Resistance Change Rate Research Articles

Enhanced hydrogen gas sensing characteristics of CuO/ZnO heterojunction for thickness-dependence and its application

In this study, we experimentally verified the synthesis of ZnO and CuO thin films using a droplet-based hydrothermal method and their hydrogen sensing performance. The hydrogen gas detection performance of the fabricated heterostructured gas sensor was evaluated based on the results of an experiment conducted while controlling the temperature and hydrogen concentration in the gas chamber. According to the responses of single metal oxide sensors made of each ZnO and CuO and their heterojunction sensors, CuO deposited with 7 cycles on 5 cycles of ZnO had a resistance change rate of about 164 % and the change of the resistance took 3 s in the environment of 4 % hydrogen at 300 °C. This sensor showed the highest response rate and fastest reaction time out of all. CuO/ZnO showed the highest reaction at 300 °C, confirming its selective reaction to hydrogen. To solve the problem of metal oxide-based gas sensors with low selectivity, the operating principle of the heterojunction between metal oxide that has selective gas reactivity was analyzed and experimentally verified. Additionally, the fabricated sensor was confirmed to have selective responsiveness to different gases at various temperatures. Using these characteristics, it was confirmed that this heterostructure based sensor can be used as a sensor array for electronic nose that could classify unknown gases using the same sensor at various temperatures.

Mechanical behavior monitoring of composite hybrid bonded‐riveted joints using high‐stability MXene sensors

AbstractComposite adhesive rivet hybrid connection structure has been more and more recognized and applied in aerospace, automobile, and other industries due to its high strength, corrosion resistance, and good stability. However, due to the particularity of the composite structure and the complex nonlinear coupling factors existing in the bearing process of the adhesive rivet hybrid connection structure, it is difficult to carry out structural health monitoring of the composite adhesive rivet hybrid connection structure. In this paper, a new fabrication technique is proposed to fabricate MXene thin film sensors with excellent performance. The MXene sensor can be tailored to the required size and arrangement to monitor the hybrid connection structure. The multi‐stage loading‐unloading test verifies the feasibility of using the MXene sensor to monitor the hybrid connection structure. The monitoring curves of the MXene sensor for composite adhesive rivet mixed connection structure specimens under low‐speed impact test and vibration fatigue test were obtained, and the sensing mechanism of the MXene sensor was explained. The proposed monitoring method based on the MXene sensor is suitable for the health monitoring of adhesive rivet hybrid connection structures under tensile‐compression, impact, and vibration conditions.Highlights MXene sensors can be integrated into composite hybrid bonded‐riveted joints without defects. MXene sensors combined with flexible circuits can form a high‐stability monitoring array. Monitor the mechanical behavior of bonded and riveted areas by the resistance change rate of MXene sensors. Real‐time monitor the micro damage and acceleration changes under the vibration environments.

High efficient personal thermoregulatory device: Metallized interface layer between flexible polyimide substrate and foam copper heat sink enables thermal resistance reduction

Customizable flexible thermoelectric devices (f-TED) designed for personal thermal management (PTM) have the potential to substantially diminish energy consumption while enhancing comfort. Currently, studies focus on optimizing thermoelectric device performance and reducing radiator thermal resistance, neglecting the crucial interface between them. In this innovative work, the interface layer between the flexible polyimide substrate of f-TED and the foam copper heat sink was metallized, thereby significantly mitigating the thermal resistance at the interface. In contrast to the conventional thermal conductive adhesive, the metallized welding thermoelectric system (4 × 4 cm² in the plane) demonstrates a 37.0 % augmentation in cooling temperature difference (5.4 ℃ → 7.4 ℃) at 0.3 A. When bending 1000 times (r: ∞ → 20 mm → ∞ → …), the change rate of internal resistance is less than 1.5 %. At a temperature difference of 20 K, it reaches a maximum output power as high as 4.45 mW. Furthermore, an intelligent personal thermal management system was developed. Users can monitor and adjust the working status of the f-TED in real-time via a mobile terminal, achieving personalized thermoregulation. In actual human wear tests, the highest cooling temperature difference reached 13.7 °C, which is one of the highest reported values. This work holds significant implications for advancing f-TED technology innovation, personalized thermoregulation, energy conservation, and environmental protection.

