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On the Sensitivity of Mode-Localized Accelerometers Operating in the Nonlinear Duffing Regime
No full textMode-localized sensors have attracted great attention due to the high parametric sensitivity and common mode rejection to temperature drift. The reported results from such sensors has largely relied on operation in the linear regime. However, operation at specific bifurcation points in the nonlinear regime can enable improvements in relevant performance metrics. This paper theoretically and experimentally reveals the operation of mode-localized sensors with respect to applied stiffness perturbations while operating in the nonlinear Duffing regime. The operation of a mode-localized accelerometer is optimized with benefit of the insights gained from theoretical analysis with operation at the top bifurcation point in the nonlinear regime. A prototype accelerometer device demonstrates a noise floor of 85 ng/√Hz and a bias instability of 130 ng, establishing a new benchmark for sensors employing vibration mode localization as a sensing paradigm
Rotation Equivariant Orientation Estimation for Omnidirectional Localization
No full textDeep learning based 6-degree-of-freedom (6-DoF) direct camera pose estimation is highly efficient at test time and can achieve accurate results in challenging, weakly textured environments. Typically, however, it requires large amounts of training images, spanning many orientations and positions of the environment making it impractical for medium size or large environments. In this work we present a direct 6-DoF camera pose estimation method which alleviates the need for orientation augmentation at train time while still supporting any SO (3 ) rotation at test time. This property is achieved by the following three step procedure. Firstly, omni-directional training images are rotated to a common orientation. Secondly, a fully rotation equivariant DNN encoder is applied and its output is used to obtain: (i) a rotation invariant prediction of the camera position and (ii) a rotation equivariant prediction of the probability distribution over camera orientations. Finally, at test time, the camera position is predicted robustly due to an in-built rotation invariance, while the camera orientation is recovered from the relative shift of the peak in the probability distribution of camera orientations. We demonstrate our approach on synthetic and real-image datasets, where we significantly outperform standard DNN-based pose regression (i) in terms of accuracy when a single training orientation is used, and (ii) in training efficiency when orientation augmentation is employed. To the best of our knowledge, our proposed rotation equivariant DNN for localization is the first direct pose estimation method able to predict orientation without explicit rotation augmentation at train time
Evaluation of methodologies for assessing self‐healing performance of concrete with mineral expansive agents: An interlaboratory study
No full textSelf‐healing concrete has the potential to optimise traditional design approaches; however, commercial uptake requires the ability to harmonize against standardized frameworks. Within EU SARCOS COST Action, different interlaboratory tests were executed on different selfhealing techniques. This paper reports on the evaluation of the effectiveness of proposed experimental methodologies suited for self‐healing concrete with expansive mineral additions. Concrete prisms and discs with MgO‐based healing agents were produced and precracked. Water absorption and water flow tests were executed over a healing period spanning 6 months to assess the sealing efficiency, and the crack width reduction with time was monitored. High variability was reported for both reference (REF) and healing‐addition (ADD) series affecting the reproducibility of cracking. However, within each lab, the crack width creation was repeatable. ADD reported larger crack widths. The latter influenced the observed healing making direct comparisons across labs prone to errors. Water absorption tests highlighted were susceptible to application errors. Concurrently, the potential of water flow tests as a facile method for assessment of healing performance was shown across all labs. Overall, the importance of repeatability and reproducibility of testing methods is highlighted in providing a sound basis for incorporation of self‐healing concepts in practical applications
Reshaping the emission of a THz quantum cascade laser frequency comb through an on-chip graphene modulator
No full textGraphene possesses a peculiar potential for the development of optoelectronic components capable to actively manipulate infrared light [1]. Its electrostatically tunable optical conductivity, band structure and transport characteristics, and the possibility to be grown over large areas, offer an intriguing playground for engineering, at the nanoscale, amplitude modulators, spatial light modulators and switches, combining high efficiency (> 50%) intensity modulation, reasonably high speeds (> s response times), and spectral tunability in the underexploited high (> 1.5 THz) terahertz-frequency range [2] , where frontier applications in quantum communications, quantum computing, adaptive and quantum optics are still at their infancy
Assessing the sources of particles at an urban background site using both regulatory instruments and low-cost sensors – a comparative study
No full textMeasurement and source apportionment of atmospheric pollutants are crucial for the assessment of air quality and the implementation of policies for their improvement. In most cases, such measurements use expensive regulatory-grade instruments, which makes it difficult to achieve wide spatial coverage. Low-cost sensors may provide a more affordable alternative, but their capability and reliability in separating distinct sources of particles have not been tested extensively yet. The present study examines the ability of a low-cost optical particle counter (OPC) to identify the sources of particles and conditions that affect particle concentrations at an urban background site in Birmingham, UK. To help evaluate the results, the same analysis is performed on data from a regulatory-grade instrument (SMPS, scanning mobility particle sizer) and compared to the outcomes from the OPC analysis. The analysis of the low-cost sensor data manages to separate periods and atmospheric conditions according to the level of pollution at the site. It also successfully identifies a number of sources for the observed particles, which were also identified using the regulatory-grade instruments. The low-cost sensor, due to the particle size range measured (0.35 to 40 µm), performed rather well in differentiating sources of particles with sizes greater than 1 µm, though its ability to distinguish their diurnal variation, as well as to separate sources of smaller particles, at the site was limited. The current level of source identification demonstrated makes the technique useful for background site studies, where larger particles with smaller temporal variations are of significant importance. This study highlights the current capability of low-cost sensors in source identification and differentiation using clustering approaches. Future directions towards particulate matter source apportionment using low-cost OPCs are highlighted
