Academic literature on the topic 'SU8 Thermal Actuator'

In the current paper, report the detailed thermomechanical analysis of a polymeric thermal actuator integrated in a microelectromechanical systems microgripper, is reported. The inclusion of an actuator design which eliminates completely the parasitic resistance of the cold arm improves considerably the thermal efficiency of the system and enables large displacements at lower input voltages and operating temperatures than reported previously. Two different microgrippers built using a trilayer polymer/metal/polymer combination of SU8/gold/SU8 have been modelled, fabricated, and tested. As opposed to standard models, heat transfer by conduction to the ambient as well as between adjacent beams has been modelled. A semi-empirical approach for the calculation of conductive heat transfer coefficients has also been provided. The analysis combines simulations with electrical, deflection, and spatially resolved temperature measurements. The latter was carried out using infrared thermography, its use in polymeric actuators reported here for the first time. The good agreement between the models and the experimental data support the conclusions of the basic analytical model, i.e. thermal losses are dominated by two conduction mechanisms (into the ambient and between the hot and cold arms), and encourage its use for qualitative thermal design assessment and optimization.

In this paper, design, simulation and optimization of a novel electrothermally-activated polymeric microactuator capable of generating combination of bidirectional lateral and rotational motions are presented. The composite structure of this actuator is consisted of a symmetric meandered shape silicon skeleton, a SU8 thermal expandable polymer and a thin film chrome layer heater. This actuator is controlled by applying appropriate voltages on its four terminals. With the purpose of dimension optimization, a numerical parametric study is executed. The modeled actuator which is 1560 μm long, 156 μm wide and 30 μm thick, demonstrates a remarkable lateral displacement of 23 μm at power consumption of 38 mW and a considerable rotation of about 7.5° at the same power consumption but with excitation of different terminals.

The paper presents a theoretical and experimental investigation of a thermo-mechanical model of an actuator composed of a shape memory alloy wire arranged in series with a bias spring. The developed mathematical model considers the dynamics of the actuator in the thermal and mechanical domains. The modelling accuracy is increased through the developed algorithm for modelling the minor and sub minor hystereses, thus removing the disadvantages of the classical model. The algorithm improves the accuracy, especially when using pulse-width modulation control, for which minor and sub minor hystereses are likely to occur. Experimental studies show that the system is very sensitive, and there are physical factors whose presence cannot be considered in the mathematical model. The experimental research has shown that setting constant values of the duty cycle is impossible to obtain a stable value of displacement and force. The comparison between the developed mathematical model results and the experimental results shows that the differences are acceptable. The improved modelling serves as a basis for designing such actuators and creating an improved automatic feedback control system to maintain a given displacement (force) or trajectory tracking.

In this manuscript, a compact electromagnetic dual actuation positioning system (CEDAPS) based on the Lorentz force principle that features a 10 mm range and nanometer-scale resolution with flexure guides is presented. Firstly, the stiffness of the flexure mechanism is modelled. Secondly, based on it, the primary coil is designed, and from its performance, a suitable secondary coil is made to compensate for the deficiency of the primary actuation subsystem. The characteristics of the forces generated by these coils are also evaluated by an electromagnetic FEA simulation. Thirdly, a control scheme is presented that combines the performances of these two actuators, and finally, a prototype is fabricated to evaluate the performance. The results show a 10 nm resolution for a 10 mm (±5 mm) stroke with low sub-micron sinusoidal tracking errors and nanometer accuracy for step tracking under the proposed control scheme. The thermal properties of the system are also presented.

The work reported here was aimed at improving the practical efficiency of the model-based development and integration of electromechanical actuators. Models are proposed to serve as preliminary design, virtual prototyping, and validation. The first part focuses on the early phases of a project in order to facilitate the identification of modelling needs and constraints, and to build a top-level electromechanical actuator model for preliminary studies and sub-specification. Detailed modelling and simulation are then addressed with a mixed view on the control, power capability, and thermal balance. Models for the power chain are firstly considered by focusing on the key practical issues in modelling the electric motor, power electronics, and mechanical power transmission. The same logic is applied to the signal and control chain with practical considerations concerning the parameters of the controller, its digital implementation, the sensors, and their signal conditioning. Numerous orders of magnitude are provided to justify the choices made and to facilitate decision-making for and through simulation activities.

