Actuator Applications Research Articles

Responsive Magnetic Polymer Nanocomposites through Thermal-Induced Structural Reorganization.

Polymer nanocomposites (PNCs), which feature a hybrid network of soft polymers filled with nanoparticles, hold promise for application in soft robots due to their tunable physiochemical properties. Under certain environmental conditions, PNCs undergo stimuli-responsive structural rearrangement and transform the energy of the ambient environment into diverse uses, for example, repairing the injuries and reconfiguring the shapes of the materials. We develop PNCs with the ability of thermal-responsive restructuring by the stepwise assembly of functional components, including magnetite nanoparticles, silylated cellulose, and polydimethylsiloxane. We investigate the dynamic changes of the nano- and submicron structure of the magnetic PNCs upon the stimulation of heating based on a combined analytical approach: using dynamic mechanical analysis to interpret the viscoelastic properties of the PNC and in situ small-angle X-ray scattering to quantify the clustering of NPs. Based on these results, we formulate a structural model for the heating-induced evolution of the nano- to submicrometer assemblies in the magnetic PNC. Moreover, thermal-induced restructuring of magnetic PNCs leads to additional favorable functions, such as the abilities of healing, welding, reprocessing, and responses to photo and magneto stimuli. Our design provides a versatile means to develop responsive PNCs for applications in soft robots, sensors, and actuators.

A theoretical and computational model for the synergy of electrostriction and photovoltaic effect to create photostriction

The phenomenon of photostriction, which involves generating mechanical actuation in response to light, is observed in a very limited number of materials from ferroelectric, semiconductors, and organic material classes. This limited choice of materials, combined with their responsiveness to narrow light spectra, has constrained the broader adoption of photostriction in practical applications. This study introduces a novel approach by integrating photovoltaic and electrostrictive couplings in composites made of a photovoltaic matrix with ferroelectric inclusions, yielding an apparent photostrictive effect. By leveraging the simultaneous action of both photovoltaic and electrostrictive effects, the composite efficiently converts irradiated optical energy into mechanical energy, enabling mechanical actuation across a broader range of materials and light spectra. First, we develop a computational framework for intertwined multiphysics coupling of the photovoltaic effect with nonlinear electrostriction, based on a novel constitutive model. Then, to evaluate all the effective properties that define the composite's behavior, we introduce a multiphysics-coupled homogenization framework capable of computing elastic, electrostrictive, dielectric, and thermal properties. Finally, a shell finite element formulation based on the assumptions of first-order shear deformation theory is used to analyze the behavior of the homogenized photo-electrostrictive composite based actuator. This study demonstrates the feasibility of the proposed composite by examining the deflection response of structures laminated with this photostrictive composite. Several case studies are conducted to provide insights into the development and characterization of photo-electrostrictive composites, which hold great potential for applications in mechanical actuation, shape morphing, and beyond.

Advancements in Micro/Nanorobots in Medicine: Design, Actuation, and Transformative Application

Advancements in Micro/Nanorobots in Medicine: Design, Actuation, and Transformative Application

Electrostrictive Structural Transitions and Tensorial Electro-Optics in Mesomorphic Blue Phase Crystals.

Electrostriction is present in all dielectrics, but the electrostriction itself is generally minuscule and is even insignificant in low-dielectric-constant materials. Herein, extraordinary electrostriction is found in mesomorphic blue phase (BP) crystals, which are fluidic "giant" crystals with a lattice constant of several hundred nanometers and contain 107-108 molecules in each unit cell. In situ optical observations revealed that the BP crystals exhibit -19.5% to 15.7% electrostrictive actuation at weak field strengths (<3 V/μm), during which a transient monoclinic phase is found. The monoclinic phase occurs in the form of twinning and single crystals successively, which acts as an intermediate state to dominate the pathway of electrostrictive structural transition. Furthermore, we experimentally confirmed that a tensorial crystal-optic effect is induced in BPs by electrostriction, which updates our conventional understanding about liquid crystalline materials that the electro-optics has always been considered as a scalar effect. This work reveals the structural polymorphism in electrostrictive soft crystals, which, in the meantime, provides additional degrees-of-freedom for their advanced applications in nano or micro actuators, flexible electronics, and photonics of next generation, by precisely manipulating the soft crystalline structures and their crystal-optic characteristics.