Energy absorption and self-sensing performance of 3D printed CF/PEEK cellular composites
No full textWe report the energy absorption and piezoresistive self-sensing performance of 3D printed discontinuous carbon fiber (CF)-reinforced polyetheretherketone (PEEK) cellular composites. Experiments conducted on three different 2D lattices with hexagonal, chiral and re-entrant topologies of the same relative density (33%) and CF loading (30 wt%) reveal that the CF/PEEK hexagonal lattice (HL), due its relatively brittle response, shows about 40% and 9% decrease in specific energy absorption (SEA) under in-plane and out-of-plane compression, respectively, compared with PEEK HL. While the collapse response of PEEK HL is nearly insensitive to the strain-rate over 43 ≤ ε̇ ≤ 106 s−1, we observe a twenty-fold increase in peak stress and a five-fold increase in SEA under in-plane impact loading over the same range of strain-rates for the CF/PEEK HL. The CF/PEEK lattices exhibit pronounced piezoresistive response under both in-plane and out-of-plane compression with maximum sensitivity of 3.1 and 5.2, respectively, for the re-entrant lattice, offering insight into the damage-state. Higher damage sensitivity indicates faster percolation of new contacts due to folds forming between the cell walls within the lattice under compression. The energy-absorbing and strain- and damage-sensing nature of 3D printed CF/PEEK lattices demonstrated here offers insight into the design of lightweight, high-performance multifunctional lattices
Long-Term Reliability Evaluation of Power Modules with Low Amplitude Thermomechanical Stresses and Initial Defects
No full textIn renewable energy and grid applications, solder-attached power modules are subject to fatigue stress cycles of low amplitudes, but the devices will be in service for decades. This article aims to understand the slow aging process by focusing on the initial defects and their growth under the stress cycles of concern. A finite-element analysis (FEA) is performed to obtain the thermomechanical stress distribution around the defects, which is combined with the solder material's property to give a lifetime model. Effort is made to validate the model by power cycling plus microscale computed tomography (CT) scanning. It is found that a void in the solder layer may first transform into a crack on the material boundary, which then grows progressively more rapidly until device failure. A numerical example is shown for evaluating the lifetime of an IGBT power module in a 'soft-open-point' (SOP) converter designed for an 11-kV power network
Anchor penetration depth in sandy soils and its implications for cable burial
No full textModern society is dependent on offshore cables and consequently cable faults lead to major disruption and economic loss. The most effective way to protect offshore cables from anchor damage is to bury them in the seabed, but current guidance is ambiguous. This paper attempts to produce more rational design guidance for anchor penetration in sand based on centrifuge modelling, allowing suitable burial depths for cables to be calculated based on the more useful metrics of anchor or ship size. A miniature anchor was dragged through sand of different densities within a centrifuge with maximum anchor penetration being measured. The most significant factor that influences anchor penetration depth is the size of the anchor, investigated by completing centrifuge tests at different g-levels. A linear relationship was recorded between anchor size and penetration depth which was used to develop new guidelines for cable burial. The new chart is clear and easy to use, with the cable burial depths given in relation to anchor size, anchor mass and ship mass. Use of this chart will enable the safe and economic burial of cables, and lead to a decrease in the impact of anchor damage to offshore cables
Superconducting fault current limiter (SFCL): Experiment and the simulation from finite-element method (FEM) to power/energy system software
No full textThe superconducting fault current limiter (SFCL) has been regarded as one of most popular superconducting applications. This article reviews the modern energy system with two major issues (the power stability and fault-current), and introduces corresponding approaches to mitigate these issues, including the importance of using SFCL. Then the article presents the experiment of a resistive-type SFCL used for a power electronic circuit. The experiment well matched the advanced finite-element method (FEM) SFCL model, from which the reliability of FEM SFCL model was confirmed. Afterwards, the FEM model and the power system software PSCAD were used to model a large-scale resistive-type SFCL. Under the same simulation conditions the FEM model well matched the PSCAD model. The FEM method has the advantages of offering specific electromagnetic modeling on superconducting part. The PSCAD SFCL model has much faster simulation speed and can directly cope with all ranges of power networks. This article presents a new vision and an all-in-one study to link the experiment, the numerical model, and the power/energy system software model, and their agreement can be extremely helpful for researchers and engineers to find useful evidences and reliable methods to confidently carry out successful SFCL designs for the electrical energy system
Interval state estimation in active distribution systems considering multiple uncertainties
No full textDistribution system state estimation (DSSE) plays a significant role for the system operation management and control. Due to the multiple uncertainties caused by the non-Gaussian measurement noise, inaccurate line parameters, stochastic power outputs of distributed generations (DG), and plug-in electric vehicles (EV) in distribution systems, the existing interval state estimation (ISE) approaches for DSSE provide fairly conservative estimation results. In this paper, a new ISE model is proposed for distribution systems where the multiple uncertainties mentioned above are well considered and accurately established. Moreover, a modified Krawczyk-operator (MKO) in conjunction with interval constraint-propagation (ICP) algorithm is proposed to solve the ISE problem and efficiently provides better estimation results with less conservativeness. Simulation results carried out on the IEEE 33-bus, 69-bus, and 123-bus distribution systems show that the our proposed algorithm can provide tighter upper and lower bounds of state estimation results than the existing approaches such as the ICP, Krawczyk-Moore ICP(KM-ICP), Hansen, and MKO