Outer Contacts Research Articles

A revised elastic-plastic contact model of cycloidal pinwheel based on length scale

This study explores the relationship between surface roughness and characteristic scale through theoretical analyses and experimental data. Considering the concavity and convexity of cycloidal gear tooth profile curvatures, a curved surface contact coefficient model suitable for both inner and outer contacts, with either equal or unequal curvatures, has been developed. Moreover, a fractal contact model is constructed for cycloidal pinwheels. This model considers scale correlation and analyzes the influence of microscopic parameters on the elastic-plastic critical grade and the behavior of the contact area. Additionally, the influence of the micro-convex body frequency index on surface contact performance is explored to provide theoretical insights for improving the elastic contact ratio and reducing wear on contact surfaces.

Ion Migration and Space‐Charge Zones in Metal Halide Perovskites Through Short‐Circuit Transient Current and Numerical Simulations

AbstractThe inherent ion migration in metal halide perovskite materials is known to induce deleterious and highly unstable dark currents in X‐ and γ‐ray detectors based on those compounds upon bias application. Dark current slow drift with time is identified as one of the major drawbacks for these devices to satisfy industrial requirements. Because dark current establishes the detectability limit, current evolution, and eventual growth may mask photocurrent signals produced by incoming X‐ray photons. Relevant information for detector assessment is ion‐related parameters such as ion concentration, ion mobility, and ionic space‐charge zones that are eventually built near the outer contacts upon detector biasing. A combined experimental (simple measurement of dark current transients) and 1D numerical simulation method is followed here using single‐crystal and microcrystalline millimeter‐thick methylammonium‐lead bromide that allows extracting ion mobility within the range of µion ≈ 10−7 cm2 V−1 s−1, while ion concentration values approximate Nion ≈ 1015 cm−3, depending on the perovskite crystallinity.

Double-Layer Hydrogel with Glucose-Activated Two-Stage ROS Regulating Properties for Programmed Diabetic Wound Healing.

Slow healing of wounds induces great pain in diabetic patients. However, developing new approaches to promote diabetic wound healing is still one of the toughest challenges in the medical field. Here, we constructed a new double-layer hydrogel to effectively regulate reactive oxygen species (ROS) on the wound and promote diabetic wound healing. The inner layer contains glucose oxidase (Gox), ferrocene-modified quaternary ammonium chitosan (Fc-QCs), and poly(β-cyclodextrin) (Pβ-CD), which is used to generate hydroxyl radicals (•OH) for antibacterial in the early stage of wound healing and collapses gradually. The outer layer is composed of gelatin and dopamine. In the later stage of wound healing, the outer layer contacts the skin, which is beneficial for ROS clearance on the wound. Antibacterial, ROS scavenging, and wound healing experiments have shown that the double-layer hydrogel possesses two-stage ROS regulating properties for programmed diabetic wound healing. In conclusion, it will be one of the most potential dressings for treating diabetic wounds in the future.

Complementary symmetric Hall plates with a hole and four outer extended contacts

The electrical properties of Hall plates are described by the resistance matrix. Its even part corresponds to a resistor network, its odd part reflects the Hall output voltage. For singly connected and symmetric Hall plates closed formulae of the resistance matrix are known. There are also relations between complementary geometries, where contacts and insulating boundaries are swapped. This work gives the resistance matrix and relations between complementary geometries for Hall plates with one hole. The contacts may have arbitrary sizes, yet the plates must have two perpendicular axes of mirror symmetry, and the magnetic field has to be small.

Bioinspired Vascular Stents with Microfluidic Electrospun Multilayer Coatings for Preventing In-Stent Restenosis.

In-stent restenosis (ISR) is seriously affecting the long-term prognosis of vascular interventional therapy and leading to enormous medical burdens. Great efforts have been devoted to developing functional vascular stents with desired features and properties for effective ISR prevention. Here, a multifunctional bionic vascular stent with designed coatings prepared using microfluidic electrospinning technology is presented. Such stents are composed of biocompatible, drug-loaded methylacrylated gelatin-polyethylene glycol diacrylate (GelMA-PEGDA) and polycaprolactone composite nanofibers on 316L stainless steel stents by an easy-to-operate step-by-step spraying method. Benefitting from the addition of polydopamine during the fabrications, the drug-loaded composite nanofibers can adhere well to both the stent and the vascular wall. Furthermore, as the inner fibrous layer of the stent contacting the lumen is equipped with heparin-vascular endothelial growth factor (Hep-VEGF), it plays an anticoagulation role and promotes the growth of endothelial cells; while the outer layer contacts the vascular wall and releases rapamycin slowly, which can restrain smooth muscle proliferation. By implanting this into the rabbit carotid artery, the multi-functional bionic demonstrates that the vascular stent can achieve good anti-thrombosis and in-stent restenosis effects, which indicates its potential values in vascular intervention and other biomedical fields.