Applications of Piezoelectric-based Sensors, Actuators, and Energy Harvesters

Applications of Piezoelectric-based Sensors, Actuators, and Energy Harvesters

Piezoelectric Property Amplification in 0.46PNN-0.23PIN-0.31PT Ceramics via Optimized Low-Temperature Sintering and Defect Chemistry

Piezoelectric Property Amplification in 0.46PNN-0.23PIN-0.31PT Ceramics via Optimized Low-Temperature Sintering and Defect Chemistry

Large Electromechanical Response and Field-Induced Shape Memory Effect in Ferroelectric Ceramics.

Electric-field-induced shape memory effect has potential applications in electromechanical actuator. Here, this study proposes the a phase structure design routine in (1-x)(75Na0.5Bi0.5TiO3-25SrTiO3)-xPbTiO3 ceramics to obtain large electromechanical response and shape memory effect. It is found that the shape memory effect is closely related to the bending deformation induced by asymmetric polarization between positive and negative electrodes, which is resulted from the reductions of Bi3+ and Pb2+ because of electron injection from negative electrode. In addition, the content of ferroelectric phase with P4mm structure and c/a ratio increase with PbTiO3 content increasing, and the coercive field of the ceramics is also enhanced by the PbTiO3 addition, Combing the crystal structure and chemical composition, the field-induced deformation achieves 2.77% and shape memory effect is 1.75% at 80kVcm-1 and 0.1Hz in the ceramic with the content of PbTiO3 is 40%.

Additive Manufacturing of Ni–Ti SMA by the Sinter-Based MoldJet Method

Abstract Additive Manufacturing (AM) of Shape Memory Alloys (SMA), and specifically Ni–Ti alloys, is an evolving field with significant potential to applications in actuation, energy harvesting, and refrigeration. Sinter-based AM technologies show promise in tailoring and controlling the microstructure and properties of Ni–Ti, because the metal particles remain in the solid-state throughout the process. Here, we report on the manufacturing and characterization of Ni–Ti produced using a novel sinter-based MoldJet method: a wax-based mold is deposited layer-by-layer using jet-printing, and its cavities are simultaneously filled with metallic paste. This additive process produces a green body that is sintered to form a dense metal part. The low content of organic binder in the metallic paste results in reduced carbon and oxygen contamination compared to other sinter-based AM methods. Consequently, the reduced formation of carbides and oxides enhances the thermomechanical properties. Here, we show that Ni–Ti produced via MoldJet exhibits a superelastic response with a substantial recoverable strain of 5.6% in tension and 4.5% in compression, and irrecoverable plastic strain below 0.2%. The results indicate that MoldJet is a promising method for AM of Ni–Ti for advanced applications. Specifically, we show that the obtained material properties are adequate for elastocaloric cooling devices.

Manipulating Dynamic Light-Driven Solid-Liquid Transition and Static Reversible Photochromism via Organic Cocrystal Strategy.

Developing of molecular crystalline materials with light-induced multiple dynamic deformation in space dimension and photochromism on time scales has attracted much attention for its potential applications in actuators, sensoring and information storage. Nevertheless, organic crystals capable of both photoinduced dynamic effects and static color change are rare, particularly for multi-component cocrystals system. In this study, we first report the construction of charge transfer co-crystals allows their light-induced solid-to-liquid transition and photochromic behaviors to be controlled by trans-stilbene (TSB) as an electron donor and 3,4,5,6-Tetrafluorophthalonitrile (TFP) as an electron acceptor. In this case, the dynamic photo-responsive solid-to-liquid phase transition is due to the photoisomerization of TSB under UV irradiation, while the accumulation of melted droplets during solid-state photochemical process causes mechanical deformation of TSB-TFP cocrystals. The subsequent reversible photochromic behavior is attributed to the emergence of free radicals through a photo-induced electron transfer. Moreover, TSB-TFP microcrystals present typical excitation wavelength dependent emission (EWDE) fluorescence by surfactant-mediated method. This work realizes the dynamic-static photochemical cascade processes in response to light irradiation in an organic cocrystal system, providing the effective method for a new type of smart photo-responsive materials.

