Composite Fiber Sensor Research Articles

Highly Elastically Deformable Coiled CNT/Polymer Fibers for Wearable Strain Sensors and Stretchable Supercapacitors.

Stretchable yarn/fiber electronics with conductive features are optimal components for different wearable devices. This paper presents the construction of coil structure-based carbon nanotube (CNT)/polymer fibers with adjustable piezoresistivity. The composite unit fiber is prepared by wrapping a conductive carbon CNT sheath onto an elastic spandex core. Owing to the helical coil structure, the resultant CNT/polymer composite fibers are highly stretchable (up to approximately 300%) without a noticeable electrical breakdown. More specifically, based on the difference in the coil index (which is the ratio of the coil diameter to the diameter of the fiber within the coil) according to the polymeric core fiber (spandex or nylon), the composite fiber can be used for two different applications (i.e., as strain sensors or supercapacitors), which are presented in this paper. The coiled CNT/spandex composite fiber sensor responds sensitively to tensile strain. The coiled CNT/nylon composite fiber can be employed as an elastic supercapacitor with excellent capacitance retention at 300% strain.

Multifunctional sensors for respiration monitoring and antibacterial activity based on piezoelectric PVDF/BZT-0.5BCT nanoparticle composite nanofibers

In clinical practice, combining sensitive and efficient sensors that have antibacterial properties with masks is a convenient way to monitor vital signs. Therefore, developing flexible pressure sensors with high sensitivity and antibacterial properties is the key for such smart devices. In our work, poly (vinylidene fluoride) (PVDF) nanofibers (NFs) with a high piezoelectric phase were fabricated by electrospinning with an optimized spinning voltage and collecting roller speed. Ba(Ti0.8Zr0.2)O3-0.5(Ba0.7Ca0.3)TiO3 (BZT-0.5BCT) nanoparticles (NPs) synthesized by the hydrothermal method were introduced into PVDF NFs to improve their piezoelectric response to external strain. With 20 wt% 0.5BZT-BCT NPs, the PVDF/BZT-BCT fiber composite sensor showed an output voltage up to 6.37 V with superior sensitivity (0.24 V Kpa−1), a short response time (∼50 ms), good durability over a wide time range and a low detection limit (2.50 mg). The sensor was built in a mask that demonstrated high sensitivity in monitoring the respiratory rate as well as antimicrobial resistance to Echerichia coli (E. coli) and Staphylococcus aureus (S. aureus). Furthermore, this composite fiber sensor can also be applied for the detection of body movement. The multifunctional 0.5BZT-BCT/PVDF fiber composite sensor may find clinical applications.

Bioinspired, Mechanically Robust Chemiresistor for Inline Volatile Organic Compounds Sensing

AbstractThere are advantages to polymer/nanoparticle composite‐based volatile organic compounds (VOCs) sensors, such as high chemical and physical stability, operability under extreme conditions, flexible use in manufacturing, and low cost. Nevertheless, their lower limit of detection due to thickness‐dependent diffusion has constrained their application. Inspired by the metaxylem in vascular plants and its vertical conduits and horizontal pits that enable efficient transpiration, a polymer/nanoparticle composite‐based sensor is fabricated with a controllable, spontaneously formed, hollow core for inline VOCs transportation, and porous microstructure for radial direction diffusion. The hollow core is surrounded by an inner porous layer (thermoplastic polyurethane (TPU)), a middle sensing layer (TPU/graphene nanoplatelets/multiwalled carbon nanotubes), and an outer mechanically durable layer (TPU). This multilayered structure shows a 600% higher response rate compared to a single‐layered composite fiber sensor, with a low limit of detection (e.g., ≈15 ppm for xylene) and high selectivity based on the Flory–Huggins interaction parameter. This flexible and stretchable sensor also demonstrates a dual parameter sensing capability from VOC concentrations and uniaxial strain deformation. Via a one‐step fiber spinning procedure, this self‐induced hollow fiber offers a unique method of microstructural design, which enables the detection of low‐concentration VOCs by polymer/nanoparticle‐based sensors.