Revealing fundamentals of charge extraction in photovoltaic devices through potentiostatic photoluminescence imaging

Revealing fundamentals of charge extraction in photovoltaic devices through potentiostatic photoluminescence imaging

Micro-structuration effects on local magneto-transport in [Co/Pd]IrMn thin films

We measured the local magneto-transport (MT) signal with an out-of-plane magnetic field, including magneto-resistance (MR) and Extraordinary Hall effect (EHE), in exchange-biased [Co/Pd]IrMn thin multilayers that are micro-structured with a 100 μm window. We found that when measured locally around the window, the MT signal deviate from the expected behavior. We studied possible causes, including film micro-structuration, electrical contact geometry as well as magnetic field angular tilt. We found that tilting the magnetic field direction with respect to the normal direction does not significantly affect the MT signal, whereas the positioning and geometry of the contacts seem to highly affect the MT signal. For comparison purposes, we carried these MT measurements using the Van-der-Pauw method on a set of four microscopic contacts directly surrounding the window, and on another set of micro-contacts located outside the window, as well as a set of four contacts positioned several millimeters away of each other at the corners of the wafer. If the contacts are sufficiently far apart, the EHE and MR signals have the expected shape and are not significantly affected by the presence of the window. If, on the other hand, the contacts are micro-positioned, the shape of the EHE signal is drastically deformed, and may be modeled as a mix of the standard EHE and MR signals measured on the outer contacts. Furthermore, if the micro-contacts are located directly around the window, the deformation is amplified, and the weight of the MR signal in the mix is further increased by about 40 %. This suggests that the electron path in the Hall geometry is disturbed by both the proximity of the electrodes and by the presence of the window, which both contribute to the deformation for about two-third and one third, respectively.

Transport through dynamic pseudogauge fields and snake states in a Corbino geometry

We propose a Corbino-disk geometry of a graphene membrane under out-of-plane strain deformations as a convenient path to detect pseudo-magnetic and electric fields via electronic transport. The three-fold symmetric pseudo-magnetic field changes sign six times as function of angle, leading to snake states connecting the inner and outer contacts and to nearly quantized transport. For dynamical strain obtained upon AC gating, the system supports an AC pseudo-electric field which, in the presence of the pseudo-magnetic field, produces a net electronic charge current in the absence of an external voltage, via a pseudo-Hall effect.

Geology and geochemistry-based metallogenic exploration model for the eastern Tethys Himalayan metallogenic belt, Tibet

The Tethyan Himalaya is the fourth metallogenic belt discovered to date within the Tibetan Plateau and contains chromite, gold and Sb–polymetallic mineralization. The belt records a series of complex tectonic–magmatic events that include the break-up, subduction, collision, detachment, and obduction of the Eastern Gondwana continent, all of which generated ideal conditions for ore formation. However, this area remains under-explored, with only limited knowledge of the deposit types present in this area and their relationship to tectonic and magmatic events. This has hampered mineral exploration in the region. This study uses previous research and mineral exploration in this region, combined with knowledge of mineralization in adjacent regions, to suggest the presence of three main deposit types (ophiolitic chromite, orogenic Au, and hydrothermal vein Sb–polymetallic deposits), and highlights the potential for this area to host as yet undiscovered island arc-type porphyry Cu–Au and leucogranite-related Sn–(Be) mineralization. This study summaries the relationship between the tectonic evolution and magmatism within the region and the mineralization, establishing a temporal and spatial framework for mineralization within the eastern Tethys Himalayan metallogenic belt.Improved knowledge of the geochemical signatures of mineralization, obtained using compositional data analysis (CoDA) combined with geological information, enabled the identification of nine compositional balances, including the presence of sedimentary units, accretionary wedge structures, leucogranites, mafic–ultramafic rocks, chromite mineralization, Au mineralization, and Sb–polymetallic mineralization. This study establishes a predictive mineral exploration model for the eastern Tethys Himalayan metallogenic belt and combines this model with geological and geochemical data to identify areas for future exploration. These targets include a 50-km-long ophiolitic belt in the Nedong area that is highly prospective for chromite mineralization; a positive Au–Cu–Mo geochemical anomaly in the Qonggyai–Qusum area that is prospective for orogenic Au mineralization; and positive Au–Cu–Mo geochemical anomalies in the Nianzha, Sangri, and Gyaca areas that are prospective for exploration for Xiongcun-type island arc-associated porphyry Cu–Au mineralization, as well as deep-seated extensions to known Sb–polymetallic mineralization and the inner and outer contacts of the Lhozhag and Cuonadong leucogranite, all of which are prospective for exploration for Sn–(Be) mineralization.

