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In this study, a piezoelectric nanogenerator (PENG) based on multilayer composite fiber had good and stable piezoelectric output performance, which could realize biomechanical energy collection and human movement monitoring. The polyvinylidene fluoride‐hexafluoryl propylene (P(VDF‐HFP)) composite fiber doped with MXene was used as a promising piezoelectric functional layer (MPFP). By electrospinning, P(VDF‐HFP) composite fiber was constructed by alternating electrospinning with polyurethane (TPU) nanofibers layer by layer. The adoption of MXene as a functional filler promoted the transformation of P(VDF‐HFP) from α to piezoelectric β‐crystal, the piezoelectric β‐crystal content of P(VDF‐HFP) increased, and the dielectric properties and polarization levels were enhanced. At the same time, the multi‐layer structure design improved the piezoelectric sensitivity and mechanical properties of the composite fiber, and the composite fiber was more flexible and had longer tensile strain. With excellent dielectric and mechanical properties, 3MPFP/TPU/3MPFP/TPU multilayer composite fibers showed piezoelectric sensitivity of 10.88 V/kPa. Under the action of palm pressing, the PENG generated an open circuit voltage of 25 V, and the voltage signal of the device under different motion forms had specific characteristics such as peak value, frequency, and shape, which could be used to realize the analysis of human motion forms. This study provided an efficient, simple, and creative new idea for the application of flexible energy storage electronic devices, PENGs, and piezoelectric sensors. [ABSTRACT FROM AUTHOR]

In recent years, the convergence of smart electronic textile (e‐textile) and digital technology has emerged as a transformative shift in healthcare, offering innovative solutions for point‐of‐care diagnostics. However, the development of textile electronics with exceptional functionality and comfort still remains challenging. Here, all‐electrospun piezoelectric smart e‐textile empowered is reported by Internet of Things (IoT) and machine learning for advanced point‐of‐care diagnostics. The resulting e‐textile exhibits exceptional breathability (b ≈ 4.13 kg m−2 d−1), flexibility, water‐resistive properties (water contact angle ≈137°), and mechano‐sensitivity of 1.5 V N−1 due to its mechanical‐to‐electrical energy conversion abilities. It can efficiently monitor different critical biomedical healthcare signals, such as, arterial pulse and respiration rate. Importantly, the e‐textile sensor demonstrates remarkable attributes, generating an open circuit voltage of 10.5 V, a short circuit current of 7.7 µA, and power density of 4.2 µW cm−2. Moreover, the e‐textile provides real‐time, non‐invasive monitoring of human physiological movements through IoT. It is worth highlighting that the machine learning showcases an impressive 96% of accuracy in detecting respiratory signals, representing a significant accomplishment. Thus, this e‐textile has enormous potential in remote patient monitoring and early disease detection, aiming to reduce healthcare costs, enhance patient outcomes, and improve the overall quality of medical care. [ABSTRACT FROM AUTHOR]

The sense of touch and perception of hand motion form an essential part of the somatic sensory system. Although piezoelectric sensors demonstrate high sensitivity and linearity, they are traditionally not employed for electronic skins because of their limited stretchability. Here, a printed, skin‐conformal, electronic system consisting of stretchable piezoelectric pressure sensors and carbon nanotube strain gauges capable of identifying tactile sensations and joint movements on the hand is introduced. The pressure sensor demonstrates both high sensitivity (19.9 mV kPa−1) and linearity (0.1–1000 kPa) while being reliably stretchable to above 15%. To complement the pressure sensing functionality, a strain gauge is fabricated in a rapid stamp printing process and designed to demonstrate excellent mechanical reliability with up to 70% strain and high sensitivity (36.5‐gauge factor). These sensors can seamlessly conform to numerous anatomical regions and cover wide areas of the skin, making them ideal for deployment in an electronic skin. Finally, the sensors are integrated with a flexible microelectronic device to demonstrate their functionality in human touch and prosthetic hand applications. [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]

Vascular grafts, widely utilized in managing cardiovascular diseases (CVD), are susceptible to postoperative complications. Recent strides in intelligent vascular grafts leveraging flexible bioelectronics enable hemodynamic and vascular health monitoring. However, their practical application faces challenges, notably biomechanical compatibility and endothelialization. Here, an all‐in‐one piezoelectric vascular graft (PVG) constructed by encapsulating a polyvinylidene fluoride (PVDF) nanofiber mat with patterned silver nanowire (AgNW) electrodes between two layers of polycaprolactone (PCL) nanofiber mats is presented. The meticulously optimized PVG, featuring PVDF and PCL nanofibers with average diameters of ≈950 and 250 nm, respectively, showcases remarkable endothelialization and mechanical performance akin to native blood vessels. The exquisite piezoelectric properties of PVDF nanofibers imbue PVG with outstanding mechanical sensing capabilities, boasting a sensitivity of 11 mV kPa−1 and stability exceeding 50 000 cycles, facilitating precise hemodynamic monitoring. Notably, artificial artery model tests demonstrate PVG's ability to diagnose vascular health status accurately based on detected hemodynamic data. Furthermore, the developed PVG exhibits nontoxicity, good hemocompatibility (hemolytic ratio < 1%), and histocompatibility. This pioneering technology, validated through ex vivo and in vivo experiments, represents a significant stride in precise vascular health management, unlocking diverse potential applications. [ABSTRACT FROM AUTHOR]

