Phase Compensation Research Articles

Adaptive super-twisting sliding mode observer based positionless direct torque control strategy for PMSM

ABSTRACT A novel rotor position estimation technique utilising the super-twisting sliding mode observer (STSMO) was introduced to address diminishing reliability in position sensors of permanent magnet synchronous motors (PMSMs). A cutting-edge direct torque control (DTC) strategy for PMSM functioning without reliance on a position sensor was proposed to address the challenges of increased chattering and limited perturbation resistance resulting from fixed sliding mode parameters in standard STSMOs. This strategy employed an adaptive super-twisting sliding mode observer (ASTSMO). This method enhanced the system’s response speed and estimation accuracy by facilitating online adjustment of sliding mode coefficients. A rigorous stability analysis of the observer was presented. A hyperbolic tangent function of the segmented square root was introduced as a substitute for the conventional sign function to mitigate chattering and eliminate the need for low-pass filters and phase compensation. This approach simplified the system’s complexity while improving angle estimation accuracy, response speed, and observer stability. Additionally, a phase-locked loop (PLL) was used to estimate the rotor angle, which improved the accuracy of the rotor angle estimation. Comprehensive simulations and experimental validations demonstrated that the proposed ASTSMO could suppress system’s chattering under varying operational conditions, exhibiting superior estimation accuracy and stability compared to the traditional STSMO.

A metal-only transmission metasurface with dual-layer configuration for generation of orbital angular momentum wave

In this paper, we present a metal-only transmission metasurface adopting dual-layer elements with I-shaped grooves etched on each layer, which is designed for orbital angular momentum (OAM) generation. The special arrangement of the grooves on the elements results in a wider phase compensation range, and by varying the length of the grooves, a full 360° phase coverage with a transmission amplitude of more than −2 dB can be achieved at 10 GHz. As a proof of concept, a metal-only transmission metasurface composed of 400 elements is designed, fabricated, and measured. The simulated and measured results suggest that the OAM transmitted waves with the mode l = −1 can be efficiently generated by a double-layer metal-only metasurface at around 10 GHz. Compared with conventional configurations of OAM transmitted beam generation, this configuration has great potential for high power microwave and space environment applications.

Terahertz programmable metasurface based on solid-state plasma

Terahertz modulation technology based on programmable metasurfaces can respond in real time to external signals or environmental changes, enabling flexible and adaptive control of terahertz waves. This technology demonstrates significant potential and importance across various fields, including communication, imaging, scientific research, security monitoring, and industrial applications. This paper proposes a terahertz programmable metasurface based on solid-state plasma, utilizing solid-state plasma devices to achieve dynamic control of properties such as the amplitude and phase of terahertz waves. Compared to traditional silicon-based devices, GaAs/AlGaAs heterostructures enhance both the forward current and solid-state plasma concentration of the metasurface devices by two orders of magnitude, with carrier concentrations exceeding 1019 cm−3. Additionally, we designed a solid-state plasma metasurface containing 12×12 supercells, achieving dynamic modulation of terahertz waves in the elevation direction through different coding schemes. Furthermore, this paper explores the stealth control mechanism of solid-state plasma metasurfaces, achieving effective cloaking of detection targets through specific phase compensation.

Critical, compensation and hysteresis behaviors studies in the ferrimagnetic Blume-Capel model with mixed half-integer spin-(3/2, 7/2): Exact recursion relations calculations

The exact recursion relations are used to study the mixed half-integer spin-(3/2, 7/2) Blume-Capel Ising ferrimagnetic system on the Bethe lattice. Ground-state phase diagrams are computed in the (DA /q|J|, DB /q|J|) plane to reveal different possible ground states of the model. Using the thermal changes of the order-arameters, interesting temperature dependent phase diagrams are constructed in the (DA/|J|, kT/|J|), (DB/|J|, kT/|J|) planes as well as in the (D/|J|, kT/|J|) plane where D = DA = DB. It is revealed that the system exhibits first- and second-order phase transitions and compensation temperatures for specific model parameter values. Under the constraint of an external magnetic field, the model also produces multi-hysteresis behaviors as single, double and triple hysteresis cycles. Particularly, the impacts of the ferrimagnetic coupling J on the remanent magnetization and the coercitive fields for selected values of the other physical parameters of the system are pointed out. Our numerical results are qualitatively consistent with those reported in the literature.

