Sensitivity Vector Research Articles

A high sensitivity and wide frequency band vector hydrophone using PZT-based four spiral beam structure

The utilization of a high sensitivity and wide frequency band vector hydrophone exhibits significant potential in the exploration of underwater target. However, enhancing these performance remains a challenge due to limitations in materials and structures. Herein, we report a micro-electro-mechanical system (MEMS) vector hydrophone (FSPVH) built on lead zirconate titanate (PZT) film with four spiral beam structure and polyamide (PA) microsphere. The optimization of the structural dimensions and PZT thin film distribution has been the result of simulation. The FSPVH have been fabricated using MEMS technology, and the prototype has been assembled. The FSPVH was tested in a standing bucket wave calibration system. The results show that FSPVH achieve a sensitivity of −181.5 dB (0 dB = 1 V/μPa) at 1100 Hz, and the work bandwidth is 20–1330 Hz. Meanwhile, it exhibits a satisfactory “8″ shape directivity. This work provide theory and technique supports of vector hydrophone with high sensitivity and wide frequency band.

Sensitivity volume as figure-of-merit for maximizing data importance in electrical impedance tomography

Objective. Electrical impedance tomography (EIT) is a noninvasive imaging method whereby electrical measurements on the periphery of a heterogeneous conductor are inverted to map its internal conductivity. The EIT method proposed here aims to improve computational speed and noise tolerance by introducing sensitivity volume as a figure-of-merit for comparing EIT measurement protocols. Approach. Each measurement is shown to correspond to a sensitivity vector in model space, such that the set of measurements, in turn, corresponds to a set of vectors that subtend a sensitivity volume in model space. A maximal sensitivity volume identifies the measurement protocol with the greatest sensitivity and greatest mutual orthogonality. A distinguishability criterion is generalized to quantify the increased noise tolerance of high sensitivity measurements. Main result. The sensitivity volume method allows the model space dimension to be minimized to match that of the data space, and the data importance to be increased within an expanded space of measurements defined by an increased number of contacts. Significance. The reduction in model space dimension is shown to increase computational efficiency, accelerating tomographic inversion by several orders of magnitude, while the enhanced sensitivity tolerates higher noise levels up to several orders of magnitude larger than standard methods.

Aerodynamic Modification of High-Rise Buildings by the Adjoint Method

This study presents a novel numerical methodology that is designed for the dynamic adjustment of three-dimensional high-rise building configurations in response to aerodynamic forces. The approach combines two core components: a numerical simulation of fluid flow and the adjoint method. Through a comprehensive sensitivity analysis, the influence of individual variables on aerodynamic loads, including lift and drag coefficients, is assessed. The findings underscore that the architectural design, specifically the building’s construction pattern, exerts the most substantial impact on these forces, accounting for a substantial proportion (76%). Consequently, the study extends its evaluation to the sensitivity of fluid flow across various sections of the tower by solving the adjoint equation throughout the entire fluid domain. As a result, the derived sensitivity vector indicates a remarkable reduction of approximately 31% in the applied loads on the tower. This notable improvement has significant implications for the construction of tall buildings, as it effectively mitigates aerodynamic forces, ultimately enhancing the overall comfort and structural stability of these architectural marvels.

Study of the phase characteristics of vibration sensors and conditions of orthogonalization of their measuring basis for the systems of vibration control and vibration testing of materials

To identify the most vibration-sensitive structures of the materials during vibration tests, it is necessary to determine the vibration vector in an orthogonal basis The effectiveness of the tests depends on the accuracy of the vector measurement. The transverse sensitivity of tri-axial vibration transducers, which have found vast application in various vibration measuring and material testing systems, leads to increased measurement errors and limits the frequency range of measurements. The errors can be reduced to almost zero using the proposed method of electronic orthogonalization, which involves rotation of the sensitivity vectors until they coincide with the orthogonal basis, resulting in zero transverse sensitivity. This approach has been successfully developed and works rather well in the low frequency band of the vibration transducer frequency response, wherein the amplitude-characteristics are linear and there is no phase shift in the channels. An emphasis is made on the influence of the phase characteristics of vibration sensors on the formation of orthogonalizing matrices that determine the requirements for an orthogonalizer. The structure of the installation for automated recording amplitude-frequency and phase-frequency responses of the vibration transducer, methodology and results of experimental study of a tri-axial piezoelectric accelerometer (TPA) with one inertia element and oblique-angle measuring basis are presented. The results obtained under vibration activated in three mutually perpendicular directions along the measuring axes show that the transducer measuring system is properly designed to provide for effective broadband orthogonalization of the measuring basis. The results obtained can be used to develop orthogonalizing transducers that eliminate transverse sensitivity in a wide frequency range, as well as to improve the design of sensors and their metrological characteristics.

