Thermal Actuator Research Articles

Highly Aligned Carbon Nanotube‐Based Bi‐Material Microactuators with Reduced Intertube Slipping

AbstractBi‐material microcantilevers have been widely used as both thermal sensors and thermal actuators. Carbon nanotubes (CNT) are prominent candidates for bi‐material actuators due to the negative coefficient of thermal expansion (CTE) at the axial direction that allows for higher thermal sensitivity. However, CNT‐based actuators generally suffer not only from intertube slipping due to weak interactions between the assembled CNTs but also from poor control over orientation assembly. To address these challenges, a new class of closely packed, highly aligned CNT microcantilevers reinforced by ceramic interlocking is here proposed, followed with deposition of Al thin film to form the bi‐material actuators. The investigations of the mechanical properties and thermal response of CNT microcantilevers indicate that the slipping between the tubes limits both the strength and the thermal sensitivity of the bi‐material microcantilevers. Intertube deposition of Al2O3 as ceramic interlocking is used to reinforce the binding strength between the tubes, and increases in the mechanical strength as well as thermal sensitivity of the microcantilevers have been achieved.

A new way to obtain NiTi SMA superelastic meshes: investment casting followed by hot rolling

In this work, NiTi superelastic meshes are manufactured through plasma melting followed by an injection into a mesh ceramic coating mold obtained by the lost wax technique. This is the first time such a manufacturing sequence is reported for NiTi SMA. Focus is given to the feasibility and efficiency of the manufacturing process. The as-cast NiTi meshes were afterward heat-treated and hot-rolled for thickness reduction and to increase malleability. After manufacturing, the meshes’ thermomechanical properties were characterized. Differential scanning calorimetry showed that at room temperature the NiTi meshes can either be used as thermal actuators (using the shape memory effect) or as superelastic devices, depending on whether heating or cooling is performed prior to the application. This behavior leaves great potential for applications in engineering systems and biomedical uses. The superelastic behavior of the NiTi meshes was characterized through tensile tests at room temperature, showing very good cycling stability and strain recovering up to 4%. In the future, microstructural and biocompatibility investigations of the product will be evaluated to optimize the manufacturing process.

A comparative study of Ac-dielectric barrier discharge versus Ns-dielectric barrier discharge plasma actuators in an incompressible turbulent mixing layer

A comparison between ac-dielectric barrier discharge (DBD) and ns-DBD plasma actuators is performed in a low-speed turbulent mixing layer to assess differences in their control mechanisms (momentum versus thermal). The mean flow response to actuation is matched for the two cases at a single downstream location to gauge scaling of relevant parameters (carrier frequency, energy per pulse, etc). The similarity between local behavior downstream is found to extend to the global flow, both in the mean and fluctuating components. However, the ns-DBD requires approximately six times more electrical energy to achieve the same control as the ac-DBD in this specific flow. An analysis of the flow field very near the splitter plate trailing edge sheds light on the difference in momentum versus thermal actuation mechanisms. A velocity deficit is observed for both actuators, but a thermal bump effect is evident in the ns-DBD case while a near surface jet is observed in the ac-DBD case.

NanoThermoMechanical AND and OR Logic Gates

Today’s electronics cannot perform in harsh environments (e.g., elevated temperatures and ionizing radiation environments) found in many engineering applications. Based on the coupling between near-field thermal radiation and MEMS thermal actuation, we presented the design and modeling of NanoThermoMechanical AND, OR, and NOT logic gates as an alternative, and showed their ability to be combined into a full thermal adder to perform complex operations. In this work, we introduce the fabrication and characterization of the first ever documented Thermal AND and OR logic gates. The results show thermal logic operations can be achieved successfully through demonstrated and easy-to-manufacture NanoThermoMechanical logic gates.

