Angular Compensation Research Articles

Theoretical Substantiation of Methods for Reducing the Near-Side Radiation of Antennas for an Earth Satellite Communication Station

Within the framework of this article, various methods of reducing the lateral radiation of the antenna are considered, which mainly relate to the angular directions directly adjacent to the direction of the main radiation of the antenna for an earth satellite communication station. The relevance of this issue is beyond doubt, since it is the behavior of the antenna's diagrammatic orientation in this area that most significantly determines the electromagnetic compatibility of various satellite communication systems. The presence of axial shading leads to a significant increase in the near side lobes. The specified deformation of directional properties in a certain plane can be eliminated by using an additional radiator, the phase center of which in this plane coincides with the phase center of the antenna. Shadow radiation compensation is carried out only in a beam of regions close to the plane perpendicular to the straight line connecting the centers of the main and auxiliary antennas. The angular compensation area can be significantly expanded if the phase centers of the main and auxiliary antennas are combined. This rather trivial conclusion is still waiting for its non-trivial technical implementation. Wide-angle compensation of lateral radiation is proposed to be carried out by two auxiliary antennas located parallel to the suppression plane. The best results can be obtained by optimizing the opening shape of the auxiliary radiators. Studies show that the optimal variant of the directional pattern occurs when the mentioned irradiators are made in the form of rectangles with a length of 0,295 and a height of 0,117 from the opening radius of the main antenna, and the distribution in the openings of the auxiliary antennas is cosine-shaped. In this case, it is possible to suppress the radiation level to -40 dB.

Abrasive Waterjet Machining.

The abrasive waterjet machining process was introduced in the 1980s as a new cutting tool; the process has the ability to cut almost any material. Currently, the AWJ process is used in many world-class factories, producing parts for use in daily life. A description of this process and its influencing parameters are first presented in this paper, along with process models for the AWJ tool itself and also for the jet-material interaction. The AWJ material removal process occurs through the high-velocity impact of abrasive particles, whose tips micromachine the material at the microscopic scale, with no thermal or mechanical adverse effects. The macro-characteristics of the cut surface, such as its taper, trailback, and waviness, are discussed, along with methods of improving the geometrical accuracy of the cut parts using these attributes. For example, dynamic angular compensation is used to correct for the taper and undercut in shape cutting. The surface finish is controlled by the cutting speed, hydraulic, and abrasive parameters using software and process models built into the controllers of CNC machines. In addition to shape cutting, edge trimming is presented, with a focus on the carbon fiber composites used in aircraft and automotive structures, where special AWJ tools and manipulators are used. Examples of the precision cutting of microelectronic and solar cell parts are discussed to describe the special techniques that are used, such as machine vision and vacuum-assist, which have been found to be essential to the integrity and accuracy of cut parts. The use of the AWJ machining process was extended to other applications, such as drilling, boring, milling, turning, and surface modification, which are presented in this paper as actual industrial applications. To demonstrate the versatility of the AWJ machining process, the data in this paper were selected to cover a wide range of materials, such as metal, glass, composites, and ceramics, and also a wide range of thicknesses, from 1 mm to 600 mm. The trends of Industry 4.0 and 5.0, AI, and IoT are also presented.

Survey of Temperature Dependence of the Damping Parameter in the Ferrimagnet Gd3Fe5O12

The damping parameter ${\alpha}_{\text{FM}}$ in ferrimagnets defined according to the conventional practice for ferromagnets is known to be strongly temperature dependent and diverge at the angular momentum compensation temperature, where the net angular momentum vanishes. However, recent theoretical and experimental developments on ferrimagnetic metals suggest that the damping parameter can be defined in such a way, which we denote by ${\alpha}_{\text{FiM}}$, that it is free of the diverging anomaly at the angular momentum compensation point and is little dependent on temperature. To further understand the temperature dependence of the damping parameter in ferrimagnets, we analyze several data sets from literature for a ferrimagnetic insulator, gadolinium iron garnet, by using the two different definitions of the damping parameter. Using two methods to estimate the individual sublattice magnetizations, which yield results consistent with each other, we found that in all the used data sets, the damping parameter ${\alpha}_{\text{FiM}}$ does not increase at the angular compensation temperature and shows no anomaly whereas the conventionally defined ${\alpha}_{\text{FM}}$ is strongly dependent on the temperature.