A highly stretchable carbon nanotubes/thermoplastic polyurethane fiber-shaped strain sensor with porous structure for human motion monitoring

Highly flexible and stretchable strain sensors play an important role in the wearable electronic systems. Up to now, it is still an enormous challenge to achieve a good balance between the wide response range and high sensitivity for a resistive-type flexible strain sensor. In this work, we prepared a fiber-shaped strain sensor based on thermoplastic polyurethane (TPU) and multi-walled carbon nanotubes (MWCNTs) via a simple and cost-efficient wet-spun method. The production process can satisfy continuous and large-scale preparation. The generation of the interesting porous structure is related to the solvent exchange in solidification process and beneficial to the improvement of the sensing range. In the uniaxial stretching test, the MWCNTs/TPU fiber-shaped sensor showed an ultra-wide workable strain range (320%), a high sensitivity (gage factor of 22.2 within 160% strain and 97.1 for strain of 160–320%) and a fast response time (<200 ms). The MWCNTs/TPU composite fiber sensor exhibited good reproducibility and excellent durability in multi-cycle test (9700 cycles at 100% strain). The mechanism of the response behavior was studied through the tunneling theory. The strain sensor shows potential applications in human motion detections including bending of the fingers, elbows and knee, squatting and squat-jumping. The present paper provides an effective strategy for the design of high performance fiber-shaped wearable electronic systems.

Investigation on high sensitivity RI sensor based on PMF

This paper reports a high sensitive refractive index composite fiber sensor comprising the polymer micro-fiber fabricated by directly drawing method from poly(methyl methacrylate) colloid. Through the evanescent wave coupling method, the whole sensing system was built by means of micro-manipulation under microscope. The dip wavelength in the measured spectrum caused by the models interference shifted obviously when the surrounding refractive index changed. The approximate linear relationship between surrounding refractive index and dip wavelength shift was obtained experimentally. The measurement sensitivity have been demonstrated up to 1490nm/RIU with the surrounding refractive index ranging from 1.3333 to 1.3403 by using the polymer micro-fiber with a diameter of 6.6μm.

A Stretchable and Highly Sensitive Graphene-Based Fiber for Sensing Tensile Strain, Bending, and Torsion.

Wearable sensors are increasingly finding their way into applications of kinesthetic sensing, personal health monitoring, and smart prosthetics/robotics. A graphene-based composite fiber sensor with a "compression spring" structure is fabricated, featuring the ability of detecting multiple kinds of deformation. This fiber sensor is integrated into wearable sensors for monitoring human activities and intricate movements of robotics successfully.

Scattering Matrix Approach to Informing Damage Monitoring and Prognosis in Composite Bolted Connections

Structural health monitoring refers to the process of making an assessment, based on nondestructive, in-situ, autonomous measurements, about the ability of a structure to perform its intended function. This paper presents work done on a bolted connection in carbon-fiber reinforced polymer composite materials. A composite specimen is bolted in a double lap joint configuration to a test apparatus that applies an increasing tensile load. Ultimately, the load results in bearing failure of the material around the bolt hole. To monitor the progression of damage, macro fiber composite sensors are bonded in a circular array around the bolt hole. These sensors are then used to generate ultrasonic guided waves, a popular technique in nondestructive evaluation because of the favorable combination of propagation distance and sensitivity to damage. As the specimen is subjected to increasing load levels, measurements are taken repeatedly and compared with one another. Because damage will change the local mechanical properties of the material, the ultrasonic waves passing through the damaged region will be scattered differently in each direction, resulting in a different waveform arriving at the other surrounding sensors. By applying appropriate signal processing techniques, these changes may be interpreted as indicating the extent of damage that has occurred in the specimen. Preliminary analysis is presented demonstrating the correlation between changes in received strain signals and increasing damage levels.