Manipulating Dynamic Light‐Driven Solid‐Liquid Transition and Static Reversible Photochromism via Organic Cocrystal Strategy

Developing of molecular crystalline materials with light‐induced multiple dynamic deformation in space dimension and photochromism on time scales has attracted much attention for its potential applications in actuators, sensoring and information storage. Nevertheless, organic crystals capable of both photoinduced dynamic effects and static color change are rare, particularly for multi‐component cocrystals system. In this study, we first report the construction of charge transfer co‐crystals allows their light‐induced solid‐to‐liquid transition and photochromic behaviors to be controlled by trans‐stilbene (TSB) as an electron donor and 3,4,5,6‐Tetrafluorophthalonitrile (TFP) as an electron acceptor. In this case, the dynamic photo‐responsive solid‐to‐liquid phase transition is due to the photoisomerization of TSB under UV irradiation, while the accumulation of melted droplets during solid‐state photochemical process causes mechanical deformation of TSB‐TFP cocrystals. The subsequent reversible photochromic behavior is attributed to the emergence of free radicals through a photo‐induced electron transfer. Moreover, TSB‐TFP microcrystals present typical excitation wavelength dependent emission (EWDE) fluorescence by surfactant‐mediated method. This work realizes the dynamic‐static photochemical cascade processes in response to light irradiation in an organic cocrystal system, providing the effective method for a new type of smart photo‐responsive materials.

A Review of the Applications and Challenges of Dielectric Elastomer Actuators in Soft Robotics

As an electrically driven artificial muscle, dielectric elastomer actuators (DEAs) are notable for their large deformation, fast response speed, and high energy density, showing significant potential in soft robots. The paper discusses the working principles of DEAs, focusing on their reversible deformation under electric fields and performance optimization through material and structural innovations. Key applications include soft grippers, locomotion robots (e.g., multilegged, crawling, swimming, and jumping/flying), humanoid robots, and wearable devices. The challenges associated with DEAs are also examined, including the actuation properties of DE material, material fatigue, viscoelastic effects, and environmental adaptability. Finally, modeling and control strategies to enhance DEA performance are introduced, with a perspective on future technological advancements in the field.

Design and validation of a programmable dual-tunnel soft pneumatic origami actuator with a large maximum shrinkage rate for reciprocating motion

Abstract. Soft actuators have attracted significant research in various domains owing to their flexible motion characteristics. However, the applications of soft actuators are constrained by their low force-to-weight ratio and maximum shrinkage rate, which is the ratio of the maximum stroke to the extreme length of the actuator, considerably augmenting the driving energy and occupied area. This paper presents a novel dual-tunnel soft pneumatic origami actuator capable of providing a large maximum shrinkage rate for reciprocating motion. The inner tunnel is constructed by the origami mechanism chamber, and the outer tunnel is formed by the origami mechanism in conjunction with the outer soft skin. A programmable design method for the proposed actuator is presented, based on its geometric parameter model and stiffness model. A kinematics model is developed to analyze the motion behavior and characteristics of the actuator's reciprocating motion. The prototype is fabricated using lightweight materials, such as oriented polypropylene and hard cardboard, on which tensile and load experiments are conducted. The results verify the motion characteristics of the soft actuator and the accuracy of the model. Compared to other linear actuators, the soft origami actuator is lightweight (weighing 5 g), has a large maximum shrinkage rate (61 %) and boasts a force-to-weight ratio of 600. The design demonstrates the extensive application potential of soft actuators with the origami mechanism.

Dynamic stiffness formulation for the vibration response of functionally graded nanoplates considering the neutral surface position with microstructural defects

In the present paper, the dynamic stiffness matrix of a functionally graded nanoplate (FG-nP) has been developed and used to carry out a vibration analysis. The nonlocal elasticity theory in conjunction with classical plate theory (CPT) has been used to drive the governing equations of motion using Hamilton’s principle. The nonlocal elasticity theory incorporates the length scale parameter, which can withhold the small-scale effect that is necessary for model FG-nP. The pioneer Wittrick–Williams algorithm is employed to evaluate the dynamic stiffness matrix. The property of the FG-nP has been calculated using the power law. The authenticity and efficacy of the present formulation have been ascertained using various validation studies. The accurate prediction of the effect of porosity inclusions on different volume fraction indexes, boundary conditions, and higher vibration modes has been reported. The influence of the nonlocal parameter, boundary conditions, various gradation techniques, and geometric parameters on vibration behavior has been extensively explored. The results show the versatility of the proposed approach in addressing small scaled complex engineering structures. This research significantly contributes to the understanding and analysis of functionally graded nanoplates, providing valuable insights for applications in aerospace, structural systems, sensors, actuators, and energy harvesting devices.

Stiffness Tunable Magnetic Actuators Based on Shape Memory Polymer/NdFeB Composite for Segmental Controllable Motion.

