Resistance Change Rate Research Articles

State-of-Health Estimation for LiFePO4 Battery System on Real-World Electric Vehicles Considering Aging Stage

Comprehensive and accurate estimation methods of the state of health (SOH) of battery systems play a significant role in online monitoring for the safe and reliable operation of electric vehicles (EVs). Most existing estimation techniques are established on top of data from well-controlled experimental environments and tend to focus on a single health feature, thus not practical for real-world EVs’ SOH monitoring throughout the life cycle. To address this problem, based on real-world EV operation data, a novel SOH estimation model is presented for LiFePO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> battery systems in EVs with consideration of degradation mechanisms. The ohmic resistance and the peak value of the incremental capacity (IC) curve are extracted from a large number of electric buses as health features. The influence of temperature on the ohmic resistance is eliminated by exponential fitting, which transforms ohmic resistance into the relative change rate of ohmic resistance. With joint considerations of the two health features and the mechanism of battery aging, three stages of SOH degradation can be quantitively described. The test results show that the proposed model is able to track SOH degradation from 0 to over 300 000 km and reflect the SOH of the battery more comprehensively in the early and late life cycles of the battery compared with single-health-feature methods.

3D printing stretchable core-shell laser scribed graphene conductive network for self-powered wearable devices

Graphene-based flexible electronics, particularly those with self-powered ability and stretchability, are greatly promising candidates in the applications of portable and wearable devices. However, complicated deformation of human body and harsh environment inevitably leads to the degradation of conductivity of wearable electronics due to the intrinsic brittleness and crack sensitivity of graphene. Herein, a metamaterial-inspired stretchable and stable conductive network fabricated by 3D printing polyether-ether-ketone (PEEK) and double-side laser scribing graphene (LSG) techniques is demonstrated, which is called LSGCN. The double-side LSG covers the outer surfaces of printed PEEK filaments and forms a special core-shell structure, and its conductivity is 2.72 times of traditional flat graphene. Moreover, the parametric design of LSGCN can increase the stretchability of the structure from 20% to 118%, while ensuring that the change rate of resistance is limited to 1.06 within the 60% strain range. Based on the triboelectric effect, we also demonstrate LSGCN-based self-powered devices, including wearable smart belts and human-computer interaction gloves. Particularly, the LSGCN glove integrates 21 interactive channels, and it can work as the input equipment to control the simulated calculator, display the slides and even play the 3D games. This hybrid-fabricating method of LSGCN provides a novel strategy to fabricate stretch-stable conductive structures for applications in bio-energy harvesting and self-powered sensing devices, which opens up a new avenue for the future Internet of Things.

Preparation of multi-axial compressible 3D PVDF nanofibre/graphene wearable composites sensor sponge and application of integrated sensor

Compared with piezoelectric and capacitive sensor devices, piezoresistive sensor devices have a simple preparation process and good sensing performance, and are the most widely used in flexible strain sensing. The sensing performance of piezoresistive flexible strain sensors is usually characterized by parameters such as sensitivity, sensing range and durability. The development of piezoresistive sensor devices with multiple excellent properties at the same time is the current research hotspot. In this study, a PVDF nanofibre/graphene multiaxial compressible composites sponge sensor was prepared by combining nanotechnology with a freeze-drying method, and then integrated bridge circuit devices through multiple sensing sponges. The sensor device prepared in this study is a multifunctional wearable device with high sensitivity, wide sensing range and good durability. Results show that the addition of excessive graphene significantly improves the pore morphology, in which it is a cube porous with a uniform size. The thicker porous wall formed by the entanglement of graphene sheets improves the mechanical strength of the sensor. The sponge sensor also has excellent elasticity, whilst the elastic recovery rate can be as high as 90% when the compression reaches more than 80%. When compressed in different directions, it has a wide sensing range, whilst the resistance change rate can be from 110% to 0.5%, all of which are regular wave curves. The bridge circuit integrated device of multiple sensing sponges obviously improves the overall sensitivity of the sensor under the same compression ratio, the compression ratio is reduced and the service life is increased. This conclusion lays a research foundation for the application of multi-module piezoresistive sensor integration in the field of smart wearables.

