Self-powered Piezoelectric Sensor Research Articles

Advanced Materials for Energy Harvesting and Soft Robotics: Emerging Frontiers to Enhance Piezoelectric Performance and Functionality.

Piezoelectric energy harvesting captures mechanical energy from a number of sources, such as vibrations, the movement of objects and bodies, impact events, and fluid flow to generate electric power. Such power can be employed to support wireless communication, electronic components, ocean monitoring, tissue engineering, and biomedical devices. A variety of self-powered piezoelectric sensors, transducers, and actuators have been produced for these applications, however approaches to enhance the piezoelectric properties of materials to increase device performance remain a challenging frontier of materials research. In this regard, the intrinsic polarization and properties of materials can be designed or deliberately engineered to enhance the piezo-generated power. This review provides insights into the mechanisms of piezoelectricity in advanced materials, including perovskites, active polymers, and natural biomaterials, with a focus on the chemical and physical strategies employed to enhance the piezo-response and facilitate their integration into complex electronic systems. Applications in energy harvesting and soft robotics are overviewed by highlighting the primary performance figures of merits, the actuation mechanisms, and relevant applications. Key breakthroughs and valuable strategies to further improve both materials and device performance are discussed, together with a critical assessment of the requirements of next-generation piezoelectric systems, and future scientific and technological solutions.

Self-powered piezoelectric sensor based on BaTiO3/MWCNTs/PVDF electrospun nanofibers for wireless alarm system

Abstract The piezoelectric constant of polyvinylidene fluoride (PVDF) is inferior to that of piezoelectric ceramics, which will impede the efficient application in smart systems. In this work, we modulated the content of BaTiO3/multi-wall carbon nanotubes (MWCNTs) in the BaTiO3/MWCNTs/PVDF electrospun nanofibers to facilitate the β phase formation in the PVDF to enhance the piezoelectric properties of BaTiO3/MWCNTs/PVDF films. The BaTiO3 combined with MWCNTs through chemical bands can enhance the electrostatic interaction at the vicinity of BaTiO3-PVDF interface to induce augmentation of the local conformational disorder and result in the enhanced nucleation and stabilization of β phase in the BaTiO3/MWCNTs/PVDF films. When the ratio between BaTiO3 and MWCNTs is about 3:1, the PVDF-BM-3 can deliver the output voltage of 39.5 V under 250 kPa with a frequency of 10 Hz. The PVDF-BM-3 electrospun nanofibers as triggers used in the wireless alarm system can achieve comparable sensitivity under different external stresses. This work paves a new promising pathway for self-powered piezoelectric sensors in the Internet of Things.

A self-powered flexible piezoelectric sensor patch for deep learning-assisted motion identification and rehabilitation training system

Artificial intelligence-assisted wearable devices have attracted great interest in medical treatment and healthcare. However, wearable electronic devices are expensive to manufacture and usually depend on external power supply. Herein, a flexible self-powered piezoelectric sensor patch (SPP) using Polyvinylidene fluoride (PVDF) fibrous film as the functional layer is demonstrated for the assessment and motion identification of wrist joint rehabilitation training. PVDF fibrous film is prepared by a triboelectric nanogenerator (TENG)-driven near-field electrospinning system with a special designed synchronous mechanical switch. The results show that this flexible SPP has a high sensitivity of 0.2768 V KPa−1 at pressures from 1 to 75 kPa. Such excellent flexibility allows us to attach the SPP to the finger as a tactile sensor for rehabilitation assessment of wrist joint flexibility. In addition, long short-term memory network model is used to process the collected data from the SPP for motion identification. The test accuracy of the SPP wrist motion identification reaches 92.6%, which afford a potential way to understand the progress of the rehabilitation training of patients' wrists. Generally, this flexible SPP shows great promise for applications in the fields of motion monitoring, medical diagnosis and rehabilitation training based on artificial intelligence.

