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Significantly enhanced energy harvesting performance in lead-free piezoceramic via a synergistic design strategy
Abstract
With the rapid development of the Internet of Things, there exists an urgent necessity for high performance piezoelectric energy harvesters to facilitate the construction of more efficient wireless sensor systems....
Stretchable self‐powered sensors are of significant interest in next‐generation wearable electronics. However, current strategies for creating stretchable piezoelectric sensors based on piezoelectric polymers or 0–3 piezoelectric composites face several challenges such as low piezoelectric activity, low sensitivity, and poor durability. In this paper, a biomimetic soft‐rigid hybrid strategy is used to construct a new form of highly flexible, high‐performance, and stretchable piezoelectric sensor. Inspired by the hinged bivalve Cristaria plicata, hierarchical droplet‐shaped ceramics are manufactured and used as rigid components, where computational models indicate that the unique arched curved surface and rounded corners of this bionic structure can alleviate stress concentrations. To ensure electrical connectivity of the piezoelectric phase during stretching, a patterned liquid metal acts as a soft circuit and a silicone polymer with optimized wettability and stretchability serves as a soft component that forms a strong mechanical interlock with the hierarchical ceramics. The novel sensor design exhibits excellent sensitivity and durability, where the open circuit voltage remains stable after 5000 stretching cycles at 60% strain and 5000 twisting cycles at 180°. To demonstrate its potential in heathcare applications, this new stretchable sensor is successfully used for wireless gesture recognition and assessing the progression of knee osteoarthritis.
The µW‐level power density of flexible piezoelectric energy harvesters (FPEHs) restricts their potential in applications related to high‐power multifunctional wearable devices. To overcome this challenge, a hierarchical design strategy is proposed by forming porous piezoceramics with an optimum microstructure into an ordered macroscopic array structure to enable the construction of high performance FPEHs. The porous piezoceramic elements allows optimization of the sensing and harvesting Figure of merit, and the array structure causes a high level of effective strain under a mechanical load. The introduction of a network of polymer channels between the piezoceramic array also provides increased device flexibility, thereby allowing the device to attach and conform to the curved contours of the human body. The unique hierarchical piezoceramic array architecture exhibits superior flexibility, a high open circuit voltage (618 V), high short circuit current (188 µA), and ultrahigh power density (19.1 mW cm⁻²). This energy density value surpasses previously reported high‐performance FPEHs. The ultrahigh power flexible harvesting can charge a 0.1 F supercapacitor at 2.5 Hz to power high‐power electronic devices. Finally, the FPEH is employed in two novel applications related to fracture healing monitoring and self‐powered wireless position tracking in extreme environments.
Railway tracks must be managed appropriately because their conditions significantly affect railway safety. Safety is ensured through inspections by track maintenance staff and maintenance based on measurements using dedicated track geometry cars. However, maintaining regional railway tracks using conventional methods is becoming difficult because of their poor financial condition and lack of manpower. Therefore, a track condition diagnostic system is developed, wherein onboard sensing devices are installed on in-service vehicles, and the vibration acceleration of the car body is measured to monitor the condition of the track. In this study, we conduct long-term measurements using the system and evaluate changes in the track conditions over time using car-body vibration data. Filed test results showed that sections with degraded tracks were identified using car-body vibration data. The track degradation trend can be constructed using the results obtained. Furthermore, this study demonstrated that the track maintenance effect could be confirmed. A method for improving train position using the yaw angular velocity is proposed. The track irregularity position can be shown more clearly by monitoring the track condition using position-corrected data using the proposed method. It is also shown that the time-frequency analysis of measured car-body vertical acceleration is effective for evaluating the track condition more clearly.
The prevalence of wearable/implantable medical electronics together with the rapid development of the Internet of Medicine Things call for the advancement of biocompatible, reliable, and high‐efficiency energy harvesters. However, most current harvesters are based on toxic lead‐based piezoelectric materials, raising biological safety concerns. What hinders the application of lead‐free piezoelectric energy harvesters (PEHs) is the low power output, where the key challenge lies in obtaining a high piezoelectric voltage constant (g33) and harvesting figure of merit (d33 × g33). Here, micron pores are introduced into phased boundary engineered high‐performance (K, Na)NbO3‐based ceramic matrix, resulting in the state‐of‐the‐art g33 and the highest d33 × g33 values of 57.3 × 10⁻³ Vm N⁻¹ and 20887 × 10⁻¹⁵ m² N⁻¹ in lead‐free piezoceramics, respectively. Concomitantly, ultrahigh energy harvesting performances are obtained in porous ceramic PEHs, with output voltage and power density of 200 V and 11.6 mW cm⁻² under instantaneous force impact and an average charging rate of 14.1 µW under high‐frequency (1 MHz) ultrasound excitation, far outperforming previously reported PEHs. Porous ceramic PEHs are further developed into wearable and bio‐implantable devices for human motion sensing and percutaneous ultrasound power transmission, opening avenues for the design of next‐generation eco‐friendly WIMEs.