Grease film thickness measurement in rolling bearing contacts

Rolling bearings are the second most used machine components. They work in what it is called elastohydrodynamic lubrication regime. The geometry of rolling element bearings makes the direct measurement of the lubricant film thickness a challenging task. Optical interferometry is widely used in laboratory conditions for studying elastohydrodynamic lubrication however it cannot be used directly in rolling element bearings thus the only suitable methods are electrical techniques. Of these, film thickness measurement based on electrical capacitance of the contacts has been used in the past by a number of authors. One of the limitations of the capacitance method, when used in rolling bearings, is that it cannot distinguish between the contacts of every rolling element and raceway on one hand and on the other between the inner and outer ring contacts. In the present study the authors used an original test rig which can measure the film thickness for only one ball and separately for the inner and outer rings of a radial ball bearing. This paper thus shows for the first-time results of the lubricant film thickness, at the inner and outer raceways, in grease lubricated rolling bearings.

Transformation Characteristics of High-Current Vacuum Arcs With Still-Spaced Contacts Under TMF–AMF Combined Magnetic Fields

A novel double-type contact system with still-spaced contacts was proposed to offer a better arc control and a electric field shielding effect to the eroded inner contacts, especially during the capacitive interrupting process. The experimental double-type contact system consisted of the inner moving transverse magnetic field (TMF) contacts and the outer still-spaced axial magnetic field (AMF) contacts, which was called as TMF–AMF contacts. The objective of this paper is to determine the transformation characteristics of high-current vacuum arcs with still-spaced contacts under TMF–AMF combined magnetic fields. The experimental investigation includes the vacuum arcing behaviors, the arc voltage, and the arc current transformation characteristics. The arc current in the tests varied over a range from 0 to 30 kA at 50 Hz. The contacts material was CuCr25 (25% Cr). A high-speed charge-coupled device video camera was used to record the vacuum arc appearance. The experiments indicate that the vacuum arc current can transform successfully from the inner TMF contacts to the outer still-spaced AMF contacts for the novel TMF–AMF double-type contacts. The partial arc current flowed through the outer still-spaced contacts was mainly at the latter half of the vacuum arc duration and less than 50% of the total arc current. The value and polarity of the arc current also play a significant role in the arc current transformation characteristics of the TMF–AMF contacts with still-spaced contacts. Moreover, with the vacuum arc expanding to the still-spaced contacts, the variation of the Lorentz force of the arc column would weaken the rotation of the arc column and strengthen the transformation characteristics of the vacuum arc column to the still-space AMF contacts significantly.

Dynamic response of internally nested hemispherical shell system to impact loading

The dynamic deformation behaviors of the internally nested hemispherical shell system (INHSS), were explored experimentally and computationally. Two specimens with different ratios of inner shell thickness δ to outer shell thickness Δ were tested in a drop weight machine. For the specimen with smaller δ/Δ, non-axisymmetric deformation mode occurred with a stable force platform and longer loading history, while for the specimen with larger δ/Δ, axisymmetric deformation was exhibited. Meanwhile, experimentally validated finite element model was employed to study the deformation mechanism after the critical point when the outer shell contacts with the inner shell based on the ratio of square of shell thickness to radius. Subsequently, parametric studies are conducted by varying governing factors, including thickness, radius and offset distance of the inner shell. Results show that the dynamic deformation process and energy absorption capability of the INHSS depends on the thickness and radius of the inner shell.

