Type Of Strain Sensor Research Articles

Ultra-stretchable, robust, self-healable conductive hydrogels enabled by the synergistic effects of hydrogen bonds and ionic coordination bonds toward high-performance e-skins

Ionic conductive hydrogels as electronic skins (e-skins) have showcased pivotal potentials in the realm of human health monitoring and human–machine interfaces. However, developing intelligent hydrogel with remarkable stretchability and mechanical elasticity is yet challenging. Herein, high-performance ion-conducting hydrogels with unprecedented mechanical properties and good transparent, conductive, self-healing properties are constructed via free-radical polymerization of acrylic acid (AA) within the polyvinyl alcohol (PVA) network, and the subsequent freeze–thaw (F-T) treatment and Zr4+ ion immersion crosslinking technique. Profiting from the synergy of multiple intermolecular/intramolecular hydrogen bonds between different polymers and coordination bonds of carboxyl-Zr4+, the resultant PVA/PAA/Zr4+ hydrogel exhibits high transparency (∼97 %), superior conductivity (0.6089 S/m), a long elongation at break (2053 %), robust self-healing efficiency (96.3 %), high deformation-tolerate property, and notable mechanical repeatability. These multifaceted attributes render the hydrogel to serve as an ionic conductor for capacitive/resistive −type strain sensor. The hydrogel-based resistive-type strain sensor features a wide detection range (0.5 %-800 %), rapid response time (150 ms), long-term stability, and consistent output stability, making it promising in monitoring diverse human motions and seamless human–machine interactions. Additionally, the hydrogel sensor demonstrates excellent linear response in ultra-wide range (0–900 % strain), high sensitivity, and excellent cycling stability in a capacitive mode, enabling to be used for accurately detecting the weights of objects. As such, this work advances the development of ionic conductive hydrogel as flexible and wearable electronic devices.

Auxetic kirigami structure-based self-powered strain sensor with customizable performance using machine learning

Recently, soft material based wearable sensors have discovered numerous applications in healthcare, sports monitoring, and virtual reality/augmented reality (VR/AR) systems. For these sensors, fulfilling user-specified requirements rather than just improving the sensor performance has become an important issue. In this study, a self-powered piezo-transmittance type strain sensor based on auxetic structures was optimized for configurable and user-specified characteristics using a machine-learning surrogate model. The sensor mechanism is based on the optical transmittance change induced by the gap opening of the auxetic kirigami structure. The sensor performance was analyzed according to the geometric design variables, and the optimal design was determined using Bayesian and Gaussian process to maximize the sensor performance for different purposes. The optimally designed geometries were used for self-powered sensors on a structural health monitoring (SHM) system, a human motion monitoring (HMM) system for monitoring sports performance and incorporated into an AR system.

Temporal changes in strain condition on all lateral surfaces during pretreatment before timber drying

Wood drying, such as boxed-heart square timber, often involves surface checks, which spoils the appearance of wood products and reduces their market value. Pretreatments are performed to avoid the surface checks, but detailed information about surface strain during timber drying remains unclear. In this study, surface strain detections were performed using two types of strain sensors (strain gauge and optical fiber strain sensor) to understand the surface dimensional changes during a series of pretreatments, consisting of steaming and high temperature and low humidity treatment. Simultaneous strain measurements based on the optical fiber sensor grasped the surface strain distributions in each lateral surface during timber drying; contraction behaviors were observed in the middle part of most surfaces in the early steaming stage, while one surface showed expansion. A remarkable expansion was detected in one surface during the high temperature and low humidity treatment, although most of the other surfaces showed gradual contraction behaviors. It was also discovered that the above detected behaviors were gradually reduced with the progress of each pretreatment.

Collagen-Based Organohydrogel Strain Sensor with Self-Healing and Adhesive Properties for Detecting Human Motion.

Conductive hydrogels are ideal for flexible sensors, but it is still a challenge to produce such hydrogels with combined toughness, self-adhesion, self-healing, anti-freezing, moisturizing, and biocompatibility properties. Herein, inspired by natural skin, a highly stretchable, strain-sensitive, and multi-environmental stable collagen-based conductive organohydrogel was constructed by using collagen (Col), acrylic acid, dialdehyde carboxymethyl cellulose, 1,3-propylene glycol, and AlCl3. The resulting organohydrogel exhibited excellent tensile (strain >800%), repeatable adhesion (>10 times), self-healing [self-healing efficiency (SHE) ≈ 100%], anti-freezing (-60 °C), moisturizing (>20 d), and biocompatible properties. This organohydrogel also possessed good electrical conductivity (σ = 3.4 S/m) and strain-sensitive properties [GF (gauge factor) = 13.65 with the maximal strain of 400%]. Notably, the organohydrogel had a considerable low-temperature self-healing performance (SHE = 88% at -24 °C) and rapid underwater self-healing property (SHE = 92%, self-healing time <20 min). This type of strain sensor could not only accurately and continuously monitor the large-scale motions of the human body but also provide an accurate response to the human tiny motions. This work not only proposes a development strategy for a multifunctional conductive organohydrogel with multiple environmental stability but also provides potential research value for the construction of biomimetic electronic skin.