Micro-electromechanical system (MEMS) micromirrors have been in development for many years, but the ability to steer beams to angles larger than 20° remains a challenging endeavor. This paper details a MEMS micromirror device capable of achieving large motion for both tip/tilt angles and piston motion. The device consists of an electrothermal actuation assembly fabricated from a carefully patterned multilayer thin-film stack (SiO2/Al/SiO2) that is epoxy bonded to a 1 mm2 Au coated micromirror fabricated from an SOI wafer. The actuation assembly consists of four identical actuators, each comprised of a series of beams that use the inherent residual stresses and coefficient of thermal expansion (CTE) mismatches of the selected thin films to enable the large, upward, out-of-plane deflections necessary for large-angle beamsteering. Finite element simulations were performed (COMSOL v5.5) to capture initial elevations and tip/tilt motion displacements and achieved <10% variance in comparison to the experiment. The measured performance metrics of the micromirror include tip/tilt angles of ±23°, piston motion of 127 µm at sub-resonance, and dynamics characterization with observed resonant frequencies at ~145 Hz and ~226 Hz, for tip/tilt and piston motion, respectively. This unique single element design can readily be scaled into a full segmented micromirror array exhibiting an optical fill-factor >85%, making it suitable for optical phased array beam control applications.

Passive safety systems in a nuclear reactor allow to simplify the overall plant design, beside improving economics and reliability, which are considered to be among the salient goals of advanced Generation IV reactors. This work focuses on investigating the application of a self-actuated, gravity-driven shutdown system in a small lead-cooled fast reactor and its dynamic response to an initiating event. The reactor thermal-hydraulics and neutronics assessment were performed in advance. According to a first-order approximation approach, the passive insertion of shutdown assembly was assumed to be influenced primarily by three forces: gravitational, buoyancy and fluid drag. A system of kinematic equations were formulated a priori and a MATLAB program was developed to determine the dynamics of the assembly. Identifying the delicate nature of the balance of forces, sensitivity analysis for coolant channel velocities and assembly foot densities yielded an optimal system model that resulted in successful passive shutdown. Transient safety studies, using the multi-point dynamics code BELLA, showed that the gravity-driven system acts remarkably well, even when accounting for a brief delay in self-actuation. Ultimately the reactor is brought to a sub-critical state while respecting technological constraints.

Noninvasive tuning of the mechanical resonance frequencies of suspended parallel nanomembranes in various monolithic arrays is achieved by piezoelectric control of their tensile stress. Parametric amplification of their thermal fluctuations is shown to be enhanced by the piezoelectric actuation and amplification factors of up to 20 dB in the sub-parametric oscillation threshold regime are observed.

This paper presents an experimental test room in a curtain wall building where an innovative monitoring and control system was implemented and tested. The proposed solution is composed by an IR-based comfort sensor that measures the PMV (Predicted Mean Vote) index for 2 room’s sub-zones and provides the optimal air temperature set-points. The overall control system includes a distributed sensors and actuators network, also embedded into the façade modules, to measure indoor and outdoor parameters and to regulate fan-coils, windows opening and shadings with a sub-zonal approach. Initial results turn out to provide an energy saving of about 20% with an improvement of thermal/visual comfort and IAQ conditions.

