Search

Effects of varying Mn and Ni concentrations on the structure and piezoresistive properties of CuMnNi films deposited by magnetron sputtering with a segmented target were investigated. An increase in the Ni content refines the CuNi film grains, inducing an increase in defects such as internal micropores and a decrease in film density. At the same time, the positive piezoresistive coefficient of the film changes to negative. When 17.5 at.% Ni was added, the negative piezoresistive coefficient of the CuNi film was −2.0 × 10−4 GPa−1. The doping of Ni has a weakening effect on the positive piezoresistive effect of the film. Adding Mn into Cu refines the film grains while increasing the film density. The surface roughness of the film decreases with the increase in Mn content. When the Mn content was 16.7 at.%, the piezoresistive coefficient reached the largest recorded value of 23.81 × 10−4 GPa−1, and the film exhibited excellent repeatability in multiple piezoresistive tests. After the CuMn film with 16.7 at.% Mn was annealed at 400 °C for 2 h, the film grains grew slightly and the film residual stress decreased. The optimization of the film structure can reduce the scattering of electrons during transportation. The piezoresistive coefficient of the film was further improved to 35.78 × 10−4 GPa−1. [ABSTRACT FROM AUTHOR]

In pressure sensors, four piezoresistors connected in a Wheatstone bridge are often provided with a voltage varying between 5 and 10 V. Unfortunately, this voltage is a source of drifts created by electric heating. This study focuses on the internal heating and piezoresistive effect of piezoresistors represented by the variation of their resistivity. To do this, we use the finite difference method (FDM) to solve the heat transfer equation, taking into account the conduction in Cartesian coordinates for the variable regime. We examine how the temperature affects the piezoresistivity in these sensors when the potential is applied. In this case, the variation of the temperature has been calculated as a function of applied voltage, as well as for the operating time of the sensor. Furthermore, the evolution of resistivity over time was determined for several geometric properties of the membrane using the mobility model. This was established for different doping levels. Additionally, the change in resistivity due to the application of voltage was evaluated. It was observed that resistivity is greatly affected by the temperature rise produced by the applied voltage when the device is actuated for a prolonged time. Consequently, this results in drifting in the output response of the sensor. [ABSTRACT FROM AUTHOR]

In this study, we investigated the capacitive effect and the electromagnetic coupling on the measurement chain induced by impact experiments with a gas gun or powder gun. Reduced bandwidth and noise were noticed on experimental signals. Rogowski coil measurements were added on the cables to characterize the electromagnetic coupling. The perturbation currents on the cables were quantified depending on the configuration. The gauge, the transmission line and the conditioning system were modeled. The calculations reproduced the electrical wave arrival time, the transmission line transfer impedance and the conditioning system transfer impedance; and the bandwidth limitation has been displayed. A capacitive effect with the piezoresistive manganin gauge embedded into the sample was identified, depending on the experimental setup. [ABSTRACT FROM AUTHOR]

In-situ formed free carbon nanodomain is an unique feature of polymer-derived ceramics (PDCs), which plays a significant role to affect the properties of PDCs, especially for the electoral property and piezoresistivity. In this study we report an enhanced piezoresistive properties of amorphous silicon carbonitrides (SiCN) ceramics derived by divinylbenzene (DVB)-modified polysilazane. Microstructure analysis indicated that the free carbon phase in SiCN ceramics is gradually increasing in order degree and concentration with increasing content of DVB. The average spacing between the conducting particles decreases with increasing concentration of free carbon, resulting in an enhanced internal electric field. The effects of DVB concentration on the piezoresistive properties of SiCN ceramics are also discussed, finding that the DVB has a significant effect on the piezoresistive properties. [ABSTRACT FROM AUTHOR]

Structural health monitoring (SHM) using self‐sensing cement‐based materials has been reported before, where nano‐fillers have been incorporated in cementitious matrices as functional sensing elements. A percolation threshold is always required in order for conductive nano‐fillers modified concrete to be useful for SHM. Nonetheless, the best pressure/strain sensitivity results achieved for any self‐sensing cementitious matrix are <0.01 MPa−1. In this work, we introduce for the first‐time novel partially reduced graphene oxide based electronic textile (e‐textile) embedded in plain and as well as in polymer‐binder‐modified cementitious matrix for SHM applications. These e‐textile embedded cementitious composites are independent of any percolation threshold due to the interconnected fabric inside the host matrix. The piezo‐resistive response was measured by applying direct and cyclic compressive loads (ranging from 0.10 to 3.90 MPa). A pressure sensitivity of 1.50 MPa−1 and an ultra‐high gauge factor of 2000 was obtained for the system of the self‐sensing cementitious structure with embedded e‐textiles. The sensitivity of this new system with embedded e‐textile is an order of magnitude higher than the state‐of‐the‐art nanoparticle based self‐sensing cementitious composites. The composites showed mechanical stability and functional durability over long‐term cyclic compression tests of 1000 cycles. Additionally, a two time‐constant model was used to validate the experimental results on decay response of the e‐textile embedded composites. [ABSTRACT FROM AUTHOR]

This study proposes an eddy current-based tensile force estimation technique for a post-tensioning (PT) tendon under varying temperature conditions. The tensile force in the internal PT tendon is inferred by measuring the compressive stress on the external anchor head. A dual-coil probe consisting of two identical eddy current coils with orthogonal orientations measures the unidirectional loading level based on the piezoresistive effect. The temperature effect is eliminated using identical eddy current signal alternations in the coils under temperature variation. The performance of the proposed technique was evaluated by estimating the tensile force of a PT tendon under various loading and temperature conditions. The uniqueness of this study lies in the (1) design and fabrication of a dual-coil probe for unidirectional loading level estimation, (2) elimination of the effect of temperature on tensile force estimation, and (3) experimental validation under various loading and temperature conditions. [ABSTRACT FROM AUTHOR]