TiB2‐Modified Polymer‐Derived Ceramic SiCN Double‐Layer Thin Films Fabricated by Direct Writing for High‐Temperature Application

The thermal stability at high temperatures is the first design principle of high‐temperature thin‐film sensors. To improve the thermal stability of the thin‐film sensor, a TiB2‐modified SiCN double‐layer thin‐film resistor grid with a thickness of 18 μm is fabricated on an alumina substrate via direct writing. Owing to their in situ–generated SiO2–B2O3–TiO2 thermally grown oxide protective layer on the surface and TiB2 percolation paths inside, the produced films exhibit large high‐temperature oxidation resistance, electrical conductivity and high‐temperature‐resistance stability. In the thermal cycling test up to 800 °C, the TiB2‐modified SiCN films exhibit a negative‐temperature coefficient of resistance and excellent repeatability and stability. The resistance change rate at 800 °C for 1 h is only 1.1%. With the flexible manufacturing and high‐temperature stability of such ceramic films, this work on double‐layer ceramic films can be applied to in situ monitoring of hot components at high temperature.

Experimental and numerical investigation on the mechanical and electrical properties of multiwalled carbon nanotube/waterborne polyurethane coated 3D printing carbon fiber reinforced composites

AbstractMechanical–electrical properties and failure behavior of 3D printed carbon fiber reinforced composites with multiwalled carbon nanotube (MWCNT)/waterborne polyurethane (WPU) conductive coating were studied to develop a performance monitoring method for composites. The results indicated that the coating materials could obtain good mechanical–electrical properties and sensitivity factor. Scanning electron microscopy images show that multiple conductive channels exist in the coating. The coating is well bonded to the composites. In order to obtain more details, mechanical–electrical coupling simulation was conducted. The experiment and simulation are in good agreement. The correlation between the strain of composite part and the electrical resistance change rate of the coating is validated. Furthermore, the multi‐scale observations reveal the failure mechanism including composite‐coating debonding, brittle fracture of polyamide matrix, fiber breakage, and pull‐out in the composite part, as well as ductile fracture of WPU matrix and MWCNT pull‐out in the coating part. This study can provide some insights for structural health monitoring of composites.

Interfacial prediction and tensile damage tracking of carbon fiber reinforced polyamide 66 using Z-axis electrical resistance method

Deformation monitoring of the inner fabric is important to ensure the quality of continuous fiber-reinforced composites. A Z-axis electrical resistance (Z-ER) mapping method was utilized as an accurate evaluation method to predict the internal composition and deformation of carbon fiber reinforced polyamide composites (CF/PA) during tensile load. The electrical resistance change rate (ERC) in the tensile direction and the Z-ER for tensile stress were utilized to detect the tensile damage of carbon fiber reinforced polyamide composites. Based on the Z-ER mapping, the internal state of carbon fiber reinforced polyamide composites was categorized into three types: uniform electrical resistance (ER), large standard deviation (SD), and tilt ER. The evaluation method was also able to predict the probability of defective CF/PA exhibiting that the normal tensile failure behavior was approximately 31.5%. This process of detection can be integrated as an in-line evaluation technique to automate and standardize carbon fiber reinforced polyamide composite manufacturing.

Test Strip Platform Spin-Off for Telomerase Activity Detection: Development of an Electrochemical Biosensor.

Telomerase overexpression has been associated directly with cancer, and the enzyme itself is recognized within the scientific community as a cancer biomarker. BIDEA’s biosensing strip (BBS) is an innovative technology capable of detecting the presence of telomerase activity (TA) using electrochemical impedance spectroscopy (EIS). This BBS is an interdigital gold (GID) electrode array similar in size and handling to a portable glucose sensor. For the detection of the biomarker, BBS was modified by the immobilization of a telomere-like single strand DNA (ssDNA) on its surface. The sensor was exposed to telomerase-positive extract from commercially available cancer cells, and the EIS spectra were measured. Telomerase recognizes the sequence of this immobilized ssDNA probe on the BBS, and the reverse transcription process that occurs in cancer cells is replicated, resulting in the ssDNA probe elongation. This surface process caused by the presence of TA generates changes in the capacitive process on the electrode array microchip surface, which is followed by EIS as the sensing tool and correlated with the presence of cancer cells. The telomerases’ total cell extraction protocol results demonstrate significant changes in the charge-transfer resistance (Rct) change rate after exposure to telomerase-positive extract with a detection limit of 2.94 × 104 cells/mL. Finally, a preliminary study with a small set of “blind” uterine biopsy samples suggests the feasibility of using the changes in the Rct magnitude change rate (Δ(ΔRct/Rcti)/Δt) to distinguish positive from negative endometrial adenocarcinoma samples by the presence or absence of TA.

