Search Results (91)

Polyurethane (PU) foam, renowned for its structural versatility, elasticity, compressibility, and adaptability, has garnered significant attention for its use in flexible strain sensors due to its capability to detect mechanical deformation. This review presents a comprehensive analysis of both the studies and recent advancements in PU foam-based strain sensors, particularly those incorporating conductive materials. The review begins by examining the chemical composition and structural characteristics of PU foam, followed by a discussion of various fabrication methods and their effects on sensor performance. It also explores the sensing mechanisms, including piezoresistive, piezoelectric, and capacitive effects. Moreover, key applications in motion detection, health monitoring, and environmental and industrial sensing are examined. Finally, the review addresses technological advancements, current challenges, and prospects. Full article

The rapid development of wearable electronics requires multifunctional, transient electronic devices to reduce the ecological footprint and ensure data security. Unfortunately, existing transient electronic materials need to be degraded in chemical solvents or body fluids. Here, we report green luminescent, water-soluble, and biocompatible piezoelectric nanofibers developed by electrospinning green carbon quantum dots (G-CQDs), mulberry silk fibroin (SF), and polyvinyl alcohol (PVA). The introduction of G-CQDs significantly enhances the piezoelectric output of silk fibroin-based fiber materials. Meanwhile, the silk fibroin-based hybrid fibers maintain the photoluminescent response of G-CQDs without sacrificing valuable biocompatibility. Notably, the piezoelectric output of a G-CQD/PVA/SF fiber-based nanogenerator is more than three times higher than that of a PVA/SF fiber-based nanogenerator. This is one of the highest levels of state-of-the-art piezoelectric devices based on biological organic materials. As a proof of concept, in the actual scenario of a rope skipping exercise, the G-CQD/PVA/SF fiber-based nanogenerator is further employed as a self-powered wearable sensor for real-time sensing of athletic motions. It demonstrates high portability, good flexibility, and stable piezoresponse for smart sports applications. This class of water-disposable, piezo/photoactive biological materials could be compelling building blocks for applications in a new generation of versatile, transient, wearable/implantable devices. Full article

Conducting polymers (CPs) have emerged as promising materials for gas sensors due to their organic nature coupled with unique and versatile optical, electrical, chemical, and electrochemical properties. This review provides a comprehensive overview of the latest developments in conducting polymer-based gas sensors. First, the fundamental gas sensing mechanisms in CPs-based sensors are elucidated, covering diverse transduction modes including electrochemical, chemiresistive, optical, piezoelectric, and field-effect transistor-based sensing. Next, the various types of conducting polymers employed in gas sensors, such as polypyrrole, polyaniline, polythiophene, and their composites are introduced, with emphasis on their synthesis methods, structural characteristics, and gas sensing response properties. Finally, the wide range of applications of these sensors is discussed, spanning industrial process control, environmental monitoring, food safety, biomedical diagnosis, and other fields, as well as existing issues such as long-term stability and humidity interference, and a summary of the biocompatibility and regulatory standards of these conductive polymers is provided. By integrating insights from sensing mechanisms, materials, and applications, this review offers a holistic understanding of CPs-based gas sensors. It also highlights future research directions, including device miniaturization, AI-assisted gas identification, multifunctional integrated sensing systems, wearable and flexible sensor platforms, and enhanced sensitivity, selectivity, and on-site detection capabilities. Full article

Human–computer interaction (HCI) enables communication between humans and computers, which is widely applied in various fields such as consumer electronics, education, medical rehabilitation, and industrial control. Human motion monitoring is one of the most important methods of achieving HCI. In the present work, a novel human motion monitoring sensor for contact touch and gesture recognition is fabricated based on polyester elastomer (PTE) synthesized from diols and diacids, with both piezoelectric and triboelectric properties. The PTE sensor can respond to contacted and contactless me-chemical signals by piezoelectric and triboelectric responding, respectively, which enables simultaneous touch control and gesture recognition. In addition, the PTE sensor presents high stretchability with elongation at break over 1000% and high durability over 4000 impact cycles, offering significant potential for consumer electronics and wearable devices. Full article

