Variation Of Electrical Resistivity Research Articles

Robust inversion of 1D magnetotelluric data using the Huber loss function

AbstractIn this study, a robust 1D inversion was performed on magnetotelluric (MT) data by utilizing the Huber loss function to avoid misleading interpretation of results, which is caused by the presence of outliers in the data. The MT method utilizes the ratio between the electric field (E) and the magnetic field (H), which are perpendicular to each other, to obtain impedance values (Z). These values are used to extract subsurface information in the form of electrical resistivity variations with depth. In the study, forward modeling of the 1D MT responses was conducted by recursively calculating Z values. Robust inversion was performed using the Huber loss function as an objective function to minimize the difference between the calculated and observed data. The Huber loss function combines the squared loss and the absolute loss to anticipate the presence of outliers in MT observation data. The robust inversion was performed on synthetic data with additional noise and field data. The inversion process utilized 50 layers with a thickness of 500 m, a hyperparameter $$\varvec{\delta }= 5\times {10}^{-2}$$ δ = 5 × 10 - 2 , $$\lambda =0.01$$ λ = 0.01 , and $${\lambda }_{t}=100$$ λ t = 100 . The number of iterations used was 500 for inversions that used synthetic data and 3000 for inversions that used field data. The robust inversion scheme using the Huber loss function successfully overcame the presence of outliers and accurately estimated the actual model parameters, both for synthetic data and field data that contained outliers. The misfit was relatively small and close to zero, indicating that the inversion code works well.

Strategies for Enhanced Optical Performance and Durability of VO2‐Based Thermochromic Windows

Due to the growing need for smart windows for buildings to reduce energy usage, vanadium dioxide (VO2) has been investigated as a potential material for thermochromic smart windows due to its ease of implementation and simplicity in industrial production. VO2 undergoes a reversible phase shift from a monoclinic (M, P21/c) semiconductor to a rutile (R, P42/mnm) metal at a critical temperature of 68 °C. This transition is accompanied by acute variations in IR reflectance, transmittance, and electrical resistance. Despite substantial developments in thermochromic materials, their optical and transition properties are still unsatisfactory. In the past several decades, many methods for enhancing optical properties have been reported, including composite films, multilayer structures, and element doping. Recent developments in thermochromic smart windows to improve both optical properties and durability have been surveyed in this review. Additionally, future growth trends have been provided by the possibility of commercially manufacturing VO2 smart windows.

A flexible bimodal self-powered optoelectronic skin for comprehensive perception of multiplexed sensoring signals

Multi-modal electronics skin that mimics collaborative operation of natural skin establishes a substantial foundation for next-generation smart healthcare, biomimetic science and related interdisciplinary fields. However, the power consumption of multi-channels and the decoupling complexity of fused-information that determine the effectiveness of the system still remain enormous challenge. Here, a bimodel self-powered optoelectronic fusion system with a vertical integration structure to achieve mechanical and illumination perception is reported, enabling simultaneous monitoring of human motion signal and environmental illumination. This device comprises a photo-conductive layer of MAPbI3-PVA and a teflon (PTFE) friction layer of TENG-based sensor, characterizing the mechanical and illuminance information in the form of pulse electrical signals and continuous resistance variation curves, respectively. This bimodel sensor exhibits the highest photoelectric responsivity of 64 mA/W and saturated output power of 156 μW/cm2 within the visible illumination range. Moreover, the environmental and mechanical stability of the device have been significantly improved, which is attributed to the inherent flexibility and hydrophilicity of PVA wrapped in perovskite grains. Finally, A 3×3 bimodel array is attached onto the volunteer's cervical vertebra for classifying motion posture and ambient illuminance by monitoring the surface tension distribution under different lighting conditions, validating the feasibility and promotion potential for application scenarios.

Investigation on NTC/PTC effects of cement-based self-heating composites with varied conductive filler contents

The present study systematically investigated the influence of varied conductive filler contents on the negative/positive temperature coefficient (NTC/PTC) effects in cement-based self-heating composites. Different composite formulations containing varying proportions of carbon nanotubes (CNT) and carbon fiber (CF) were prepared and subjected to self-heating tests at different input voltages. Analysis of temperature and electrical conductivity data obtained during the tests elucidated the NTC/PTC effects. Additionally, diverse analytical techniques were employed to characterize the physicochemical properties of the samples. Results indicated a correlation between NTC and PTC effects and thermal expansion as well as variations in electrical resistivity with increasing temperature. Moreover, a specific temperature and electrical resistivity range is identified where the NTC effect transitions to the PTC effect, a transition range influenced by the conductive filler content. Enhanced heat-generation accelerated the PTC effect by inducing structural alterations in the sample's physicochemical composition.