Construction of Conductive Polymer Coatings onto Flexible PDMS Foam Composites with Exceptional Mechanical Robustness for Sensitive Strain Sensing Applications

AbstractFlexible piezoresistive‐sensing materials with high sensitivity and stable sensing signals are highly required to meet the accurate detecting requirement for human motion. Herein, a conductive poly(3,4‐ethylenedioxythiophene): poly(styrenesulfonate) / polydimethylsiloxane foam (P:P@p‐PSF) composite with strong interfacial action is designed. The porous structures and good interface combination not only show outstanding mechanical flexibility and reliability but also possess high sensitivity at a relatively wide strain range. The P:P@p‐PSF sensor achieves extreme sensitivity (Gauge Factor) of 6.25 in the subtle strain range of 1%–8%. Furthermore, the sensor forms a highly interconnected conductive network induced by the serious deformation of elastic‐interconnect pores, thus providing extremely sensitive sensing behavior for a relatively wide strain range (97.4% resistance change rate at 60% compressive strain). Moreover, the sensor presents repeatable stability and good thermal adaptation, which would meet the critical requirements of subtle vital signs, human motion monitoring, and so on. This work supplies insight into the design of a new flexible sensor material to overcome the weak interface problem and the flexible mismatch between conductive filler and matrix, showing great application potential in the field of electronic skin.

Synthesis and Characteristic Valuation of a Thermoplastic Polyurethane Electrode Binder for In-Mold Coating.

A polyurethane series (PHEI-PU) was prepared via a one-shot bulk polymerization method using hexamethylene diisocyanate (HDI), polycarbonate diol (PCD), and isosorbide derivatives (ISBD) as chain extenders. The mechanical properties were evaluated using a universal testing machine (UTM), and the thermal properties were evaluated using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The PHEI-PU series exhibited excellent mechanical properties with an average tensile strength of 44.71 MPa and an elongation at break of 190%. To verify the applicability of different proportions of PU as an electrode binder, PU and Ag flakes were mixed (30/70 wt%) and coated on PCT substrates, the electrodes were evaluated by four-point probe before and after 50% elongation, and the dispersion was evaluated by scanning electron microscopy (SEM). The electrical resistance change rate of PHEI-PU series was less than 20%, and a coating layer with well-dispersed silver flakes was confirmed even after stretching. Therefore, it exhibited excellent physical properties, heat resistance, and electrical resistance change rate, confirming its applicability as an electrode binder for in-mold coating.

Experimental study on resistivity evolution law and precursory signals in the damage process of gas-bearing coal

The occurrence of elevated gas pressure leads to the distortion of the internal pore structure within the coal matrix, thereby exerting a substantial influence on the destabilization of the coal body. This disturbance further contributes to intricate changes in coal resistivity. To delve into the process of gas-induced damage and its implications for coal resistivity, this research employs nuclear magnetic resonance (NMR) technology as a means to characterize coal samples. Moreover, a controlled loading experimental equipment is devised for gas-bearing coal, while concurrently gathering data on resistivity and acoustic emission (AE). The result shows that with increasing applied stress, the change in resistivity within gas-bearing coal exhibits a progressive intensification, manifesting a notable “V”-shaped pattern. This pattern is characterized by an initial rapid decline, succeeded by a subsequent swift increase during the failure stage. The AE signals exhibit a synchronized consistency with the observed resistivity change. With increasing gas pressure, the coal's resistivity exhibits heightened fluctuations, and notably, the range of resistivity at failure under a pressure of 3 MPa is 2.27 times greater compared to that at 0 MPa. Furthermore, the damage variable and constitutive equation for gas-bearing coal based on resistivity is established. The critical value for damage (DE) occurs 1.75 s before the critical value of the resistivity change rate, and 3.88 s earlier than the actual occurrence of damage in the coal body. The correlation between the verified damage and measured stress exceeds 0.8, demonstrating a strong correlation at different stages. The research results contribute to understanding the evolution mechanism of gas instability and hold considerable significance for preventing coal and gas outburst disasters.

