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BiFeO3–BaTiO3 (BF–BT) ceramics with high Curie temperature and excellent piezoelectric coefficient are expected to be applied in high-temperature piezoelectric sensors and actuators. However, its resistivity decreases rapidly with temperature and impedes its further applications. Moreover, normal methods such as doping modification cannot address this issue. In the present work, bismuth layered Bi4Ti2.93(Zn1/3Nb2/3)0.07O12 (BIT) and perovskite 0.36BiScO3-0.64PbTiO3 (BSPT) ceramics were selected as insulating layers and were, respectively, sintered with 0.7BF–0.3BT ceramics to form laminated ceramics. The heterojunction structures effectively prevent carrier migration, and both resistivities of BIT and BSPT laminated ceramics were increased from 106 to 108−9 Ω cm at 300 °C. In addition, piezoelectric properties of the BSPT-type laminated ceramics are much higher than that of BF–BT ceramics, in which the bipolar strain was increased from 0.04% to 0.1% (4 kV/mm), and d33 was increased from 140 to 237 pC/N. Therefore, designing the insulating layer may be an effective method to realize the high-temperature application for BF–BT ceramics. [ABSTRACT FROM AUTHOR]

Aiming at the interferences caused by vibrations on the target monitoring system of satellite platforms, an experimental system of optical–mechanical–electrical joint image stabilization based on inertial sensors and piezoelectric fast mirrors was studied. First of all, the data from the fiber optic gyroscope and the detector are combined and processed. After that, the predicted intentional velocity is subtracted from the real-time gyroscope data, and the vibration displacement is obtained using an integral. The feedback amount is calculated using the processor according to the vibration displacement, the piezoelectric fast mirror is controlled to compensate the vibration interferences, and the purpose of stabilizing the images is achieved. The experimental results show that under a vibration interference of 300 μ rad /s, the image stabilization control frequency of the system reaches 500 Hz, the relative error between image frames is better than 3 μ rad , and the intra-frame stabilization performance of the detector meets the requirements on stabilized image and target detection for space targets on the star-carrying platform. [ABSTRACT FROM AUTHOR]

Real-time monitoring of structural health status is very important for supersonic aircraft, since the long-term operation in harsh service environments, such as high temperatures, can cause potential damage. Structural health monitoring (SHM) based on lamb wave has been approved to be a critical technique for the reliable operation of supersonic aircraft, but is limited by the operating temperature of conventional piezoelectric sensors, which makes it difficult to meet the high-temperature monitoring requirements. The BiFeO 3 –BaTiO 3 ceramics exhibit excellent piezoelectric properties and high Curie temperature (T c), making them promising for high-temperature SHM of supersonic aircraft. Here, we fabricated a piezoelectric sensor using 0.67BiFeO 3 -0.33BaTiO 3 -0.25%molMnO 2 (BF33BTMN-025) ceramic, which exhibits a piezoelectric charge constant (d 33) of 135 pC/N at room temperature and a T c of 448 °C. The BF33BTMN-025 ceramic sensor operates effectively at temperatures up to 200 °C and maintains stable damage monitoring sensitivity as well. Compared with Pb(Zr, Ti)O 3 (PZT), BaTiO 3 (BTO) and other piezoelectric sensors commonly used in SHM field, the BF33BTMN-025 ceramic sensor has a higher operating temperature and a comparable sensitivity. Our work demonstrates that the BF33BTMN-025 ceramic sensor can be employed as piezoelectric sensor for high-temperature SHM, which has a wide application potential in the field of real-time monitoring of supersonic aircraft. [ABSTRACT FROM AUTHOR]

Ultrasound and photoacoustic imaging are important imaging modalities with significant applications in clinical diagnosis and biomedical research. However, current capacitive and piezoelectric ultrasound detectors face challenges related to sensitivity and bandwidth, particularly at higher frequencies. These challenges can hinder their ability to achieve high spatial resolution and deep penetration for imaging purposes. Optical ultrasound sensors offer high sensitivity and show great potential for developing ultrasound/photoacoustic imaging systems. Among all methods of optical ultrasound detection, integrated photonics, with its superior advantages in miniaturization, sensitivity, and integration capability with electronics, could be next‐generation photoacoustic/ultrasound imaging technology. This review explores the device structure designs and applications of ultrasound/photoacoustic sensing based on integrated photonics, analyzes their performance metrics as ultrasound detectors, and discusses some perspectives on future developments and trends in this field. [ABSTRACT FROM AUTHOR]

With the rapid development of information technology (e.g., Internet of Things (IoT) and artificial intelligence (AI)), piezoelectric sensor (i.e., piezoelectric nanogenerator, PENG) receives an increasing number attention in the field of self‐powered wearable devices. Taking piezoelectric fiber as an example, it shows promising application for wearable devices owing to its light weight and high flexibility compared with block electronic devices. However, it still remains a challenge to fabricate low‐cost and high‐performance piezoelectric fiber via a large‐scale but efficient method. In this study, via extrusion molding and leaching, a core‐sheath piezoelectric sensor is facilely fabricated, whose core and sheath layer are respectively slender steel wire (i.e., electrode) and PVDF microfibrillar bundle (PMB) (i.e., piezoelectric layer). Such piezoelectric sensor shows decent output performance in both pressing (12.3 V) and bending (0.32 V) mode. Meanwhile, it possesses sensitive stress responsiveness when serving for self‐powered sensing. Furthermore, such piezoelectric sensors can realize wearable signal transmission and human motion monitoring, showing promising potential for wearable devices in the future. This work proposes a large‐scale but efficient method for fabricating high‐performance PVDF microfibril based piezoelectric fiber, opening a new pathway to develop self‐powered sensors following the concept of polymer “structuring” processing. [ABSTRACT FROM AUTHOR]

Flexible high-performance piezoelectric nanogenerator (PENG) excel in converting mechanical energy into electrical energy and exhibit remarkable sensitivity, a feature that is paramount for the development of self-driven piezoelectric sensors. In this study, electrospinning technology was used to prepare poly (vinylidene fluoride-co-trifluoroethylene) [P(VDF-TrFE)] based piezoelectric nanofiber composite films containing potassium-sodium niobate nano particles (KNN NPs) and Nb 2 CT x co-doping, as well as single-component doping. The co-doped composite film attained an optimal β-phase content of 91.33%. Owing to the enhanced dipole alignment and interface charge polarization, the piezoelectric performance of the co-doped composite film was significantly enhanced compared to that of single-component doping. The co-doped piezoelectric composite film displayed a stable maximum output voltage of 20 V and an output current of 1.46 μA. The peak instantaneous power output was measured at 9.9 μW under the optimal resistive load of 10 MΩ. Durability testing over 2000 cycles affirmed the excellent mechanical stability of the piezoelectric composite film. Moreover, the fabricated piezoelectric composite film showed considerable potential in applications such as monitoring human activities and serving as an early warning system for natural disasters such as landslides, as indicated by the test results. [ABSTRACT FROM AUTHOR]

