Proposed Compensation Approach Research Articles

Improvement in repeatability of ultrasonic array imaging in materials with high structural noise

Developments of automated systems in recent years have improved fast non-destructive evaluation (NDE) of complex structures. This opens up the possibility of looking for small changes between repeat measurements, either to increase the detectability of small defects, or to more accurately characterise the growth of known defects. In this paper, we study the effect of positioning inaccuracy, array element variability, and couplant wave velocity variability on inspection repeatability performance. We propose a post-processing approach to compensate for the degradation in repeatability due to changes in these parameters between inspections. A two-medium, ray-based, forward model is used to quantitatively study the effect of these parameters on inspection repeatability, and the results show a good agreement with experiments. The study indicates positioning inaccuracy and couplant wave velocity variability are the dominant factors affecting inspection repeatability and that the effect of element variability is negligible. We find the repeatability is profoundly sensitive to positioning inaccuracy, which requires a method to measure and correct for the difference between nominally identical inspection positions. Modest differences in wave velocity in the couplant can be tolerated, provided that the relative difference in true couplant wave velocity and that assumed in imaging calculations is preserved. The proposed compensation approach is shown to offer significant performance advantages for baseline subtraction and early-stage crack detection.

Distributed Delay Compensation for a Hybrid Simulation System of Space Manipulator Capture

The simulation of the target capture process of space manipulator is of great significance for the manipulator and task verification. By integrating the physical and numerical simulation, the hardware-in-the-loop (HIL) simulation is very suitable to simulate the complicated contact dynamics of the target capture process of the multibody manipulator in three-dimensional space. However, the time delays in the system loop lead to HIL simulation error and even system instability. In this article, a distributed delay compensation approach is proposed for the hybrid simulation system of space manipulator capture. The force delay, calculation delay, actuation delay, and mechanism delay in the system loop are compensated in situ. Compared with lumped compensation, distributed compensation has stronger robustness to the signal noise and better adaptability to the varying contact natural frequency. Simulations and experiments show that the proposed compensation approach can guarantee the system stability and simulation accuracy.

A Magnetic Tuning Mechanism to Compensate Frequency Ratio Deviation in Coupled Resonators for Improving Sensing Resolution With High Sensitivity

A magnetic tuning mechanism to compensate the frequency ratio deviation in coupled resonators is proposed in this paper for fulfilling the potential of nonlinear internal resonance to sensing applications. A magnetic tuning theory is constructed to deduce theoretical expressions of 1:3 internal resonance with lumped parameter model and multi-scale method. The effectiveness of the proposed magnetic tuning mechanism is experimentally demonstrated by taking a two-cantilever resonator system as an example, with 1:3 internal resonance characteristics under different magnetic forces. The possibility to compensate frequency ratio deviation caused by manufacturing, assembling and other errors generated in production and service processes is further analytically and experimentally studied to improve sensing resolution and increase detection accuracy, achieving an adjustment range from 164.3Hz to 146.5Hz in frequency and 1:2.83 to 1:3.17 in frequency ratio. The proposed compensation approach is believed to be universally applicable to cantilever-based sensors with the need for frequency matching.

A combined digital linearization and channel estimation approach for IM/DD fast-OFDM systems

A combined digital linearization and channel estimation scheme is proposed and experimentally demonstrated for short-reach intensity-modulation and direct-detection (IM/DD) optical Fast-OFDM systems. Known 2PAM-Fast-OFDM sequences are used for training a memoryless polynomial based adaptive post-distorter and for FFT-based channel estimation in IM/DD 4PAM-Fast-OFDM systems. The 2PAM signals are transmitted only over the odd SCs of the training sequences. With the combined compensation scheme, significant BER improvements are achieved for 10- and 22-km length 12.5 Gbit/s SMF links. Compared with a conventional IM/DD Fast-OFDM, the receiver sensitivity of the proposed IM/DD Fast-OFDM system is improved by about 3 dB at a bit error ratio (BER) of 10–3, after 22-km SMF transmission. In addition, the experimental results for different bias voltages and under strong filtering effects show that the proposed compensation approach can deal with some degree of MZM bias drift and can be applied for realistic wideband optical Fast-OFDM systems.

