Actuator Applications Research Articles

Effect of SiO2-Li2O3-CuO additive on piezoelectric properties of PMS-PZT ceramics at low sintering temperature

Lead zirconate titanate (PZT) based piezoelectric ceramics are applied in ultrasonic transducers and multilayer actuators fields universally. Excellent piezoelectric properties of PZT-based ceramics of low sintering temperature are crucial for the applications of high-power motors and multilayer piezo-actuators due to the reduction of cost and energy consumption. In this paper, a ternary solid-solution ceramic system 0.05Pb(Mn1/3Sb2/3)O3-0.47PbZrO3-0.48PbTiO3 (PMS-PZT) was studied. A new complex additive composed of SiO2-Li2O3-CuO was doped into the PMS-PZT ceramics. The doping of CuO and Li2O3 was discovered to be able to lower the sintering temperature and remain electric properties efficiently, while the doping of SiO2 can decrease the grain size and increase the density. All ceramic samples were fabricated by solid-phase reaction method and sintered in the low temperature range from 800 °C to 1000 °C. The phase structure, morphology of natural surface and electrical properties of ceramics doped by 0.5 wt% additive were characterized. The 0.5 wt% additive doped PMS-PZT ceramics exhibit remarkable comprehensive piezoelectric properties sintered at 900 °C (d33 = 343 pC/N, Qm = 1016, Tc = 328 °C, tanδ = 0.4 % (at 25 °C), εr = 1344, d33* = 490 pm/V). The sintering temperature 900 °C is significantly below the melting point of Ag (961.9 °C) and Cu (1083.4 °C), so the more cost-effective Cu internal electrodes and Ag rich Ag/Pd electrodes can be used to substitute the expensive Pd rich Ag/Pd internal electrodes in the production of devices composed of multilayer ceramic. The research of this work provides an important candidate additive for the applications of high-performance transducers and multilayer actuators with low cost.

The structural evolution and electric field-induced strain performance of Bi0.5(Na0.41K0.09)TiO3–Ba(Fe0.5Sb0.5)O3 lead-free piezoelectric ceramics

In recent years, lead-free Bi0.5Na0.5TiO3 (BNT) based piezoelectric ceramics with excellent strain properties have gained widespread recognition for their application in high-precision displacement actuators. The (1-x)(0.82Bi0.5Na0.5TiO3-0.18K0.5Bi0.5TiO3)-xBa(Fe0.5Sb0.5)O3 ceramics were fabricated through the die-pressing method in this work. The effect of BFS introduction on the dielectric, ferroelectric and microstructure characteristics of BNKT ceramics was systematically investigated. Among these compositions, the BNKT-0.015BFS ceramics exhibited a piezoelectric strain coefficient (d33*) of 658 pm/V at an electric field of 55 kV/cm, while achieving a strain response of 0.51 % at 85 kV/cm. The observed improvement in strain performance can be attributed to the evolution from non-ergodic relaxor state to ergodic relaxor state caused by BFS substitution. Furthermore, transmission electron microscopy (TEM) explicitly confirmed coexistence of rhombohedral and tetragonal phase and revealed the morphology of nanosized domains. This study adds to a deeper comprehension of the characteristics of strain response enhancement in BNT-based ceramics, opening up avenues for designing novel lead-free piezoelectric ceramics with outstanding electromechanical performance.

Mesogen Organizations in Nematic Liquid Crystal Elastomers Under Different Deformation Conditions.

Liquid crystal elastomers (LCEs) exhibit unique mechanical properties of soft elasticity and reversible shape-changing behaviors, and so serve as potentially transformative materials for various protective and actuation applications. This study contributes to filling a critical knowledge gap in the field by investigating the microscale mesogen organization of nematic LCEs with diverse macroscopic deformation. A polarized Fourier transform infrared light spectroscopy (FTIR) tester is utilized to examine the mesogen organizations, including both the nematic director and mesogen order parameter. Three types of material deformation are analyzed: uniaxial tension, simple shear, and bi-axial tension, which are all commonly encountered in practical designs of LCEs. By integrating customized loading fixtures into the FTIR tester, mesogen organizations are examined across varying magnitudes of strain levels for each deformation mode. Their relationships with macroscopic stress responses are revealed and compared with predictions from existing theories. Furthermore, this study reveals unique features of mesogen organizations that have not been previously reported, such as simultaneous evolutions of the mesogen order parameter and nematic director in simple shear and bi-axial loading conditions. Overall, the findings presented in this study offer significant new insights for future rational designs, modeling, and applications of LCE materials.