Summary Little is known about the correlation between subjective perception and objective measures of sleep quality in particular in the oldest‐old. The aim of this study was to perform longitudinal home sleep monitoring in this age group, and to correlate results with self‐reported sleep quality. This is a prospective longitudinal home sleep‐monitoring study in 12 oldest‐old persons (age 83–100 years, mean 93 years, 10 females) without serious sleep disorders over 1 month using a contactless piezoelectric bed sensor (EMFIT QS). Participants provided daily information about perceived sleep. Duration in bed: 264–639 min (M = 476 min, SD = 94 min); sleep duration: 239–561 min (M = 418 min, SD = 91 min); sleep efficiency: 83.9%–90.7% (M = 87.4%, SD = 5.0%); rapid eye movement sleep: 21.1%–29.0% (M = 24.9%, SD = 5.5%); deep sleep: 13.3%–19.6% (M = 16.8%, SD = 4.5%). All but one participant showed a weak (r = 0.2–0.39) or very weak (r = 0–0.19) positive or negative correlation between self‐rated sleep quality and the sleep score. In conclusion, longitudinal sleep monitoring in the home of elderly people by a contactless piezoelectric sensor system is feasible and well accepted. Subjective perception of sleep quality does not correlate well with objective measures in our study. Our findings may help to develop new approaches to sleep problems in the oldest‐old including home monitoring. Further studies are needed to explore the full potential of this approach. [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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

Employing density functional theory within the Wien2k code, first‐principle calculations are conducted to explore the impact of applied pressure up to 80 GPa on the structural, mechanical, thermal, and electronic characteristics of BaPbO3. Demonstrating metallic behavior with ductile attributes, BaPbO3 exhibits a decreasing anisotropic nature under escalating pressure. Evaluation of cubic elastic constants, optimization curves, and enthalpy of formation indicates the compound's mechanical and thermodynamic stability under high pressure conditions. Calculated values of C11 and C44 reflect heightened resistance to unidirectional compression and increased stiffness under pressure. These mechanical properties position BaPbO3 as a promising candidate for diverse industrial applications across varying pressure ranges, including utilization in piezoelectric materials (0–20 GPa) and high‐pressure sensors. Additionally, charge density contours suggest a combination of ionic (Ba─Pb) and covalent bonding (Pb─O) within the compound's constituent atoms. The material can exhibit potential applications as a piezoelectric sensor at 0–20 GPa, high‐pressure actuators ≈20 GPa, and as a high melting temperature resistive substrate for laser welding and cutting materials. [ABSTRACT FROM AUTHOR]

Electromechanically converted piezoelectric materials have great applications in actuators, sensors, and energy harvesters. Organic piezoelectric materials are environmentally friendly, easy to prepare, and have a low molecular mass compared to conventional inorganic piezoelectric materials. Here, we present an organic hydrogen bonding piezoelectric material, lamivudine hydrate, which crystallized in the P21 space group at room temperature and exhibits a decent d33 value of 21 pC N−1. This value is comparable to that of the commercial piezoelectric material, Tri‐Glycine Sulfate (TGS, d33=22 pC N−1). Moreover, lamivudine hydrate possesses a superior g33 value of 826×10−3 V m N−1, which is much higher than that of commercial TGS and most of the piezoelectric ceramics. While the lamivudine crystal was refined in the P43212 space group, showing no piezoelectric activity. The presence of crystalline water plays a crucial role in establishing its polar structure and achieving high piezoelectric properties of lamivudine hydrate crystal. The decent d33 and g33 values make it a promising candidate for advanced materials in high‐performance piezoelectric sensors, particularly in applications involving flexible, wearable, and biomechanical devices. [ABSTRACT FROM AUTHOR]

With increasing concerns about noise pollution, the pursuit of highly dependable piezoelectric acoustic sensors for real‐time noise monitoring has come to the forefront of scientific research. Lead‐based perovskite piezoelectric films, exemplified by lead zirconate titanate Pb(Zr,Ti)O3 (PZT), surpass traditional piezoelectric materials such as ZnO and AlN in their piezoelectric properties, promising substantial advancements in next‐generation acoustic sensor technologies. However, the toxic nature of lead in PZT materials poses formidable environmental and human health risks. In an unprecedented breakthrough, it presents the pioneering development of an environmentally benign lead‐free piezoelectric Micro‐Electro‐Mechanical System (MEMS) acoustic sensor based on potassium sodium niobate (K,Na)NbO3 (KNN) film. High‐quality <001> textured 3 µm‐thick KNN film is successfully integrated into commercially used Si substrate, rendering exceptional piezoelectricity (transverse piezoelectric coefficients e31* of ≈8.5 C m−2) with satisfactory thermal stability. The atomic‐scale Z‐contrast imaging and piezoresponse force microscopy characterizations reveal that the outstanding piezoresponse originates from the local coexistence of multiple phases and the enhancement of extrinsic piezoelectric contributions from in‐plane polarization anisotropy. Finite element simulation is employed to design the triangular cantilever structure and annular diaphragm structure, each corresponding to different operating bandwidths. The resultant MEMS acoustic sensors stand out with outstanding acoustic performance (the high sensitivity and expansive receiving field of view), which are attributed to the microstructural engineering at multi‐length scales for the excellent piezoelectric properties of KNN film. These features enable sensitive acoustic monitoring in various environments, including large‐scale power grids and urban traffic. [ABSTRACT FROM AUTHOR]