Enhanced sensitivity, precise measurements and accuracy are the key factors to identify the performance of any sensor. In this paper, p-polycrystalline silicon micro-pressure sensor has been designed which works on the principle of piezoresistive effect. A theoretical modeling and computational simulation of the circular Si-diaphragm have been performed through the extensive study of stress and frequency response with the help of finite element method (FEM) within the framework of COMSOL. For a thin diaphragm (∼ 50  μ m), the Eigen frequency and the frequency generated in a diaphragm under the influence of pressure has been optimized within the pressure range from 1–25 kPa. The modes of vibrations generated in the diaphragm have been optimized at wide-frequency range ∼ 200–800 kHz at various pressure values. The findings of the presented research have suggested that for a ∼ 50  μ m thin diaphragm, the optimized fundamental frequency is ∼ 310 kHz for showing better piezoresistive response which results into enhanced sensitivity. Moreover, the simulation results show that for the designed sensor, the pressure sensitivity of ∼ 11.51 mv/psi has been conveyed. [ABSTRACT FROM AUTHOR]

Conductive nanocomposites have been explored extensively for structural health monitoring (SHM) due to their self-sensing nature via the piezoresistive effect. Combined with a non-invasive conductivity imaging modality such as electrical impedance tomography (EIT), piezoresistivity is a powerful tool for SHM. To date, however, the combination of the piezoresistive effect and EIT has been limited to just damage detection. From a SHM perspective, it may be more beneficial to pre-emptively predict failure before it occurs. To that end, we propose a novel methodology for failure prediction in nanocomposites using piezoresistive inversion. Our approach makes use of a genetic algorithm (GA) to determine the mechanical state of the structure using conductivity changes observed via EIT. First, a rectangular nanocomposite specimen with a central hole is manufactured. Second, the specimen is loaded in tension to induce stress concentrations near the hole. Third, EIT is used to image the resulting stress concentration-induced conductivity changes near the hole. Fourth, GA-enabled piezoresistive inversion is implemented to determine the underlying displacements from the observed conductivity changes. The strains are then determined from kinematic relations and the stresses from constitutive relations. Lastly, a failure criterion is used to predict failure. By validating our results with finite element analysis and digital image correlation, we demonstrate that the proposed approach can accurately predict the onset of failure and therefore enable unprecedented SHM capabilities in piezoresistive nanocomposites. [ABSTRACT FROM AUTHOR]

Highlights • Piezoresistivity of cement-based sensors is affected by materials, loading, measurements and environmental conditions. • Both conductive and non-conductive phases influence piezoresistivity of sensors and there is optimal conductor content. • Manufacturing procedure significantly affects the dispersion of conductors and microstructure of cement-based sensors. • Increased temperature and humidity can enhance piezoresistivity of sensors but decrease it when certain limits are exceeded. Abstract Cement-based sensors are increasingly used in smart concrete to self-sense and monitor the damages and cracks through the measurements of concrete electrical resistivity. The fundamental concepts, key components, manufacturing process, piezoresistivity measurements, and primary applications of cement-based sensors are reviewed in this paper. Various materials, mechanical and environmental factors affecting concrete piezoresistive properties are explicated. Some contradictory results from different studies are reported and discussed. Future perspectives of piezoresistive cement-based sensors are also delineated. The review reveals that there is an optimal conductor content, below which the sensor would perform more like plain concrete with high resistivity and low sensitivity, while excessively higher than which, the dispersion of the conductive phase could become difficult, thus increasing resistivity. The manufacturing process, such as the dispersion method of conductors and curing condition, plays a significant role in conductor distribution, matrix density and pore structure of the sensors, which, together with rheology of the sensor composite, consequently alters the piezoresistive properties of the sensors. In addition to responding to mechanical loading, cement-based piezoresistive sensor also has a great potential for monitoring behaviour of concrete under freeze-thaw cycling. It is expected that this review will provide not only an orientation for new researchers to explore and engage in related studies but also an insight for experienced researchers to perform transformational examinations into cement-based piezoresistive sensors. [ABSTRACT FROM AUTHOR]

This paper reports the stress and frequency analysis of dynamic silicon diaphragm during the simulation of micro-electro-mechanical-systems (MEMS) based piezoresistive pressure sensor with the help of finite element method (FEM) within the frame work of COMSOL software. Vibrational modes of rectangular diaphragm of piezoresistive pressure sensor have been determined at different frequencies for different pressure ranges. Optimal frequency range for particular applications for any diaphragm is a very important so that MEMS sensors performance should not degrade during the dynamic environment. Therefore, for the MEMS pressure sensor having applications in dynamic environment, the diaphragm frequency of 280 KHz has been optimized for the diaphragm thickness of 50  μ m and hence this frequency can be considered for showing the better piezoresistive effect and high sensitivity. Moreover, the designed pressure sensor shows the high linearity and enhanced sensitivity of the order of (∼ 0.5066 mV/psi). [ABSTRACT FROM AUTHOR]

