Piezoelectric Composites Research Articles

88 - Dental Piezoelectric Composites with Antimicrobial, Mineralization and Tissue Regeneration Functionalities

88 - Dental Piezoelectric Composites with Antimicrobial, Mineralization and Tissue Regeneration Functionalities

Graphene doping to enhance the mechanical energy conversion performances of GR/KNN/P(VDF-TrFE) flexible piezoelectric sensors.

Flexible piezoelectric composite, combining high piezoelectricity of filler and flexibility of polymer, provides a new research idea for developing flexible piezoelectric sensors (FPSs) with high piezoelectric output performance. FPSs based on GR/KNN/P(VDF-TrFE) three-phase composites are fabricated via doping a mass fraction of 15 wt% potassium sodium niobate (KNN) ceramic powder and various contents of graphene (GR) nanosheets into a P(VDF-TrFE) matrix. We find that an appropriate amount of GR is responsible for the enhanced crystallinity and β-phase of P(VDF-TrFE). When the GR content is 0.15 wt%, the three-phase composite film exhibits a dielectric constant (εr) of 20.9 and a quasi-static piezoelectric constant (d33) of -28.4 pC N-1. Under three different test scenarios of a ball drop experiment, a surface of the mouse wheel, and an action of 2.5 MPa external stress, this GR/KNN/P(VDF-TrFE)-based FPS shows high piezoelectric output voltages of 7.4 V, ∼2.0 V, and 15.4 V, respectively. Moreover, the FPS retains its performance even after an extended period of cantilever vibration cycles (2200). Thus, the conductive filler GR is responsible for promoting the energy conversion performance of the piezoelectric polymer, which also provides an application candidate of this GR/KNN/P(VDF-TrFE) film in FPSs.

Performance enhancements of Pb(Mg1/3Nb2/3)O3-xPbTiO3 single crystal/epoxy 1–3 composite by alternating current polarization

Pb(Mg1/3Nb2/3)O3-xPbTiO3 single crystal/epoxy 1–3 piezoelectric composite was designed to decrease acoustic impedance and to improve the electromechanical property, which was vital to the ultrasound transducers. The piezo-/dielectric properties of the PMNT/epoxy 1–3 composites prepared by the different poling methods were measured. It was found that piezoelectric coefficient d33, dielectric constant ε33T/ε0, and electromechanical factor kt of composites exhibited the significant increases of 16.41%, 6.89%, and 1.97% under optimized alternating current polarization (ACP), compared with those of the samples using direct current polarization (DCP). The domain patterns suggested that the remarkable regular striped domain and high domain wall density of the ACP sample could result in performance enhancements. The ACP composite-based transducer's bandwidth (BW) and relative sensitivity (RS) were improved by 6.27% and 1.93 dB. These results indicated that the ACP effectively enhances the piezoelectric composite's performances, and BW and RS of the transducer based on ACP piezoelectric materials are improved simultaneously.

Comparing Different Electrodes of Piezoelectric Single Crystal Composites for Underwater Acoustic Transducers

Electrodes are critical to piezoelectric single crystal composites (PSCCs) as they directly determine the efficiency and reliability of piezoelectric devices. Currently, a comprehensive comparison of the major properties of different electrodes on PSCCs, particularly their adhesive performance, is highly needed because the cross-linked structure and large surface-displacement fluctuations of PSCCs likely cause the peeling and failure of electrodes. Herein, we compared electronic conductivity and adhesive performance of different electrodes for PSCCs including magnetron sputtering Au (MS Au), electron beam evaporation Au (BE Au), and low-temperature silver paste (LTSP) electrodes. The results demonstrate that the LTSP electrodes exhibited the highest adhesion strength of 3.5 MPa compared to MS Au (2.1 MPa) and BE Au (0.9 MPa) electrodes on PSCCs. In addition, the adhesion strength of electrodes on PSCCs was lower than that on piezoelectric single crystals owing to the existence of the polymer phase. In terms of electrical conductivity, the LTSP electrodes displayed the highest resistivity of 2.25 × 10–6 Ω·m, and MS Au and BE Au electrodes showed similar resistivities of 6.8 × 10–8 and 7.6 × 10–8 Ω·m, respectively. This work provides important information in choosing electrodes for PSCCs, thus benefiting the design for underwater acoustic transducers.