With the rapid development of self‐powered electronics such as wearables, implantable devices, and sensor networks, there is an increasing demand for power sources that have a high power density and a long lifespan to keep the entire system operational. Flexible piezoelectric materials with the capability of mechanical‐to‐electrical energy conversion have attracted significant interest because of their immense potential for harvesting human biomechanical energy. Herein, 3 mol.% yttrium stabilized zirconia ribbon ceramic is selected as a unique substrate to manufacture a large‐scale and all‐ceramic flexible Pb(Zr0.52Ti0.48)O3 piezoelectric energy harvester via the cost‐effective one‐step process. The flexible piezoelectric energy harvester delivers excellent performance with an open‐circuit voltage of ~105 V and short‐circuit current of ~0.58 µA under mechanical strain equivalent to human movement. Moreover, the output voltage of a flexible piezoelectric energy harvester varies linearly with strain, allowing it a promising candidate as a self‐powered strain sensor. Of particular importance is that a large‐scale piezoelectric energy harvester (4 × 4 cm2) can simultaneously light up eight commercial light emitting diodes without any external power source and circuit. This research provides an innovative approach to the fabrication of high‐performance and large‐scale flexible piezoelectric energy harvesters as well as self‐powered micromechanical devices. A large‐scale and all‐ceramic flexible Pb(Zr0.52Ti0.48)O3 (PZT) piezoelectric energy harvester is developed with the unique 3 mol% yttrium stabilized zirconia ribbon ceramic as a flexible substrate, which delivers excellent output performance and mechanical stability under mechanical strain equivalent to human‐movement. This research provides an innovative approach to the fabrication of high‐performance and large‐scale flexible piezoelectric energy harvesters as well as self‐powered micromechanical devices.
Halide perovskite‐based mechanical energy harvesters display excellent electrical output due to their unique ferroelectricity and dielectricity. However, the high toxicity and moisture sensitivity impede their practical applications. Herein, a stretchable, breathable and stable nanofiber composite (LPPS‐NFC) is fabricated through electrospinning of lead‐free perovskite/poly(vinylidene fluoride‐co‐hexafluoropropylene) (PVDF‐HFP) and styrene‐ethylene‐butylene‐styrene. The Cs3Bi2Br9 perovskites serve as efficient electron acceptors and local nucleating agents for the crystallization of polymer chains, thereby enhancing the electron‐trapping capacity and polar crystalline phase in LPPS‐NFC. The excellent energy level matching between Cs3Bi2Br9 and PVDF‐HFP boosts the electron transfer efficiency and reduces the charge loss, thereby promoting the electron‐trapping process. Consequently, this LPPS‐NFC‐based energy harvester displays an excellent electrical output (400 V, 1.63 μA cm−2, and 2.34 W m−2), setting a record of the output voltage among halide perovskite‐based nanogenerators. The LPPS‐NFC also exhibits excellent stretchability, waterproofness and breathability, enabling the fabrication of robust wearable devices that convert mechanical energy from different biomechanical motions, into electrical power to drive common electronic devices. The LPPS‐NFC‐based energy harvesters also endure extreme mechanical deformations (washing, folding and crumpling) without performance degradation, and maintain stable electrical output up to five months, demonstrating their promising potential for uses as smart textiles and wearable power sources. This article is protected by copyright. All rights reserved
In this paper, we review, compare, and analyze previous studies on vibration energy harvesting and related technologies. First, the paper introduces the basic aspects of vibration energy acquisition in the railway environment, including vibration frequency, train speed, energy flow in the train, and vibration energy harvesting potential. Generally, the methods for scavenging vibration energy caused by passing trains can be divided into four categories: electromagnetic harvesters, piezoelectric harvesters, triboelectric harvesters and hydraulic harvesters. The structure, output performance, merits and disadvantages of different energy harvesting strategies are summarized and compared. The application of vibration energy harvesters is explained as supplying power to monitoring sensors on the line side and the vehicle side. Finally, the paper addresses the challenges and difficulties that have not been completely resolved in the current research literature, including system stability, durability, and economy. Some recommendations to fill these research gaps are put forward for further investigation.
Softening of piezoelectric materials facilitates the development of flexible wearables and energy harvesting devices. However, as one of the most competitive candidates, piezoelectric ceramic‐polymer composites inevitably exhibit reduced power‐generation capability and weak mechanical strength due to the mismatch of strength and permittivity between the two phases inside. Herein a flexible, air‐permeable, and high‐performance piezoceramic textile composite with a mechanically reinforced hierarchical porous structure is introduced. Based on a template‐assisted sol‐gel method, a three‐order hierarchical ceramic textile is constructed by intertwining submillimeter‐scale multi‐ply ceramic fibers that are further formed by twisting micrometer‐scale one‐ply ceramic fibrils. Theoretical analysis indicates that large mechanical stress can be easily induced in the multi‐order hierarchical structure, which greatly benefits the electrical output. Fabricated samples generate an open‐circuit voltage of 128 V, a short‐circuit current of 120 µA, and an instantaneous power density of 0.75 mW cm−2, much higher than the previously reported works. The developed multi‐order and 3D‐interconnected piezoceramic textile shows satisfactory piezoelectricity (d33 of 190 pm V−1), air permeability (45.1 mm s−1), flexibility (Young's modulus of 0.35 GPa), and toughness (0.125 MJ m−3), collectively. The design strategy of obtaining balanced properties promotes the practicality of smart/functional materials in wearables and flexible electronics. The hierarchically interconnected piezoceramic textile is constructed by intertwining submillimeter‐scale multi‐ply ceramic fibers that are further formed by twisting micrometer‐scale one‐ply ceramic fibrils. The developed multi‐order and 3D‐interconnected piezoceramic textile shows satisfactory piezoelectricity (d33 of 190 pm V−1), air permeability (45.1 mm s−1), flexibility (Young's modulus of 0.35 GPa,), and toughness (0.125 MJ m−3), collectively.