Abstract The present paper investigates the damage monitoring using the piezoresistive effect on the glass fiber-reinforced polymer (GFRP) omega stringers reinforced through-the-thickness by tufting. The experiments consisted of the electric resistance measurements from the tufted yarns during the pull-off tests on omega stringers. Acoustic emission (AE) and digital image correlation (DIC) techniques were also performed throughout the tests in order to evaluate the acoustic activity and the strain field respectively. Furthermore, non-supervised AE clustering was carried out and aided to determine the main damage events. The results presented that electric resistance measurements are in good correlation with the AE clusters, especially with those related to the delamination and tuft yarns fracture. Besides, these damage events are well distinguished from the electric resistance data. Also, DIC images exhibited that electric resistance is sensitive to local strain field as expected to piezoresistivity measurements. Therefore, tufting reinforcements have shown to be an interesting monitor of the structural health in real time, further their well-known ability to increase the mechanical out-of-plane properties of laminate composites. [ABSTRACT FROM AUTHOR]

Abstract Niobium-containing diamond-like carbon (Nb-DLC) films were deposited in a reactive high power impulse magnetron sputtering (HIPIMS) process, using a niobium target in an argon/acetylene atmosphere. Investigations of the electrical properties revealed their good suitability to serve as sensor material in strain gauges, with an elevated gauge factor of 35.5 and the possibility to adapt the temperature coefficient of the electrical resistance (TCR) to values near zero. Structure analysis of the crystallinity, chemical composition, and morphology of this material give insights of the correlations between structure and piezoresistive properties. A structure zone model in relation to the Nb content was developed, combining the results of the different measurements. Highlights • Preparation of Nb-DLC by a combined HIPIMS/PECVD process • High gauge factor combined with a low TCR • TCR can be adapted, temperature compensation is possible. • Deeper perception on material structure • Structure zone model of Nb-DLC [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • CNTs were systematically fragmented by high density ultrasonic energy. • PMMA composites with fragmented CNTs exhibited lower electrical conductivity. • Electromechanical sensitivity was higher for composites with fragmented CNTs. • Contributions of piezoresistive mechanisms are discussed. Abstract Multiwall carbon nanotubes (MWCNTs) were systematically fragmented using high density ultrasonic energy and used as fillers of a poly (methyl methacrylate) matrix (PMMA). MWCNT fragmentation was confirmed by scanning electron microscopy and atomic force microscopy. Dedicated MWCNT length measurements yielded a log-normal statistical distribution, with mean value of 1.33 μm for the as-received MWCNTs and 0.66 μm for the fragmented MWCNTs. Higher electrical percolation threshold and lower electrical conductivity were obtained for MWCNT/PMMA composites (0.01–1 wt.% MWCNT concentration) using the fragmented MWCNTs. Higher electro-mechanical (piezoresistive) sensitivity under tensile tests was measured for PMMA nanocomposites with fragmented MWCNTs, which was explained by a competition of mechanisms related to the MWCNT length. [ABSTRACT FROM AUTHOR]

Fiber-reinforced composites have seen growing demands and widespread use in a variety of fields, including aviation, civil engineering, and the automobile industry. Fiber-reinforced composites must be monitored by nondestructive methods because of their tendency to have complicated and often visually undetectable failure mechanisms. Incorporating self-sensing capabilities into composites through nanofiller modification to leverage the piezoresistive effect is one approach for monitoring these materials. In this method, electrical resistivity is a function of mechanical strains, allowing for intrinsic self-sensing. To date, predictive modeling efforts in this field have mostly concentrated on microscale piezoresistivity. Research on modeling resistivity changes in macroscale fiber–matrix material systems has been limited, and even less research has been conducted to evaluate the impact of continuous fiber reinforcement. To bridge this gap, an analytical model that predicts changes in the resistivity of a material system with nanofiller-modified polymer and continuous fiber reinforcement is proposed. The cornerstone of this strategy is the establishment of an electrical concentric cylindrical model. We begin by defining our domain, which consists of concentric cylinders representing a continuous reinforcing fiber surrounded by a nanofiller-modified matrix. Next, the system is homogenized such that we can predict the change in the axial and transverse resistivity of the concentric cylinders. It is envisaged that the results herein presented will serve as a stepping stone towards the creation of a laminate theory of piezoresistivity. [Display omitted] • Novel macroscale piezoresistivity model for fiber composites with conductive matrices • Electrically homogenize the piezoresistive response of the system via CCA approach • Model predictions compared with inhomogenous (exact) solution and rule of mixtures • CCA model accurately predicts piezoresistivity for conductive matrix + fiber systems • The rule of mixtures is inadequate for modeling piezoresistivity [ABSTRACT FROM AUTHOR]

Highlights • Mechanical properties of CNF-RPC were presented. • CNF-RPC showed excellent electrical and piezoresistive performances. • CNF-RPC behaved a good deicing ability when CNFs contents reached 1.0%. Abstract This paper aimed to develop carbon nanofiber (CNF) reinforced reactive powder concrete (CNF-RPC) with multi-functional properties. Water to binder ratio (w/b) was kept at 0.2 and CNFs dosage ranged from 0% to 2% by volume of the total cementitious materials. Flexural and compressive strengths of CNF-RPC were determined for each dosage of CNFs. Piezoresistive performance of CNF-RPC was investigated while the piezoresistivity of CNFs added cement paste and mortar were also performed. Moreover, deicing performance of CNF-RPC was experimentally researched and numerally simulated using finite element analysis. Results indicated that RPC with appropriate content of CNFs performed favorable mechanical properties and excellent self-sensing performance. While CNFs content was close to the post-percolation threshold zone, CNF-RPC presented an obvious deicing performance. When CNFs content was in the percolation threshold zone, resistance of CNF-RPC rarely changed with measurement time. RPC containing CNFs (CNF-RPC) was more conductive and demonstrated a higher sensitivity and linearity of self-sensing performance than CNFs added cement paste and mortar samples. [ABSTRACT FROM AUTHOR]

