Field Sensor Research Articles

The regulation and its application of the charge decay rate in triboelectric nanogenerator.

The decay rate of charge in the friction layer is one of the key factors affecting the output performance of triboelectric nanogenerators (TENG). Reducing the decay rate of the triboelectric charge can increase the charge-carrying capacity of the friction layer and improve the output current and voltage of the TENG. This makes a friction generator more suitable for discontinuous driving environments. In contrast, increasing the decay rate of the charge in the friction layer can greatly improve the recovery time of the device, although it reduces the output performance of the generator. This is conducive to the application of friction generator in the field of sensors. In this study, polystyrene (PS) and carbon nanotubes (CNTs) were added to polyvinylidene fluoride (PVDF) nanofibers to adjust the charge decay time in the friction layer, thereby regulating the output performance of the friction generator and sensor. When the amount of added PS in the PVDF nanofiber reached 20%, the charge density on the friction surface increased by 1.9 times, and the charge decay time decreased by 64 times; when 0.1 wt% CNTs were added in the PVDF nanofiber, the charge decay time increased by more than 10 times. The former is more conducive to improving the power generation performance of the TENG, and the latter significantly improves the stability and repeatability of TENG-based sensors.&#xD.

Biocomposite silk fibroin hydrogel with stretchability, conductivity and biocompatibility for wireless strain sensor

As a natural biopolymer material, silk fibroin with unique mechanical properties can be used in the preparation of biocomposite hydrogels for strain sensors. But, the electromechanical properties of biocomposite hydrogel strain sensors are still insufficient, such as the deterioration of electrical signals and low sensitivity, which need to develop a hydrogel with a stable transmission network for electric conduction. Herein, a silk fibroin biocomposite hydrogel is prepared by incorporating tannic acid and MXene nanosheets into a polyacrylamide and silk fibroin double network. The electromechanical properties of hydrogels are improved by optimizing the proportion of material components. As a result, the double network structure and supramolecular interaction enhance the stretchability of hydrogels (692% fracture strain). The hydrogel also exhibits good biocompatibility and conductivity (0.85 S/m), which shows the application prospect in wearable sensors. The wireless strain sensor assembled by this biocomposite hydrogel presents good portability and sensing performance, such as high sensitivity (gauge factor = 6.04), wide working range (500% strain), and outstanding stability (1000 cycles at 100% strain). The results indicate that the hydrogel strain sensor can be used to monitor human body movement. The biocomposite hydrogel is expected to be applied in the field of wearable strain sensors, and this study can provide a new way for the design of flexible electronic materials.

Gas concentration and refractive index sensor based on plasmonic induced absorption in metal-insulator-metal waveguide coupled with arc resonators structure

In this paper, the plasmonic induced absorption (PIA) effect is numerically studied in a plasmonic metal-insulator-metal (MIM) waveguide coupled with disk and arc-shaped resonators. The PIA spectrum characteristics and magnetic field distributions are investigated by the Finite difference-time domain method (FDTD) method, the PIA effect originated from the coupling of two resonance modes excited by the disk resonator and the arc-shaped resonator. The coupling mode theory (CMT) is used to fit the PIA transmission spectrum, and the calculated result fits well with the simulated spectrum. A double PIA spectrum can be observed by introducing another arc-shaped resonator both on the same or the opposite side. Three different structures are designed to achieve the PIA effect, and we found the PIA response can be easily tuned by altering the structure’s parameters. Three structures are designed and compared, the PIA spectra exhibit high refractive index (RI) sensing with maximum sensitivity of 867.2nmRIU−1. Besides, the proposed structure can also be used as a gas concentration (GC) sensor when the polyhexamethylene biguanide (PHMB) is introduced, a maximum sensitivity of 142.1 pm/ppm is achieved for the proposed structure II, the maximum figure of merit (FOM) and Q value are 57.8 and 65.9, respectively. Therefore, the results represented in this paper will be beneficial in the fields of high-performance refractive index and gas sensors.

Laser-Scribed Graphene for Human Health Monitoring: From Biophysical Sensing to Biochemical Sensing.

