Thermal Actuator Research Articles

Thermal responsive smart lanthanide luminescent hydrogel actuator

Among stimuli-responsive soft materials, thermal responsive hydrogels are the most attractive one because temperature is the most easily regulated external stimuli. We here report a thermal responsive bilayer smart luminescent hydrogel actuator with tough mechanical strength and thermal reversible deformation behavior. The bilayer hydrogel is composed of Poly(N-isopropylacrylamide)-Laponite-Tb complex (PNIPAM-Lap-Tb·L3) layer and Poly(N,N-dimethylacrylamide)-Laponite-Eu complex (PDMA-Lap-Eu·L3) layer. Upon alternative heating and cooling, the PNIPAM-Lap-Tb·L3 layer undergoes reversible shrink and expansion, while the PDMA-Lap-Eu·L3 layer is not affected, leading to asymmetric deformation behavior. The luminescent intensity of the bilayer hydrogel was enhanced by heating, and the maximum bending angle was 371° in 15 min. By processing the bilayer hydrogel into complex 2D and 3D structure, we further demonstrate their great potential as smart soft actuators.

Novel four-port RF phase change switches based on GeTe thin film

An indirect-heated phase-change switch (PCS) using germanium telluride (GeTe) has been fabricated using thermal actuation driven by thin film heater on the model. Switches require a low ON-state resistance and a high OFF-state resistance with OFF/ON resistance ratio of 105. The finite element analysis simulation is applied to simulate the temperature of individual node GeTe with different microwave heating pulses. Finally, in order to reduce the phase-change time and increase the switching speed of indirectly heated switching structures, a new four-port indirectly heated phase change switching structure is proposed. In this paper, the heat dissipation of the switch is increased by etching deep grooves on the back of the switch. This structure obviously reduces the phase change time compared to conventional indirectly heated phase change switches the time between ON-state and OFF-state is reduced by more than 19% and the total process is reduced by more than 47%. The GeTe PCSs with etched grooves not only significantly increases the switching speed, but also reduces the risk of recrystallization of the phase change material.

Experimental investigation of vibration control of flexible rotors using shape memory alloys

Vibration is an essential subject for the design of rotordynamic systems, being responsible for compromising the integrity and causing risks to operational functioning. This work deals with an experimental investigation of the semi-active vibration controller for a rotordynamic system using shape memory alloy (SMA) elements. SMAs are smart materials that present thermomechanical coupling represented by solid phase transformations that promote either stiffness change or hysteretic dissipation. In this regard, they are useful in controllers employing thermal actuation from electric current through the Joule effect. This paper presents a proof of concept of a controller using SMA elements. An experimental apparatus is proposed considering a typical rotor system using SMA wires at the bearings. In this regard, proper temperature variations allow the system to cross critical resonant conditions.

Tunable Bound States in the Continuum in a Reconfigurable Terahertz Metamaterial

AbstractBound states in the continuum (BIC) is an exotic concept describing systems without radiative loss. BICs are widely investigated in optics due to numerous potential applications including lasing, sensing, and filtering, among others. This study introduces a structurally tunable BIC terahertz metamaterial fabricated using micromachining and experimentally characterized using terahertz time domain spectroscopy. Control of the bending angle of the metamaterial by thermal actuation modifies the capacitance enabling tuning from a quasi‐BIC state with a quality factor of 26 to the BIC state. The dynamic response from the quasi‐BIC state to the BIC state is achieved by blueshifting the resonant frequency of the LC mode while maintaining a constant resonant frequency for the dipole mode. Additional insight into the tunable electromagnetic response is obtained using temporal coupled mode theory (CMT). The results reveal the effectiveness of bi‐layer cantilever‐based structures to realize tunable BIC metamaterials with potential applications for nonlinear optics and light‐matter control at terahertz frequencies.

Shape Memory Alloy (SMA) Actuators: The Role of Material, Form, and Scaling Effects.

Shape memory alloys (SMAs) are smart materials that are widely used to create intelligent devices because of their high energy density, actuation strain, and biocompatibility characteristics. Given their unique properties, SMAs have been found to have significant potential for implementation in many emerging applications in mobile robots, robotic hands, wearable devices, aerospace/automotive components, and biomedical devices. In this review, we summarize the state-of-the-art of thermal and magnetic SMA actuators in terms of their constituent materials, form, and scaling effects, including their surface treatments and functionalities. We also analyze the motion performance of various SMA architectures (wires, springs, smart soft composites, and knitted/woven actuators). Based on our assessment, we emphasize current challenges of SMAs that need to be addressed for their practical application. Finally, we suggest how to advance SMAs by synergistically considering the effects of material, form, and scale. This article is protected by copyright. All rights reserved.