Lithium niobate (LiNbO₃) has remarkable ferroelectric properties, and its unique crystal structure allows it to undergo significant spontaneous polarization. Lithium niobate plays an important role in the fields of electro-optic modulation, sensing and acoustics due to its excellent electro-optic and piezoelectric properties. Thin-film LiNbO₃ (TFLN) has attracted much attention due to its unique physical properties, stable properties and easy processing. This review introduces several main preparation methods for TFLN, including chemical vapor deposition (CVD), molecular beam epitaxy (MBE), pulsed laser deposition (PLD), magnetron sputtering and Smartcut technology. The development of TFLN devices, especially the recent research on sensors, memories, optical waveguides and EO modulators, is introduced. With the continuous advancement of manufacturing technology and integration technology, TFLN devices are expected to occupy a more important position in future photonic integrated circuits. Full article

This research study aims to explore the synergistic effects of incorporating polyvinylidene fluoride (PVDF) into polyvinyl alcohol (PVA) hydrogels to enhance their suitability for triboelectric sensors applications. The preparation process employs a method of freezing/thawing conducted in dimethyl sulfoxide (DMSO), followed by solvent replacement with water. This approach effectively preserves PVDF in its α phase, eliminating piezoelectric effects and enhancing the hydrogels’ mechanical properties. The use of DMSO contributes to reduced pore size, while incorporating PVDF significantly improves the three-dimensional network structure of the hydrogels, resulting in enhanced thermal and chemical resistance. Thorough characterization of the resulting PVA/PVDF composite hydrogels, prepared with varying ratios of PVA to PVDF (10:0, 8:2, and 5:5), was conducted by using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), electrochemical impedance spectroscopy (EIS), rheology, and thermogravimetric analysis (TGA). Notably, the composite hydrogels were tested in pressure sensors and human voice sensors, demonstrating their capability to recognize different patterns associated with various letters. The incorporation of PVDF significantly enhanced the signal-to-noise ratio in PVA/PVDF-based sensors compared with those made solely from PVA, highlighting a notable improvement in voice detection. The enhancements were quantified as 56% for “a”, 35% for “r”, and 47% for “m”. Full article

With the advent of the intelligent era, flexible piezoelectric tactile sensors, as key components for sensing information and transmitting signals, have received worldwide attention. However, piezoelectric pressure sensors are still currently limited, which severely restricts their practical applications. Furthermore, the demonstrations conducted in labs are not accurate to real-world scenarios. Thus, there is an urgent need to further optimize the intrinsic piezoelectric performance and usage characteristics to meet application requirements. As a representative piezoelectric, polyvinylidene fluoride (PVDF) exhibits significant advantages in terms of excellent flexibility, chemical stability, high electromechanical conversion, low cost, and appropriate acoustic impedance, which allow it to serve as the core matrix in flexible pressure sensors. This paper aims to summarize very recent progress in flexible piezoelectric sensors based on PVDF, including their composition modulation, structure optimization, and applications. Based on a comprehensive summary of recent representative studies, we propose rational perspectives and strategies regarding PVDF-based piezoelectric sensors and provide some new insights for the research and industrial communities. Full article

Surface acoustic wave-based (SAW) sensors are of great interest due to their high sensibility and fast and stable responses. They can be obtained at an overall low cost and with an intuitive and easy-to-use method. The chemical sensitization of a piezoelectric transducer plays a key role in defining the properties of SAW sensors. In this study, we investigate the structural and adhesion properties of a new class of coating material based on polyurethane polymeric composites. We used dark-field microscopy (DFM) and scanning electron microscopy (SEM) to observe the microstructure of polyurethane composite coatings on piezoelectric sensor elements and to analyze the effects of the chemical resistance and adhesion test (CAT) on the coating layers obtained with the polyurethane polymeric composites. The results of the microscopy showed that all polyurethane composite coatings exhibited excellent uniformity and stability after chemical adherence testing (CAT). All of the observations were correlated with the results of the ultrasonic analysis, which demonstrated the role of polyurethane as a binder to form the stable structure of the composites and, at the same time, as an adhesion promoter, increasing the chemical resistance and the adherence of the coating layer to the complex surface of the piezoelectric sensor element. Full article

