Search Results (33)

In recent years, there has been growing interest in the development of metal-free, environmentally friendly, and cost-effective biopolymer-based piezoelectric strain sensors (bio-PSSs) for flexible applications. In this study, we have developed a bio-PSS based on pure deoxyribonucleic acid (DNA) and curcumin materials in a thin-film form and studied its strain-induced current-voltage characteristics based on piezoelectric phenomena. The bio-PSS exhibited flexibility under varying compressive and tensile loads. Notably, the sensor achieved a strain gauge factor of 407 at an applied compressive strain of −0.027%, which is 8.67 times greater than that of traditional metal strain gauges. Furthermore, the flexible bio-PSS demonstrated a rapid response under a compressive strain of −0.08%. Our findings suggest that the proposed flexible bio-PSS holds significant promise as a motion sensor, addressing the demand for environmentally safe, wearable, and flexible strain sensor applications. Full article

Thin-film sensors are regarded as advanced technologies for in situ condition monitoring of components operating in harsh environments, such as aerospace engines. Nevertheless, these sensors encounter challenges due to the high-temperature oxidation of materials and intricate manufacturing processes. This paper presents a simple method to fabricate high temperature-resistant oxidized SiCN precursor and La(Ca)CrO₃ composite thin film temperature sensors by screen printing and air annealing. The developed sensor demonstrates a broad temperature response ranging from 200 °C to 1100 °C with negative temperature coefficients (NTC). It exhibits exceptional resistance to high-temperature oxidation and maintains performance stability. Notably, the sensor’s resistance changes by 3% after exposure to an 1100 °C air environment for 1 h. This oxidation resistance improvement surpasses the currently reported SiCN precursor thin-film sensors. Additionally, the sensor’s temperature coefficient of resistance (TCR) can reach up to −7900 ppm/°C at 200 °C. This strategy is expected to be used for other high-temperature thin-film sensors such as strain gauges, heat flux sensors, and thermocouples. There is great potential for applications in high-temperature field monitoring. Full article

Thermoplastic polyurethane (TPU) has been widely used as the elastic polymer substrate to be combined with conductive nanomaterials to develop stretchable strain sensors for a variety of applications such as health monitoring, smart robotics, and e-skins. However, little research has been reported on the effects of deposition methods and the form of TPU on their sensing performance. This study intends to design and fabricate a durable, stretchable sensor based on composites of thermoplastic polyurethane and carbon nanofibers (CNFs) by systematically investigating the influences of TPU substrates (i.e., either electrospun nanofibers or solid thin film) and spray coating methods (i.e., either air-spray or electro-spray). It is found that the sensors with electro-sprayed CNFs conductive sensing layers generally show a higher sensitivity, while the influence of the substrate is not significant and there is no clear and consistent trend. The sensor composed of a TPU solid thin film with electro-sprayed CNFs exhibits an optimal performance with a high sensitivity (gauge factor ~28.2) in a strain range of 0–80%, a high stretchability of up to 184%, and excellent durability. The potential application of these sensors in detecting body motions has been demonstrated, including finger and wrist-joint movements, by using a wooden hand. Full article

Electronic skin (e-skin) has attracted tremendous interest due to its diverse potential applications, including in physiological signal detection, health monitoring, and artificial throats. However, the major drawbacks of traditional e-skin are the weak adhesion of substrates, incompatibility between sensitivity and stretchability, and its single function. These shortcomings limit the application of e-skin and increase the complexity of its multifunctional integration. Herein, the synergistic network of crosslinked SWCNTs within and between multilayered graphene layers was directly drip coated onto the PU thin film with self-adhesion to fabricate versatile e-skin. The excellent mechanical properties of prepared e-skin arise from the sufficient conductive paths guaranteed by SWCNTs in small and large deformation under various strains. The prepared e-skin exhibits a low detection limit, as small as 0.5% strain, and compatibility between sensitivity and stretchability with a gauge factor (GF) of 964 at a strain of 0–30%, and 2743 at a strain of 30–60%. In physiological signals detection application, the e-skin demonstrates the detection of subtle motions, such as artery pulse and blinking, as well as large body motions, such as knee joint bending, elbow movement, and neck movement. In artificial throat application, the e-skin integrates sound recognition and sound emitting and shows clear and distinct responses between different throat muscle movements and different words for sound signal acquisition and recognition, in conjunction with superior sound emission performance with a sound spectrum response of 71 dB (f = 12.5 kHz). Overall, the presented comprehensive study of novel materials, structures, properties, and mechanisms offers promising potential in physiological signals detection and artificial throat applications. Full article