The global energy crisis and environmental pollutions caused mainly by the increased consumption of nonrenewable energy sources prompted researchers to explore alternative energy technologies that can harvest energies available in the ambient environment. Mechanical energy is the most ubiquitous ambient energy that can be captured and converted into useful electric power. Piezoelectric transduction is the prominent mechanical energy harvesting mechanism owing to its high electromechanical coupling factor and piezoelectric coefficient compared to electrostatic, electromagnetic, and triboelectric transductions. Thus, piezoelectric energy harvesting has received the utmost interest by the scientific community. Advancements of micro and nanoscale materials and manufacturing processes have enabled the fabrication of piezoelectric generators with favorable features such as high electromechanical coupling factor, piezoelectric coefficient, flexibility, stretch-ability, and integrate-ability for diverse applications. Besides that, miniature devices with lesser power demand are realized in the market with technological developments in the electronics industry. Thus, it is anticipated that in near future, many electronics will be powered by piezoelectric generators. This paper presents a comprehensive review on the state-of-the-art of piezoelectric energy harvesting. The piezoelectric energy conversion principles are delineated, and the working mechanisms and operational modes of piezoelectric generators are elucidated. Recent researches on the developments of inorganic, organic, composite, and bio-inspired natural piezoelectric materials are reviewed. The applications of piezoelectric energy harvesting at nano, micro, and mesoscale in diverse fields including transportation, structures, aerial applications, in water applications, smart systems, microfluidics, biomedicals, wearable and implantable electronics, and tissue regeneration are reviewed. The advancements, limitations, and potential improvements of the materials and applications of the piezoelectric energy harvesting technology are discussed. Briefly, this review presents the broad spectrum of piezoelectric materials for clean power supply to wireless electronics in diverse fields.
Concrete compression is complex. Yet, understanding this behavior is indispensable for design. There are three main factors that affect concrete compression results: the specimen size, shape, and friction at its ends. These factors affect the observed phenomena, and they affect each other. This paper aims to review the current knowledge on concrete compression and the effect of size, shape and friction on it. Understanding their effects is essential for a safer design and more effective testing. Most of the advancements in this topic is old, with a few exceptions. So, this review highlights the gaps in knowledge, and reintroduces them once again. Concrete design codes should consider the size effect in calculations. Reducing friction is recommended to lower the strength variation. Reduced friction may also be used for testing smaller specimens more reliably. This leads to more accurate, and more economic concrete testing.
In today’s healthcare environment, the Internet of Things technology provides suitability among physicians and patients, as it is valuable in numerous medicinal fields. Wireless body sensor network technologies are essential technologies in the growth of Internet of Things healthcare paradigm, where every patient is monitored utilising small-powered and lightweight sensor nodes. A dual-hop, inter–wireless body sensor network cooperation and an incremental inter–wireless body sensor network cooperation with energy harvesting in the Internet of Things health-based paradigm have been investigated and designed in this work. The three protocols have been named and abbreviated as follows: energy harvesting–based dual-hop cooperation, energy harvesting–based inter–wireless body sensor network cooperation and energy harvesting–based incremental inter–wireless body sensor network cooperation. Outage probabilities for the three designed protocols were investigated and inspected, and mathematical expressions of the outage probabilities were derived. The simulation and numerical results showed that the energy harvesting–based incremental inter–wireless body sensor network cooperation provided superior performance over the energy harvesting–based inter–wireless body sensor network cooperation and energy harvesting–based dual-hop cooperation by 1.38 times and 5.72 times, respectively; while energy harvesting–based inter–wireless body sensor network cooperation achieved better performance over energy harvesting–based dual-hop cooperation by 1.87 times.
Texturing is an effective approach to improving the piezoelectricity of piezoelectric ceramics. In this work, <001> textured Li⁺‐doped 0.852Bi0.5Na0.5TiO3–0.11Bi0.5K0.5TiO3–0.038BaTiO3 ternary lead‐free piezoelectric ceramics are prepared by the reactive templates grain growth (RTGG) method. X‐ray diffraction (XRD) results demonstrate a high orientation degree of 77% along the <001> direction. Outstanding electro‐strain response, which is higher than most of reported BNT‐based textured ceramics, is achieved due to the contribution of oriented‐grains along the <001> direction. A large electro‐strain of 0.55% with a relatively low hysteresis is obtained at 6.5 kV/mm with corresponding large signal piezoelectric coefficient (d33∗) of 846 pm/V in the textured ceramics, which is 49% higher than that of the random ceramics. Besides, the electro‐strain could reach as high as 0.52%@5.5 kV/mm (d33∗ = 945 pm/V) at 100°C. These results indicate that the RTGG is an effective way to design high performance lead‐free piezoelectric materials.
The 0.5 wt% MnO2‐doped 0.95(K0.5Na0.5)(Nb0.965Sb0.035)O3‐0.01CaZrO3‐0.04(Bi0.5K0.5)(Hf0.98Ti0.02)O3 (95KNNS‐1CZ‐4BKHT) lead‐free ceramics with grain size from 0.31 to 3.83 µm are fabricated by hot‐press sintering (HPS), microwave sintering (MS), conventional sintering (CS), two‐step sintering (TSS), and a combination of two of the above‐mentioned methods. Then, the grain size effects on the phase transition, electrical properties, domain structure, and temperature stability of the ceramics are investigated. The phase structure evolves from single rhombohedral (R) phase to coexisted rhombohedral‐tetragonal (R‐T) phases around 1 µm. The electromechanical properties are strongly grain size dependent. The values of piezoelectric coefficient (d33) and planar electromechanical coupling factor (kp) first rise sharply when the grain size is less than 1 µm, and then increase mildly in the grain size range from 2.55 to 3.04 µm and finally almost remain a constant (≈450 pC N−1 and 54%) when the grain size is larger than 3.31 µm. The R‐T phase coexistence and strip‐like nanodomain structure characterized by an easier switching feature contribute to the high piezoelectric and electromechanical properties of coarse‐grained samples. This work not only clarifies the relationship between grain size and electrical properties in KNN‐based ceramics, but also provides a novel strategy for developing high‐performance lead‐free piezoceramics. (K,Na)NbO3‐based ceramics with grain size from 0.31 to 3.83 µm are fabricated. The grain size effects are investigated. The phase structure evolves from single rhombohedral (R) phase to coexisted rhombohedral‐tetragonal (R‐T) phases around 1 µm. The enhanced piezoelectricity is obtained in coarse‐grained samples. The R‐T phase boundary, typical strip‐like nanodomains, and easier domain switching are the origins of the enhanced piezoelectricity.
