Piezoelectric Voltage Constant Research Articles

Phase evolution and piezoelectric properties of SnO2 doped KNN based piezoceramics

The present research focuses on the electrical properties of lead-free piezoceramics (0.985-x)(K0.485Na0.485Li0.03)(Nb0.96Sb0.04)O3-0.015(Bi0.5Na0.5)ZrO3-xSnO2 (KNNLS-BNZ-xSnO2, x = 0.003, 0.006, 0.009, 0.012, and 0.015). This study examines the influence of varying SnO2 doping levels on the microstructure and piezoelectric properties of the ceramics. All the ceramics prepared demonstrate pure perovskite structure without any secondary phases. The Rietveld refinement analysis of XRD data reveals the existence of multiphase evolution around room temperature. The tetragonality (c/a) and cell volume of the ceramics tend to rise with an increase in Sn4+ content, potentially leading to improved ferroelectric characteristics. The optimum values obtained were Curie temperature (Tc) = 395 oC, remnant polarization (Pr) = 21.07 μC/cm2, piezoelectric coefficient (d33)=357 pC/N, piezoelectric voltage constant (g33) = 24 × 10−3 Vm/N, and figure of merit (FOMoff) = 10.34 pm2/N, corresponding to the ceramic doped with x = 0.012 SnO2. The findings indicate that an optimal amount of Sn4+ in the host composition KNNLS-BNZ improves piezoelectric properties by constructing an R-O-T phase boundary near room temperature. This study suggests that the ceramic with x = 0.012 SnO2 exhibits a favorably high Tc coupled with an exceptional energy harvesting capability, making it a suitable candidate for energy harvesting applications.

3D printing of lead zirconate titanate piezoelectric ceramics via digital light processing (DLP)

Research of piezoelectric ceramics via DLP technology has drawn considerable interest due to its high geometrical flexibility. However, the poor curing properties limit the use of DLP technology to fabricate piezoelectric ceramics. Herein, we overcome this challenge in prepared lead zirconate titanate (PZT) piezoelectric ceramics via DLP technology by incorporating ultralow refractive index and ultraviolet light absorptivity of soluble starch in PZT ceramic slurry. After the post-process, the relative density of printed PZT ceramic with 20 vol% soluble starch could reach about 89.51% of theoretical density. The printed PZT ceramic exhibits remarkable dielectric permittivity, remnant polarization, piezoelectric strain constant, piezoelectric voltage constant, figure of merit and electromechanical coupling factor of 2196, 35.56 μC/cm2, 373 pC/N, 1.92 × 10−2 Vm/N, 7.16 × 10−12 m2/N and 42.28%, respectively. The results achieved in this research indicate that our work provides a promising route for fabrication of advanced ceramics with high performance and designed complex structures by digital light processing.

Additive Manufacturing of Piezoelectric Niobium-Doped Lead Zirconate Titanate (PZT-N) by Binder Jetting

Binder jetting is an emerging indirect additive manufacturing technique for ceramic materials, which could be employed to produce application-oriented designed components impossible to achieve with traditional processes and featuring enhanced performances. In our study, niobium-doped lead zirconate titanate (PZT-N) powder, usually processed through the standard press-and-sinter route, was employed as the raw material. First, the powder was characterized in terms of granulometry and flowability to assess its suitability for the printing process. Then, shaping by binder jetting was studied, and the effect of three levels of binder saturation (75–90–105%) on the green bodies was assessed. Finally, the microstructure of the sintered samples was studied using SEM, to investigate the effect of thermal treatments on the grain size distribution and residual porosity (~40%). The piezoelectric properties were measured and compared to those of conventionally processed material. The piezoelectric charge and voltage constants (d33 and g33) were evaluated to determine the possible use of printed parts as porous piezoelectric components to be exploited in hydrophones in the direct mode.

Identification of biomolecule-based electronic materials from a first-principles study of aliphatic amino acids.