Study on the Conductivity and Pressure Sensitivity Performance of Carbon Fiber Geopolymer

This study uses slag (SL), fly ash (FA), and carbon fiber (CF) as raw materials to fabricate a conductive geopolymer, exploring the impact of CF content on its workability and mechanical performance. The conductivity and pressure sensitivity performance of the geopolymer are tested using an embedded four‐electrode method. The findings indicate that the incorporation of CF reduces the fluidity of the geopolymer and shortens its setting time. With the increase of CF content, the compressive strength increases first and then decreases, while the flexural strength increases gradually when the CF content is 0.2 v%, the percolation threshold is reached, and the resistivity is 268 Ω·cm. The geopolymer exhibits good pressure sensitivity performance under both monotonic and cyclic loading. With a stress amplitude of 15 MPa and a loading rate of 1 kN/s, the specimen’s resistance change rate can reach −38.4%. The pressure sensitivity performance is optimal, with good repeatability and stability.

Kinetics in low-temperature-isothermal oxidation of tungsten carbide under different humidity conditions

The isothermal oxidation experiments of tungsten carbides (WC) were carried out at levels of inequality in relative humidity (RH) levels and below 200 °C. Evaluated resistivity fluctuations and structural transformations during the low-temperature corrosion process were detected. In this paper, we present a detailed investigation into the resistivity behavior of WC under varying humidity conditions. Our innovative approach enabled us to witness a rapid decrease in resistivity under conditions of 85 % RH and 85 °C, from 0.00374 Ω-cm to 0.00177 Ω-cm, followed by a stable linear increase after 0.7 h at a constant rate of 0.000924 Ω-cm/h. Notably, a clear correlation between humidity levels and resistance change rates was found, where higher humidity led to faster resistivity changes. In sharp contrast, a resistivity change rate of less than 5 % under the conditions of water and oxygen independently was observed. The low-temperature oxidation mechanism of WC was described by XRD and XPS spectra. Moreover, the Nernst-Einstein equation and Wagner's model are used to establish the relationship between resistivity and oxidation degree for analyzing and predicting the reaction kinetics and oxidation behavior, indicating that the oxidation degree of WC increased logarithmically with oxidation time.

Full-field contact dynamic mechanical properties of tread rubber material under rolling and slippery conditions based on digital image correlation

The dynamic mechanical properties of rolling tire on special road surface were closely related to the vehicle’s handling stability, driving safety and braking effectiveness. The tire tread rubber material was the only contact part of the vehicle with the road surface, so the strain distribution characteristics of tread rubber material within the contact patch of rolling tire on thin water film pavement played a crucial role in the mechanical characteristics of vehicle. In this paper, a non-contact tire tread rubber rolling mechanical test system was developed. The improved digital image correlation (DIC) method was used to obtain the full-field strain distribution of tread rubber blocks. The effects of load and velocity on the strain rate of the marked points, the full-field strain distribution in the region of interest and rolling resistance were investigated under thin water film pavement. The experimental results were compared with dry condition to analyze the effect of water film on the rolling dynamic characteristics. The results showed that the strain rate increased first and then fluctuated under the action of thin water film. With the increase of speed and load, the full-field strain distribution of tread rubber contact patch was gradually occupied by low strain zone. The change rate of rolling resistance firstly increased and then decreased with the increase of rotational speed.

Inverted Molding with Porous Skeleton Nickel Foam for Preparing Flexible Multi-Wall Carbon Nanotubes Pressure Sensors

The application of traditional pressure sensors in health monitoring is limited by their initial rigidity. Flexible pressure sensors have thus received extensive attention owing to their excellent device flexibility. In this paper, we demonstrate a method of constructing flexible pressure sensors by inverting porous skeleton nickel foam based on multi-wall carbon nanotubes (MWCNTs) and polydimethylsiloxane (PDMS). MWCNTs and PDMS were mixed to form a composite conductive film, and the mass fraction of MWCNTs was optimized by evaluating the resistance change rate of the composite film. The optimized value of the mass fraction was 5%, which was used to prepare the flexible pressure sensors. The response, hysteresis, and stability of the sensors were further characterized. Pulse signals of humans were detected through flexible sensors, which can be used to evaluate cardiovascular conditions of the human body. These performance characteristics and the application demonstration show that our flexible pressure sensors have good prospects in human health care.