Flexible piezoelectric sensors combine advantages including low‐cost, flexibility, multi‐functions, present a huge market prospect. In this research, multiwalled carbon nanotubes (MWCNT)/MXene/polyacrylonitrile (PAN) piezoelectric composites films for flexible piezoelectric sensors are fabricated by electrospinning technology, the planar zigzag conformation content of 97.98% in PAN composite fibers is achieved owing to the synergistic effect of MWCNT and MXene, the synergistic effect of MWCNT and MXene nanoparticles can also efficiently promote the mechanical performance and piezoelectric output. The piezoelectric sensor exhibits fast response time (10.21 ms), a possible mechanism is proposed to explain the improvement of piezoelectric effect. The sensor can measure human pulse, distinguish human movements, the fabricated sensor has broad practical value in the field of healthcare, its' use can contribute to stable and accurate measurements of physiological parameters, enabling applications in various healthcare and fitness monitoring scenarios. [ABSTRACT FROM AUTHOR]

Flexible piezoelectric sensors have been spotlighted as an essential human–machine interface (HMI) by obtaining high‐quality data from omnipresent biomechanical inputs. Because human voice is the most intuitive bio‐signal among them, flexible piezoelectric acoustic sensors (f‐PAS) have a potential to shift the paradigm of HMI technologies. Despite the reported outstanding performance such as high sensitivity and speaker recognition accuracy, the theoretical investigation of f‐PAS has been insufficient to realize future customized development, because sensing principles are fundamentally different from commercialized microphones. Here, a theoretical framework of self‐powered f‐PAS by using mechanical and electrical physics is introduced. First of all, the basic theory of f‐PAS is compared with the auditory system of human cochlear. Based on the biomimetic trapezoidal shape, the resonant frequencies are analyzed with various structural and material conditions. In addition, the piezoelectricity of f‐PAS is derived to predict the sensitivity and SNR prior to experiments. To investigate sensor properties under the medium condition that is similar to human ear, the acoustic responses depending on the states of matter are theoretically compared. Finally, the distance limit of f‐PAS is studied with the correlations between piezoelectricity and sound pressure, which would provide novel strategies of functional material design for future applications of f‐PAS. [ABSTRACT FROM AUTHOR]

This study multifunctional wearable bioelectronics (MWBs) integrated with a piezoelectric sensor and a micropatterned temperature sensor for accurate detection of human physiological signals. Piezoelectric nanocomposite uniformity, stretchability, and adhesion is improved through the functionalization of nanoparticles with glycidyl silane and nonionic surfactants dispersion in the organic polymer matrix. Additionally, crack‐free nanometal layers are deposited on the nanocomposite interface with high adhesion by thiol silane functionalization and oxygen plasma treatment. The MWBs exhibit a temperature sensitivity of 7.1 Ω °C−1 (R2 of 0.999) between 30 °C to 40 °C, a pressure sensitivity of 72 mV kPa−1 (R2 of 0.998) within 0.5 kPa to 10 kPa, and a stable mechanical durability. MWBs have demonstrated to detect subtle pulse waveforms at an arm‐mimicking phantom and human skin, respectively. Furthermore, MWBs are applied to analyze physiological signal characteristics caused by human stress, demonstrating its potential for use in healthcare electronics in various medical applications. [ABSTRACT FROM AUTHOR]

Advanced transducer materials have become increasingly important with the rapid development of the internet of things and flexible electronics. Herein, fully transparent flexible polyvinylidene fluoride/polydimethylsiloxane (PVDF/PDMS) composite piezoelectric films are fabricated using scrape coating techniques based on electrospun PVDF nanofiber films. Compared to the electrospun PVDF, the PVDF/PDMS not only owns high transparency and a more uniform and stable structure but also has superior piezoelectric properties. Based on the electrospun PVDF and the PVDF/PDMS films, flexible piezoelectric sensors are developed, which can effectively detect weak mechanical signals including finger tapping and bending signals, radial artery pulses, and environmental sound signals. The PVDF/PDMS sensor performs better than the electrospun PVDF sensor and presents great potential for applications in flexible sensors and transducers. Especially, thanks to their high transparency, the PVDF/PDMS composite piezoelectric films lend themselves easily to application fields requiring transparent sensors such as imperceptible sensors and human‐machine interfaces, display devices, electronic skins, intelligent windows, etc. [ABSTRACT FROM AUTHOR]

Finding damages and their prevalence in structures is a very challenging problem. In order to identify potential structural damage, non‐destructive methods are not very helpful. One of the most popular piezoelectric ceramic materials used worldwide is macromolecular lead zirconate titanate (PZT), also known as Pb[Zr(x)Ti(1‐x)]O3. PZT transducers are proving to be a successful alternative for assessing the structure's health. The Macro‐molecular PZT's self‐actuating and sensing properties are utilized by the electromechanical impedance (EMI) method. In this capacity, the macro‐molecular PZT patches serve as co‐located actuators and sensors and make use of ultrasonic vibrations to produce a distinctive admittance "signature" of the structure. PZT patches perform exceptionally well in terms of damage sensitivity. The higher modes of vibration are locally activated by the local application of an AC source on the PZT transducers attached to the host structure. The alteration of the admittance response is a sign of injury to the transducer's vicinity. In the current study, the damage percentage and its location in a 150 × 150 × 150 mm concrete cube are being examined. Regression analysis is also used to determine the concrete cube's strength. This method also can identify hair‐like cracks at an early stage, which explains how it can shield the building from serious failures. [ABSTRACT FROM AUTHOR]

