Showing papers on "Gauge factor published in 2015"

Stretchable, Transparent, Ultrasensitive, and Patchable Strain Sensor for Human-Machine Interfaces Comprising a Nanohybrid of Carbon Nanotubes and Conductive Elastomers.

Abstract: Interactivity between humans and smart systems, including wearable, body-attachable, or implantable platforms, can be enhanced by realization of multifunctional human–machine interfaces, where a variety of sensors collect information about the surrounding environment, intentions, or physiological conditions of the human to which they are attached. Here, we describe a stretchable, transparent, ultrasensitive, and patchable strain sensor that is made of a novel sandwich-like stacked piezoresisitive nanohybrid film of single-wall carbon nanotubes (SWCNTs) and a conductive elastomeric composite of polyurethane (PU)-poly(3,4-ethylenedioxythiophene) polystyrenesulfonate (PEDOT:PSS). This sensor, which can detect small strains on human skin, was created using environmentally benign water-based solution processing. We attributed the tunability of strain sensitivity (i.e., gauge factor), stability, and optical transparency to enhanced formation of percolating networks between conductive SWCNTs and PEDOT phases at ...

Highly Stretchable and Sensitive Strain Sensors Using Fragmentized Graphene Foam

Abstract: Stretchable electronics have recently been extensively investigated for the development of highly advanced human-interactive devices. Here, a highly stretchable and sensitive strain sensor is fabricated based on the composite of fragmentized graphene foam (FGF) and polydimethylsiloxane (PDMS). A graphene foam (GF) is disintegrated into 200–300 μm sized fragments while maintaining its 3D structure by using a vortex mixer, forming a percolation network of the FGFs. The strain sensor shows high sensitivity with a gauge factor of 15 to 29, which is much higher compared to the GF/PDMS strain sensor with a gauge factor of 2.2. It is attributed to the great change in the contact resistance between FGFs over the large contact area, when stretched. In addition to the high sensitivity, the FGF/PDMS strain sensor exhibits high stretchability over 70% and high durability over 10 000 stretching-releasing cycles. When the sensor is attached to the human body, it functions as a health-monitoring device by detecting various human motions such as the bending of elbows and fingers in addition to the pulse of radial artery. Finally, by using the FGF, PDMS, and μ-LEDs, a stretchable touch sensor array is fabricated, thus demonstrating its potential application as an artificial skin.

Highly Sensitive and Stretchable Multidimensional Strain Sensor with Prestrained Anisotropic Metal Nanowire Percolation Networks

Abstract: To overcome the limitation of the conventional single axis-strain sensor, we demonstrate a multidimensional strain sensor composed of two layers of prestrained silver nanowire percolation network with decoupled and polarized electrical response in principal and perpendicular directional strain. The information on strain vector is successfully measured up to 35% maximum strain with large gauge factor (>20). The potential of the proposed sensor as a versatile wearable device has been further confirmed.

Flexible and Highly Sensitive Strain Sensors Fabricated by Pencil Drawn for Wearable Monitor

Abstract: Functional electrical devices have promising potentials in structural health monitoring system, human-friendly wearable interactive system, smart robotics, and even future multifunctional intelligent room. Here, a low-cost fabrication strategy to efficiently construct highly sensitive graphite-based strain sensors by pencil-trace drawn on flexible printing papers is reported. The strain sensors can be operated at only two batteries voltage of 3 V, and can be applied to variously monitoring microstructural changes and human motions with fast response/relaxation times of 110 ms, a high gauge factor (GF) of 536.6, and high stability >10 000 bending–unbending cycles. Through investigation of service behaviors of the sensors, it is found that the microcracks occur on the surface of the pencil-trace and have a major influence on the functions of the strain sensors. These performances of the strain sensor attain and even surpass the properties of recent strain sensing devices with subtle design of materials and device architectures. The pen-on-paper (PoP) approach may further develop portable, environmentally friendly, and economical lab-on-paper applications and offer a valuable method to fabricate other multifunctional devices.