In this study, thin films of zinc oxide doped with fluorine ZnO: F were deposited via ultrasonic spray pyrolysis (USP) with an atomic ratio of [F/Zn] in a starting solution of 15 at.% on borosilicate glass coverslips and SiO₂/Si substrates. The structure, electrical resistivity, and thickness were obtained via X-ray diffraction, the four-point technique, and profilometry, respectively. A ZnO: F piezoresistor was modeled at the fixed end of the cantilever through lithography and chemical etching. A SiO₂/Si cantilever structure was used to evaluate the piezoresistivity of a ZnO: F thin film, and temperature coefficient of resistance (TCR) measurements were performed in an electric furnace. The strain on the ZnO: F piezoresistor caused by the application of masses at the free end of the cantilever was determined using a theoretical equation, in addition to a simulation in the COMSOL Multiphysics 5.3a FEM (finite element method) software considering the dimensions and materials of the manufactured device. The ZnO: F thin films were hexagonal wurtzite (phase 002), with thicknesses in the range from 234 nm to 295 nm and with resistivities of the order of 10⁻² Ω.cm. The ZnO: F thin-film piezoresistor showed a gauge factor (GF) of 12.7 and a TCR of −3.78 × 10⁻³ %/K up to 525 K, which are suitable properties for sensor development. Full article

In this work, VO₂ based thermal sensing thin film synthesized on flexible muscovite substrates by direct oxidation of deposited vanadium metal, were investigated for the impact of doping and strain on their electrical properties. We investigated both undoped and Ti doped VO₂ on muscovite substrate and compared with those on Quartz substrate. Both doped and undoped VO₂ were found to undergo phase transition due to effect of heat as well as mechanical strain on muscovite substrate. On the other hand, the Ti doped VO₂, on both quartz and muscovite substrate showed significant reduction in the transition temperature compared to the undoped VO₂ thin films on these two substrates. When subjected to mechanical strain, the VO₂ thin film on muscovite substrates resulted in a decrease or an increase in resistance depending on whether the applied strain was tensile or compressive, respectively. The resistance change was also steeper around the transition temperature compared to room temperature, exhibiting high gauge factor. This metal doped VO₂ on flexible muscovite substrate has the significantly low transition temperature which causes the VO₂ film to undergo phase transition at a near-room temperature and enables it to be used as a temperature sensor with enhanced sensitivity. Full article

Aero-engine turbine stator blades are often used in harsh environments with high temperatures and high pressure and are prone to fatigue fractures. Real-time and accurate monitoring of blade surface stress and strain is critical to ensure safe operation. In this study, thin-film strain gauges (TFSGs) that can be used in high-temperature environments above 1000 °C were designed and fabricated using a PtRh6 thin film as the sensitive material. The hysteresis effect of the stress transfer upon establishing a thermo-mechanical coupling finite element model of the Inconel718 high-temperature nickel-based alloy equal-strength beam PtRh6 TFSGs was analyzed and the optimal combination of thin-film thickness and longitudinal grid length of wire-grid TFSGs was determined. In order to solve the problem of high-temperature insulation, the insulating properties of a single-layer Al₂O₃ insulating film, a single-layer ZrO₂ insulating film, a double-layer Al₂O₃/ZrO₂ composite insulating film, and a four-layer Al₂O₃/ZrO₂/Al₂O₃/ZrO₂ composite insulating film at high temperature were compared and studied using scanning electron microscopy to analyze the microscopic morphology and composition of the four insulating film structures. The results showed that the four-layer Al₂O₃/ZrO₂/Al₂O₃/ZrO₂ composite insulating film had the best insulating properties at high temperatures. On this basis, an Al₂O₃/ZrO₂/Al₂O₃/ZrO₂ composite insulating film, PtRh6 sensitive layer, and Al₂O₃ protective film were sequentially deposited on a high-temperature nickel-based alloy equal-strength beam using DC pulsed magnetron sputtering technology to obtain an Inconel718 high-temperature nickel-based alloy equal-strength beam PtRh6 TFSG. Its gauge factor (GF) and temperature coefficient of resistance (TCR) were calibrated, and the results showed that the sensor could be used in harsh environments of 1000 °C. The above results provide new ideas for measuring stress and strain in aerospace under high-temperature and high-pressure environments. Full article

