Amplitude Errors Research Articles

Hybrid phase-correction metasurfaces for accurate near-field manipulation

Although metasurface has attracted significant attention in recent years due to its ability to manipulate electromagnetic waves, discrepancies are often observed when comparing the designed and realized near-field performances. Among various contributing factors, one important issue is related to the fact that the elements arranged on a metasurface are typically designed under the assumption of normal incident excitation, whereas in practice they are actually excited at various oblique incidence angles depending on the element's relative position to the feed antenna. This introduces amplitude and phase errors in the reflection or transmission coefficients of the elements within the metasurface, thereby affecting its overall performance. In this paper, a hybrid phase-correction method is proposed to compensate for the effect of oblique incidence on metasurfaces. The actual oblique incidence angles are decomposed into elevation and azimuth directions: In the elevation direction, the element characteristics under oblique incidence replace those under normal incidence, while in the azimuth direction, element rotation is introduced to compensate for the local effects. Near-field focusing and holographic metasurfaces are designed to verify the proposed hybrid phase-correction method. Full-wave electromagnetic simulations show that the proposed metasurface has the advantage in sidelobe levels without significant costs in terms of the amount of element-level computations. Finally, the near-field focusing metasurfaces are fabricated, and the measured results further demonstrate the potential of the proposed design for accurate near-field manipulation.

Dual-wavelength synchronous control method for liquid crystal optical phased array

The liquid crystal optical phased array (LCOPA), as a key beam steering device, has gained increasing significance in the field of space laser communication. With the rapid advancement of space laser communication technology, the demand for precise synchronous control of multi-wavelength beams has significantly increased, particularly in ensuring reliable communication links through synchronized control of signal and beacon beams. The signal beam is primarily utilized for data transmission, while the beacon beam is responsible for path calibration and real-time tracking. However, due to the limitations of natural dispersion effects, conventional LCOPA control methods struggle to achieve synchronized manipulation of beams at different wavelengths, resulting in error accumulation and response delays in communication links, thereby compromising the accuracy and efficiency of information transmission. To address this challenge, this study proposes and validates a dual-wavelength synchronous control method based on LCOPA. The method establishes a phase optimization principle centered on minimizing the least-squares error of complex amplitudes and expands the phase modulation capability of LCOPA hardware, thereby overcoming the natural dispersion governed by the grating equation. Simulation and experimental results demonstrate that this method achieves exceptionally high beam pointing accuracy, meeting the demands of high-precision information transmission in multi-wavelength laser communication. This study provides an innovative technical pathway for the application of LCOPA in multi-wavelength laser communication and establishes a solid theoretical foundation for future experimental research on multi-wavelength control.

Dynamic displacement measurement of a wind turbine tower using accelerometers: tilt error compensation and validation

Abstract. For vibration-based structural health monitoring (SHM) of wind turbine support structures, accelerometers are often used. Besides the structural acceleration, the measured quantity also contains the acceleration component due to gravity, which is known as tilt error. This tilt error must be quantified and taken into account; otherwise it can lead to incorrect evaluations, especially in the fatigue estimation or the dynamic displacement estimation using accelerometers. The standard solution is to explicitly measure the tilt angle, which requires an additional sensor for each measurement point and is not applicable for already recorded measurements without tilt information. Therefore, a novel tilt error compensation method is presented by using the static bending line. As a result the influence of the tilt error can be estimated in advance, and no additional sensors for tilt measurement are needed. The compensation method is applied to accelerometer measurements of an onshore wind turbine tower and validated with contactless absolute distance measurements from a terrestrial laser scanning (TLS) system. The position and frequency-dependent tilt error of the investigated tower has a significant influence on the quasi-static motion below 0.2 Hz with a minimum amplitude error of 9 %, whereas the normalised bending mode shapes around 0.3 Hz are only slightly affected.