A friction coefficient of tire model for cornering simulation is generally set inductively to be consistent with experimental results. However, the inductively set friction coefficients have no clear relationship with the viscoelasticity of the rubber, so they cannot be used in the design of rubber formulations to obtain the desired friction coefficient. In this study, we propose a new tire mechanical model for cornering simulation that includes a friction coefficient deductively derived from the viscoelasticity of rubber based on the Persson's multiscale friction theory. In this model, the contact pressure, sliding velocity, and lateral stress distributions are calculated based on an elliptical contact patch. Because the proposed model analytically connects the lateral force with the viscoelasticity of rubber, it is applicable to rubber design for achieving the targeted cornering properties. The validity of the model was experimentally verified using an internal drum machine with quartz piezoelectric sensors on an aluminium road segment. With appropriate parameter settings, the friction coefficient distribution in the length direction calculated by the proposed model agreed well with the experimental results compared to the elliptical contact patch tire model. [ABSTRACT FROM AUTHOR]

Fabric-based composites with superior mechanical properties and excellent perceptive function are highly desirable. However, it remains a huge challenge to attain structure-function integration, especially for hybrid fabric composites. Herein, a skin-inspired interface modification strategy is proposed toward this target by constructing a hybrid smart fabric system consisting of two types of smart fabrics: carbon nanotube (CNT)/MXene-modified aramid fabrics and zinc oxide nanorod (ZnO NR)-modified carbon fabrics. Based on that, flexible piezoelectric pressure sensors with skin-like hierarchical perception interfaces are fabricated, which demonstrate superb sensitivity of 2.39 V·kPa-1 and are capable of various wearable monitoring tasks. Besides, the interface-modified hybrid fabric reinforced plastics can also be fabricated, which are proven to possess 13.6% higher tensile strength, 10.1% elastic modulus. More impressively, their average energy absorption can be improved by 111.9%, accompanied with inherent damage alert capability. This offers a paradigm to fabricate structure-function integrated hybrid smart fabric composites for the smart clothing and intelligent aerial vehicles. [ABSTRACT FROM AUTHOR]

In marine scientific research, ocean monitoring is crucial where the batterypowered sensor devices are placed under the water to collect different information like temperature, pressure, and turbidity in underwater sensor networks (UWSNs). Thus, keeping these devices active for longer periods is challenging. In the last decades, the piezoelectric transducer (PZT) material has been used widely for constructing more environmentally friendly energy harvesting systems. The PZT harvester offers a promising solution by eliminating the need for batteries for running devices in the future with less maintenance. The PZT harvester allows the system to generate higher voltage to run low-power devices. This paper designed and developed a new renewable energy harvester system using PZT transducers for running different types of underwater sensor devices like temperature, turbidity, and obstacle sensors. The proposed PZT-based energy harvester employs a twostage amplification model for generating higher voltage and current to run multiple devices. The sensing information collected from these sensors is transmitted to the cloud which is later utilized for analysis and decisionmaking. Experiment results show the proposed PZT-based energy harvester can generate a voltage of 13 volts (V) and a current of 43.3 milliampere (mA) equivalent to 562 milliwatt (mW) which is very good to run multiple low-power underwater sensor devices. [ABSTRACT FROM AUTHOR]

Manganese mercury thiocyanate (MMTC), a nonlinear optical organometallic single-crystal material, was successfully grown by the Sankaranarayanan-Ramasamy (SR) method. The as-grown MMTC crystals were subjected to 50 shock pulses and designated as MMTC50S. The lattice parameters were measured by single-crystal x-ray diffraction (XRD) with values of a, b, and c of 11.3150 Å, 11.3150 Å, and 4.2720 Å with a tetragonal system for the pure MMTC, and values of 11.3180 Å, 11.3180 Å, and 4.2737 Å for MMTC50S, respectively. Fourier transform infrared (FTIR) spectroscopy was used to identify the functional groups present in the MMTC50S crystal. Scanning electron microscopy (SEM) was used to assess the surface morphology, which revealed a pattern of minor defects and minor dislocations in the MMTC50S crystal in contrast to the pure form because of the shock pulses on the MMTC crystal to create the MMTC50S specimen. The UV-visible spectrum showed increased absorption for the MMTC50S crystal. Fluorescence (FL) studies revealed blue fluorescence emission for MMTC50S. Dielectric measurements were carried out and the dielectric constant was calculated for the grown sample. The piezoelectric coefficients and sensor response at room temperature were also determined for MMTC and MMTC50S. The maximum sensitivity for the MMTC50S with a red light-emitting diode (LED) was 8.88%, whereas the blue LED achieved 9% sensitivity. [ABSTRACT FROM AUTHOR]

Road roughness, defined by the International Roughness Index (IRI), is a critical criterion for ride quality and comfort, meticulously monitored by road authorities to address maintenance needs. This paper introduces a new method to explore the suitability of bicycles as probe vehicles for measuring nonmotorized road roughness. For this purpose, polyvinylidene fluoride (PVDF) sensors are attached to the front wheel of a mountain bike to capture road roughness through tire–road interaction. To validate this approach, a study was conducted on a motorized dual-lane road, where each direction spanned 660 m, totaling 1,320 m, to verify the method's accuracy in measuring IRI. Data from both the PVDF sensors and their specific locations were recorded simultaneously. The values obtained from a laser profilometer vehicle served as benchmark reference points for the PVDF sensor readings. Thirty-two features are extracted from the PVDF sensor data. The Support Vector Regression (SVR) algorithm is then used to estimate IRI values from these features. The mean absolute percentage error (MAPE) results of the data sets for the distances covered by 15, 30, and 50 full rotations of the bicycle's front wheel, corresponding to 30, 60, and 100 m, respectively, are found to be 13.64%, 10.73%, and 5.34%. These results highlight the potential of this innovative approach as a reliable tool for determining road roughness on nonmotorized pathways. [ABSTRACT FROM AUTHOR]

A spiral‐artificial basilar membrane (S‐ABM) sensor is reported that mimics the basilar membrane (BM) of the human cochlea and can detect sound by separating it into 24 sensing channels based on the frequency band. For this, an analytical function is proposed to design the width of the BM so that the frequency bands are linearly located along the length of the BM. To fabricate the S‐ABM sensor, a spiral‐shaped polyimide film is used as a vibrating membrane, with maximum displacement at locations corresponding to specific frequency bands of sound, and attach piezoelectric sensor modules made of poly(vinylidene fluoride‐trifluoroethylene) film on top of the polyimide film to measure the vibration amplitude at each channel location. As the result, the S‐ABM sensor implements a characteristic frequency band of 96‐12,821 Hz and 24‐independent critical bands. Using real‐time signals from discriminate channels, it is demonstrated that the sensor can rapidly identify the operational noises from equipment processes as well as vehicle sounds from environmental noises on the road. The sensor can be used in a variety of applications, including speech recognition, dangerous situation recognition, hearing aids, and cochlear implants, and more. [ABSTRACT FROM AUTHOR]