Highlights • Embedding CNFs/epoxy sensors into concrete components is studied at first time. • The piezoresistive performances of the CNFs/epoxy sensors are evaluated. • A compensation circuit is proposed to eliminate the effect of temperature. • The calibration and monitoring curves exhibited a consistent variation trend. Abstract In this study, embedded strain sensors based on the principle of piezoresistivity were fabricated by epoxy-based composites filled with different contents of carbon nanofibers (CNFs). The piezoresistive performances and relevant parameters including gauge factor, linearity, repeatability and hysteresis of these sensors were investigated. A compensation circuit was proposed to eliminate the influence of temperature on sensing signals of the sensors. The CNFs/epoxy sensors were embedded into concrete cylinders to monitor their compressive strains under monotonic and cyclic loadings, thereby assessing practical applications of the CNFs/epoxy sensors as strain sensors for monitoring concrete structures. The results indicate that the sensors containing 0.58 vol% of CNFs, which have a gauge factor of 37.1, a linearity of 5.5%, a repeatability of 3.8% and a hysteresis of 6.3%, exhibited better piezoresistive performance compared to those containing 0.29 vol% of CNFs. The calibration and monitoring curves exhibited a consistent variation trend when the cylinders embedded with sensors were subjected to monotonic and cyclic loadings. This demonstrates that the CNFs/epoxy sensors have considerable potential to be used as embedded strain sensors for structural health monitoring of concrete structures. [ABSTRACT FROM AUTHOR]

In this paper, carbon nanofibers (CNFs) with high aspect ratio were dispersed into epoxy matrix via mechanical stirring and ultrasonic treatment to fabricate self-sensing CNFs/epoxy composites. The mechanical, electrical and piezoresistive properties of the nanocomposites filled with different contents of CNFs were investigated. Based on the tunneling conduction and percolation conduction theories, the mechanisms of piezoresistive property of the nanocomposites were also explored. The experimental results show that adding CNFs can effectively enhance the compressive strengths and elastic moduli of the composites. The percolation threshold of the CNFs/epoxy composites is 0.186 vol% according to the modified General Effective Media Equation. Moreover, the stable and sensitive piezoresistive response of CNFs/epoxy composites was observed under monotonic and cyclic loadings. It can be demonstrated that adding CNFs into epoxy-based composites provides an innovative means of self-sensing, and the high sensitivity and stable piezoresistivity endow the CNFs/epoxy composites with considerable potentials as efficient compressive strain sensors for structural health monitoring of civil infrastructures. [ABSTRACT FROM AUTHOR]

The piezoresistivity, expressed as the relative resistance variation with imposed strain for conductive polymer nanocomposites, was analyzed by employing two models, developed elsewhere, and a new one proposed in the present work. The corresponding experimental results of three different types of polymer nanocomposites, namely styrene-butadiene rubber reinforced with carbon black and multi walled carbon nanotubes, poly-vinylidene-fluoride and polypropylene reinforced with multi-walled carbon nanotubes, were comparatively studied, on the basis of the employed models. An effort was made to explore the working mechanisms which control the relative resistance change with strain. The effect of polymer type, the strain range and the nano-filler type and weight fraction were investigated. [ABSTRACT FROM AUTHOR]

Electrical impedance tomography is a method of noninvasively imaging the internal conductivity distribution of a domain. Because many materials exhibit piezoresistivity, electrical impedance tomography has considerable potential for application in structural health monitoring. Despite its numerous benefits such as being low cost, providing continuous sensing, and having the ability to be employed in real time, electrical impedance tomography is limited by several important factors such as the ill-posed nature of the inverse problem and the requirement for large electrode arrays to produce quality images. Unfortunately, current methods of mitigating these limitations impose upon the benefits of electrical impedance tomography. Herein, we propose a multi-physics approach of enhancing electrical impedance tomography without sacrificing any of its benefits. This approach is predicated on coupling global conductivity changes with the electrical impedance tomography inversion process thereby adding additional constraints and rendering the problem less illposed. Additionally, we leverage physically motivated global conductivity changes in the context of piezoresistive nanocomposites. We demonstrate this proof of concept with numerical simulations and demonstrate that by incorporating multiple conductivity changes, the rank of the sensitivity matrix can be improved and the quality of electrical impedance tomography reconstructions can be enhanced. The proposed method, therefore, has the potential of easing the implementation burden of electrical impedance tomography while concurrently enabling high-quality images to be produced without imposing on the major advantages of electrical impedance tomography. [ABSTRACT FROM AUTHOR]

The mechanical properties, electrical conductivity and piezoresistive response of thermosetting polymer nanocomposites comprising carbon nanotubes (CNTs, one-dimensional topology, 1D), few-layer thermally reduced graphene oxide (FLG, two-dimensional topology, 2D), cubic-shaped few-layer graphene shells (CGSs, three-dimensional topology, 3D), and hybrid combinations of them (1D-2D and 1D-3D) are investigated. It is observed that the most electro-conductive materials are formed when CGSs, CNTs or a hybrid combination of both are used, likely because of the lower defect density of CGSs and the higher aspect ratio of CNTs. The mechanical properties and piezoresistive sensitivity are higher for composites comprising CNTs or a 1D-2D hybrid combination of CNTs and FLGs. While the increased mechanical properties for these two groups of composites are attributed to the higher aspect ratio/lateral size, higher number of dangling bonds and functionalities, and higher specific surface area (for the case of FLGs) of their fillers, the increased piezoresistive sensitivity is explained in terms of their higher excluded volume within the composite. [ABSTRACT FROM AUTHOR]