Parametric investigation on laser interaction with polyimide for graphene synthesis towards flexible devices

Graphene, is one of the prominent materials in device fabrication due to its high conductive and high flexural strength for electrodes/device applications. The latest technique for graphene synthesis i.e. carbonization of polyimide by laser patterning has received much attention because of its capability to create various functional materials and flexible devices. The requirement of graphene demands larger volume production where laser-induced graphene (LIG) by consideration of pulse overlap could prove to be the solution if a recipe is prepared through appropriate optimization. The present study focused on the CO2 laser (λ = 10.6 µm) interaction with polyimide by generating raster pattern with varying pulse overlap in linear direction. The raster pattern is fabricated at different laser energies and pulse overlap with a constant 30% line overlap between two consecutive lines, in the lateral direction, for synthesizing LIG at relatively low laser power. Various combinations of laser fluences (46 J cm−2, 56 J cm−2, 66 J cm−2) and pulse spot overlap (60%, 70%, and 80%) were used for the polyimide carbonization. Both experimental and numerical simulation (using ComsolTM) results present an insight that optimal control of laser pulse overlap shows significant effect on crystallinity and electrical resistivity of synthesized graphene. The macroscopic quality of the raster pattern is investigated through the optical microscope. Detailed Raman spectro-microscopic analysis is carried out to study the defect to graphenization ratio and its impact on the properties of graphene synthesized. Through Raman analysis, the average in-plane crystallite length of graphene synthesis was observed from 27.732 ± 4–37.132 ± 6 nm. At last, a resistive type strain sensor was fabricated to check the stability of LIG and its reliability for repetitive loading conditions. The pulse overlap photo-thermal model, and its finite element analysis implementation presents better understanding towards optimizing the promising technique towards synthesizing LIG.

Aligned Carbon Nanotube-Based Sensors for Strain Monitoring of Composites

This paper presents a proof of concept of an aligned carbon nanotube (CNT) based strain sensor tested on the surface of a conventional aeronautic laminate. Two type of strain sensors were produced, type S and type T, in which the CNT alignment was parallel (Y) and transversal (X) to strain direction, respectively. Their electrical resistance response was thoroughly evaluated during cyclic tensile tests. Despite some disparities of the relative electrical resistance behavior in specific strain cycles, probably due to one-off interferences in the CNT conductive mechanism, the obtained gauge factor (GF) values were quite stable. Also, the electrical resistance anisotropy was evaluated and its opposite behavior when the samples were strained in Y- and X-directions may be used as strain direction indicator. Being able to quantify and indicate strain direction with just one 10×10 mm CNT patch, this sensor has proven to be suitable for strain sensing applications, namely for structure health monitoring of advanced composites.

Superhydrophobic and wearable TPU based nanofiber strain sensor with outstanding sensitivity for high-quality body motion monitoring

Nowadays, stretchable, flexible and wearable strain sensors are becoming more and more important for their abilities to monitor human health and body motions. However, it still exists some challenges to develop a new type of strain sensor with high sensitivity, the properties of anti-harsh environments and multidirectional monitoring. Here, we put forward a flexible, multi-functional, wearable and conductive nanofiber composite (WCNC) strain senor with handy preparation method, consisting of elastic thermoplastic polyurethane (TPU) with decorated acid modified carbon nanotubes (ACNTs), coupled silver nanowires (AgNWs) and solidified polydimethylsiloxane (PDMS). The sequential decorations of ACNTs, AgNWs and PDMS enhance the conductivity, superhydrophobicity, and strain sensing performance of the TPU-based nanofibrous membrane. The WCNC (TPU/ACNTs/ AgNWs/ PDMS) possesses a quite low resistance about 1.22 Ω/cm2 (conductivity is up to 3506.8 S/m), superior superhydrophobicity (contact angle is up to 153.04°) and self-cleaning property. Furthermore, the WCNC strain sensor possesses high sensitivity and large working strain (gauge factor is nearly 1.36 × 105 with the working strain ranging from 38% to 100%), which illustrates that the WCNC has a quite large work strain under extremely high GF, and has never been reported before. On account of its outstanding sensing performance, the WCNC can be used to monitor the different movements of human bodies and simultaneously monitor sensor signals in multiple vertical directions, achieving more accurate results.