The biosafety and sustainability of inorganic perovskites or organic piezopolymers is a major concern in the field of wearable piezoelectric sensors. Naturally occurring, silk fibroin (SF), is a promising alternative for the realization of organic piezoelectric devices due to its excellent biocompatibility and tunable material properties. Nevertheless, its scope for practical sensing applications is limited by the weak innate piezoelectricity of 1 pC N−1. This research aims to improve the piezoelectricity of pristine SF by intrinsically growing non‐toxic metal‐free perovskite (MFP) to achieve organic and bendable silk fibroin‐metal free perovskite (SF‐MFP) composite films. The increase in MFP loading has an influence on the resulting morphology and crystallinity of SF‐MFP films. In comparison to pristine SF, the films with the highest perovskite loading exhibit an enhanced normal piezoelectric response of 4.6 pm V−1. The poled SF‐MFP sensors display an appreciable sensitivity of 0.61 ± 0.05 V N−1 with a fast response time and outstanding stability arising from a synergistic combination of mechanically robust SF and piezoelectric MFP. Furthermore, these sensors can detect various joint bending and muscle movements in human subjects, proving their suitability for wearable bioelectronics. This research demonstrates the potential of biomaterials and organic perovskites for the development of biocompatible and sustainable wearable piezoelectric solutions. [ABSTRACT FROM AUTHOR]

The global overabundance of electronic waste and ever‐increasing concerns regarding the energy‐and material‐intensive manufacturing processes associated with traditional electronics are driving the development of solution‐processed, degradable electronics. Of note, the industry‐dominating prevalence of harmful lead‐based materials in sensing and actuating devices drives the push for more eco‐friendly solution‐processed piezoelectric systems. Yet current ecofriendly multi‐material printing processes are limited by both the conventional challenges of multilayer processes as well as the low‐temperature thermal constraints of biodegradable materials. Herein, a novel approach for fabricating fully printed, sustainable piezoelectric transducers on paper substrates is presented. Low‐temperature screen‐printing processes are used to integrate non‐toxic KNbO3 layers with degradable carbon‐ or zinc‐based conductive inks into devices. The influence of electrode material on device characteristics is assessed, with effective piezoelectric coefficients reported as high as 4.6 pC N−1 and 5.1 pC N−1 for devices with carbon and zinc electrodes respectively. The potential of the developed technology is then demonstrated through the first‐ever instance of fully printed piezoelectric force sensors and acoustic speakers comprised entirely of green materials. By demonstrating entirely printable green piezoelectric devices compatible with various electrode materials, this work serves as a step towards developing more complex sustainable piezoelectric technologies in the future. [ABSTRACT FROM AUTHOR]

Hard piezoelectric properties are investigated in lead‐free BiFeO3–BaTiO3 (BF–BT) ceramics. Rhombohedral (R) phase ceramics of (1 – x)BF–xBT (x = 0.20–0.30) were prepared using a conventional solid‐state reaction and water‐quenching process. The R structure is observed in x = 0.20–0.275, and the R and tetragonal phases coexist at x = 0.30. The piezoelectric charge sensor coefficient (d33) and electromechanical planar coupling factor (kp) increase with increasing BT content, whereas the mechanical quality factor (Qm) decreases. The x = 0.20 ceramic shows the best hard piezoelectric properties: the highest Qm = 403 and the highest TC = 607°C. In contrast, x = 0.30 ceramic shows soft piezoelectric properties: d33 = 301 pC/N and kp = 0.33 with TC = 510°C. These results show that the BF–BT system in R‐phase‐rich region has good hard piezoelectric properties for transducer applications. [ABSTRACT FROM AUTHOR]

The successful fabrication and application of 3D‐printed piezoelectric sensors, made from polyvinylidene fluoride‐barium titanate nanocomposites, for continuous blood pressure (BP) monitoring, is presented. The sensors are fabricated using direct‐ink write 3D printing technique possessing excellent flexibility, rendering them ideal for wearable applications. Key printing parameters, such as nozzle size and pressure, are optimized to achieve a β‐phase of 70% and an overall crystallinity of 48.3%. The sensors are characterized under dynamic pressures and show excellent linearity with a coefficient of determination (R2) of 0.99 and a pressure sensitivity of 0.024 V kPa−1, and demonstrate durability over 3600 cycles. The performance of our piezoelectric sensors is compared with a standard BP monitoring device for a subject, and a strong correlation with a standard deviation of 3.87 and 0.63 mmHg for sytolic BP and diastolic BP, respectively, is found. The development of sensors through 3D printing, as demonstrated in this study, represents a significant scientific advancement in the field of personalized healthcare. This novel approach enables the creation of customized wearable devices tailored for real‐time health monitoring of BP and heart rate. [ABSTRACT FROM AUTHOR]

Emerging piezoelectric technologies have promoted the development of self‐powered sensing systems by addressing the power supply issue of wearable electronics, offering fascinating prospects in Internet of Things. Despite tremendous progress in stretchability, there remain a lot of urgent and unmet needs for stretchable self‐powered piezoelectric sensors toward real‐world applications: (i) lack of practicability due to the low sensitivity in the stretching mode; (ii) self‐healing ability after mechanical damage to enhance device sustainability and durability; (iii) requirements of biocompatibility as electronics attach to human body. In this review, the trends, challenges, and solutions in elastomer‐based stretchable self‐powered piezoelectric sensors, focusing on their material design and fabricating strategy for high sensitivity, self‐healing ability, and biocompatibility is introduced. The structure‐property relationships of these novel strategies and their emerging applications is discussed and highlighted. Finally, the current challenges and perspectives for the development of stretchable self‐powered piezoelectric sensors are presented. [ABSTRACT FROM AUTHOR]