Laser-scribed graphene (LSG), a classic three-dimensional porous carbon nanomaterial, is directly fabricated by laser irradiation of substrate materials. Benefiting from its excellent electrical and mechanical properties, along with flexible and simple preparation process, LSG has played a significant role in the field of flexible sensors. This review provides an overview of the critical factors in fabrication, and methods for enhancing the functionality of LSG. It also highlights progress and trends in LSG-based sensors for monitoring physiological indicators, with an emphasis on device fabrication, signal transduction, and sensing characteristics. Finally, we offer insights into the current challenges and future prospects of LSG-based sensors for health monitoring and disease diagnosis.

Hygroscopic paper enhanced using hydroxyapatite coating for wearable TENG sensors

Wearable triboelectric nanogenerators (TENGs) have attracted considerable attention in the field of self-powered sensors that can be worn on the skin directly without packaging because of their breathability, conformability, and sensitivity to collect biomechanical energy. However, high humidity on the skin can affect the wearable TENG output performance, substantially affecting the sensor performance and stability. When worn for a long time, humidity can even cause skin inflammation. Thus, for a wearable TENG, moisture control and biocompatibility are also key factors that need to be addressed. Herein, we report a hygroscopic and biocompatible paper-based TENG using a hydroxyapatite (HAP) mineral coating to enhance the paper fiber. The mineral coating can maintain the surface of the paper fiber, which will not cause large external deformation of the paper fiber under a force, avoid squeezing out excess water, and keep the friction surface dry, avoiding humidity affecting the output performance. Without interfering with the performance of the TENG, the maximum water absorption of the HAP composite paper is ∼8 μL. The HAP composite paper–based TENG (4 cm2) has an open-circuit voltage and short-circuit current 5.8 times and 4.2 times that of pure paper, respectively, and can obtain 80.4 mW/m2 output and directly light 117 LEDs. At relative humidity values of 25.7 %, 43.1 %, and 58.8 %, the performance retained the peak values of 80.2 %, 68 %, and 63.7 %, respectively. Even at a high relative humidity of 71.7 %, the triboelectric performance of HAP composite paper is retained 59.3 %, and the stability under humidity is better than that of pure paper (45.6 %). In addition, the mineral paper can even work with tissue fluid and output performance decreases by 43.8 %. The mineral-enhanced paper TENG with high power generation performance, hygroscopicity, biocompatibility, and degradability provides a new perspective for disposable wearable sensors, even in medical treatment.

Glucose sensing performance of bimetallic MOFs CoFe-ZIF/CC for enzyme-free saliva sensor applications

Co-ZIF is widely believed as a promising material which shows potential in MOFs based enzyme-free sensors. However, the research of Co-ZIF in glucose sensor filed has been hampered, due to its poor electronic conductivity and slow ion diffusion caused by closed rhombohedral dodecahedron structure. In this work, the obtained Co0.95Fe0.05-ZIF presents highly opened nanosheet structure on CC, resulting in rich open active sites and ions moving channels. Compared with other reported ZIFs, the Co0.95Fe0.05-ZIF/CC exhibits excellent sensing performance with a high sensitivity of 3232.30 μA mM−1 cm−2 in the range of 0.20–1.00 mM and a low detection limit of less than 5 μM, due to its highly opened nanosheet structure. The Co0.95Fe0.05-ZIF/CC also shows excellent selectivity, repeatability and reproducibility for glucose detection. Furthermore, the variation trend of test results measured by this saliva sensor without any sample pre-treatment, is consistent with that of commercial blood glucose meter, indicating its potential in real applications. This synthesis strategy also provides a new direction of structure construction for high performance MOFs in enzyme-free glucose sensor field.