Underwater Laguerre-Gaussian beam propagation and phase compensation method

Laguerre-Gaussian (LG) beams experience phase twist after long-distance transmission, making the orbital angular momentum (OAM) indistinguishable. This phenomenon becomes more severe in water due to the higher refractive index. Based on the physical principles of LG beams, this paper derives the mathematical expression for LG beam transmission in water to address this issue. It organizes and analyses the physical significance of each term. The exponential term responsible for phase twist is separated and phase compensation is applied to the initial LG beam. Simulation results show that after transmission through water, traditional LG beams exhibit a clockwise twisted distribution of isophase lines. By applying the phase compensation method proposed in this paper, the phase of the initial LG beam is modulated and when the LG beam reaches the observation plane, the isophase lines become straight, verifying the effectiveness of the method. This compensation method holds significant value for LG beams in advanced physics research.

Detecting flying objects in synthetic aperture radar images using Moving Target Indicator methods

AbstractThe growing proliferation of synthetic aperture radar (SAR) sensors brings the tantalising prospect of extending their utility into ‘novel’ applications. One potential extension is the detection of fast moving and accelerating flying objects in SAR imagery. However, since SAR image formation typically assumes the scene to be static over the coherent processing interval, moving objects give rise to blurred point spread functions, significant range migration and even potential aliasing of target signatures. The result is reduced target to clutter ratio (TCR) and poor detection performance. Successful detection of airborne targets thus requires compensation for potentially large target acceleration and velocity values observed over the comparatively long dwell times typical of practical SAR collection paradigms. This paper considers this problem and presents two main ideas to achieve this goal: a carefully constructed Moving Target Indicator (MTI) detection method implemented using real‐world Ingara SAR data, and a theoretical ground clutter suppression method. The MTI detection method combines several well‐known techniques for the flying target detection problem: interferometric processing, clutter suppression, and autofocus, and provides an extended acceleration phase compensation technique for highly accelerating targets such as planes. This proposed processing pipeline has been applied to experimental data of a plane during take off (a challenging Doppler unambiguous moving target), with the goal of continued detecting and tracking of this target. A generalised SAR signal model is presented that parameterises a flying moving target signature in terms of range and azimuthal target velocities and accelerations. Data driven approaches for estimating these motion parameters are examined and applied to experimental data acquired with the Ingara SAR sensor. The detection method was found to improve TCR by around 6 dB, along with superior detection and tracking performance. Following this, a theoretical study into suppressing ground clutter via multi‐channel cross‐track interferometry is investigated. Three separate ground clutter suppression methods, coherent subtraction, conventional beamforming, and minimum variance distortionless response (MVDR) beamformer, are presented then analysed using stochastic simulations. The MVDR adaptive beamformer method was found to provide the best performance for the scenario simulated.

Low‐frequency oscillation damping strategy for power system based on virtual dual‐input power system stabilizer

AbstractTo keep pace with the construction of the new‐type power system, virtual synchronous generator control, as a classical method of virtual inertia control, has been widely adopted due to its electromechanical characteristics similar to synchronous generator. However, the introduction of rotor motion equations leads to low‐frequency oscillation issues in virtual synchronous generator units similar to synchronous machines. To address this challenge, this paper constructs the Phillips‐Heffron model of the virtual synchronous generator grid‐connected system and analyses the mechanism of low‐frequency oscillation in virtual synchronous generator through the damping torque method. Subsequently, a virtual dual‐input power system stabilizer is proposed by drawing inspiration from the design principles of the traditional dual‐input power system stabilizer to suppress low‐frequency oscillations in the power system. The structure of the virtual dual‐input power system stabilizer is provided, and the phase compensation method is used to optimize the parameters of the virtual dual‐input power system stabilizer. Finally, the effectiveness of the proposed virtual dual‐input power system stabilizer is verified by simulation comparison.