The effects of embedded piezoelectric fiber composite sensors on the structural integrity of glass-fiber–epoxy composite laminate

Piezoelectric fiber composite sensors (PFCSs) made from micro-sized lead zirconate titanate (PZT) fibers have many advantages over the traditional bulk PZT sensors for embedded sensor applications. PFCSs as embedded sensors will be an ideal choice to continuously monitor the stress/strain levels and health conditions of composite structures. PFCSs are highly flexible, easily embeddable, have high compatibility with composite structures, and also provides manufacturing flexibility. This research is focused on examining the effects of embedding PFCS sensors (macro-fiber composite (MFC) and piezoelectric fiber composite (PFC)) on the structural integrity of glass-fiber–epoxy composite laminates. The strengths of composite materials with embedded PFCSs and conventional PZT sensors were compared, and the advantages of PFCS sensors over PZTs were demonstrated. Initially a numerical simulation study is performed to understand the local stress/strain field near the embedded sensor region inside a composite specimen. High stress concentration regions were observed near the embedded sensor corner edge. Using PFCS leads to a reduction of 56% in longitudinal stress concentration and 38% in transverse stress concentration, when compared to using the conventional PZTs as embedded sensors. In-plane tensile, in-plane tension–tension fatigue, and short beam strength tests are performed to evaluate the strengths/behavior of the composite specimens containing embedded PFCS. From the tensile test it is observed that embedding PFCS and PZT sensors in the composite structures leads to a reduction in ultimate strength by 3 and 6% respectively. From the fatigue test results it is concluded that both embedded PFCS and PZT sensors do not have a significant effect on the fatigue behavior of the composite specimens. From the short beam strength test it is found that embedding PFCS and PZT sensors leads to a reduction in shear strength by 7 and 15% respectively. Overall the pure PZT sensors seem to have low compatibility with composites when compared to PFCSs.

On Mechanical Properties of Composite Sandwich Structures With Embedded Piezoelectric Fiber Composite Sensors

The smart sandwich structures have been widely used in the aerospace, automobile, marine, and civil engineering applications. A typical smart sandwich structure is usually comprised of two stiff face skins separated by a thick core with variety of embedded sensors to monitor the performance of the structures. In this study, the smart composite sandwich structure (CSS) samples are fabricated with glass microballoons syntactic foam core and resin infused glass-fiber face skins (with piezoelectric fiber composite sensors (PFCS) embedded inside the resin infused glass-fiber face skins). One of the main concerns associated with embedding sensors inside composite structures is the structural continuity, compatibility, and interface stress concentrations caused by the significant differences in material property between sensor and host structures. PFCS are highly flexible, easily embeddable, highly compatible with composite structures and their manufacturing processes, which makes them ideal for composite health monitoring applications. In this study, in-plane tensile, tension–tension fatigue, short beam shear, and flexural tests are performed to evaluate the effect on strengths/behavior of the CSS samples due to embedded PFCS. Then carefully planned experiments are conducted to investigate the ability of the embedded PFCS to monitor the stress/strain levels and detect damages in CSS using modal analysis technique. The tensile tests show that both the average ultimate strength and the modulus of elasticity of the tested laminate with or without embedded PFCS are within 7% of each other. The stress–life (S-N) curves obtained from fatigue tests indicates that the fatigue lives and strengths with and without the PFCS are close to each other as well. From short beam and flexural test results, it is observed that embedded PFCS leads to a reduction of 5.4% in the short beam strength and 3.6% in flexural strength. Embedded PFCS’s voltage output response under tension–tension fatigue loading conditions has been recorded simultaneously to study their ability to detect the changes in input loading conditions. A linear relationship has been observed between the changes in the output voltage response of the sensor and changes in the input stress amplitude. This means that by constantly monitoring the output response of the embedded PFCS, one could effectively monitor the magnitude of stress/strain acting on the structure. Experiments are also performed to explore the ability of the embedded PFCS to detect the damages in the structures using modal analysis technique. Results from these experiments show that the PFCS are effective in detecting the initiations of damages like delamination inside these composite sandwich structures through changes in natural frequency modes. Hence embedded PFCS could be an effective method to monitor the health of the composite sandwich structures’ in-service conditions.

