With increasing advancement in material science and computational power of current computers that allows us to analyze high dimensional systems, very light and large structures are being designed and built for aerospace applications. One example is a reflector of a space telescope that is made of membrane structures. These reflectors are light and foldable which makes the shipment easy and cheaper unlike traditional reflectors made of glass or other heavy materials. However, one of the disadvantages of membranes is that they are very sensitive to external changes, such as thermal load or maneuvering of the space telescope. These effects create vibrations that dramatically affect the performance of the reflector. To overcome vibrations in membranes, in this work, piezoelectric actuators are used to develop distributed controllers for membranes. These actuators generate bending effects to suppress the vibration. The actuators attached to a membrane are relatively thick which makes the system heterogeneous; thus, an analytical solution cannot be obtained to solve the partial differential equation of the system. Therefore, the Finite Element Model is applied to obtain an approximate solution for the membrane actuator system. Another difficulty that arises with very flexible large structures is the dimension of the discretized system. To obtain an accurate result, the system needs to be discretized using smaller segments which makes the dimension of the system very high. This issue will persist as long as the improving technology will allow increasingly complex and large systems to be designed and built. To deal with this difficulty, the analysis of the system and controller development to suppress the vibration are carried out using vector second order form as an alternative to vector first order form. In vector second order form, the number of equations that need to be solved are half of the number equations in vector first order form. Analyzing the system for control characteristics such as stability, controllability and observability is a key step that needs to be carried out before developing a controller. This analysis determines what kind of system is being modeled and the appropriate approach for controller development. Therefore, accuracy of the system analysis is very crucial. The results of the system analysis using vector second order form and vector first order form show the computational advantages of using vector second order form. Using similar concepts, LQR and LQG controllers, that are developed to suppress the vibration, are derived using vector second order form. To develop a controller using vector second order form, two different approaches are used. One is reducing the size of the Algebraic Riccati Equation to half by partitioning the solution matrix. The other approach is using the Hamiltonian method directly in vector second order form. Controllers are developed using both approaches and compared to each other. Some simple solutions for special cases are derived for vector second order form using the reduced Algebraic Riccati Equation. The advantages and drawbacks of both approaches are explained through examples. System analysis and controller applications are carried out for a square membrane system with four actuators. Two different systems with different actuator locations are analyzed. One system has the actuators at the corners of the membrane, the other has the actuators away from the corners. The structural and control effect of actuator locations are demonstrated with mode shapes and simulations. The results of the controller applications and the comparison of the vector first order form with the vector second order form demonstrate the efficacy of the controllers. / Ph. D.

Exoskeletons and humanoid robots require high-power, low-weight, and back-driveable actuators. This paper describes the design and analysis of a high-force linear series elastic actuator for a lower body exoskeleton. The actuator is powered by two motors and utilize a liquid cooling system to increase its maximum continuous torque. The actuator is capable of outputting a maximum continuous force of 4800N and a maximum speed of 0.267 m/s with a maximum continuous motor current of 18A. The Titanium leaf spring was used in the actuator to provide compliance. The spring has a median stiffness of 587 N/mm with standard deviation of 38 N/mm, validated by experiments. Dynamic model was created to analyze the normal modes and can be used for developing model-based controllers. / Master of Science / Compliant Linear actuators with ball screw have become popular for humanoids robots and exoskeleton. The use of ball screw lead to high efficiency, high gear ratio and high back-drivability. The compliance or the ''softness'' of the actuator comes from Titanium leaf spring, which can storage energy during gait cycle and protect motor and the ball screw from impacts of walking. The custom liquid cooling system improves the force density for the actuator. Beam theory analysis, heat transfer analysis, and dynamics analysis were performed to provides insights for the actuator system.