Structural Design and DLP 3D Printing Preparation of High Strain Stable Flexible Pressure Sensors.

Flexible pressure sensors are crucial force-sensitive devices in wearable electronics, robotics, and other fields due to their stretchability, high sensitivity, and easy integration. However, a limitation of existing pressure sensors is their reduced sensing accuracy when subjected to stretching. This study addresses this issue by adopting finite element simulation optimization, using digital light processing (DLP) 3D printing technology to design and fabricate the force-sensitive structure of flexible pressure sensors. This is the first systematic study of how force-sensitive structures enhance tensile strain stability of flexible resistive pressure sensors. 18 types of force-sensitive structures have been investigated by finite element design, simultaneously, the modulus of the force-sensitive structure is also a critical consideration as it exerts a significant influence on the overall tensile stability of the sensor. Based on simulation results, a well-designed and highly stretch-stable flexible resistive pressure sensor has been fabricated which exhibits a resistance change rate of 0.76% and pressure sensitivity change rate of 0.22% when subjected to strains ranging from no tensile strain to 20% tensile strain, demonstrating extremely low stretching response characteristics. This study presents innovative solutions for designing and fabricating flexible resistive pressure sensors that maintain stable sensing performance even under stretch conditions.

Hybrid additive manufacturing of ultra-fine high-resolution shell–core structured conductive mesh-based flexible transparent electrodes for flexible displays

ABSTRACT Metal mesh transparent electrodes present a promising alternative to Indium-Tin Oxide (ITO) due to their adjustable period and favourable trade-off between transmittance and conductivity. In this work, a template-free, non-high temperature hybrid additive manufacturing approach of the polyacrylonitrile (PAN)/Cu core–shell structure high-resolution metal mesh flexible transparent electrode (FTE) is proposed. The electric field-driven (EFD) 3D printing method was employed to print ultra-fine lines with widths as low as 1 μm. The composite-plating process combining electroless plating and electroplating has solved the structural defects of single deposition process. The prepared FTE has an excellent conductivity down to 1 Ω/sq and 89% light transmission (at 550 nm). Its exceptional mechanical properties and environmental stability make it suitable for diverse working environments. Even after undergoing 2000 bends at a radius of 3 mm, the resistance change rate remains as low as 1.4%. The resistance exhibits an approximately 8% change rate in the acid–base environment experiments conducted over 72 h. The flexible touch screen prepared with this FTE exhibits excellent writing performance in both flat and curved working scenarios. Furthermore, the significant potential of this FTE in the field of optoelectronics is effectively demonstrated through its exceptional luminescent performance in electroluminescent devices.

Polyelectrolyte microgels-enhanced double-crosslinking polyacrylamide hydrogel sensing with stretchable, transparent, and fast response

The development of medical sensor materials is progressing towards flexibility, wearability, and intelligence. Hydrogel, a new type of medical material, possesses excellent mechanical properties, high flexibility, and good biocompatibility. It is expected to become the foundation of a new generation of wearable devices. However, traditional hydrogels have limitations in recovery, conductivity, and stability, which restricts their practical applications as sensors. To address these limitations, this study presents a novel approach by preparing polyelectrolyte microgels (PMs) to reinforce conventional polyacrylamide (PAAm) hydrogels. The resulting double cross-linker hydrogel (DC-PMs/PAAm), containing PMs and N, N’-methylenebis (acrylamide) as cross-linkers, exhibits good transparency (90% at 550 nm) and mechanical properties (147 kPa, 880%). Notably, the DC-PMs/PAAm hydrogel demonstrates graded sensitivity factors in different strain ranges (GF at 0–150%, 150–350%, and 350–800% strain, were 2.47, 5.34, and 9.01, respectively). In addition, the hydrogel has a fast response time of 150 ms, which can detect large and subtle movements of the human body in real-time. Furthermore, DC-PMs/PAAm hydrogel maintains a stable resistance change rate during 1000 rapid cycles (100% strain) monitoring. Therefore, it is expected to be used as wearable device in the medical and health fields.