Regulating the microstructure and hydrophilicity of cellulose nanofibers using taurine and the application in humidity sensor and actuator

Exploring the interrelationships between microstructure, hydrophilicity, humidity response, and material stability through molecular structure design and low-cost preparation, and manufacturing sensing and driving materials with a perfect balance between structures and properties is crucial for biomimetic robots and intelligent devices. Herein, inspired by the capillary phenomenon, the cellulose nanofiber (CNF) was grafted by using taurine to form the “micro cilia” microstructure on its surface (CNF-TAU). By controlling the cilia density and symmetry, the hydrophilicity of the materials was adjusted, and the water was allowed to quickly separate from the inside of the materials, which led to improving the humidity sensitivity and stability of materials. Concretely, compared with CNF, the puncture load, tearing strength, and elongation at break of the CNF-TAU-1.0 were improved by 11.95 times, 2.16 times, and 15.6 %, respectively, and excellent tensile strength was presented. Moreover, the hydrophilicity of CNF-TAU was first weakened and then enhanced with TAU content increasing. At last, the CNF-TAU-1.0 (WCA 55.43°) was selected and blended with single-layer graphene oxide (GO) to prepare CNF-TAU/GO composite films by vacuum filtration. The results indicated that the composite film had excellent mechanical (room and high humidity), humidity responsiveness, and humidity gradient-driven properties. In detail, the CNF-TAU/GO-10 % composite film had the generated stable induced voltage (68.4 mV), the fast response/recovery time (0.3 s/0.9 s), the large max. bending angle (178.4°), and the drive cycle stability (1000 cycles). Moreover, the composite film could be applied to produce biomimetic soft robots, such as human fingers and butterfly-shaped robots.

Synthesis, dielectric and ferroelectric properties in BSCT ceramics

The present work is on the investigation of dielectric and ferroelectric properties of Ba(0.70-x) SmxCa0.30TiO3; BSCT (x = 0.000, 0.005, 0.010, 0.015, 0.020 and 0.030) ceramics. The samples were prepared by the conventional solid-state reaction route method. The perovskite tetragonal structure was confirmed by X-ray diffraction analysis. The dielectric constant ‘ε’ and tangent loss ‘tanδ’ was measured over a temperature range (30 °C–150 °C) and frequency (100 Hz–100 kHz). All the samples show very small value of tanδ (<3 %) at 30 °C. The Curie temperature ‘Tc’ was found to decreases with increase the Sm-content. PE hysteresis loops were recorded at the different electric fields at 30 °C. The maximum value of electric field induced strain was observed for the sample with x = 0.015. The results show that the prepared samples are suitable for potential actuator and capacitor applications.

Temperature‐Responsive Anisotropic Bilayer Hydrogel Actuators with Adaptive Shape Transformation for Enhanced Actuation and Smart Sensor Applications

Temperature‐Responsive Anisotropic Bilayer Hydrogel Actuators with Adaptive Shape Transformation for Enhanced Actuation and Smart Sensor Applications

Influence of HFP monomer segments on the crystal structure and electromechanical responses of a P(VDF-TrFE-CFE-HFP) tetrapolymer