A 1-bit passive reconfigurable metasurface for wide-angle scanning and broad-beam reflection

ABSTRACT A reconfigurable reflective metasurface design is proposed in this letter, allowing for beam scanning capabilities. This paper integrates a tunable capacitor into the metasurface unit. This paper integrates a tunable capacitor into the metasurface unit. The resonant characteristics of the metasurface unit are controlled by the tunable capacitor, which can be adjusted by changing the rotation angle of the metal plate on the tunable capacitor. By rotating the metal plate of the capacitor, it achieves state 1 at maximum capacitance and state 0 at minimum capacitance, resulting in a phase difference of 180° ± 20° between the states, thereby enabling 1-bit phase control. Leveraging the principle of phase compensation, the phase distribution of the array is designed to exhibit directional radiation characteristics. A reflective metasurface composed of a 20 × 20-element array is designed and simulated with these characteristics. The simulation results indicate that the scanning angle of the array-reflected beam can reach ± 50°, with a peak gain exceeding 14.6 dBi, an average gain of 13.8 dBi, and a gain loss of 1.5 dB. The beam’s 3 dB beamwidth exceeds 15°, enabling broader coverage. Joint simulations in typical indoor scenarios confirm the improved signal strength, highlighting the array’s versatility. This design allows the reflective array to function as a passive reflector relay, effectively improving signal coverage in indoor NLOS.

Detection of Flight Target via Multistatic Radar Based on Geosynchronous Orbit Satellite Irradiation

As a special microwave detection system, multistatic radar has obvious advantages in covert operation, anti-jamming, and anti-stealth due to its configuration of spatial diversity. As a high-orbit irradiation source, a geosynchronous orbit satellite (GEO) has the advantages of a low revisit period, large beam coverage area, and stable power of ground beam compared with traditional passive radar irradiation sources. This paper focuses on the key technologies of flight target detection in multistatic radar based on geosynchronous orbit satellite irradiation with one transmitter and multiple receivers. We carry out the following work: Firstly, we aim to address the problems of low signal-to-noise ratio (SNR) and range cell migration of high-speed cruise targets. The Radon–Fourier transform constant false alarm rate detector-range cell migration correction (RFT-CFAR-RCMC) is adopted to realize the coherent integration of echoes with range cell migration correction (RCM) and Doppler phase compensation. It significantly improves the SNR. Furthermore, we utilize the staggered PRF to solve the ambiguity and obtain multi-view data. Secondly, based on the aforementioned target multi-view detection data, the linear least square (LLS) multistatic positioning method combining bistatic range positioning (BR) and time difference of arrival positioning (TDOA) is used, which constructs the BR and TDOA measurement equations and linearizes by mathematical transformation. The measurement equations are solved by the LLS method, and the target positioning and velocity inversion are realized by the fusion of multistatic data. Finally, using target positioning data as observation values of radar, the Kalman filter (KF) is used to achieve flight trajectory tracking. Numerical simulation verifies the effectiveness of the proposed process.