Assessing the vibration signature produced by a rotating component of the wind turbine enables the identification of operational conditions and the detection of potential faults at an early stage. The main purpose is to enhance the sustainability of wind turbines while increasing the lifespan and uptime of their operational systems. This vibration analysis is based on the processing of the signal provided by sensors, which often incorporates piezoelectric transducers. This paper evaluates the consequences of employing piezoelectric sensors used for vibration measurement on electrical machines integrated into wind turbines by conducting a life cycle assessment (LCA). The widespread use of piezoelectric materials is due to their high sensitivity to vibrations, although their selection is also influenced by regulatory restrictions. This research focuses on the environmental impact of piezoelectric accelerometers used commonly in condition monitoring systems. The collected literature data on the manufacturing processes are inputted into the LCA model which is powered by the Ecoinvent 3 database. The impact assessment is carried out using the European ILCD 2011 Midpoint+ method by calculating the unique scores of the selected impact categories. The results are presented and discussed in terms of environmental indicators, as well as ecological recommendations on the design. [ABSTRACT FROM AUTHOR]

Sarcopenia is an age-related syndrome characterized by the loss of skeletal muscle mass and function. Community screening, commonly used in early diagnosis, usually lacks features such as real-time monitoring, low cost, and convenience. This study introduces a promising approach to sarcopenia screening by dynamic plantar pressure monitoring. We propose a wearable flexible-printed piezoelectric sensing array incorporating barium titanate thin films. Utilizing a flexible printer, we fabricate the array with enhanced compressive strength and measurement range. Signal conversion circuits convert charge signals of the sensors into voltage signals, which are transmitted to a mobile phone via Bluetooth after processing. Through cyclic loading, we obtain the average voltage sensitivity (4.844 mV/kPa) of the sensing array. During a 6 m walk, the dynamic plantar pressure features of 51 recruited participants are extracted, including peak pressures for both sarcopenic and control participants before and after weight calibration. Statistical analysis discerns feature significance between groups, and five machine learning models are employed to screen for sarcopenia with the collected features. The results show that the features of dynamic plantar pressure have great potential in early screening of sarcopenia, and the Support Vector Machine model after feature selection achieves a high accuracy of 93.65%. By combining wearable sensors with machine learning techniques, this study aims to provide more convenient and effective sarcopenia screening methods for the elderly. [ABSTRACT FROM AUTHOR]

Sleep plays a role in maintaining our physical well-being. However, sleep-related issues impact millions of people globally. Accurate monitoring of sleep is vital for identifying and addressing these problems. While traditional methods like polysomnography (PSG) are commonly used in settings, they may not fully capture natural sleep patterns at home. Moreover, PSG equipment can disrupt sleep quality. In recent years, there has been growing interest in the use of sensors for sleep monitoring. These lightweight sensors can be easily integrated into textiles or wearable devices using technology. The flexible sensors can be designed for skin contact to offer continuous monitoring without being obtrusive in a home environment. This review presents an overview of the advancements made in flexible sensors for tracking body movements during sleep, which focus on their principles, mechanisms, and strategies for improved flexibility, practical applications, and future trends. [ABSTRACT FROM AUTHOR]

Nerve injury can lead to defects in related motor functions. It is critical to achieve long‐term and convenient real‐time evaluation of motor function recovery status during nerve injury repair. In this study, an implantable PLLA/BTO piezoelectric sensor (PBPS) with good biodegradability and biocompatibility for real time evaluation of the motor function recovery after nerve injury is developed. PLLA fibers doped with BTO are employed as piezoelectric material in PBPS, which can convert the biomechanical signals generated by motion into electrical signals. PBPS can be implant simultaneously with commonly used tissue scaffolds for treatment in the rats with sciatic nerve injury. The linearity of the pressure and the output voltage of PBPS is ≈0.9445. For the evaluation effectiveness, as the treatment process progresses, the signals generated by PBPS exhibited good consistency with EMG signals, indicating effectively evaluation of the motor function. Moreover, the integration of PBPS and wireless module can break the limitations of time and space for sensing and realize wireless evaluation of motor function in rat. The implantable sensor based on PBPS may bring new ideas for the development of implantable bioelectronics. [ABSTRACT FROM AUTHOR]

Cellulose‐based piezoelectric composites have attracted extensive attention in recent years due to their low cost, easy molding, high flexibility, and biocompatibility in the manufacture of piezoelectric nanogenerators (PENG) and sensors. In this work, cellulose nanofibril (CNF)/MXene@ZnO (CM@ZnO) piezoelectric composite films with “brick‐rebar‐mortar” structure are prepared by growing ZnO on the mixed substrate via a high‐efficiency two‐step hydrothermal method. As a hard bridge, ZnO welds CNF and MXene together to construct the “brick‐rebar‐mortar” structure, which greatly improves the piezoelectric performance. Its tensile strength reaches 65.13 ± 3.61 MPa, as well as that the longitudinal piezoelectric constant (d33) attains 14.3 ± 1.3 pC N−1. Under the force of 300 KPa, the open‐circuit voltage (VOC) and short‐circuit current (ISC) of CM@ZnO PENG are as high as 17.15 V and 997 nA, respectively. Under the force of 100 KPa, it can charge a 1.0 µF commercial capacitor to 6.07 V in 400 s. The assembled flexible piezoelectric sensor can accurately collect the pressure or vibration signal caused by bending the wrist (0.59 V) with excellent sensitivity. The performance demonstrates the feasibility of its application in wearable smart devices and provides a reference for new cellulose‐based PENGs. [ABSTRACT FROM AUTHOR]

Bio-inspired strategies for robotic sensing are essential for in situ manufactured sensors on the Moon. Sensors are one crucial component of robots that should be manufactured from lunar resources to industrialize the Moon at low cost. We are concerned with two classes of sensor: (a) position sensors and derivatives thereof are the most elementary of measurements; and (b) light sensing arrays provide for distance measurement within the visible waveband. Terrestrial approaches to sensor design cannot be accommodated within the severe limitations imposed by the material resources and expected manufacturing competences on the Moon. Displacement and strain sensors may be constructed as potentiometers with aluminium extracted from anorthite. Anorthite is also a source of silica from which quartz may be manufactured. Thus, piezoelectric sensors may be constructed. Silicone plastic (siloxane) is an elastomer that may be derived from lunar volatiles. This offers the prospect for tactile sensing arrays. All components of photomultiplier tubes may be constructed from lunar resources. However, the spatial resolution of photomultiplier tubes is limited so only modest array sizes can be constructed. This requires us to exploit biomimetic strategies: (i) optical flow provides the visual navigation competences of insects implemented through modest circuitry, and (ii) foveated vision trades the visual resolution deficiencies with higher resolution of pan-tilt motors enabled by micro-stepping. Thus, basic sensors may be manufactured from lunar resources. They are elementary components of robotic machines that are crucial for constructing a sustainable lunar infrastructure. Constraints imposed by the Moon may be compensated for using biomimetic strategies which are adaptable to non-Earth environments. [ABSTRACT FROM AUTHOR]