Biomolecule-based electronic materials can enable health innovations by virtue of their intrinsic bioactivity and physical properties. However, the ultra-wide bandgap and limited piezoelectric properties of most biomaterials prevent them from reaching their full potential. Herein, the electronic structures and electromechanical properties of aliphatic amino acid crystals are investigated based on density functional theory. L-Met is found to be a wide bandgap p-type semiconductor, and the much-reduced bandgap of 2.88 eV is ascribed to the sulphur atoms in L-Met. L-Leu has a shear piezoelectric voltage constant of 2.706 V mN-1 that is over an order of magnitude higher than that of lead zirconate titanate, and good toughness and ductility are also revealed in L-Leu from mechanical property investigations. This study illustrates a computational approach to find smart and multifunctional biomaterials and inspire their growth and applications.

Multilevel Structure Engineered Lead‐Free Piezoceramics Enabling Breakthrough in Energy Harvesting Performance for Bioelectronics

AbstractThe 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.

Bond engineering of molecular ferroelectrics renders soft and high-performance piezoelectric energy harvesting materials

Piezoelectric materials convert mechanical stress to electrical energy and thus are widely used in energy harvesting and wearable devices. However, in the piezoelectric family, there are two pairs of properties that improving one of them will generally compromises the other, which limits their applications. The first pair is piezoelectric strain and voltage constant, and the second is piezoelectric performance and mechanical softness. Here, we report a molecular bond weakening strategy to mitigate these issues in organic-inorganic hybrid piezoelectrics. By introduction of large-size halide elements, the metal-halide bonds can be effectively weakened, leading to a softening effect on bond strength and reduction in polarization switching barrier. The obtained solid solution C6H5N(CH3)3CdBr2Cl0.75I0.25 exhibits excellent piezoelectric constants (d33 = 367 pm/V, g33 = 3595 × 10−3 Vm/N), energy harvesting property (power density is 11 W/m2), and superior mechanical softness (0.8 GPa), promising this hybrid as high-performance soft piezoelectrics.

High‐power piezoelectric energy harvester produced using [0 0 1]‐textured (Na, K)NbO3‐based lead‐free piezoceramics

AbstractHigh‐power piezoelectric energy harvesters (PEHs) require piezoceramics with a large kp and d33 but small εT33/ε0 values. The [0 0 1]‐textured 0.96(Na, K)(Nb1−xSbx)–0.04SrZrO3 piezoceramics (x = 0.025 and 0.045) exhibited the improved electromechanical coupling factor (kp) and piezoelectric charge constant (d33); however, the increase of dielectric constant (εT33/ε0) was not significant. Further, the textured piezoceramic with x = 0.045 shows the large d33 × g33 value of 21.5 pm2/N, where g33 is piezoelectric voltage constant, indicating that texturing is a good technique to fabricate the piezoceramics for PEH. The impedance curve of the PEH consisting of the metal substrate and textured piezoceramic shows a piezoelectric resonance peak at a low frequency, which is the same as the mechanical resonance frequency of the PEH. Hence, the PEH can be considered a piezoelectric material. The figure of merit of the PEH was determined using the mechanical quality and electromechanical coupling factor calculated from the impedance curve of the PEH. A large power output of 1.7 mW was obtained from the type‐1 PEH at the resonance frequency produced using the textured thick film (x = 0.045). Hence, this PEH can be used as a permanent power source for microelectronic devices in the Internet of Things.

Ultrahigh sensitive flexible sensor based on textured piezoelectric composites for preventing sports injuries

Textured piezoelectric composites (PCs) based on dielectrophoresis (DEP) reveal great merits in both improving sensitivity and maintaining flexibility, thus trending to be promising candidates for high sensitive flexible sensors. However, the DEP technique shows poor applicability in fabricating textured PCs with high filling content, which severely limits further improvement of piezoelectric performance. Herein, we propose a new strategy to enhance DEP force by decorating Cu nanoparticles on Ba0.85Ca0.15Ti0.9Zr0.1O3 (BCZT) particles, thus textured BCZT@Cu/PDMS PCs with high filling content are obtained. The results proved that the enhanced DEP force is contributed by the excellent conductivity and capability of distorted electric fields of decorated Cu nanoparticles. Consequently, an ultrahigh piezoelectric voltage constant (g33) of 720 × 10−3 Vm/N was achieved, which is much larger than that in other counterparts. Furthermore, the as-prepared piezoelectric sensor exhibits excellent sensitivity and flexibility, which can fit vulnerable joints like a band-aid seamlessly. On this basis, a flexible sport health monitoring system was developed, which shows great capabilities in real-time warn of the risky actions, rectification of wrong postures, and sports injury prevention.