A comparative study of experimental and simulated ultrasound beam propagation through cranial bones

Objective.Transcranial ultrasound is used in a variety of treatments, including neuromodulation, opening the blood-brain barrier, and high intensity focused ultrasound therapies. To ensure safety and efficacy of these treatments, numerical simulations of the ultrasound field within the brain are used for treatment planning and evaluation. This study investigates the accuracy of numerical modelling of the propagation of focused ultrasound through cranial bones.Approach.Holograms of acoustic fields after propagation through four human skull specimens were measured for frequencies ranging from 270 kHz to 1 MHz, using both quasi-continuous and pulsed modes. The open-source k-Wave toolbox was employed for simulations, using an equivalent-source hologram and a uniform bowl source with parameters that best matched the measured free-field pressure distribution.Main results.The average absolute error in k-Wave simulations with sound speed and density derived from CT scans compared to measurements was 15% for the spatial-peak acoustic pressure amplitude, 2.7 mm for the position of the focus, and 35% for the focal volume. Optimised uniform bowl sources achieved calculation accuracy comparable to that of the hologram sources.Significance.This method is demonstrated as a suitable tool for prediction of focal position, size and overall distribution of transcranial ultrasound fields. The accuracy of the shape and position of the focal region demonstrate the suitability of the sound speed and density mapping used here. However, large errors in pressure amplitude and transmission loss in some individual cases show that alternative methods for mapping individual skull attenuation are needed and the possibility of considerable errors in pressure amplitude should be taken into account when planning focused ultrasound studies or interventions in the human brain, and appropriate safety margins should be used.

Block-Based Mode Decomposition in Few-Mode Fibers

A block-based mode decomposition (BMD) algorithm is proposed in this paper, which reduces computational complexity and enhances noise resistance. The BMD uses randomly selected sample blocks of the beam images to restore mode coefficients instead of all pixels in the beam images. It allows for blocks of any shape, such as triangles. In noise-free simulations, compared to the spatially degenerated mode decomposition (SPMD) algorithm, the BMD algorithm requires only 1% of the multiplication operations, thereby significantly increasing the computational efficiency while maintaining a high mode decomposition accuracy. In simulations with noise, increasing the signal-to-noise ratio (SNR) reduces decomposition errors across all configurations. The amplitude error of BMD can outperform SPMD by 15 dB. The experimental results show that BMD has a better performance than SPMD.

TID damage assessment on LVDS links for the ATLAS muon barrel spectrometer readout system

This work reports on Total Ionizing Dose (TID) assessment on off-the-shelf LVDS links that will be used for the new trigger and readout system of the ATLAS muon barrel spectrometer within the HL-LHC program. We developed an experimental setup that allows to investigate TID effects on the currents drawn by the devices under test and on their signal integrity, including variations in amplitude, rise/fall time, and bit error rate. No significant variations of these quantities has been observed after integrating the ATLAS target dose of 84.6 Gy. In order to investigate high-dose effects, the irradiation has been extended up to 15.4 kGy. No post-annealing effects were observed. These results complement existing literature, proving the robustness of off-the-shelf LVDS links for the ATLAS environment.

The effect of eccentricity error on the static load sharing characteristics of PTBTS based on 3D-LTCA method

Eccentricity error represents a common error form in gear transmission systems. Its presence significantly impacts the time-varying meshing stiffness (TVMS) and transmission error among gear pairs, consequently exerting a notable influence on the load sharing coefficient (LSC) of power two branching transmission system (PTBTS). In this paper, the static load sharing model of PTBTS is constructed based on the equilibrium relationships of gear pair with the consideration of position angle, meshing phase, eccentricity error and so on. Additionally, a TVMS model for multi-branching transmission system is established using the three-dimensional load tooth contact analysis (3D-LTCA) method. Finally, the stiffness model and static load sharing model are coupled to achieve precise modeling of the PTBTS static characteristics, and the impact of eccentricity error amplitude and phase on the static load sharing characteristics of PTBTS are studied. The results indicate a substantial influence of eccentricity error and eccentric phase on the load sharing characteristics of the system. As the eccentricity error amplitude increases, the load sharing performance of the system deteriorates. However, it is noteworthy that the static load sharing characteristics of the system can be enhanced by adjusting the eccentricity error phase to an appropriate setting.