Highly Stretchable and Sensitive Unidirectional Strain Sensor via Laser Carbonization

Abstract: In this paper, we present a simple and low-cost technique for fabricating highly stretchable (up to 100% strain) and sensitive (gauge factor of up to 20 000) strain sensors. Our technique is based on transfer and embedment of carbonized patterns created through selective laser pyrolization of thermoset polymers, such as polyimide, into elastomeric substrates (e.g., PDMS or Ecoflex). Embedded carbonized materials are composed of partially aligned graphene and carbon nanotube (CNT) particles and show a sharp directional anisotropy, which enables the fabrication of extremely robust, highly stretchable, and unidirectional strain sensors. Raman spectrum of pyrolized carbon regions reveal that under optimal laser settings, one can obtain highly porous carbon nano/microparticles with sheet resistances as low as 60 Ω/□. Using this technique, we fabricate an instrumented latex glove capable of measuring finger motion in real-time.

Thickness-Gradient Films for High Gauge Factor Stretchable Strain Sensors.

Abstract: High-gauge-factor stretchable strain sensors are developed by utilizing a new strategy of thickness-gradient films with high durability, and high uniaxial/isotropic stretchability based on the self-pinning effect of SWCNTs. The monitoring of detailed damping vibration modes driven by weak sound based on such sensors is demonstrated, making a solid step toward real applications.

Knitted Strain Sensor Textiles of Highly Conductive All-Polymeric Fibers

Abstract: A scaled-up fiber wet-spinning production of electrically conductive and highly stretchable PU/PEDOT:PSS fibers is demonstrated for the first time The PU/PEDOT:PSS fibers possess the mechanical properties appropriate for knitting various textile structures The knitted textiles exhibit strain sensing properties that were dependent upon the number of PU/PEDOT:PSS fibers used in knitting The knitted textiles show sensitivity (as measured by the gauge factor) that increases with the number of PU/PEDOT:PSS fibers deployed A highly stable sensor response was observed when four PU/PEDOT:PSS fibers were co-knitted with a commercial Spandex yarn The knitted textile sensor can distinguish different magnitudes of applied strain with cyclically repeatable sensor responses at applied strains of up to 160% When used in conjunction with a commercial wireless transmitter, the knitted textile responded well to the magnitude of bending deformations, demonstrating potential for remote strain sensing applications The

Tunable piezoresistivity of nanographene films for strain sensing.

Abstract: Graphene-based strain sensors have attracted much attention recently. Usually, there is a trade-off between the sensitivity and resistance of such devices, while larger resistance devices have higher energy consumption. In this paper, we report a tuning of both sensitivity and resistance of graphene strain sensing devices by tailoring graphene nanostructures. For a typical piezoresistive nanographene film with a sheet resistance of ∼100 KΩ/□, a gauge factor of more than 600 can be achieved, which is 50× larger than those in previous studies. These films with high sensitivity and low resistivity were also transferred on flexible substrates for device integration for force mapping. Each device shows a high gauge factor of more than 500, a long lifetime of more than 104 cycles, and a fast response time of less than 4 ms, suggesting a great potential in electronic skin applications.

Highly Stretchable and Ultrasensitive Strain Sensor Based on Reduced Graphene Oxide Microtubes–Elastomer Composite

Abstract: Strain sensors with excellent flexibility, stretchability, and sensitivity have attracted increasing interests. In this paper, a highly stretchable and ultrasensitive strain sensor based on reduced graphene oxide microtubes-elastomer is fabricated by a template induced assembly and followed a polymer coating process. The sensors can be stretched in excess of 50% of its original length, showing long-term durability and excellent selectivity to a specific strain under various disturbances. The sensitivity of this sensor is as high as 630 of gauge factor under 21.3% applied strain; more importantly, it can be easily modulated to accommodate diverse requirements. Implementation of the device for gauging muscle-induced strain in several biological systems shows reproducibility and different responses in the form of resistance or current change. The developed strain sensors show great application potential in fields of biomechanical systems, communications, and other related areas.

Highly sensitive piezo-resistive graphite nanoplatelet-carbon nanotube hybrids/polydimethylsilicone composites with improved conductive network construction.

Abstract: The constructions of internal conductive network are dependent on microstructures of conductive fillers, determining various electrical performances of composites. Here, we present the advanced graphite nanoplatelet-carbon nanotube hybrids/polydimethylsilicone (GCHs/PDMS) composites with high piezo-resistive performance. GCH particles were synthesized by the catalyst chemical vapor deposition approach. The synthesized GCHs can be well dispersed in the matrix through the mechanical blending process. Due to the exfoliated GNP and aligned CNTs coupling structure, the flexible composite shows an ultralow percolation threshold (0.64 vol %) and high piezo-resistive sensitivity (gauge factor ∼ 10(3) and pressure sensitivity ∼ 0.6 kPa(-1)). Slight motions of finger can be detected and distinguished accurately using the composite film as a typical wearable sensor. These results indicate that designing the internal conductive network could be a reasonable strategy to improve the piezo-resistive performance of composites.