Piezoelectric voltage constant and sensitivity enhancements through phase boundary structure control of lead-free (K,Na)NbO3-based ceramics

The piezoelectric voltage constant (g33) is a material parameter critical to piezoelectric voltage-type sensors for detecting vibrations or strains. Here, we report a lead-free (K,Na)NbO3 (KNN)-based piezoelectric accelerometer with voltage sensitivity enhanced by taking advantage of a high g33. To achieve a high g33, the magnitudes of piezoelectric charge constant d33 and dielectric permittivity εr of KNN were best coupled by manipulating the intrinsic polymorphic phase boundaries effectively with the help of Bi-based perovskite oxide additives. For the KNN composition that derives benefit from the combination of εr and d33, the value of g33 was found to be 46.9 × 10−3 V·m/N, which is significantly higher than those (20 – 30 × 10−3 V·m/N) found in well-known polycrystalline lead-based ceramics including commercial Pb(Zr,Ti)O3 (PZT). Finally, the accelerometer sensor prototype built using the modified KNN composition demonstrated higher voltage sensitivity (183 mV/g) when measuring vibrations, showing a 29% increase against the PZT-based sensor (142 mV/g).

Enhanced electrical and energy harvesting performances of lead-free BMT modified BNT piezoelectric ceramics

ABSTRACT Lead-free (1-x) (Bi0.5Na0.5)TiO3-xBi(Mg0.5Ti0.5)O3 or (1-x)BNT-xBMT (x = 0–0.20) piezoelectric ceramics have been investigated for phase evolution, microstructure, dielectric, ferroelectric, piezoelectric, electric field-induced strain, energy storage density, energy harvesting, and magnetic properties. All compositions exhibited high density sintered ceramics (~ 6.13–6.30 g/cm3). With increasing modifier content, the crystal structure changed from rhombohedral to cubic phase. When BMT content was added, the grain size and Tm were found to increase. The x = 0.05 ceramic showed good piezoelectric (low-field d33 = 159 pC/N) and ferroelectric (Pr = 23.84 µC/cm2, Ec = 34.41 kV/cm) properties. The BMT additive also produced an improvement in electric field-induced strain, energy storage efficiency, and magnetic properties. The highest piezoelectric voltage constant (g33 = 26.29 × 10−3 Vm/N) and the off-resonance figure of merit (FoM) for energy harvesting (~ 4.18 pm2/N) were also obtained for the x = 0.05 ceramic, which was ~ 3.4 times (240%) as compared to the pure BNT ceramic. This suggested that the ceramic has a potential to be one of the promising lead-free piezoelectric candidates for further use in piezoelectric energy harvesting applications.

High-temperature workable flexible piezoelectric energy harvester comprising thermally stable (K,Na)NbO3-based ceramic and polyimide composites

Composite-based piezoelectric devices have been widely investigated to realize a semi-permanent power supplier or self-powered sensors with high flexibility; however, their working temperatures are mostly restricted below 200 °C. Herein, we report high-temperature and flexible composite-based piezoelectric energy harvesters (f-PEHs) comprising lead-free (K,Na)NbO 3 (KNN)-based ceramic dispersants and polyimide matrix. The KNN-based ceramics with different BiScO 3 (BS) compositions of 0.0025 and 0.01 were synthesized via a solid-state reaction and characterized under high-temperature conditions. Thereafter, the output voltage, current signals, and effective power of f-PEHs with 0.0025BS- and 0.01BS-doped KNN-based particles were measured at the temperature range from room temperature (RT) to 300 °C. The 0.0025BS KNN-adopted f-PEH not only generated 130% higher output voltage (∼4 V) and 137% higher current (∼0.24 μA) than the device with 0.01BS-doped KNN at RT, but also has superior electrical outputs compared to those harvested from the 0.01BS KNN-adopted f-PEH over all temperature ranges. These measurement results corresponded well with the trend of change in piezoelectric voltage constants and piezoelectric figure of merit characterized from ceramic discs, respectively. Moreover, theoretical and quantitative analyses using finite element method simulations proved that 0.0025BS is more suitable for the fabrication of high-temperature f-PEH compared to 0.01BS. This work can serve as a guide for developing a fully flexible and high-temperature workable f-PEH to realize self-powered sensor systems in high-temperature environments. • High-temperature workable flexible piezoelectric energy harvesters (f-PEHs) were fabricated using piezo-ceramic and polyimide. • Temperature-dependent piezoelectric properties of (K,Na)NbO 3 -based ceramics were characterized under high-temperature. • A fabricated energy harvester generated an output voltage of ∼4 V and a current of ∼0.24 μA under repeated bendings. • A fabricated energy harvester exhibits exceptional high-temperature stability over the temperature range from 30 to 300 °C.