Fracture strength and fatigue endurance in Gd-doped ceria thermal actuators

We studied the stability of the mechanical properties and the fatigue endurance of Gd-doped ceria (CGO), which is a promising electromechanically active material for microelectromechanical systems (MEMS). Specifically, the fracture strength and long-term operation of plate-type circular (2 mm diameter) thermal actuators made of ≈1.15 μm thick Ce0.95Gd0.05O1.975 (CGO5) were investigated. Excitation voltage of 10 V at the frequency range between 1 and 2.1 MHz induces Joule heating effect that can generate an in-plane strain of ≈0.1 %. The operation temperature ranged from 25 °C to 80 °C and the temperature shift, caused by the AC heating, was about 80 K at 10 V. Critical fracture was found to occur at out-of-plane displacements between ∼35 and ∼42 μm, which corresponds to the average bending stress of ∼44 MPa at the center of the plate. During long-term operation, the actuators exhibit gradual decrease in the response, probably due to contact degradation. However, structural damage or mechanical fatigue was not found even after 107 cycles at a stress level of ∼30 % of the critical fracture strength.

Analysis of Coefficient of Thermal Expansion in Carbon Black Filled PDMS Composite

Polymer composites are gaining attention due to their superior thermal properties. Especially carbon black /carbon nanotubes/ graphene filled polymer composites are used in energy harvesting, thermal actuators and MEMS. The coefficient of thermal expansion (CTE) is one of the most important properties in the polymer composite. In the present study, thermal expansion of polydimethylsiloxane (PDMS) matrix is filled with carbon black particle of varied volume fraction is modeled. Two-dimensional finite element (FE) model is computed in order to explain the thermal expansion behavior of the polymer composite and same is carried out for ambient to 70 K temperature. A 2D regular arrangement of circular particle packing model is set up and simulated. The FE model predicts that filler geometry has a little effect on the thermal expansion than the percentage of filler in the composite. Thermal expansion of composite is compared with the theoretical model. It shows that the CTE of composite reduces as the filler percentage increase, also gives good agreement in the both models. Hence, it is found that the addition of carbon black to the polymer composite could make it perform significantly better in thermal expansion.

Heat transfer enhancement by localised time varying thermal perturbations at hot and cold walls in a rectangular differentially heated cavity

The objective of this work it is to determine the optimal properties of a thermal disturbance to enhance the heat transfer in a rectangular differentially heated cavity of aspect ratio 4. So, we study numerically the effect on the heat transfer of one or two small thermal actuators (5% of active plate surface) applied at the active walls of this kind of cavity. Thermal disturbances are sine or square waves. Influences of wave characteristics (amplitude, frequency, phase shift) and the vertical location of the disturbance area are investigated for various Rayleigh numbers below its first critical value (RaH=1.02×108). Only a fluid with Prandtl number equal to 0.71 (air) is considered. Flows are calculated solving the 2D unsteady Boussinesq–Navier–Stokes equations using the Spectral Element Method programmed in the Nek5000 opencode. A detailed description of the coupling between one or two thermal disturbances and cavity flow is presented. The main contribution of this work is that the best position to enhance the heat transfer is 70% of the hot plate height or 30% of the cold plate height, and not 0.1 for the hot plate (0.9 for the cold one) which is generally admitted. At this position this increase reaches 5.5% by disturbing at both active walls with local synchronised square waves of amplitude ε=1, of frequency f=0.403 and at a state slightly below the first critical Rayleigh number.

Kinetostatic modeling and characterization of compliant mechanisms containing flexible beams of variable effective length

Flexible beams of variable effective length, serve both transmission and actuation functionalities in compliant mechanisms, have been employed in many devices, e.g., thermal actuators and continuum robots. This difunctional feature is favorable when utilized for operations in confined space. However, the length variation introduces modeling difficulties, which poses a new challenge to designers. To accurate model flexible beams of variable effective length and characterize the behaviors of associated compliant mechanisms form the primary objectives of this study. The chained beam constraint model is revisited and extended to model beams of variable effective length. Modeling of a chevron shape thermal in-plane microactuator and a continuum mechanism are provided to demonstrate the effectiveness of the proposed method. The predicted results have a high degree of accuracy as compared to experimental results and nonlinear finite element results.