Effects of the in-plane uniaxial and biaxial strains on the electronic and optical properties of the graphene/β-Si3N4 heterostructure

van der Waals heterostructures can enable adjustment of graphene's electronic properties, which is important for the application of graphene-based electronic devices. The structural, electronic and optical properties of heterostructures composed of graphene and β-Si3N4 under different strain conditions are studied in this paper using first-principle calculation. The result shows that the heterojunction constituted with β-Si3N4 opens a small bandgap at the Brillouin zone Γ, which is about 0.099 eV, and the bandgap is highly sensitive to the direction and magnitude of strain. Under uniaxial compressive (tensile) strain, the heterojunction bandgap increases linearly, reaching 1.901 eV and 1.614 eV at −11 % and 11 %, respectively; under biaxial strain, the heterojunction bandgap decreases linearly with the compressive strain, decreasing to 0.087 eV at −11 %, and increases linearly with the tensile strain, reaching 0.113 eV at 11 %. And the rate of the bandgap under uniaxial strain is larger than that under biaxial strain, which suggests that the uniaxial strain regulation is more effective. Optical property study shows that uniaxial (biaxial) compressive strain improves the light absorption of the heterojunction in the blue-ultraviolet region band, especially when the uniaxial compressive strain reaches 9 %, the light absorption of the heterojunction increases significantly in the whole spectral interval. These research results will provide a theoretical basis for the practical applications of graphene and β-Si3N4 heterostructures in the fields of pressure sensors and optical modulators.

Zinc oxide bridges the nanofillers to enhance the wear resistance and stability of triboelectric nanogenerators

Triboelectric nanogenerators (TENGs) have received widespread attention as a means of harvesting mechanical energy from the environment and converting it into electricity. As people continue to explore the field of infinite sensors, traditional TENGs have faced persistent challenges in practical application, mainly due to the poor abrasion resistance and stability of the existing polymers commonly used. Herein, the polyphenylene sulfide (PPS) was melt blended with liquid crystal polymer (LCP) to be used as matrix, and the interfacial bonding strength between the matrix and filler was improved by zinc oxide (ZnO) grafted carbon nanotubes/graphene oxide (CNTs/GO). Under friction conditions of 100 N load and 0.5 m/s, the friction coefficient and wear rate of resultant nanocomposites were significantly reduced to 0.2 and 2.09 × 10-5 mm3/N, respectively. The abrasion resistant TENG (AR-TENG) was fabricated based on 0.3ZnO/CNTs/GO/LCP/PPS exhibited outstanding electrical output performance, which was attributed to the high dielectric constant of 5.3, improved surface roughness and interfacial contact area of composites. Consequently, this study reported a novel approach to tailor AR-TENG into a highly abrasion resistant and stable sensor. This customization enabled the AR-TENG to operate reliably in harsh environments (high temperatures and humidity), thereby expanding its potential applications.

Tuning ZnO-based piezoelectric nanogenerator efficiency through n-ZnO/p-NiO bulk interfacing

ZnO based piezoelectric nanogenerators (PENG) hold immense potential for harvesting ambient vibrational mechanical energy into electrical energy, offering sustainable solutions in the field of self-powered sensors, wearable electronics, human–machine interactions etc. In this study, we have developed flexible ZnO-based PENGs by incorporating ZnO microparticles into PDMS matrix, with ZnO concentration ranging from 5 to 25 wt%. Among these, the PENG containing 15 wt% ZnO exhibited the best performance with an open-circuit output voltage/short-circuit current of ~ 42.4 V/2.4 µA. To further enhance the output performance of PENG, p-type NiO was interfaced with ZnO in a bulk hetero-junction geometry. The concentration of NiO was varied from 5 to 20 wt% with respect to ZnO and incorporated into the PDMS matrix to fabricate the PENGs. The PENG containing 10 wt% NiO exhibits the best performance with an open-circuit output voltage/short-circuit current of ~ 65 V/4.1 µA under loading conditions of 30 N and 4 Hz. The PENG exhibiting the best performance demonstrates a maximum instantaneous output power density ~ 37.9 µW/cm2 across a load resistance of 20 MΩ under loading conditions of 30 N and 4 Hz, with a power density per unit force and Hertz of about ~ 0.32 µW/cm2·N·Hz. The enhanced output performance of the PENG is attributed to the reduction in free electron concentration, which suppresses the internal screening effect of the piezopotential. To assess the practical utility of the optimized PENG, we tested the powering capability by charging various commercial capacitors and used the stored energy to illuminate 10 LEDs and to power a stopwatch displays. This work not only presents a straightforward, cost-effective, and scalable technique for enhancing the output performance of ZnO-based PENGs but also sheds light on its underlying mechanism.

A Proposed Device for Controlling the Flow of Information Based on Weyl Fermions.