In the fields of medical and sports science, it is required to evaluate muscle activity qualitatively and quantitatively. Currently, mechanomyogram (MMG) that can reflect the mechanical activity of muscle fibers is attracting attention. The purpose of this study is to develop a sensor that can measure MMG during exercise. In this study, a small and flexible MMG sensor using P(VDF/TrFE), which is a piezoelectric polymer material, spun into nanofibers by the electrospinning method has been fabricated and evaluated. By the fabricated electrospinning equipment and the obtained fabrication conditions of the nanofibers MMG sensor has been fabricated by using piezoelectric polymer fibers. By using nanofiber nonwoven fabric for the sensor element, the flexible sensor has been realized. In a sound wave reception experiment assuming MMG measurement, the P(VDF/TrFE) nonwoven fabric element showed that the element detected the sound pressure. Additionally, MMG during isometric contraction and pedaling motion has been measured using the fabricated sensor. The results show that the proposed sensor is effective for measuring MMG during exercise. [ABSTRACT FROM AUTHOR]

In this paper, a self‐powered piezoelectric sensor is developed for pressure monitoring. Though molecular design and processing optimum of piezoelectric materials, the the accuracy of pressure sensing was significantly improved, and the sphygmic signal of the human body can be detected. In particular, the prepared sensor is capable to be integrated under flexible OLED display to realize sphygmic signal detection. Thus, a new under‐screen flexible OLED health sensing device is realized. [ABSTRACT FROM AUTHOR]

Wearable flexible electronic devices are increasingly becoming an important part of the future rolling touch screen, health care equipment, electronic skin and other fields. It is worth noting that piezoelectric sensors are widely used because of their self‐powered capability, fast response, and relatively simple circuits. Among them, Indium‐tin‐zinc oxide thin‐film transistor (ITZO TFT) has high field effect mobility, low energy consumption, and can be used as an amplifier for signal amplification of flexible sensing systems. In this paper, we constructed a flexible piezoelectric sensor (PZ) based on electrospun PVDF and hydrothermally assisted growth of ZnO nanorods. Besides, this PZ sensor has higher sensitivity than the individual PVDF piezoelectric sensor. The sensor can not only be used for detection of static objects, but also for the capture of tiny physiological signals of human body, such as vibration of vocal cords, pulse beat, etc., showing superiority in dynamic and static signal detection. At the same time, the sensor can be integrated with ITZO TFT, which can still achieve stable signal acquisition and show application prospects as future brain‐computer interface and intelligent robotics manufacturing. [ABSTRACT FROM AUTHOR]

In this study, gold nanoparticles (AuNPs) were grown on the surface of a metal‐organic framework (UiO‐66−NH2). The resulting AuNPs/UiO‐66−NH2 composite nanomaterials were further used for antibody immobilization on a microcantilever surface. By harnessing the robust signal processing capabilities of integrated circuits, a highly sensitive piezoelectric microcantilever sensor was constructed. The incorporation of nanomaterials resulted in enhanced antibodies immobilization amount, thereby improving the immunosensor's sensitivity. Under optimized experimental conditions, a promising linear correlation (R=0.993) was observed between the voltage output intensity of the microcantilever sensor and the logarithmic PCT concentration within a range of 0.1–50 ng/mL. The constructed microcantilever immunosensor based displayed several advantages such as simplicity, rapidity, high sensitivity, and low cost. Moreover, it potentially provided a novel approach to detect other biomolecules. [ABSTRACT FROM AUTHOR]

To better understand how normal stress heterogeneity affects earthquake rupture, we conducted laboratory experiments on a 760 mm poly (methyl‐mathacrylate) PMMA sample with a 25 mm "bump" of locally higher normal stress (∆σbt). We systematically varied the sample‐average normal stress (σn‾ $\overline{{\sigma }_{n}}$) and bump prominence (∆σbt/σn‾ ${{\increment}\sigma }_{\text{bt}}/\overline{{\sigma }_{n}}$). For bumps with lower prominence (∆σbt/σn‾<6 ${{\increment}\sigma }_{\text{bt}}/\overline{{\sigma }_{n}}< 6$) the rupture simply propagated through the bump and produced regular sequences of periodic stick‐slip events. Bumps with higher prominence (∆σbt/σn‾>6 ${{\increment}\sigma }_{\text{bt}}/\overline{{\sigma }_{n}} > 6$) produced complex rupture sequences with variable timing and ruptures sizes, and this complexity persisted for multiple stick‐slip supercycles. During some events, the bump remained locked and acted as a barrier that completely stopped rupture. In other events, a dynamic rupture front terminated at the locked bump, but rupture reinitiated on the other side of the bump after a brief pause of 0.3–1 ms. Only when stress on the bump was near critical did the bump slip and unload built up strain energy in one large event. Thus, a sufficiently prominent bump acted as a barrier (energy sink) when it was far from critically stressed and as an asperity (energy source) when it was near critically stressed. Similar to an earthquake gate, the bump never acted as a permanent barrier. In the experiments, we resolve the above rupture interactions with a bump as separate rupture phases; however, when observed through the lens of seismology, it may appear as one continuous rupture that speeds up and slows down. The complicated rupture‐bump interactions also produced enhanced high frequency seismic waves recorded with piezoelectric sensors. Plain Language Summary: Natural faults have complex geometries, but are idealized as planar surfaces in most models and laboratory setups. To study the effect of one isolated "bump" of high normal stress, we conducted laboratory experiments on a 760 mm poly (methyl‐mathacrylate) sample with a 25 mm long section of locally high normal stress. We varied both the average normal stress applied to the sample and the prominence of the bump to explore how more dramatic bumps could affect sequences of slip events. When the bump was small and stress was nearly uniform, the bump had little effect and the entire fault consistently slipped the same amount, at the same time. When the bump was large and the bump stress was much higher than stress elsewhere on the sample, different sections of the fault slipped independently resulting in complex sequences with large variations in event sizes. Smaller events slipped areas around the bump without slipping the bump. In some cases, the bump could be by‐passed and the entire fault slipped, except the bump. But the bump was never able to permanently stop these slip events. Eventually, the bump was stressed close to its limit and slipped which created larger events than otherwise expected. Key Points: A 25 mm‐long bump of high normal stress can cause persistently complex rupture sequences on a 760 mm‐long sampleA sufficiently prominent bump (∆σbt/σn‾>6 ${{\increment}\sigma }_{\text{bt}}/\overline{{\sigma }_{n}} > 6$) can stop rupture; but slip can sometimes re‐initiate on the other side of the bumpA prominent bump can act as an asperity or a barrier depending on strength excess, resulting in a variety of event sizes [ABSTRACT FROM AUTHOR]