One of the challenging problems in the research and development of vibration sensors relates to the formation of Ohmic contacts for the removal of an electrical signal. In some cases, it is proposed to use arrays of carbon nanotubes (CNTs), which can serve as highly elastic electrode materials for vibration sensors. The purpose of this work is to study the effect of a current-collecting layer of CNTs grown over silicon on the properties of a lead zirconate titanate (PZT) film, which is frequently employed in mechanical vibration sensors or energy harvesters. For the experiments, a vibration sensor mock-up was created with the PZT-CNT-Ni-V-SiO₂-Si and PZT-CNT-Ni-V-Si structures where an array of vertically oriented CNTs was grown over an oxidized or high-alloyed silicon substrates by plasma chemical deposition from a gas phase. Then, a thin film of PZT was applied to the CNT layer with a high-frequency reactive plasma spraying. For comparison, the PZT film was applied to silicon without a CNT layer (PZT-Si structure). The calculated average value of the piezoelectric module is 112 pm/V for the Ni-PZT-PT-Ni-Si-SiO₂ sample, and 35 pm/V for PZT-Ni-SiO₂-Si. It can be seen that the contact realized with the help of CNT ensures more than three times the best efficiency in terms of the piezoelectric module. The value of the piezoelectric module of the vibration sensor with the PZT-CNT-Ni-V-Si structure was 186 pm/V, and the value of the residual polarization was 23.2 µC/cm², which is more than eight and three times, respectively, higher than the values of these properties for the vibration sensor with the PZT-Si structure. It is shown that the vibration sensor can operate in the frequency range of 0.1–10 kHz. Full article

This study has investigated the effects of different annealing temperatures on the microstructure, chemical composition, phase structure, and piezoelectric properties of ZnO films. The analysis focuses on how annealing temperature influences the oxygen content and the preferred c-axis (002) orientation of the films. It was found that annealing significantly increases the grain size and optimizes the columnar crystal structure, though excessive high-temperature annealing leads to structural degradation. This behavior is likely related to changes in oxygen content at different annealing temperatures. High resolution transmission electron microscopy (HR-TEM) reveals that the films exhibit high-resolution lattice stripes, confirming their high crystallinity. Although the films exhibit growth in multiple orientations, the c-axis (002) orientation remains the predominant crystallographic growth. Further piezoelectric property analysis demonstrates that the ZnO films annealed at 400 °C exhibit enhanced piezoelectric performance and stable linear piezoelectric behavior. These findings offer valuable support for optimizing the piezoelectric properties of ZnO films and their applications in piezoelectric sensors. Full article

The advancement of wearable technology has entered a new phase, leading to the creation of various wearable sensors due to the rise of technologies like IoT and AI. Wearable chemical sensors are essential components of wearable electronics and hold significant promise in monitoring health. This review reports on the recent achievements and advantages of portable smart chemical sensing for health monitoring and discusses portable chemical sensing using frictional/piezoelectric electrochemical generators, photovoltaics and thermal power accumulators. This paper also evaluates the potential of wearable chemical sensors for health monitoring. Full article

The small dimensions of microfluidic channels allow for fast diffusive or passive mixing, which is beneficial for time-sensitive applications such as chemical reactions, biological assays, and the transport of to-be-detected species to sensors. In microfluidics, the need for fast mixing within milliseconds arises primarily because these devices are often used in fields where rapid and efficient mixing significantly impacts the performance and outcome of the processes. Active mixing with acoustics in microfluidic devices involves using acoustic waves to enhance the mixing of fluids within microchannels. Using sharp corners and wall patterns in acoustofluidic devices significantly enhances the mixing by acoustic streaming around these features. The streaming patterns around the sharp edges are particularly effective for the mixing because they can produce strong lateral flows that rapidly homogenize liquids. This work presents extensive characterizations of the effect of sharp-edged structures on acoustic mixing in bulk acoustic wave (BAW) mode in a silicon microdevice. The effect of side wall patterns in different angles and shapes, their positions, the type of piezoelectric transducer, and its amplitude and frequency have been studied. Following the patterning of the channel walls, a mixing time of 25 times faster was reached, compared to channels with smooth side walls exhibiting conventional BAW behavior. The average locally determined acoustic streaming velocity inside the channel becomes 14 times faster if sharp corners of 10° are added to the wall. Full article