On the dual Craig–Bampton method for the forced response of structures with contact interfaces

Assembled structures are characterized by contact interfaces that introduce a local non-linearity and affect the dynamics of the assembly in terms of resonance frequencies and vibration levels. To assess the forced response levels of the assemblies during the design, nonlinear dynamic analyses are performed and, in order to reduce the computation time, spatial and temporal reductions of the governing equations must be used. A classical way to achieve temporal reduction is to implement the harmonic balance method to turn the time-domain differential governing equations into frequency-domain algebraic equations. Due to the local nature of contact interfaces, which usually involve a subset of degrees of freedom (dofs) of the structure, a common strategy to achieve spatial reduction is to use component mode synthesis (CMS), by retaining the contact dofs as master dofs. In this paper, a recent CMS approach, named dual Craig–Bampton method (Rixen in J Comput Appl Math, 2004. doi: 10.1016/j.cam.2003.12.014 ), is applied to the nonlinear forced response of structures with contact interfaces. The spectral orthogonality of the two subsets of mode shapes used as a projection basis is exploited to write a set of algebraic equations of the contact dofs in the frequency domain, with no need to compute the reduced matrices of the system. Different formulations of the governing equations are proposed for different configurations (i.e., outer contacts, inner contacts and structures with floating components), and two academic numerical test cases are used to demonstrate the method.

Nonequilibrium chemical potential in a two-dimensional electron gas in the quantum-Hall-effect regime

The nonequilibrium state of a two-dimensional electron gas in the quantum-Hall-effect regime is studied in Hall bars equipped with additional inner contacts situated within the bar. The magnetic-field dependence of the voltage drop between different contact pairs are studied at various temperatures. It was found that the voltage between the inner and outer contacts exhibits peaks of significant amplitude in narrow magnetic-field intervals near integer filling factors. Furthermore, the magnetic-field dependence of the voltage in these intervals exhibits a hysteresis, whereas the voltage between the outer contacts remains zero in the entire magnetic-field range. The appearance of the observed voltage peaks and their hysteretic behavior can be explained by an imbalance between the chemical potentials of edge and bulk states, resulting from nonequilibrium charge redistribution between the edge and bulk states when the magnetic field sweeps under conditions of the quantum Hall effect. The results of the study significantly complement the conventional picture of the quantum Hall effect, explicitly indicating the existence of a significant imbalance at the edge of the two-dimensional electron gas: the experimentally observed difference between the electrochemical potentials of the edge and bulk exceeds the distance between Landau levels by tens of times.

Compact two-dimensional CMOS Hall sensor based on switchable configurations of four three-contact elements

This paper reports a novel CMOS sensor of compelling design simplicity for the measurement of both in-plane magnetic field components Bx and By at the same location. The device is operated through only four contacts and using a single control signal. It consists of four separate n-wells arranged as two orthogonal pairs. Each n-well segment forms a three-contact vertical Hall element (3CVHE) whose two outer contacts are used for the electrical interconnection of the four 3CVHEs into a conducting loop. The central contacts of each 3CVHE serve as drive and sense contacts enabling offset reduction by the spinning-current method. The operating principle of the novel device is derived from the magnetic field dependent resistance matrix of the individual 3CVHEs. The two-axis sensing capability of the sensor is achieved by selectively switching the interconnections among the four 3CVHEs, whereby the device is made sensitive alternatingly to Bx and By. Integrated transmission gates (TG) serve as switches. Appropriate design ensures the electrical symmetry of the sensor, which results in a low equivalent offset field of 0.2 to 0.4mT. For a nominal B field of 3.7mT the RMS error of the measured magnitude and angle of B are extracted to be only 42 μT and 0.7°, respectively.