Cette thèse est effectuée dans le cadre du projet Européen "PlasmAero" dont le but est de développer et d'étudier des actionneurs plasmas, et de démontrer leur capacité à contrôler des écoulements aérodynamiques. L'actionneur plasma à Décharge à Barrière Diélectrique (DBD) de surface est un moyen innovant pour contrôler un écoulement en utilisant le vent électrique induit par la force électrohydrodynamique (EHD) générée au sein du gaz ionisé. Une première partie est dédiée à l'étude des actionneurs plasmas. L'influence de la géométrie de l'électrode active d'une DBD est précisée par des mesures électriques, optiques et mécaniques. Les régimes de la décharge de surface peuvent être totalement modifiés, tout commel'évolution de la force EHD en fonction du temps, calculée ici par bilan intégral. Une géométrie optimisée permet de supprimer le régime de décharge streamer et d'augmenter l'efficacité de l'actionneur de 0,65 à 0,97 mN/W. De plus, des configurations à multi-électrodes (sliding discharge et multi-DBD) sont étudiées et développées. Une multi-DBD à potentiels alternés a permis d'obtenir un vent électrique record de 10,5 m/s.L'étude du contrôle d'un écoulement décollé à mi-corde ou en bord de fuite sur l'extrados d'un profil NACA 0015 fait l'objet de la seconde partie de la thèse. Une DBD standard à deux électrodes, une multi-DBD à six électrodes et une DBD de type "nanoseconde" sont utilisées pour agir sur une séparation à des nombres de Reynolds atteignant 1,3μ106, avec une transition naturelle ou déclenchée. Les résultats démontrent que le contrôle permet de repousser efficacement la séparation, améliorant ainsi les performances aérodynamiques du profil
This work is conducted in the framework of the European PlasmAero project that aims to demonstrate how plasma actuators can be used to control aircraft aerodynamic. Surface Dielectric Barrier Discharge (DBD) is an innovative solution to control a flow with the electric wind induced by the electrohydrodynamic (EHD) force produced by a surface discharge. A first part is dedicated to plasma actuators study. The exposed electrode shape of a DBD actuator is investigated by electrical, optical and mechanical characterization. Discharges properties and EHD force evolution is fully dependent of exposed electrode shape. With an optimized active electrode shape, streamer discharge is cancelled while actuator effectiveness is increased from 0.65 to 0.97 mN/W. Flow field induced by multiple electrode design is also investigated. An innovative multi-DBD design is proposed. Inhibition of mutual interaction between successive DBD actuators and exposed electrode shape optimization conduct to an electric wind velocity of 10.5 m/s. In a second part, the control of boundary layer separation on a NACA 0015 airfoil is investigated. An ac DBD, a multi-DBD and a nanosecond DBD are used to manipulate separation at a Reynolds number Re = 1.3μ106, with tripped and natural boundary layer. Results show that actuators can effectively remove the separation existing without actuation