Sensitivity and uncertainty analysis of effective multiplication factor of KRITZ-1 benchmark using ENDF/B-VIII.0 and JEFF3-3 nuclear data libraries

Sensitivity and uncertainty analysis have been performed to estimate the uncertainty in the effective neutron multiplication factor, keff, of the KRITZ-1 benchmark and to identify which nuclear reactions and isotopes of interest could be significantly influencing it. First, the adjoint-weighted perturbation method using the KSEN card of the MCNP6 code is applied to compute the sensitivity vectors for 235U, 238U, 1H, 16O, and 10B isotopes with the JEFF-3.3 and ENDF/B-VIII.0 nuclear data libraries. Then, the sensitivity vectors and covariance matrices were combined to calculate the uncertainty in keff due to uncertainties in nuclear data. The 44 group covariance matrices have been processed with the NJOY21 system.It was found that the uncertainty in keff is mostly due to uncertainties on ν‾p , fission cross section of 235U, the capture cross section of the two isotopes 238U and 1H in the aforementioned data libraries

Angular magnetic field dependence of a doubly clamped magnetoelectric resonator

Angular dependence of magnetic field response of fully suspended resonant microelectromechanical double-clamped magnetoelectric beams was investigated as the basis for a vector magnetometer utilizing the magnetically induced change in fundamental resonance frequency. Strain-coupled magnetostrictive iron cobalt (FeCo) and piezoelectric aluminum nitride layers together constitute a magnetoelectric heterostructure with a high magnetic field sensitivity of 70 Hz/mT along the beam axis and a transfer function of 47 V/T at 10 Hz. The fundamental frequency shift to an external magnetic field is found to be strongly anisotropic with a relative variation of more than 3% between perpendicular and parallel field orientations with respect to the long axis of the beam at a field of 100 mT. This design can form the basis for an on-chip high sensitivity vector magnetometer operating with ultra-low power when multiplexed with two or more resonators.

Frontoparietal network homogeneity as a biomarker for mania and remitted bipolar disorder and a predictor of early treatment response in bipolar mania patient

ObjectivePrevious studies have revealed the frontoparietal network (FPN) plays a key role in the imaging pathophysiology of bipolar disorder (BD). However, network homogeneity (NH) in the FPN among bipolar mania (BipM), remitted bipolar disorder (rBD), and healthy controls (HCs) remains unknown. The present study aimed to explore whether NH within the FPN can be used as an imaging biomarker to differentiate BipM from rBD and to predict treatment efficacy for patients with BipM. MethodsSixty-six patients with BD (38 BipM and 28 rBD) and 60 HCs participated in resting-state functional magnetic resonance imaging and neuropsychological tests. Independent component analysis and NH analysis were applied to analyze the imaging data. ResultsRelative to HCs, BipM patients displayed increased NH in the left middle frontal gyrus (MFG), and rBD patients displayed increased NH in the right inferior parietal lobule (IPL). Compared to rBD patients, BipM patients displayed reduced NH in the right IPL. Furthermore, support vector machine results exhibited that NH values in the right IPL could distinguish BipM patients from rBD patients with 69.70 %, 57.89 %, and 91.67 % for accuracy, sensitivity, and specificity, respectively, and support vector regression results exhibited a significant association between predicted and actual symptomatic improvement based on the reduction ratio of the Young` Mania Rating Scale total scores (r = 0.466, p < 0.01). ConclusionThe study demonstrated distinct NH values in the FPN could serve as a valuable neuroimaging biomarker capable of differentiating patients with BipM and rBD, and NH values of the left MFG as a potential predictor of early treatment response in patients with BipM.