Magnetic damping of ferromagnetic and exchange resonance modes in a ferrimagnetic insulator

Understanding the damping is an important fundamental problem with widespread implications in magnetic technology. Ferrimagnetic materials offer a rich platform to explore not only the damping of the ferromagnetic mode, but also the damping of the high-frequency exchange mode very promising for ultrafast devices. Here we use time-resolved magneto-optical Kerr effect to investigate the ferromagnetic and exchange resonance modes and their damping in the bismuth-doped gadolinium iron garnet over a broad range of magnetic fields (0--10 T) and temperatures (50--300 K) including the magnetization and angular compensation points. These two resonance modes are excited via the inverse Faraday effect and unambiguously identified by their distinct frequency dependence on temperature and magnetic field. The temperature-dependent measurements in the external magnetic field ${H}_{\mathrm{ext}}=2\phantom{\rule{0.16em}{0ex}}\mathrm{T}$ revealed that the intrinsic damping of the ferromagnetic mode is always smaller than the one of the exchange modes and both have a maximum near the angular compensation point. These results are fully consistent with recent predictions of atomistic simulations and a theory based on two-sublattice Landau-Lifshitz-Bloch equation. We also demonstrate that the damping of these modes varies differently as a function of ${H}_{\mathrm{ext}}$. We explain the observed behaviors by considering the different features of the effective fields defining the precession frequencies of the ferromagnetic and exchange modes.

Domain-wall motion driven by a rotating field in a ferrimagnet

We theoretically study a ferrimagnetic domain-wall motion driven by a rotating magnetic field. We find that, depending on the magnitude and the frequency of the rotating field, the dynamics of a ferrimagnetic domain wall can be classified into two regimes. First, when the frequency is lower than a certain critical frequency set by the field magnitude, there is a stationary solution for the domain-wall dynamics, where a domain-wall in-plane magnetization rotates in-phase with the external field. The field-induced precession of the domain wall gives rise to the translational motion of the domain wall via the gyrotropic coupling between the domain-wall angle and position. In this so-called phase-locking regime, a domain-wall velocity increases as the frequency increases. Second, when the frequency exceeds the critical frequency, a domain-wall angle precession is not synchronous with the applied field. In this phase-unlocking regime, a domain wall velocity decreases as the frequency increases. Moreover, the direction of the domain-wall motion is found to be reversed across the angular compensation point where the net spin density of the ferrimagnet changes its sign. Our work suggests that the dynamics of magnetic solitons under time-varying biases may serve as platform to study critical phenomena.

Domain wall dynamics in antiferromagnetically coupled double-lattice systems

In ferromagnetic materials, the rich dynamics of magnetic domain walls (DWs) under magnetic field or current have been successfully described using the well-known q-{\phi} analytical model. We demonstrate here that this simple unidimensional model holds for multiple-sublattice materials such as ferrimagnetic alloys or synthetic antiferromagnets (SAF) by using effective parameters, and is in excellent agreement with double-lattice micromagnetic simulations. We obtain analytical laws for the DW velocity and internal precession angle as a function of net magnetisation for different driving forces (magnetic field, spin transfer and spin-orbit torques) and different propagation regimes in ferrimagnetic alloys and SAFs. The model predicts that several distinctive dynamical features occur near or at the magnetic and the angular compensation points when the net magnetization or the net angular momentum of the system vanishes, and we discuss the experimental observations that have been reported for some of them. Using a higher degree-of-freedom analytical model that accounts for inter-sublattice distortions, we give analytical expressions for these distortions that agree with the micromagnetic simulations. This model shows that the DW velocity and precession rate are independent of the strength of the inter-sublattice exchange coupling, and justifies the use of the simpler effective parameters model.

Real-time target alignment system for high-power high-repetition rate laser operations using a five degree-of-freedom hybrid mechanism

This paper presents a real-time position control solution for the targets used in the high-repetition rate laser operations of high-power laser facilities. The control system is designed based on an Abbe-compliant, in-process position measurement system of targets, employing a plane mirror interferometer and a five degree-of-freedom hybrid mechanism. An error model is developed to characterise the position feedback information of target for a high-repetition rate process to determine the effects of the non-collocation of the sensor’s measurement point and target on the control system’s performance – a challenge for the real-time position control of targets. Behaviour of the control system is investigated with the error model and experimental data. It is found that a controller’s position compensation scheme can be ineffective due to the erroneous position feedback as a result of the non-linear position information associated with the non-collocated measurement point and the actual target. To solve the problem, an angular compensation technique is proposed.

Measurement of the tilt of a moving domain wall shows precession-free dynamics in compensated ferrimagnets

One fundamental obstacle to efficient ferromagnetic spintronics is magnetic precession, which intrinsically limits the dynamics of magnetic textures. We experimentally demonstrate that this precession vanishes when the net angular momentum is compensated in domain walls driven by spin–orbit torque in a ferrimagnetic GdFeCo/Pt track. We use transverse in-plane fields to provide a robust and parameter-free measurement of the domain wall internal magnetisation angle, demonstrating that, at the angular compensation, the DW tilt is zero, and thus the magnetic precession that caused it is suppressed. Our results highlight the mechanism of faster and more efficient dynamics in materials with multiple spin lattices and vanishing net angular momentum, promising for high-speed, low-power spintronic applications.