Enhanced energy harvesting performance in lead-free multi-layer piezoelectric composites with a highly aligned pore structure

The harvesting of mechanical energy from our living environment via piezoelectric energy harvesters to provide power for next generation wearable electronic devices and sensors has attracted significant interest in recent years. Among the range of available piezoelectric materials, porous piezoelectric ceramics exhibit potential for both sensing and energy harvesting applications due to their reduced relative permittivity and enhanced piezoelectric sensing and energy harvesting figures of merit. Despite these developments, the low output power density and the lack of optimized structural design continues to restrict their application. Here, to overcome these challenges, a lead-free multi-layer porous piezoelectric composite energy harvester with a highly aligned pore structure and three-dimensional intercalation electrodes is proposed, fabricated and characterized. The effect of material structure and multi-layer configuration of the porous piezoelectric ceramic on the dielectric properties, piezoelectric response and energy harvesting performance was investigated in detail. Since the relative permittivity is significantly reduced due to the introduction of aligned porosity within the multi-layer structure, the piezoelectric voltage coefficient, energy harvesting figure of merit and output power are greatly enhanced. The multi-layer porous piezoelectric composite energy harvester is shown to generate a maximum output current of 80 μA, with a peak power density of 209 μW cm−2, which is significantly higher than other porous piezoelectric materials reported to date. Moreover, the generated power can charge a 10 μF capacitor from 0 V to 4.0 V in 150 s. This work therefore provides a new strategy for the design and manufacture of porous piezoelectric materials for piezoelectric sensing and energy harvesting applications.

Vortex induced vibration energy harvesting using magnetically coupled broadband circular-array piezoelectric patch: Modelling, parametric study, and experiments

Piezoelectric composites have become increasingly important in energy harvesting from vibration and, more recently, flow-induced vibration. The compatibility of piezoelectric devices has allowed tuning harvesters to the system's natural frequency to maximize the energy harvesting performance. However, the narrowband characteristic in piezoelectric composites is susceptible to efficiency losses when there are changes in the ambient surrounding. Thus, magnetic coupling introduces nonlinearity and can increase the broadband energy harvesting performance to account for slight variations. This paper proposes a piezoelectric energy harvester used in a pipe array to harvest oscillations from vortex-induced vibration. Adding a magnetic coupler introduces bandwidth enhancement characteristics that can accommodate slight changes in the freestream velocity. A computational simulation was used to compare different coupler shapes that can direct water flow toward the harvester array. The results show that an elliptical coupler works best and that a solid coupler has up to 50 % better performance than a hollow coupler. The experimental results showed that narrowband voltage output could reach up to 9 V in a pipe array. Furthermore, the broadband performance of magnetic coupling increased the bandwidth by up to 33 % in different orientations and distances.

Application of piezoelectric composites to control operation of a gas foil bearing – prototype design and testing

Essential parts of rotating machineries are supporting nodes, i.e., bearing systems. They assure required rotational degrees of freedom and feature desired load carrying capacity. Following the specificity of a technical solution considered, various types of bearings may be taken into account to effectively address the requirements regarding the speed and load. Specifically, gas foil bearings (GFB) are used in high-speed and lightly-loaded rotating machineries, e.g., auxiliary power units. In fact, they can operate up to several hundreds of thousands rpm, also for a wide temperature range. The current work reports an application of piezoelectric composites to control operation of a GFB. The authors present the developed bearing’s prototype installation which is equipped with a specialized multifunctional structural component that advantageously allows to both characterize GFB’s operational parameters and modify them. The experimental results confirm the usability of the proposed actively-controlled configuration of a GFB.

Molten-State Dielectrophoretic Alignment of EVA/BaTiO3 Thermoplastic Composites: Enhancement of Piezo-Smart Sensor for Medical Application.