Differential‐sampling control algorithm and theoretical analysis for programmable‐Josephson‐voltage‐standard traceability application

AbstractThe programmable Josephson voltage standard (PJVS) provides a new way and higher accuracy for the traceability of traditional measurement standards. To improve the applicability and reduce the uncertainty of the PJVS, a PJVS‐based analog‐to‐digital converter (ADC) scheme for the alternating‐current (AC) voltage measurement is proposed and the theoretical error model is derived based on discrete Fourier transform. The influence of the amplitude and phase error of the AC voltage is simulated; an adaptive differential‐sampling control algorithm is proposed to control the relative amplitude and phase between the AC voltage and PJVS voltage, improving the error of the PJVS‐based ADC. Furthermore, the authors obtained the exponential decay algorithm error curve that varies with phase error and the M‐shaped variation curve with sampling error by simulation and a PJVS‐based ADC with different sampling DVM, which provides possibilities for optimizing the measurement error of the PJVS‐based ADC.

Subaperture moving strategy and related systematic errors in stitching interferometry of X-ray mirrors

For high-precision metrology of X-ray mirrors, the subaperture moving strategy significantly impacts the accuracy of stitching interferometry. In this work, we investigated the systematic errors associated with various subaperture moving strategies of rotational stitching (RS), rotational displacement stitching (RDS), and displacement stitching (DS) in measuring X-ray mirrors. The effects of stitching strategies on a flat mirror and a spherical mirror with a radius of curvature (RoC) of 180 m and 60 m were compared. For the mirror with RoC of 60 m, the DS strategy showed the smallest height error of 3.3 nm (RMS) between algorithm-based stitching and the Nanometer Optical component Measuring machine (NOM), while RS showed a large error of 37.4 nm (RMS). The different regions of the interferometer aperture have different amplitudes of retrace errors, defocusing errors, and lateral distortion, which can lead to accumulations of systematic errors using the RS strategy. By reducing the pixel size from 0.268 mm/pixel to 0.089 mm/pixel, the measurement accuracy using the same RDS strategy improved from 7.4 nm (RMS) to 4.4 nm (RMS). Based on the optimal stitching strategy, the measurement accuracy of residual figure error of the X-ray mirror with a radius of curvature of 30 m reaches 0.2 nm (RMS).

Применение критерия косинусного рассогласования при учёте наличия рэлеевского шума в задаче моноимпульсной пеленгации

The aim of the work is to develop a modified algorithm for passive monopulse direction finding and to estimate the precision of this algorithm. A non-zero average value of the amplitude error of the recorded signals is a feature of the input data for the problem of direction finding. It is proposed to estimate and take into account the average value of the amplitude error, while estimating bearing. The proposed solution is based on optimizing the cosine mismatch function between the measured and estimated amplitudes. To increase the computational efficiency of the method, a partial analytical optimization of the cosine mismatch by the average amplitude error was performed. The result of modeling shows that it is advisable to use the proposed mismatch function, when the signal-to-noise ratio is less than 15 dB. To improve performance the obtained analytical expression of the average amplitude error should be used. The proposed method makes it possible to provide a bearing error not exceeding ~ 0.1 of the beam width of the radiation pattern with a signal-to-noise ratio of ~ 6 dB.

Analysis of the differences and similarities in electromagnetic forces of different equivalent structures of Bi-2212 circular wire