High sensitivity vector torsion sensor based on a single Stress-Applying fiber Sagnac interferometer

A vector torsion sensor based on a Single Stress-Applying Fiber (SSAF) Sagnac interferometer is proposed and experimentally demonstrated. Taking use of the high birefringence and structural asymmetry of the SSAF, the spectrum of SSAF based Sagnac interferometer shows both wavelength shift and intensity variation with the change of torsion angle. A torsion sensitivity as high as 53.3 nm/(rad/m) can be achieved by wavelength demodulation and 4.3 dB/(rad/m) by intensity demodulation. In addition, the torsion direction can be also recognized in the torsion angle range from −50° to 50°. The temperature cross sensitivity is 0.03 rad/m/℃ by wavelength demodulation in the temperature range from 20℃ to 38℃. The advantages of high sensitivity, direction recognition, multi-parameter demodulation and simple structure make the sensor great potential in civil engineering, surgical robot and other applications.

An adjoint-based drag reduction technique for unsteady flows

A framework based on a continuous adjoint-based analysis of steady and unsteady flows to predict and control the drag force due to surface morphing is presented. By establishing a relation between perturbations in the body shape and in the boundary condition on a certain geometry, we derive an analytical expression of the sensitivity to changes in the geometry of the body and its relation to the sensitivity to the perturbation of the boundary conditions. The methodology is evaluated on the incompressible flow around a cylinder for steady and unsteady flows. A reduction of the drag coefficient was obtained and investigated by several surface deformations, conducted in the direction of the sensitivity vector field obtained by solving the derived adjoint problem. In unsteady flows, the sensitivity field is computed by integrating the unsteady adjoint problem backward in time from the unsteady flow solution. Two different types of deformations based on the calculated sensitivity were applied: time-averaged deformation and time-dependent. Attempting the latter, a deformation at each time step, did not yield the same satisfactory results as the time-averaged in terms of expected drag reduction. We provide a theoretical reasoning for the difference between both methodologies, together with an insight into the physics of the sensitivity vector field distribution relating it to the drag force sources.

Dynamic measurement of 3D displacements using dual-camera lensless Fourier transform digital holography.

Dynamic 3D displacement field measurement is an effective means to characterize the electrical performance stability and structural soundness of microsystems. Combining off-axis lensless Fourier transform multiplexed digital holography and multi-illumination profilometry, a dual-wavelength dual-camera optical setup with a multi-illumination system is developed to simultaneously acquire four phase images with different sensitivity vectors, as well as the object shapes. Meanwhile, the shared reference wave in off-axis lensless Fourier holography gives a convenient way for sensitivity vector modification and phase image registration, which are based on the stereo checkerboard calibration method. The dynamic 3D displacement fields and the strain maps of an energized integrated circuit board reveal that the inhomogeneous thermal expansion may cause some damage to chips, such as pin desoldering and microstructure fracture.

Orthogonalization of the measuring basis of triaxial vibration transducers by the method of successive approximations

The transversal sensitivity of tri-axial vibration transducers, which have found vast application in various vibration measuring and material testing systems, decreases the accuracy of measurements. We present a solution to the problem of eliminating the error attributed to the presence of the transverse sensitivity. The measurement error depends on many factors including the ratio of vibration components along the sensitivity axes, the width of the vibration spectrum, and the presence of intrinsic resonances of the vibration transducers in the main and transverse directions. The developed method provides almost complete compensation of the error. Analysis of the components of sensitivity vectors along the measuring directions showed that the transversal sensitivity vectors are in fact the parasitic penetrations from other directions, and can be decomposed along the measuring axes. To orthogonalize the sensitivity vectors during calibration, the sensitivity vectors should be rotated until they coincide with the orthogonal directions. A measuring basis with zero transverse sensitivities is thus obtained, and the sensitivity matrix is reduced to a diagonal form. With this approach the fundamentals and practical algorithm using successive approximations of triaxial transducer calibration with orthogonalization are outlined. Each orthogonalization step is illustrated by the current sensitivity matrix, showing the progress of transversal sensitivity reduction. The results of the developed tri-axial transducer coupled to a special preamplifier-converter with transversal sensitivities reduced to nearly zero values using the developed method are presented. Since calibration is carried out without dismantling of a vibration transducer, it can be carried out not only during its manufacture, but also during verification upon operation, which increases the service life. The use of the described technique not only improves the metrological parameters of vibration transducers, but also provides a significant reduction of the requirements for the accuracy of manufacturing their measuring system, thus reducing the production costs. The presented method is promising for the developing new precise multi-axis vibration transducers and measuring systems on their base.