A comparative study on the electrical contact behavior of CuZn40 and AgCu10 alloys under fretting wear: Effect of current load

The current load is one of the most significant factors in the reliability of electrical contact under fretting conditions. In this paper, the fretting wear experiments are conducted for CuZn40 and AgCu10 alloys with varied current loads. The variations of electrical contact resistance (ECR), ECR endurance, temperature, and wear volume with the increasing current load of two alloy materials under fretting conditions are investigated, and the differences between their electrical contact behaviors are compared. The microstructures of the surface wear morphology are examined to reveal the mechanisms of fretting wear and electrical contact failure. In addition, the fretting wear volume evolution of both alloys under different fretting cycles is studied. The results show the current load impacts the wear morphology. The wear particles become smaller and the oxide layer becomes stable with the increase of current load. The effect of current load on ECR and temperature is more significant for CuZn40 alloy. The ECR endurance for both materials first increases and then decreases. This is attributed to two competitive mechanisms controlling the evolution of ECR endurance under varied current loads.

An integrated nanofiller spray and nanosecond pulse electrically-assisted method for synergistically interlaminar toughening and in-situ damage monitoring of CFRP composites

Nanomaterials have already been explored their potential for interlaminar toughening and crack-monitoring capabilities within the field of composite materials. However, efficient enhancement of interlaminar fracture toughness remains an unresolved challenge. Herein, a novel integrated filler spray and nanosecond pulsed electric field (nsPEF)-assisted curing technique is proposed for the fabrication of high-performance composite material system for the first time. The spraying technique proves to be an effective approach for depositing fillers, including carbon nanotubes (CNTs), graphene nanoplatelets (GNPs), and carbon nanofibers (CNFs), onto carbon fiber prepreg. Meanwhile, the nsPEF-assisted technique is utilized to enhance the wettability of resin to fiber, thus reducing void defects. The efficacy of this integrated technique is evidenced by the particularly low content of fillers (0.047 wt%). The experimental results show a substantial reduction of porosity in the composite by 49.36% (from 1.56% to 0.79%). Meanwhile, the mode I initiation and steady-state toughness of samples with CNTs and GNPs are remarkably improved by up to 47% and 82%, respectively, compared to the baseline. This represents the most significant improvement reported to date for non-functionalized CNTs and GNPs at such low concentrations. Moreover, the relative electrical resistance variation (ΔR/R0%) of CNT/GNP sensors used for in-situ damage sensing increased by ∼ 14%. This work pioneers the investigation of the synergistic effects of two promising techniques for preparing composite materials, offering advantages in terms of simplicity, multifunctionality, and the potential for industrial scalability.

Polyimide aerogels with a dual electrically conductive network for electromagnetic interference shielding, piezoresistive sensing, and thermal management

The constant iteration of wearable devices necessitates lightweight electromagnetic shielding materials with multiple functions. In this study, an elastic reduced graphene oxide/polyimide (rGO/PI) aerogel skeleton was prepared through freeze-drying and thermal annealing. Then the highly conductive two-dimensional (2D) transition metal carbide (MXene) was coated onto the rGO/PI skeleton using vacuum impregnation to fabricate MXene@rGO/PI composite aerogels. Due to the dual electrically conductive network formed by rGO and MXene, the MXene@rGO/PI composite aerogels exhibit exceptional electromagnetic interference shielding effectiveness (EMI SE) of 58.7 dB in the X-band at a density of 0.063 g cm−3. Additionally, these composite aerogels demonstrate sensitive piezoresistive sensing capabilities (the electrical resistance variation caused by compressive stress) for detecting human body motion and also possess excellent thermal management properties including efficient Joule heating (up to 108 °C at 10 V) and superior thermal insulation performance. This work presents a feasible strategy for developing polymer-based composites for multi-functional applications such as wearable electronics.

Variation of first pop-in loads in nanoindentation to detect chemical short-range ordering in the equiatomic Cr-Co-Ni medium-entropy alloy

The variations of the first pop-in load in nanoindentation with annealing temperature and time have been investigated both by experiment and theoretical molecular dynamics (MD) simulations for the equiatomic Cr-Co-Ni medium-entropy alloy (MEA). Regardless of the loading rates, the first pop-in load tends to increase with the increase in electrical resistivity consistently by experiment and MD simulations. The trend in the variation of pop-in load with annealing temperature/time coincides with what is observed in the variation of electrical resistivity in our previous study, indicating that the first pop-in load in nanoindentation can thus be used to qualitatively detect the evolution of short-range ordering (SRO) in the Cr-Co-Ni MEA, and that the peak temperature for SRO for the equiatomic Cr-Co-Ni MEA is 673 K. MD simulations indicate that the first pop-in corresponds to the nucleation of partial dislocation loops beneath the indenter for both annealing conditions and that the increased first pop-in load in nanoindentation is attributed to the higher energy barrier for the nucleation of dislocation loops due to the higher degree of SRO.