Flexible MoS2 Field-Effect Transistors for Gate-Tunable Piezoresistive Strain Sensors.

Abstract: Atomically thin molybdenum disulfide (MoS2) is a promising two-dimensional semiconductor for high-performance flexible electronics, sensors, transducers, and energy conversion. Here, piezoresistive strain sensing with flexible MoS2 field-effect transistors (FETs) made from highly uniform large-area films is demonstrated. The origin of the piezoresistivity in MoS2 is the strain-induced band gap change, which is confirmed by optical reflection spectroscopy. In addition, the sensitivity to strain can be tuned by more than 1 order of magnitude by adjusting the Fermi level via gate biasing.

Stretchable Silver Nanowire–Elastomer Composite Microelectrodes with Tailored Electrical Properties

Abstract: We introduce a photolithography process compatible with soft and rigid substrates, enabling the fabrication of complex 3D interconnected patterns of silver nanowire (AgNW) networks embedded in polydimethylsiloxane (PDMS). Dimensions of the AgNW micropatterns are controlled within the film plane by photolithography, whereas thickness is controlled via a novel and uniform deposition technique using centrifugation. We report the first systematic characterization of the electromechanical properties of such microelectrodes with finest stretchable feature of 15 μm. We observe a geometry-dependent behavior of the gauge factor not only by changing the thickness of the microelectrodes, as it has been commonly reported so far, but also by varying their lateral dimensions. The presented nanocomposites exhibited sheet resistances down to 0.6 Ω/sq, gauge factors ranging from 0.01 to 100, and stretchability above 50% uniaxial strain. This versatile process allows for the production of highly sensitive strain sensors an...

Comparative electromechanical damage-sensing behaviors of six strain-hardening steel fiber-reinforced cementitious composites under direct tension

Abstract: This research investigates the electromechanical damage-sensing behavior of strain-hardening steel fiber-reinforced cement composites (SH-SFRCs) with six types of steel fibers (1.5% volume fraction content) within an identical mortar matrix (90 MPa). The six types of steel fibers studied are long twisted (T30/0.3), long smooth (S30/0.3), long hooked (H30/0.375), medium twisted (T20/0.2), medium smooth (S19/0.2), and short smooth (S13/0.2) steel fibers. The damage-sensing behavior was evaluated by measuring the changes in the electrical resistance during direct tensile tests. The electrical resistivity of the SH-SFRCs clearly decreased as the tensile strain increased until the post-cracking point, owing to the generation of multiple micro-cracks during strain-hardening. All the SH-SFRCs investigated had nominal gauge factors ranging between 50 and 140; these values are much higher than the commercially conventional gauge factor, which involves metal and is around 2. Both T30/0.3 and T20/0.2 produced the highest gauge factor, i.e., the best damage-sensing capacity, whereas S13/0.2 produced the highest electrical conductivity.

Flexible CNT-array double helices Strain Sensor with high stretchability for Motion Capture.

Abstract: Motion capture is attracting more and more attention due to its potential wide applications in various fields. However, traditional methods for motion capture still have weakness such as high cost and space consuming. Based on these considerations, a flexible, highly stretchable strain sensor with high gauge factor for motion capture is fabricated with carbon nanotube (CNT) array double helices as the main building block. Ascribed to the unique flexible double helical CNT-array matrix, the strain sensor is able to measure strain up to 410%, with low hysteresis. Moreover, a demonstration of using this strain sensor for capture hand motion and to control a mechanical hand in real time is also achieved. A model based on finite difference method is also made to help understand the mechanism of the strain sensors. Our work demonstrates that strain sensors can measure very large strain while maintaining high sensitivity, and the motion capture based on this strain sensor is expected to be less expensive, more convenient and accessible.

