Linear Electrical Resistivity Research Articles

Sewing and adhesive bonding technologies for smart clothing production

PurposeThis paper aims to present investigations of the influence of sewing and adhesive bonding technology on the aesthetic, mechanical and conductive properties of the e-textile package. Commercially available conductive textiles are tested for the production of e-textile package by most common cut-and-sewn clothing production technologies.Design/methodology/approachSewing, adhesive bonding and seam sealing technologies used to obtain e-textile packages with woven and knitted conductive textiles. Produced e-textile packages described in terms of thickness, bending rigidity and general appearance. Exploitation properties of prepared samples tested by cycle tensile experiment and discussed on the basis of variation of linear electrical resistance property.FindingsResearch has shown that a reliable e-textile package can be obtained by applying cut-and-sew technology for conductive tracks of silver coated woven and knitted material. Seam sealing by thermoplastic polymer layer has an impact on the electrical and deformation properties of the samples. To create attractive smart clothing design, the appropriate joining method and its technological parameters must be chosen to ensure the durability and safety of e-textile packages.Originality/valueThe findings of the research are of substantial value for the production of e-textiles by cut-and-sewn technologies. The required shape of the conductive textile element for various applications can be cut and joined to the garment parts using traditional sewing or adhesive bonding techniques.

Transport in the two-dimensional Fermi-Hubbard model: Lessons from weak coupling

We use quantum kinetic theory to calculate the thermoelectric transport properties of the 2D single band Fermi-Hubbard model in the weak coupling limit. For generic filling, we find that the high-temperature limiting behaviors of the electrical ($\sim T$) and thermal ($\sim T^2$) resistivities persist down to temperatures of order the hopping matrix element $T\sim t$, almost an order of magnitude below the bandwidth. At half filling, perfect nesting leads to anomalous low temperature scattering and nearly $T$-linear electrical resistivity at all temperatures. We hypothesize that the $T$-linear resistivity observed in recent cold atom experiments is continuously connected to this weak coupling physics and suggest avenues for experimental verification. We find a number of other novel thermoelectric results, such as a low-temperature Wiedemann-Franz law with Lorenz coefficient $5\pi^2/36$.

Changes in Porosity, Electrical and Surface Properties after Laundering of Heat-treated AgNW/PDMS/PU Nanofiber-web

In this study, to investigate the effects of heat treatment and polydimethylsiloxane (PDMS) coating on durability to laundering, the changes in the porosity, electrical resistance, and surface property of the heat-treated silver nanowire (AgNW)/PDMS/polyurethane (PU) nanofiber-web before and after laundering were examined. To prepare the conductive specimens, PU nanofiber-web, 1 wt% of AgNW dispersion in ethanol, and two types of PDMS precursors were used. A total of four specimens were prepared: Specimen A (The AgNW/PU nanofiber-web), Specimen AH (The heat-treated AgNW/PU nanofiber-web), Specimen AP (The PDMS-coated AgNW/PU nanofiber-web), and Specimen AHP (The heat-treated AgNW/PDMS/PU nanofiber-web). The specimen was rinsed and dehydrated after laundering under the conditions according to ISO 6330. To investigate the changes of porosity after a single washing cycle, mean pore diameter and pore size distribution were measured. Linear electrical resistance and microscopic surface view of the specimen were evaluated. As a result, many micro-pores were distributed in Specimen AH because of the heat treatment. After laundering, Specimen AH still had the micro-pores, and thus, the heat treatment improved the durability to laundering. Also, the electrical resistance of Specimen AH was only changed slightly even after laundering, which was because the heat treatment strengthened the bonding between the nanofibers and the silver nanowires, thus the silver nanowires sufficiently remained on the specimen surface even after laundering. And, Specimen AH showed that the silver nanowires formed a network even after laundering and were evenly covered with silver nanowires onto the specimen surface. This result affected the aforementioned electrical performance, and in fact, the electrical resistance of Specimen AH was the lowest regardless of laundering. However, it was impossible to measure the porosity of Specimen AP and Specimen AHP due to the PDMS coating. Therefore, the heat treatment affected the durability to laundering as well as the electrical conductivity to increase, but PDMS coating blocked the micro-pores of the nanofiber-web and enabled higher initial resistance.

Improved Electrical Conductivity of Polyurethane Nanoweb Coated with Graphene Ink through Heat Treatment