Hydrogels, known for their unique ability to retain large amounts of water, have emerged as pivotal materials in both tissue engineering and biosensing applications. This review provides an updated and comprehensive examination of cutting-edge hydrogel technologies and their multifaceted roles in these fields. Initially, the chemical composition and intrinsic properties of both natural and synthetic hydrogels are discussed, highlighting their biocompatibility and biodegradability. The manuscript then probes into innovative scaffold designs and fabrication techniques such as 3D printing, electrospinning, and self-assembly methods, emphasizing their applications in regenerating bone, cartilage, skin, and neural tissues. In the realm of biosensing, hydrogels’ responsive nature is explored through their integration into optical, electrochemical, and piezoelectric sensors. These sensors are instrumental in medical diagnostics for glucose monitoring, pathogen detection, and biomarker identification, as well as in environmental and industrial applications like pollution and food quality monitoring. Furthermore, the review explores cross-disciplinary innovations, including the use of hydrogels in wearable devices, and hybrid systems, and their potential in personalized medicine. By addressing current challenges and future directions, this review aims to underscore the transformative impact of hydrogel technologies in advancing healthcare and industrial practices, thereby providing a vital resource for researchers and practitioners in the field. Full article

The search for a synthesis method to create longer ZnO NWAs with high-quality vertical alignment, and the investigation of their electrical properties, have become increasingly important. In this study, a hydrothermal method for growing vertically aligned arrays of ZnO nanowires (NWs) using localized heating was utilized. To produce longer NWs, the temperature environment of the growth system was optimized with a novel reaction container that provided improved thermal insulation. At a process temperature above ~90 °C, ZnO NWs reached a length of ~26.8 µm within 24 h, corresponding to a growth rate of 1.1 µm/h, nearly double the rate of 0.6 µm/h observed in traditional chemical bath growth using a glass reactor. The densely grown NWs (~1.9/µm²), with a diameter of ~0.65 µm, exhibited a preferred hexagonal c-axis orientation and were vertically aligned to the (100) silicon (Si) substrate. These NW structures have multiple applications, e.g., in piezotronic strain sensors, gas sensing, and piezoelectric energy harvesting. As proof of concept, a piezoelectric nanogenerator (PENG) was fabricated by embedding the NWs in an S1818 polymer matrix over a 15 mm × 15 mm area. Under repeated impulse-type compressive forces of 0.9 N, a maximum peak output voltage of ~95.9 mV was recorded, which is higher by a factor of four to five than the peak output voltage of 21.6 mV previously obtained with NWs measuring ~1.8 µm in length. Full article

The high toxicity of hydrogen sulfide combined with poor sensitivity at room operating temperature urge for the development of new sensitive materials for sensors complying with this requirement, as well as a fast response and low cost. In this work, we have successfully developed materials for surface acoustic wave (SAW) sensors sensitive to H₂S gas that provide a reversible response at room temperature. The sensitive materials were created by plasma-enhanced chemical vapor deposition of a-CH films using methane as a precursor with argon and argon admixed with hydrogen or nitrogen and applied on piezoelectric quartz substrates. Smooth films, with an AFM root mean square below 1.5 nm, were obtained in all cases, although slight topographical variations were noted, depending on the gas types. XPS detected varying degrees of oxidation, indicating that the assisting gases played a crucial role in introducing oxygen-containing functional groups, thus influencing the material’s surface chemistry and sensitivity response. A hydrogen plasma treatment was applied on the a-CH deposited sensors as a further sensor preparation step. The hydrogen plasma treatment resulted in significant modifications in the topographical features, including roughness increase and notable variations in the surface aspect ratios, as confirmed through AFM data analysis, which involved advanced pixel height analysis and line profile processing. X-ray photoelectron spectroscopy (XPS) studies indicated the formation of new functional groups, increased defect density, and a significant reduction in electron transitions following hydrogen plasma treatment. The sensors demonstrated a reversible response to H₂S gas within 8 to 20 ppm concentration ranges, effectively detecting these levels. The sensitivity of the sensors was significantly enhanced, up to 39% through hydrogen plasma treatment, reaching an improved overall performance in detecting low concentrations of H₂S down to 0.9 ppm. These findings highlight a-CH thin films as an excellent candidate for next-generation SAW sensors. The study also suggests the potential for experimenting with various assisting gases during plasma deposition and additional plasma treatments to push detection capabilities to below ppm levels. Full article