Bi-2212 high-temperature superconducting circular wire exhibit excellent superconducting and electromagnetic properties, making them the preferred material for the next generation of high-temperature superconducting cables, as they can be wound in multiple layers. However, the high stress generated during the transmission of large current by the cable may damage the equipment, and the current density, magnetic field and stress distribution are different in the constant external field and the alternating external field environment. Therefore, it is critical to study the difference between the electromagnetic field distribution and the stress distribution of the circular wire in different forms of external field. In this paper, we focus on Bi-2212 circular wires and establish three types of two-dimensional finite element models using homogenization methods. We emphasize the electromagnetic field, radial stress, and circumferential stress distribution characteristics under constant magnetic field and alternating magnetic field environments. We analyze the similarities and differences among these three equivalent models under the two different external field conditions. When the background magnetic field remains constant, the electromagnetic field, radial stress, and circumferential stress exhibit a center-symmetric distribution. Under an alternating magnetic field, the electromagnetic field and stress exhibit an upper-lower symmetric distribution, with the amplitude being smaller on the left side than on the right side. When the amplitude of the background magnetic field is the same, the electromagnetic field and stress have larger amplitudes under an alternating magnetic field. When the alternating field frequency is large, the current penetration depth in the superconducting region decreases, and a part of the current is driven to Ag and Ag-Mg alloys. The Filament-matrix Homogenized Model accurately reflects the distribution patterns of the electromagnetic field and stress. Under an alternating magnetic field, the Bundle-matrix Homogenized Model has a smaller error in stress amplitude compared to the original structure.

Research on Voltage Self-Calibration Sensing Technology Based on Measurement Circuit Topology Changes

In capacitance-coupled voltage-sensing technology, the degree of coupling capacitance is affected by the sensing area, relative position deviation, and other factors, and thus the measurement coefficient is often difficult to determine accurately and presents greater implementation difficulties in actual deployment. This paper proposes a dynamic reconfiguration based on the measurement circuit topology of the voltage sensor adaptive calibration method in order to measure voltage sensor gain in the process of automatic measuring. Firstly, the basic principle of voltage measurement is introduced, and the self-calibration method is proposed, considering the influence of the sensing area and the relative position error on the change in the coupling capacitance. On this basis, the influence of calibration accuracy on sensor structure parameters is analyzed using network sensitivity analysis, and the parameter selection principle is given, according to which the selection criterion of parameter optimization is formulated to complete the sensor design. By analyzing the coupling effect of the three-phase measurement, the installation method of the sensing structure is proposed. An experimental platform is built to test the accuracy of the voltage measurement of the sensor under laboratory conditions. The experimental results show that the maximum relative error of the voltage measurement amplitude is 2.24%. In order to verify the feasibility of the sensor technology designed, the measurement models that integrate communication, acquisition, and processing are installed on both ends of the circuit breaker wire, and the voltage waveform generated during the circuit breaker closing process is recorded in real time. The experimental results show that the sensor technology can accurately record the voltage waveform of the signal to be measured, and the feasibility of its application in switchgear equipment signal measurement is preliminarily verified by the results.

An Active Control Method Based on the Study of Dynamic Characteristics of Integrated Electric Drive Systems

<div>Integrated electric drive systems are characterized by high power density, reliability, and controllability, making them increasingly prevalent in the realm of electric commercial vehicles. However, the direct coupling between the motor shaft and the transmission system has introduced a series of undesirable torsional vibration phenomena. To investigate the dynamic characteristics of electric drive systems in operation for electric commercial vehicles, a comprehensive modeling approach is employed. This modeling framework takes into account key factors such as gear backlash, structural flexibility, and electromagnetic spatiotemporal excitations. Based on this model, the influence of the electrical system on time-varying gear mesh stiffness, gear transmission error, bearing forces, and other factors is investigated. Building upon this foundation, the article proposes an approach for active harmonic voltage injection. This method effectively reduces torque fluctuations, decreases the amplitude and fluctuation of gear mesh stiffness and gear transmission error, lowers the vibration accelerations of each shaft, and enhances the reliability of the integrated electric drive system.</div>

Analysis of Self-Injection-Coupled Quadrature Oscillator: Oscillation Amplitude and Phase Error

Analysis of Self-Injection-Coupled Quadrature Oscillator: Oscillation Amplitude and Phase Error

Comparison of synergy extrapolation and static optimization for estimating multiple unmeasured muscle activations during walking