Multifunctional PVDF/CeO2@PDA nanofiber textiles with piezoelectric and piezo-phototronic properties for self-powered piezoelectric sensor and photodetector

In recent years, multifunctional sensors have attracted significant attention due to their ability to detect different types of signals. However, it still remains a challenge to develop flexible materials with multiple sensing functions. Herein, we propose a strategy to fabricate multifunctional flexible textiles (PCP) that can apply piezoelectric and piezo-phototronic effects to self-powered piezoelectric sensor and photodetector (PD) by utilizing the synergistic effect of polydopamine-coated cerium oxide (CeO2@PDA) nanoparticles and poly (vinylidene fluoride) (PVDF). The CeO2@PDA nanoparticles served as local nucleating agents and photosensitizers for the PVDF, enhancing the polar crystalline phase and inducing piezoelectric effect, semiconductor, and optical process coupling in PCP textiles. The piezoelectric sensors consisting of PCP textiles produced extremely high sensitivity (1–10 kPa: 1.27 V/kPa; 10–50 kPa: 0.085 V/kPa; 50–100 kPa: 0.02 V/kPa) and significant electrical output (25.5 V and 0.37 μA). Besides, the piezoelectric sensor had extensive applications including pulse wave measurement, limb motion detection, and active voice recognition. It's especially noteworthy that the PD based on PCP textiles is sensitive for the detecting of sunlight illumination as confirmed by response time (tOn = 2 s and tOff = 4.6 s). Meanwhile, the fabricated self-powered PD showed significant improvement in output current, confirming the realization of the piezo-phototronic effect in PCP textiles. In this work, the low-cost and high-efficiency multifunctional sensing materials were successfully prepared, providing a novel approach for the next generation of self-powered piezoelectric sensors and photodetectors.

Enhancing the performance of molecule-based piezoelectric sensors by optimizing their microstructures.

By combining the rigidity of inorganic components with the flexibility of organic components, molecule-based ferroelectrics emerge as promising candidates for flexible, self-powered piezoelectric sensors. While it is well known that the performance of piezoelectric sensor devices depends not only on the materials' piezoelectric properties but also on the device architecture, research into enhancing molecule-based piezoelectric sensor performance through microstructure optimization has never been investigated. Here, we report the synthesis of a molecule-based ferroelectric, [(2-bromoethyl) trimethylammonium][GaBr4] ([(CH3)3NCH2CH2Br][GaBr4]) (1), which exhibits a piezoelectric coefficient (d 33) of up to 331 pC N-1. Our investigation reveals that the power density of a composite piezoelectric sensor device made from 1@S-PDMS(800#) (with microstructures) is twelve times that of 1-Flat-PDMS (without microstructures), due to a synergistic combination of piezoelectric and triboelectric effects. Interestingly, this flexible piezoelectric sensor can effectively detect human physiological signals, such as finger bending, breathing, and speech recognition, without the need for an external power supply.

Paper-based ZnO self-powered sensors and nanogenerators by plasma technology

Nanogenerators and self-powered nanosensors have shown the potential to power low-consumption electronics and human-machine interfaces, but their practical implementation requires reliable, environmentally friendly and scalable processes for manufacturing and processing. Furthermore, the emerging flexible and wearable electronics technology demands direct fabrication onto innovative substrates such as paper and plastics typically incompatible with high process temperatures. This article presents a plasma synthesis approach for the fabrication of piezoelectric nanogenerators (PENGs) and self-powered sensors on paper substrates. Polycrystalline ZnO nanocolumnar thin films are deposited by plasma-enhanced chemical vapour deposition on common paper supports using a microwave electron cyclotron resonance reactor working at room temperature yielding high growth rates and low structural and interfacial stresses. Applying Kinetic Monte Carlo simulation, we elucidate the basic shadowing mechanism behind the characteristic microstructure and porosity of the ZnO thin films, relating them to an enhanced piezoelectric response to periodic and random inputs. The piezoelectric devices are assembled by embedding the ZnO films in polymethylmethacrylate (PMMA) and using Au thin layers as electrodes in two different configurations, namely laterally and vertically contacted devices. We present the response of the laterally connected devices as a force sensor for low-frequency events with different answers to the applied force depending on the impedance circuit, i.e. load values range, a behaviour that is theoretically analyzed. The characterization of the vertical devices in cantilever-like mode reaches instantaneous power densities of 80 nW/cm2 with a mean power output of 20 nW/cm2. Besides, we analyze their actual-scenario performance by activation with a fan and handwriting. Overall, this work demonstrates the advantages of implementing plasma deposition for piezoelectric films to develop robust, flexible, stretchable, and enhanced-performance nanogenerators and self-powered piezoelectric sensors compatible with inexpensive and recyclable supports.