The multilayer composite film system was designed in this study. The multilayer composite film was constructed by alternating electrospinning of MXene doped with polyacrylonitrile (PAN) nanofilm and thermoplastic polyurethane (TPU) nanofilm as piezoelectric functional layer. After utilizing nanofilm material, the piezoelectric sensor was prepared and subsequently examined for its piezoelectric sensitivity, piezoelectric output, and mechanical characteristics. MXene/PAN/TPU multilayer composite films showed good piezoelectric output performance. The final experimental data showed that the piezoelectric sensor of the MXene/PAN/TPU-based system achieved 0.16 kPa−1 piezoelectric sensitivity, 150ms/140ms response time and recovery time, good output voltage and output current, and good output stability. In human biological motion detection, the generator produced a maximum output voltage of 30 V when pressed by the palm. Tests such as palm pressing, finger tapping, and footstomping demonstrated the potential of piezoelectric sensors in human energy harvesting and motion monitoring. Multilayer composite films had flexible mechanical properties and sensitive piezoelectric response and had broad application prospects in piezoelectric sensors and piezoelectric nanogenerators. [ABSTRACT FROM AUTHOR]

The goal of this research article is to investigate the effects of using two-dimensional functionally graded materials on the performance of piezoelectric sensors/actuators when subjected to simultaneous complex loading conditions. The considered disc-shaped sensors/actuators have nonuniform thicknesses and undergo asymmetric hygro-thermo-electro-mechanical loading. A power-law model is used to grade the materials radially, whereas the cosine function, which includes two independent parameters, describes the pattern along the circumferential direction. Comparing the results obtained by using the finite element method with those of one-dimensional graded structures leads to promising outcomes. For example, the radial displacement exhibits vital changes that varied between - 13 and 31 % . This is beneficial for such structures in terms of enhancing their sensing/actuating abilities. Also, the tangential stress can be reduced substantially by about 39.5 % through the proper selection of the corresponding material parameters. In addition, this reduction of the tangential stress has a positive effect on the von Mises stress that can be decreased by nearly 33 % . Accordingly, the structure would have improved durability and sustain higher loads. These findings would revolutionize the manufacturing of smart structures and enhance their behaviors under severe conditions. [ABSTRACT FROM AUTHOR]

The emergence of curved shield tunnels poses a significant construction challenge. If the quality of the segment assembly is not guaranteed, many segment cracks and damage will result from the stress concentration. Sensing the contact stresses between segmental joints is necessary to improve the quality of segments assembled for shield tunnel construction. Polyvinylidene difluoride (PVDF) piezoelectric material was chosen for the sensor because it can convert contact stresses into electrical signals, allowing the state of the segmental joints to be effectively sensed. It matches the working environment between the segmental joints of the shield tunnel, where flexible structures such as rubber gaskets and force transfer pads are present. This study proposes a piezoelectric sensing method for segmental joints in shield tunnels and conducts laboratory tests, numerical analyses, and field tests to validate the feasibility of the method. The results indicate that the PVDF film sensor can effectively sense the entire compression process of the gasket with different amounts of compression. The piezoelectric cable sensor can effectively sense the joint offset direction of the gasket. For differently shaped sections, the variation in the force sensed by the piezoelectric cable sensors was different, as verified by numerical simulation. Through the field test, it was found that the average contact stress between the segmental joints was in the range of 1.2-1.8 MPa during construction of the curved shield tunnels. The location of the segmental joints and the type of segment affect the contact stress value. The field monitoring results show that piezoelectric sensing technology can be successfully applied during assembly of the segments for effective sensing of the contact stress. [ABSTRACT FROM AUTHOR]

To enhance the piezoelectric properties of poly (vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE))-based composites and prepare a piezoelectric sensor with high sensitivity, two types of potassium sodium niobate (KNN) fillers, micro-particles (MPs) and micro-rods (MRs), were individually doped into a P(VDF-TrFE) matrix to form composites using a traditional solution-casting process. Identically, the two groups of P(VDF-TrFE)-based piezoelectric composites doped with KNN MPs and KNN MRs exhibited an enhanced β -phase and typical ferroelectricity with high residual polarization (P r), which resulted in good piezoelectric constant (d 33) and sensing electrical response. In contrast, the KNN MRs/P(VDF-TrFE) composite showed better piezoelectric output performance compared to the KNN MPs/P(VDF-TrFE) composite in all test scenarios, which is attributed to its depressed dielectric permittivity owing to the ameliorative conductivity dielectric loss. An output voltage (U) of 16 V, 4 V, and 6 V were recorded using 10 g zirconium ball impacting, finger tapping, and finger bending, respectively, in the KNN MRs/P(VDF-TrFE) sensors. This research demonstrates the impact of the filler shape on the electrical performance of P(VDF-TrFE)-based piezoelectric composites, which provides a reliable reference to enhance the energy harvesting and conversion performance of self-powered electronic devices. [ABSTRACT FROM AUTHOR]

The piezoelectric effect refers to a physical phenomenon where piezoelectric materials generate an electric field when subjected to mechanical stress or undergo mechanical deformation when subjected to an external electric field. This principle underlies the operation of piezoelectric sensors. Piezoelectric sensors have garnered significant attention due to their excellent self-powering capability, rapid response speed, and high sensitivity. With the rapid development of sensor techniques achieving high precision, increased mechanical flexibility, and miniaturization, a range of flexible electronic products have emerged. As the core constituents of piezoelectric sensors, flexible piezoelectric composite materials are commonly used due to their unique advantages, including high conformability, sensitivity, and compatibility. They have found applications in diverse domains such as underwater detection, electronic skin sensing, wearable sensors, targeted therapy, and ultrasound diagnostics for deep tissue. The advent of flexible piezoelectric composite materials has revolutionized the design concepts and application scenarios of traditional piezoelectric materials, playing a crucial role in the development of next-generation flexible electronic products. This paper reviews the research progress on flexible piezoelectric composite materials, covering their types and typical fabrication techniques, as well as their applications across various fields. Finally, a summary and outlook on the existing issues and future development of these composite materials are provided. [ABSTRACT FROM AUTHOR]

Flexible materials with both in-plane and out-of-plane piezoelectric coefficients are needed in the development of advanced nanoelectromechanical systems. However, the challenge is to find flexible materials with the coexistence of in-plane and -out-of-plane piezoelectric responses, which hinders the progress of high-performance piezoelectric sensor development. In this paper, we propose the flexible XMAY2 (X = I; M = Ti, Zr; A = Al, Ga; Y = S, Se) monolayers, which belong to the group III-VI XMAY2 family, which showcase notable in-plane and out-of-plane piezoelectric coefficients. The in-plane (d11) and out-of-plane (d31) piezoelectric coefficients of the XMAY2 monolayers vary from 5.20 to 7.04 pm/V and from −0.23 to 0.48 pm/V, respectively. The large in-plane and out-plane piezoelectric responses coexist (d11 = 7.04 pm/V; d31 = 0.48 pm/V) in the IZrGaS2 monolayer, which is larger than other materials in the XMAY2 family, such as SMoSiN2 (d11 = 2.51; d31 = 0.28 pm/V). In addition, the mechanical and transport properties of XMAY2 demonstrate its impressive flexibility characteristics as well as its efficient electrical conductivity. Due to inversion symmetry breaking in both atomic structure and charge distribution of XMAY2 monolayers, the group III-VI XMAY2 family exhibits a potentially rich scope of applications in the field of piezoelectricity. [ABSTRACT FROM AUTHOR]