Dielectrophoresis has recently been used for developing high performance elastomer-based structured piezoelectric composites. However, no study has yet focused on the development of aligned thermoplastic-based piezocomposites. In this work, highly anisotropic thermoplastic composites, with high piezoelectric sensitivity, are created. Molten-state dielectrophoresis is introduced as an effective manufacturing pathway for the obtaining of an aligned filler structure within a thermoplastic matrix. For this study, Poly(Ethylene-co Vinyl Acetate) (EVA), revealed as a biocompatible polymeric matrix, was combined with barium titanate (BaTiO3) filler, well-known as a lead-free piezoelectric material. The phase inversion method was used to obtain an optimal dispersion of the BaTiO3 within the EVA thermoplastic matrix. The effect of the processing parameters, such as the poling electric field and the filler content, were analyzed via dielectric spectroscopy, piezoelectric characterization, and scanning electron microscopy (SEM). The thermal behavior of the matrix was investigated by thermogravimetric analysis (TGA) and differential scanning calorimetry analysis (DSC). Thermoplastic-based structured composites have numerous appealing advantages, such as recyclability, enhanced piezoelectric activity, encapsulation properties, low manufacturing time, and being light weight, which make the developed composites of great novelty, paving the way for new applications in the medical field, such as integrated sensors adaptable to 3D printing technology.

Selection of piezoeloectric material and fiber volume fraction to maximize the electrical power produced by macro-fiber composite energy harvesters

A piezoelectric Macro fiber composite (MFC) materials developed in the last decade found widespread applications such as vibration sensing, actuation and structural health monitoring. Unlike conventional ceramic piezoelectric materials (PZT), these composites show many advantages such as flexibility, reliability and high actuation capacity. However, increasing their energy harvesting capabilities still remains a challenge. Modeling and simulation of electrical energy harvesters using MFC patches provide a mean for geometrical optimization and appropriate choice of the MFC composite. This paper proposes a linear analytical model for prediction of the electro-mechanical response of bimorph harvesters using MFC patches. Homogenization technique is used to describe the equivalent piezoelectric properties of the composite structure of the MFC patch. This paper investigates the effect of the volume fraction of the fibers and the material choice of the piezoelectric fibers and epoxy matrix on the generated electrical power. It has been found that an increased fiber volume fraction causes a decrease of the voltage, the power and the velocity amplitudes for a range of load resistance. However, an increase in the fiber volume fraction FVF is achieved by an increase of the current amplitude for a range of load resistance. Maximum amount of power is generated by the bimorph MFC harvester for an FVF of 86% which corresponds to the reference configuration. The piezoelectric fiber material has a significant influence on the output power. In fact, the SONOX-P502 generated the greatest electrical power. However, the material of the matrix has a negligible effect on the generated power.

Improved corona discharge-based modified poling method for 0–3 PZT/PEGDA piezoelectric composites

Among piezo composites, 0–3 type ceramic/polymer-based composites have balanced properties and flexible manufacturing processes, allowing them to tackle challenges in wearable electronics and sensing technology. However, due to a misfit between the dielectric coefficients of the ceramic particles and polymer matrix, poling 0–3 composites is difficult. Therefore, in this study, we develop a novel poling method that combines the merits of normal corona poling and oil-based poling methods to activate a lead zirconium titanate (PZT)/Polyethylene glycol diacrylate (PEGDA) composite. The influence of various parameters (voltage, temperature, poling duration, and time of ageing) on the piezoelectric and dielectric properties of the PZT/polymer composite were evaluated. For the 0–3 PZT/PEGDA composites (67 wt%), the optimal poling parameters were found to be 60 min poling duration, 25 °C, and 24 kV. The d33 (32 pC/N) obtained by the proposed poling method is about 3 times that obtained by the normal corona poling method (11 pC/N). This modified poling method was shown to be more effective than the conventional method for a range of filler contents (50 wt%, 67 wt%, and 75 wt%). It was also found that the d33 value of the PZT/PEGDA composite increased over time and was attributed to the increase of the composite dielectric constant after poling. Finally, sensing elements were assembled from the poled samples and evaluated, which shows the potential for detecting tiny signals in sensing and soft robotics.