Traditional Chinese medicine (TCM) is an experienced‐based discipline and plays an important role in the current medical system. Digitalizing key features is the best way to con‐duct an in‐depth analysis of TCM. However, due to its complex generation mechanism, the crucial pulse‐taking procedure is hard to be digitalized and analyzed. This article fabricated a flexible piezoelectric sensor to gather data for the pulse‐taking procedure. The sensitivity of the proposed flexible sensor reached 0.34 V/kPa, so we adopted peripheral circuits to make its output signals stay in a reasonable range (± 0.5 V) for convenient data collection. We used the sensor to recognize whether a woman is pregnant since it has solid golden standards. The pulse signal was fused via mapping the signal spectrogram into a 3‐dimension tensor. The fused matrix was then processed by GoogleNet and reached a 90.48% correction rate. This result shows that the pulse condition has statistical differences, which solidified the objectivity of pulse diagnosis and escalated the TCM's digitalization level. [ABSTRACT FROM AUTHOR]

Development of artificial mechanoreceptors capable of sensing and pre‐processing external mechanical stimuli is a crucial step toward constructing neuromorphic perception systems that can learn and store information. Here, bio‐inspired artificial fast‐adaptive (FA) and slow‐adaptive (SA) mechanoreceptors with synapse‐like functions are demonstrated for tactile perception. These mechanoreceptors integrate self‐powered piezoelectric pressure sensors with synaptic electrolyte‐gated field‐effect transistors (EGFETs) featuring a reduced graphene oxide channel. The FA pressure sensor is based on a piezoelectric poly(vinylidene fluoride‐trifluoroethylene) (P(VDF‐TrFE)) thin film, while the SA pressure sensor is enabled by a piezoelectric ionogel with the piezoelectric‐ionic coupling effect based on P(VDF‐TrFE) and an ionic liquid. Changes in post‐synaptic current are achieved through the synaptic effect of the EGFET by regulating the amplitude, number, duration, and frequency of tactile stimuli (pre‐synaptic pulses). These devices have great potential to serve as artificial biological mechanoreceptors for future artificial neuromorphic perception systems. [ABSTRACT FROM AUTHOR]

Additively manufactured flexible and high‐performance piezoelectric devices are highly desirable for sensing and energy harvesting of 3D conformal structures. Herein, the study reports a significantly enhanced piezoelectricity in polyvinylidene fluoride (PVDF) achieved through the in situ dipole alignment of PVDF within PVDF‐2D molybdenum disulfide (2D MoS2) composite by 3D printing. The shear stress‐induced dipole poling of PVDF and 2D MoS2 alignment are harnessed during 3D printing to boost piezoelectricity without requiring a post‐poling process. The results show a remarkable, more than the eight‐fold increment in the piezoelectric coefficient (d33) for 3D printed PVDF‐8wt.% MoS2 composite over cast neat PVDF. The underlying mechanism of piezoelectric property enhancement is attributed to the increased volume fraction of β phase in PVDF, filler fraction, heterogeneous strain distribution around PVDF‐MoS2 interfaces, and strain transfer to the nanofillers as confirmed by microstructural analysis and finite element simulation. These results provide a promising route to design and fabricate high‐performance 3D piezoelectric devices via 3D printing for next‐generation sensors and mechanical–electronic conformal devices. [ABSTRACT FROM AUTHOR]

Herein, the density functional theory is used to study the structural, mechanical, electrical, optical, and hydrogen evolution reaction (HER) properties of monolayer structures (α,β)–S2C2N2$\left(\right. \alpha , \beta \left.\right) – \left(\text{S}\right)_{2} \left(\text{C}\right)_{2} \left(\text{N}\right)_{2}$ and (α,β)–SCN/CN$\left(\right. \alpha , \beta \left.\right) – \text{SCN} / \text{CN}$. They are claimed to be stable monolayer structures by phonon dispersion and ab initio molecular dynamics (AIMD). Compared to graphene (≈340 N m−1), the (α,β)–SCN/CN$\left(\right. \alpha , \beta \left.\right) – \text{SCN} / \text{CN}$ shows a higher Young's modulus (≈429, 414 N m−1). Moreover, the piezoelectric stress coefficient of α‐SCN/CN$\text{SCN} / \text{CN}$ (d11$d_{11}$=2.65 pm V−1) is comparable with bulk piezoelectric α‐quartz (d11$d_{11}$=2.3 pm V−1). Exciton effect at M point causes redshift and enhancement of light absorption of α‐SCN/CN$\text{SCN} / \text{CN}$ and β–SCN/CN$\beta – \text{SCN} / \text{CN}$. The overpotential of β–SCN/CN$\beta – \text{SCN} / \text{CN}$ is only –0.072 V. Besides, the (α,β)–SCN/CN$\left(\right. \alpha , \beta \left.\right) – \text{SCN} / \text{CN}$ gives a small effective electron mass of about 0.2(m0). It is worth mentioning that the monolayer structures (α,β)–S2C2N2$\left(\right. \alpha , \beta \left.\right) – \left(\text{S}\right)_{2} \left(\text{C}\right)_{2} \left(\text{N}\right)_{2}$ show the semimetal phases. Due to the unique semimetal phase, the absorption of β–S2C2N2$\beta – \left(\text{S}\right)_{2} \left(\text{C}\right)_{2} \left(\text{N}\right)_{2}$ has an excellent performance in the near‐infrared (NIR) region. It can be enhanced at the NIR region and extended to the middle infrared region when applying tensile stress. These results provide more choices for 2D materials in electrocatalysis, piezoelectric sensors, visible light devices, and infrared photodetectors. [ABSTRACT FROM AUTHOR]