Foldable and highly flexible transparent conductive electrode based on PDMS/ Ag NWs/PEDOT: PSS

In this work, we can transfer poly (3,4-ethylenedioxythiophene): poly (styrenesulfonate) (PEDOT: PSS) from the glass substrate to the polydimethylsiloxane (PDMS) substrate by using HNO3 treatment, without losing the resistance and transmittance of the transparent conductive film, which overcome the hydrophobic characteristic of the PDMS substrate. The silver nanowires (Ag NWs) based flexible transparent electrode with PDMS as substrate is prepared. The PDMS/Ag NWs/PEDOT: PSS composite film shows a high transmittance of over 84.07% and low sheet resistance of 9.05 Ω/sq, and its quality factor can reach 218.2. Moreover, the transparent conductive film has an excellent folding performance. After 200 repeated folding experiments, the resistance change rate is only 7.8%. The heater prepared by using the composite film can reach a maximum heating temperature of 184.4 °C, and repeat the on-off operation several times under the condition of 55 °C, which proves the promising application of transparent conductive film in wearable devices for human bodies.

Determination of Moisture Content and Shrinkage Strain during Wood Water Loss with Electrochemical Method.

Moisture content and shrinkage strain are essential parameters during the wood drying process. The accurate detection of these parameters has very important significance for controlling the drying process and minimizing drying defects. The presented study describes an electrochemical method to determine wood moisture content and shrinkage strain during drying, and the accuracy of this method is also evaluated. According to the results, the electrical resistance of the samples increased with the decrease in wood moisture content. As the moisture content changed from 42% to 12%, the resistance increased from 1.0 × 107 Ω to 1.2 × 108 Ω. A polynomial fitting curve was fitted with a determination coefficient of 0.937 to describe the relationship between moisture content and electrical resistance. In addition, both the shrinkage strain and resistance change rate increased with the decrease in wood moisture content, especially for the moisture content range of 23% to 8%, where the shrinkage strain and resistance change rate increased by 4% and 30%, respectively. The shrinkage strain increased exponentially with the increase in the resistance change rate; thereby, an exponential regression equation was proposed with a determination coefficient of 0.985, expressing the correlation between the two. This demonstrates the feasibility of the electrochemical method for measuring wood moisture content and shrinkage strain.

Self-Monitoring of Reinforced Concrete Beam Bending with Carbon Nanofiber Polyurethane Composite

To examine the intelligent sensing properties of polyurethane cement mixed with carbon nanofiber and used as beam reinforcement material, 7 reinforced concrete T-beams were made and reinforced with carbon nanofiber polyurethane cement material (CPUC). Four-point bending tests were conducted. Reinforcing concrete beams with CPUC material might increase the yield load and ultimate load of beams significantly. The overall stiffness of the reinforced beam was enhanced. CPUC played a significant inhibitory role in the formation and development of beam cracks. A sudden change in the rate of CPUC resistance can be used to monitor the yield of a steel bar, and then, a safety warning for the components can be launched. By establishing a model of the relationship between the resistance change rate and the external load, the bearing capacity of the beam is evaluated in real time, and the dual effects of reinforcement and health monitoring of the beam are realized simultaneously.

Mo Contact via High-Power Impulse Magnetron Sputtering on Polyimide Substrate

It has always been a huge challenge to prepare the Mo back contact of inorganic compound thin film solar cells (e.g., CIGS, CZTS, Sb2Se3) with good conductivity and adhesion at the same time. High-power impulse magnetron sputtering (HiPIMS) has been proposed as one solution to improve the properties of the thin film. In this study, the HiPIMS technology replaced the traditional DC power sputtering technology to deposit Mo back contact on polyimide (PI) substrates by adjusting the experimental parameters of HiPIMS, including working pressure and pulse DC bias. When the Mo back contact is prepared under a working pressure of 5 mTorr and bias voltage of −20 V, the conductivity of the Mo back contact is 9.9 × 10−6 Ω·cm, the residual stress of 720 MPa, and the film still has good adhesion. Under the minimum radius of curvature of 10 mm, the resistivity change rate of Mo back contact does not increase by more than 15% regardless of the 1680 h or 1500 bending cycle tests, and the Mo film still has good adhesion in appearance. Experimental results show that, compared with traditional DC sputtering, HiPIMS coating technology has better conductivity and adhesion at the same time, and is especially suitable for PI substrates.