Predicting thermal stability of organic solar cells through an easy and fast capacitance measurement

Degradation of organic photovoltaic (OPV) devices is currently a topic under intense research as it is one of the main limitations towards the commercialization of this technology. Morphological changes at both active layer and interfaces with the outer contacts are believed to determine main key issues to be overcome. In-line techniques are essential to rule out any effect arising during sample fabrication. Unfortunately, the number of physical techniques able to provide morphological information on complete and operational devices is certainly limited. In this work, we study the thermal degradation of bulk heterojunction (BHJ) solar cells composed by different donor polymers with techniques developed to provide in-situ information on operational devices. Capacitance measurement as a function of temperature monitors the electrical integrity of the active layer and provides the threshold temperature (TMAX) at which the whole device becomes thermally unstable. We found a direct correlation between the threshold temperature TMAX, obtained by capacitance–temperature measurements on complete OPV devices, and the power conversion efficiency decay measured at 85°C. Devices tend to be thermally stable when the temperature of the thermal stress is below TMAX, while above TMAX evident changes in the active layer or at the active layer/electrode interface are also detected by confocal fluorescence microscopy. The capacitance method gives precious guidelines to predict the thermal stability of BHJ solar cells using an accelerated and easy test.

Modeling and fabrication of single cantilever piezoelectric microgenerator with optimized Zno active layer

This paper presents design and fabrication process details of a piezoelectric generator with a thin-film zinc oxide (ZnO) layer. Structure of the piezoelectrical cantilever beam harvester consists of ZnO layer in between two insulating Al2O3 layers and outer aluminium contacts deposited on a silicon substrate. This multilayer system was prepared by the combination of radio-frequency and direct-current magnetron sputtering. Geometrical arrangement of the substrate holder and deposition target was optimized in order to reduce the disruptive effect of the high energy ions bombardment on the ZnO film microstructure. We present ZnO microstructure characterization by means of X-ray diffraction and scanning electron microscopy related to the estimation of internal micro-strains, crystallite sizes and deposition rates. Maximum generated open-circuit voltage achieved close to the cantilever resonant frequency of 595Hz was 0.975V.

A Novel Vacuum Interrupter Contact Design for Improved High Current Interruption Performance Based on a Double-TMF Arc Control System

A new two-contact system with double-transversal magnetic field (TMF) structure is investigated regarding its potential for high current interruption. It consists of two concentric TMF contacts, in which the inner contact has a disk-shaped structure (spiral contact) and the outer contact a cup-shaped structure. This contact assembly gives several advantages over the use of single-TMF contacts, as the constricted high-current arc might either split between both inner and outer contacts or commute from the inner to the outer contact and continue its rotation. In both scenarios, we expect a better distribution of the arc energy over a larger contact surface. B-field simulation and Lorentz force calculation are carried out to investigate whether two constricted arcs, with one burning on the inner contact and the other on the outer contact, can coexist given their mutual attraction. Single-phase high current interruption tests were carried out to compare the performance of this new double-TMF contact system with that of a standard spiral-type single-TMF one. These tests have revealed superior performance of the new double-TMF contact system, which could interrupt current amplitude at least 20% higher than the one interrupted by the single-TMF contact system.

2D in-plane Hall Sensing Based on a New Microdevice Coupling Concept

A 2D Hall microdevice for synchronous measurement of two in-plane magnetic-field components, using an original coupling concept based on two identical parallel-field three-contact (3C) silicon Hall elements positioned at right angle and integrated on the same chip, is presented. The two pairs of outer contacts of 3C Hall transducers are connected via two load resistors, converting simultaneously and independently the current changes in Bx and By magnetic fields into Hall voltages. Since the supply currents in both structures are equal, the magnetosensitivities are the same, too. At a fabrication of the devices on a common silicon chip, the output temperature drifts are perfectly matched. The high measurement accuracy, performance and compensated channel offsets of this 2D magnetometer are achieved by the minimal interface components between both sensors. The suggested sensing microsystem is appropriate for many contactless measurement instruments.

Experimental Rig for Measuring Lubricant Film Thickness in Rolling Bearings

Electrical capacitance has been applied in the past for measuring the lubricant film thickness in rolling element bearings. The main difficulty arises from the fact that the measured capacitance is a combination of the capacitances of many rolling elements, which come in contact with both the inner and outer rings. Besides, the capacitance of the Hertzian contact itself and the surrounding area must also be separated. It results in a complex system which, in order to be solved for the film thickness at a particular location on the bearing many approximations have to be made. In the present study the authors use an experimental rig in which the capacitance of a single ball can be isolated. Moreover the capacitance of the ball – inner ring and ball – outer ring contacts can be measured separately.