BackgroundCalibrated electromyography (EMG)-driven musculoskeletal models can provide insight into internal quantities (e.g., muscle forces) that are difficult or impossible to measure experimentally. However, the need for EMG data from all involved muscles presents a significant barrier to the widespread application of EMG-driven modeling methods. Synergy extrapolation (SynX) is a computational method that can estimate a single missing EMG signal with reasonable accuracy during the EMG-driven model calibration process, yet its performance in estimating a larger number of missing EMG signals remains unknown.MethodsThis study assessed the accuracy with which SynX can use eight measured EMG signals to estimate muscle activations and forces associated with eight missing EMG signals in the same leg during walking while simultaneously performing EMG-driven model calibration. Experimental gait data collected from two individuals post-stroke, including 16 channels of EMG data per leg, were used to calibrate an EMG-driven musculoskeletal model, providing “gold standard” muscle activations and forces for evaluation purposes. SynX was then used to predict the muscle activations and forces associated with the eight missing EMG signals while simultaneously calibrating EMG-driven model parameter values. Due to its widespread use, static optimization (SO) applied to a scaled generic musculoskeletal model was also utilized to estimate the same muscle activations and forces. Estimation accuracy for SynX and SO was evaluated using root mean square errors (RMSE) to quantify amplitude errors and correlation coefficient r values to quantify shape similarity, each calculated with respect to “gold standard” muscle activations and forces.ResultsOn average, compared to SO, SynX with simultaneous model calibration produced significantly more accurate amplitude and shape estimates for unmeasured muscle activations (RMSE 0.08 vs. 0.15, r value 0.55 vs. 0.12) and forces (RMSE 101.3 N vs. 174.4 N, r value 0.53 vs. 0.07). SynX yielded calibrated Hill-type muscle–tendon model parameter values for all muscles and activation dynamics model parameter values for measured muscles that were similar to “gold standard” calibrated model parameter values.ConclusionsThese findings suggest that SynX could make it possible to calibrate EMG-driven musculoskeletal models for all important lower-extremity muscles with as few as eight carefully chosen EMG signals and eventually contribute to the design of personalized rehabilitation and surgical interventions for mobility impairments.

Reduced Monocular Accommodation Abilities with Laptop Usage Under Scotopic Ambient Illumination

Laptops are widely used even in dark scotopic rooms. This study compares monocular accommodation statuses with laptop usage under three illuminations. Thirty university students read on a laptop for 5 minutes under scotopic, mesopic, and photopic conditions. The monocular amplitude of accommodation, accommodation facility, and accommodation error are measured for each illumination. Repeated measure ANOVA shows a significant difference in the amplitude, facility, and error between different illuminations [F (1.49, 43.18) = 10.61, p<0.001], [F (1.65, 36.30) = 6.78, p=0.005] and [F (2, 56) = 3.65, p=0.032]. Scotopic illumination reduces monocular accommodation abilities with laptop usage.

Research on Multi-Parameter Error Model of Backcalculated Modulus Using Abaqus Finite Element Batch Modeling Based on Python Language

The error in modulus backcalculation is a crucial component in validating the rationality and reliability of results for engineering applications. The objective of this study is to identify the theoretical limitations associated with backcalculated modulus errors under typical parameter uncertainties and to determine the primary factors contributing to these errors. Firstly, using the actual measurements or data from the Long-Term Pavement Performance (LTPP) project, the statistical distributions of errors for typical parameters in the modulus backcalculation model were determined. Subsequently, a factor level table for orthogonal experimental design was developed, leading to the construction of 81 orthogonal design experimental schemes and their corresponding theoretical pavement structure models based on the actual error distributions. The deflection responses of 81 theoretical pavement structure models were then computed using an ABAQUS finite element batch analysis method devised in Python. Furthermore, a multi-parameter error model for modulus was established using multiple linear regression and variance analysis. Finally, the theoretical limitations of modulus errors under actual errors were analyzed. The results show that the errors of thickness, load amplitude and load frequency follow a normal distribution, while the distribution of backcalculated modulus errors follows an approximate mixed Gaussian distribution. When the errors of multiple parameters are combined randomly, the modulus errors range from −100% to 595%, and the probability of the modulus errors being less than 15% is highest in the asphalt surface layer, followed by the subgrade, and then the base and subbase layers. Within the same error range, the modulus error is random. However, with different error ranges, the overall level of modulus error increases in proportion to the size of those ranges. Compared to factors such as thickness, load amplitude, and load frequency, the errors in deflections have a highly contribution rate on the modulus errors exceeding 99%.