Multi-Angle Liquid Flow Measurement Using Ultrasonic Linear Array Transducer.

Most ultrasonic flowmeters utilize several wedge sensors for transmission and reception. Thus, the location and alignment of the sensors are critical factors that determine the performance of the ultrasonic flowmeter. In this study, we proposed an ultrasound liquid flowmeter utilizing a 128-element linear array transducer with a transmit delay control for varying the incidence angles of ultrasound wave transmission. The performance of the flowmeter was evaluated at flow rates of 0–50 L/min in a specially designed pipe system. Flow estimation was performed with the transit-time method using cross-correlation with phase zero-crossing for sub-sample estimation. While a single plane wave approach performed invasive electromagnetic measurements with only 74% accuracy as a reference, a multiple angular compensation method with 24 angles was proposed to increase the accuracy of measurements up to 93%. This study demonstrated the capability of the non-invasive single-sided ultrasonic flowmeter with a linear array transducer for liquid flow measurements in the metal pipe system.

Current driven domain wall dynamics in ferrimagnetic strips explained by means of a two interacting sublattices model

The current-driven domain wall dynamics along ferrimagnetic elements are here theoretically analyzed as a function of temperature by means of micromagnetic simulations and a one dimensional model. Contrarily to conventional effective approaches, our model takes into account the two coupled ferromagnetic sublattices forming the ferrimagnetic element. Although the model is suitable for elements with asymmetric exchange interaction and spin-orbit coupling effects due to adjacent heavy metal layers, we here focus our attention on the case of single-layer ferrimagnetic strips where domain walls adopt achiral Bloch configurations at rest. Such domain walls can be driven by either out-of-plane fields or spin transfer torques upon bulk current injection. Our results indicate that the domain wall velocity is optimized at the angular compensation temperature for both field-driven and current-driven cases. Our advanced models allow us to infer that the precession of the internal domain wall moments is suppressed at such compensation temperature, and they will be useful to interpret state-of-the art experiments on these elements.

An Angular Position-Based Two-Stage Friction Modeling and Compensation Method for RV Transmission System

An Angular Position-Based Two-Stage Friction Modeling and Compensation Method for RV Transmission System

Angular glint compensation for seekers based on multicarrier techniques

To solve the problem caused by angular glint in the terminal guidance process, which effects steady target tracking and results in the final miss, the influence of angular glint on the seeker's angle tracking and angular glint compensation methodology using multiple output angle error equation with different detection frequencies at single sensing period to extract the unknown parameters of the target model based on the orthogonal multicarrier technique is proposed here. The method is verified reasonable and feasible through the simulation analysis, the analysis result can be applied to improve the tracking precision of the seeker's terminal guidance process.

Research on Instability Boundaries of Control Force for Trajectory Correction Projectiles

The balance of stability and maneuverability is the foundation of the trajectory correction projectile. For the terminal correction projectile without an attitude feedback loop, a larger control force is expected which may cause an instability. This paper proposes a novel method to derive instability boundaries for the control force magnitude. No additional coordinate system is needed in this method. By introducing the concept of angular compensation matrix, the exterior ballistic linearized equations considering control force are established. The necessary prerequisite for a stable flight under control is given by the Routh stability criterion. The instability boundaries for the control force magnitude are derived. The results of example flights are 13.5% more accurate compared with that in relevant research. Numerical simulations demonstrate that if the control force magnitude lies in the unstable scope derived in this paper, the projectile loses its stability. Furthermore, the effects of the projectile pitch, velocity, and roll rate on flight stability during correction are investigated using the proposed instability boundaries.

一种机载红外光谱相机的角位置误差补偿技术

一种机载红外光谱相机的角位置误差补偿技术

Broadband and omnidirectional light harvesting enhancement in photovoltaic devices with aperiodic TiO2 nanotube photonic crystal

Design of more effective broadband light-trapping elements to improve the light harvesting efficiency under both normal and tilted light for solar cells and other photonic devices is highly desirable. Herein we present a theoretical analysis on the optical properties of a novel TiO2 nanotube aperiodic photonic crystal (NT APC) following an aperiodic sequences and its photocurrent enhancement effect for dye-sensitized solar cells (DSSCs) under various incidence angles. It is found that, compared to regular PC, the designed TiO2 NT APC owns broader reflection region and a desired omnidirectional reflection (ODR) bandgaps, leading to considerable and stable photocurrent enhancement under both normal and oblique light. The effects of the structural parameters of the TiO2 NT APC, including the average lattice constant and the common sequence difference, on the optical properties, ODR bandgaps and absorption magnification of the integrated DSSCs are investigated in detail. Moreover, the angular dependence of photocurrent enhancement and angular compensation effect of such TiO2 NT APCs are also provided to offer a guidance on the optimum structural parameters design under different engineering application conditions.