Ancillary Services to Mitigate Non-linear and Unbalanced Load Based on CPT Using a DFIG Power Plant

The increase of renewable energy sources and non-linear loads on the utility grid introduces challenges in maintaining the nominal conditions of the utility grid. A viable approach to addressing some of these challenges is to utilize renewable energy conversion systems that accomplish supplementary functions in addition to supplying active power. This paper presents the implementation of ancillary services to mitigate non-linear and unbalanced loads using a single Doubly Fed Induction Generation (DFIG) power plant. For this, the Conservative Power Theory (CPT) is used to provide three types of services simultaneously: active filtering, reactive power compensation, and unbalanced phase compensation. A back-to-back converter is used to control the power flow in the DFIG and employ ancillary services. Two control strategies are compared: in the dq reference frame and the $\alpha \beta$ reference frame. Simulations in MatLab/Simulink are used to evaluate the response of the CPT and the control strategies. The ancillary services performance is analyzed using the indicator based on standards and CPT factor. The results show that the indicators comply with the standards depending on the active power supply. Moreover, $\alpha\beta$ reference frame exhibits better performance than $dq$ reference frame.

A novel approach to simulate moving targets in automotive radar applications

AbstractIn the field of automotive radar testing, radar target simulators (RTS) based on fibre delay technology are limited by production processes, typically achieving distance steps of only 1 cm. Meanwhile, simulators utilising digital DRFM (Digital Radio Frequency Memory) technology face similar constraints, with a minimum distance step size of 3 cm, dictated by the ADC sampling rate (corresponding to a sampling rate of 5 GHz). In both types of simulators, abrupt changes in target distance result in phase discontinuities due to the step size being greater than the wavelength, ultimately distorting the target velocity spectrum. This paper proposes a phase compensation method based on instantaneous frequency measurement for a digital DRFM simulator, which ensures the continuity of the phase in the RTS output signal, achieving an ideal simulation of the target velocity spectrum. Additionally, it enables millimetre‐level distance stepping.

Improved abdominal T1 weighted imaging at 0.55T.

Breath-held fat-suppressed volumetric T1-weighted MRI is an important and widely-used technique for evaluating the abdomen. Both fat-saturation and Dixon-based fat-suppression methods are used at conventional field strengths; however, both have challenges at lower field strengths (<1.5T) due to insufficient fat suppression and/or inadequate resolution. Specifically, at lower field strengths, fat saturation often fails due to the short T1 of lipid; and Cartesian Dixon imaging provides poor spatial resolution due to the need for a long ΔTE, due to the smaller Δf between water and lipid. The purpose of this work is to demonstrate a new approach capable of simultaneously achieving excellent fat suppression and high spatial resolution on a 0.55T whole-body system. We applied 3D stack-of-spirals Dixon imaging at 0.55T, with compensation of concomitant field phase during reconstruction. The spiral readouts make efficient use of the requisite ΔTE. We compared this with 3D Cartesian Dixon imaging. Experiments were performed in 2 healthy and 10 elevated liver fat volunteers. Stack-of-spirals Dixon imaging at 0.55T makes excellent use of the required ΔTE, provided high SNR efficiency and finer spatial resolution (1.7 × 1.7 × 5 mm3) compared Cartesian Dixon (3.5 × 3.5 × 5 mm3), within a 17-s breath-hold. We observed successful fat suppression, and improved definition of structures such as the liver, kidneys, and bowel. We demonstrate that high-resolution single breath-hold volumetric abdominal T1-weighted imaging is feasible at 0.55T using spiral sampling and concomitant field correction. This is an attractive alternative to existing Cartesian-based methods, as it simultaneously provides high-resolution and excellent fat-suppression.

A 43.5dB Gain Unipolar a-IGZO TFT Amplifier with Parallel Bootstrap Capacitor for Bio-signals Sensing Applications.