The electromechanical properties of PVDF-based polymers, namely converting electrical into mechanical energy, are mainly decided by the crystal structure and domain size of the target product. Thus, we prepare the poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)), its terpolymer poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) (P(VDF-TrFE-CFE)), and tetrapolymer poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene -hexafluoropropylene) (P(VDF-TrFE-CFE-HFP)) films for comparison, respectively, where the role of the introduction of third and fourth monomers in the electromechanical properties of P(VDF-TrFE) is completely disclosed. Because of introducing CFE and HFP monomers, P(VDF-TrFE) with the ferroelectricity has converted into the relaxor ferroelectric P(VDF-TrFE-CFE-HFP) with a slimmer P-E loop while maintaining good maximum polarization (Pm). Since the nano ferroelectric domains in the relaxor ferroelectric material are easy to reverse along the polarizing electric field, The P(VDF-TrFE-CFE-HFP) sample achieved a dielectric constant (εr) of ∼29 and a strain in the thickness direction (S33) of ∼ -5%, respectively, while the εr and S33 of P(VDF-TrFE) sample are ∼11 and ∼-0.8 %, respectively. This research indicates the availability of the third and fourth monomers for improving the electromechanical effect of such electrostrictive polymers, having wide applications in flexible actuators, transformers, sensors, and so forth.

Adaptive sliding mode control with disturbance estimation for hydraulic actuator systems and application to rock drilling jumbo

For achieving high-performance control of hydraulic actuator systems, an adaptive sliding mode control with disturbance estimation algorithm is proposed and successfully applied to the hydraulic actuator systems of rock drilling jumbo. A switching extended state observer for hydraulic actuator systems is proposed, which combines the advantages of the linear extended state observer and the nonlinear extended state observer to estimate system disturbances more efficiently. The designed parameter adaptive law provides adaptivity to the system parameters, while the disturbance estimation algorithm can online estimate the unknown disturbances, such integration can enhance the adaptability and robustness of the sliding mode control algorithm. Rigorous simulation tests and practical application experiments are conducted to evaluate the performance of the proposed controller. The reliability of the designed parameter adaptive law and switching extended state observer is validated in detail in simulation studies. In the application experiments of rock drill jumbo, the results indicate the proposed controller is superior to sliding mode control with disturbance estimation and PID control. The average error of the developed controller is reduced by 58 %, 54 %, and 56 % compared to the sliding mode control with disturbance estimation controller, and 82 %, 78 %, and 79 % compared to the PID controller in tracking the low-frequency, high-frequency, and superimposed sinusoidal signals, respectively. Moreover, both the convergence of the uncertain parameters and the estimation of the unknown disturbances in the experiments are satisfactory. These experimental results adequately demonstrate the practical application value of the proposed controller.

Random field site inequality for ergodicity modification in BNT-based materials: From a phenomenological view

Achieving a simplified BNT-based composition with giant strain properties is challenging, since traditional chemical substitutions rely on trial-and-error experiments and complicates the composition. Herein, we comprehend the strain regulation mechanism from a view of relaxors and propose strain regulation rules based on classical relaxor theory. In BNT-based systems, site inequality of the random field for the ergodicity modification is observed, arising from the discrepant random field-driven (e.g., intensity and action position) structural distortions. From a phenomenological view, B-site substitution is effective in regulating relaxation behaviors due to the stronger lattice softening effect. This work points out the essence of regulating strain properties in BNT-based systems, and the proposed phenomenological relaxation regulation rules are believed to advance the development of actuator applications.

Optimized strain property in Sm3+ doped 0.67BiFeO3-0.33BaTiO3 ceramics by electric field induced lattice distortion and domain wall motion

BiFeO3-BaTiO3 based ceramics with good piezoelectric properties and high Curie temperature are potential candidates for high temperature piezoelectric actuators. In this study, a high strain value of about 0.376 % and the low strain hysteresis of 13.3 % achieved in 0.67Bi1-xSmxFeO3-0.33BaTiO3 (0.1 ≤ x ≤ 2.0) ceramics. The contribution from the E-induced nanodomains and/or PNRs wall motion by fine-tuning Sm3+ contributes the increased strain; The contribution from the converse piezoelectric effect and the electrostrictive effect enhanced with the increase of x, due to the enlarged lattice shrinkage by replacing Sm3+ with small ionic radius and subsequent lattice distortion under high electric field. The strategy to simultaneously enhance the E-induced lattice distortion and nanodomains and/or PNRs wall motion of strain and balance their fractions to reduce the strain hysteresis may provide new insights to meet the practical applications of high-precision displacement actuators.