Carbon fiber reinforced polymer (CFRP) material is an exceptionally and light fiber-reinforced polymer that can be used as a smart sensor due to its remarkable piezoresistivity. This study presents a comparative study on piezoresistive characteristics of CFRP tendons manufactured by two different methods, i.e., the vacuum process method (VPM) and the brush process method (BPM). The tensile and resistance tests were conducted simultaneously on two groups of CFRP tendon specimens respectively by VPM and BPM to investigate their differences in initial resistances, piezoresistive performance and sensitivity. Test results showed that the initial resistance of the CFRP tendons prepared by the VPM is larger than those prepared by the BPM. The resistances of the CFRP tendon specimens by two methods increase uniformly with increasing strain. The resistance increases more quickly at the same strain increment for specimens prepared by BPM compared with those for VPM. Three stages can be observed according to the variation of fractional change in resistance (d R / R ) with tensile strain. The scope of d R / R varies from 0% to 55% for BPM specimens, which is much wider than that for VPM specimens, which fall within 8.5%. The result is that BPM specimens are more sensitive than that of VPM. The values of sensitivity ‘ K ’ obtained for BPM specimens varying from 22 to 28 are much bigger than that for VPM ranging from 2.7 to 3.5. For BPM specimens, the pre-tension process can tighten up the fibers to reduce crimp and significantly reduce the amounts of bubbles during the brush process. However, the specimens prepared by VPM without undergoing the pre-tension process showed a relative looser state and carbon fibers might crimp. [ABSTRACT FROM AUTHOR]

Recent advances in nanotechnology have guided the development of a new generation of multifunctional construction materials. An example of this are cement-based composites, some of which can be used not just to pave roads but also to monitor them. A cement composite, integrating a carbon black (CB) filler, was used as a piezoresistive sensor to identify different cyclic compressive loadings, at temperatures ranging from 15 °C to 45 °C. The mechanical essays were performed under realistic conditions using 600 cm 3 specimens and uniaxial loads typical of automobile traffic. A linear and reversible pressure-sensing performance was found with gauge factors ranging from 40 to 60. Overall, these results show that CB/cement composites can act as stress-sensitive materials for traffic monitoring. [ABSTRACT FROM AUTHOR]

Strain sensors can be embedded in civil engineering infrastructures to perform real-time service life monitoring. Here, the sensing capability of piezoresistive cement-based composites loaded with carbon black (CB) particles is investigated. Several composite mixtures, with a CB filler loading up to 10% of binder mass, were mechanically tested under cyclic uniaxial compression, registering variations in electrical resistance as a function of deformation. The results show a reversible piezoresistive behaviour and a quasi-linear relation between the fractional change in resistivity and the compressive strain, in particular for those compositions with higher amount of CB. Gage factors of 30 and 24 were found for compositions containing 7 and 10% of binder mass, respectively. These findings suggest that the CB-cement composites may be a promising active material to monitor compressive strain in civil infrastructures such as concrete bridges and roadways. [ABSTRACT FROM AUTHOR]

The piezoresistivity and smart property under flexure in concrete for water-binder ratio of 0.38 were investigated by adding well-dispersed carbon fibers and graphite to improve its mechanical and smart performance. Thence, the reveal of the smart property under flexure was demonstrated from the experiment by three-point loading as well as the relationship between the strain and variance ratio of resistance was in discussion. The result shows successful in cement mixing by carbon fibers and graphite in 0.7 wt% and 2.5 wt% in mechanical and smart performance which implies that carbon fibers are capable partially replaced by graphite. In addition, the strain dependent resistivity characteristic was able to drawn by quadratic polynomial while the microtopography of the composite material was uncovered by the scanning electron microscopy (SEM). [ABSTRACT FROM AUTHOR]

This paper studied the piezoresistive effects of cementitious composites filled with nano graphite platelets (NGPs). Experiments are performed to investigate the electrical responses of cementitious composites filled with NGPs when subjected to cyclic compressive stress under different quasi static and dynamic loading conditions such as different loading amplitudes, different loading rates and constant loading within the elastic regime of these composites. Meanwhile, the cementitious composites filled with NGPs are explored for the application in measuring dynamical loading rate. The results demonstrated that cementitious composites filled with NGPs possess sensitive piezoresistive effect and stable repeatability to different loading conditions. [ABSTRACT FROM AUTHOR]