Due to issues with Pb toxicity, there is an urgent need for high performance Pb-free alternatives to Pb-based piezoelectric ceramics. Although pure BaTiO3 material exhibits fairly low piezoelectric coefficients, further designing of such a material system greatly enhances the piezoelectric response by means of domain engineering, defects engineering, as well as phase boundary engineering. Especially after the discovery of a Ba(Zr0.2Ti0.8)O3–x(Ba0.7Ca0.3)TiO3 system with extraordinarily high piezoelectric properties (d33 > 600 pC/N), BaTiO3-based piezoelectric ceramics are considered as one of the promising Pb-free substitutes. In the present contribution, we summarize the idea of designing high property BaTiO3 piezoceramic through domain engineering, defect-doping, as well as morphotropic phase boundary (MPB). In spite of its drawback of low Curie temperature, BaTiO3-based piezoelectric materials can be considered as an excellent model system for exploring the physics of highly piezoelectric materials. The relevant material design strategy in BaTiO3-based materials can provide guidelines for the next generation of Pb-free materials with even better piezoelectric properties that can be anticipated in the near future.
Largely distributed networks of sensors based on the small electronics have great
potential for health care, safety, and environmental monitoring. However, in order to have
a maintenance free and sustainable operation, such wireless sensors have to be
self-powered. Among various energies present in our environment, mechanical energy is widespread
and can be harvested for powering the sensors. Piezoelectric and triboelectric
nanogenerators (NGs) have been recently introduced for mechanical energy harvesting.
Here we introduce the architecture and operational modes of self-powered autonomous
wireless sensors. Thereafter, we review the piezoelectric and triboelectric NGs focusing
on their working mechanism, structures, strategies, and materials.
Energy harvesting exploits ambient sources of energy such as mechanical loads, vibrations, human motion, waste heat, light or chemical sources and converts them into useful electrical energy. The applications for energy harvesting include low power electronics or wireless sensing at relatively lower power levels (nW to mW) with an aim to reduce a reliance on batteries or electrical power via cables and realise fully autonomous and self-powered systems. This review focuses on flexible energy harvesting system based on polyvinylidene fluoride based polymers, with an emphasis on manipulating and optimising the properties and performance of the polymeric materials and related nanocomposites through structuring the material at multiple scales. Ferroelectric properties are described and the potential of using the polarisation of the materials for vibration and thermal harvesting using piezo- and pyro-electric effects are explained. Approaches to tailor the ferroelectric, piezoelectric and pyroelectric properties of polymer materials are explored in detail; these include the influence of polymer processing conditions, heat treatment, nanoconfinement, blending, forming nanocomposites and electrospinning. Finally, examples of flexible harvesting devices that utilise the optimised ferroelectric polymer or nanocomposite systems are described and potential applications and future directions of research explored.
In-home healthcare services based on the Internet-of-Things (IoT) have great business potential; however, a comprehensive platform is still missing. In this paper, an intelligent home-based platform, the iHome Health-IoT, is proposed and implemented. In particular, the platform involves 1) an open-platform-based intelligent medicine box (iMedBox) with enhanced connectivity and interchangeability for the integration of devices and services, 2) intelligent pharmaceutical packaging (iMedPack) with communication capability enabled by passive radio-frequency identification (RFID) and actuation capability enabled by functional materials, and 3) flexible and wearable bio-medical sensor device (Bio-Patch) enabled by the state-of-the-art inkjet printing technology and system-on-chip. The proposed platform seamlessly fuses IoT devices (e.g., wearable sensors, intelligent medicine packages, etc.) with in-home healthcare services (e.g., telemedicine) for an improved user experience and service efficiency. The feasibility of the implemented iHome Health-IoT platform has been proven in field trials.
High-performance piezoelectric materials are desirable for piezoelectric sensing applications. In this paper, piezoelectric α-BiB3O6 (BIBO) crystals were explored for high temperature sensing. Dielectric, piezoelectric and electromechanical properties were evaluated by using the impedance method, from which the piezoelectric charge coefficients were determined to be d14 = 10.9, d16 = 13.9, d21 = 16.7, d22 = 40.0, d23 = 2.5, d25 = 4.3, d34 = 18.7 and d36 = 13.0 pC/N, with corresponding piezoelectric voltage coefficients g14 = 122, g16 = 144, g21 = 225, g22 = 538, g23 = 34, g25 = 58, g34 = 165 and g36 = 121 × 10−3 V m N−1 at room temperature (RT). Of particular significance is that the receiving sensitivity of BIBO crystals was found to be 47.2 pm2 N−1, nearly one order of magnitude higher than that of LiNbO3 crystals. Moreover, the BIBO crystals were found to possess a high mechanical quality factor Qm (13000 at RT and >1000 at 600 °C), low dielectric loss (<0.1% at RT and 15% at 600 °C and 1 kHz), high electrical resistivity (2.5 × 108 Ω cm at 600 °C) and high temperature stability of piezoelectric coefficients (variations <±10%). All these properties demonstrate that BIBO crystals are promising for piezoelectric sensing over a broad temperature range.