Feasibility of tracking involuntary head movement for MRI using a coil as a magnetic dipole in a time-varying gradient

Accurate tracking involuntary head movements is fairly a challenging problem in MR imaging of the brain. Though there are few techniques available to monitor the head movement of the subject for a prospective motion correction, it is still an unsolved problem in MRI. In this theoretical study, we aim to describe an analytical investigation to track head movement inside an MR scanner by calculating the change in induced voltage in the head-mounted coils during the execution of time-varying gradients. We derive an expression to calculate the change in induced voltage in a coil placed in a time-varying gradient. We also derive a general equation to investigate the changes in the induced voltage in a set of coils mounted onto the head for the planar position and orientation of the coils. Each coil is considered as a magnetic dipole with location and sensitivity vectors. The changes of the vectors can track the head movement in the MR scanner by measuring the changes in the induced voltage in the coils. The dipole concept is valid for a wide range of coils. The changes in induced voltage in the coils are linear due to small changes in pose of the head. Movement parameters are estimated from the induced voltage changes. If the random noise voltage is less than 100 μV, it does not significantly affect movement parameters because the change in induced voltage in the coils dominates over the small noise voltage. This method and array of the coils may provide a real-life solution to the long-standing problem of head motion during MRI.

Reliability analysis of flexural provisions of FRP-RC beams and sensitivity analysis based on FORM

A reliability analysis was conducted based on the flexural strength recommendations provided by the ACI 440.1R-15 guide concerning the glass fiber-reinforced polymer-reinforced concrete (GFRP-RC) beams. A statistical investigation was carried out by compiling the dataset of 235 specimens from the technical literature on the model uncertainty of the beams to select the best probability distribution. As such, two failure modes of concrete crushing and GFRP rupture were examined. Reliability was analyzed using the first-order reliability method (FORM) via iHLRF algorithm. Importance sampling was also employed to determine the efficiency of the FORM. Findings reveal that the flexural requirements of ACI 440.1R-15 regarding the FRP-RC beams are conservative for both failure modes, particularly the GFRP rupture failure. Subsequently, importance vector α and sensitivity vectors δ and η were conducted to rank the effect of the most important random variables and their probability distribution parameters on the reliability index. Results from the importance vector α demonstrate that the random variable d is the most significant variable in both failure modes amongst the examined design variables. Thus, uncertainty contributed with d has the greatest effect on the reliability index. Moreover, based on the results from sensitivity vectors δ and η, varying the mean and standard deviation of the random variable ML leads to maximum change in total failure probability of the problem. Finally, strength reduction factors of 0.65 and 0.75 were respectively proposed through calibration so as to reach the target reliability index for GFRP rupture and concrete crushing.