This paper investigated the influence of embedded electrode and pasted electrode on the resistivity behavior of carbon nanofibers (CNFs) cement paste by using the alternating current (AC) method. The dosage of CNFs ranged from 0.75% to 3.125 % by volume of cement and the samples were measured after four treatment conditions including oven dried for 3 days, being sealed for 30 days, immersed in tap water or 3.5% NaCl solution for 30 days respectively. The piezoresistive performances of carbon nanofibers cement pastes (CNFP) with two types of electrodes under oven dry state were also studied. Results indicated that the average value and variability coefficient (Cv) of electrical resistivity were reduced by the increase of AC frequency only if the CNFs content was less than 2.5 vol.%. The immersion of water and NaCl solution reduced the resistivity of CNFP when the CNFs dosage is below 2.5 vol.%. The CNFP with pasted electrodes presented higher resistivity than the specimen with embedded electrodes when the CNFs content was lower than 3.125 vol.%. However, as the CNF content exceeded 2.5vol.%, the resistivity of CNFP with two types of electrodes were almost the same. The CNFP with two electrode types presented different piezoresistive performances at various amount of CNFs. A computational model for the piezoresistivity of CNFs cement paste was obtained from this research. The results of this research also demonstrated the improving effects of CNFs on the ductility and axial compressive strength of CNFP. [ABSTRACT FROM AUTHOR]

Due to the growing demand for tactile sensors, the possibility of detecting an external uniaxial pressure by the piezoresistive measuring of a conductive filler/elastomer composite was investigated. A series of piezoresistive models are discussed. Novel highly sensitive piezoresistive foams with excellent elasticity were fabricated using vapor-grown carbon fiber ( VGCF), two-component silicone elastomer and a new type of thermally expandable micro beads foaming agent to overcome the disadvantages of the silicone elastomer in the utilization of a tactile sensor. Deformations of the foams caused by uniaxial pressure were observed using scanning electron microscopy from cross-sections. Effects of the VGCF and the foaming agent on the piezoresistivitiy were investigated. The piezoresistive mechanisms of the foams are discussed according to the measurements, and good fit was found between the theoretical calculations and the experimental piezoresistivity measurements. It is found that the addition of the micro beads foaming agent can improve the piezoresistivity of the VGCF/silicone foam and increase the sensitivity and repeatability for its application in a tactile sensor. © 2016 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

The electrical and piezoresistive response of hybrid nanocomposites comprising a combination of few-layer thermally reduced graphite oxide (TRGO) and multiwall carbon nanotubes (MWCNTs) mixed with natural rubber is reported. The influence of the structure and morphology of the TRGO, and MWCNTs on the electrical and piezoresistive response of these nanocomposites is examined. All composites showed a different nonlinear piezoresistive behavior depending on the nanostructure (or combination) used. The hybrid combination of 2 wt.% TRGOs and 2 wt.% MWCNTs increased the electrical conductivity of the polymer 13 orders of magnitude, change that was not possible to achieve by using only TRGOs. This outcome can be attributed to the formation of a highly interconnected percolation network, and indicates that the morphology of the nanostructure plays a paramount role in the electrical and piezoresistive behavior of the nanocomposite. Platelet-type carbon nanostructures of the graphene family used as fillers for polymer composites may not outperform the electrical behavior of rod-type ones such as MWCNTs, but a tailored combination of both may be beneficial for the development of piezoresistive-based sensors. [ABSTRACT FROM AUTHOR]

The piezoresistivity of graphite sheet filled silicone rubber composite (which is a typical composite with 2–3 structure) during compression is researched. If the graphite sheet content is low, the electrical resistance of the composite increases with the increase of the pressure. If the graphite sheet content is medium, the resistance decreases first and then increases with the increase of the pressure. When the graphite sheet content is high, the resistance decreases with the increase of the pressure. The piezoresistive mechanism of the composite is explained by using the theory on the “effective conductive path”. Based on the analyses of the piezoresistivity, the optimal graphite sheet content for the development of the piezoresistive sensor has been determined. [ABSTRACT FROM AUTHOR]

Wide range of improvements in the silicon integrated circuits and micromachining technology enables the development of various sensing instruments. Micro Electro Mechanical System (MEMS) technology enables fabrication of micromachined components and batch fabrication through Very Large Scale Integrated (VLSI) processing. In MEMS piezoresistive pressure sensor, temperature can be considered as the main environmental condition which affects the system performance. In this work, a study on the effects of temperature and doping concentration in a boron implanted piezoresistor for a high sensitive silicon based MEMS piezoresistive pressure sensor is discussed. Using the fundamental semiconductor equations, the dependance of conductivity and hence the resistivity of a piezoresistor on operating temperature and impurity doping concentration is analysed. It is also being observed that in physical environment, the effect of stress on the performance of MEMS pressure sensor will be more compared with the temperature and for a given pressure output voltage varies in a linear manner. FEA simulation tool CoventorWare® has been used for the simulation. [ABSTRACT FROM AUTHOR]

Structural health monitoring (SHM) including the real-time cure monitoring and non-destructive evaluation (NDE) in-service has been highly demanded with respect to smart composite material for the safe working of civil structures. Carbon fiber–reinforced polymer (CFRP) material is extremely strong and light fiber-reinforced polymer which can be used as electrical resistors due to its obvious piezoresistivity. This study presents an experimental investigation into the piezoresistive effect of CFRP tendon prepared by PAN-based carbon fiber and resin matrix modified with different carbon powder contents (i.e. 0%, 2%, 4%, 6%, and 8% by weight). Tests results showed that the mean value of initial electric resistance exhibited a decrease trend with increasing carbon powder content until it becomes stable when the powder content is greater than 6%. Electric resistance rate (dR/R) versus strain (ε) for different CFRP tendon specimens shows similar three stages regardless the carbon powder contents. An approximate liner relationship between dR/R and ε can be observed in the first stage for all tested specimens. Tests results also indicated that the sensitivity ( K ) increased with the increasing carbon fiber content at the beginning and followed by a decrease. The change law of K and its mechanism were evaluated and discussed from the microscopic point of view. Based on the analysis and low-energy theory, a coupled mechanical and electrical model combined resistivity scalar field response and structural strain vector field was established. The model provided herein was thereafter assessed and verified by comparing with existing tensile testing results. The consistence of the growth trend between the model and test results indicates the feasibility and reliability of the coupled model. [ABSTRACT FROM AUTHOR]