With the advent of the intelligence era, flexible piezoelectric tactile sensors are the key components for sensing information and sending signals. The performance parameters of piezoelectric sensors are closely related to the selection of piezoelectric materials. Compared with conventional piezoelectric materials, polyvinylidene fluoride (PVDF) has significant advantages in flexibility, stretchability, chemical stability, electromechanical conversion, ease of use, and acoustic propagation impedance. As a result, PVDF has become a popular topic of research. This paper introduces the working principle of piezoelectric materials and flexible piezoelectric sensors based on PVDF materials and details the research progress of different materials based on PVDF for the preparation of flexible piezoelectric tactile sensors, such as: PVDF and its copolymers for the preparation of flexible piezoelectric sensors and PVDF doped with other functional materials for the preparation of flexible piezoelectric sensors. In this paper, the advantages and disadvantages of different materials and the development prospects of PVDF flexible piezoelectric sensors are summarized to provide some insights for high‐performance flexible PVDF piezoelectric sensors. [ABSTRACT FROM AUTHOR]

Smart at‐ or online process sensors, which employ machine learning (ML) to process data, have been the subject of extensive research in recent years, due to their potential for real‐time process control. In this paper, a passive acoustic emission process sensor has been used to detect gas–liquid regimes within a stirred, aerated vessel using novel ML approaches. Pressure fluctuations (acoustic emissions) in an air‐water system were recorded using a piezoelectric sensor installed on the external wall of three identical cylindrical tanks of diameter, T = 160 mm, filled to a volume of 5 L (height, H = 1.5 T). The tanks were made of either glass, steel, or aluminium, and each tank was equipped with a Rushton turbine of diameter, D = 0.35 T. The investigated flow regimes, flooding, loading, complete dispersion, and un‐gassed, were obtained by changing the air feed flow rates and by varying the impeller speed. The acoustic spectra obtained were processed to select an optimal number of features characterizing each of the regimes, and these were used to train three different ML algorithms. The pre‐processing includes a principal component analysis (PCA) step, which reduces the volume of data fed to the ML algorithms, saving computational time up to a factor of 5. The algorithms (decision tree, k‐nearest neighbour, and support vector machines) were challenged to use these features to identify the correct flow regime. Accurate predictions of the three gas–liquid regimes of interest have been achieved. The accuracy of the prediction ranges from 90% to 99%, and this difference is related to the material used for the vessel. [ABSTRACT FROM AUTHOR]

The reliable function in vivo of self‐powered implantable bioelectric devices (iBEDs) requires biocompatible, seamless, effective interactions with biological tissues. Herein, an implantable tissue‐adhesive piezoelectric soft sensor (TPSS), in which the piezoelectric sensor converts biomechanical signals into electrical signals, and the adhesive hydrogel (AH) strengthens this conversion by seamlessly adhering the sensor on the wet and curvilinear surface, is proposed. The optimized AH exhibits strong adhesion to various organic or inorganic surfaces, including six commonly used engineering materials and three biological tissues. As a pressure sensor, TPSS proves good in vitro electrical performance with a high output of 8.3 V, long‐term stability of over 6000 cycles, and high energy power density of 186.9 µW m−2. In a large animal experiment, TPSS seamlessly adheres to the right‐side internal carotid artery of a Yorkshire pig to monitor blood pressure during a surgical operation. Compared to commercial sensors that work by inserting into tissues, TPSS does not cause any damage and can be peeled off after service. The integration of adhesive hydrogel and self‐powered pressure sensors enables biocompatible, seamless, and more efficient interactions between the biological system and iBEDs, which also contributes to next‐generation implantable bioelectronics with features of battery‐free, intelligent, and accurate. [ABSTRACT FROM AUTHOR]

Recent progress in flexible sensors and piezoelectric materials has enabled the development of continuous monitoring systems for human physiological signals as wearable and implantable medical devices. However, their non‐degradable characteristics also lead to the generation of a significant amount of non‐decomposable electronic waste (e‐waste) and necessitate a secondary surgery for implant removal. Herein, a flexible and biodegradable piezoelectric material for wearable and implantable devices that addresses the problem of secondary surgery and e‐waste while providing a high‐performance platform for continuous and seamless monitoring of human physiological signals and tactile stimuli is provided. The novel composition of bioresorbable poly(l‐lactide) and glycine leads to flexible piezoelectric devices for non‐invasive measurement of artery pulse signals in near‐surface arteries and slight movement of the muscle, including the trachea, esophagus, and movements of joints. The complete degradability of piezoelectric film in phosphate‐buffered saline at 37 °C is also shown. The developed pressure sensor exhibits high sensitivity of 13.2 mV kPa−1 with a response time of 10 ms and shows good mechanical stability. This piezoelectric material has comparable performance to commonly used non‐degradable piezoelectric materials for measuring physiological signals. It can also be used in temporary implantable medical devices for monitoring due to its degradable nature. [ABSTRACT FROM AUTHOR]