In the context of intelligent components in industrial applications in the automotive, energy or construction sector, sensor monitoring is crucial for security issues and to avoid long and costly downtimes. This article discusses component-inherent thin-film sensors for this purpose, which, in contrast to conventional sensor technology, can be applied inseparably onto the component’s surface via sputtering, so that a maximum of information about the component’s condition can be generated, especially regarding deformation. This article examines whether the sensors can continue to generate reliable measurement data even after critical component loads have been applied. This extends their field of use concerning plastic deformation behavior. Therefore, any change in sensor properties is necessary for ongoing elastic strain measurements. These novel fundamentals are established for thin-film constantan strain gauges and platinum temperature sensors on steel substrates. In general, a k-factor decrease and an increase in the temperature coefficient of resistance with increasing plastic deformation could be observed until a sensor failure above 0.5% plastic deformation (constantan) occurred (1.3% for platinum). Knowing these values makes it possible to continue measuring elastic strains after critical load conditions on a machine component in terms of plastic deformation. Additionally, a method of sensor-data fusion for the clear determination of plastic deformation and temperature change is presented. Full article

Carbon black (CB) is a low-cost and excellent conductive material, and polyvinyl alcohol (PVA) is a non-conductive material with the advantages of easy processing and high mechanical stability. Here, we report a CB/PVA-based flexible conductive polymer film suitable for small strain detection and humidity detection. Thin film is formed by depositing the CB/PVA dispersion liquid droplets on a cleaned silicon/silicon dioxide (Si/SiO₂) substrate. Theoretically, CB/PVA films can be transferred or formed on other substrates, such as polydimethylsiloxane, which have the advantage of flexibility. The droplet deposition method not only enhances the controllability of the film thickness and wastage of materials, but also improves the sensitivity of the prepared film. The electrical conductivity of the CB/PVA composite film and the relationship between the resistance change and strain were measured by the four-point bending method, which showed a good gauge factor of 30 when the strain rate was 0.007%. In addition, the sensor also showed excellent sensing performance and repeatability at humidity levels ranging from 10% to 70% RH. These results demonstrate that the CB/PVA thin film prepared in this work has the advantages of a simple fabrication process, low-cost, multifunctional properties, and high device sensitivity, providing further insights for detecting minor strain and humidity. Full article

This paper investigates the feasibility and performance of the fabrication of platinum high-temperature thin-film strain sensors on nickel-based alloy substrates by additive manufacturing. The insulating layer was made of a dielectric paste by screen printing process. A 1.8-micron-thick platinum film was deposited directly on the insulating layer. The four-wire resistance measurement method was used to eliminate the contact resistance of the solder joints. Comprehensive morphological and electrical characterization of the platinum thin-film strain gauge was carried out, and good static and dynamic strain responses were obtained, which confirmed that the strain gauge was suitable for in situ strain monitoring of high-temperature complex components. Full article

The in-situ strain/stress detection of hot components in harsh environments remains a challenging task. In this study, ZrB₂/SiCN thin-film strain gauges were fabricated on alumina substrates by direct writing. The effects of ZrB₂ content on the electrical conductivity and strain sensitivity of ZrB₂/SiCN composites were investigated, and based on these, thin film strain gauges with high electrical conductivity (1.71 S/cm) and a gauge factor of 4.8 were prepared. ZrB₂/SiCN thin-film strain gauges exhibit excellent static, cyclic strain responses and resistance stability at room temperature. In order to verify the high temperature performance of the ZrB₂/SiCN thin-film strain gauges, the temperature-resistance characteristic curves test, high temperature resistance stability test and cyclic strain test were conducted from 25 °C to 600 °C. ZrB₂/SiCN thin-film strain gauges exhibit good resistance repeatability and stability, and highly sensitive strain response, from 25 °C to 600 °C. Therefore, ZrB₂/SiCN thin-film strain gauges provide an effective approach for the measurement of in-situ strain of hot components in harsh environments. Full article