In this work we propose a novel device for controlling the flow of information using Weyl fermions. Based on a previous work by our group, we show that it is possible to fully control the flow of Weyl fermions on several different channels by applying an electric field perpendicular to the direction of motion of the particles on each channel. In this way, we can transmit information as logical bits, depending on the existence or not of a Weyl current on each channel. We also show that the response time of this device is exceptionally low, less than 1 ps, for typical values of its parameters, allowing for the control of the flow of information at extremely high rates of the order of 100 Petabits per second. Alternatively, this device could also operate as an electric field sensor. In addition, we demonstrate that Weyl fermions can be efficiently guided through the proposed device using appropriate magnetic fields. Finally, we discuss some particularly interesting remarks regarding the electromagnetic interactions of high-energy particles.

Relatively Low‐Frequency Magnetic Field Detection System Using Metglas/PZT‐5B Sensor

The magnetoelectric (ME) sensor is a new and promising type of magnetic field sensor with ultrahigh sensitivity. However, there are few reports on the research of real‐time measurement system which can promote its practical application. Herein, a novel real‐time measuring approach for weak AC magnetic fields at relatively low frequency is proposed using Metglas/PZT‐5B ME sensors. The system mainly consists of an oscilloscope, a signal generator, and a program developed with LabVIEW programming. Real‐time measurement of relatively low‐frequency magnetic fields has been achieved by using frequency upconversion methods, simultaneously displaying the frequency and magnitude of the magnetic field. As a result, the real‐time measurement system is able to detect a weak AC magnetic field as low as 0.1 nT@1 Hz, which is promising to push the ME sensor to practical application.

Impacts of diffusive ion migration on ferroelectric properties in BaTiO3 composite

Multiferroic composites, combining ferroelectric and ferromagnetic properties, hold significant promise in today’s technology landscape in a diverse array of fields including information storage devices, energy harvesters, current and magnetic field sensors, tunable devices, and various other domains. Exploring the interaction between these materials and their impact on multiferroic properties is crucial for advancing miniaturized, high-performance devices. A deeper understanding of the interplay between ionic dynamics and microstructure is essential for engineering these composites effectively. This study examines the deterioration of the ferroelectric property of BaTiO3 composite with the incorporation of the magnetic BaFe12O19. The composite is synthesized using the conventional solid-state reaction method. Structural analysis involves x-ray diffraction, Raman spectroscopy, and field-emission scanning electron microscopy. The dielectric and ferroelectric investigations, as well as magnetic analysis, are conducted. The study shows the existence of the electron hopping between different oxidation states of the cations and it elevates the material’s conductivity and, generates a leakage current that largely affects the ferroelectric properties by preventing saturation polarization.

Magnetic proximity sensor based on colossal magnetoresistance effect

Magnetic proximity sensors are widely used to determine the distance to ferromagnetic or highly conductive materials and to investigate their shape or to detect their motion. In this study, a magnetic proximity sensor incorporating a cylindrical permanent magnet and a scalar magnetic field sensor (measuring the magnitude of the field independently from its orientation) based on the phenomenon of colossal magnetoresistance in manganite films is presented. Two versions of the sensor, one with a solid cylindrical magnet and one with a hollow cylindrical magnet, were constructed and tested. A steel plate and a superconducting YBaCuO disk were used to investigate the static response. The measurements of the dynamic behavior were carried out with rotating steel and duralumin plates. The results of the static experiments and modelling showed that the output response (change of the magnetic field) of the sensor had a hyperbolic relationship with the distance between the sensor and the measured object. This change was positive for solid cylindrical magnet design and negative for hollow cylindrical magnet design when the target was steel. In contrast, the solid magnet-based sensor produced a negative signal for the superconducting material, while the hollow cylindrical magnet sensor showed a positive signal. It was found that the main features of the dynamic response of the proximity sensors can be explained by the magnetization of steel and the induction of eddy currents in duralumin. The present study demonstrates that the proposed magnetic proximity sensor can be successfully used to search for ferromagnetic objects, investigate the properties of superconductors and detect the motion of non-ferromagnetic conductive materials and can have advantages over conventional magnetic proximity sensors.