Highly efficient piezotronic strain sensors with symmetrical Schottky contacts on the monopolar surface of ZnO nanobelts

Abstract: Piezotronic strain sensors have drawn a lot of attention since the piezotronic theory was established. In this work, we developed a flexible piezotronic strain sensor based on an indium-doped ZnO nanobelt, of which the top surface was the monopolar surface. By connecting two electrodes with the two ends of the top surface of the nanobelt, the strain sensor was constructed. Compared with a nanorod/nanowire based strain sensor, this monopolar surface device avoids the need to identify the polar direction. Under strain, a static potential with the same value and polarity was generated by the coupling effect of the piezoelectric effect and the Poisson effect. This induced piezopotential influenced the Schottky barrier heights at the interfaces of both the source and drain electrodes, resulting in current changes with the same trend at forward and reverse biases. By applying a series of periodical strains, the sensor showed clear, fast and accurate current responses. The gauge factor achieved for compressive strain was 4036. This type of piezotronic strain sensor with a polar surface facing upward presented a high performance and easier fabrication, showing promise for applications in electrical mechanical sensors and MEMS.

Improved strain sensing property of functionalised multiwalled carbon nanotube/polyaniline composites in TPU matrix

Abstract: Polyaniline (PANI)/functionalised multiwalled carbon nanotube (FMWCNT) based conductive thermoplastic polyurethane (TPU) films were prepared to study their strain sensing property. The composites were prepared by solution casting method using FMWCNT coated with polyaniline. The coating was done by in-situ and ex-situ polymerization of aniline. The composites thus prepared were designated as FMWCNT-PANI/TPU (I) and FMWCNT-PANI/TPU (E), respectively. The electrical resistivity and resistivity – strain behaviour of these composites were measured. The percolation threshold and the strain sensitivity of these films depended on the dispersion of conductive fillers in the polymer matrix. The well-dispersed filler in FMWCNT-PANI/TPU (I) composites resulted in low percolation threshold and improved strain sensitivity. These composites with 2 weight% filler content, showed a gauge factor of 1075 at 100% strain and exhibited high reversibility in resistivity upon elongating to 20%. A coating of PANI on FMWCNT reduced its entanglement and enhanced the interfacial interaction between the nano fillers and TPU, leading to improved strain sensitivity. The experimental data for strain sensing was in good agreement with the theoretical equations derived from a model based on the tunneling theory by Simmons.

Development and Characterization of a Novel Interdigitated Capacitive Strain Sensor for Structural Health Monitoring

Abstract: Monitoring of structural health plays a crucial role in condition-based maintenance and degradation prediction of infrastructures. In this paper, we developed a novel interdigitated capacitive (IDC) strain sensor which could be integrated in a wireless monitoring system for structural health monitoring (SHM) applications. The IDC sensors were fabricated by laser-micromachining a 127- $\mu \text{m}$ -thick brass sheet followed by encapsulation in deformable thermoset polymers. The wireless monitoring system was implemented using a commercial wireless module (eZ430-RF2500 from Texas Instruments) which could provide multi-modality monitoring simultaneously. A graphical user interface was developed to display and store data as well as perform real-time analysis remotely. The wireless communication distance was up to 35 m inside buildings. The sensitivity of the sensor was characterized in both stretching and bending aspects, yielding a limit of detection with respect to strain of 0.025%. The gauge factor was found in the range of 6–9 which is much higher than those of commercially available strain gauges. The bending detection is reliable up to 20°. Hysteresis and temperature dependence were also investigated, revealing predictable responses. Finally, the entire system was demonstrated with both single and multiple sensors for a real-time SHM case.

Modeling of mesoscale dispersion effect on the piezoresistivity of carbon nanotube-polymer nanocomposites via 3D computational multiscale micromechanics methods

Abstract: In uniaxial tension and compression experiments, carbon nanotube (CNT)-polymer nanocomposites have demonstrated exceptional mechanical and coupled electrostatic properties in the form of piezoresistivity. In order to better understand the correlation of the piezoresistive response with the CNT dispersion at the mesoscale, a 3D computational multiscale micromechanics model based on finite element analysis is constructed to predict the effective macroscale piezoresistive response of CNT/polymer nanocomposites. The key factors that may contribute to the overall piezoresistive response, i.e. the nanoscale electrical tunneling effect, the inherent CNT piezoresistivity and the CNT mesoscale network effect are incorporated in the model based on a 3D multiscale mechanical–electrostatic coupled code. The results not only explain how different nanoscale mechanisms influence the overall macroscale piezoresistive response through the mesoscale CNT network, but also give reason and provide bounds for the wide range of gauge factors found in the literature offering insight regarding how control of the mesoscale CNT networks can be used to tailor nanocomposite piezoresistive response.