A Review on PVDF Nanofibers in Textiles for Flexible Piezoelectric Sensors

Textiles are turning into a suitable next-generation sensing platform because of their good breathability, softness, and structural elasticity. Besides, research on self-powered piezoelectric sensors is a hot topic in wearable applications; they can perform long-term sensing and monitoring. Therefore, this paper mainly reviews the development progress of PVDF-based textiles on flexible piezoelectric sensors. In this paper, we first introduce the principle of the piezoelectric effect and the classification of piezoelectric materials; then we summarize the structure and characteristics of nanofiber mat-based, yarn-based, and fabric-based flexible piezoelectric sensors and the approaches that are employed to fabricate PVDF-based textile piezoelectric sensors such as melt spinning, electrospinning, and stretch forming processes, and so on. At last, we review their applicability in the application of electronic skin, human–computer interaction, healthcare, and human movement monitoring and demonstrate the facing difficulties and the future research directions of PVDF-based textile flexible sensors.

Remarkably enhanced piezoelectric and ferroelectric characteristics of Er:ZnO upon graphene addition for wearable self-powered piezoelectric sensors

Flexible Er-ZnO/PDMS and Er-GO/ZnO/PDMS nanogenerators with high energy harvesting performance were developed. The output voltage and current density of Er-doped ZnO, Er-doped GO/ZnO (1:10) and Er-doped GO/ZnO (1:5) nanocomposites-based piezoelectric harvesters were (70 V, 1.85 µAcm−2), (80 V, 2.16 µAcm−2) and (100 V, 2.47 µAcm−2), respectively. The Er-doped GO/ZnO wearable sensor showed output voltages of 4 V and 9 V by bending the human wrist and elbow, respectively. In addition, a remarkable improvement of the remnant polarization (Pr) and a favourable reduction of the coercive field (Ec) were achieved for Er-doped ZnO and Er-doped GO/ZnO nanocomposites. The corresponding values of Pr and Ec for pure ZnO, Er-doped ZnO, Er-doped GO/ZnO (1:10) and Er-doped GO/ZnO (1:5) nanostructures were (0.06 μC/cm2, 6.50 kV/cm), (8.75 μC/cm2, 4.74 kV/cm), (13.25 μC/cm2, 3.98 kV/cm) and (8.913 μC/cm2, 3.54 kV/cm), respectively. The enhanced piezoelectric and ferroelectric properties of Er-doped ZnO and Er-doped GO/ZnO nanocomposites make them futuristic hybrids with immense potential for designing pressure biosensors, mechanical energy harvesters and environmentally friendly ferroelectric-based memory devices.

Improved piezoelectricity of porous cellulose material via flexible polarization-initiate bridge for self-powered sensor

Self-powered piezoelectric sensors based on cellulose nanocrystal (CNC) porous materials are light-weight and portable, whereas using unmodified CNCs can hardly obtain enough piezoelectric properties without external strong polarization due to its irreversible deformation caused by low toughness. Here, we bonded rod-like CNCs with a soft polymer, poly ethylene glycol (PEG), and hypothesized that PEG could toughen the material and its dielectric signal could induce the CNC polarization. We further adsorbed graphene (GR) as surface electrodes to prepare a CNC-PEG-GR piezoelectric porous material with density of 0.096 g·cm−3. The voltage output reached maximum when the frequency matched the dielectric relaxation frequency of PEG. We also increased the length-diameter ratio of porous material pores from 1.1 to 3.3 by adjusting its freeze-drying process, and the voltage output could reach to 0.7 V at a moderate ratio. They could be conveniently integrated into portable self-powered sensors applied to the intelligent wearable electronic devices.