Flexible bending sensors are crucial components of flexible/wearable electronics. However, their broad application is restricted by their difficulty in sensing different bending directions and, more importantly, their significant output attenuation after long cycles. Herein, a new design of an All‐in‐One piezoelectric bending sensor is proposed, in which double‐deck, cross‐over 3D interdigital microelectrodes (silver nanowires (Ag NWs)) are embedded in a piezoelectric polymer film (poly(vinylidene fluoride‐trifluoroethylene (P(VDF‐TrFE))). The piezoelectric film with the embedded 3D microelectrodes exhibits a high anisotropy coefficient (η90∘${{\eta }_{90^\circ }}$ > 1) based on dual piezoelectric modes (d31 and d33), which renders it more sensitive to different bending directions. More importantly, the homogeneous interconnected interface and heterogeneous microinterlocked interface formed inside the sensor significantly enhance its interface mechanical properties, with at least a tensile strength of 51 MPa, a shear strength of 28 MPa, and an interfacial toughness of 300 J m−2, which are nearly two orders of magnitude greater than those of conventional sandwich architectures. The prepared All‐in‐One sensor shows an extremely stable piezoelectric output over as many as 16 00 000 bending cycles, which represents a remarkable breakthrough. Furthermore, a single sensor can be used to remotely control the multidirectional motion of a smart car, demonstrating enormous potential in practical applications. [ABSTRACT FROM AUTHOR]

Mass concrete is widely used in large-scale projects, including metro upper cover structures, water conservancy dams, and heavy equipment foundations, among others, necessitating the process of health monitoring in mass concrete construction. The development of reliable and simple strength-monitoring methods for mass concrete is challenging because the inner temperature of mass concrete is high and changes a lot. This study proposes a strength-monitoring approach for mass concrete using barium titanate–bismuth ferrite/polyvinylidene fluoride (BT–BFO/PVDF) nanocomposite piezoelectric sensors, wherein the new sensors are embedded as actuators and sensors in mass concrete. The stress wave generated by the BT–BFO/PVDF piezoelectric sensors is used to monitor the specimen's strength for 28 days. The piezoelectric voltage received by the sensors in mass concrete is analyzed. The experimental results indicate that the signal received by the BT–BFO/PVDF sensors is not easily affected by the internal temperature of mass concrete compared with that of the traditional PVDF piezoelectric sensors. The signal parameters sensitive to concrete strength variation and the change trend of concrete strength are closely related to the piezoelectric voltage. Therefore, the proposed approach using BT–BFO/PVDF nanocomposite piezoelectric sensors is efficient (error < 10%) in mass concrete monitoring. Moreover, the monitoring results do not need temperature compensation. The physical meaning of the obtained strength prediction formula is proposed. An experimental system based on PVDF dynamic strain-sensing characteristics is established. [ABSTRACT FROM AUTHOR]

The majority of the cell wall of a plant is composed of cellulose. Cellulose is an outstanding abundant, fibrous, and water-insoluble polymer on earth. The excellent hierarchical structure and semicrystalline nature of plant cellulose permit the easy isolation of nanofibers and nanocrystals through mechanically and chemically applied top-down destruction strategies. The cellulose molecules in nanocomposites can be separated into types such as bacterial nanocellulose (BNC), crystalline nanocellulose (CNC), and cellulose nanofibrils (CNF), which are biodegradable, environmentally friendly, and possess remarkably improved properties compared to conventional materials. Generally, they are deliberated as second-generation renewable resources, which assist as a superior replacement for petroleum-based materials. Research studies on nanocellulose are extensively accelerating due to petroleum-based materials issues like CO2 emissions, plastic based-pollution, and the absence of renewable energy. Research studies regarding these materials are interestingly increasing due to their outstanding properties such as biocompatibility, renewability, higher mechanical and lower density values, while sustainable production still associated with various challenges. Here, we comprehensively review the recent developments in nanocellulose production structural dimensions, properties, and applications, dedicated to drug delivery system, food industry, piezoelectric sensors, actuators, energy generators biosensing and bioimaging electronic devices. [ABSTRACT FROM AUTHOR]

Large piezoelectric voltage coefficient (g 33) and figure of merit (FOM 33) are the key parameters of perovskite ceramics for piezoelectric sensors and energy harvesters. Here, the Bi(Zn 2/3 Nb 1/3)O 3 (BZN) member with a low tolerance factor is introduced into the BiScO 3 -PbTiO 3 (BS-PT) perovskite high-temperature piezoelectric matrix to decouple the piezoelectric coefficient (d 33) and dielectric constant (ε r) by modulating the morphotropic phase boundary and grain size. For the optimal 0.38BS-0.01BZN-0.61PT ceramic that benefits from the decoupling of d 33 and ε r , its Curie temperature, g 33 and FOM 33 are as high as 436 °C, 38.6 mV·m·N−1 and 16.5×10−12 m2·N−1, respectively. Furthermore, the 0.38BS-0.01BZN-0.61PT ceramic also shows the technical advantages of large g 33 and FOM 33 even at harsh elevated temperatures (≥ 200 °C). Due to its outstanding comprehensive performances above, the 0.38BS-0.01BZN-0.61PT ceramic surpasses many other BS-PT-based piezoceramics. These results demonstrate that the 0.38BS-0.01BZN-0.61PT material is a promising competitor for high-temperature electromechanical coupling applications. • The BS-BZN-PT MPB ceramic has a high T C of 436 °C. • The variations of d 33 and ε r are decoupled in the BS-BZN-PT system. • The BS-BZN-PT MPB ceramic has a large g 33 of 38.6 mV·m·N−1. • The BS-BZN-PT MPB ceramic has a high FOM 33 of 16.5×10−12 m2·N−1. [ABSTRACT FROM AUTHOR]

Water insoluble polymeric materials with well‐oriented structures have attracted great attention in the area of membrane science, biological tissues, and organs, electromagnetic interference shielding device as well as piezoelectric/piezoresistive sensors due to its unique and essential functions originating from the anisotropic structures. Ice‐templating is a facile method to prepare directional porous materials with regulable pore size and cell thickness which is only applicable to aqueous systems. Derived from this methodology, crystallizable solvent templating methods have been utilized to architect water insoluble polymeric materials with anisotropic pores. This review is aimed to elaborate the fundamental principles of the critical factors that influence the physics involved in directional freezing of the particulate non‐aqueous systems. Solvent templates with low melting point and high melting point are discussed, which both allow the easy removal of crystallizable templates while keeping the aligned channels within the polymeric matrix intact. Last but not least, cryo‐polymerization and removal of water‐soluble polymers to obtain special forms of water‐insoluble polymer‐oriented pore materials are also included. This review provides prompt advancement and valuable information about the preparation and application of water insoluble polymeric materials with oriented structures using ice‐templating. [ABSTRACT FROM AUTHOR]

Given global water scarcity and the quest for sustainable energy, there's a pressing need for integrated approaches addressing water‐energy interdependence worldwide. A practical approach for this challenge involves the implementation of fog water collectors. Herein, a polyvinylidene fluoride (PVDF) multifunctional device capable of harvesting water and electricity from wind is developed and tested, collecting up to 365 mg cm−2 h−1 of fog water. Due to the piezoelectric nature of electrospun PVDF, these yarns and meshes not only serve as piezoelectric sensors, enabling the detection of incoming fog flow and determination of its speed and, bust also harvest electricity by charging a capacitor, making it a green and renewable power source. In this study, promising insights are offered into developing efficient fog water collection methods and utilizing piezoelectric fiber‐based yarns and meshes for multifunctional applications in sustainable water management, energy harvesting, and sensing in a single device. [ABSTRACT FROM AUTHOR]