Tensile damage self-monitoring of carbon fiber/epoxy 3D braided composites with electrical resistance method

Electrical resistance method (ERM) has great potential in self-monitoring structural health for carbon fiber composites due to carbon fiber conductivity. Here we report the correlation between tensile damages and electrical resistance changes of 3D braided composites subjected to monotonic and cyclic tensile loading. Experimental and finite element methods were utilized to reveal the electrical resistance variation and damage evolution under monotonic tensile loading. We found that the electrical resistance changes under monotonic tensile loading could be segmented into three regions, namely, linear growth region, transition region and exponential growth region, corresponding to different damage modes. Synchronous and reversible electrical resistance changes at a low strain level (12% of fracture strain) cyclic loading proved the stability and repeatability of self-monitoring capability. While, the abrupt electrical resistance changes at a high strain level (75% of fracture strain), indicated catastrophic failure of the composites. Such kind of correspondence between tensile damages and electrical resistance change under tensile loading enables ERM to achieve the in-situ structural health monitoring of 3D braided composites without relying on external sensors.

Investigation of the influence of technological parameters on the copper deposition process

The possibility of electroplating copper coatings on chemically and chemical-galvanically nickel-plated acrylic fibers has been studied. The effect of electrolyte pH, its composition, current strength at the 1st and 2nd cathodes, as well as the metallization time on the electrophysical, physical and mechanical properties of copper-containing fibers have been studied.
 Electrically conductive fibers with different copper contents have been obtained. Regularities have been established for the change in the electrical properties of fibers depending on the content of copper. The studies have shown that with an increase in the copper content, the electrical conductivity, the uniformity of the coating and the uniformity of the electrophysical properties (for chemical-galvanically nickel-plated fiber) increase. In the case of copper plating of chemically nickel-plated fiber, the coefficient of variation in electrical resistance increases with increasing plating time, despite the fact that the copper content increases, and the coefficient of variation in copper content and electrical resistance decreases.

Humidity Sensing Analysis of ZnxCo2−xO4 (0.0 ≤ x ≤ 1.0) Nanocomposite Solid State, Thin and Thick Film Sensors at Room Temperature

This paper reports the performance of the humidity sensing properties of cobalt zincate nanocomposite synthesized via conventional precipitation method. X-ray diffraction (XRD) outline revealed amorphous nature of nanocomposite. Scanning Electron Microscopy (SEM) images show sphere-shaped morphology all over the surface. Optical characterization of the film was carried out by Ultra Violet (UV)-visible spectrophotometer. By Tauc plot the estimated value of band gap of the film was found 3.81 eV. The variations in electrical resistance of the pellet and films were measured with change in Relative Humidity (RH%). As RH% increases, the resistance of each pellet decreases for the range 10% to 95%. The activation energy calculated from Arrhenius plot was found 0.58 eV. This investigation demonstrates the potential of ZnxCo2−xO4 nanocomposite for x < 1 based sensor for humidity sensing which is unique.

Improvement of thermoelectric performance of flexible compound Ag2S0.55Se0.45 by means of partial V-substitution for Ag

The effects of the partial V-substitution for Ag on the thermoelectric (TE) properties are investigated for a flexible semiconducting compound Ag2S0.55Se0.45. Density functional theory calculations predict that such a partial V-substitution constructively modifies the electronic structure near the bottom of the conduction band to improve the TE performance. The synthesized Ag1.97V0.03S0.55Se0.45 is found to possess a TE dimensionless figure-of-merit (ZT) of 0.71 at 350 K with maintaining its flexible nature. This ZT value is relatively high in comparison with those reported for flexible TE materials below 360 K. The increase in the ZT value is caused by the enhanced absolute value of the Seebeck coefficient with less significant variation in electrical resistivity. The high ZT value with the flexible nature naturally allows us to employ the Ag1.97V0.03S0.55Se0.45 as a component of flexible TE generators.