An increasing trend in creating materials with a greater extent of sustainability from an ecological and financial perspective involves usage of bio resources and industrial residues. In this paper, leftover bamboo micro particles (BMP) from bamboo factories were collected and used as fillers with polyvinylidene fluoride (PVDF) matrix in varying concentrations (1, 3, 5, 7, and 9 wt.%) to fabricate low‐cost composite films using solvent casting route for mechanical energy harvesting purpose. Out of the prepared samples, PVDF with 5 wt.% BMP showed maximum electroactive phase content (82%), tensile strength (34.23 MPa), and piezoelectric voltage (6.5 V) among the untreated samples. PVDF with 5 wt.% BMP is then subjected to NaOH treatment for further enhancement in overall performance. PVDF with 5 wt.% treated BMP also showed 467% increment in output voltage and 235% increment in output current as compared to pure PVDF. The piezoelectric output voltage of PVDF with 5 wt.% treated BMP is then measured under impact loading conditions to determine its suitability as an impact sensor. A bamboo‐based piezoelectric impact sensor that is highly sensitive and cost‐effective opens enormous possibilities for sustainability and circular economies. [ABSTRACT FROM AUTHOR]

Electrospun polyvinylidene fluoride (PVDF) nanofibers have been widely used in the fabrication of flexible piezoelectric sensors and nanogenerators, due to their excellent mechanical properties. However, their relatively low piezoelectricity is still a critical issue. Herein, a new and effective route to enhance the piezoelectricity of PVDF nanofiber mats by electrospraying zinc oxide (ZnO) nanoparticles between layers of PVDF nanofibers is demonstrated. As compared to the conventional way of dispersing ZnO nanoparticles into PVDF solution for electrospinning nanofiber mats, this approach results in multilayered PVDF+ZnO nanofiber mats with significantly increased piezoelectricity. For example, 6.2 times higher output is achieved when 100% of ZnO (relative to PVDF quantity) is electrosprayed between PVDF nanofibers. Moreover, this new method enables higher loading of ZnO without having processing challenges and the maximum peak voltage of ≈3 V is achieved, when ZnO content increases up to 150%. Additionally, it is shown that the samples with equal amount of material but consisting of different number of layers have no significant difference. This work demonstrates that the proposed multilayer design provides an alternative strategy to enhance the piezoelectricity of PVDF nanofibers, which can be readily scaled up for mass production. [ABSTRACT FROM AUTHOR]

The application of biodegradable films based on the piezoelectric effect of poly‐l‐lactic acid (PLLA) in sensors, transducers, actuators, and so on has gradually become one of the emerging research focuses. In this work, a flexible PLLA sensor with UV‐curable acrylate film packaging is proposed for human behavior recognition. The acrylic films with different proportions have different mechanical and surface properties, showing good flexibility, ductility, and skin adhesion. The morphology and crystal structure of the PLLA films and UV curable substrate obtained under the various postprocessing conditions and different proportions are examined by scanning electron microscopy, X‐ray diffraction, Raman, and ATR‐FTIR spectroscopy. In addition, by comparing six groups of PLLA films with different treatment conditions, the device made on film stretched four times and annealed for 8 h has the best performance. This sensor has good response ability to impact, vibration, and bending strain, and can be applied to human behavior recognition, such as touch, wrist bending, and swallowing. [ABSTRACT FROM AUTHOR]

Flexible pressure sensors have attracted a lot of attention in fields such as medicine and healthcare due to their ease of making wearable devices. However, the development of flexible pressure sensors is facing the challenges of a complex manufacturing process and high cost. Herein, a zinc oxide (ZnO) piezoelectric film flexible pressure sensor with a 3 × 3 sensor array presented through an extremely simple and ultralow‐cost fabrication process is reported. The 3 × 3 sensor array in series and again, in parallel. The output voltage of the 3 × 3 sensor array is significantly higher compared to the original thin‐film piezoelectric sensors at the same film thickness. The ZnO flexible pressure sensor shows good linear sensitivity and high durability over 4000 cycles of loading in the test range of 0–14 N. The response and recovery times tend to decrease as the dynamic pressure increases in the experimental range. Furthermore, a high‐precision dynamic force calibration system through a comparison between the open‐loop and closed‐loop strategies used in the dynamic force calibration experiments that are performed is presented. Potential applications of the sensor are demonstrated, including elbow flexure and finger tapping. The sensor also shows the ease of massive fabrication. [ABSTRACT FROM AUTHOR]

Herein, a simple and low‐cost fabrication method for flexible piezoelectric pressure sensors with hierarchical structures over large areas is presented. First, polyvinylidene fluoride (PVDF) and barium titanate (BaTiO3, BTO) composite membranes are fabricated through near‐field electrospinning, and the hierarchical structured membrane (HSM) is obtained by spreading the flat membrane on the designed mold and drying. Then, the effect of encapsulation schemes on the piezoelectric properties of the sensor is investigated by combining different membranes with different PDMS substrates. The output voltage under periodic loads shows that the encapsulation scheme of "the hierarchical structured membrane with a hierarchical structured substrate" (HHS) can provide the highest peak voltage attributed to its largest contact area, which increases the active area (deformation area) for piezoelectricity generation. Also, the HHS with a bulge of 2 mm can produce a maximum output voltage of 2.32 V under a periodic load of 2 N, 2.5 Hz. Finally, the HHS pressure sensors are used for monitoring human motions, including joint bending, walking, and jumping, and the results show that the presented hierarchically microstructured flexible piezoelectric pressure sensor has great potential for applications of for human‐activity monitoring and wearable bioelectronic devices. [ABSTRACT FROM AUTHOR]