Design, fabrication and development of polymer microcantilever for flow rate measurement and thermal actuation Research Supervisors: Prof. K. Rajanna and Dr. G. R. Jayanth Microcantilevers are sensitive micromechanical platforms used to detect small forces and surface stresses arising due to changes in physical environment. They are popularly used as mechanical probes in scanning probe microscopy to obtain 3D surface topography of samples upto atomic scale resolution. These microcantilevers find applications in biosensing, environment monitoring, air flow measurement, microbolometry, Atomic Force Microscopy (AFM), etc,. Furthermore, microcantilevers form versatile, compliant platforms for producing mechanical actuation. Microcantilever based actuators are used as RF switches, biomanipulators, microrelays and microfluidic valves. Conventionally, microcantilevers are fabricated using silicon, silicon nitride or silicon dioxide. However, in recent times polymers are being used as alternate materials for fabricating microcantilevers. These polymer microcantilevers offer several advantages and versatilities. The aim of the present thesis work is to the design, fabricate, characterize and evaluate the performance of piezoresistive SU8 microcantilevers for low flow rate measurement and thermal actuation. Finite element (FE) simulation was used to determine the stress distribution across a stressed microcantilever structure. The results of FE simulations enable suitable piezoresistor design for integration with the cantilever. Various surface micromachining techniques were attempted to fabricate freely suspended SU8 microcantilevers with gold thin film piezoresistors. Electrical interconnection was established using ball bump aided epoxy bonding technique. The fabricated SU8 microcantilever sensor was mechanically characterized and its strain sensitivity was evaluated. These sensors were employed for low gas flow rate measurement in the range 0 to 100 mL/min. The sensor response was found to be linear, repeatable and consistent with different flow rates. The fabricated SU8 microcantilever device also exhibited thermomechanical actuation. Hence, the performance of the device due to Joule heating of the piezoresistor was studied in detail. A nonlinear thermomechanical model was proposed to accurately estimate the thermal behaviour of the polymer microcantilever. This study underscores the need to consider nonlinear thermo-elastic properties of polymers while modeling their thermomechanical response. Both finite element simulation and experimental result indicate nonlinear thermomechanical response of the SU8 based thermal actuator. The developed microsystem presents simultaneous sensing and actuation mechanisms. Hence, they are suitable for integration with Lab-on-chip-devices. This thesis in divided into 8 chapters and the brief summary is as follows: Chapter 1 This chapter gives a brief introduction to the state-of-art scenario of MEMS technology and its relevance in the field of sensors and actuators. Later, an overview of micromachining techniques used for the fabrication of MEMS devices is discussed. Microcantilever based devices and their applications are discussed. In particular, their use as non-thermal flow sensors is presented. Also, the need for polymeric microcantilever sensors for low gas flow rate measurement is discussed. At the end, the objective, scope of present work and the organization of the thesis are discussed. Chapter 2 The aspect of SU8 microcantilever design for flow measurement is presented. Relevant piezoresistivity theory required for the design of thin film piezoresistor is explained. Finite element simulation was used to identify regions of maximum stress in the microcantilever due to fluid flow interactions. The geometry and shape of thin film piezoresistor was chosen based on the simulation results. Finally, the optimal design parameters of piezoresistive SU8 microcantilever sensor are summarized. Chapter 3 This chapter describes the processes involved in the fabrication of piezoresistive SU8 microcantilevers. Surface micromachining techniques such as wet oxidation, lift-off, thin film deposition, sacrificial layer etching etc were used during the fabrication. Wet oxidation was used to grow uniform, dense oxide for sacrificial layer. Gold thin films were deposited using RF sputtering technique and patterned using UV photolithography. SU8 microcantilevers were patterned using photolithography and freely suspended SU8 microcantilevers were obtained by selectively etching the sacrificial layer. The issues of residual stress in suspended SU8 microcantilever are discussed. Finally, an optimal fabrication process was obtained to build SU8 microcantilever with integrated piezoresistor. Chapter 4 The fabricated flow sensor needs to be connected with the external circuitry via electrical interconnects. This chapter discusses the process of packaging and electrical interconnection with the fabricated SU8 microcantilever sensor. The issues of making wire bonding onto SU8 chip using conventional wire bonding techniques are described. Alternate wire bonding techniques such as epoxy bonding was attempted. Finally, ball bump aided epoxy bonding technique was developed and used for making electrical interconnection with the sensor. Chapter 5 In this chapter the fabricated and packaged microcantilever sensor was characterized to evaluate its electro-mechanical performance. The sensor response was evaluated experimentally by providing known mechanical displacement via precisely controlled piezostage. At the end, the sensor characteristics such as gauge factor of the piezoresistor, deflection sensitivity of the microcantilever sensor, its hysteresis, linearity and repeatability were also obtained. Chapter 6 This chapter describes the performance study of piezoresistive SU8 cantilever sensor for low gas flow rate measurement in the range 10 to 500 mL/min. The measured flow sensitivity was about 1.103×10-5 mL/min. Finite element simulations were used to estimate the cantilever deflection due to gas flow. The simulation results show quadratic dependence of cantilever deflection on gas flow rate. For a flow rate between 0 to100 mL/min, the experimental results agree well with the simulation results showing a linear trend in this range. Chapter 7 This chapter presents the nonlinear thermomechanical analysis and thermal actuation of fabricated SU8 microcantilevers. The thermomechanical analysis of the actuator incorporates nonlinear temperature-dependent properties of SU8 polymer to accurately model its thermal response during actuation. The issues of residual stress developed within the SU8 microstructure during fabrication are discussed and a novel strategy was proposed to release the residual stress in the fabricated actuators. The thermomechanical response of the actuator was obtained experimentally. The measured average actuation range of about 8.5 μm was produced for an actuation current of 5 mA. It was found that the results of nonlinear thermomechanical analysis agree well with the experimental result. Chapter 8 The chapter summarizes the results and conclusions drawn from the present work. Also, the scope of future work is discussed.