Pipelines are an important transportation form in industry. However, pipeline corrosion, particularly that occurring internally, poses a significant threat to safe operations. To detect the internal corrosion of a pipeline, a method utilizing piezoelectric sensors alongside singular spectrum analysis is proposed. Two piezoelectric patches are affixed to the exterior surface of the pipeline, serving the roles of an actuator and a sensor, respectively. During the detection, the signals excited by the actuator are transmitted through the pipeline's wall and are received by PZT2 through different paths, and the corresponding piezoelectric sensor captures the signals. Then, the response signals are denoised by singular spectrum analysis, and the first several wave packets in the response signals are selected to establish a feature for pipeline corrosion detection. At last, the envelope area of the selected packets is calculated as a feature to detect corrosion. To validate the proposed method, corrosion monitoring experiments are performed. The experimental results indicate that the envelope area of the first several wave packets from the response signals, following singular spectrum analysis, can serve as a feature to assess the degree of pipeline corrosion, and the index has a monotonic relationship with the corrosion depth of the pipeline. This method provides an effective way for pipeline corrosion monitoring. [ABSTRACT FROM AUTHOR]

Advancing the development of high‐temperature piezoelectric sensors requires high‐performance piezoelectric materials with high Curie temperatures, wherein the charge signals can be efficiently collected at elevated temperatures. The bismuth layer‐structured ferroelectric (BLSF) bismuth titanate‐ferrite (Bi5Ti3FeO15, BTF) has recently attracted considerable attention because of its high Curie temperature (TC) of ∼761°C. However, the piezoelectric properties of BTF‐based compounds have not been extensively investigated because of their extremely poor piezoelectric performances and low electrical resistivities at elevated temperatures. Herein, tungsten‐substituted BTF (BTF‐100xW) ceramics were synthesized using a solid‐state reaction method. X‐ray diffraction refinement results confirmed the lattice distortion of the BO6 octahedron, while piezoelectric force microscopy images verified an increase in the domain wall density with tungsten modification, both of which contribute to significant enhancement of the piezoelectric properties of BTF‐100xW as intrinsic and extrinsic contributions, respectively. Remarkably, BTF‐3W exhibits a high TC of 793°C and a large piezoelectric constant (d33) of 24.3 pC/N, which is over three times that of BTF (7.1 pC/N). Importantly, the substitution of tungsten decreases the concentration of oxygen vacancies, increases the direct current electrical resistivity, and improves the electrical homogeneity at high temperatures, resulting in extremely stable piezoelectric and electromechanical properties at high temperatures, with a high in‐situ relative d33 of >90% at 400°C and a small variation in the electromechanical coupling factor (kp) of <8% at temperatures up to 450°C. These results suggest that the tungsten‐substituted BTF is a potential candidate for high‐temperature piezoelectric ceramics, and is a promising material for applications in high‐temperature piezoelectric sensors. [ABSTRACT FROM AUTHOR]

Self‐powered pressure detection using smart wearable devices is the subject of intense research attention, which is intended to address the critical need for prolonged and uninterrupted operations. Current piezoelectric and triboelectric sensors well respond to dynamic stimuli while overlooking static stimuli. This study proposes a dual‐response potentiometric pressure sensor that responds to both dynamic and static stimuli. The proposed sensor utilizes interdigital electrodes with MnO2/carbon/polyvinyl alcohol (PVA) as the cathode and conductive silver paste as the anode. The electrolyte layer incorporates a mixed hydrogel of PVA and phosphoric acid. The optimized interdigital electrodes and sandpaper‐like microstructured surface of the hydrogel electrolyte contribute to enhanced performance by facilitating an increased contact area between the electrolyte and electrodes. The sensor features an open‐circuit voltage of 0.927 V, a short‐circuit current of 6 µA, a higher sensitivity of 14 mV/kPa, and outstanding cycling performance (>5000 cycles). It can accurately recognize letter writing and enable capacitor charging and LED lighting. Additionally, a data acquisition and display system employing the proposed sensor, which facilitates the monitoring of athletes' rehabilitation training, and machine learning algorithms that effectively guide rehabilitation actions are presented. This study offers novel solutions for the future development of smart wearable devices. [ABSTRACT FROM AUTHOR]

High-temperature piezoelectric vibration sensors play a crucial role in the accurate monitoring of the dynamic mechanical conditions in aerospace, automotive, and energy generation systems. However, the use of conventional piezoelectric materials in high-temperature environments is restricted owing to their limited Curie temperatures. In this study, we grew a piezoelectric crystal Bi12SiO20 (BSO) with the crystal cut optimized for high longitudinal piezoelectric coefficient and low piezoelectric crosstalk behaviors. Subsequently, a compression-type piezoelectric vibration sensor utilizing the BSO bulk crystal was developed and fabricated for structural health monitoring under high temperatures. The impact of pre-tightening torques on the sensor performance was investigated. Moreover, the sensor performance was analyzed under temperatures up to 650 °C. The BSO-based sensor exhibited an average sensitivity of ∼3.89 pC/g between 25 and 650 °C under 160 Hz frequency, with a variation of 5.5%. Additionally, the BSO-based sensor demonstrated ultra-stable sensitivity at 600 °C, highlighting its strong sensing capabilities and reliability under high temperatures. Thus, the BSO-based vibration sensor is a promising option for structural health monitoring applications under high temperatures. [ABSTRACT FROM AUTHOR]

Composite pressure vessels are seeing increasing demand in the oil and gas sector due to their excellent corrosion resistance. However, the assessment of the fatigue state of those structures still an open question. The goal of this work is use elastic wave data to access the fatigue damage (exudation). The Dynamic Time Warping method is proposed as a means of extracting features from guided wave ultrasound data that can describe the on-going fatigue induced damage of glass-fibre reinforced plastic pipes under fatigue-cycle loading. To test its efficiency, three pipe samples were fatigue tested to failure under internal pressure cycles with maximum values of 45 bar, 55 bar and 65 bar, and minimum pressures equal to 10% of the maximum, at a frequency of 0.8 Hz. A Guided Wave monitoring system consisting of a set of permanently attached piezoelectric sensors produced signals which were processed to obtain the Dynamic Time Warping distance, that was then used to obtain a Damage Index that expresses the cumulative fatigue damage suffered by the samples for each loading level. These results were comparable to data obtained from surface-mounted strain-gauges, even though temperature variations of up to 20 °C occurred during the tests and no direct temperature compensation was applied to the GW signals. The Dynamic Time Warping distance presents smaller influence of temperature and was able to better access the exudation of the samples. [ABSTRACT FROM AUTHOR]