This study found out a heat treatment condition to improve the electrical conductivity of polyurethane (PU) nanoweb treated with non-oxidized graphene (nOG) ink. Electrical conductivity was imparted to the PU nanoweb (Pardam, s.r.o., Czech Republic) by a dip-coating process utilizing 1 wt% of nOG ink. To enhance the electrical conductivity, post heat treatment was conducted. The first specimen was completely dried at room temperature (20 °C) for 24 hours (Specimen GU), and the rest of the specimens were treated at 40 °C, 60 °C, 80 °C, and 100 °C for 1 hour (Specimen G40, G60, G80, and G100). To confirm the microstructure of the specimens, a FE-SEM (Field emission scanning electron microscopy) was utilized. The linear electrical resistance was evaluated using a Digital multimeter. Also, the thickness and weight of the specimens were measured by Cross section polisher and Analytical balance respectively. After that, the chemical structures were inspected using a FT-IR (Fourier transform infrared spectroscopy). As a result, when the heat treatment temperature was higher, the specimens were well immersed and more nOG ink was covered onto the surface of the treated specimens. Also, the electrical resistance of the specimens decreased in accordance with increased heat treatment temperature. The thickness and add-on of the specimens increased as the heat treatment temperature increased. The changes of band position of C=O, C-O-C, -NH- bending were observed by FT-IR analysis. Therefore, this study demonstrated that the heat treatment temperature played a significant role in the improvement of electrical conductivity, and the nOG/PU nanoweb had the most enhanced electrical conductivity when treated at 100 °C.

Protocol to assess the quality of transmission lines within smart textile structures

The washability issue is always a challenge for electronic textiles in terms of application. It reduces their reliability, makes them not robust enough, and therefore not ready for the market. In this study, a novel protocol was designed to test the performance of conductive threads under wet situation in order to simulate the washing cycle. In this content, two commercially available silver-plated polyamide threads having the same thread count were used and washing results of each thread were discussed. Transmission lines with silver-plated polyamide threads onto cotton woven fabric were produced via sewing (single-line stitch) and embroidery techniques (three-line stitch) to improve the conductivity and robustness. For the simulation of the wash process, Martindale abrasion tester was used under wet and dry conditions. Moreover, felts of abrasion tester and transmission lines were put into different solutions, i.e., water, water with standardized detergent and water with commercially available detergent. After wetting specimens, abrasion tests were performed on transmission lines, and linear electrical resistance measurements were recorded with the multi meter before abrasion and every 1500 cycles up to 4500 cycles in wet conditions and also after drying the transmission lines. Finally, abrasion impact on silver-plated polyamide threads was investigated by optical microscope. It has been found that silver coating on the conductive thread was damaged when subjected to abrasion cycles, especially in wet states. Water itself has stress impact on samples provoking the electrical resistance increase rapidly. Commercial detergent with water was found to have the most damaging effect on the conductive threads because of extra particles presence to enhance the washing performance. In terms of integration methods, better electrical conductivity values were achieved in three-line embroidery transmission lines due to multiple interconnection points in the embroidery network.

Processing of metallic fiber hybrid spun yarns for better electrical conductivity

ABSTRACTThis research was aimed at processing of metallic fiber hybrid spun yarns consisting of polyester/stainless steel and viscose/stainless steel staple fibers to achieve better electrical conductivity. Conventional ring spinning machine and ring twister machine were used to produce the single and plied yarns respectively. The linear electrical resistance of yarns was analyzed with reference to the three levels of twist multiplier (TM) for same yarn count, three levels of yarn fineness (Ne) at the same TM level, and number of plies for the same final yarn count. These results showed that by increasing twist, the electrical conductivity of yarn was increased. However, yarn fineness was in inverse relation with the electrical conductivity of yarns. The effect of yarn plying and twisting to produce the Ne 10s yarn was also found critical in governing the electrical properties. The electrical conductivity of viscose and stainless steel hybrid yarn was found more sensitive to increase with an increase in relative humidity contrary to that of polyester and stainless steel hybrid yarns. The findings of the study are significant to produce the hybrid spun conductive yarns for their potential applications in a variety of tailor-made functional, protective and smart textiles.

Development and characterization of conductive ring spun hybrid yarns

Development of conductive yarns for smart textile applications is the most demanding area of research these days. This study was aimed to investigate the effect of yarn constructional parameters, and relative humidity on electromechanical properties of conductive ring spun hybrid yarns. Stainless steel (SS) fibre was blended with polyester and viscose fibre separately on 12% and 24% weight basis to produce hybrid conductive yarns at three different levels of twist factor. The electromechanical properties of yarns were evaluated in response to change in blend type, blend ratio, twist factor, and relative humidity. The content of SS fibre is found to be more effective followed by the twist factor and blend type to govern the linear electrical resistance (LER) of conductive yarns. In addition, on increasing relative humidity, the LER of viscose stainless steel (VS) hybrid yarns are found to drop significantly than that of polyester stainless steel (PS) hybrid yarns.

Strain sensing of printed carbon nanotube sensors on polyurethane substrate with spray deposition modeling

Abstract The unique mechanical and electrical properties of carbon nanotubes represent a potential for developing a piezo-resistive strain sensor for smart structures. This study demonstrated a new processing technique of multi-walled carbon nanotube strain sensors with tunable strain gauge factors. A digital-controlled spraying-evaporation deposition process that uses a 12-array bubble jet nozzle attached to a digital x-y plotter combined with a heated substrate which induces evaporation of the solvent was developed. The demonstrated fabrication technique has advantages such as high efficiency, low cost and scalability. The experimental results showed that the prepared carbon nanotube strain sensors are capable of measuring strains through highly linear electrical resistance change. The gauge factors of the fabricated strain sensors could be easily tuned by controlling the number of printed layers of carbon nanotubes. In this work, strain sensors were fabricated with printed carbon nanotube layers ranging from 10 to 50 layers and strain gauge factors were measured in a range of 0.61–6.42. Moreover, the dynamic loading test results revealed that the printed carbon-nanotube strain sensors exhibited excellent durability and stability at cyclic strain. These superior sensing capabilities of the fabricated CNT sensors make them a promising candidate for wearable smart electronics and structural health monitoring applications.