Verification of Non-invasive Blood Glucose Measurement Based on Pulse Wave by FBG Sensor System

In order to grasp the biological information on a daily basis, more detailed information can be obtained as the number of measurements increases. In blood glucose level measurement, it is necessary to reduce the burden on the subject in order to increase the number of measurements, and non-invasive measurement is required. We measured the strain of the radial artery using the Fiber Bragg Grating (FBG) sensor, which is an optical fiber type strain sensor. The FBG sensor was a non-invasive measurement method that could measure strain signals simply by installing it on the surface of the living body on the radial artery. This strain signal was continuously measured by the developed wearable FBG sensor system. This study was conducted on a total of 9 subjects, 7 males and 2 females. A calibration model for calculating blood glucose level was constructed by Partial Least Squares (PLS) regression analysis using the signal waveforms measured by 7 subjects. The data of the remaining two subjects were substituted into the calibration model to calculate the predicted blood glucose level. The blood glucose level prediction accuracy was 19mg/dl, and all Error Grid Analysis (EGA) results were plotted in the A or B zone. The data of these two subjects were measured continuously, it was possible to show the transition of blood glucose level. Therefore, it was shown that the transition of the blood glucose level of the subject whose blood glucose level calculation calibration model has no data can be calculated from the signals continuously measured by the portable FBG sensor system.

Verification of the Propagation Range of Respiratory Strain Using Signal Waveform Measured by FBG Sensors.

The FBG (Fiber Bragg grating) sensor is an optical fiber type strain sensor. When a person breathes, strain occurs in the lungs and diaphragm. This was verified using an FBG sensor to which part of the living body this respiratory strain propagates. When measured in the abdomen, the signal waveforms were significantly different between breathing and apnea. The respiratory cycle measured by the temperature sensor attached to the mask and the strain cycle measured by the FBG sensor almost matched. Respiratory strain was measured in the abdomen, chest, and shoulder, and the signal amplitude decreased with distance from the abdomen. In addition, the respiratory rate could be calculated from the measured strain signal. On the other hand, respiratory strain did not propagate to the elbows and wrists, which were off the trunk, and the respiratory time, based on the signal period, could not be calculated at these parts. Therefore, it was shown that respiratory strain propagated in the trunk from the abdomen to the shoulder, but not in the peripheral parts of the elbow and wrist.

A silicone-based soft matrix nanocomposite strain-like sensor fabricated using Graphene and Silly Putty[formula omitted

Off-the-shelf planar strain gauges are ubiquitous and are generally designed for materials with a large elastic modulus such as steel or aluminum. Correspondingly, the strain gauges themselves are stiff and do not deform substantially under applied stress. Pairs of this type of strain gauge are typically used in a Wheatstone bridge circuit allowing the measurement of very small changes in resistance due to the changes in sensing element cross-sectional area to be measured. However, their use with softer low-modulus materials is limited due to the larger elastic deformations involved. The conductive property of graphene is leveraged to produce a different type of strain sensor that is sensitive yet also capable of significant elastic deformation. The graphene is dispersed in a silicone-based polymer matrix such that the deformation induces a change in resistance that can be measured using a voltage divider circuit. The target application for which this sensor is developed is to measure strain in a pressurized length of soft Tygon® tubing which is often used in pumping fluids through microfluidic devices. However, the silicone-based graphene polymer can easily be applied to a variety of other shapes and soft materials.