Crumpled graphene induced by commercial Heat-Shrinkable material for chemiresistive biosensors toward cancer biomarker detection

Chemiresistive biosensors have revolutionized the field of biomedical diagnosis owing to the novel properties of graphene layered materials that can enhance their sensitivity. We propose a commercial heat-shrinkable material (polystyrene) induced crumpled graphene for cancer biomarker detection. After heating polystyrene, the thermally induced transformation causes the shrinkage and deformation of graphene, resulting in the graphene structure becoming crumpled and thus increasing the surface area. Low-damage plasma treatment is used to oxidize the surface of crumpled graphene with high controllability, forming the bioactive graphene oxide. The DNA probe is then immobilized on graphene oxide via a chemical covalent-amide bond to facilitate hybridization with the biological target miRNA-21. Because the attachment of the miRNA-21 on the oxidized crumpled graphene alters the conductivity, we measure its electrical resistance change rate as a sensor response. The results demonstrate that the sensor response linearity increases with miRNA-21 concentration (10 nM to 1 pM) with the linearity of 0.988 and the limit of detection of 1.74 pM. The results of the real-time applicability test reveal a very high performance with low interference. Therefore, a crumpled graphene-based chemiresistive biosensor has good sensitivity with valuable selectivity, and its biomarker detection raises the possibility of using these sensors for real-time cancer determination and other screening applications in the future.

Flexible solid-state Zn-Co MOFs@MXene supercapacitors and organic ion hydrogel sensors for self-powered smart sensing applications

Stable and continuous detection of physiological signals without an external power supply is a crucial technology to realize wearable electronics as the next generation of flexible electronic devices. In this work, a self-powered smart system with flexible solid-state Zn-Co MOFs@MXene supercapacitors and polyacrylamide-BaTiO3/NaCl (PAM-BTO/NaCl) organic ionic hydrogel sensors are designed. The supercapacitor demonstrates a high energy density of 51 Wh/kg at a power density of 1.59 kW/kg. In particular, it maintains exceptional mechanical flexibility under different bending environments. The resistance change rate of the organic ionic hydrogel sensor exhibits a linear response within the strain range of 0–400 % and 400–600 %, respectively, and it shows outstanding electromechanical stability with almost unchanged performance under multiple identical tensile strains. Furthermore, the self-powered integrated system can be conveniently used for real-time detection of human motion and small strains. These findings highlight the unlimited application potential of self-powered integrated system in wearable devices.

Strong Connection of Single-Wall Carbon Nanotube Fibers with a Copper Substrate Using an Intermediate Nickel Layer.

Lightweight carbon nanotube fibers (CNTFs) with high electrical conductivity and high tensile strength are considered to be an ideal wiring medium for a wide range of applications. However, connecting CNTFs with metals by soldering is extremely difficult due to the nonreactive nature and poor wettability of CNTs. Here we report a strong connection between single-wall CNTFs (SWCNTFs) and a Cu matrix by introducing an intermediate Ni layer, which enables the formation of mechanically strong and electrically conductive joints between SWCNTFs and a eutectic Sn-37Pb alloy. The electrical resistance change rate (ΔR/R0) of Ni-SWCNTF/solder-Cu interconnects only decreases ∼29.8% after 450 thermal shock cycles between temperatures of -196 and 150 °C, which is 8.2 times lower than that without the Ni layer. First-principles calculations indicate that the introduction of the Ni layer significantly improves the heterogeneous interfacial bond strength of the Ni-SWCNTF/solder-Cu connections.

Effect of high temperature on macroscopic properties and microstructure of metallurgical coke

Coke produces powder in high-temperature environments, which leads to a decrease in coke strength and affects the smooth operation of blast furnace. To study the effect of high temperature on the macroscopic properties and microstructure, two types of coke were heated to 1100–1400 °C in conditions that simulated a blast-furnace heating regime. The results showed that the weight of the tamping coke (T-coke) and top-charging coke (TC-coke) was reduced by 9.04 g and 8.7 g, respectively, and the coke strength after reaction was reduced by 4.23% and 3.86% with an increase in temperature from 1100 °C to 1400 °C. In addition, the electrical resistance of T-coke and TC-coke decreased from ambient temperature to 1400 °C. The rate of change in electrical resistance had a negative correlation with the coke strength after reaction, which decreased as the change in electrical resistance increased. Comparing the optical texture index, carbon layer spacing, carbon structure parameters, and percentage of large pores in the coke with the heating temperature, it was found that high temperatures led to a decrease in the anisotropic texture of the coke, an increase in the degree of graphitization, partial conversion of amorphous carbon to graphitic carbon, and an increase in the percentage of large pores. Furthermore, the larger the pore area of the coke, the smaller were its pore wall hardness and elastic modulus. These results suggest that a decrease in anisotropic texture and an increase in large pores and the degree of graphitization decrease resistance to temperature, leading to lower strength after reaction.