Health monitoring of composite single lap joints with highly sensitive MWCNTs film sensors

In this paper, a method with highly sensitive multi-wall carbon nanotubes (MWCNTs) film sensors was put forward to evaluate the health condition of glass fiber-reinforced composite single lap joints in real time. With this method, the single lap joint fracture can be predicted when the resistance change rate reached 1.11% to 5.89% approximately. Meanwhile, for the single lap joints, the reality can be found that the farther distance was from the interface to different layers, the more easily defect might emerge under the force introduced in the interface plane. And the stress in the middle area of the interface for the joint was greater than that in the edge when it was stretched. The results of experiments indicated that the effectiveness of MWCNTs sensors to monitor the health condition of the single lap joints was confirmed.

The Effect of the Addition of Graphene Nanoplatelets on the Selected Properties of Cementitious Composites

The aim of the current study is to investigate the properties of graphene nanoplatelets-cementitious composites in a consistent sense. The influence of the addition of 2D graphene nanoplatelets (GNPs) on the workability, setting time, flowability, strengths and piezoresistive properties were studied. The dosage of the GNPs is 0 0.05, 0.1, 0.3, 0.5, 0.7, and 1.0 wt% of the binder material. PVP type surfactant was used to disperse GNPs. The experimental results showed that the addition of GNPs increases the water requirement for normal consistency and decreases the flowability. A small amount of GNPs (0.05 wt%) can facilitate the setting. When the dosage of GNPs is above 0.1 wt%, it leads to the delay of the setting time. In terms of the strengths, the addition of GNPs can considerably promote the flexural strength, while the compressive strength is slightly decreased until 28 days. A pre-treatment procedure consisting of drying specimens at 105°C for 1 day can be regarded as a proper way to enhance the piezoresistive properties of the GNPs-mortar. Piezoresistive properties under two different cyclical loading schemes were measured using the GNPs-mortar with 1 wt% GNPs. It has been shown that the average resistance change rate increases with the amplitude increasing and a reduction is observed for the sustained cyclical loading condition. In the end, the influence of the microcracks on the piezoresistive properties was investigated. This study will contribute to future developments of cementitious composites incorporating GNPs for a variety of applications.

Fabrication of a type of silk/PEDOT conductive fibers for wearable sensor

Flexible high-conductivity fibers have attracted much attention due to their great potential in the field of wearable electronic devices. However, how to ensure high conductivity and flexibility is still a challenge. In this paper, the flexible silk fibers were used as the substrate, and manganese oxides were generated on the surface by potassium permanganate treatment. On this basis, the flexible high conductivity silk fibers with a resistivity of 1.47 Ω·cm were prepared by in-situ chemical polymerization of 3,4-ethylenedioxythiophene(EDOT) on the surface of silk fibers. The surface morphology and chemical composition of silk fibers were characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma emission spectrometry (ICP). The results confirmed that a large amount of MnO 2 was synthesized and deposited on the surface of the silk fibers. The flexible conductive silk prepared by this method had good temperature sensitivity (- 0.47%/K), good stability and repeatability under cyclic tension, and the relative resistance change rate was 9.1%. Meanwhile, due to the binding force between the surface-active groups of the silk fibers and poly(3,4-ethylenedioxythiophene) (PEDOT), the conductive silk fibers exhibited good stability against water washing, demonstrating a broad application prospects in the field of wearable sensors.

The influence of temperature on the damping characteristic of hydraulic shock absorbers

This paper presents the results of bench-tests and calculations assessing the influence of temperature on the performance of a two-pipe hydraulic shock absorber. The shock absorber prepared for the tests was cooled with dry ice to a temperature corresponding to that associated with the average winter conditions in a temperate climate. The temperature range of the shock absorber during testing was ensured via equipping it with a thermocouple and monitoring it with a thermal imaging camera. During testing, the shock absorber was subjected to kinematic forces of a selected frequency with two different, fixed displacement amplitudes. The results of the tests showed a direct correlation between the decrease of component resistance at lower temperatures. The rate of change in resistance was higher at lower temperatures. It was also found that the energy dissipated in one shock cycle decreased linearly with an increasing temperature. Finally, a method for determining the ideal use temperature of the shock absorber for the assumed operating conditions was also presented.