Minuscule pressure/stress detection with high sensitivity can recognize and deal with potential hazards timely, which is crucial for guaranteeing the security of human and stability of social functioning. Lithium niobate (LiNbO 3) single crystal possessing excellent piezoelectric and ferroelectric properties is suitable for fabricating piezoelectric pressure sensors. Therefore, in this paper, the pressure sensors based on LiNbO 3 single crystals with parallel connected structure were researched. Sensors with parallel connected structure can improve the sensitivity from 4.86 V/N of single sheet structure to 8.71 V/N under the stress between 0.01 N and 0.2 N at 30 °C. Both types of the sensors can detect the minuscule stress low to 0.01 N and minuscule pressure generated by balloon pump, blowing largely or slowly. The influence of temperature on sensors was also researched, and the results exhibited that sensors performed well from 30 °C to 60 °C and still sustained high sensitivity of 5.26 V/N of parallel connected structure and 3.71 V/N of single sheet structure at 60 °C. Besides, the response time of sensors to the pressure of balloon pump is 60 ms under different temperature. These excellent properties indicate the great potential applications of fabricated sensors in practical minuscule pressure/stress detection. [ABSTRACT FROM AUTHOR]

The vibration energy of the track slab can be converted into electric energy for wireless sensors by piezoelectric energy harvesters. A track laminated circular plate harvester (TLCP harvester) is designed in this paper based on foundation excitation. The central frequency of the harvester is 222 Hz, which is matched with the 222.8 Hz of the track slab. The stiffness curve, damping, equivalent capacitance, and electromechanical coupling coefficient of the harvester are obtained through the experiment. The harmonic balance method and Runge–Kutta's voltage results are consistent with the experimental results. The frequency responses verify the jump phenomenon and soft characteristics. The experiment results show that the maximum output power is 8.07 mW under 7 kΩ load resistance, and the maximum RMS power is 0.3804 mW under 5 kΩ load resistance. This paper develops a safe and high-efficiency piezoelectric energy harvester for track slabs. [ABSTRACT FROM AUTHOR]

Predictive maintenance (PM) is a data-driven approach to performing proactive maintenance by analyzing the condition of the equipment in any industrial setting. The high-precision sensors are widely adapted to meticulously analyze critical maintenance conditions using such a datadriven approach. In a similar context, a fiber brag grating (FBG) sensor is a passive and high-precision sensor that is widely used in industries where conventional sensors are not preferred. Broadly, this article presents four sub elements of the proposed integrated system such as the design of the sensor element, signal processing scheme (SPS), machine learning (ML) model for predicting anomalies, and decision support system (DSS) to suggest maintenance actions. Also, this article highlights an experimental case study on vibration monitoring and analysis of real-time signals for making proactive maintenance decisions. An FBG vibration sensor of center wavelength 1,550 nm is designed and utilized to acquire real-time vibration signatures of a rotating machine under test. A piezoelectric vibration sensor is used with the FBG sensor to compare the vibration response obtained during the test. Pre-processing of raw signals is performed using a moving average filter (MAV) followed by a low pass filter to nullify the effect of noise. To obtain proactive maintenance decisions, a DSS model is prepared by considering the processed vibration signatures. Various maintenance conditions are tested during the experimental analysis and detailed results analysis are presented. [ABSTRACT FROM AUTHOR]

Ballistocardiography (BCG) studies ballistic forces on the body generated during a heartbeat. As it is an unobtrusive detection method, that requires sensors measuring small dynamic forces. Piezoelectric sensors are ideal, but improvements in sensitivity are needed. Here, a universal method is demonstrated to obtain enhanced effective transverse charge constants by utilizing thin and long sensors fabricated upon compliant substrates. This approach is validated using the uniquely printable and patternable piezoelectric polymer, poly(vinylidene fluoride‐co‐trifluoroethylene) (P(VDF‐TrFE). Discrete sensors detect displacements of less than 1 µm, dynamic forces of ∼mN, and accelerations of ≈1 mm−1 s2. Since the sensor is screen‐printable, it is upscaled to a human‐sized array (60 × 90 cm, 255 sensors). High quality spatially resolved BCG measurements of a person is demonstrated in seated and supine positions. The obtained heart rate is verified using photoplethysmography. This development opens the door to ever‐more sensitive piezoelectric sensors, crucial for applications including and beyond healthcare. [ABSTRACT FROM AUTHOR]

Interest in flexible photonics has been motivated by the development of artificial smart skins. In particular, coupling of photonics and mechanics can offer opportunities to realize ultrasensitive strain sensor, however, low‐cost fabrication of flexible sensing device with desired photonic functionality remains a challenge. Hereby, the study reports an ultrasensitive strain‐gauge sensor based on the poly(ethylenenaphthalate (PEN))/monocrystal Au/MgF2/CsPbBr3 nanorod/Al2O3/polyacrylonitrile (in short P/mAu/M/CPB@Al2O3@PAN), which are sensitive to nanoscale structure alterations of PEN substrate via the stress response of the single‐mode laser based on the piezoelectric‐effect. Wherein a low‐threshold single‐mode lasing (Pth ≈ 170 nJ cm−2) is achieved through coating Al2O3 on the CsPbBr3 nanorod, producing the higher quality factor (Q ≈ 1637) to guarantee a much higher sensitivity in sensing application. Reversible spectral regulating of ≈3 nm in single‐mode‐lasing wavelength, with a subnanometre scale resolution <0.4 nm and the wavelength sensitivity (Sλ) as high as 160 nm RIU−1, is validated in response to applied strain ranging from −1.31% to 1.31%. This work not only represents essential progress in construction of ultrasensitive and cost‐effective flexible photonic sensor, but also lays the foundation for the potential application in smart photonic skins. [ABSTRACT FROM AUTHOR]

With the increasing application of electrospun PVDF webs in piezoelectric sensors and energy-harvesting devices, it is crucial to understand their responses under complex mechanical excitations. However, the dependence of the piezoelectric effect on mechanical excitation properties is not fully comprehended. This study aims to investigate the piezoelectric output of randomly oriented electrospun PVDF nanofiber webs fabricated through different electrospinning processes at various mechanical excitation frequencies. The electrospun PVDF web was sandwiched between two textile electrodes, and its piezoelectric output as a full-textile sensor was measured across a frequency range from 0.1 Hz to 10 Hz. The experimental results revealed that the piezoelectric output of the electrospun PVDF web exhibited a nearly linear increase at excitation frequencies below 1.0 Hz and then reached an almost constant value thereafter up to 10 Hz, which is different from the hybrid PVDF or its copolymer web. Furthermore, the dependency of the piezoelectric output on the excitation frequency was found to be influenced by the specific electrospinning process employed, which determined the crystalline structure of electrospun PVDF nanofibers. These findings suggest that determining an appropriate working frequency for randomly oriented electrospun PVDF nanofiber webs is essential before practical implementation, and the piezoelectric response mode in different mechanical activation frequency ranges can be used to detect different human physiological behaviors. [ABSTRACT FROM AUTHOR]