This review covers energy harvesting technologies associated with pyroelectric materials and systems. Such materials have the potential to generate electrical power from thermal fluctuations and is a less well explored form of thermal energy harvesting than thermoelectric systems. The pyroelectric effect and potential thermal and electric field cycles for energy harvesting are explored. Materials of interest are discussed and pyroelectric architectures and systems that can be employed to improve device performance, such as frequency and power level, are described. In addition to the solid materials employed, the appropriate pyroelectric harvesting circuits to condition and store the electrical power are discussed.
Many technical communities are vigorously pursuing research topics that contribute to the Internet of Things (IoT). Nowadays, as sensing, actuation, communication, and control become even more sophisticated and ubiquitous, there is a significant overlap in these communities, sometimes from slightly different perspectives. More cooperation between communities is encouraged. To provide a basis for discussing open research problems in IoT, a vision for how IoT could change the world in the distant future is first presented. Then, eight key research topics are enumerated and research problems within these topics are discussed.
Investigations in the development of lead-free piezoelectric ceramics have recently claimed comparable properties to the lead-based ferroelectric perovskites, represented by Pb(Zr,Ti)O3, or PZT. In this work, the scientific and technical impact of these materials is contrasted with the various families of “soft” and “hard” PZTs. On the scientific front, the intrinsic nature of the dielectric and piezoelectric properties are presented in relation to their respective Curie temperatures (T
C) and the existence of a morphotropic phase boundary (MPB). Analogous to PZT, enhanced properties are noted for MPB compositions in the (Na,Bi)TiO3-BaTiO3 and ternary system with (K,Bi)TiO3, but offer properties significantly lower. The consequences of a ferroelectric to antiferroelectric transition well below T
C further limits their usefulness. Though comparable with respect to T
C, the high levels of piezoelectricity reported in the (K,Na)NbO3 family are the result of enhanced polarizability associated with the orthorhombic-tetragonal polymorphic phase transition being compositionally shifted downward. As expected, the properties are strongly temperature dependent, while degradation occurs through the thermal cycling between the two distinct ferroelectric domain states. Extrinsic contributions arising from domains and domain wall mobility were determined using high field strain and polarization measurements. The concept of “soft” and “hard” lead-free piezoelectrics were discussed in relation to donor and acceptor modified PZTs, respectively. Technologically, the lead-free materials are discussed in relation to general applications, including sensors, actuators and ultrasound transducers.
Here, a multiscale regulation strategy is proposed to simultaneously improve both Q m and d 33 in PZT piezoelectric ceramics. The obtained piezoelectric materials exhibit promising potential for high-power piezoelectric applications.
The demand for ultra-high temperature piezoelectric sensors in industrial applications has witnessed a rapid upsurge. In this study, the piezoelectric properties of La2Ti2O7 (LTO) piezoelectric ceramics with perovskite-like layered structure...
A gradient-index phononic crystal (GRIN PnC) capable of manipulating wave propagation can serve as an excellent input wave energy focusing platform for amplifying energy harvesting power generation. However, despite its remarkable focusing capability, the finite wavelength of the propagating elastic waves in the focal area causes voltage cancellation inside a piezoelectric element under multimode strains having opposite directions; this limits the capacity of the GRIN PnC-based energy harvesting system. This study demonstrates a rational electrode configuration for a piezoelectric energy harvesting (PEH) device that can maximize the performance of a given GRIN PnC platform. The multimode strain analysis experimentally performed on the PEHs distributed over the focusing area confirms that the patterned electrode PEH configuration is the most effective in alleviating strain and voltage cancellation while efficiently transferring the focused elastic wave energy. Furthermore, a proper combination of electrical connections between the patterned electrodes substantially increases the piezoelectric potential across the ceramic by maximizing the strain difference. The simultaneous tailoring of the piezoelectric ceramic composition and the electrode configuration leads to a maximum power generation of 7.06 mW even under off-resonance conditions, the largest ever reported in elastic wave energy harvesting.
Through the simultaneous use of composite design and template grain growth technology, the comprehensive performance of KNN-based piezoelectric ceramics has been significantly improved via the synergy of the textured structure and multiphase coexistence.