Experimental investigation into the sensitivity of elastically coated piezoelectric polyvinylidene fluoride films to an impact force

This paper presents an experimental study on the effect of an elastic coating on the sensitivity to an impact force on a polyvinylidene fluoride (PVDF) film by using a model consisting of a top mass, a coated/uncoated PVDF film, and a base block. The sensitivity of the PVDF film is determined by measuring the voltage outputs from the PVDF film and an impact hammer, which is used to excite the top mass. The effects of the constraints at the top and bottom surfaces of an uncoated PVDF film on the sensitivity are examined first. Experimentally, the shear-free and perfectly bonded constraints are approximated by applying oil and epoxy glue to the interfaces between the PVDF film and the top mass/base block. The sensitivities of the PVDF film for these two constraints are determined analytically, thus explaining the roles of the stress components in the thickness and in-plane directions of the film in generating the voltage outputs. The approximated shear-free boundary condition using oil at the interface allows an experimental determination of the piezoelectric voltage constant of the PVDF film in the poling direction. Rubber and polyurethane are used for constructing the coated PVDF films. Even a thin layer of elastic coating is capable of significantly increasing the sensitivity of the PVDF film. For example, 3 mm rubber layers allow a 27 dB increase in the low-frequency sensitivity. A system including an elastically coated PVDF film provides an additional 10 dB increase at frequencies close to its first resonance frequency, resulting in a total 37 dB increase in the system sensitivity. The increased sensitivity may be explained as being due to the increased shear force between the elastic material and PVDF film as the thickness of the elastic layer increases. The dominating effect of the shear force is illustrated by the experimental and finite-element analysis as the thickness of the rubber coating gradually increases. The high rate of increase of the sensitivity as a function of rubber thickness can be observed when the thickness is under 0.8 mm.

Enhanced energy harvesting performance of Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 ceramics by Mn-doping defect engineering

Piezoelectric energy harvesting has recently attracted widespread attention due to its promising development of self-powered applications. However, the low piezoelectric voltage constant and high damping loss limit the implementation of high-performance perovskite ferroelectrics as high-efficiency energy harvesters. Here, the energy harvesting properties of Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 ceramics were significantly improved utilizing Mn-doping defect engineering. After doping Mn, the figure of merit of FOMoff-resonance and FOMon-resonance increased by 109.8% and 643.5%, respectively, while the energy transduction efficiency η increased by 18.52%. Our work provides an effective optimization strategy of energy harvesting properties of PT-based perovskite ferroelectrics.

3D printed 0–3 type piezoelectric composites with high voltage sensitivity

Piezoelectric composites made of piezoelectric ceramic particles and polymer composites combine the performance advantages of both components and have broad application prospects. However, the preparation of complex structures is still a challenge, for which 3D printing technology provides a perfect solution. The aim of the present study is to investigate the principle and process optimization of the stereolithography of 0–3 type piezoelectric composites through simulation and experiments. In particular, a modified three-phase model of a spherical shell is applied to elucidate the influence of the elastic modulus between the ceramic particles and the matrix on the piezoelectric properties of the composites at the macroscopic level. This enables the piezoelectric properties of the composites to be predicted more accurately, and guides the surface grafting modification of piezoelectric ceramic powders. Furthermore, the problem of weak interface bonding in piezoelectric composites caused by poor compatibility between hydrophilic particles and the hydrophobic matrix is successfully solved by preprocessing the PZT ceramic powder via activating the particle surface hydroxyl groups and grafting a silane coupling agent onto the piezoelectric ceramic powder. As a result, the particles are bonded to the matrix by covalent bonds, which increases the elastic modulus of the interface transition layer and modifies the stress transfer efficiency. For instance, the piezoelectric strain constant (d33) of piezoelectric composite containing 60 wt% functionalized PZT particles is increased from 20 to 37 pC/N. The printing accuracy, piezoelectric properties, and mechanical characteristics of the piezoelectric composites are thoroughly investigated, and the reliability of the proposed theoretical model and simulation results is verified. The piezoelectric composites are uniformly compact and have a low residual pore rate. The piezoelectric composite with a solid content of 60 wt% has a volume density of 2.27 g/cm3 and a Young's modulus of 535.44 MPa. Most importantly, its piezoelectric voltage constant (g33) is 167.2 × 10−3 Vm/N, which is more than seven times higher than that of homogeneous PZT and results in high voltage sensitivity.