There is a growing demand for flexible and soft electronic devices. In particular, stretchable, skin-mountable, and wearable strain sensors are needed for several potential applications including personalized health-monitoring, human motion detection, human-machine interfaces, soft robotics, and so forth. This Feature Article presents recent advancements in the development of flexible and stretchable strain sensors. The article shows that highly stretchable strain sensors are successfully being developed by new mechanisms such as disconnection between overlapped nanomaterials, crack propagation in thin films, and tunneling effect, different from traditional strain sensing mechanisms. Strain sensing performances of recently reported strain sensors are comprehensively studied and discussed, showing that appropriate choice of composite structures as well as suitable interaction between functional nanomaterials and polymers are essential for the high performance strain sensing. Next, simulation results of piezoresistivity of stretchable strain sensors by computational models are reported. Finally, potential applications of flexible strain sensors are described. This survey reveals that flexible, skinmountable, and wearable strain sensors have potential in diverse applications while several grand challenges have to be still overcome. [ABSTRACT FROM AUTHOR]

The piezoresistivity is a change in the electrical resistivity of a semiconductor when mechanical stress is applied. A number of studies of the polycrystalline diamond (PCD) piezoresistivity have been reported before. And it was examined that the shear piezoresistive coefficients in single crystalline Silicon (Si) and Germanium (Ge) are exceptionally large due to its crystal orientation anisotropy. However, the single crystalline diamond (SCD) piezoresistivity has been rarely investigated with respect to crystal orientation anisotropy. In this study, the piezoresistive coefficients π 11 , π 12 and π 44 of SCD were measured experimentally with the SCD piezoresistors fabricated from the boron (B)-doped SCD thin films. It was found that the coefficient π 44 of SCD at 4.5 ppm B/C ratio were 18.3 and 12.0 times as large as the coefficient π 11 of that and the coefficient π 44 of PCD, respectively. [ABSTRACT FROM AUTHOR]

In recent years, “smart structures” experienced significant popularity in civil engineering. Such structures, referred to as intelligent structures , are built with combination of smart and conventional materials and have intelligent systems that cannot only gather information and perform tasks, but also sense variation in conditions of the materials and adapt accordingly. Conductive Hot Mix Asphalt (HMA) mixtures are constructed by modifying with electrically conductive materials. Conductive HMA mixtures would potentially make many technologies applicable to pavements including, but not limited to; thermal electric de-icing of airport runways or highways, cathodic protection of concrete bridge decks, pavement damage sensing, truck weigh-in-motion, and so forth. Dispersing carbon nanofibers (CNF) in HMA mixtures makes it a smart material as it develops a piezoresistive effect. The main objective of the study is to develop a smart HMA mixture by using electrically conductive material such as carbon nanofibers (CNF). The CNF modified HMA mixtures would have the ability to respond to loading. An exploratory investigation for piezoresistive response of CNF modified HMA mixtures under various types of loading, frequencies, and temperatures were evaluated. Stress–strain response due to applied load and its relationship with the change in resistivity was discussed. It was found that out of two type of CNF used in the study one provide better piezoresistive response of HMA. It was determined that embedment of copper wire electrodes is the most effective method to achieve smooth and consistent electrical response. Furthermore, polymer modified binders showed promising piezoresistive effect for medium to high temperature range. [ABSTRACT FROM AUTHOR]

In this work, a coupled electromechanical peridynamics formulation is presented which is used to study the electrical and piezoresistive response of a carbon nanotube (CNT) reinforced polymer nanocomposite material. CNT nanocomposites are multiscale materials which have unique piezoresistive properties arising from mechanisms operating from the nanoscale to the macroscale. The origin of piezoresistivity in CNT nanocomposites is a nanoscale phenomenon known as electron hopping or the electrical tunneling effect which allows an electric current to flow between neighboring CNTs even when not in contact, thereby forming a conductive network. A nanoscale representative volume element of a CNT bundle is chosen, i.e. a local region of high CNT volume fraction within the polymer matrix, wherein coupled electromechanical peridynamic equations are solved to evaluate the effective electrical and piezoresistive properties. The peridynamics formulation is used to introduce electron hopping in a unique way, through electron hopping bonds which have a horizon distance and conductivity dictated by the appropriate physics operating at the nanoscale. The effective electromechanical response depends on parameters such as CNT volume fraction, properties of the polymer matrix between CNTs and applied strain which are investigated in detail. Both quasistatic and dynamic loading conditions are considered where the effective electromechanical response is found to depend on variations in the local conductivity of intertube regions. [ABSTRACT FROM AUTHOR]

The influence of mechanical strain on the conductivity (piezoresistivity) of intrinsic and doped hydrogenated amorphous and microcrystalline silicon (a-Si:H and μ-Si:H) thin films as well as indium tin oxide and aluminum doped zinc oxide is examined under uniaxial tension and compression. The aim of this work is to characterize and model the influence of stress on thin film solar cells. The resistivity of intrinsic a-Si:H and μ-Si:H as well as that of n-type a-Si:H and μ-Si:H decreases with increasing tensile strain whereas it is increasing for both p-type materials. Both ITO and ZnO:Al show no significant change in resistivity with tensile strain until a critical strain value of roughly 0.5% that initiates fracture and introduces a non-reversible resistivity increase. Such irreversible changes occur for silicon layers at higher strains (1%). Silicon nitride buffer layers decrease the value of this critical strain. Tensile tests inside a scanning electron microscope demonstrate that such irreversible changes are related to crack formation when a certain tensile strain is exceeded. Analytical and numerical calculations are performed to estimate the influence of strain on the efficiency of p-i-n solar cells, which is roughly +/−0.3% for a biaxial strain of +/−1%. [ABSTRACT FROM AUTHOR]