Soft magnetic robots have attracted extensive research interest recently due to their fast-transforming ability and programmability. Although the inherent softness of the matrix materials enables dexterity and safe interactions, the contradiction between the easy shape transformation of the soft matrices and load carrying capacity, as well as the difficulty of independently controllable motion of individual segments, severely limits its design space and application potentials. Herein, we have proposed a strategy to adjust the modulus of shape memory polymer composite embedded with hard magnetic particles by in situ Joule heating of printed circuit, which can reversibly change the stiffness from 4.1 GPa at 25°C to 10.9 MPa at 70°C. The stiffness tunable magnetic robots realize the compatibility of fast reversible shape transformation and high load carrying capacity. Furthermore, multiple separated Joule circuits are designed for the independently controllable motion of individual segments. The simulation of Joule heating and magnetic actuation is used to guide the design of devices. The concept of simultaneously programming magnetic anisotropy and stiffness proposed in this work greatly expands the design space and new applications of magnetic actuators, including soft grippers for heavy loads and bionic hand with independent motion of fingers.

Three-Dimensional Printable Magnetic Hydrogels with Adjustable Stiffness and Adhesion for Magnetic Actuation and Magnetic Hyperthermia Applications.

Stimuli-responsive hydrogels hold immense promise for biomedical applications, but conventional gelation processes often struggle to achieve the precision and complexity required for advanced functionalities such as soft robotics, targeted drug delivery, and tissue engineering. This study introduces a class of 3D-printable magnetic hydrogels with tunable stiffness, adhesion, and magnetic responsiveness, prepared through a simple and efficient "one-pot" method. This approach enables precise control over the hydrogel's mechanical properties, with an elastic modulus ranging from 43 kPa to 277 kPa, tensile strength from 93 kPa to 421 kPa, and toughness from 243 kJ/m3 to 1400 kJ/m3, achieved by modulating the concentrations of acrylamide (AM) and Fe3O4 nanoparticles. These hydrogels exhibit rapid heating under an alternating magnetic field, reaching 44.4 °C within 600 s at 15 wt%, demonstrating the potential for use in mild magnetic hyperthermia. Furthermore, the integration of Fe3O4 nanoparticles and nanoclay into the AM precursor optimizes the rheological properties and ensures high printability, enabling the fabrication of complex, high-fidelity structures through extrusion-based 3D printing. Compared to existing magnetic hydrogels, our 3D-printable platform uniquely combines adjustable mechanical properties, strong adhesion, and multifunctionality, offering enhanced capabilities for use in magnetic actuation and hyperthermia in biomedical applications. This advancement marks a significant step toward the scalable production of next-generation intelligent hydrogels for precision medicine and bioengineering.

Two-Dimensional Ferroelectric Materials: From Prediction to Applications.

Ferroelectric materials hold immense potential for diverse applications in sensors, actuators, memory storage, and microelectronics. The discovery of two-dimensional (2D) ferroelectrics, particularly ultrathin compounds with stable crystal structure and room-temperature ferroelectricity, has led to significant advancements in the field. However, challenges such as depolarization effects, low Curie temperature, and high energy barriers for polarization reversal remain in the development of 2D ferroelectrics with high performance. In this review, recent progress in the discovery and design of 2D ferroelectric materials is discussed, focusing on their properties, underlying mechanisms, and applications. Based on the work discussed in this review, we look ahead to theoretical prediction for 2D ferroelectric materials and their potential applications, such as the application in nonlinear optics. The progress in theoretical and experimental research could lead to the discovery and design of next-generation nanoelectronic and optoelectronic devices, facilitating the applications of 2D ferroelectric materials in emerging advanced technologies.

Amplifying the Sensitivity of Electrospun Polyvinylidene Fluoride Piezoelectric Sensors Through Electrical Polarization Process for Low-Frequency Applications

Piezoelectric sensors convert mechanical stress into electrical charge via the piezoelectric effect, and when fabricated as fibers, they offer flexibility, lightweight properties, and adaptability to complex shapes for self-powered wearable sensors. Polyvinylidene fluoride (PVDF) nanofibers have garnered significant interest due to their potential applications in various fields, including sensors, actuators, and energy-harvesting devices. Achieving optimal piezoelectric properties in PVDF nanofibers requires the careful optimization of polarization. Applying a high electric field to PVDF chains can cause significant mechanical deformation due to electrostriction, leading to crack formation and fragmentation, particularly at the chain ends. Therefore, it is essential to explore methods for polarizing PVDF at the lowest possible voltage to prevent structural damage. In this study, a Design of Experiments (DoE) approach was employed to systematically optimize the polarization parameters using a definitive screening design. The main effects of the input parameters on piezoelectric properties were identified. Heat treatment and the electric field were significant factors affecting the sensor’s sensitivity and β-phase fraction. At the highest temperature of 120 °C and the maximum applied electric field of 3.5 kV/cm, the % β-phase (F(β)) exceeded 95%. However, when reducing the electric field to 1.5 kV/cm and 120 °C, the % F(β) ranged between 87.5% and 90%. The dielectric constant (ɛ′) of polarized PVDF was determined to be 30 at an electric field frequency of 1 Hz, compared to a value of 25 for non-polarized PVDF. The piezoelectric voltage coefficient (g33) for polarized PVDF was measured at 32 mV·m/N at 1 Hz, whereas non-polarized PVDF exhibited a value of 3.4 mV·m/N. The findings indicate that, in addition to a high density of β-phase dipoles, the polarization of these dipoles significantly enhances the sensitivity of the PVDF nanofiber mat.