Structural phase transition, relaxor behavior, and ultra-low strain hysteresis in BaTiO3 ceramics modified by BiYO3

In this study, the structural properties, phase transition, relaxor behavior, and strain properties of (1−x)BaTiO3‒xBiYO3 (x= 0.02‒0.15 mol) ceramics were investigated. The room temperature x-ray diffraction and Raman spectroscopy results reveal that (1−x)BaTiO3‒xBiYO3 ceramics undergo phase transition from tetragonal to pseudo-cubic structure with x increasing. The curves of dielectric constant and loss tangent as a function of temperature and frequency show that the dielectric constant was changing from being dependent on temperature to being independent of it upon increasing BiYO3 amount, which is induced obvious dielectric relaxation behavior. Slimmer polarization–electric field (P–E) loops and lower remnant polarization (Pr ) were observed for samples with x ⩾ 0.08. The transition between the ferroelectric and relaxor states leads to the narrow strain–electric field (S–E) loops, which exhibit a high electric field-induced strain of 0.192% and an ultra-low strain hysteresis of 10.4% at an electric field of 70 kV cm−1 for x= 0.04. This excellent performance indicates that 0.96BaTiO3‒0.04BiYO3 ceramic may be promising lead-free materials for high-precision displacement actuators applications.

3D printing of flexible piezoelectric composite with integrated sensing and actuation applications

3D printing of flexible piezoelectric composites (3D-FPCs) is increasingly attracting the attention due to its unique advantage for customized smart applications. However, current research mainly focuses on the 0–3 piezoelectric composites, in which the piezoelectric ceramics are embedded in polymer matrix in the form of particles. The poor connectivity between particles much reduces the conduction of strain and charge in the composites, seriously limiting its application in actuation. In this work, a continuous lead zirconate titanate (PZT) double-layer ceramic scaffold was prepared by 3D printing and assembled with epoxy resin and interdigital electrodes together to manufacture a multifunctional device. The 3D-FPCs exhibit a free strain of 1830 ​ppm in actuating and are able to actuate a stainless-steel cantilever beam to produce a tip displacement of 5.71 ​mm. Additionally, the devices exhibit a sensitivity of 26.81V/g in sensing applications. Furthermore, 3D-FPCs are demonstrated as actuators for mobile small robots and wearable sensors for sensing joint activities.

A Novel Design of a Torsional Shape Memory Alloy Actuator for Active Rudder.

SMA actuators are a group of lightweight actuators that offer advantages over conventional technology and allow for simple and compact solutions to the increasing demand for electrical actuation. In particular, an increasing number of SMA torsional actuator applications have been published recently due to their ability to supply rotational motion under load, resulting in advantages such as module simplification and the reduction of overall product weight. This paper presents the conceptual design, operating principle, experimental characterization and working performance of torsional actuators applicable in active rudder in aeronautics. The proposed application comprises a pair of SMA torsion springs, which bi-directionally actuate the actuator by Joule heating and natural cooling. The experimental results confirm the functionality of the torsion springs actuated device and show the rotation angle of the developed active rudder was about 30° at a heating current of 5 A. After the design and experiment, one of their chief drawbacks is their relatively slow operating speed in rudder positioning, but this can be improved by control strategy and small modifications to the actuator mechanism described in this work.

Strain-dependent electronic, mechanical and piezoelectric properties of ZrSiO3 2D monolayer: A first principle approach

This study investigated the mechanical stability, elastic anisotropy, electronic and piezoelectric properties of ZrSiO₃ 2D monolayer subjected to varying degrees of strain. The monolayer films were characterized under strains ranging from −6% to +6 %, and different material properties were analyzed to understand their response to mechanical deformation using density functional theory with the Quantum Espresso code. The calculated values of cohesive and strain energy revealed that the material exhibited a symmetrical response to tension and compression within a strain value range of −2% to +2 %. Electronic properties showed strain-induced modifications: the band gap of the material decreases under tensile strain and increases under compressive strain. The material remained mechanically stable and ductile under the applied strain range of −6% to +6 %. Present investigations conveyed the modifications produced by strain on elastic anisotropy and piezoelectric characteristics of the material, finding their applications in strain-sensitive sensors, actuators, and energy-harvesting devices.