The paper discusses the promises and challenges of using laser as a source of energy and means of control for untethered microdevices. Achieving the desired device operation with available controls in the laser signal is a challenge that requires redesign of current microactuators and invention of new ones. In addition, for multiple target spots on a device, the laser beam can be multiplexed or separate lasers can be used simultaneously. Shaping of the control signal based on such variables of the laser as output power, pulse width, and beam spot is a combined effort of accordingly designing the microdevice and selecting the device materials. The paper presents a parametric design evaluation of two versions of stick-and-slip microrobots actuated by commonly used thermal actuators. A detailed parametric analysis with varying actuator geometries predicts that actuation at speeds comparable with electrostatically and electromagnetically actuated microrobots is also possible with laser power. Initial experiments on regular chevron actuators show that pulsed laser can be effectively used to drive microdevices.

The contemporary satellites usually utilize louvers as variable emissivity surfaces (VES) for the thermal control subsystem. This means is only particularly scalable down and the next generation of small satellites definitely requires new techniques for thermal control. Further, the low mass, volume and cost of the micro and nanosatellite require additional features from the future VES. Besides high reliability, which is an unconditional requirement for a space application, the other criteria are as follows: low mass, deep modulation of emissivity, low heat leak in off-state, fast reaction time, passive action, as well as other lower level criteria. These requirements are complex and sometimes contradictory. The current approaches to find alternatives to the traditional mechanical louvers branch in several directions: electrophoretic, electrochromic, electrostatics actuated VES, MEMS shutters, etc. None of the current solutions is successful in meeting all of the posed criteria. We present a novel VES subsystem, particularly developed for use in micro and nanosatellites. The concept is simple, reliable and very efficient. The bionic structure, a flower-like design, is made from a thin and elastic foil. The artificial flower consists from a peduncle, fixed to the satellite radiator panel and 4–6 petals. The upper surface of the petal is made as the second-surface mirror and the lower surface is the gold plated or the first-surface mirror. The kinematic mechanism which opens and closes the artificial flower is the shape memory actuator located in the petal root. The SMA actuators are trained as the “two way actuators”. The “two way” memory effect has been recognized as difficult to control and suffering from amnesia. However, the new learning process of the shape memory actuators enables more than 350.000 cycles without SMA parameter degradation. The artificial flower works as follow: when the sun irradiates the flower and/or the radiator temperature exceeds the preset value, the SMA actuators bend and open the flower. In such a manner the flower exposes the highly reflective surface to the sun and shadows the satellite radiator until the sun sets again. The flower structure is without any friction-connected kinematic movements, thus the reliability of device should be high. The mass of the flower is less than 450 g/m2, the heat leak trough the open flower is >2% and the efficiency of the closed flower is <80%. The SMA actuator is passive and quite resistant to the radiation, oxygen and EDS.

This paper presents the work conducted towards the realization of a novel tactile display system composed of miniature thermo-fluidic actuators. An application of the system particularly relevant to blind individuals is communication with computers through touch. The development of programmable spatio-temporal pattern of touch actuation based on bubble formation and vapor pressure has remarkable scope, not only because of the flexibility and wearability but also the high levels of motion amplitude and force of actuation not achieved so far by other means. The design specifications of the tactile display involved packaging of the miniature actuators in such a manner that the display can be conveniently attached at the tip of the human finger with desirable spatial resolution, and achieving the optimum force that can be felt through the human finger. However, there were challenges that were faced by the authors while miniaturizing the actuators for suitability in sub-millimeter spatial resolution desirable for the tactile display. The paper reports on the design, prototype development and experimental results and brings out the limitations along with possible solutions being pursued by the authors. The progressive efforts through fabrication and testing of different prototype thermo-fluidic actuators ranging from 3mm diameter bore to sub-millimeter sizes and the corresponding difficulties faced in the form of cooling requirements, hysteresis effects, and fabrication challenges are elucidated. The paper reports on packaging of actuators as an array of tiny tubes spaced as close as possible, and establishment of parameters, namely, amplitude of actuation and switching frequency, along with force generation adequate for tactile perception.