The improvement of wearable electronics is making energy harvesters appealing, as they lessen the requirement for regular recharge of wearable gadgets. In this work, fully printed, flexible piezoelectric nanogenerators (PENGs) with excellent performance were created using a 3D printing technology. This fully‐printing method is based on triethoxyvinylsilane (TEVS) coated barium titanate (BTO) nanoparticles, Polyvinylidene fluoride‐co‐trifluoroethylene (PVDF−TrFE), and silver electrode for additive manufacturing. The organic vinyl silane (VS) functional groups, which form a strong bond between inorganic nanoparticles and polymer, contribute to the homogeneous dispersion of BTO nanoparticles in the matrix. Composites with well‐distributed VS−BTO nanoparticles have fewer defects owing to stacking gaps, resulting in reduced charge annihilation during the transmission of the charge from inorganic nanoparticles to polymer. These fully printed VS−BTO/PVDF−TrFE PENGs outperform their untreated counterpart in terms of output voltage and power density, with a higher output voltage of 54 V even after 13,500 cycles and a higher power density of 28.5 μW cm–2. In practice, as‐printed devices may actively adapt to human movement due to their incredible flexibility and sensitivity, displaying their detection capability. The as‐printed piezoelectric sensor array is also enhanced for the detection of pulse from multipoint mechanical activity identification. The fully printed PENGs developed in this work show excellent potential to be used in wearable electronics for a new generation of sensing applications. This article is protected by copyright. All rights reserved
Implantable medical electronics (IMEs) are now becoming increasingly prevalent for diagnostic and therapeutic purposes. Despite extensive efforts, a primary challenge for IMEs is reliable wireless power and communication to provide well-controlled, therapeutically relevant effects. Ultrasonic energy transfer and communication (UETC) employing traveling ultrasound waves to transmit energy has emerged as a promising wireless strategy for IMEs. Nevertheless, conventional UETC systems are rigid, bulky, and based on toxic lead-based piezoelectric materials, raising efficiency and safety concerns. Here, we present a novel transcutaneous UETC system based on a two-dimensional flexible lead-free piezoelectric array (f-LFPA) that hybridizes high-performance (piezoelectric coefficient d33 ≈ 503 pC N-1) (K,Na)NbO3-based eco-friendly piezo-units with soft structural components. The newly developed lead-free piezo-unit exhibits submicron ferroelectric domains and superior energy harvesting figures of merit (d33g33 ≈ 20 000 × 10-15 m2 N-1), resulting in the prepared f-LFPA demonstrating a high output voltage of 22.4 V, a power density of 0.145 W cm-2, and a signal-to-noise ratio of more than 30 dB within the FDA safety limits, while maintaining the flexibility for wide-angle receiving. Further ex vivo experiment demonstrates the adequate power supply capabilities of the f-LFPA and its possible application in future implantable eco-friendly bioelectronics for diagnostics, therapy, and real-time monitoring.
Although high piezoelectric coefficients have recently been observed in poly(vinylidene fluoride-co-trifluoroethylene) [P(VDF-TrFE)] random copolymers, they have low Curie temperatures, which makes their piezoelectricity thermally unstable. It has been challenging to achieve high piezoelectric performance from the more thermally stable PVDF homopolymer. In this report, we describe how high-power ultrasonic processing was used to induce a hard-to-soft piezoelectric transition and improve the piezoelectric coefficient d31 in neat PVDF. After high-power ultrasonication for 20 min, a uniaxially stretched and poled PVDF film exhibited a high d31 of 50.2 ± 1.7 pm V-1 at room temperature. Upon heating to 65 °C, the d31 increased to a maximum value of 76.2 ± 1.2 pm V-1, and the high piezoelectric performance persisted up to 110 °C. The enhanced piezoelectricity was attributed to the relaxor-like secondary crystals in the oriented amorphous fraction, broken off from the primary crystals by ultrasonication, as suggested by differential scanning calorimetry and broadband dielectric spectroscopy studies.
It is well known that Poly(vinylidene fluoride) (PVDF) polymer and its composites exhibit limited piezoelectricity only after strong electric field poling (SEFP) to align randomly oriented molecular dipoles inside. Here, we report that a (Pb, Zr)TiO3 (PZT) particles doped PVDF-polymer nanocomposite shows a large poling-free piezoelectric (PFP) coefficient and strong electromechanical coupling after experiencing mechanically directional stress field (MDSF). Analyses based on WAXD, FTIR, and HRTEM reveal that the MDSF actives and then induces a crystal phase transformation (CPT) from disordered star-shape nanocrystals to ordered, self-poled chain-shape high-β nanocrystalline fibers. PFM scanning images further show the existence of well-defined polarization. Furthermore, a 7-layer series-connected, self-powered circular pressure sensor was fabricated using multi-material 3D-printing technology, which exhibits a high sensitivity of 235 mV/kPa and a high-power density of 0.9 mW/cm² under a dynamic pressure of 255 kPa, and it is near 8 times higher than that of a conventional, poled single-layer PVDF sensor. Finally, a (3 × 3) real-time lighting tactile sensor array is 3D printed, confirming its feasibility for practical application. The MDSF-induced CPT and large PFP effect are significant because it may open a way to fabricate piezopolymer integrated devices without SEFP.
The bond strength between ultra-high-performance concrete (UHPC) and normal-strength concrete (NSC) is difficult to measure owing to the strong bond performance in a rough repair surface, particularly in the substrate failure mode. It is worth developing a relatively simple testing method to measure the bond strength of UHPC–NSC. A modified direct tensile test was conducted to measure the bond strength in this study. Moreover, the effects of interfacial parameters and testing methods on bond strength between UHPC and NSC were investigated. A total of 135 composite specimens were fabricated to measure the bond strength. Slant shear and direct tensile tests were performed to obtain the UHPC–NSC bond strength. Three types of substrate surfaces were obtained using a high-pressure water-treated substrate at different times. Moreover, the effectiveness of the modified direct tensile test method to measure the UHPC–NSC bond strength was verified. The results suggested that the bond failure mode of the NSC substrate failed for a rough surface (average sand-filling depth equal to or larger than 0.63 mm). The results of all the methods to evaluate the surface roughness of the substrate were consistent. Additionally, the direct tensile bond strength had a higher coefficient of variation than that of the modified direct tensile test method. Thus, the modified direct tensile test method, rather than the direct tensile bond strength, could reflect the effect of roughness on bond performance, specifically on rough surfaces.