In this paper, a high gain amplifier with phase compensation loop is presented. A structure of parallel gate cross-coupled transistors to both ends of differential pair drain and source is designed to improves the load impedance, which obtains sufficient gain and further reduces power consumption. A novel capacitor bootstrap load circuit is proposed. The capacitor bootstrap topology is constructed by the drain source resistance of the transistor working in the cut-off region, where the gate source parasitic capacitor of the transistor is in parallel with the bootstrap capacitor rather than the existing series structure, thereby only a small bootstrap capacitor is required. By avoiding the use of large capacitors, chip area can be effectively reduced without compromising performance such as gain and bandwidth. The amplifier is fabricated using 10-μm n-type a-IGZO TFT technology. Measurement results show that the proposed amplifier achieves a voltage gain of 43.5dB and a common mode rejection ratio of 61.2dB while maintaining low power consumption. The amplifier also exhibits a -3dB bandwidth covering 0.4~2.1KHz, encompassing major bioelectric frequency bands. A real-time ECG signal was successfully captured using the fabricated TFT amplifier and gel electrodes. It has great potential in flexible sensing and acquisition applications such as electro cardiogram (ECG), electro encephalogram (EEG), pulse detection, and other wearable applications.

A Wideband High Gain Transmit‐Array Antenna Exploiting Polarization‐Rotated Metasurface Cell

ABSTRACTA novel polarization‐insensitive transmit‐array (TA) antenna using linear polarization‐rotated (PR) metasurface (MS) unit cells has been proposed in this article. Firstly, we design a wideband polarization‐insensitive polarization‐rotated MS unit cell. The MS cell can provide high transmission for incident linear polarized waves with polarization rotation by 90°. Then, we investigate the stability of the MS cell under the oblique incident wave. The proposed MS cell keeps a stable response under oblique incident wave over ± 30°. To verify the excellent performance of the proposed MS. We design a high‐gain TA antenna consisting of a standard feed horn and an aperture with a gradient phase. The gradient phase compensation is provided by varying the geometric dimension of the proposed MS. The obtained TA antenna works in a wide band with high gain. We fabricated the aperture and set up a prototype of TA antenna to verify our work. We measure the TA antenna and the results show a wide operating band from 14.2 to 18 GHz with a pick gain of 23.9 dBi. The favorable performance of the TA antenna is a good candidate in satellite systems and long‐distance satellite system. Furthermore, the angular stability of the MS cell is also verified by realizing the beam scanning performance. An over ± 30° scan range is obtained. Good beam scanning can be used in radar detection and expand signal coverage.

Two-tone RF signal phase drift measurement system

Modern electronic circuits designed for various applications, such as telecommunications, radar systems, and high-energy physics experiments, require increasing performance of RF signal phase (propagation delay) drift in the signal chain reaching millidegree (or femtosecond) stability levels at hundreds of MHz or GHz frequencies. Therefore, long-term phase change measurements are getting difficult and sensitive to effects rarely considered in earlier designs. Consequently, new and more precise techniques for phase drift measurements and compensation must be developed.This paper presents the concept of a novel RF signal phase drift measurement system based on a unique two-tone approach to accurately measure the phase drift, providing an improved alternative to traditional measurement methods. The idea can be used in systems with digital signal processing of measurement signals. An auxiliary (2nd tone) signal is introduced in the RF chain to allow for extracting phase changes introduced by the system components.The principles of the system are explained, including mathematical basics. Next, a detailed description of a sample system, illustrating how the concept can be practically implemented, is presented. The measured test system achieved a temperature coefficient of a signal propagation delay of just 0.67 fs/°C @ RF frequency of 162.5 MHz. The paper concludes by discussing the system’s performance and highlighting its strengths and limitations. Furthermore, the authors outlined plans for future research and potential improvements to the system.

Single to multiple digital holograms for phase compensation and defect detection

Digital holography enables quantitative phase imaging based on interference. A digital hologram often encodes the phase information along with aberrations or deformations. This article reviews phase analysis and its diverse application solutions and challenges in digital holography including aberrations removal in a single hologram, defect and deformation detection using dual-holograms, and defect location in multi-holograms. The state-of-the-art of the techniques are presented and discussed in detail for phase analysis, separation, and quantification. Phase analysis in digital holography can provide high precision, high resolution, rapid quantitative and intelligent imaging abilities.

Miniaturized on-chip optical differentiator based on 2F-structured metasurfaces.