A Drifter-Based Self-Powered Piezoelectric Sensor for Ocean Wave Measurements.

Recently, piezoelectric materials have received remarkable attention in marine applications for energy harvesting from the ocean, which is a harsh environment with powerful and impactful waves and currents. However, to the best of the authors’ knowledge, although there are various designs of piezoelectric energy harvesters for marine applications, piezoelectric materials have not been employed for sensory and measurement applications in marine environment. In the present research, a drifter-based piezoelectric sensor is proposed to measure ocean waves’ height and period. To analyze the motion principle and the working performance of the proposed drifter-based piezoelectric sensor, a dynamic model was developed. The developed dynamic model investigated the system’s response to an input of ocean waves and provides design insights into the geometrical and material parameters. Next, finite element analysis (FEA) simulations using the commercial software COMSOL-Multiphysics were carried out with the help of a coupled physics analysis of Solid Mechanics and Electrostatics Modules to achieve the output voltages. An experimental prototype was fabricated and tested to validate the results of the dynamic model and the FEA simulation. A slider-crank mechanism was used to mimic ocean waves throughout the experiment, and the results showed a close match between the proposed dynamic modeling, FEA simulations, and experimental testing. In the end, a short discussion is devoted to interpreting the output results, comparing the results of the simulations with those of the experimental testing, sensor’s resolution, and the self-powering functionality of the proposed drifter-based piezoelectric sensor.

Self-powered flexible piezoelectric sensors based on self-assembled 10 nm BaTiO₃ nanocubes on glass fiber fabric

Hardness or brittleness limits the broad applications of currently available high-performance piezoelectric sensors in emerging fields like human-machine interface and wearable electronics, while existing technologies for fabricating flexible piezoelectric sensors often require high-temperature sintering or complex processes. Here, we reported flexible piezoelectric sensors based on 10 nm BaTiO3 nanocubes self-assembled on glass fiber fabric (GFF). The simple self-assembly process avoids high temperature sintering process which can well maintain the mechanical performance of GFF. Owing to the superior piezoelectric performance of BaTiO3 nanocubes and robust mechanical properties of GFF, the integrally fabricated flexible piezoelectric sensors achieved high sensitivity (101.09 nA kPa−1 and 3.31 V kPa−1 in the low pressure range of 0–10 N) and short response time (19 ms). The sensors can intelligently identify handwriting or recognize the user of keyboard, and the initially collected electrical signals are essentially the same as those after 3000 bending cycles. This work provides a novel self-assembly process to develop fabric-based flexible electronics, which promotes the development of self-powered piezoelectric sensors and creates advancements in human-machine interfaces.

An Effective Self-Powered Piezoelectric Sensor for Monitoring Basketball Skills.

Self-powered piezoelectric sensor can achieve real-time and harmless monitoring of motion processes without external power supply, which can be attached on body skin or joints to detect human motion and powered by mechanical energy. Here, a sensor for monitoring emergent motion is developed using the PVDF as active material and piezoelectric output as sensing signal. The multi-point control function enables the sensor to monitor the sequence of force order, angle change, and motion frequency of the “elbow lift, arm extension, and wrist compression” during shooting basketball. In addition, the sensor shows can simultaneously charge the capacitor to provide more power for intelligence, typically Bluetooth transmission. The sensor shows good performance in other field, such as rehabilitation monitoring and speech input systems. Therefore, the emerging application of flexible sensors have huge long-term prospects in sport big data collection and Internet of Things (IoT).