Enantioselective separation and electrochemical sensing of d- and l-tryptophan at ultratrace level using molecularly imprinted micro-solid phase extraction fiber coupled with complementary molecularly imprinted polymer-fiber sensor

Highly efficient enantioselective separation and quantitative recoveries of d- and l-tryptophan in aqueous and real samples can be achieved, with a monolithic molecularly imprinted polymeric fiber that serves both for micro-solid phase extraction and ultratrace sensing, without any false-positive (non-specific) contribution and cross-reactivity, in the range of 0.15–30.00 ng mL −1 with detection limit as low as 0.0261 ng mL −1 (relative standard deviation = 0.64%, signal/noise = 3). The proposed method combining molecularly imprinted micro-solid phase extraction fiber and a complementary molecularly imprinted polymer–carbon composite fiber sensor is proven to be useful for clinical diagnosis of stress-related diseases caused by acute tryptophan depletion.

Poly(o-anisidine)–polystyrene composite fibers via electrospinning process: Surface morphology and chemical vapor sensing

The electrospinning technique was utilized to produce camphorsulfonic acid (CSA) doped poly(o-anisidine) (POA)–polystyrene (PS) composite fibers in the non-woven mat form with different fiber characteristics, depending on the proportion of components in spinning solutions. CSA doped POA–PS composite fibers were fabricated onto interdigited gold substrates for use as chemical vapor sensors. The resultant composite fiber sensor responded to high polar volatile chemicals by showing a decrease in electrical resistance during the sensing measurement. The sensitivity of the composite fiber sensor when exposed to water vapor was higher than that of the composite fiber sensor subjected to ethanol vapor due to high polarity together with low vapor pressure of water compared with those of ethanol. The surface morphology of the non-woven composite fiber mat after chemical vapor sensing was unchanged. This work opens up the possibility of using the derivatives of polyaniline as a component in composite fibers for chemical sensing applications by taking advantages of their good solubility in common solvents as well as detectable electrical changes in terms of the relatively small amount of composite fibers needed.

Imprinted polymer–carbon consolidated composite fiber sensor for substrate-selective electrochemical sensing of folic acid

Molecularly imprinted polymers (MIPs) are often electrically insulating materials. Due to the presence of diffusion barrier(s) in between such MIP coating and electrode surface and the absence of a direct path for the conduction of electrons from the binding sites to the electrode, the development of electrochemical sensor is significantly restricted. The direct use of MIPs those possess intrinsic electron-transport properties, is highly limited. These problems are resolved by the design of an original, substrate-selective MIP-fiber sensor that combines conventional insulating MIP and conducting carbon powder in consolidated phase. A layer of conducting carbon particles, arranged orderly as ‘carbon strip’, is inducted in the polymer for direct electronic conduction. MIP–carbon composite (monolithic fiber) in this work is prepared via in situ free radical polymerization of a new monomer (2,4,6-trisacrylamido-1,3,5-triazine, TAT) and subsequent cross-linkage with ethylene glycol dimethacrylate, in the presence of carbon powder and template (folic acid), at 55 °C in a glass capillary. The detection of folic acid with the MIP-fiber sensor was found to be specific and quantitative (detection limit 0.20 ng mL −1, RSD = 1.3%, S/N = 3), in aqueous, blood serum and pharmaceutical samples, without any problem of non-specific false-positive contribution and cross-reactivity.

Development of a highly sensitive and selective hyphenated technique (molecularly imprinted micro-solid phase extraction fiber–molecularly imprinted polymer fiber sensor) for ultratrace analysis of folic acid

A simple polymerization strategy is reported in this work which allows molecularly imprinted polymeric fiber (monolith) fabrication for direct use in sensing devices. This is advantageous for achieving higher degree of enrichment of target analyte (folic acid) from the complex matrices of real samples, without any surface fouling, cross-reactivity, and non-specific (false-positive) contributions. In order to measure serum folic acid at ultratrace level to detect spina bifida, a neural tube defect in mother, and other acute cases of proteomic diseases, the hyphenation between molecularly imprinted micro-solid phase extraction fiber and a complementary molecularly imprinted polymer–carbon composite fiber sensor has been found quite efficient. The primitive diagnosis of many chronic diseases is feasible by estimating folic acid as biomarker, with the detection limit as low as 0.0036 ng mL −1 (relative standard deviation = 0.13%, signal/noise = 3) in human blood serum.