Dual network hydrogel sensors based on borate ester bond: Multifunctional performance in high conductivity, stretchability, mechanical strength, and anti-freezing properties

Conductive polymer hydrogels have attracted great attention due to their application prospects in the fields of health care monitoring, wearable electronics and soft robots. Developing hydrogel sensors with robust mechanical characteristics, outstanding sensing abilities, the ability to self-heal and adhere effectively is critical, yet it remains a major challenge. Here, we present a simple one-pot method to prepare a dual-network flexible hydrogel based on polyvinyl alcohol (PVA), acrylamide (AM), pyridine-4-boronic acid derivatives (PBAD), and lithium chloride (LiCl). The cross-linked network is established through reversible and dynamic borate ester bonds, hydrogen bonds, electrostatic interactions and coordination bonds, imparting outstanding mechanical and self-healing characteristics to the material. The incorporation of PBAD not only imparts high conductivity (9.84 mS·cm−1) and sensitive sensing performance (GF = 13.89) to the hydrogel, but also synergistically improves its elongation (1689 %), tensile strength (0.6 MPa), and toughness (5.74 MJ/m3). In addition, based on the participation of LiCl, the hydrogel shows outstanding anti-freezing properties. This work is expected to provide new ideas for the assembly of high performance flexible sensor and to expand their application in electronic skin, wearable devices, and soft actuators.

Low-temperature co-fired PNN-PZT-based multilayer piezoelectric actuator with low cost and high reliability

Developing low-temperature co-fired MLAs for the commercial application of micro-nano actuation and manipulation has recently become a research highlight. To simultaneously achieve high piezoelectric response and low co-firing temperature below 960 °C, a PNN-PZT-0.02 Sr piezoceramic incorporated with Li2O-Bi2O3-CuO sintering additives and its MLA with the dimension of 7×7×3 mm3 were prepared using tape-casting and subsequent co-firing methods. The piezoceramic mainly composed of a triple phase (M, R, and T) co-existence shows a dense microstructure, indicating a good sintering-assistance effect. Even sintering at 920 °C, the piezoceramic possesses d33 ∼ 683 pC/N and kp ∼ 0.64, possibly surpassing most reported PZT-based piezoceramics. The MLA co-fired at 940 °C possesses a good Ag-ceramic interface without holes, aggregation or delamination. Also, it shows high maximum displacement (≥ 20 μm), high stiffness (118.5 N/μm @ 150 V), excellent thermal stability and 109-cycle reliability. A flat and defect-free electrode morphology is conducive to decreased leakage current. However, high tanδ primarily induced by the residual glassy phase and (Pb, Bi) oxides is the drawback. These findings give a novel paradigm for low-cost and high-reliability MLAs using pure Ag as inner electrodes by triple-phase controlling and nano-heterogeneity.

Defect dipole stretching enables ultrahigh electrostrain.

Piezoelectric actuators have been extensively utilized as micro-displacement devices because of their advantages of large output displacement, high sensitivity, and immunity to electromagnetic interference. Here, we propose a straightforward approach to design <110>-oriented defect dipoles by introducing A-site vacancies and oxygen vacancies in (K0.48Na0.52)0.99NbO2.995 ceramics. As a result, we achieve ultrahigh electrostrains of 0.7% at 20 kV cm-1 (with an effective piezoelectric strain coefficient d33* = 3500 pm V-1), outperforming the performance of existing piezoelectric ceramics at the same driving field. The exceptional electrostrain is primarily attributed to the large stretching of defect dipoles when subjected to an applied electric field, a phenomenon that has been experimentally confirmed. Moreover, the strong interaction between these defect dipoles and <110> spontaneous polarizations plays a critical role in minimizing hysteresis and ensuring excellent fatigue resistance. Our findings present a practical and effective strategy for developing high-performance piezoelectric materials tailored for advanced actuator applications.

Hard- and Soft-Coded Strain Stiffening in Metamaterials via Out-of-Plane Buckling Using Highly Entangled Active Hydrogel Elements.