Ambipolar surface conduction in oxygen sub-stoichiometric molybdenum oxide films

The surface electric conduction in amorphous and crystallized molybdenum oxide films was studied as a function of electronic structure by current–voltage and simultaneous spectroscopic ellipsometry measurements on structures of the kind Al/Molybdenum oxide (MoOx)/Al, at temperatures up to 400 °C and in ambient air. At room temperature, both amorphous and crystalline MoOx samples were found to be sub-stoichiometric in oxygen. The random distribution of oxygen vacancies and the imperfect atomic ordering induced the creation of an intermediate band (IB) located near the valence band and of individual electronic gap states. At temperatures below 300 °C, the conduction was found to exhibit ambipolar character in which electrons and holes participated, the former moving in the conduction band and the latter in the IB and though gap states. Above 300 °C, due to samples gradual oxidation and improvement of atomic ordering (samples crystallization), the density of states in the IB and the gap gradually decreased. The above in their turn resulted in the gradual suppression of the ambipolar character of the conduction, which at 400 °C was completely suppressed and became similar to that of ordinary n-type semiconductor. The above phenomena were found to be reversible, so as the semiconducting MoOx samples were returning to room temperature the ambipolarity of the conduction was gradually re-appearing giving rise to an unusual phenomenon of “metallic” temperature variation of electrical resistance when electrons were injected.

Material-enabled damage inspection of multifunctional shape memory alloy tufted composite T-joints

The through-the-thickness reinforcement of carbon-epoxy composite joints with shape memory alloy (SMA) tufts has shown significant improvement of the mechanical strength, fracture toughness, and delamination resistance. This study explores the thermal-electric properties of SMA filaments tufted in composite T-joints to exhibit multiple functionalities including material-enabled thermographic inspection and structural health monitoring via in-situ strain sensing. Infrared thermography image analysis was performed on both pristine and damaged T-joint specimens subject to pull-off testing. Experimental results showed that the heat generated by SMA tufts measured by an infrared camera provided accurate indication of delamination perpendicular to the tuft direction. SMA tufts were also used as strain sensors embedded within the T-joint. Local changes of the electrical resistance in SMA filaments, both separately and within the joint, were observed during pulling loads. Digital Image Correlation measurements exhibited good correlation between electrical resistance variations and the opening of delamination. These results pave the way for the development of multifunctional composite joining systems combining enhanced through-the-thickness damage tolerance and self-sensing capabilities.

Numerical analysis of 40 MW HTS motor electromagnetic characteristics for ship electric propulsion

In recent years, with the development of ship electric propulsion system, High Temperature Superconducting (HTS) motors have gained attention as a promising potential resolution due to their high-power density and the progression of cryogenic refrigeration technology. We present an electromagnetic characteristics numerical analysis of 40 MW, 120 rpm, HTS synchronous motor which is a semi-superconducting motor: in fact, it has a superconducting rotor composed of YBCO material and a conventional stator. Combining electric resistivity variation of rotor copper shielding sleeve in low temperature environment and YBCO coil critical current, the electromagnetic behavior of the 40 MW HTS synchronous motor is analyzed with non-ferromagnetic stator support structure. To assess the effects of varying stator winding currents and thickness on eddy current losses of the copper shielding sleeve, calculations were done, and a preliminary discussion was initiated. This study has certain reference significance for electromagnetic design and optimization of multi-ten MW HTS motors, especially used in ship electric propulsion system.

Silicone/ broadleaf wood fiber /MWCNTS composite stretchable strain sensor for smart object identification

Stretchable strain sensors have been rapidly developing in recent years. Fabricating strain sensors with both large workable strain range and high sensitivity via a low-cost and straightforward process is still challenging. Here, this work created a multi-walled carbon nanotubes (MWCNTs) / broadleaf wood fiber (BWF) film, the highly micro-porous network of which allows a slow infiltration of liquid silicone in a vacuum environment to form an elastic composite, serving as a stretchable strain sensor. The sensor showed an ultra-wide strain of up to 440% and high sensitivity of GF (gage factor) of 3.3 at 0∼200% strain and of 7.8 at 200∼440% strain. In addition, the sensor is able to endure 5500 cyclic loading/unload at 100% strain with no damage in its mechanical structure and small variation in electrical resistance. To demonstrate its practicality, the sensor was incorporated into a soft pneumatic griper and utilized as a bending sensor to detect the griper deformation. The system demonstrated a high accuracy of 99.33% in the classification of lab beakers using a data-driven framework built with a trained Support Vector Machine (SVM) algorithm.