Identification of homogeneous chemical kinetic regimes of methane-air ignition

Sensitivity analysis results for ignition delay time (IDT) may be very different depending on the initial temperature, pressure and equivalence ratio φ, but similar in some regions of these variables. This phenomenon was investigated systematically by carrying out ignition simulations and local sensitivity calculations of methane−air mixtures using the Aramco-II-2016 mechanism at 14,417 combinations of initial temperature (changed between 500 and 3000 K), initial pressure (0.05−500 atm) and φ (0.05−8.0) values. The cluster analysis of the sensitivity vectors identified five large kinetically homogeneous regions. Each region has well defined borders in the (T, p φ) space and can be characterized by different sets of important reactions. The related kinetic scheme is very different in each region. Regions 1 and 2 are dominated by catalytic cycles based on species CH3O2/CH3O2H and HO2/H2O2/CH3O, respectively. In regions 3, 4, and 5 the H atoms are converted to CH3 in an identical chain branching sequence, but the back conversion is via three different routes. Literature experimental data on the IDTs of methane−air mixtures were sorted according to these five regions. Regions 1 to 5 contain 214, 328, 3, 0, and 237 experimental data points, respectively. In regions 1, 2 and 5 the data points are well reproduced by the Aramco-II-2016 mechanism, but little or no experimental information is available about kinetic regions 3 and 4. Further experimental exploration of the ignition of methane−air mixtures may aim the study of these regions. A similar approach can be used for the characterization of other combustion systems and sorting the related experimental data.

Effective 3D-transient electromagnetic inversion using finite-element method with a parallel direct solver

The correct interpretation of time-domain or transient electromagnetic (TEM) data relies on effective inversion techniques. Herein, we have developed an effective 3D-TEM inversion method based on the vector finite-element method. The domain was discretized with unstructured tetrahedra to simulate complex geologic structures. We develop a second-order backward-Euler scheme, rigorously with nonuniform time-step sizes, to approximate the time derivative of the electric field. The waveform was directly simulated and considered in the forward modeling and inversion. In a 3D inversion, the most time-consuming element of the workflow is solving a large system of linear equations. To alleviate this problem, we adopt a parallel direct solver for solving a large system of equations involved in forward modeling and sensitivity calculations. We use the Gauss-Newton approach to solve the inverse problem and formulate the least-squares problem to obtain model updates. We avoided the explicit sensitivity calculation by solving the matrix-vector multiplication between the sensitivity matrix (or its transpose) and vector. The developed inversion algorithm is validated using several realistic synthetic models. Finally, we apply the method to practical TEM data with complex topography for coal mine goaf detection. We thus obtain a detailed 3D resistivity model that revealed the layering structure and some localized anomalies related to the coal mine goaf.

Detecting Changes in Boundary Conditions based on Sensitivity-based Statistical Tests

Structural health monitoring is a promising technology to automatically detect structural changes based on permanently installed sensors. Vibration-based methods that evaluate the global system response to ambient excitation are suited to diagnose changes in boundary conditions, i.e. changes in member prestress or imposed displacements. In this paper, these changes are evaluated based on sensitivity-based statistical tests, which are capable of detecting and localizing parametric structural changes. The main contribution is the analytical calculation of sensitivity vectors for changes in boundary conditions (i.e., changes in prestress or support conditions) based on stress stiffening, and the combination with a numerically efficient algorithm, i.e. Nelson’s method. One of the main advantages of the employed damage diagnosis algorithm is that, although it uses physical models for damage detection, it considers the uncertainty in the data-driven features, which enables a reliability-based approach to determine the probability of detection. Moreover, the algorithm can be trained and the probability of detecting future damages can be predicted based on data from the undamaged structure—in an unsupervised learning mode—making it particularly relevant for unique structures, where no data from the damaged state is available. For proof of concept, a numerical case study is presented. The study assesses the loss of prestress in a two-span reinforced concrete beam and showcases suitable validation approaches for the sensitivity calculation.

Combined Usage of Hydraulic Model Calibration Residuals and Improved Vector Angle Method for Burst Detection and Localization in Water Distribution Systems

This paper proposes a combined usage of the hydraulic model calibration residuals and an improved vector angle method for the Battle of the Leakage Detection and Isolation Methods (BattLeDIM). The proposed method starts with the hydraulic model decomposition and followed by data partition, with both procedures aimed at simplifying the BattLeDIM problem. Next, a calibration residuals–based burst detection approach is used, in which the nodal demands of the hydraulic model are calibrated in real-time using a newly developed algorithm based on prior information. The burst detection is achieved by identifying the anomalous calibration residuals. Finally, the locations of pipe bursts are approximated by an improved vector angle method, which compares the angle between each pipe’s sensitivity vector and the vector of calibration residuals. Application results to the BattLeDIM problem indicate the proposed method is effective and efficient in burst detection and localization, with nearly all abrupt bursts (9 out of the total 19 bursts) in 2019 being successfully detected within 5–10 min after their occurrence, and 7 out of 10 detected bursts being localized with a spatial difference less than 300 m from the true burst pipes. Performance comparisons with the Kalman filtering–based burst detection method have been conducted, and the obtained results indicate the proposed method has better performance under both consistent and varying operation conditions, as well as in detectability for small bursts. Lessons learned from this battle and future works are summarized towards the development of a more effective and robust burst detection and localization method.