A Resonant Pressure Microsensor with Temperature Compensation Method Based on Differential Outputs and a Temperature Sensor.

This paper presents the analysis and characterization of a resonant pressure microsensor, which employs a temperature compensation method based on differential outputs and a temperature sensor. Leveraging a silicon-on-insulator (SOI) wafer, this microsensor mainly consists of a pressure-sensitive diagram and two resonant beams (electromagnetic driving and electromagnetic induction) to produce a differential output. The resonators were vacuum packaged with a silicon-on-glass (SOG) cap using anodic bonding and the wire interconnection was realized by sputtering an Au film on highly topographic surfaces using a hard mask. After the fabrication of the resonant pressure microsensor, systematic experiments demonstrated that the pressure sensitivity of the presented microsensor was about 0.33 kPa/Hz. Utilizing the differential frequency of the two resonators and the signal from a temperature sensor to replace the two-frequency signals by polynomial fitting, the temperature compensation method based on differential outputs aims to increase the surface fitting accuracy of these microsensors which have turnover points. Employing the proposed compensation approach in this study, the errors were less than 0.02% FS of the full pressure scale (a temperature range of −40 to 85 °C and a pressure range of 200 kPa to 2000 kPa).

Thermal Drifts of Capacitive Flow Meters: Analysis of Effects and Model-Based Compensation

Capacitive sensing has become a favorable measurement technology for flow metering in pneumatic conveying systems. Multielectrode sensing structures and tomographic signal evaluations enable spatially resolved flow parameter estimation, which is of particular interest for pneumatically conveyed solids due to inhomogeneous particle distributions within the pipeline. The noninvasive working principle of capacitive sensors is an important feature for the application in industrial processes with harsh environments. However, cross sensitivities of the capacitive probe cause effects, such as temperature drifts of the measurements. For a reliable operation of capacitive flow meters in harsh environments, induced drifts have to be compensated. In this article, we present the detailed analyses of thermal effects within capacitive sensors. Based on the findings, a model-based temperature compensation approach is developed within the Bayesian framework. The performance of the proposed compensation approach is analyzed by a measurement-based validation within a climate chamber and by a simulation-based uncertainty quantification. The capability to obtain temperature-independent estimates with calibration measurements acquired at room temperature is demonstrated.

CASH-RAM: Enabling In-Memory Computations for Edge Inference Using Charge Accumulation and Sharing in Standard 8T-SRAM Arrays

Machine Learning (ML) workloads being memory- and compute-intensive, consume large amounts of power running on conventional computing systems, restricting their implementations to large-scale data centers. Transferring large amounts of data from the edge devices to the data centers is not only energy expensive, but sometimes undesirable in security-critical applications. Thus, there is a need for building domain-specific hardware primitives for energy-efficient ML processing at the edge. One such approach - in-memory computing , eliminates frequent and unnecessary data-transfers between the memory and the compute units, by directly computing the data where it is stored. However, the analog nature of computations introduces non-idealities, which degrades the overall accuracy of neural networks. In this paper, we propose an in-memory computing primitive for accelerating dot-products within standard 8T-SRAM caches, using charge-sharing. The inherent parasitic capacitance of the bitlines and sourcelines is used for accumulating analog voltages, which can be sensed for an approximate dot product. The charge sharing approach involves a self-compensation technique which reduces the effects of non-idealities, thereby reducing the errors. Our results for ternary weight neural networks show that using the proposed compensation approaches, the accuracy degradation is within 1% and 5% of the baseline accuracy, for the MNIST and CIFAR-10 dataset, respectively, with an energy-delay product improvement of $38\times $ over the standard von-Neumann computing system. We believe that this work can be used in conjunction with existing mitigation techniques, such as re-training approaches, to further enhance system performance.