A 1.02 μW Autarkic Threshold-Based Sensing and Energy Harvesting Interface Using a Single Piezoelectric Element

A self-powered piezoelectric sensor interface employing part of the signal that is not intended for measurement to sustain its autonomous operation was designed using XH018 (180 nm) technology. The aim of the proposed circuit, besides the energy self-sufficiency of the sensor, is to provide an interface that eliminates the effect of the harvesting process on the piezoelectric output signal which contains context data. This is achieved by isolating part of the signal that is desirable for sensing from the harvesting process so that the former is not affected or distorted by the latter. Moreover, the circuit manages to self-start its operation, so no additional battery or pre-charged capacitor is needed. The circuit achieves a very low power consumption of 1.02 μW. As a proof of concept, the proposed interfacing circuit is implemented in order to be potentially used for weigh-in-motion applications.

Superflexible and Lead-Free Piezoelectric Nanogenerator as a Highly Sensitive Self-Powered Sensor for Human Motion Monitoring

HighlightsContinuous piezoelectric BaTi0.88Sn0.12O3 (BTS) films were deposited on glass fiber fabrics successfully.Superflexible, highly sensitive self-powered piezoelectric sensors were fabricated based on polarization-free BTS.Low curie temperature would be a benefit for flexible piezoelectric sensors because small alterations of force will trigger large changes in polarization.The superflexible sensors are highly desirable for wearable devices to detect human motion.

Harbor seal whisker inspired self-powered piezoelectric sensor for detecting the underwater flow angle of attack and velocity

Nowadays, there are high demands for robust, low-powered, miniaturized and light-weight sensors which can assist unmanned underwater vehicles (UUVs) in detecting hydrodynamic flow phenomena. Inspired by harbor seal whisker, this work presented a novel self-powered sensor for sensing the flow angle of attack and velocity, which provided a fine application foreground for UUVs’ navigation. The sensor featured a pillar emulating the whisker interaction with water flow, and a d33 mode piezoelectric diaphragm imitating the nerve in cheek of the harbor seal. The pillar had a high aspect ratio (height/diameter) and an ellipse cross section whose ratio of the minor axis to the major axis was around 0.484. The polarization reorientation realized by interdigitated electrodes and the resonant property of the sensor were numerically calculated. Prototype fabrication was accomplished by utilizing stereolithography and microfabrication. Impedance and phase spectra of the sensor under different electrode configurations were tested to illustrate its dynamic property. By employing an oscillating sphere to emulate underwater perturbations, sensor output under the excitation of oscillatory flows was examined. Its capability of detecting distinct water flow angles of attack was verified by experimental results. The sensitivity of the sensor in sensing water flow velocity was as high as 1.445 V/(m/s).

Piezoelectric sensor based on graphene-doped PVDF nanofibers for sign language translation

The tracking of body motion, such as bending or twisting, plays an important role in modern sign language translation. Here, a subtle flexible self-powered piezoelectric sensor (PES) made of graphene (GR)-doped polyvinylidene fluoride (PVDF) nanofibers is reported. The PES exhibits a high sensitivity to pressing and bending, and there is a stable correlation between bending angle and piezoelectric voltage. The sensitivity can be adjusted by changing the doping concentration of GR. Also, when the PES contacts a source of heat, a pyroelectric signal can be acquired. The positive correlation between temperature and signal can be used to avoid burns. The integrated sensing system based on multiple PESs can accurately recognize the action of each finger in real time, which can be effectively applied in sign language translation. PES-based motion-tracking applications have been effectively used, especially in human–computer interaction, such as gesture control, rehabilitation training, and auxiliary communication.

Wireless Single-Electrode Self-Powered Piezoelectric Sensor for Monitoring.