Optical and electrical properties of ITO film on flexible fluorphlogopite substrate

Indium Tin Oxide (ITO) films were prepared, at room temperature, on a fluorphlogopite substrate using magnetron sputtering technology. At various temperatures of 500 °C, 600 °C, 700 °C, 800 °C, and 900 °C, the samples were (had) annealed for 2 h (a 2-h duration). The results showed improvement in the crystalline performance of ITO film at selected annealing temperatures, with a significant reduction in resistivity at 800 °C. The lowest resistivity is 4.08 × 10−4 Ω-cm, which is nearly an order of magnitude lower than the unannealed sample. All samples have an average light transmittance above 85% in the visible light range (400–800 nm), and with increasing annealing temperature, the average light transmittance tends to decrease. Besides, at the sensitive wavelength of 550 nm, the light transmittance is as high as 93.74%. The sheet resistance testing of the sample was through the number of bending times, which revealed that with the increase of the number of bending, the sheet resistance increases. However, after 1200 bending times, the change rate of the sheet resistance remains below 5%. Thus, the ITO film prepared on the flexible fluorphlogopite substrate revealed excellent optical and electrical properties, good flexibility, and improved stability after high-temperature annealing, which guarantees successful application in flexible electronic devices.

Experimental study on the strain self-sensing properties of nano carbon black modified resin based CFRP bars

In order to explore the influence of nano carbon black content on the piezoresistive effect of resin based CFRP bars, 2%, 4%, 6%, 8%, 10% nano carbon black modified resin were used as matrix, and the roller extrusion process was adopted to prepare CFRP bars. The initial resistivity, the response of resistance change and the relationship between sensitivity change and strain under static tensile test were compared and analyzed. The results show that the strain sensitivity of CFRP bars can be significantly improved, and the discreteness of test data can be reduced by adding uniformly dispersed carbon black into the resin matrix. The optimum content of carbon black is 6%, the sensitivity is 25.4 in the strain range of 0 ∼ 1.2%, and the linear relationship between resistance change rate and strain is satisfied, and the determinable coefficient is 0.985. When the content of carbon black is more than 6%, the effect of modification on the sensing properties of CFRP bars is not obvious.

Quantitative Evaluation Method and Application of Airflow Stability of Mine Ventilation System

A quantitative analysis method is proposed for airflow stability evaluation of complex ventilation networks. The influences of resistance change on airflow and its variation laws are analyzed by mathematical statistics method based on the simulation of airflow state in ventilation network. It is proposed that the airflow change rate is used as the quantitative evaluation index of airflow stability, and the sensitivity branches and dominant branches of ventilation system are determined by the airflow change rate matrix. A set of airflow direction discriminants of complex network is derived based on the deep analysis of the correlation among resistance, airflow and airflow change rate of branches. The results show that the stability quantitative analysis results and airflow direction discrimination results of this method are consistent with the results of computer simulation of airflow state, and the airflow direction discriminants can be applied to any complex network.

Research on flexible silver nanowire electrode for organic light-emitting devices

By spin-coating silver nanowires (AgNWs) and polymethyl methacrylate (PMMA), applying pressure imprint and plasma treatment, we obtained flat AgNW thin film with a sheet resistance of 20 Ω/sq and a transmittance of 78% at 550 nm with low surface roughness. No significant change in sheet resistance was observed after cyclic bending (bending radius is 5 mm) test and tape test. After 1 000 bending tests, the change rate of sheet resistance was only 8.3%. The organic light-emitting devices (OLEDs) were prepared by using such AgNW electrodes and a maximum brightness of 5 090 cd/m2 was obtained. Compared with the AgNWs electrode without any treatment, the present AgNW electrodes have lower sheet resistance and better hole injection. Our results show spin-coated with flat layers, embossed and plasma-treated AgNW electrodes are suitable for manufacturing flexible organic optoelectronic devices.

Experimental Study on Mechanics and Pressure Sensitivity of Carbon Fiber RPC

To study the mechanical properties and conductivity enhancement effect of carbon fiber (CF) on reactive powder concrete (RPC), this work systematically investigated the changes in the compressive strength, elastic modulus, Poisson’s ratio, and pressure sensitivity of RPC under standard curing system. With age, CF content, and pressure sensitivity as parameters, the micro-method for scanning mechanism was used to study the effect mechanism of CF content on RPC. The experimental results showed that with the increase of carbon fiber content, poisson's ratio and compressive strength of carbon fiber RPC tended to increase first and then decrease. The elastic modulus decreased first and then increased, and 0.75% was the turning point of fiber content. With the increase of carbon fiber content, the resistivity decreases gradually, while the resistivity change rate (FCR) shows a trend of increasing and decreasing first, and there is a strong corresponding relationship between strain and FCR.When the CF content is 0.75%, the maximum FCR is 38.8%, which is increased by 33%. the CF RPC with a CF content of 0.75% is the highest stress and strain sensitivity group, reaching 2.05%/Mpa and 513.7, respectively.