Fuel-Driven Redox Reactions in Electrolyte-Free Polymer Actuators for Soft Robotics.

Polymers that undergo shape changes in response to external stimuli can serve as actuators and offer significant potential in a variety of technologies, including biomimetic artificial muscles and soft robotics. Current polymer artificial muscles possess major challenges for various applications as they often require extreme and non-practical actuation conditions. Thus, exploring actuators with new or underutilized stimuli may broaden the application of polymer-based artificial muscles. Here, we introduce an all-solid fuel-powered actuator that contracts and expands when exposed to H2 and O2 via redox reactions. This actuator demonstrates a fully reversible actuation magnitude of up to 3.8% and achieves a work capacity of 120 J/kg. Unlike traditional chemical actuators, our actuator eliminates the need for electrolytes, electrodes, and the application of external voltage. Moreover, it offers athermal actuation by avoiding the drawbacks of thermal actuators. Remarkably, the actuator maintains its actuated position under load when not stimulated, without consuming energy (i.e., catch state). These fuel-powered fiber actuators were embedded in a soft humanoid hand to demonstrate finger-bending motions. In terms of two main actuation metrics, stress-free contraction strain and blocking stress, the presented artificial muscle outperforms reported polymer redox actuators. The fuel-powered actuator developed in this work creates new avenues for the application of redox polymers in soft robotics and artificial muscles.

Repeatable compressive functionality of 3D printed shape-memory thin-walled corrugated structures

This work aimed to investigate the compressive and shape recovery performance of the 3D printed shape-memory corrugated tubes (SMCTs). The structures were manufactured by fused deposition modeling technique and made from the shape memory polymer. The effects of corrugation number and amplitude on crushing and shape recovery behaviors were studied by shape memory experiment. Compression experimental results indicated that the mode transition of diamond-mixed-ring occurred with the corrugation number and amplitude increasing. After induced by thermal actuation, all structures could complete the shape recovery process with the shape recovery ratio above 98% within 20 s. Ten consecutive shape memory (compressive and recovery) cycles were carried out to analyze the repeatable compression functionality. The specific energy absorption of corrugated tubes presented the significant convergent tendency, while straight tubes showed a continuous decrease. The repeatable compressive and recovery characteristics with stable mechanical properties were achieved by applying the corrugation design. The theoretical model was developed to predict the mean crushing force of SMCTs in each cycle. Considering the shape memory cycling effect, the attenuation coefficient was introduced into the model. The prediction data for SMCTs were well agreed to the experimental results. The finding of this study offered a promising design concept for developing the advanced reversible energy absorber and implementing in multi-functional applications.

Green Flexible Electronics: Natural Materials, Fabrication, and Applications.

The emergence of plastic electronics satisfies the increasing demand for flexible electronics. However, it has caused severe ecological problems. Flexible electronics based on natural materials are increasing to hopefully realize the "green" and eco-friendly concept. Herein, recent advances in the design and fabrication of green flexible electronics are reviewed. First, this review comprehensively introduces various natural materials and derivatives, focusing particularly on fibroin and silk, wood and paper, plants, and biomass. Second, fabrication techniques for modifying natural materials, including physical and chemical methods, are presented, after which their merits and demerits are thoroughly discussed. Green flexible electronics based on natural materials, comprising electrical wires/electrodes, antennas, thermal management devices, transistors, memristors, sensors, energy-harvesting devices, energy-storage devices, displays, actuators, electromagnetic shielding, and integration systems, are described in detail. Finally, perspectives on the existing challenges and opportunities to employ natural materials in green flexible electronics are presented.