Physics-Informed Approximation of Internal Thermal History for Surface Deformation Predictions in Wire Arc Directed Energy Deposition

Abstract This work presents a physics-informed fusion methodology for deformation detection using multi-sensor thermal data. A challenge with additive manufacturing (AM) is that abnormalities commonly occur due to rapid changes in the thermal gradient. Different non-destructive in-situ thermal sensors capture parts of the thermal history but are limited by the visible temperature spectrum and sensor field of view of the fabrication process. Various sensors mitigate problems with the loss of thermal history information; however, it brings forth challenges with integrating different data streams and the need to interpolate the internal thermal history. This study develops a thermal data-informed heat flux methodology that fills the gap in fusing numerical temperature approximation with data-driven knowledge of the surface of additive manufactured components. First, this study fuses infrared (IR) thermal data complexities during the AM process with the Goldak double ellipsoidal heat flux to model the energy input into the component. Second, a thermal physics-informed model input (PIMI) is created with thermal data-informed heat flux to capture internal thermal history. Lastly, a regression convolutional neural network (CNN) captures the relationship between the three-dimensional thermal gradient and the resulting surface deformation. The rapid thermal gradient formation and identification of deformation is a key step toward using thermal history data and machine learning to improve quality control in AM. The proposed surface deformation detection model achieved an mean squared error of 1.14 mm and an R2 of 0.89 in the case study when fabricating thin-walled structures.

β-phase formation of poly(vinylidene fluoride) foam based on the porous morphology control via supercritical carbon dioxide

The increase of electroactive β phase of poly(vinylidene fluoride) (PVDF) is important in energy harvesting applications. In this work, a green method of supercritical CO2 physical foaming was applied to obtain the PVDF foams with high content of β-crystal by utilizing the biaxial stretching when the cells grew, which were applied in the field of piezoelectric sensors. By changing the foaming condition, the PVDF foams with various structures were obtained, and a comprehensive study on the crystal transformation of them was carried out. The PVDF foam with increased β crystals content was more accessible to obtain at a high saturation pressure, corresponding to the large expansion ratio and small cell size. The acquisition of β crystals mainly came from the α-β solid-solid phase transformation during decompression, rather than the annealing process. Due to the introduction of cell structure, the piezoelectric output performance of the sample was effectively amplified. The produced PVDF foam with the β-crystal content of 30%, exhibited the low density of 0.11 g/cm3 and the highest piezoelectric output of 4.1 V (corresponding to a specific voltage of 35 V‧cm3/g). This foaming strategy provides guidance for lightweight design and high-performance fabrication of piezoelectric materials.

Scientometric analysis of textile sensors

Textile sensors have been widely used in many applications such as healthcare, sports, and entertainment. Focusing on the scientific evolution in the research field of textile sensors, this paper presents a comprehensive review on the academic publications, research hotspots, and major research directions in the field based on scientometric analysis. Totally 3,820 papers published between the year 1991 and 2023 were retrieved and investigated from the Web of Science Core Collection. The software CiteSpace and VOSviewer were adopted to perform scientometric analysis on the collaboration between countries, regions, and institutions. In addition, the citations and co-citations of authors, the source journals, the references, and the co-occurrence of keywords were analyzed. Furthermore, five main research directions in the field of textile sensors were also summarized in this paper, and the most promising and potentially profitable research direction could be health monitoring. The analysis result shows that the research hotspots in recent years include the development of triboelectric nanogenerator, the manufacture of transparent skin-like sensors and optical fiber sensors, the process of data collected from wearable textile sensors, and the design of new materials such as nanocomposites for textile sensors.

Tunable temporal dynamics of dipole response in graphene-wrapped core–shell nanoparticles

The investigation on the temporal dynamics of graphene-wrapped core–shell nanoparticles under the illumination of a Gaussian impulse have been carried out. By altering the graphene layers and the aspect ratio of the core–shell structure, we can adjust the resonant modes into typical cases in regime of terahertz. Accordingly, different scenarios for the temporal evolution are detected, which include two kinds of ultrafast oscillation with exponential decay tendency, pure exponential decay, and Gaussian shape, when the pulse duration of the incident pulse is much shorter than, similar to, and much longer than the localized surface plasmon lifetime. To one's interest, when the coupling between two resonant modes exists, one predicts the long-periodic oscillation, whose period is just the difference between the frequencies of the resonant modes. Hence, the intrinsic properties of the ultrafast oscillation can be hardly influenced by the input signals. Further quantitative calculation demonstrate that the periods of the ultrafast oscillations can be tuned by different physical mechanisms, which are, respectively, based on the self-interacting correction of a single resonance and the strong coupling between the resonant modes in frequency domain. Our results may be applicable in the fields of optical sensors, optical information processing, and other nanophotonic devices.