Robust Fabrication of Anisotropic Bilayer Hydrogel Embedded With a Gradient Structure in One Layer: Enhanced Temperature‐Responsive Bending, Shape Programmability, and Actuator and Sensor Applications

ABSTRACTAnisotropic hydrogel actuators with gradient structures offer tunable mechanical properties, like directional stiffness or bending. However, creating these gradient‐structured bilayer hydrogels is challenging, as current methods rely on complex, single‐force programming. Developing a double‐actuating bilayer hydrogel with temperature‐responsive and auxiliary layers could address these limitations and enhance their applicability. In this study, an anisotropic hydrogel actuator was developed using a simple, cost‐effective method to create a unique multi‐asymmetric structure with an embedded gradient in one layer. The resulting hydrogels exhibited excellent temperature‐responsive bending (360° within 9 s) and adaptive, complex shape‐programmable deformation (2D letters, flowers, butterflies, leaves). In addition, the hydrogels demonstrated good shape memory, mechanical strength, and conductivity. Prototypes of a hydrogel gripper and humidity alarm were successfully fabricated, showcasing the potential of this strategy for designing smart hydrogels for applications in sensors, smart humidity alarms, grippers, and actuators.

Estimation of piezoelectric material parameters of ring-shaped specimens

Abstract The estimation of accurate piezoelectric material parameters is a fundamental prerequisite for simulation-driven design of piezoelectric actuators and sensors. Previous studies show that a full set of material parameters can be determined in an inverse procedure using a single disc-shaped specimen with an electrode structured for increased sensitivity with respect to all material parameters. However, in the case of high-power actuator applications, ring-shaped piezoelectric components are often employed, necessitating an adaptation of the previously developed method. The alteration in geometry introduces some advantages. Accordingly, there is no longer any requirement to modify the electrode structure in order to enhance sensitivity. The method to estimate the material parameters presented here consists of a total of three stages. An initial, approximate estimation of the material parameters is determined using analytical approximations for the resonance frequencies from the IEEE standard. These values are optimised in an inverse procedure that employs analytic expressions for the electrical impedance of piezoelectric rings as the forward model. Further refinement is achieved by using Finite Element (FE) simulations as the forward model again in an inverse procedure. The method is applied to electrical impedance measurement data, yielding material parameters for hard piezoelectric rings. The result shows a good agreement between the simulation and measurement results, indicating realistic material parameter values.

Giant electrostriction in textured La2Ce2O7 ceramics: A promising lead-free alternative for electromechanical conversion

The search for high-performance, lead-free materials with tailored electromechanical properties is crucial for the advancement of energy harvesting and actuator technologies. While piezoelectric materials offer promising solutions, balancing high piezoelectric response with low dielectric permittivity remains a significant challenge. Recent research has highlighted the potential of “giant” electrostriction as an alternative approach, offering substantial electromechanical responses with more favorable electrical properties. This work investigates the electrostrictive and dielectric properties of non-textured and textured La2Ce2O7 ceramics. Our findings reveal a substantial electrostrictive coefficient [M33 ≈ 10−18 (m/V)2, exceeding conventional electrostrictive materials], coupled with a high effective piezoelectric response (d33eff = 40 pm/V at E = 100 kV/cm) and a high effective piezoelectric voltage coefficient (g33eff = 146–205 × 10−3 Vm/N). Notably, [111]-texturing of La2Ce2O7 significantly reduces dielectric losses, further enhancing its suitability for energy harvesting and actuator applications. The combination of electromechanical and dielectric properties creates conditions for high energy-harvesting performance, comparable to lead-containing ceramics and far superior to lead-free alternatives. Combined with temperature stability and compatibility with Si-based microfabrication, La2Ce2O7 emerges as a promising lead-free alternative for high-performance electromechanical energy conversion applications.