The Thermal Time Constant of an Electrothermal Microcantilever Resonator

Background: The thermal time constant is the core parameter for determining the dynamic response of the electrothermal actuators and the corresponding maximum operational frequency. Aim: Since it is necessary to determine how the thermal actuation is taking place within the cantilever, this paper presents two models for the thermal time constant of bimetal microcantilevers. One model was based on the bimetallic effect, and the second was based on temperature gradients in layers Methods: In order to investigate and check the validity of the two roposed model, the device was actuated electrothermally and the thermal time response was estimated. A driving voltage was applied to the platinum electrode. The first model is based on the interface thermal resistance between the base and the top electrode layer. The second model assumes that the temperature gradients within the base layer are responsible for thermal actuation. Results: The microcantilever was excited electrothermally with a resonance frequency of 1.89 MHz. The bimetallic effect was found to be less able to stimulate the microcantilever at this resonance frequency. Therefore, the conclusion was that thermal actuation occurred as a result of temperature variation within the SiC base layer. Conclusion: The results also indicated that temperature variations within one of the two materials in contact may be responsible for thermal actuation, especially if the material has high thermal conductivity.

Lamé Resonator Integrated With Chevron-Shaped Thermal Actuators to Improve Motional Resistance and Temperature Stability

This paper presents a capacitive bulk mode resonator operating in Lamé mode, where the motional resistance and temperature stability are enhanced by implementing a set of chevron-shaped thermal actuators to reduce the transducer air gaps. The chevrons are heated using micro-heaters that are integrated on the actuator. The device is fabricated in the PiezoMUMPS standard microfabrication process by MEMSCAP. The measured resonant frequency for the fabricated device was observed to be 17.9 MHz. It has been experimentally shown that the transducer air gap can be reduced from 2.5 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu m$</tex-math> </inline-formula> to 0.5 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu m$</tex-math> </inline-formula> by applying a heater voltage of 2.7 V at atmospheric pressure. In the proposed resonator, the transmission loss can be reduced by 8.54 dB when the actuators are biased at 1.8 V in vacuum, as opposed to when the actuator is off. Under these conditions, the thermal actuators each consume 39 mA. In addition, the implemented thermal actuators can function as integrated heaters that increase the temperature of the suspended square structure to compensate for ambient temperature variations. As such, applying a voltage of 1.8 V in vacuum reduces the resonant frequency from 17.95 MHz to 17.91 MHz, while applying a voltage of 2.6 V at atmospheric pressure reduces the resonant frequency from 17.97 MHz to 17.86 MHz.2022-0188

Design, fabrication, nonlinear analysis, and experimental validation for an active sandwich beam in strong electric field and thermal environment

In the present work, an efficient one-dimensional finite element (1D-FE) framework considering layerwise mechanics with full electro-mechanical coupling has been developed for the laminated smart sandwich beams submitted to active damping. Nonlinear constitutive relations of piezo-thermo-elasticity at large electric field with temperature-dependent material properties have been considered. The efficient layerwise theory (ELWT) considers the normal deformation of the piezoelectric sensing/actuating patches/layers due to the more significant value of piezoelectric strain coefficient d33. The electric potential variation across the thickness of the PZT sensor/actuator has been assumed quadratic. The state space format of the dynamical system has been constructed based on a reduced order model in modal space. The feedback linearization approach has been applied to the nonlinear system of equations to design an equivalent linear optimal control strategy. An experimental facility has been developed to test the accuracy of the present nonlinear FE model. This facility consists of a thermal chamber with a heating system, air gun, actuation & sensing units with band-pass filters, a smart sandwich beam equipped with PZT-SP5H patches, a data acquisition system, and a computer with LabVIEW software. Open- and closed-loop responses from the present 1D-FE model have been compared with those obtained through experimentation at different temperatures. It has been observed that the current nonlinear FE model correctly captures the dynamic behavior of the vibrating smart sandwich beam at different operating temperatures and strong electric field. The study shows a strong dependence of the PZT materials on thermal chamber temperature and actuation field. New results for a smart sandwich beam are also presented to study the performance of PZT-SP5H patches as sensors/actuators for nonlinear active shape and vibration control in a thermal environment. The effect of piezoelectric actuator/sensor thickness, patch size, position, and applied mechanical load on the active shape and vibration control has been discussed.