Ferroelectric materials have attracted significant interest due to their wide potential in energy harvesting, sensing, storage, and catalytic applications. For monolithic and dense ferroelectric materials, their performance figures of merit for energy harvesting and sensing are limited by their high relative permittivity, and their low surface area can limit piezo- or pyro-catalytic applications. As a result, the introduction of porosity into dense ferroelectric materials can enhance performance for a variety of piezoelectric and pyroelectric applications. In this review, the piezoelectric, pyroelectric, ferroelectric and mechanical properties of porous ferroelectrics are presented, and the fabrication processes to create porous ferroelectric materials are classified and discussed. Simulations of the poling process and resulting piezo- and pyro-electric properties are also described to understand the underlying science of these fascinating porous materials and develop new approaches towards materials design. Applications of porous ferroelectric materials in specific fields are then summarized. Finally, conclusions and future perspectives for porous ferroelectric materials are provided. This journal is
With the rapid development of the Internet of things (IoT), wearable electronics, how to power them has been a great challenge, as the traditional powering method via batteries suffers from the problems of batteries’ limited capacity and lifetime. Piezoelectric nanogenerators (PENGs) is one of the most promising solutions, as they can convert the ubiquitous and versatile mechanical energy into electricity. Since its invention in 2006, the PENG has achieved tremendous progress. Its voltage has increased from a few millivolts to hundreds of volts, and its current has increased from nanoampere to hundreds of microamperes. In this review, the working mechanisms of PENGs are discussed at first to point out how to improve PENGs’ output theoretically. Then, according to the theoretical analysis, concrete methods including developing piezoelectric materials with high electromechanical response, structural optimization to scale up the electricity generated by individual nanomaterials are discussed. Next, considering the mismatch between the pulse signal generated by PENGs and the stable power supply requirement for conventional electronics, power extraction circuits are discussed. Finally, an outlook of future developments of high output PENGs is given.
Novel portable power sources that featured with high flexibility, built-in sustainability and enhanced safety have attracted ever-increasing attention in the field of wearable electronics. Herein, a novel flexible self-charging sodium-ion full battery was feasibly fabricated by sandwiching BaTiO3-P(VDF-HFP)-NaClO4 piezoelectric gel-electrolyte film into advanced Na3V2(PO4)3@C cathode and hard carbon anode. Except the considerable flexibility and electrochemical storage performance, the as-designed device also delivers sound self-charging capability via various stress patterns, no matter static compressing, repeated bending or continuous palm patting. The serially connected self-charged devices are able to drive several electronic devices with good working state. Specifically, a unique theory of electromagnetic field was successfully introduced to deduce the direct self-charging mechanism, where no rectifier was applied and the battery was charged by the built-in piezoelectric component. This work presents an innovative approach to achieve new sustainable and safety flexible sodium-ion battery for self-powered wearable electronics.
Energy harvesting utilizing piezoelectric materials has recently attracted extensive attention due to the strong demand of self-powered electronics. Unfortunately, low power density and poor long-term stability seriously hinder the implementation of lead-free piezoelectrics as high-efficiency energy harvesters. For the first time, we demonstrate that tailoring grain orientations of lead-free ceramics via templated grain growth can effectively produce ultrahigh power generation performance and excellent endurance against electrical/mechanical fatigues. Significantly improved fatigue resistance was observed in (Ba0.94Ca0.06)(Ti0.95Zr0.05)O3 grain-oriented piezoceramics ( with ~99% [001]c texture) up to 106 bipolar cycles, being attributed to the enhanced domain mobility, less defect accumulation, and thus the suppressed crack generation/propagation. Excitingly, the novel energy harvesters, which were developed based on the textured ceramics with high electromechanical properties, possessed ~9.8 times enhancement in output power density compared to the non-textured counterpart, while maintaining stable output features up to 106 vibration cycles. The power densities, which increased from 6.4 µW/mm3 to 93.6 µW/mm3 with raising acceleration excitation from 10 m/s2 to 50 m/s2, are much higher than those reported previously on lead-free energy harvesters. This work represents a significant advancement in piezoelectric energy harvesting field and can provide guidelines for future efforts in this direction.
This paper combines experimental and modelling studies to provide a detailed examination of the influence of porosity volume fraction and morphology on the polarisation-electric field response of ferroelectric materials. The broadening of the electric field distribution and a decrease in the electric field experienced by the ferroelectric ceramic medium due to the presence of low-permittivity pores is examined and its implications on the shape of the hysteresis loop, remnant polarisation and coercive field is discussed. The variation of coercive field with porosity level is seen to be complex and is attributed to two competing mechanisms where at high porosity levels the influence of the broadening of the electric field distribution dominates, while at low porosity levels an increase in the compliance of the matrix is more important. This new approach to understanding these materials enables the seemingly conflicting observations in the existing literature to be clarified and provides an effective approach to interpret the influence of pore fraction and morphology on the polarisation behaviour of ferroelectrics. Such information provides new insights in the interpretation of the physical properties of porous ferroelectric materials to inform future effort in the design of ferroelectric materials for piezoelectric sensor, actuator, energy harvesting, and transducer applications.