Piezoresistive effect of p-type silicon nanowires fabricated by a top-down process using FIB implantation and wet etching

Abstract: The piezoresistive effect in silicon nanowires (SiNWs) has attracted a great deal of interest for NEMS devices. Most of the piezoresistive SiNWs reported in the literature were fabricated using the bottom up method or top down processes such as electron beam lithography (EBL). Focused ion beam (FIB), on the other hand, is more compatible with CMOS integration than the bottom up method, and is simpler and more capable of fabricating very narrow Si nanostructures compared to EBL and photolithography. Taking the advantages of FIB, this paper presents for the first time the piezoresistive effect of p-type SiNWs fabricated using focused ion beam implantation and wet etching. The SiNWs were locally amorphized by Ga+ ion implantation, selectively wet-etched, and thermally annealed at 700 °C. A relatively large gauge factor of approximately 47 was found in the annealed SiNWs, indicating the potential of using the piezoresistive effect in top-down fabricated SiNWs for developing NEMS sensors.

Very large strain gauges based on single layer MoSe2 and WSe2 for sensing applications

Abstract: Here, we propose a strain gauge based on single-layer MoSe2 and WSe2 and show that, in these materials, the strain induced modulation of inter-valley phonon scattering leads to large mobility changes, which in turn result in highly sensitive strain gauges. By employing density-functional theory bandstructure calculations, comprehensive scattering models, and the linearized Boltzmann equation, we explain the physical mechanisms for the high sensitivity to strain of the resistivity in single-layer MoSe2 and WSe2, discuss the reduction of the gauge factor produced by extrinsic scattering sources (e.g., chemical impurities), and propose ways to mitigate such sensitivity degradation.

The effect of strain on the electrical conductance of p-type nanocrystalline silicon carbide thin films

Abstract: This paper presents for the first time the effect of strain on the electrical conductance of p-type nanocrystalline SiC grown on a Si substrate. The gauge factor of the p-type nanocrystalline SiC was found to be 14.5 which is one order of magnitude larger than that in most metals. This result indicates that mechanical strain has a significant influence on the electrical conductance of p-type nanocrystalline SiC, which is promising for mechanical sensing applications in harsh environments.

Bio-inspired mechanics of highly sensitive stretchable graphene strain sensors

Abstract: Graphene woven fabrics (GWFs) can sense large strain up to 10% with the highest gauge factors (105) thus far reported. This result promises key applications particularly in sensing strains of soft materials such as biological tissues, but the mechanism of such super gauge factor (SGF) property was not very clear. Through a bio-inspired Voronoi polycrystalline micromechanics model together with experimental validations, we show that the successive cracking, the “fish-scale” like network structure of GWFs, and the superlubricity between overlapped graphene flakes play crucial roles resulting in the SGF property. We also reveal the influences of overlapping width, graphene strip size, Poisson's ratio of the substrate material, size effect, interfacial resistance, and network size to the SGF property. These results can guide the design of GWFs with desired sensing performance.

Nearly isotropic piezoresistive response due to charge detour conduction in nanoparticle thin films.

Abstract: Piezoresistive responses of nanoparticle thin-film strain sensors on flexible polyimide substrates were studied. Disordered interparticle tunneling introduces microscopic detour of charge conduction so as to reduce gauge factors. The disorder also results in large resistance change when current flows in the direction perpendicular to a unidirectional strain, reducing response anisotropy. For practical usages, stability and endurance of these strain sensors are confirmed with 7 × 104 bending cycles. Cracks form in devices under prolonged cyclic bending and slightly reduce gauge factor.

Multi-Layer Transparent Force Sensor

Abstract: An optically transparent force sensor element includes multi-layer electrodes of two materials having different gauge factors to increase sensitivity of measured force magnitude. A passivation layer is positioned between the electrode layers in each element. One gauge factor may be positive while the other gauge factor may be negative.

Transparent strain sensors in an electronic device

Abstract: One or more strain sensors can be included in an electronic device. Each strain sensor includes a strain sensitive element and one or more strain signal lines connected directly to the strain sensitive element. The strain sensor(s) are used to detect a force that is applied to the electronic device, to a component in the electronic device, and/or to an input region or surface of the electronic device. A strain sensitive element is formed or processed to have a first gauge factor and the strain signal line(s) is formed or processed to have a different second gauge factor. Additionally or alternatively, a strain sensitive element is formed or processed to have a first conductance and the strain signal line(s) is formed or processed to have a different second conductance.