Global Performance Indices for Dynamic Crystals as Organic Thermal Actuators

Crystal adaptronics is an emergent materials science discipline at the intersection of solid-state chemistry and mechanical engineering that explores the dynamic nature of mechanically reconfigurable, motile, and explosive crystals. Adaptive molecular crystals bring to materials science a qualitatively new set of properties that associate long-range structural order with softness and mechanical compliance. However, the full potential of this class of materials remains underexplored and they have not been considered as materials of choice in an engineer's toolbox. A set of general performance metrics that can be used for quantification of the performance of these prospective dynamic materials as micro- and macroactuators is presented. The indices are calculated on two selected representatives of thermosalient solids-materials that undergo rapid martensitic transitions accompanied with macroscopic locomotion. Benchmarking of their performance against extensive set of data for the existing actuator classes and visualization using materials property charts uncover the hidden potential and advantages of dynamic crystals, while they also reveal their drawbacks for actual application as actuators. Altogether the results indicate that, if the challenges with fabrication and implementation in devices are overcome, adaptive molecular crystals can have far-reaching implications for emerging fields such as smart microelectronics and soft microrobotics.

Spring-Shaped Inductor Tuned With a Microelectromechanical Electrothermal Actuator

We present a spring-shaped tunable inductor, fabricated using a silicon-on-insulator (SOI) multiuser micro-electromechanical system process. The inductor has a simple planar design and is monolithically integrated in the SOI wafer. The inductor is tuned using a thermal actuator on the same silicon structure layer. Thus, the complexity and cost of fabrication are greatly minimized. The device is compact, with dimensions of 0.90 mm × 0.55 mm. In addition to cost-effective design and small surface area, the device has good tuning range and Q -factor. The experimental results show that the inductor can be tuned to 20%, 17%, and 15% at 2, 3, and 5 GHz, respectively. In air at 0 and 11.5 V, Q -factors of 7.27 and 4.64 obtained at 2 GHz, and 7.21 and 5.92 at 5 GHz. The series resonance frequency is >20 GHz.

Modeling and optimization of thermally excited carbon black and polymer composite actuator

As of late, actuators in view carbon black, carbon nanotube and graphene were shown in the extraordinary potential application in the field of drug delivery system, relay switches, robotics, energy harvesting and so on. Now a day electro-thermal and photo-thermal driven actuator based on polymer composite show larger actuation compare to the traditional thermal actuator. Though, the impact of structural dimensions and material parameters on the actuator execution ought to be investigated further. Since it is a critical point in the design and fabrications of the high-performance actuatorIn the present work, finite element (FE) analysis is adopted to simulate the thermally driven bilayer actuator and investigated the performance based on carbon black and polymer composite. Thus, the computational method is carried out to design and optimize the geometry and material parameters such as thickness, the coefficient of thermal expansion and so on. FE simulation results demonstrate that each layer thickness of the actuator has an important role in curvature deformation. A maximum curvature is obtained of 8.9 m-1 by simulation, which is a decent expected value in light of the geometry and material. Furthermore, a larger change in temperature and CTE between two layers additionally predicts the more prominent bending curvature. Consequently, this investigation is relied upon to give a theoretical baseline to plan and fabrication of CB based thermal actuator for a greater actuation performance.

A blend of stretching and bending in nematic polymer networks.

Nematic polymer networks are (heat and light) activable materials, which combine the features of rubber and nematic liquid crystals. When only the stretching energy of a thin sheet of nematic polymer network is minimized, the intrinsic (Gaussian) curvature of the shape it takes upon (thermal or optical) actuation is determined. This, unfortunately, produces a multitude of possible shapes, for which we need a selection criterion, which may only be provided by a correcting bending energy depending on the extrinsic curvatures of the deformed shape. The literature has so far offered approximate corrections depending on the mean curvature. In this paper, we derive the appropriate bending energy for a sheet of nematic polymer network from the celebrated neo-classical energy of nematic elastomers in three space dimensions. This task is performed via a dimension reduction based on a modified Kirchhoff-Love hypothesis, which withstands the criticism of more sophisticated analytical tools. The result is a surface elastic free-energy density where stretching and bending are blended together; they may or may not be length-separated, and should be minimized together. The extrinsic curvatures of the deformed shape not only feature in the bending energy through the mean curvature, but also through the relative orientation of the nematic director in the frame of the directions of principal curvatures.