Piezoelectric energy harvesters are at the front of scientific research as enablers of renewable, sustainable energy for autonomous wireless sensor networks. Crucial for this disruptive technology is the achievable output power. Here we show, analytically, that the maximum output energy per unit volume, under a single sinusoidal excitation, is equal to 1/(4 − 2k²) × 1/2dgX², where k² is the electromechanical coupling coefficient, d and g are the piezoelectric charge and voltage coefficient, respectively, and X is the applied stress. The expression derived is validated by the experimentally measured output energy for a variety of piezoelectric materials over an unprecedented range of more than five orders of magnitude. As the prefactor 1/(4 − 2k²) varies only between 1/2 and 1/4 the figure of merit for piezoelectric materials for energy harvesters is not k², as commonly accepted for vibrational harvesters, but dg. The figure of merit does not depend on the compliance, or Young's modulus. Hence we argue that commonly used brittle inorganic piezoelectric ceramics can be replaced by soft, mechanically flexible polymers and composite films, comprising inorganic piezoelectric materials embedded in a polymer matrix.
To develop lead-free compounds with high electromechanical properties is a critical issue for the piezoelectric materials development. Bi0.5Na0.5TiO3 (BNT) and its solid solutions are the famous lead-free family. There have been lots of efforts contributed to improve their piezoelectric properties by doping or texturing. Here, we developed 3-1 type porous 0.94Bi0.5Na0.5TiO3–0.06BaTiO3 (BNT-6BT) ceramic by a freeze-casting technique. The porous ceramics showed enhanced piezoelectric coefficient (d33) and electrical-induced strain. The d33 can reach 182 pC/N and the maximum strain is 0.42% at an electric field of 70 kV/cm, which is much higher than values on the dense BNT-6BT ceramic. These enhanced properties would be explained by the domain structures and the surface effect. With the previous studies, this result indicates that the 3-1 type porous structure has the potential to be widely applied to improve the piezoelectric properties of the lead-free ferroelectric ceramics.
Recently, smart systems have met with large success. At the origin of the internet of things, they are a key driving force for the development of wireless, sustainable, and independent autonomous smart systems. In this context, autonomy is critical, and despite all the progress that has been made in low-power electronics and batteries, energy harvesters are becoming increasingly important. Thus, harvesting mechanical energy is essential, as it is widespread and abundant in our daily life environment. Among harvesters, flexible triboelectric nanogenerators (TENGs) exhibit good performance, and they are easy to integrate, which makes them perfect candidates for many applications and, therefore, crucial to develop. In this review paper, we first introduce the fundamentals of TENGs, including their four basic operation modes. Then, we discuss the different improvement parameters. We review some progress made in terms of performance and integration that have been possible through the understanding of each operation mode and the development of innovative structures. Finally, we present the latest trends, structures, and materials in view of future improvements and applications.
© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Porous BiScO3-0.64PbTiO3 (BS-0.64PT) ceramics were fabricated by using burnable plastic sphere technique (BURPS). Self-synthesized polystyrene microsphere (PS, φ360 nm) was used as pore forming agent (PFA). Porosity of the porous ceramics was regulated by adjusting sintering temperature and volume fraction of PFA. The porous ceramics were characterized by means of X-Ray diffraction (XRD) and scanning electron microscopy (SEM). All samples were pure tetragonal perovskite. Properties of the porous ceramics, including porosity, piezoelectric coefficient (d33) and dielectric properties (Ɛr) were measured. Electromechanical coupling coefficients (kp, kt, k31), mechanical quality factor (Qm), piezoelectric coefficient (d31, dh), hydrostatic voltage coefficient (gh), acoustic impedance (Z), hydrostatic figure of merit (HFOM) were derived from impedance spectrum. Sintering temperature and volume fraction of PFA were optimized to bring out porous ceramics with highest gh and HFOM. Porous ceramic with 50 vol% PS microspheres sintered at 1000 °C possessed porosity of 17.12%, with gh and HFOM to be 0.024 V/m·Pa and 6087×10−15/Pa, respectively.
A highly-efficient, lightweight, flexible, piezoelectric lead zirconate titanate (PZT) thin-film nanogenerator is demonstrated by employing the laser lift-off transfer technique and a lateral electrode structure. As reported by K. J. Lee and co-workers on page 2514, this large-area PZT thin-film nanogenerator can convert to the highest output performance from a slight mechanical deformation and provides the feasibility of fully flexible self-powered electronics.
Freeze casting of aqueous suspension was investigated as a method for fabricating hydroxyapatite (HA) porous ceramics with lamellar structures. The rheological properties of HA suspensions employed in the ice-templated process were investigated systematically. Well aligned lamellar pores and dense ceramic walls were obtained successfully in HA porous ceramics with the porosity of 68–81% and compressive strength of 0.9–2.4 MPa. The results exhibited a strong correlation between the rheological properties of the employed suspensions and the morphology and mechanical properties of ice-templated porous HA ceramics, in terms of lamellar pore characteristics, porosities and compressive strengths. The ability to produce aligned pores and achieve the manipulation of porous HA microstructures by controlling the rheological parameters were demonstrated, revealing the potential of the ice-templated method for the fabrication of HA scaffolds in biomedical applications.
Ba(Zr0.085Ti0.915)O3 (BZT) ceramics were grain-oriented (textured) in the -orientation using the Templated Grain Growth (TGG) process. The
piezoelectric response of the textured samples was enhanced when poled and measured in the -textured direction. The d33-coefficients for samples measured with a low drive field (33-coefficients were at least three times greater than randomly-oriented BZT ceramics and equally greater than many lead-free
piezoelectric ceramics reported in literature. This work successfully demonstrated that grain-oriented BZT ceramics display
piezoelectric coefficients (d33-coefficients) that are similar to currently used lead-based materials. This strategy may allow these ceramics to potentially
replace some of the lead-based ceramics that are currently being used in various low-temperature and low-drive piezoelectric
applications.