Integrated Fibrous Iontronic Pressure Sensors with High Sensitivity and Reliability for Human Plantar Pressure and Gait Analysis.

Flexible sensing systems (FSSs) designed to measure plantar pressure can deliver instantaneous feedback on human movement and posture. This feedback is crucial not only for preventing and controlling diseases associated with abnormal plantar pressures but also for optimizing athletes' postures to minimize injuries. The development of an optimal plantar pressure sensor hinges on key metrics such as a wide sensing range, high sensitivity, and long-term stability. However, the effectiveness of current flexible sensors is impeded by numerous challenges, including limitations in structural deformability, mechanical incompatibility between multifunctional layers, and instability under complex stress conditions. Addressing these limitations, we have engineered an integrated pressure sensing system with high sensitivity and reliability for human plantar pressure and gait analysis. It features a high-modulus, porous laminated ionic fiber structure with robust self-bonded interfaces, utilizing a unified polyimide material system. This system showcases a high sensitivity (156.6 kPa-1), an extensive sensing range (up to 4000 kPa), and augmented interfacial toughness and durability (over 150,000 cycles). Additionally, our FSS is capable of real-time monitoring of plantar pressure distribution across various sports activities. Leveraging deep learning, the flexible sensing system achieves a high-precision, intelligent recognition of different plantar types with a 99.8% accuracy rate. This approach provides a strategic advancement in the field of flexible pressure sensors, ensuring prolonged stability and accuracy even amidst complex pressure dynamics and providing a feasible solution for long-term gait monitoring and analysis.

A novel measurement‐protection‐integrated current transformer based on hybrid core and magnetic field sensor

AbstractCurrent transformers (CTs) are widely used for energy metering, relay protection, condition monitoring and control circuits. However, CT saturation may lead to non‐negligible measurement errors and relay malfunctions, posing a threat to the stability and security of the power grid. In order to address the problem of CT saturation, a novel measurement‐protection‐integrated current transformer (MPICT) is proposed. First, the working states of the MPICT are summarised and the approximate expressions for the steady‐state measuring characteristics, the transient response characteristics, and the measurement errors are derived from the equivalent circuit model. Then, the feasibility of the MPICT and the theoretical analyses are verified by the 3D FEM simulation imitating the presented MPICT excited by diverse currents. Finally, a down‐scale prototype is fabricated and a series of tests are conducted in the laboratory to validate the effectiveness of the equipment. The simulation and experimental results suggest that the output of the MPICT can accurately reconstruct the primary current waveform, even if the primary current contains decaying or constant DC component.

Scalable and Ultra-Sensitive Nanofibers Coaxial Yarn-Woven Triboelectric Nanogenerator Textile Sensors for Real-Time Gait Analysis.

Yarn-woven triboelectric nanogenerators (TENGs) have greatly advanced wearable sensor technology, but their limited sensitivity and stability hinder broad adoption. To address these limitations, Poly(VDF-TrFE) and P(olyadiohexylenediamine (PA66)-based nanofibers coaxial yarns (NCYs) combining coaxial conjugated electrospinning and online conductive adhesive coating are developed. The integration of these NCYs led to enhanced TENGs (NCY-TENGs), notable for their flexibility, stretchability, and improved sensitivity, which is ideal for capturing body motion signals. One significant application of this technology is the fabrication of smart insoles from NCY-TENG plain-woven fabrics. These insoles are highly sensitive and possess antibacterial, breathable, and washable properties, making them ideal for real-time gait monitoring in patients with diabetic foot conditions. The NCY-TENGs and their derivatives show immense potential for a variety of wearable electronic devices, representing a considerable advancement in the field of wearable sensors.