Metamaterials show elaborate mechanical behavior such as strain stiffening, which stems from their unit cell design. However, the stiffening response is typically programmed in the design step and cannot be adapted postmanufacturing. Here, we show hydrogel metamaterials with highly programmable strain-stiffening responses by exploiting the out-of-plane buckling of integrated pH-switchable hydrogel actuators. The stiffening upon reaching a certain extension stems from the initially buckled active hydrogel beams. At low strain, the beams do not contribute to the mechanical response under tension until they straighten with a resulting step-function increase in stiffness. In the hydrogel actuator design, the acrylic acid concentration hard-codes the configuration of the metamaterial and range of possible stiffening onsets, while the pH soft-codes the exact stiffening onset point after fabrication. The utilization of out-of-plane buckling to realize subsequent stiffening without the need to deform the passive structure extends the application of hydrogel actuators in mechanical metamaterials. Our concept of out-of-plane buckled active elements that stiffen only under tension enables strain-stiffening metamaterials with high programmability before and after fabrication.

Giant field-induced strain with excellent fatigue performance in (Al0.5Nb0.5)4+-modified 0.85Bi0.5Na0.5TiO3-0.11Bi0.5K0.5TiO3-0.04BaTiO3 piezoelectric ceramics

Utilizing a conventional solid-state reaction procedure, (Al0.5Nb0.5)4+-modified 0.85Bi0.5Na0.5TiO3-0.11Bi0.5K0.5TiO3-0.04BaTiO3 (BNKT-BT) samples were synthesized. The impact of (Al0.5Nb0.5)4+ on the crystal structure, ferroelectric, dielectric, and AC impedance properties was systematically investigated. The XRD patterns demonstrate that the crystal structures of all samples exhibit typical pseudo-cubic features. According to the XPS, the doping of (Al0.5Nb0.5)4+ reduces the concentration of oxygen vacancies inside the ceramics, which significantly affects the relaxation properties. This substitution successfully triggers a change from a non-ergodic relaxor (NR) state to an ergodic relaxor (ER) state, which is ascribed to the weakening of the pinning effect of the oxygen vacancies on the polar nanoregions (PNRs). The ceramics exhibit an enormous monopolar strain of 0.468 % under 60 kV/cm, accompanied by an inverse piezoelectric coefficient (d33*) of 780 pm/V, surpassing the performance of numerous other BNT-based piezoelectric ceramics. After 1×104 switching cycles, the strain value changes slightly, indicating excellent fatigue performance. The considerable strain arises from a reversible transformation of the ER phase to the ferroelectric phase induced by an electric field. This research suggests that (Al0.5Nb0.5)4+-doped BNKT-BT ceramics have good prospects for application in actuators and sensors.

Design and application of bidirectional soft actuator with multiangle chambers

PurposeThis study aims to introduce a novel bidirectional soft actuator as an enhancement to conventional pneumatic network actuators. This improvement involves integrating air chambers positioned at specific angles to improve stability, adaptability and grasping efficiency in various environments.Design/methodology/approachThe design approach incorporates air chambers positioned at a 45° angle relative to the horizontal direction at the actuator's terminus, along with additional chambers at a 90° angle. Mathematical models are developed for longitudinal and transverse bending, as well as for obliquely connected cavities, based on the assumption of piecewise constant curvature. Analyses are conducted on output forces, bending characteristics and end contact areas for both transverse and longitudinal ends.FindingsThe proposed soft actuator surpasses traditional pneumatic network actuators in gripping area due to the inclusion of a diagonal air cavity and a transverse pneumatic network structure at the terminus. As a result, it provides torsion and gripping force in both directions. Testing on a dedicated platform with two variants of grippers demonstrates superior gripping force capability and performance in complex environments.Practical implicationsThrough the design of multiangle chambers, the soft actuator exhibits diverse driving angles and morphological variations, offering innovative design perspectives for industrial grasping.Social implicationsThe design of multiangle chambers facilitates personalized configurations of soft actuators by researchers, enabling tailored angles for specific interaction environments to achieve desired functionalities. This approach offers novel insights into soft actuator design, addressing more prevalent industrial grasping challenges.Originality/valueThis study introduces a novel soft actuator design that significantly enhances gripping capabilities in comparison to conventional pneumatic network actuators. The incorporation of specific air chamber configurations and mathematical modeling provides valuable insights for the development of adaptable and efficient robotic grippers for industrial and household applications.