Flexible conductive Ag nanowire/cellulose nanofibril hybrid nanopaper for strain and temperature sensing applications

With the rapid development of smart wearable devices, flexible and biodegradable sensors are in urgent needs. In this study, “green” electrically conductive Ag nanowire (AgNW)/cellulose nanofiber (CNF) hybrid nanopaper was fabricated to prepare flexible sensors using the facial solution blending and vacuum filtration technique. The amphiphilic property of cellulose is beneficial for the homogeneous dispersion of AgNW to construct effective electrically conductive networks. Two different types of strain sensors were designed to study their applications in strain sensing. One was the tensile strain sensor where the hybrid nanopaper was sandwiched between two thermoplastic polyurethane (TPU) films through hot compression, and special micro-crack structure was constructed through the pre-strain process to enhance the sensitivity. Interestingly, typical pre-strain dependent strain sensing behavior was observed due to different crack densities constructed under different pre-strains. As a result, it exhibited an ultralow detection limit as low as 0.2%, good reproducibility under different strains and excellent stability and durability during 500 cycles (1% strain, 0.5 mm/min). The other was the bending strain sensor where the hybrid nanopaper was adhered onto TPU film, showing stable and recoverable linearly sensing behavior towards two different bending modes (tension and compression). Importantly, the bending sensor displayed great potential for human motion and physiological signal detection. Furthermore, the hybrid nanopaper also exhibited stable and reproducible negative temperature sensing behavior when it was served as a temperature sensor. This study provides a guideline for fabricating flexible and biodegradable sensors.

A S-shaped long-period fiber grating with ultra-high strain sensitivity

A S-shaped long-period fiber grating (SLPFG) is presented in this paper as a new type of strain sensor with ultra-high strain sensitivity. The sensor is fabricated by using the CO2-laser-polished method. It is illustrated by experiments that the WLFPG has structural stability and repeatability. The strain sensitivity of the proposed sensor reaches 29.3 pm/με in the range of 0–1000 με, and the temperature sensitivity is 76.3 pm/°C in the range of 30–170 °C. Compared to other CO2-laser-induced long-period fiber gratings (CO2-LPFGs), the strain sensitivity of the SLPFG is nearly ten times higher.

Auxetic elastomers: Mechanically programmable meta-elastomers with an unusual Poisson’s ratio overcome the gauge limit of a capacitive type strain sensor

How can we modulate the inherent Poisson’s ratio value of soft elastomeric materials? The theoretical limit value of the Poisson’s ratio of isotropic materials can be defined from −1 to 0.5 but elastomers generally take the Poisson’s ratio of 0.5. Herein, we introduce and establish the concept of a mechanical meta elastomer called “auxetic elastomer”. This is a continuum-solid elastomer having unique programmable elastic properties of Poisson’s ratio that are beyond their conventional ranges, and include in-plane negative and out-of-plane high positive Poisson’s ratios. Leveraging these unique deformation characteristics, we applied auxetic elastomers as a soft dielectric material for a highly stretchable capacitive-type strain sensor that overcomes the inherent performance limitations in terms of the low gauge factor.

Highly stretchable and wearable strain sensors using conductive wool yarns with controllable sensitivity

Wearable strain sensors for various applications, such as human motion detection, soft robotics, and healthcare have recently received extensive attention. Although a number of strain sensors based on various active materials have been proposed, a simple and practical method to obtain both high stretchable and sensitive strain sensors remains challenging. This paper presents a simple, scalable and environment-friendly fabrication method for wearable strain sensors, based on wool yarns, as abundant, lightweight, and stretchable natural materials. A simple coating technique was used to achieve highly conductive wool yarns using a conductive ink. Different types of strain sensors were then fabricated by changing the shape of the active material within the elastomer to tune their sensitivity. In detail, the conductive yarns were sandwiched within the Ecoflex in the form of a straight line (CWY-1 strain sensors) or serpenoid curves (CWY-2 and CWY-3 strain sensors). The strain sensors were fully characterized up to 200% of applied tensile strain. Gauge factors of 5 and 7.75 were found within the percentage stretch ranges of 0–127 and 127–200 %, respectively, for the CWY-1 strain sensors. We have also demonstrated the ability of the strain sensors to monitor human muscle and joints movements.

Highly stretchable, rapid-response strain sensor based on SWCNTs/CB nanocomposites coated on rubber/latex polymer for human motion tracking

PurposeThe purpose of this study is to present a highly stretchable and flexible strain sensor with simple and low cost of fabrication process and excellent dynamic characteristics, which make it suitable for human motion monitoring under large strain and high frequency.Design/methodology/approachThe strain sensor was fabricated using the rubber/latex polymer as elastic carrier and single-walled carbon nanotubes (SWCNTs)/carbon black (CB) as a synergistic conductive network. The rubber/latex polymer was pre-treated in naphtha and then soaked in SWCNTs/CB/silicon rubber composite solution. The strain sensing and other performance of the sensor were measured and human motion tracking applications were tried.FindingsThese strain sensors based on aforementioned materials display high stretchability (500 per cent), excellent flexibility, fast response (approximately 45 ms), low creep (3.1 per cent at 100 per cent strain), temperature and humidity independence, superior stability and reproducibility during approximately 5,000 stretch/release cycles. Furthermore, the authors used these composites as human motion sensors, effectively monitoring joint motion, indicating that the stretchable strain sensor based on the rubber/latex polymer and the synergetic effects of mixed SWCNTs and CB could have promising applications in flexible and wearable devices for human motion tracking.Originality/valueThis paper presents a low-cost and a new type of strain sensor with excellent performance that can open up new fields of applications in flexible, stretchable and wearable electronics, especially in human motion tracking applications where very large strain should be accommodated by the strain sensor.