Study on Suppression of Transverse Mechanical Coupling of Rectangular Double-Laminated Bending Vibration Elements

Rectangular double-laminated piezoelectric elements are widely used in low frequency transducers. At present, most of these piezoelectric elements use a piezoelectric ceramic laminated structure. In this work, the bending vibration properties of double-laminated piezoelectric ceramic elements with different transverse dimensions were analyzed by the finite element method. It was found that there was a strong transverse mechanical coupling, and the transverse dimensions had a great effect on the bending vibration. To suppress the transverse mechanical coupling effect, a double-laminated piezoelectric element based on a 2-2 piezoelectric composite was designed. The simulation results show that the bending vibration performance of the double-laminated composite element is not affected by the transverse size. The 2-2 piezoelectric composite double-laminated and ceramic elements were prepared. In addition, simulation and experimental results indicate that the transverse mechanical coupling of the bending vibration of the piezoelectric composite double-laminated element is effectively suppressed, the vibration frequency is reduced by about 100 Hz, and the vibration displacement is increased by 2.2 times, in comparison with the piezoelectric ceramic double-laminated element.

Study of 1-3 piezoelectric composites based on phononic crystals theory

To further improve the working performance of 1-3 piezoelectric composites, in this paper, they are regarded as two-dimensional phononic crystals, the band structures, transmission characteristics and vibration modes are firstly calculated by the finite element method, and the suppression of lateral vibration by 1-3 piezoelectric composite structure is investigated based on band gap theory to obtain a purer thickness vibration. Secondly, the influence of the lattice system on the band gap as well as the overall working performance of piezoelectric composites is analyzed, finite element models of square and hexagonal lattice piezoelectric composites are established, and their operating parameters such as transmitting voltage response level and total radiated power are calculated by simulation. This study shows that the working frequency of 1-3 piezoelectric composites can be set in the band gap of phononic crystals to obtain better lateral vibration suppression; compared with square lattice, 1-3 piezoelectric composites with piezoelectric phase hexagonal lattice arrangement can obtain larger working bandwidth and higher total radiated power in the thickness mode, the overall working performance is better. This study is a guideline for the design and application of piezoelectric components in the fields of acoustics and medicine.

Characterization for the key parameters of 1-3 piezoelectric composite in thickness vibration mode

1-3 piezoelectric composite has been widely used in underwater acoustic and ultrasonic transducer, and its thickness vibration mode is most commonly used by transducer. The resonance frequency and the conductance are two key parameters of this mode, because they determine the working frequency of transducer and electrical match, respectively. In order to characterize these parameters, the electromechanical equivalent model of thickness vibration mode was established to obtain the admittance equation, and then the key parameters were calculated. Meanwhile, 1-3 piezoelectric composite samples with different structural parameters were prepared and tested, and the theoretical model was verified. Finally, the theoretical model was used to characterize the variation of resonance frequency and conductance with the structural parameters to guide the design of 1-3 piezoelectric composite.

Charge-Boosting Strategy for Wearable Nanogenerators Enabled by Integrated Piezoelectric/Conductive Nanofibers.

The surface charge density enhancement by incorporating conductive paths into organic/inorganic piezoelectric composites is considered to be an effective way to achieve high-performance piezoelectric nanogenerators (PENGs). However, it is challenging to boost the charge density of aligned piezoelectric nanofibers due to the difficulty in efficiently building well-distributed conductive paths in their dense structure. In this work, a charge boosting strategy was proposed for enhancing the surface charge density of aligned piezoelectric nanofibers, that is, synchronously preparing piezoelectric/conductive hybrid nanofibers to realize the effective conductive paths for transferring the underlying charges to the surface of the PDMS/BaTiO3 composites. To this end, antimony-doped tin oxide (ATO) conductive nanofibers and barium titanate (BaTiO3) piezoelectric nanofibers with the same preparation conditions were selected and synchronously prepared by the polymer template electrospinning technology, followed by the calcination process. Benefiting from the well-distributed conductive paths for transferring the charges, the open-circuit voltage and short-circuit current of a PENG with 12 wt% ATO in hybrid nanofibers reached 46 V and 14.5 μA (30 kPa pressure), respectively, which were much higher than the pristine BaTiO3-based PENG. The high piezoelectric performance of the developed PENGs guaranteed their great potential applications in powering wearable microelectronics and monitoring human activity. This charge boosting strategy via the piezoelectric/conductive hybrid nanofibers may inspire the further development of high-performance energy harvesting technology.