Enantioselective recognition of d- and l-tryptophan by imprinted polymer-carbon composite fiber sensor

Electrochemical sensors demonstrating enantioselectivity to tryptophan enantiomers, with high selectivity and sensitivity, were fabricated by the use of a monolithic fiber of molecularly imprinted polymer-carbon composite. The recognition mechanism and performance of these sensors were evaluated by differential pulse anodic stripping voltammetry. The sensor imprinted for l-tryptophan not only discriminated the target from its analogues and other amino acids but also responded specifically in racemic mixture in aqueous, biological, and pharmaceutical samples. The binding kinetics of L-tryptophan was also established with the help of anodic stripping cyclic voltammetry and chronocoulometry. The detection limit for L-tryptophan was as low as 0.24 ng mL(-1) (signal/noise=3) which is appropriate for biomarking diseases, caused by an acute tryptophan-depletion, in clinical setting.

Evaluation of embedded optical fiber sensors in composites: EFPI sensor response to fatigue loading

AbstractExtrinsic Fiber Fabry‐Perot Interferometric (EFPI) sensors were fabricated and embedded within a 16‐layer cross‐ply composite. The composites with and without the embedded EFPI sensors were subjected to tension/compression loading. The presence of the embedded sensor was not found to have adverse effect on the tension/compression fatigue properties. However, the performance of the EFPI sensor was found to degrade with fatigue cycles, with the introduction of a compressive element in the loading regime; samples were tested using stress ratios of −1, −2.5, and −3. Although the reasons for this observed degradation in the response of the sensor to applied strain is not known at present, it is speculated that this may be due to debonding of the key components of the sensor. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers

Evaluation of embedded optical fiber sensors in composites: EFPI sensor fabrication and quasi‐static evaluation

AbstractThis article reports on the fabrication and evaluation of extrinsic Fabry–Perot interferometric (EFPI) sensors when embedded in fiber‐reinforced composites and tested under quasi‐static tensile and compressive mechanical loading. The EFPI strain sensors were embedded in carbon fiber composite test specimens, and their performance was compared against a surface‐mounted extensometer and electrical resistance strain gauges. When the composite was subjected to quasi‐static tensile loading, the sensors failed around a strain level of 0.5%; under compressive loading, the sensors survived until the failure of the composite at 1.1% strain. The EFPI sensors used in this study were fabricated in‐house and the issues relating to fabrication are discussed in the context of their performance when embedded in composites. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers

Electrospun camphorsulfonic acid doped poly( o-toluidine)–polystyrene composite fibers: Chemical vapor sensing

The electrospinning technique was utilized to produce camphorsulfonic acid (HCSA) doped poly( o-toluidine) (POT)–polystyrene (PS) composite fibers in the non-woven mat form. HCSA doped POT–PS composite fibers were fabricated on an interdigited gold (Au) substrate for use as a chemical vapor sensor. The composite fiber sensor responded to volatile chemicals in different ways, depending on the polarity of sensing chemicals. The surface morphology of the non-woven composite fiber mat after chemical vapor sensing was unchanged. This study highlights that composite fibers comprised of polyaniline derivative and a spinnable polymer do have potential for use as chemical sensors due to their good solubility in common solvents and detectable electrical changes at low fiber contents.

Active fiber composite actuators for reducing acoustic radiation from cylindrical shells

Active fiber composites were developed to provide a mechanically robust method for large-area, orthotropic actuation and sensing in active structures. This presentation will describe the application of active fiber composite actuators to the reduction of acoustic radiation from a cylindrical shell by active control. The composite actuation layer is formed by small diameter piezoelectric fibers that are unidirectionally aligned and imbedded in a resin matrix system. A separate, etched, interdigital electrode layer makes the electrical connections. By nature of its structure, an active fiber composite actuator or sensor allows use of the primary piezoelectric effect in the plane of the composite. Active fiber composites are inherently tolerant of damage and can be conformed to a wide range of structural shapes. To control acoustic radiation from a cylindrical shell, active fiber composite actuators are used to generate a strain field that counteracts the strain associated with acoustically efficient shell motions. Optimal placement of the actuators is determined using numerical models verified by an experimental characterization of the shell dynamics. The control signal applied to the actuator is determined, in real time, using adaptive control. Error sensing methods using accelerometers or active fiber composite sensors were considered. [Work supported by DARPA.]