Electrodes made of multi-wall carbon nanotubes on PVDF-filters have low electrical resistance and are able to record electrocardiograms in humans

In this paper we report that electrodes made of multi wall carbon nanotubes (MWCNTs) incorporated on Polyvinylidene fluoride (PVDF) filters can be used for recording and sensing bio-electrical signals. We measured the electrical properties of MWCNTs incorporated on membranes made of cellulose (bond-paper) and PVDF filters. In addition, we performed Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM) studies with the purpose to characterize the ultra-structural properties and distribution of MWCNTs on PVDF filters. We found that the electrodes made of MWCNTs on PVDF filters, have lower resistance and consequently better conductivity compared with other typical electro-conductive materials. We also found that the topographic distribution of the MWCNTs on the PVDF filter is chaotic and non-aligned; nevertheless, MWCNTs on PVDF filters showed a linear electrical resistance without rectification. Electrodes made of MWCNTs on PVDF filters were able to record electrocardiograms in humans with similar resolution than the ones recorded with silver electrodes. The relevance and application of these findings are discussed.

Pinholes and temperature-dependent transport properties of MgO magnetic tunnel junctions

Magnetic tunnel junctions (MTJs) with thin crystalline MgO(001) barriers displaying large tunnel magnetoresistance (TMR) and low resistance-area product $(RA)$ will likely be used as the next generation sensors in read heads of ultrahigh-density hard drives. However, the thin insulating barrier may result in the presence of metallic pinholes joining the two electrodes. Here we study the transport properties of thin MgO-based low resistance MTJs (barrier thickness $t=7.5\text{ }\text{\AA{}}$), deposited by magnetron sputtering, with $RA$ values of $\ensuremath{\sim}40\text{ }\ensuremath{\Omega}\ensuremath{\mu}{\text{m}}^{2}$, reaching TMR values of $\ensuremath{\sim}60--75%$ at room temperature. We performed temperature-dependent (300--20 K) resistance $(R)$ measurements and observed different behaviors for different magnetic states: positive $dR/dT$ for the parallel (P) state, attributed to the presence of pinholes in the barrier, but a mixed character in the antiparallel (AP) state, with $dR/dT$ changing from negative to positive with decreasing temperature. This indicates an interesting competition between tunneling and metallic transport in the studied samples. To explain this transport behavior, we developed a simple model with the two conducting channels, tunnel and metallic, in parallel. The model assumes a linear variation of the electrical resistance with temperature for both conducting channels and its dependence on the MTJ magnetic state (P and AP). The modeled results show that the sign of $dR/dT$ does not give an indication of the dominant conductance mechanism and that the crossover temperature at which $dR/dT$ changes sign depends strongly on the linear electrical resistance--temperature coefficients. We performed fits to our experimental $R(T)$ data, using the proposed model, and observed that such fits reproduced the data quite well, illustrating the validity of the model.

Strain sensitivity and temperature behavior of invar alloy films

The electrical resistance–strain characteristics of Invar films has been studied for their possible application as strain gauges. The Invar films were prepared by sputtering technique and the necessary details of film preparation are given. Temperature coefficient of resistance (TCR) of the films has been measured by systematic annealing of films in vacuum. It has been found that TCR of film is of the order of 10 −3/°C. The gauge factor which is an index of the strain sensitivity, was measured for as-deposited and annealed films. Films exhibited linear electrical resistance versus strain characteristics. The gauge factor for relatively thinner films was found to be as high as 5.5 and for films with thickness greater than 500 Å, it was lower. For films annealed by heating up to temperature less than 300°C, the gauge factor value did not change. However, films annealed at temperature above 300°C, showed reduction in gauge factor.

High-temperature superconductivity in the multiphase compound system Y-Ba-Cu-O

The measurement of AC and DC magnetic susceptibilities, DC electrical resistance and magnetic hysteresis confirms the existence of a superconducting phase transition well above 77 K in the compound system Y1.2Ba0.8CuO4. The method of preparation followed yields a zero-resistance temperature of 87 K and a deviation from high-temperature linear electrical resistance behaviour at 140 K in the system Y-Ba-Cu-O. These values are, to the authors' knowledge, the highest ever reported in any stable superconducting compound. The width of the transition is also very narrow ( approximately 2K) in the specimens. The sensitivity of these materials to different heat treatments is described.

Electrical properties of cast microconductors of nickel alloys

1. The specific electrical resistivity increases most and the TCR decreases most for microconductors made from binary alloys based on nickel alloyed with Si, Cr, Mn, and Ga. 2. Alloys for casting microconductors with a broad range of linear electrical resistivity (2.5–1000 kΩ/m and TCR not over±15·10−6 deg−1 have been developed and introduced in industry.