Photo-Robotic Positioning for Integrated Optics

High positioning accuracy is a crucial need to perform successfully complex tasks such as micromanipulation and microassembly. This especially enables to provide high performances or to propose new functionalities/products, notably for integrated optical devices. The objective of the letter is to align two optical structures in multi-DOF way with very high accuracy. The originality of the approach relies on robotic positioning associated with the use of interfered reflected light irradiance as a feedback signal rather than transmitted power. Fabry–Perot interference principle is especially used to provide a fast and high accurate measurement. An opto-mechanical model that relates the optical component poses with the interfered reflected light is proposed. Experimental results are investigated based on a robotic multi-DOF platform, used to relatively align an optical component to an optical fiber. The obtained results establish that the model fits with experiments with a standard deviation below $0.0281^{\circ }$ . This model associated with an automated positioning strategy shows that it is possible to maximize reflectivity within less than 6 s, including multi-DOF angular misalignments identification and compensation.

다중 좌표계간 각도오차 보정을 통한 체계정렬 기법

ABSTRACT MRDS is a short range missile/rocket defense system which protects a main battle tank(MBT) from threats in a short range. It is composed of 2 radars, 2 infrared trackers(IRTs), 1 fire control computer(FCC), 2 launchers and countermeasures. To guarantee the performance of the MRDS, these components have to be mounted on the vehicle with the known positions and directions and it is required to compensate the alignment errors. In this paper, a system alignment method using angular error compensation is proposed to install its components within a tolerance on the MBT. The test results are presented to evaluate and verify the effectiveness of the proposed method.Key Words : System Alignment(체계정렬), MRDS(미사일/로켓 방어체계) 1. 서 론 능동파괴체계(Hard-Kill System)는 근거리 미사일/로켓 방어체계로서 전차에 탑재되어 위협체를 탐지․추적하고 대응탄을 발사하여 무력화시키는 것을 목적으로 하며, 탐지․추적센서인 탐지추적레이더와 열상추적기(IRT : InfraRed Tracker), 위협판단 및 대응을 통제하는 사격통제컴퓨터, 대응수단인 발사장치와 대응 * Corresponding author, E-mail: jsha@add.re.krCopyright ⓒ The Korea Institute of Military Science and Technology탄으로 구성된다

Real-Time Angular Sensitivity Compensation of Guided-Mode Resonance Filter

Guided-mode resonant filters (GMRFs) are promising narrowband filters with high peak efficiency, but their practical applications have been restricted by their natural high angular sensitivity. We investigated the influence of incident angle and azimuthal angle on the spectral response of GMRF, and found that the resonant peaks are mainly influenced by the incident angle. A polymer-dispersed liquid crystal layer was introduced to compensate the shift of resonant wavelength through applying proper voltage in real time, and numerical results show that a large angular compensation range of about ±4.2° can be obtained while maintaining high performance of the spectral response.

Position Sensorless Control of PMSG in Wind Energy Conversion System

This paper presents a position sensorless operating method in WECS (Wind Energy Conversion System) based on PMSG (Permanent Magnet Synchronous Generator). A position sensorless operating method for direct-drive PMSG using sliding mode observer is proposed. With this method, position angles can be estimated only by measuring phase voltages and currents. By analyzing the cause of angle error, which increases when the PMSG is operating at high speed, a new dynamic angular compensation solution is developed. This method proves to be effective and necessary by experiments based on simulink.

Dynamic space shaping of intense ultrashort laser light with blazed-type gratings

A beam shaper for dynamic transversal shaping of broadband laser pulses that utilizes a blazed ruled grating and a blazed-type grating simulated on Spatial Light Modulator was demonstrated. The introduced shaper scheme is an extension of 2f-2f scheme [Mariyenko, et al., Opt. Express 13, 7599 (2005)] where the two thin holograms with matched grating constants performed light shaping. The new scheme utilizes the diffraction gratings with different grating constants. Dispersion-free light shaping is achieved by means of the intermediate transversal light beam magnification. The magnification balances the mismatch in the grating constants resulting in total residual angular dispersion compensation. In turn, the magnified beam covers a greater area on the modulator matrix thus reducing the incident light power density by a value equal to square of the magnification factor. It translates to the safe-operation threshold extension of the modulator allowing shaping pulses that are powerful enough to be used in the applications. With a proper components selection, the throughput efficiency of the shaper can be well above 40%. A proper shaper operation was demonstrated with the 140-fs Ti:Sapphire oscillator. Theoretical calculations support the conclusions.