Effect of thickness on the performance parameters of modified 1–3 piezoelectric composites

In this study, a modified 1–3 piezoelectric composite was designed to investigate the relationship between its thickness and properties of piezoelectric composites. First, the modified 1–3 piezoelectric composite was simulated using COMSOL to obtain the resonant and anti-resonant frequencies of each piezoelectric composite thickness, and the electromechanical coupling coefficient, acoustic impedance, acoustic velocity, and frequency difference of the corresponding thickness were calculated. Second, the modified 1–3 piezoelectric composite was simplified using series-parallel theory and uniform field theory, and the relevant piezoelectric performance parameters of the piezoelectric composites of different thicknesses were calculated. The above results were verified experimentally, and the experimental results were in good agreement with the simulation results. Although the theoretical calculation results deviated slightly from the experimental results, the overall trend was consistent with the experimental results. Finally, the performance parameters of the modified 1–3 piezoelectric composite and traditional 1–3 piezoelectric composite with a thickness of 7.5 mm were compared. It was found that the acoustic impedance of this modified 1–3 piezoelectric composite was smaller than that of the traditional 1–3 piezoelectric composite, and the electromechanical coupling coefficient was larger than that of the traditional 1–3 piezoelectric composite. Therefore, this modified 1–3 piezoelectric composite has great potential for the preparation of high-performance piezoelectric ultrasonic transducers.

Electrical field stimulated modulation of cell fate of pre-osteoblasts on PVDF/BT/MWCNT based electroactive biomaterials.

The present study reports the impact of the interplay between electroactive properties of the biomaterials and electrical stimulation (ES) toward the cell proliferation, migration and maturation of osteoprogenitors (preosteoblasts; MC3T3-E1) on the electroactive poly (vinylidene difluoride) (PVDF)-based composites. The barium titanate (BaTiO3; BT; 30 wt%) and multiwalled carbon nanotubes (MWCNT; 3wt%) were introduced into the PVDF via melt mixing, which led to an enhancement of the dielectric permittivity, electrical conductivity, and surface roughness. We also present the design and development of an in-house customized 12-well plate-based device for providing different types (DC, square, biphasic) of ES to cells in culture in a programmable manner. In the presence of ES of 1V cm-1 , biophysical stimulation experiments performed using 12-well plate-based device revealed that PVDF composite (PVDF/30BT/3MWCNT) can facilitate the enhanced adhesion and proliferation of the MC3T3-E1 in non-osteogenic media, with respect to non-stimulated conditions. Importantly, MC3T3-E1 cells demonstrated significantly better migration and differentiation on the PVDF/30BT/3MWCNT under ES when compared to ES-free culture conditions. Similar enhancement with respect to alkaline phosphatase activity, intracellular Ca2+ concentration, and calcium deposition in MC3T3-E1 cells was recorded, when pre-osteoblasts were grown for 21 days on electroactive substrates. All these observations supported the activation of osteo-differentiation fates, which were further promoted in the osteogenic medium. The present study demonstrates that the synergistic interactions of ES with piezoelectric PVDF-based polymer composite can potentially enhance the proliferation, migration, and osteogenesis of the pre-osteoblast cells, rendering it a promising bioengineering strategy for bone tissue engineering.

Flexible PVDF-TrFE Nanocomposites with Ag-decorated BCZT Heterostructures for Piezoelectric Nanogenerator Applications.