Reduction of Induced Shaft Voltage and Bearing Current in Turbo Generators: Modeling, Compensation, and Practical Test

The static excitation system of a turbo generator, supplied by a rectifier, can cause induced voltages on the generator's shaft. This article proposes a complete distributed model of a turbo generator, regulated by a static excitation system, to investigate the shaft voltage and bearing current. The complete modeling of all components is proposed by considering the couplings between them in a static excitation system. When shaft voltages exceed the dielectric breakdown voltage of the lubricating oil film in journal bearings, electrical discharge current flows through the bearings. This will further reduce the life expectancy of the dielectric gradually. Two different approaches are explained and discussed in detail to keep the shaft voltages within the safe region: a passive filter and a dc–dc converter solution. Both methods along with the initial system are simulated and compared accordingly. Additionally, frequency-domain analysis has been performed for evaluating the compensating solutions. Moreover, experimental tests were carried out on a 200-MVA turbo generator, and results of the suggested passive filter with those of the proposed compensation method are compared. Both experiments and simulations confirm the mentioned issue and show the effectiveness of the proposed compensation approaches in this regard.

Generalized Inverse Multiplicative Structure for Differential-Equation-Based Hysteresis Models

In this article, a generalized inverse multiplicative structure (GIMS) is developed for the purpose of compensating for the hysteresis effect represented by the differential-equation-based hysteresis model. The GIMS approach is an approximate inverse compensation approach, and it does not require the analytical solution of the differential equations. The novelty of the proposed GIMS is that it extends the classical inverse multiplicative structure and it can be applied to construct the inverse compensator for differential-equation-based hysteresis models that can be written into the proposed unified expression. The LuGre model and the backlash-like model are employed as examples in the simulations and experiments. Both results validate the effectiveness of the proposed compensation approach.

Reconfigurable thin film filter for compensating AOI deviation effects using LC coupled cavities

An efficient technique to enhance thin-film filters’ angular tolerance is described and numerically demonstrated. The spacer refractive index is controlled using a liquid crystal (LC) in the multi-cavity thin-film filter. The angle of incident (AOI) deviation causes significant degradation in the filter performance. To circumvent the influence of the AOI deviation, a correction effect is introduced through controlling the LC refractive index, while maintaining the normal incident performance of the filter. The proposed LC-based approach has proven effective in increasing the angular tolerance of the thin-film filter. Simulation results indicate an angle-insensitive performance under a 20o incident angle cone deviation. The results illustrate the effectiveness of this approach over the C-band, where the change in the center wavelength shift was reduced from 107.57 nm to 0.38 nm. Moreover, the change in the transmission filter bandwidth was reduced by 70%. The proposed compensation approach offers flexibility in the central wavelength and in the filter bandwidth estimated at the 0.5 dB, 3 dB, and 25 dB passband ranges.

Pre-compensation of servo tracking errors through data-based reference trajectory modification

This paper presents a new dynamic error compensation approach with novel data-based closed-loop tuning scheme to enhance tracking accuracy of machine tool feed-drives. Both servo dynamics and friction disturbance induced positioning errors are pre-compensated by modifying the reference trajectory. Velocity and acceleration profiles of reference trajectory are modulated to achieve perfect tracking. Reference position profile is modified based on the pre-sliding friction regime to eliminate quadrant glitches. Optimal error compensation is achieved by a digital trajectory pre-filter whose parameters are tuned automatically by making on-the-fly iterative adjustments. Effectiveness of proposed compensation approach is validated experimentally in multi-axis feed-drive systems.

Real Time Optimal Reconfiguration of Multiphase Active Distribution Networks

Many of the practically adopted methods for feeder reconfiguration in distribution networks are based on classical switch exchange. Switch exchange has been originally developed for legacy distribution networks, and does not account for many of the complexities associated with active grids. This paper extends the classical reconfiguration method to account for reverse power flows from distributed generation, controllable loads from prosumers, and a multiphase network representation. To comply with the distribution management system real time computing requirements, previous techniques adopt a positive sequence network model so that formulas to approximately evaluate the intermediate solutions could be used without recourse to repeated power flow. This paper proposes a compensation technique for switch exchange in the power flow solution of multiphase network representations, but without requiring matrix re-factorization; the proposed technique gives an exact solution, which serves as an alternative to the approximation formulas that are usually employed with the positive sequence network representation. The proposed compensation approach is used in extending the practically adopted feeder reconfiguration method from the single-phase equivalent circuit model to the multiphase model of active grids, while being three times as fast as the approach that employs repeated power flow and matrix re-factorization.