Modeling of One-ply and Two-ply Twisted and Coiled Polymer (TCP) Artificial Muscles

Twisted and coiled polymer (TCP) muscles are recently introduced thermal actuators that offer unprecedented performance. Merits such as low cost, high load capacity, and light weight make them suitable for robotics and biomechanics. Using these actuators for practical applications requires an understanding of their behavior in response to the electrical input. In this article, a physics-based model is proposed to predict the displacement of TCP muscles with respect to the input electrical energy and the applied load. We quantified effects of temperature on coefficients of thermal expansion and elastic modulus. It is found that the change of properties above the polymer glass transition temperature has a crucial effect on the actuator performance. A stiffness model is proposed, which include the effect of change in geometry and elastic modulus of TCP muscles. Finally, a set of equations for simulating the TCP muscles are formulated in discrete time representation. The model is generalized for the two-ply case by considering the difference in geometry. The accuracy of the model is tested in comparison with experimental data, acquired at several actuation levels and applied loads, for both one-ply and two-ply configurations. The model showed a good accuracy in predicting the behavior of the actuators both in temperature and displacement. Our model was also compared with other representative models and revealed improvement in the prediction accuracy.

Optimal Thermal Actuation for Mitigation of Heat-Induced Wafer Deformation

An important step in the production of integrated circuits is the projection of the pattern of electronic connections on a silicon wafer. The light used to project the pattern moves over the wafer and induces a local temperature increase. The resulting thermal expansion of the wafer leads to a significant reduction in the imaging quality of next-generation wafer scanners. Thermal actuators that move together with the projection light can be used to improve the imaging quality. Because the placement of these actuators largely determines the performance of the resulting control system, a method to support the design of an effective thermal actuator layout is presented. The proposed method computes the smallest actuation heat load that consists of a single spatial shape and respects certain constraints on wafer deformations. A gradient-based optimization algorithm is presented to compute the optimal actuation heat load. The proposed method is applied to a wafer heating problem for which the resulting shapes of the actuation heat load have a clear physical interpretation.

Uncertainty quantification of MEMS devices with correlated random parameters

The concern about process deviations rises because that the performance uncertainty they cause are strengthened with the miniaturization and complication of Microelectromechanical System (MEMS) devices. To predict the statistic behavior of devices, Monte Carlo method is widely used, but it is limited by the low efficiency. The recently emerged generalized polynomial chaos expansion method, though highly efficient, cannot solve uncertainty quantification problems with correlated deviations, which is common in MEMS applications. In this paper, a Gaussian mixture model (GMM) and Nataf transformation based polynomial chaos method is proposed. The distribution of correlated process deviations is estimated using GMM, and modified Nataf transformation is applied to convert the correlated random vectors of GMM into mutually independent ones. Then polynomial chaos expansion and stochastic collection can be implemented. The effectiveness of our proposed method is demonstrated by the simulation results of V-beam thermal actuator, and its computation speed is faster compared with the Monte Carlo technique without loss of accuracy. This method can be served as an efficient analysis technique for MEMS devices which are sensitive to correlated process deviations.

Quadruple-Stage Actuator System for Magnetic-Head Positioning System in Hard Disk Drives

In this article, we present a magnetic-head positioning system in hard disk drives (HDDs) with a quadruple-stage actuator system. The quadruple-stage actuator system consists of a voice coil motor, a milliactuator with two piezoelectric (PZT) elements, a microactuator with two PZT elements, and a thermal actuator. The milliactuator is the first generation of a secondary actuator for a dual-stage actuator in the HDDs and moves a sway mode of a suspension in a head-stack assembly. The microactuator is the second generation of the secondary actuator for the dual-stage actuator in the HDDs and moves a yaw mode of the suspension. The thermal actuator is an actuator in a development phase for future HDDs. It consists of heaters embedded in the magnetic head and moves read/write elements a few nanometers in a horizontal direction with thermal expansion. The achievable disturbance-rejection performance of the proposed quadruple-stage-actuator system is higher than that of the conventional triple-stage actuator system because the proposed system can decrease a negative impact caused by the stroke limitation of the thermal actuator. As a result, the magnetic-head positioning system with the quadruple-stage-actuator system enables us to improve the positioning accuracy under the external vibrations by about 48 ${\%}$ from that with the triple-stage-actuator system.