Thermal micro-actuators are a promising solution to the need for large-displacement, low-power MEMS actuators. Potential applications of these devices are micro-relays, tunable impedance RF networks, and miniature medical instrumentation. In this paper the development of thermal microactuators based on SU8 is described. A polymeric sacrificial layer allows the removal of the SU8 mold to occur without the use of harsh etching conditions. In addition to silicon non-traditional for MEMS substrates such as RF-printed circuit boards have also been successfully utilized to fabricate the devices. The PCB-based devices exhibited similar characteristics, thus opening the possibility of integrating RF MEMS directly on PCBs. The actuators were benchmarked with respect to power consumption, stroke, and response time. The fabricated nickel actuators are shown to be robust with displacements in the range of 76 micrometers using 80 mW of power. Actual cooling transients were captured using a two-step constant-current excitation method. It is further demonstrated through analytical models that the thermal cooling times limit the bandwidth of these devices below 1KHz. Several commercially relevant applications of the developed actuators are also discussed. One such application is a vibro-tactile display for disabled individuals.

Microelectromechanical systems (MEMS) technologies are ideal for use in sub-millimeter scale actuatable transcatheter optical devices. Such technologies enable precise light path control in very small packages for applications such as optical coherence tomography (OCT) and photodynamic therapies. Indeed, there have been numerous published reports of such devices that utilize silicon-based MEMS technologies and actuation methods including piezoelectric, electrostatic, thermal expansive, and electromagnetic [1–4]. We report a novel, dual axis, magnetically actuated micromirror for endoscopic applications that is fabricated from a photopatternable polymer using photolithographic techniques. Our approach provides improvements over other actuation methods and silicon-based devices.

In this study, the authors conducted a model-based, engine system analysis of Electro-Mechanical Actuators (EMAs). This effort employed an existing, NASA developed, aircraft engine model. A critical engine actuator within the model was replaced by a dynamic, physics based EMA model that includes: controller, motor, drivetrain and feedback sensor sub-models. The actuator model includes simulation of the electrical, mechanical and thermal response of the system. The resulting platform was used to simulate a range of critical actuator fault conditions including: feedback resolver fault, ball-screw degradation, motor winding short, and LVDT non-linearity. Since the available experimental data from propulsion system EMAs is very limited, this platform provides an ideal opportunity to evaluate and enhance prognostic capability for critical engine applications. The model fault tests were used to demonstrate a prototype prognostics and health management (PHM) system for engine EMAs. First, the system response was used to develop an appropriate mode detection algorithm to identify the ideal system conditions for collection of diagnostic evidence. Then, using the acquired transient and steady-state system response, diagnostic data features were derived from EMA related sensors and engine performance parameters. Using these features as a starting point, a system level reasoner was created using multiple classification techniques including LDA, QDA and SVM. Using model generated data with simulated system variance, it was demonstrated that the reasoner provides excellent fault detection, isolation and severity assessment capability for all considered fault modes. Finally, a suitable actuator life model was developed and a probabilistic prognostic approach was used to determine the remaining useful life of the system. The demonstrated PHM system will significantly enhance the ability to safely operate aircraft, schedule maintenance activities, optimize operational life cycles, and reduce support costs.

Photo-thermally actuated polymer (SU-8) microgrippers were designed, simulated and characterized. The microgrippers were actuated by thermal expansion of compliant polymer parts. The required heat was transferred to the devices by laser absorption. The microgrippers were made of a single SU-8 layer and dyed before the experiments for enhanced laser absorption. Finite element simulation results were used to predict the working range of the grippers. It has been demonstrated that using a simple design 22 μm of deflection can be achieved for a micro-gripper of approximately 900 μm long. The gripping experiments have demonstrated the successful operation of polymeric photo-thermal microgrippers.

Thermal flying-height control (TFC) is now a key technology used in hard disk drives (HDD) to push the magnetic spacing to sub-5nm. The precise control of the flying height (FH) actuation is a major consideration in improving the read/write capability as well as increasing the reliability. In this paper, we investigate the response of TFC sliders to altitude change with a focus on the actuation efficiency variation with altitude. Numerical and experimental results both indicated an increase in the actuation efficiency at higher altitudes. Simulations are conducted which disclose that increased protrusion and less pushback near the transducer contribute to the efficiency increase at higher altitudes. This study is of practical importance for improving the heater and ABS designs to reduce HDD sliders’ sensitivities to altitude changes.