Selectively doped piezoelectric ceramics with tunable piezoelectricity via suspension-enclosing projection stereolithography

The macroscopic piezoelectric properties of piezoelectric materials can be regulated via localized control of microstructures to introduce site-specific electric displacement vectors, but much of the current research is centered around design and manipulation of meso-scale architectural units that are inherently limited in achieving high functionality. In this study, we propose a stereolithography-based additive manufacturing (AM) strategy to spatially tune the properties of piezoelectric ceramics at a grain-microstructural scale through selectively incorporating dopants into the ceramic materials for tailoring the grain development. The effects of different doping parameters (including ceramic solid loading, dopant type, and dopant concentration) on the microstructures and properties of printed piezoelectric ceramics are investigated. The thermodynamics and kinetics of different doping additives in the dopant-ceramic interaction are experimentally and numerically studied to enable location-specific inhibition of microstructures. Our results indicate that a doping concentration of 2 wt% promoted the homogeneity of local grain growth, resulted in a higher compressive strength and lower porosity, and improved dielectric permittivity and piezoelectric voltage constant in printed piezoelectric ceramics. Moreover, our results suggest that thermochemically stable particles (e.g., ZrO2) with a high melting point and a low vapor pressure exhibited micro-scale diffusion behaviors, in contrast to millimeter-scale diffusion behaviors of common doping additives (e.g., ZnO), which are more suitable as a locally incorporated dopant for achieving location-specific property tuning. Test cases of selectively doped piezoelectric components in predefined patterns highlight the potential of the proposed approach in creating novel piezoelectric materials with programmable location-specific properties.

Experimental and simulation studies on dielectric, AC resistivity and electromechanical properties of sodium bismuth titanate based ceramics

The experimental and simulation of dielectric, AC resistivity and dielectric resonance and anti-resonance data on (Na0.5Bi0.5)(NdxTi1-2xNbx)O3] ceramics were carried out using modified Lorentz equations as proposed by us instead of well know and generally applied laws like Arrhenius law and formulas on piezoelectricity to obtain activation energy, relaxation time, piezoelectric charge constant and voltage constant directly from the experimental data. The piezoelectric charge constant (d33) evaluated from the modeling are 864.64 p.m/V and 122.40 p.m/V; whereas the piezoelectric voltage constant (g33) are 10.88 p.m2/C and 8.55 p.m2/C for x = 0.0125 and 0.025 ceramic samples, respectively.

Ab-Initio Predictions of the Energy Harvesting Performance of L-Arginine and L-Valine Single Crystals

Biological piezoelectric materials are beginning to gain attention for their huge potential as eco-friendly energy harvesting materials. In particular, simple amino acid and peptide crystal assemblies are demonstrating large voltage outputs under applied force, and high sensitivity when detecting vibrations. Here we utilise Density Functional Theory (DFT) calculations to quantitatively predict the energy harvesting properties of two understudied proteinogenic amino acid crystals: L-Arginine and L-Valine. The work highlights the ability of quantum mechanical calculations to screen crystals as high-performance energy harvesters, and demonstrates the capability of small biological crystals as eco-friendly piezoelectric materials. L-Arginine is predicted to have a maximum piezoelectric voltage constant of gij= 274 mV m/N, with a Young’s Modulus of E = 17.1 GPa. L-Valine has a maximum predicted piezoelectric voltage constant of gij= 62 mV m/N, with a calculated Young’s Modulus of E = 19.8 GPa.