On the use of strain sensor technologies for strain modal analysis: Case studies in aeronautical applications.

This paper discusses the use of optical fiber Bragg grating (FBG) and piezo strain sensors for structural dynamic measurements. For certain industrial applications, there is an interest to use strain sensors rather than in combination with accelerometers for experimental modal analysis. Classical electrical strain gauges can be used hereto, but other types of strain sensors are an interesting alternative with some very specific advantages. This work gives an overview of two types of dynamic strain sensors, applied to two industrial applications (a helicopter main rotor blade and an F-16 aircraft), FBG sensors and dynamic piezo strain sensors, discussing their use and benefits. Moreover, the concept of strain modal analysis is introduced and it is shown how it can be beneficial to apply strain measurements to experimental modal analysis. Finally, experimental results for the two applications are shown, with an experimental modal analysis carried out on the helicopter main rotor blade using FBG sensors and a similar experiment is done with the aircraft but using piezo strain sensors instead.

10702 小型発振回路センサーによるひずみ計測

New type of strain sensor using a CMOS inverter oscillator circuit has been developed. This type sensor can omit an amplifier because a counting device measures frequency changes of circuit voltage output caused by resistance changes of a strain gauge. In this study, the authors manufactured one small prototype strain sensor using a CMOS inverter oscillator circuit. Characteristics and measurement accuracy of this small type sensor were confirmed through static tensile tests of specimens. The test results showed that the same level of accuracy as conventional sensor has been achieved by this small type sensor.

発振回路を用いた新型ひずみセンサーの開発

New type of strain sensor using a CMOS inverter oscillator circuit has been developed. The sensor could omit an amplifier because a counting device measures frequency changes of circuit voltage output caused by resistance changes of a strain gauge. Characteristics and measurement accuracy of the sensor that consists of an oscillator circuit and a strain gauge were confirmed by static tensile tests of specimens. The test results showed that the same level of accuracy as conventional sensor has been achieved by using simple compensation factor assuming of existence of internal resistance on circuit.

Temperature Sensibility of Epoxy-Matrix Carbon Fiber Smart Layer

The paper deals with the temperature sensitivity of a new type strain sensor named carbon fiber smart layer (CFSL) made of epoxy-matrix composites with short carbon fiber mats. The experiment result indicated that the epoxy matrix CFSL is sensitive to temperature variation. It exhibits NTC effect in -5°C~25°C and exhibits PTC effect in 25°C~50°C. The NTC effect is relatively gentle and the PTC effect is relatively dramatic. The mechanism of both NTC effect and PTC effect is discussed based on the temperature sensitivities of carbon fiber itself and the fiber to fiber interface. Further experiment demonstrated its temperature sensing properties in the temperature scale in which the NTC effect or PTC effect exhibits individually.

In situ reduction of gold nanoparticles in PDMS matrices and applications for large strain sensing

Various types of strain sensors have been developed and widely used in the field for monitoring the mechanical deformation of structures. However, conventional strain sensors are not suited for measuring large strains associated with impact damage and local crack propagation. In addition, strain sensors are resistive-type transducers, which mean that the sensors require an external electrical or power source. In this study, a gold nanoparticle (GNP)-based polymer composite is proposed for large strain sensing. Fabrication of the composites relies on a novel and simple in situ GNP reduction technique that is performed directly within the elastomeric poly(dimethyl siloxane) (PDMS) matrix. First, the reducing and stabilizing capacities of PDMS constituents and mixtures are evaluated via visual observation, ultraviolet-visible (UV-Vis) spectroscopy, and transmission electron microscopy. The large strain sensing capacity of the GNP-PDMS thin film is then validated by correlating changes in thin film optical properties (e.g., maximum UV-Vis light absorption) with applied tensile strains. Also, the composite's strain sensing performance (e.g., sensitivity and sensing range) is also characterized with respect to gold chloride concentrations within the PDMS mixture.