Temperature Compensation Method for Digital Cameras in 2D and 3D Measurement Applications.

This paper presents the results of several studies concerning the effect of temperature on digital cameras. Experiments were performed using three different camera models. The presented results conclusively demonstrate that the typical camera design does not adequately take into account the effect of temperature variation on the device’s performance. In this regard, a modified camera design is proposed that exhibits a highly predictable behavior under varying ambient temperature and facilitates thermal compensation. A novel temperature compensation method is also proposed. This compensation model can be applied in almost every existing camera application, as it is compatible with every camera calibration model. A two-dimensional (2D) and three-dimensional (3D) application of the proposed compensation model is also described. The results of the application of the proposed compensation approach are presented herein.

Reduced-complexity sparsity-aware joint phase noise mitigation and channel equalization in OFDM receivers

A major performance and complexity limitation in direct-conversion broadband wireless transceivers is the phase noise (PN) resulting from the inevitable imperfections in the fabrication process of the crystal oscillator. PN induces inter-carrier interference in orthogonal frequency division multiplexing (OFDM) transceivers. Assuming the availability of inaccurate PN and channel estimates, in this paper, we propose an efficient low-complexity sparsity-based design for joint PN mitigation and channel equalization in OFDM systems. Moreover, we analyze the maximum expected coherence metric for the sparsifying matrix that is used in our approach which provides some insight into its performance. Finally, our numerical simulations demonstrate the effectiveness of our proposed compensation approach compared to the state-of-the-art designs in terms of both performance and computational complexity.

Hybrid Smith predictor and phase lead based divergence compensation for hardware-in-the-loop contact simulation with measurement delay

On the ground the hardware-in-the-loop (HIL) simulation is a good approach to test the contact dynamics of spacecraft docking process in space. Unfortunately, due to the time delay in the system the HIL contact simulation becomes divergent. However, the traditional first-order phase lead compensation approach still result in a small divergence for the pure time delay. The serial Smith predictor and phase lead compensation approach proposed by the authors recently will lead to an over-compensation and an obvious convergence. In this study, a hybrid Smith predictor and phase lead compensation approach is proposed. The hybrid Smith predictor and phase lead compensation can achieve a higher simulation fidelity with a little convergence. The phase angle of the compensator is analyzed and the stability condition of the HIL simulation system is given. The effectiveness of the proposed compensation approach is tested by simulations on an undamped elastic contact process.

BiCMOS-Based Compensation: Toward Fully Curvature-Corrected Bandgap Reference Circuits

We present a novel BiCMOS-based temperature compensation technique aiming at complete correction of the curvature in the temperature response of bandgap references. The source of the appearance of this curvature is because the well-known nonlinear term $T\ln (T)$ in the base–emitter voltage ( $V_{BE}$ ) is not completely canceled across all temperature points. Here, we show that the gate-source voltage ( $V_{GS}$ ) of a subthreshold-operating MOSFET, biased with a proportional to absolute temperature current, also exhibits the $T\ln (T)$ nonlinear temperature dependence. We leverage the existence of $T\ln (T)$ in the temperature response of $V_{GS}$ to directly cancel the nonlinear term $T\ln (T)$ in $V_{BE}$ . A theoretical analysis of the proposed compensation approach is presented. As a proof of concept, a current-mode voltage reference circuit, utilizing the proposed approach, is designed in IBM’s 8HP Silicon–Germanium (SiGe) BiCMOS technology. Thermal characteristics of the compensation components are examined through extensive simulations and are also experimentally evaluated, for the first time. Measurement results of the reference circuit show that the circuit outperforms the temperature performance of the state-of-the-art SiGe reference circuits. Possible origins of observed temperature dependences and mitigation techniques are discussed. The proposed compensation approach can be realized in any BiCMOS/CMOS technology for implementing either current-mode or voltage-mode high precision reference circuits.