Evaluation of (Na1/2Bi1/2)TiO3/PVDF Piezocomposites for mechanical energy harvesting

This paper demonstrates the energy harvesting characteristics of 0–3 x(Na1/2Bi1/2)TiO3/(1-x)PVDF; 0 ≤ x (volume fraction) ≤ 0.30 composites employing the drop weight impact method. The X-ray diffraction method was adopted for ascertaining the formations of (Na1/2Bi1/2)TiO3 ceramic and (Na1/2Bi1/2)TiO3/PVDF composites. The values of bulk density, apparent porosity, free dielectric constant, piezoelectric coefficient (d33), figure of merit (FoM), and Shore D hardness were found to increase, whereas the value of tanδ first decreases up to x = 0.025 and then increases upon increasing x. Also, the value of the piezoelectric voltage constant (g33) increases up till x = 0.25 and it drops a little for x = 0.30. A remarkable increment in the contact voltage (from 7.71 V to 15.23 V for x = 0.30) with increasing impact height (h = 6–21 cm) and (from 5.37 V to 15.23 V for h = 21 cm) with increasing x was observed. The small values of water absorption (<0.099 wt%), apparent porosity (<2%), tanδ (∼10−2 at 1 kHz), and higher values of d33, g33, FoM, Shore D hardness, power output (Pdc = 2.32 μW using 47 kΩ and C = 100 pF for x = 0.30) as well as improved voltage responses, prefigure the possibility of current composite system, a better lead-free alternative for energy harvesting, piezo-detection/sensing and structural health monitoring technologies.

Energy Harvesting from Ceramic/Blended Polymer Nanocomposites: Ba0.85Ca0.15Zr0.10Ti0.90O3/Polyvinylidene Fluoride–Polytetrafluoroethylene

The mechanical impact‐based energy harvesting characteristics of 0–3ϕBa0.85Ca0.15Zr0.10Ti0.90O3/(1−ϕ)polyvinylidene fluoride–polytetrafluoroethylene (BCZT/PVDF–PTFE); volume fraction (0 ≤ ϕ ≤ 0.25) nanocomposites, fabricated using a melt‐mixing method, are presented. A scanning electron microscope is utilized to investigate the distribution of BCZT nanoceramic powder as filler in the blended polymer (PVDF–PTFE; 80:20). The X‐ray diffraction method is applied to ascertain the formations of BCZT and BCZT/PVDF–PTFE. The values of apparent porosity, water absorption, shore D hardness, dielectric constant (εr), tangent loss (tan δ), piezoelectric charge coefficient (d33) and voltage constant (g33), and figure of merit (FM) are found to increase upon increasing ϕ. A significant increment in the impact‐generated electric voltage (25.38–77.73 V) and energy (9.42–243.9 nJ) is noticed with the increasing ϕ. In addition, the small values of water absorption (&lt;0.091%) and tan δ (≈10−2) with relatively higher values of εr, d33, g33, FM, and shore D hardness, power out (Pdc = 0.47 mW using 470 Ω resistive load ϕ = 0.25 sample) as well as improved voltage generation and energy harvesting characteristics, prefigure the promise of the present composite system a superior lead‐free alternative for the applications in energy harvesting, detection/sensing, and structural health monitoring.

Novel properties of multi-poled piezoelectric network structures

We present the piezoelectric properties of multi-poled network microstructures based on cross, Gibson–Ashby and face-centred cubic base cells at a range of solid fractions and with different polarisation profiles. Piezoelectric properties are determined via computational homogenisation with the finite element method. Each polarisation profile is triple-poled, so it includes piezoelectric material poled in the x, y and z directions. The result of this is that the homogenised microstructures have fully non-zero piezoelectric coefficients and fully non-zero piezoelectric voltage constants. We show that the axial components of the effective voltage constant g 11, g 22, and g 33 can be vastly improved by ensuring struts are poled to match their orientation, so for example the piezoelectric material should be z-poled within a strut that is parallel to the z axis. We present novel extensions of commonly used figures of merit for single-poled piezoelectric materials that are relevant for the multi-poled case. We use these extended figures of merit to identify the network structures that have excellent piezoelectric properties for sensor and hydrophone applications. Furthermore, when varying the solid fraction of a given network microstructure, we show that the hydrostatic sensitivity of the meta-material increases as the acoustic impedance decreases. This property is unusual and near impossible to obtain using bulk material. Due to their highly sensitive piezoelectric response and full non-zero piezoelectric coefficients, such novel meta-materials could be utilised in next generation hydrophones, sensors, or other electromechanical devices.