Static Modeling of Bending Characteristics on V-Shaped Beam Actuator Based on Flexible Substrate

Due to the unique properties of flexible electronic devices, various microelectromechanical systems (MEMS) devices based on flexible substrate have been proposed for miniaturization, lightweight, and intelligent applications. Obviously, the deformation of flexible substrate inevitably affects the performance of flexible MEMS devices. This article first investigates the static modeling of bending characteristics on the flexible V-shaped beam actuator, which is the most representative MEMS thermal actuator. This article focused on a comprehensive static analysis of bending mechanical property based on the flexible substrate. The innovation of static modeling is obtaining variation regularity of bending characteristics by establishing the deformation coupling model of V-beam structure and flexible substrate. The V-shaped beam thermal actuators are designed and fabricated on flexible liquid crystal polymer (LCP) substrate, and the influence of bending substrate on the actuation performance of the device is revealed by calculation, simulation, and experiment. The experimental results demonstrate that the actuation current of the V-shaped beam actuator rises up proportionally with the increase of angle and the decrease of beam length. When flexible substrate bends gradually from curvature 0 to 33.3 (1/m), the rates of measured actuation current change are 17.05%, 13.70%, and 10.24%, corresponding to different angles of 13°, 20°, and 27° at $600~\mu \text{m}$ length of V-shaped beams. Meanwhile, the rates of measured actuation current change are 9.22%, 13.22%, and 13.70%, corresponding to different lengths of 400, 500, and $600~\mu \text{m}$ at 20° angle of V-shaped beams. The experimental results are consistent with the theoretical calculation results of static modeling, and the error is less than 3.7%.

Matching Magnetic Heating and Thermal Actuation for Sequential Coupling in Hybrid Composites by Design.

Sequentially coupling two material functions requires matching the output from the first with the input of the second function. Here, magnetic heating controls thermal actuation of a hybrid composite in a challenging system environment causing an elevated level of heat loss. The concept is a hierarchical design consisting of an inner actuator of nanocomposite material, which can be remotely heated by exposure to an alternating magnetic field (AMF) and outer layers of a porous composite system with a closed pore morphology. These porous layers act as heat insulators and as barriers to the surrounding water. By exposure to the AMF, a local bulk temperature of 71 °C enables the magnetic actuation of the device, while the temperature of the surrounding water is kept below 50 °C. Interestingly, the heat loss during magnetic heating leads to an increase of the water phase (small volume) temperature. The temperature increase is able to sequentially trigger an adjacent thermal actuator attached to the actuator composite. In this way it could be demonstrated how the AMF is able to initiate two kinds of independent actuations, which might be interesting for robotics operating in aqueous environments.

A Hollow Polyethylene Fiber-Based Artificial Muscle

Recently, researches on artificial muscles for imitating the functions of the natural muscles has attracted wide attention. The fiber-shape actuators, shape-memory materials or deforming devices, which are similar to human muscle fiber bundles, have extensively studied and provided more possibilities for artificial muscles. Herein, we develop a thermal responsible fiber-shaped actuator based on the low-cost hollow polyethylene fiber. The sheath-core structured fibrous actuators and the stainless-steel conductive yarn winded pre-stretched polyethylene actuators are fabricated with the heating assisted pre-stretching procedure. The actuation mechanism of the thermal-responsive orientation change of molecular chains driving the actuation is discussed and demonstrated by 2D XRD patterns. These polyethylene-based fibrous actuators displayed three significant advantages including (i) color-turning and shape-changing bifunctional response, (ii) direct joule heating actuation and (iii) effective contraction (18% shrinkage of the pristine length) and lifting ability (the ratio of lifting weight to self-weight is up to 50).

Design of a test structure based on chevron-shaped thermal actuator for in-situ measurement of the fracture strength of MEMS thin films

A novel test structure to characterize the fracture strength of MEMS (Micro-electro-Mechanical Systems) thin films is presented. The test structure is comprised of a micro fabricated chevron-shaped thermal actuator and test specimen. The test structure is capable of producing large displacement and stress while keeping a relatively low temperature gradient across the test specimen. A voltage is applied across the beams of the chevron-shaped actuator, producing thermal expansion force to fracture the test specimen. Actuator deflection is computed based on elastic analysis of structures. To verify the test structure, simulations have been implemented using COMSOL Multiphysics. A 620 μm long, 410 μm wide, 10 μm thick test structure produced stress of 7.1 GPa while the applied voltage is 5 V. The results indicate that the test structure is suitable for in-situ measurement of the fracture strength of MEMS thin films.