Effect of technological parameters on the process of copper deposition on chemically and chemical-galvanically nickel-plated fibers

Purpose This paper aims to study the possibility of electroplating copper coatings on chemically and chemical-galvanically nickel-plated acrylic fibers, to be further processed into yarn, fabrics, knitwear and nonwoven materials. Design/methodology/approach Electrically conductive fibers with different copper contents have been obtained, and the effect of electrolyte pH, its composition, current strength at the first and second cathodes, as well as the metallization time on the electrophysical, physical and mechanical properties of copper-containing fibers, has been studied. Findings The studies have shown that with an increase in the copper content, the electrical conductivity, the uniformity of the coating and the uniformity of the electrophysical properties (for chemical-galvanically nickel-plated fiber) increase. In the case of copper plating of chemically nickel-plated fiber, the coefficient of variation in electrical resistance increases with increasing plating time, even though the copper content increases, and the coefficient of variation in copper content and electrical resistance decreases. The physical and mechanical properties of copper-containing fibers differ slightly from the original (subjected to copper plating) and industrial Nitron fibers. With copper plating, the strength of the fiber practically does not decrease, and the elongation decreases somewhat, compared with the mass-produced Nitron fiber. Originality/value The physical and mechanical properties of copper-containing fibers are quite high, which makes it possible to be successfully further processed into yarn, fabrics, knitwear and nonwoven materials.

Stretchable hybrid platform‐enabled interactive perception of strain sensing and visualization

AbstractHuman–machine interactive platforms that can sense mechanical stimuli visually and digitally are highly desirable. However, most existing interactive devices cannot satisfy the demands of tactile feedback and extended integration. Inspired by the mechanoluminescence (ML) function of cephalopod skin and the sensitive perception of microcracked slit‐organs, a bioinspired stretchable interactive platform is developed by designing a stretchable poly(styrene‐block‐butadiene‐block‐styrene)/fluorescent molecule (SFM) composite followed by the in situ polymerization of pyrrole (Py) and deposition of carbon nanotubes (CNTs), which possesses a simple multilayered structure and quantitatively senses the applied strains via the variations of digital electrical resistance and visual fluorescence intensity. Using the strain‐dependent microstructures derived from the synergistic interactions of the rigid PPy/CNTs functional layer and SFM, the SFM/PPy/CNTs‐based platforms exhibit excellent strain‐sensing performance manifested by a high gauge factor (GF = 2.64 × 104), wide sensing range (~270%), fast response/recovery time (~155/195 ms), excellent stability (~15,000 cycles at 40% strain), and sensitive ML characteristics under ultraviolet illumination. Benefiting from the novel fusion of digital data and visual images, important applications, including the detection of wrist pulses and human motions, and information dual‐encryption, are demonstrated. This study demonstrates the superiority of advanced structures and materials for realizing superior applications in wearable electronics.

Мониторинговые электротомографические исследования зоны Иссык-Атинского разлома (Северный Тянь-Шань)

In 2023, monitoring geophysical studies were carried out using the electrical resistivity tomography (ERT) method along three profiles that cross the strike zone of the Issyk-Ata fault in the transverse direction. A detailed study was carried out of the observed variations in apparent electrical resistivity, which characterize the change in the electrical properties of the upper part of the Earth's crust section with a 40-minute discretization in time. Using the analysis of difference pseudo-sections of apparent resistivity, constructed based on the results of ERT monitoring, the most informative pseudo-depth interval from the point of view of geoelectric activity was determined for all three monitoring profiles. Accordingly, for a pseudo-depth of 24 m on each monitoring profile, an assessment was made of the geodynamic activity of these sections of the Issyk-Ata fault based on an analysis of the magnitude of two parameters: the amplitude of apparent resistivity variations and the correlation coefficient of electrical resistivity variations with lunar-solar solid tides. High values of these parameters, in our opinion, determine the location of modern active fault zones.

Volcanic monitoring of the 2021 La Palma eruption using long-period magnetotelluric data

Between September and December 2021, the first subaerial volcanic eruption in the Canary Islands in 50 years took place on the island of La Palma. Since November 2021, we have been conducting a long-period magnetotelluric (MT) monitoring experiment at a site located 2.4 km east of the volcanic cone. Having continuously recorded data since then, the obtained dataset shows significant changes in resistivity over the fourteen months following the eruption: more than ± 20% in apparent resistivity and ± 2 degrees in phase. These temporal variations in electrical resistivity, recorded continuously using long-period MT during both the syn- and post-eruptive stages, have not been reported to date, making this dataset unique. Four estimated impedances have been selected as representatives of the major temporal changes observed and inverted to generate new 3-D resistivity models. The results provide novel key information on the spatiotemporal evolution of the subsoil's electrical resistivity, enabling the characterization of a set of structures acting as preferred magmatic fluid pathways. Therefore, our study highlights the strong potential of MT as a volcanic monitoring tool and provides new insights about the evolution of the fluid pathways during the post-eruptive stage. These findings enhance our understanding of the magmatic system and may contribute to volcanic hazard mitigation in the future.