A 24–30‐GHz Modified Gilbert‐Cell Downconverter With High Linearity and Isolation

ABSTRACTThis paper introduces a downconverter mixer employing a modified double‐balanced Gilbert‐cell topology, designed using IHP's 0.13‐m SiGe BiCMOS technology. Distinct from the conventional topology, a resonator was employed at the emitter of the transconductance stage, which enables the utilization of transconductance stage as an active balun, allowing for direct feeding of the single‐ended input without sacrificing the advantageous of the double‐balanced topology. The integration of the resonator reduces the amplitude and phase errors within the active balun segment, thereby enhancing port‐to‐port isolation. The area occupied by the resonator is approximately 1.7 times smaller than that of an RF transformer balun typically employed in conventional double‐balanced topologies. The LO and IF differential signals are converted to single‐ended ones through transformer baluns for measurement purposes. The frequencies of operation for RF, LO, and IF are 24–30, 18–24, and 6 GHz, respectively. The conversion loss is 7.7 dB at 26 GHz, with port‐to‐port isolations exceeding 35 dB. The input 1‐dB compression point is 5.7 dBm, while the circuit consumes 65‐mW power from a 3.3‐V voltage supply. Excluding the pads, the active area of the design spans 1 mm2.

Receiving Paths Improvement of Digital Phased Array Antennas Using Adaptive Dynamic Range

In contemporary radar technology, the observation and detection of objects with low radar cross-sections remains a significant challenge. A multi-functional radar model employing a digital phased array antenna system offers notable advantages over traditional radar in addressing this issue. Nonetheless, to fully capitalize on these benefits, improving the structure of the receiving path in digital transceiver modules is crucial. A method for improving the digital receiving path model by implementing a matched filter approach is introduced. Given that the return signals from objects are often lower than the internal noise, the analog part of the digital transceiver modules must ensure that its dynamic range aligns with the level of this noise and the weak signal. The output signal level of the analog part must correspond to the allowable input range of the analog-to-digital converter. Improvements in the receiving path to achieve a fully matched model can reduce errors in the phase parameters and amplitudes of the useful signal at the output. The simulation results presented in this paper demonstrate a reduction in amplitude error by approximately 1 dB and a phase error exceeding 1.5 degrees for the desired signal at the output of each receiving path. Consequently, these improvements are expected to enhance the overall quality and efficiency of the spatial and temporal accumulation processes in the digital phased array antenna system. Furthermore, to maintain the matched filter model, we also propose incorporating an adaptive “pseudo-expansion” of the linear gain range. This involves adding a feedback stage with an automatic and adaptive bias voltage adjustment for the intermediate-frequency preamplifier in the analog part of the receiving path. Simulations to qualitatively verify the validity of this proposal are conducted using data from practical operational radar system models.

High-frequency average phase compensation method for gamma nonlinearity based on optimal-frequency strategy

The accuracy of fringe projection phase-shifting profilometry (PSP) is affected by gamma nonlinearity greatly, and the average phase compensation method is an effective technique to reduce the nonlinear error. However, double fringe patterns are commonly required, especially combined with the multi-frequency phase unwrapping method (MFPU), using 6 × 3 images in three-frequency method, which limits the measurement eiciency. To reduce the number of required images, this paper presents an efficient average phase compensation method using 6f h + 3f l + 3f u algorithm based on an optimal-frequency strategy. Six high-frequency standard and π/3 shifted 3-step phase-shifting fringe patterns are used together to generate high-accuracy wrapped phase. Three unit-frequency and three low-frequency fringe patterns are used to obtain coarse a unit-frequency wrapped phase and a coarse low-frequency wrapped phase, respectively. To ensure the robust phase unwrapping for high-frequency phase, the mathematical model of the optimal frequency is derived and determined by phase error amplitude calculation. Simulation and experimental results verified that only applying average phase compensation under the guidance of optimal-frequency selection strategy could achieve robust phase unwrapping and high-accurate measurement by reducing the nonlinear error substantially.