Cover Image, Volume 140, Issue 25

This cover image was created by Chun-Yen Liu and co-authors. Asymmetrically constructed cholesteric liquid crystal elastomers show direction-controllable thermal rolling actuation. The background shows a POM texture of the prepared liquid crystal mixture. In this manuscript, we demonstrate a novel design of cylindrical liquid crystal elastomers which were fabricated by Michael addition, and the synthesized CLCE prepolymers were then uniaxially stretched with a twisted angle and fixed with UV polymerization. The synthesized asymmetrically constructed CLCEs reveal that the gravity center shifts from the geometric center, showing thermal rolling actuation. DOI: 10.1002/app.53970

Size-dependent thermal bending of bilayer microbeam based on modified couple stress theory and Timoshenko beam theory

The bilayer microbeam can be assigned with two different thermal expansion coefficients, so that the microbeam can be used as a thermal actuator, which can provide bending with thermal loading. As a microdevice, the size effect plays an important role. In addition, the length height ratio L/h of the microbeam has to be smaller than 20, to provide sufficient support. With this ratio, the shear effect of the beam can not be ignored. In this work, considering both the size and shear effects, we modified the couple stress and Timoshenko beam theories to study the thermal bending of bilayer microbeams. By using the principle of minimum potential energy, we derived the higher-order governing equations under thermal load. Then with specified boundary conditions, we adopted the differential quadrature method to solve the governing equations. Finally, using a bilayer microbeam made of aluminum and polysilicon as an example, we verified effects of transverse shear and beam size. Results show that the size effect on beam stiffness is significant when the beam height is on the order of equivalent length scale (leq). Moreover, considering the transverse shear effect indicates that the lateral deflection of the Timoshenko beam depends on the ratio L/h: as L/h increases, the tip deflection increases and converges to the classical solution. Specifically, for a Timoshenko beam with h/leq = 15, the change in deflection can reach 44.6% when L/h is increased from 5 to 25.

One Stone, Two Birds: Spidroin‐Inspired Nanogels for High‐Performance Fibers and Photothermal Actuators

AbstractThe exciting development of hydrogels makes it a promising candidate to be applied in various fields. However, it remains a great challenge to store the precursors of hydrogels and to process them after gelation, like synthetic polymer materials. Herein, spidroin‐inspired novel nanogels with extraordinary processability, which can be spun into fibers via direct drawing and fabricated into thermal actuators easily after gelation are prepared. These soluble and spinnable nanogels are composed of a liquid metal core and a poly (acrylic acid) (PAA) shell and are entangled with each other. The as fabricated nanogels and diluted dope solution can be stored &gt;1 month. The as‐spun nanogel fibers with hierarchical structures achiev extraordinary mechanical properties (tensile stress of 575 MPa, toughness of 381 MJ m−3) and supercontraction at 60% RH. Besides, a photothermal actuator is prepared by coating the nanogels on a polyethylene substrate with a commercial shading ink, and the as‐prepared actuator shows a rapid response to near‐infrared light as well as a fast recovery. Molecular dynamics simulation reveals a possible working mechanism of the actuator. This study provides a new strategy to prepare processable nanogels with broad application prospects for smart textiles and soft robots.

Upper Body Thermal Referral and Tactile Masking for Localized Feedback.

This paper investigates the effects of thermal referral and tactile masking illusions to achieve localized thermal feedback on the upper body. Two experiments are conducted. The first experiment uses a 2D array of sixteen vibrotactile actuators (4 × 4) with four thermal actuators to explore the thermal distribution on the user's back. A combination of thermal and tactile sensations is delivered to establish the distributions of thermal referral illusions with different numbers of vibrotactile cues. The result confirms that localized thermal feedback can be achieved through cross-modal thermo-tactile interaction on the user's back of the body. The second experiment is conducted to validate our approach by comparing it with thermal-only conditions with an equal and higher number of thermal actuators in VR. The results show that our thermal referral with a tactile masking approach with a lesser number of thermal actuators achieves higher response time and better location accuracy than thermal-only conditions. Our findings can contribute to thermal-based wearable design to achieve greater user performance and experiences.

Creation of asymmetrically constructed cylindrical liquid crystal actuators with controllable thermal rolling

AbstractIn this study, we demonstrate a predesigned method for the fabrication of rolling direction controllable asymmetrically constructed cylindrical liquid crystal elastomers (CLCEs). Cylindrical liquid crystal elastomers were fabricated by Michael addition, and the synthesized CLCE prepolymers were then uniaxially stretched with a twisted angle and fixed with UV polymerization. The synthesized asymmetrically constructed CLCEs reveal that the gravity center shifts from the geometric center, showing thermal actuation. The location of the asymmetric gravity center of each of the synthesized CLCEs was estimated. Based on the location of the gravity center, rolling direction control of the synthesized CLCEs was achieved. For one synthesized CLCE, both clockwise and counterclockwise rolling are possible depending on the location of the gravity center when it was placed on a hot plate. The creation of direction controllable cylindrical thermally sensitive LCE actuators is a novel skill, which opens a new avenue for the fabrication of smart functional materials.