Electrohydrodynamic Printed Ultra-Micro AgNPs Thin Film Temperature Sensors Array for High-Resolution Sensing.

Current methods for thin film sensors preparation include screen printing, inkjet printing, and MEMS (microelectromechanical systems) techniques. However, their limitations in achieving sub-10 μm line widths hinder high-density sensors array fabrication. Electrohydrodynamic (EHD) printing is a promising alternative due to its ability to print multiple materials and multilayer structures with patterned films less than 10 μm width. In this paper, we innovatively proposed a method using only EHD printing to prepare ultra-micro thin film temperature sensors array. The sensitive layer of the four sensors was compactly integrated within an area measuring 450 μm × 450 μm, featuring a line width of less than 10 μm, and a film thickness ranging from 150 nm to 230 nm. The conductive network of silver nanoparticles exhibited a porosity of 0.86%. After a 17 h temperature-resistance test, significant differences in the performance of the four sensors were observed. Sensor 3 showcased relatively superior performance, boasting a fitted linearity of 0.99994 and a TCR of 937.8 ppm/°C within the temperature range of 20 °C to 120 °C. Moreover, after the 17 h test, a resistance change rate of 0.17% was recorded at 20 °C.

Electrical Properties of Strain-Hardening Cement Composite (SHCC) with Multi-Walled Carbon Nanotubes Exposed to High temperature up to 900 °C

Cement-based sensors mixed with carbon nanotube (CNTs) for structural health monitoring were studied to detect changes in electrical resistance under the influence of temperature, pressure, and mass. Strain-hardening concrete composite mixed with CNT was heated to 900 °C to analyze the electrical resistance characteristics at high temperatures. The temperature and electrical resistance were measured using a thermocouple and an LCR meter during the heating and cooling processes. The resistance trend changed between 300 and 400 °C during the heating process, after which the resistance change rate with respect to temperature decreased. At 700 °C or higher, the resistance became larger as the initial resistance increases. In the cooling process, when the temperature dropped below 700 °C, a rapid change in resistance was observed, and the resistance began to drop sharply between 500 °C and 600 °C to become negative resistance. Following this, self-sensing ability decreased owing to changes in the resistance with respect to temperature. Multi-walled carbon nanotubes could not be distinguished by scanning electron microscope imaging after heating.

Whole martensitic transformation process in Fe–Mn–Si–Cr shape memory alloy by improved characterization of volume resistivity

Since Fe–Mn–Si–Cr shape memory alloy (Fe-SMA) has been discovered, an improvement of the shape memory effect (SME) is challenged. Numerous attempts have been made thus far to improve SME. To effectively control such performance, it becomes imperative to comprehend the real-time behavior of the stress-induced martensitic transformation (SIMT), which is strongly related to SME, during deformation. In the past, the measurement of volume resistivity has been proposed and applied to capture the forward SIMT behavior during the tensile loading process at various strain rate. However, it is quite hard to find investigations of the reverse martensitic transformation after the loading, which is more essential for understanding SME. Therefore, a comprehensive evaluation of the whole SIMT process including the loading process at various strain rate is strongly required. In this study, an improved measurement of volume resistivity is established by introducing both the four-probe and active-dummy techniques with a development of a diameter measurement at high temperature. Then, the volume resistivity of Fe-SMA is measured during the whole deformation including loading under tension at various strain rate, unloading, and heating processes. Besides, the microstructures of Fe-SMA after unloading and heating processes are observed, respectively. Finally, the real-time whole martensitic transformation in Fe-SMA is first investigated with the novel optimization method. The negative strain rate of change in volume resistivity during whole processes can be found. More amount of austenite can be obtained at lower strain rate, resulting in a larger SME.