Analog optical computing based on Fourier optics has attracted ever-growing attention, offering unprecedented low power consumption and high parallelism computation at the speed of light. Typically, classical optical 4F systems have been widely employed as one of the most common approaches for analog optical computing. However, most existing schemes replicate the original architecture relying on two Fourier transforms and one spatial-frequency filtering, resulting in bulky size and complex structure. Here, we propose a novel, to the best of our knowledge, on-chip 2F structure that achieves ultra-miniaturized optical analog computing. Taking advantage of the exceptional design flexibility of metasurfaces, we reduce the optical path length through a combination of phase compensation and complex amplitude modulation, thereby significantly simplifying the system structure without sacrificing accuracy compared to the traditional 4F system. As a proof-of-concept demonstration, we design and fabricate an on-chip optical differentiator on a silicon-on-insulator platform, achieving 84.01% and 79.81% differentiation accuracy in simulation and experiment, respectively.

Design and optimisation of a two-stage amplifier based on a differential input stage and a common-source amplifier

Abstract. Since the emergence of integrated circuits, through the circuit structure, the production process of continuous iterative updating, so that its used in various types of electronic equipment more and more widely. Currently, operational amplifier circuits play an extremely important role in signal processing and communication systems. Amplifiers have different characteristics depending on the needs of different electronic devices. This thesis addresses the optimisation and design of the characteristics of the two-stages amplifier. Firstly, several classical amplifier structures are analysed. Select the appropriate structure and combine it into a two-stages amplifier. Simulation is carried out on cadence software and later the simulation results are analysed before parameter optimisation. On this basis, a two-stages amplifier based on a PMOS differential input stage with a common-source amplifier has been designed. It also improves the amplifier's gain, frequency range, gain bandwidth, and other performance metrics. Using PMOS self-bias circuit to improve power supply stability. Finally, based on the development hotspots of integrated circuits, the possibility of circuit optimization was analyzed. Discussions were conducted on negative feedback circuits, phase compensation methods, and other aspects.

Realization of multi-transverse-mode squeezed optical frequency combs with Gouy phase compensation

Multimode quantum light fields significantly enhance quantum state manipulation and communication capabilities by expanding the dimensionality of the Hilbert space. In this work, we elaborately design a non-horizontal cavity suitable for a Gouy phase-compensated synchronously pumped optical parametric oscillator. By injecting an optical frequency comb in HG10 mode into the cavity as the seed, we demonstrate the simultaneous generation of a bright squeezed optical frequency comb in HG10 mode and a vacuum squeezed optical frequency comb in HG01 mode. The coexistence of amplitude quadrature squeezed fields in these two orthogonal first-order Hermite-Gaussian transverse modes also suggest the presence of quadrature entanglement between the two first-order Laguerre-Gaussian modes, LG0 + 1 and LG0 - 1. This research underscores the capability of one-step generation of multi-transverse-mode squeezed optical frequency combs using a single cavity, marking a significant stride in the realm of quantum optics.

Limitations of beam-control compensation

In this paper, we use wave-optics simulations to explore the limitations of beam-control compensation. We evaluate performance in terms of the normalized power in a diffraction-limited bucket for the cases of no beam-control compensation, perfect phase compensation, and perfect full-field compensation. From these results, we are able to arrive at the following conclusions: (1) without any form of beam-control compensation, performance begins to degrade when D/r0 &gt; 1; (2) with perfect phase compensation, performance begins to degrade when D/r0 &gt; 1 and (λ/r0)/θ0 &gt; 1; and (3) with perfect full-field compensation, performance begins to degrade when D/r0 &gt; 1 and (λ/D)/θ0 &gt; 1. Here, D is the aperture diameter, r0 is the Fried parameter, λ is the wavelength, and θ0 is the isoplanatic angle. We show (1)–(3) to be true for varying aperture diameters, uniformly distributed turbulence, and varying turbulence profiles. These findings will inform the development of future laser systems that need to sense and correct for the effects of atmospheric turbulence.