Flexible piezoelectric nanogenerators are playing an important role in delivering power to next-generation wearable electronic devices due to their high-power density and potential to create self-powered sensors for the Internet of Things. Among the range of available piezoelectric materials, poly(vinylidene fluoride-trifluoroethylene) (PVDF-TrFE)-based piezoelectric composites exhibit significant potential for flexible piezoelectric nanogenerator applications. However, the high electric fields that are required for poling cannot be readily applied to polymer composites containing piezoelectric fillers due to the high permittivity contrast between the filler and matrix, which reduces the dielectric strength. In this paper, novel Ag-decorated BCZT heterostructures were synthesized via a photoreduction method, which were introduced at a low level (3 wt %) into the matrix of PVDF-TrFE to fabricate piezoelectric composite films. The effect of Ag nanoparticle loading content on the dielectric, ferroelectric, and piezoelectric properties was investigated in detail, where a maximum piezoelectric energy-harvesting figure of merit of 5.68 × 10-12 m2/N was obtained in a 0.04Ag-BCZT NWs/PVDF-TrFE composite film, where 0.04 represents the concentration of the AgNO3 solution. Modeling showed that an optimum performance was achieved by tailoring the fraction and distribution of the conductive silver nanoparticles to achieve a careful balance between generating electric field concentrations to increase the level of polarization, while not degrading the dielectric strength. This work therefore provides a strategy for the design and manufacture of highly polarized piezoelectric composite films for piezoelectric nanogenerator applications.

Bi0.5Na0.5TiO3–SrTiO3 lead-free piezoelectric composites with large strain under low driving fields

Lead-free (1-f)[0.73Bi0.5Na0.5TiO3–0.27SrTiO3]–f[0.75Bi0.5Na0.5TiO3–0.25SrTiO3] composites were synthesized using a conventional solid-state reaction method. The f = 0.5 composites exhibited a giant unipolar strain of 0.176 % under an ultralow driving field of 2 kV/mm, corresponding to a high normalized strain of 880 pm/V. This value is comparable with that of other macro ferroelectric/relaxor composite materials under higher electric fields and even higher than those for commercial lead-based piezoceramic materials. We believe that these bismuth sodium titanate-based composites are extremely competitive in the practical applications of actuators at low electric fields.

Piezoelectric composites from sandwiched polydimethylsiloxane sponges

A novel elastomer-based composite material with enhanced piezoelectric performances is proposed in this paper, which is composed of the top and bottom polytetrafluoroethylene (PTFE) solid films with the middle PTFE nanoparticle–polydimethylsiloxane (PDMS) sponge layer. To enhance the charge retention capability of elastomers, PTFE nanoparticles are introduced to form PTFE–PDMS interfaces, which can trap charges with longevity. Besides, PTFE solid films take on the role of the charge blocking layers to further improve the piezoelectric performances. As a result, the PTFE–PDMS sandwich structure shows the advantages of remarkable sensitivity (1053 pC/N), high stability, and flexibility. After a 6 h of annealing treatment at the temperature of 100 °C, no significant deterioration of the piezoelectric properties can be observed, which reveals the great thermal stability of the sandwich structure. In addition, the sandwich structure can be immersed in water for 24 h without any loss of piezoelectric activity. Finally, the experiment of lighting one LED by hand pressing successfully demonstrates that the sandwich structure has good applicability in the field of energy harvesting. Considering the excellent electrical and mechanical features, the PTFE–PDMS sandwich structure has promising applications in sensing, energy harvesting, and actuation.

Preparation and simulation of lead free NBBT/epoxy 1–3 piezoelectric composites for high frequency medical ultrasound

This paper presents the modeling and fabrication of the (1-x)Na0.5Bi0.5TiO3-xBaTiO3 single crystal/epoxy 1–3 piezoelectric composite (NBBT 1–3 composite) with large electromechanical coupling factor (kt) for high frequency ultrasonic transducers. The NBBT 1–3 composite has been modeled by performing the finite element method using the COMSOL Multiphysics software. The parameters related to NBBT crystal are refined in the modeling process and the simulation results agree well with that of the experiment. The composite has been fabricated by the dice-and-fill method with a pitch of 12 μm. The measured resonance frequency, antiresonance frequency and electromechanical coupling factor (kt) with the values of 31.88 MHz, 43.16 MHz and 71.06% are obtained, respectively. The excellent performance of NBBT/epoxy 1–3 piezoelectric composite is comparable to that of lead-based Pb(Mg1/3Nb2/3)O3–PbTiO3/epoxy 1–3 piezoelectric composites. The excellent performance and the lead-free advantages make the NBBT/epoxy 1–3 piezoelectric composites quite attractive in high frequency medical ultrasound applications especially within the human body like intravascular ultrasound imaging (IVUS).