We obtained highly conductive nanocomposites by adding conductive polymer poly(3,4-ethylenedioxythiophene)poly(styrenesulfonate) (PEDOT/PSS)-coated carbon nanotubes (CNTs) to pristine insulating Polycarbonate. Because the PEDOT/PSS ensures efficient charge transfer both along and between the CNTs, we could attribute the improvement in electrical conductivity to coating. In addition to improving the electrical conductivity, the coating also modified the piezoresistive behavior of the nanocomposites compared to the material with pristine uncoated CNTs: whereas CNT/Polycarbonate samples exhibited a very strong piezoresistive effect, PEDOT/PSS-coated MWCNT/Polycarbonate samples exhibited very little piezoresistivity. We studied this change in piezoresistive behavior in detail by investigating various configurations of filler content. We investigated how this observation could be explained by changes in the microstructure and in the conduction mechanism in the interfacial regions between the nanofillers. Our study suggests that tailoring the piezoresistive response to specific application requirements is possible. [ABSTRACT FROM AUTHOR]

The development of electronic skin (e-skin) is of great importance in human-like robotics, healthcare, wearable electronics, and medical applications. In this paper, a bioinspired e-skin design of hierarchical micro- and nano-structured ZnO nanowire (NW) arrays in an interlocked geometry is suggested for the sensitive detection of both static and dynamic tactile stimuli through piezoresistive and piezoelectric transduction modes, respectively. The interlocked hierarchical structures enable a stress-sensitive variation in the contact area between the interlocked ZnO NWs and also the efficient bending of ZnO NWs, which allow the sensitive detection of both static and dynamic tactile stimuli. The flexible e-skin in a piezoresistive mode shows a high pressure sensitivity (−6.8 kPa−1) and an ultrafast response time (<5 ms), which enables the detection of minute static pressure (0.6 Pa), vibration level (0.1 m s−2), and sound pressure (≈57 dB). The flexible e-skin in a piezoelectric mode is also demonstrated to be able to detect fast dynamic stimuli such as high frequency vibrations (≈250 Hz). The flexible e-skins with both piezoresistive and piezoelectric sensing capabilities may find applications requiring both static and dynamic tactile perceptions such as robotic hands for dexterous manipulations and various healthcare monitoring devices. [ABSTRACT FROM AUTHOR]

To improve the sensitivity and reduce the thickness of the pressure sensor based on conductive polymer composite, a piezoresistive sensor probe with a novel structure called transverse-electrodes-probe (TEP), which is different from the traditional sandwich-structure-probe (SSP), is designed. As the composite and the two electrodes are located in the same layer/three layers of TEP/SSP, TEP is thinner than SSP. The resistivity of TEP increases with the increase in the pressure, contributing to the increasing tendency of the resistance, and the increasing extent of the resistivity of TEP is larger than that of SSP during compression. The uniaxial direction of the electrodes in TEP/SSP is perpendicular/parallel to that of the pressure. Consequently, the thickness of the composite in TEP/SSP is invariant/decreased and the cross-sectional area of the composite in TEP/SSP is decreased/invariant with the increase in the pressure, contributing to the increasing/decreasing trend of the resistance of the composite during compression. The effect of the change in the dimensions on the resistance for TEP/SSP is consistent/opposite with/to the effect of the change in the resistivity. The experimental results verify that the sensitivity of TEP is higher than that of SSP. [ABSTRACT FROM AUTHOR]

In this paper, the piezoresistive response (i.e. the change of resistance under the application of strain) of polymer composites reinforced by a novel material known as fuzzy fibers is characterized by using single tow piezoresistive fragmentation tests and modeled by using a 3D computational multiscale model based on the finite element analysis. In the characterization work, the fuzzy fiber tow is embedded in a dog-bone specimen infused by epoxy, with resistance and displacement measured simultaneously to obtain its piezoresistive response. An approximately linear and stable piezoresistive response is observed within the fuzzy fiber tow region yielding gauge factors on average of 0.14. Using a 3D multiscale mechanical–electrostatic coupled code and explicitly accounting for the local piezoresistive response of the anisotropic interphase region, the piezoresistive responses of the overall fuzzy fiber reinforced polymer composites are studied parametrically in an effort to provide qualitative guidance for the manufacture of fuzzy fiber reinforced polymer composites. It is observed from the model that the fuzzy fiber reinforced polymer composites with cylindrically orthotropic carbon nanotube interphase regions are dominated by the electrical tunneling effect between the nanotubes and can yield very large gauge factors while fuzzy fibers with randomly oriented carbon nanotubes in the interphase region yield smaller gauge factors as the material is electrically saturated by the carbon nanotubes. Finally, the modeling efforts provide plausible reasons for the observed small gauge factors in experiments in the form of a combination of high concentration randomly oriented carbon nanotube interphase regions separated by sparse nanotube regions along the fuzzy fiber length. [ABSTRACT FROM AUTHOR]