each class allowed to obtain satisfying results. To unify the method for differentiating between native and mirror models, independent of their structural class, the two best ETs for each class were considered. Finally, the k-means clustering algorithm used three common ETs: probability of amino acid assuming certain values of dihedral angles Φ and Ψ, Ramachandran preferences and Coulomb interactions. The accuracies of clustering with these ETs were in the range between 0.68 and 0.76, with sensitivity and selectivity in the range between 0.68 and 0.87, depending on the structural class. The method can be applied to all fully-automated tools for protein structure reconstruction based on contact maps, especially those analyzing big sets of models.

Intuitive optics: what great apes infer from mirrors and shadows

There is ongoing debate about the extent to which nonhuman animals, like humans, can go beyond first-order perceptual information to abstract structural information from their environment. To provide more empirical evidence regarding this question, we examined what type of information great apes (chimpanzees, bonobos, and orangutans) gain from optical effects such as shadows and mirror images. In an initial experiment, we investigated whether apes would use mirror images and shadows to locate hidden food. We found that all examined ape species used these cues to find the food. Follow-up experiments showed that apes neither confused these optical effects with the food rewards nor did they merely associate cues with food. First, naïve chimpanzees used the shadow of the hidden food to locate it but they did not learn within the same number of trials to use a perceptually similar rubber patch as indicator of the hidden food reward. Second, apes made use of the mirror images to estimate the distance of the hidden food from their own body. Depending on the distance, apes either pointed into the direction of the food or tried to access the hidden food directly. Third, apes showed some sensitivity to the geometrical relation between mirror orientation and mirrored objects when searching hidden food. Fourth, apes tended to interpret mirror images and pictures of these mirror images differently depending on their prior knowledge. Together, these findings suggest that apes are sensitive to the optical relation between mirror images and shadows and their physical referents.

Supramodal agnosia for oblique mirror orientation in patients with periventricular leukomalacia

Periventricular leukomalacia (PVL) is characterized by focal necrosis at the level of the periventricular white matter, often observed in preterm infants. PVL is frequently associated with motor impairment and with visual deficits affecting primary stages of visual processes as well as higher visual cognitive abilities. Here we describe six PVL subjects, with normal verbal IQ, showing orientation perception deficits in both the haptic and visual domains. Subjects were asked to compare the orientation of two stimuli presented simultaneously or sequentially, using both a two alternative forced choice (2AFC) orientation-discrimination and a matching procedure. Visual stimuli were oriented gratings or bars or collinear short lines embedded within a random pattern. Haptic stimuli comprised two rotatable wooden sticks. PVL patients performed at chance in discriminating the oblique orientation, both for visual and haptic stimuli. Moreover when asked to reproduce the oblique orientation, they often oriented the stimulus along the symmetric mirror orientation. The deficit generalized to stimuli varying in many low level features, was invariant for spatiotopic object orientation, and also occurred for sequential presentations. The deficit was specific to oblique orientations, and not for horizontal or vertical stimuli. These findings show that PVL can affect a specific network involved with the supramodal perception of mirror symmetry orientation.