High-sensitivity two-axis vector bending sensor based on side-grooved long period grating in eccentric core fiber

A novel vector bend sensor based on side-grooved Long period grating (SG-LPG) inscribed on eccentric core fiber (ECF) was proposed and investigated. The core of the ECF is close to the surface of the fiber, which makes it very convenient to fabricate different SG-LPGs in ECF by CO2 laser with little damage. Since the direction of the SG-LPG deviates from the direction of the side core of the ECF, the sensor can identify bending directions on two orthogonal axes. At the same time, the strong refractive index modulation caused by grooves makes SG-LPG very sensitive to bending. In the curvature range of 0–2.52 m−1, the bend sensitivity in four directions reaches 27.23 nm/m−1, −25.76 nm/m−1, 14.74 nm/m−1 and −16.83 nm/m−1, respectively. Due to the simple structure, convenient fabrication, high sensitivity, and multi vectors bending detection characters, the sensor has potential in bending measurement.

A Comparison between Wavefront-Optimized and Wavefront-Guided Photorefractive Keratectomy in Patients with Moderate-to-High Astigmatism: A Randomized Clinical Trial.

Purpose:To compare clinical outcomes of wavefront-optimized (WFO) and wavefront-guided (WFG) photorefractive keratectomy (PRK) in patients with moderate-to-high astigmatism.Methods:Patients with corneal cylinder above 2 diopters and myopic spherical equivalent were randomized into WFO or WFG PRK. Visual acuity (VA), refraction, contrast sensitivity, higher-order aberrations (HOAs), and astigmatic vector differences were documented and compared for 6 months after surgery.Results:The total number of 362 eyes from 181 patients was analyzed. The amount of total aberration was reduced 2.7 root mean square (RMS) and 2.9 RMS in the WFO and WFG groups, respectively (P < 0.001 in each group and between the groups). HOAs including coma, trefoil, and spherical aberrations increased in both the groups (P < 0.001) but were significantly more in the WFO group (P < 0.001). The increased spherical aberration was similar in both the groups (P = 0.12). Surgically induced astigmatism was not significantly different between the groups (P = 0.20). The magnitude of error was significantly higher in the WFO group (P < 0.001), but the absolute angle of error and the arithmetic angle of error were not significantly different between the groups (P = 0.20 and P = 0.30, respectively).Conclusion:WFO and WFG platforms of PRK appear comparable in terms of VA, refractive correction, and total aberration. Yet, HOAs may increase especially after WFO PRK.

A modal self-excitation method of tensegrity robots

A tensegrity robot is a type of soft-rigid system, whose high compliance is prone to induce structural vibrations which traditionally should be avoided. However, a stable limit cycle oscillation at a natural frequency can be exploited to improve motion efficiency of tensegrity robots. By constructing a modal self-excitation system, we can produce limit cycle oscillation for tensegrity robots. Therefore, in this paper, we propose a method to realize modal self-excitation of under-actuated tensegrity robots. A task-space second-order structural model of a tensegrity robot is developed and a mapping between forces of cable-space and that of task-space is derived. Meanwhile, we propose a cable sensitivity vector from modal shape to guide the selection of active cables in the tensegrity robot. A modal self-excitation system is designed by combining a bandpass filter with a describing function into the control system. In this way, a limit cycle oscillation at a frequency can be formed close to the desired natural frequency. The stability of this limit cycle oscillation is analyzed by perturbation method. Modal switching excitation is also achieved by switching between different modal excitation loops online. The effectiveness of the proposed modal self-excitation method for tensegrity robots is verified by several numerical simulations and tests.