The impact resistance of layered polymer structures using polyvinyl butyral (PVB) in combination with Kevlar® fabric and ultra-high molecular weight polyethylene (UHMWPE) were fabricated and tested. Methods of wet impregnation and hot-press impregnation and consolidation of fabric with PVB and UHMWPE were used to manufacture multilayer constructs. All sandwich constructs were fixed to the surface of ballistic clay and subject to a free drop-weight test with a conical impactor having a small contact area. All tests were made at the same impact energy of 9.3 J and velocity of 2.85 m/s. The change in the resistance force was recorded using a piezoelectric force sensor at the time intervals of 40 μs. Using experimental force–time history, the change in the impactor's velocity, the depth of impactor penetration, the energy transformation at various stages of impactor interaction with the sample, and other parameters were obtained. Three indicators were considered as the main criteria for the effectiveness of a sample's resistance to impact: (1) minimum deformation, bulging, of the panel backside at the moment of impact, (2) minimum absorption of impact energy per areal density, and (3) minimal or, better yet, no destruction of structural integrity. Under the tested conditions, the rigid Kevlar–PVB–Kevlar sandwich at the frontside and relatively soft but flexible UHMWPE–Kevlar–UHMWPE layers in the middle helped to localize and absorb impact energy, while the backside Kevlar–PVB–Kevlar sandwich minimized local bulging providing the best overall performance. The front layer damage area was very shallow and less than two impactor tip diameters. The backside bulging was also less than in any other tested configurations. [ABSTRACT FROM AUTHOR]

Self-powered wearable pressure sensors based on flexible electronics have emerged as a new trend due to the increasing demand for intelligent and portable devices. Improvements in pressure-sensing performance, including in the output voltage, sensitivity and response time, can greatly expand their related applications; however, this remains challenging. Here, we report on a highly sensitive piezoelectric sensor with novel light-boosting pressure-sensing performance, based on a composite membrane of copper phthalocyanine (CuPC) and graphene oxide (GO) (CuPC@GO). Under light illumination, the CuPC@GO piezoelectric sensor demonstrates a remarkable increase in output voltage (381.17 mV, 50 kPa) and sensitivity (116.80 mV/kPa, <5 kPa), which are approximately twice and three times of that the sensor without light illumination, respectively. Furthermore, light exposure significantly improves the response speed of the sensor with a response time of 38.04 µs and recovery time of 58.48 µs, while maintaining excellent mechanical stability even after 2000 cycles. Density functional theory calculations reveal that increased electron transfer from graphene to CuPC can occur when the CuPC is in the excited state, which indicates that the light illumination promotes the electron excitation of CuPC, and thus brings about the high polarization of the sensor. Importantly, these sensors exhibit universal spatial non-contact adjustability, highlighting their versatility and applicability in various settings. [ABSTRACT FROM AUTHOR]

[Display omitted] Flexible sensors and actuators are the basis for realizing the Internet of Everything. This study identifies specific interfacial polarization and filler dispersion challenges in flexible sensors. A novel sandwich-structured flexible sensor with polydimethylsiloxane (PDMS)-filled Nb 2 CT x as the interlayer and poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)]-filled barium titanate (BTO) as the upper and lower layers was designed and fabricated. The thickness of the interlayer was optimized to be 6.2 μm, resulting in an ultrahigh sensitivity of 16.05 V/N and ultrashort response time of 626 μs. The interlayer achieved an oriented arrangement of the dipoles in the upper and lower piezoelectric films through interfacial polarization, enhancing the piezoelectric output and sensitivity. The proposed mechanism was confirmed by the dielectric properties, local piezoelectric response, cross-sectional potential simulation, and interfacial electrical calculations. Additionally, the sensor effectively distinguishes various body movements, facial micro-expressions, and throat vibrations during vocalization, and can be applied to ultrahigh-sensitive self-powered flexible piezoelectric pressure sensors. [ABSTRACT FROM AUTHOR]

Cough is a common symptom of various respiratory diseases. However, recognizing a subject's cough using acoustic imaging can be challenging due to the complexity of coughing and the vulnerability of acoustic acquisition to external interference. This research aims to address these issues by utilizing a flexible piezoelectric ionic liquid‐doped poly(L‐lactic acid) (PLLA) sensor to gather the pressure signals from the human surface. 1‐butyl‐3‐methylimidazolium bis (trifluoromethylsulfonyl)imide ([BMIm]TFSI) ionic liquid (IL) can enhance the piezoelectric performance of PLLA thin film, the corresponding output voltage, and impact sensitivity are improved to three times and 105.1% for the PLLA/IL thin film with 1 wt% IL, 140 °C annealing 2 h and four times drawing ratio. The effect of IL on the crystallization behavior and piezoelectric properties of thin films during their preparation is investigated. The flexible PLLA/IL sensor is integrated into a wearable electronic system which collects and transmits piezoelectric signals from cough‐induced vibrations to the filter for denoising, then the acquired cough data are decomposed using the Empirical Mode Decomposition method and trained in a multi‐layer perception model to detect human coughing. It's evident that the flexible piezoelectric PLLA/IL sensors can be applied to human coughing recognition and show great potential applications in intelligent healthcare. [ABSTRACT FROM AUTHOR]

Sarcopenia recognition is very crucial in the early diagnosis of sarcopenia. However, the commonly used screening methods are limited by real‐time property, portability, and convenient usability at home. Herein, an electrospun BaTiO3 film is proposed and a piezoelectric sensor with silver electrodes and polyimide substrates is fabricated. The sensor exhibits high piezoelectricity (74.2 pC N−1), sensitivity, linearity, low detection limit (0.2 mN), and significant bending ability (bending angle can exceed 90°), maintaining stable output after more than 20 000 cycles during a week. Due to its excellent performance, the piezoelectric sensor to the recognition of sarcopenia is applied and a wearable system to collect piezoelectric signals from the lower limb movements of the elderly is developed. By selecting features from these signals, eight kinds of machine learning models are employed and their performances in recognizing sarcopenia are compared in both male and female groups. The results indicate that the artificial neural network (ANN) model has the highest performance, with accuracies of 92.9% in males and 98.1% in females. This piezoelectric sensor, combined with a wireless communication module, is expected to provide crucial evidence for sarcopenia detection, offering a new, convenient, and household screening solution for early diagnosis and prevention of sarcopenia. [ABSTRACT FROM AUTHOR]

Flexible piezoelectric devices have attracted much attention in the fields of intelligent devices and biomedicine because of their high sensitivity, stability, and flexibility. In this paper, a multifunctional flexible pressure sensor was prepared by adding polyacrylonitrile (PAN) and carboxylic-terminated multi-walled carbon nanotubes (c-MWCNTs) with polyvinylidene difluoride (PVDF) as the substrate. The β -phase content of PVDF/PAN blended fibers compounded with c-MWCNT was up to 95%. At the same time, when PAN was added, the mechanical properties of the composite fibers were constantly improved. The results show that the polymer blending method can improve the comprehensive properties of PVDF composite. The flexible sensor prepared from the PVDF/PAN/c-MWCNT composite film has an output voltage of 2.1 V and a current of 7 μ A. The addition of c-MWCNT can largely improve the sensitivity of the sensor (4.19 V N−1). The sensor is attached to the finger and shows good output performance under different degrees of bending of the finger. The maximum output voltage of the sensor is 0.4 V, 0.56 V and 1.15 V when the finger bending angle is 30°, 60°, and 90°, respectively. Moreover, the developed piezoelectric sensor can monitor large-scale movements of various parts of the human body. Therefore, this composite material shows potential in areas such as motion monitoring and energy storage devices. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]