In complex environments, there are often toxic and harmful conditions, and so self-powered sensors that use wireless access have a huge advantage. However, there is still a risk of short circuit for self-powered sensors in harsh environments. A single-electrode self-powered sensor was designed, which can be used to monitor body movements such as walking and running, as well as monitoring the motion of some mechanical devices, such as peristaltic pumps, door, and window switches. By using a threshold delay algorithm, this self-powered sensor can be connected to the phone to warn the phone user to check for theft or illegal intrusion when the door and window are opened. Further research shows that the single-electrode configuration can avoid the short-circuit behavior caused by device damage so that the self-powered sensor can still work even if it is pierced. Therefore, the wireless single-electrode self-powered sensor system has better reliability and is more applicable to harsh environments.

Two-Dimensional van der Waals Materials with Aligned In-Plane Polarization and Large Piezoelectric Effect for Self-Powered Piezoelectric Sensors.

Piezoelectric two-dimensional (2D) van der Waals (vdWs) materials are highly desirable for applications in miniaturized and flexible/wearable devices. However, the reverse-polarization between adjacent layers in current 2D layered materials results in decreasing their in-plane piezoelectric coefficients with layer number, which limits their practical applications. Here, we report a class of 2D layered materials with an identical orientation of in-plane polarization. Their piezoelectric coefficients (e22) increase with layer number, thereby allowing for the fabrication of flexible piezotronic devices with large piezoelectric responsivity and excellent mechanical durability. The piezoelectric outputs can reach up to 0.363 V for a 7-layer α-In2Se3 device, with a current responsivity of 598.1 pA for 1% strain, which is 1 order of magnitude higher than the values of the reported 2D piezoelectrics. The self-powered piezoelectric sensors made of these newly developed 2D layered materials have been successfully used for real-time health monitoring, proving their suitability for the fabrication of flexible piezotronic devices due to their large piezoelectric responses and excellent mechanical durability.

Cowpea-structured PVDF/ZnO nanofibers based flexible self-powered piezoelectric bending motion sensor towards remote control of gestures

Interactive human-machine interface (iHMI) is a bridge connecting human beings and robots, which has an important requirement for perceiving the change of pressure and bending angle. Here, we designed a flexible self-powered piezoelectric sensor (PES) based on the cowpea-structured PVDF/ZnO nanofibers (CPZNs) for remote control of gestures in human-machine interactive system. Due to the synergistic piezoelectric effect of hybrid PVDF/ZnO and the flexibility of polymer, this PES exhibited excellent bending sensitivity of 4.4 mV deg−1 ranging widely from 44° to 122°, fast response time of 76 ms, and good mechanical stability. Besides, the PES could operate under both bending and pressing mode, show ultrahigh pressing sensitivity of 0.33 V kPa−1, with response time of 16 ms. When integrated in iHMI, the PES could be conformably covered on different curve surfaces, demonstrated accurate bending angle recording and fast recognition for realizing intelligent human-machine interaction. On this basis, the application of remote control of robotic hand was successfully realized in form of acting the same gesture as human hand synchronously. This CPZNs-based self-powered PES is distinct and unique in its structure and fundamental mechanism, and exhibits a prospective potential application in iHMI.

Facile Fabrication of a Flexible LiNbO3 Piezoelectric Sensor through Hot Pressing for Biomechanical Monitoring.

Wearable pressure sensors have attracted increasing attention for biomechanical monitoring due to their portability and flexibility. Although great advances have been made, there are no facile methods to produce sensors with good performance. Here, we present a simple method for manufacturing flexible and self-powered piezoelectric sensors based on LiNbO3 (LN) particles. The LN particles are dispersed in polypropylene (PP) doped with multiwalled carbon nanotubes (MWCNTs) by hot pressing (200 °C) to form a flexible LN/MWCNT/PP piezoelectric composite film (PCF) sensor. This cost-effective sensor has high sensitivity (8 Pa), fast response time (ca. 40 ms), and long-term stability (>3000 cycles). Measurements of pressure changes from peripheral arteries demonstrate the applicability of the LN/MWCNT/PP PCF sensor to biomechanical monitoring as well as its potential for biomechanics-related clinical diagnosis and forecasting.