Thermomechanical Real-Time Hybrid Simulation: Conceptual Framework and Control Requirements

Real-time hybrid simulation (RTHS) is an enabling technology that has transformed engineering experimentation and helped researchers expand modeling capabilities. However, breakthroughs are necessary to expand the range of hybrid simulation methods and, thus, enable experiments with loading conditions representing multiple hazards. This paper discusses the development of a new thermomechanical RTHS framework and a systematic approach to determining RTHS control requirements. First, the framework is established using a representative finite element model of a layered structural system subjected to thermal loading. A complete two-layer system model serves as the reference system, and it is then partitioned into a numerical layer and an experimental layer that share interface conditions. Next, a thermal actuator is introduced to impose dynamic thermal loading on the experimental subsystem, serving as a transfer system. Finally, control and performance metrics are defined to evaluate the realization of interface boundary conditions and map this to the RTHS execution. Through an illustrative example considering the influence of temperature on a lunar habitat, we demonstrate how to establish controller requirements for RTHS and demonstrate that this approach can be used to conduct RTHS on structures with thermomechanical loading.

Graphene Based Printable Conductive Wax for Low‐Power Thermal Actuation in Microfluidic Paper‐Based Analytical Devices

AbstractWax printing is one of the most widely used techniques to print hydrophobic barriers on hydrophilic microfluidic paper‐based analytical devices (µPADs) based on its simplicity, speed, and low cost, allowing large‐scale production. Nonetheless, its function is just passive, without any action on fluids. Thus, this work proposes multifunctional hydrophobic composites based on conductive graphene nanoplatelets (GNPs) integrated into the wax matrix to allow a dual role of barrier and heater, the latter being required in a large variety of temperature‐sensitive reactions and microfluidic applications. The effect of GNP weight content on the physicochemical properties of the wax, printed wax, and generated heating are evaluated. Wax prints with mechanical stability and adequate impregnation through the paper are obtained after post‐thermal curing. With respect to the functional response, controlled temperatures ranging from room temperature to ≈107 °C can be achieved after just 10 s. Two proofs of concept are presented involving thermochromic inks, specific printed systems designs, and low‐power batteries. The benefits of µPADs allied to the increased functionality and performance of the developed waxes, hold great promise to meet the requirements for a next generation of versatile, effective, and accurate µPADs for an increasing number of applications.

Performance evaluation simulation of the optical splitters integrated with unidirectional fiber elements

Abstract This study has clarified the performance evaluation simulation of the optical splitters integrated with unidirectional fiber elements. The simulative performance evaluation of electrostatic, thermal, and piezoelectric actuation based micro electro mechanical systems. The force against the displacement based electrostatic and elastic forces for parallel plate actuator is simulated by MEMSover simulation software. The voltage with angular displacement for a torsion bar actuator is clarified. Besides the lateral displacement against voltage for a comb drive actuator is reported. The dependence of the film thickness on the deflection of a bimetallic cantilever, the dependence of passive beam length on deflection of a bimorph actuator and the transient response of a bent beam actuator are demonstrated. Moreover the piezoelectric actuator force against applied voltage and the piezoelectric actuator displacement against applied voltage variations are reported.

Caterpillar-inspired soft crawling robot with distributed programmable thermal actuation.

Many inspirations for soft robotics are from the natural world, such as octopuses, snakes, and caterpillars. Here, we report a caterpillar-inspired, energy-efficient crawling robot with multiple crawling modes, enabled by joule heating of a patterned soft heater consisting of silver nanowire networks in a liquid crystal elastomer (LCE)-based thermal bimorph actuator. With patterned and distributed heaters and programmable heating, different temperature and hence curvature distribution along the body of the robot are achieved, enabling bidirectional locomotion as a result of the friction competition between the front and rear end with the ground. The thermal bimorph behavior is studied to predict and optimize the local curvature of the robot under thermal stimuli. The bidirectional actuation modes with the crawling speeds are investigated. The capability of passing through obstacles with limited spacing are demonstrated. The strategy of distributed and programmable heating and actuation with thermal responsive materials offers unprecedented capabilities for smart and multifunctional soft robots.