In this study, highly-sensitive piezoresistive strain sensors based on gold nanoparticle thin films deposited on a stretchable PDMS substrate by centrifugation were developed to measure arterial pulse waveform. By controlling carbon chain length of surfactants, pH value and particle density of the colloidal solutions, the gauge factors of nanoparticle thin film sensors can be optimized up to 677 in tensile mode and 338 in compressive mode, and the pressure sensitivity up to 350. Low pH and thin nanoparticle films produce positive influences to superior gauge factors. It has been demonstrated that nanoparticle thin film sensors on PDMS substrates were successfully applied to sense arterial pulses in different body positions, including wrist, elbow crease, neck, and chest. Full article

Hybrid nanomaterial film consisting of multi-walled carbon nanotubes (MWCNT) and graphene nanoplatelet (GNP) were deposited on a highly flexible polyimide (PI) substrate using spray gun. The hybridization between 2-D GNP and 1-D MWCNT reduces stacking among the nanomaterials and produces a thin film with a porous structure. Carbon-based nanomaterials of MWCNT and GNP with high electrical conductivity can be employed to detect the deformation and damage for structural health monitoring. The strain sensing capability of carbon-based hybrid nanomaterial film was evaluated by its piezoresistive behavior, which correlates the change of electrical resistance with the applied strain through a tensile test. The effects of weight ratio between MWCNT and GNP and the total amount of hybrid nanomaterials on the strain sensitivity of the nanomaterial thin film were investigated. Experimental results showed that both the electrical conductivity and strain sensitivity of the hybrid nanomaterial film increased with the increase of the GNP contents. The gauge factor used to characterize the strain sensitivity of the nanomaterial film increased from 7.75 to 24 as the GNP weight ratio increased from 0 wt.% to 100 wt.%. In this work, a simple, low cost, and easy to implement deposition process was proposed to prepare a highly flexible nanomaterial film. A high strain sensitivity with gauge factor of 24 was achieved for the nanomaterial thin film. Full article

This study aimed at introducing thin films exhibiting the localized surface plasmon resonance (LSPR) phenomenon with a reversible optical response to repeated uniaxial strain. The sensing platform was prepared by growing gold (Au) nanoparticles throughout a titanium dioxide dielectric matrix. The thin films were deposited on transparent polymeric substrates, using reactive magnetron sputtering, followed by a low temperature thermal treatment to grow the nanoparticles. The microstructural characterization of the thin films’ surface revealed Au nanoparticle with an average size of 15.9 nm, an aspect ratio of 1.29 and an average nearest neighbor nanoparticle at 16.3 nm distance. The plasmonic response of the flexible nanoplasmonic transducers was characterized with custom-made mechanical testing equipment using simultaneous optical transmittance measurements. The higher sensitivity that was obtained at a maximum strain of 6.7%, reached the values of 420 nm/ε and 110 pp/ε when measured at the wavelength or transmittance coordinates of the transmittance-LSPR band minimum, respectively. The higher transmittance gauge factor of 4.5 was obtained for a strain of 10.1%. Optical modelling, using discrete dipole approximation, seems to correlate the optical response of the strained thin film sensor to a reduction in the refractive index of the matrix surrounding the gold nanoparticles when uniaxial strain is applied. Full article

Research on stretchable strain sensors is actively conducted due to increasing interest in wearable devices. However, typical studies have focused on improving the elasticity of the electrode. Therefore, methods of directly connecting wire or attaching conductive tape to materials to detect deformation have been used to evaluate the performance of strain sensors. Polyaniline (PANI), a p-type semiconductive polymer, has been widely used for stretchable electrodes. However, conventional procedures have limitations in determining an appropriate metal for ohmic contact with PANI. Materials that are generally used for connection with PANI form an undesirable metal-semiconductor junction and have significant contact resistance. Hence, they degrade sensor performance. This study secured ohmic contact by adapting Au thin film as the metal contact layer (the MCL), with lower contact resistance and a larger work function than PANI. Additionally, we presented a buffer layer using hard polydimethylsiloxane (PDMS) and structured it into a dumbbell shape to protect the metal from deformation. As a result, we enhanced steadiness and repeatability up to 50% strain by comparing the gauge factors and the relative resistance changes. Consequently, adapting structural methods (the MCL and the dumbbell shape) to a device can result in strain sensors with promising stability, as well as high stretchability. Full article