Increasing compositional backscattered electron contrast in scanning electron microscopy

A method for increasing compositional or material contrast of a standard semiconductor BSE detector in a scanning electron microscope (SEM) by compensation of the topographic contrast component is proposed. Compensation is based on the physical properties of backscattered electron emission and topography information of the specimen's surface.Three analytical and semi-empirical compensation algorithms employing different physical models and approximations are implemented and compared to conventional BSE signals to show the effectivity of the proposed compensation approach.

Compensation of Velocity Divergence Caused by Dynamic Response for Hardware-in-the-Loop Docking Simulator

The hardware-in-the-loop simulation on the ground is effective to test the contact dynamics of the spacecraft in space. However, it is very challenging due to the simulation velocity divergence caused by the time delay. In this study, a compensation approach for the velocity divergence caused by the dynamic response of the motion simulator is proposed. Traditional delay compensation requires the time delay or the delay model to be known. In practice, the dynamic response of the motion simulator is time varying and unknown. This motivates development of the model-free compensation approach. It compensates the contact force from the real-time response error of the motion simulator and the real-time identified contact stiffness and damping. The proposed compensation approach is easy to implement since it does not require the dynamic response model of the motion simulator. Simulations and experiments are used to verify the effectiveness of the proposed compensation approach.

A Temperature Compensation Method for Piezo-Resistive Pressure Sensor Utilizing Chaotic Ions Motion Algorithm Optimized Hybrid Kernel LSSVM.

A piezo-resistive pressure sensor is made of silicon, the nature of which is considerably influenced by ambient temperature. The effect of temperature should be eliminated during the working period in expectation of linear output. To deal with this issue, an approach consists of a hybrid kernel Least Squares Support Vector Machine (LSSVM) optimized by a chaotic ions motion algorithm presented. To achieve the learning and generalization for excellent performance, a hybrid kernel function, constructed by a local kernel as Radial Basis Function (RBF) kernel, and a global kernel as polynomial kernel is incorporated into the Least Squares Support Vector Machine. The chaotic ions motion algorithm is introduced to find the best hyper-parameters of the Least Squares Support Vector Machine. The temperature data from a calibration experiment is conducted to validate the proposed method. With attention on algorithm robustness and engineering applications, the compensation result shows the proposed scheme outperforms other compared methods on several performance measures as maximum absolute relative error, minimum absolute relative error mean and variance of the averaged value on fifty runs. Furthermore, the proposed temperature compensation approach lays a foundation for more extensive research.

Smith predictor based delay compensation for a hardware-in-the-loop docking simulator

The hardware-in-the-loop (HIL) simulator is an important equipment to test the performance of the docking mechanisms (DMs) in the docking process of two spacecrafts on the ground. However, the design and control of the HIL simulator is very challenging due to the simulation divergence caused by the time delay. The phase lead is a common approach to compensate the time delay. In this study, it is found that the simulation is still divergent using the traditional phase lead compensation approach when the contact frequency increases to a threshold value depending on the HIL simulator. In practice, because the experimental contact frequency is time-varying and unknown, traditional phase lead compensation approach could make the system instable and divergent. The Smith predictor based delay compensation is proposed in this study. It integrates the Smith predictor and the phase lead compensation. The contact model of the DMs is not required. The simulation system is stable and convergent when the contact frequency increases and satisfies the stability condition. The HIL simulation with a little convergence is better than the divergent simulation because the previous one can be considered to have some simulation error while the latter one could destroy the hardware. The phase and stability analyses are given to prove the simulation convergence and the closed-loop stability. Simulations and experiments are used to verify the effectiveness of the proposed compensation approach.