This thesis presents the design and development of a novel biomimetic jellyfish robot that features ionic polymer metal composite actuators. The shape and swimming style of this underwater vehicle are based on oblate jellyfish species, which are known for their high locomotive efficiency. Ionic polymer metal composites (IPMC) are used as actuators in order to contract the bell and thus propel the jellyfish robot. This research focuses on translating the evolutionary successes of the natural species into a jellyfish robot that mimics the geometry, the swimming style, and the bell deformation cycle of the natural species. Key advantages of using IPMC actuators over other forms of smart material include their ability to exhibit high strain response due to a low voltage input and their ability to act as artificial muscles in water environment. This research specifically seeks to implement IPMC actuators in a biomimetic design and overcome two main limitations of these actuators: slow response rate and the material low blocking force. The approach presented in this document is based on a combination of two main methods, first by optimizing the performance of the IPMC actuators and second by optimizing the design to fit the properties of the actuators by studying various oblate species. Ionic polymer metal composites consist of a semi-permeable membrane bounded by two conductive, high surface area electrode. The IPMCs are manufactured is several variations using the Direct Assembly Process (DAP), where the electrode architecture is controlled to optimize the strain and stiffness of the actuators. The resulting optimized actuators demonstrate peak to peak strains of 0.8 % in air and 0.7 % in water across a frequency range of 0.1-1.0 Hz and voltage amplitude of 2 V. A study of different oblate species is conducted in order to attain a model system that best fits the properties of the IPMC actuators. The Aequorea victoria is chosen based on its bell morphology and kinematic properties that match the mechanical properties of the IPMC actuators. This medusa is characterized by it low swimming frequency, small bell deformation during the contraction phase, and high Froude efficiency. The bell morphology and kinematics of the Aequorea victoria are studied through the computation of the radius of curvature and thus the strain energy stored in the during the contraction phase. The results demonstrate that the Aequorea victoria stores lower strain energy compared to the other candidate species during the contraction phase. Three consecutive jellyfish robots have been built for this research project. The first generation served as a proof of concept and swam vertically at a speed of 2.2 mm/s and consumed 3.2 W of power. The second generation mimicked the geometry and swimming style of the Aurelia aurita. By tailoring the applied voltage waveform and the flexibility of the bell, the robot swam at an average speed of 1.5 mm/s and consumed 3.5 W of power. The third and final generation mimicked the morphology, swimming behavior, and bell kinematics of the Aequorea victoria. The resulting robot, swam at an average speed of 0.77 mm/s and consumed 0.7 W of power when four actuators are used while it achieved 1.5 mm/s and 1.1 W of power consumption when eight actuators are used. Key parameter including the type of the waveform, the geometry of the bell, and position and size of the IPMC actuators are identified. These parameters can be hit later in order to further optimize the design of an IPMC based jellyfish robot. / Master of Science

One of the major problems with surface-mounted or embedded induced strain actuator (ISA) patches are the considerably high stress gradients introduced at the edges of the actuator patches when an electric field is applied. These excessive stress gradients initiate debonding of the actuators from the substrate, thus affecting the mechanical reliability of the structure. This thesis is begun by investigating existing theoretical models of induced strain actuated structures, and will later use these to compare with the finite element analysis. The finite element analysis is used to explore the stress concentrations located at the edges of the actuators and begins by refining the mesh areas of the same structure focusing in on the ends of the ISA’s. This preliminary analysis is conducted on a structural configuration with a perfectly bonded actuator and proceeds to one with a finite bonding layer. After completion of the mesh refinement investigation several modifications in the design and implementation of the induced strain actuators are examined to reduce the stress concentrations at the edges of the actuators. In the finite element analysis two separate modeling considerations are examined: 1) The actuator is perfectly-bonded to the substrate. 2) A finite adhesive layer is incorporated between the actuator and the substrate. With each modeling consideration several design modifications are considered in this thesis including employing partial electrodes on the induced strain actuator surface regions instead of fully electroded surfaces, examining an actuator with a chamfered end, and using caps to reduce the stress concentrations and possibly increase the performance of the structure by allowing the induced strain actuators to utilize their piezoelectric strain coefficient in the thickness direction, d₃₃. The design modifications and different modeling techniques help to alleviate the critical stresses in the structure while gaining a better understanding of causes them. / Master of Science

4D printing is a rapidly emerging field in which 3D printed stimuli-responsive materials produce morphing and multifunctional structures, with time being the fourth dimension. This approach enables the 3D printing of pre-programmed responsive sheets, which transition into complex curved shapes upon exposure to external stimuli, resulting in a substantial reduction in material consumption and printing time (70 - 90 %). Commonly used materials for 4D printing are polymer composites, such as hydrogels, polydimethylsiloxane (PDMS), liquid crystal elastomers (LCEs), and shape memory polymers (SMPs). However, the low elastic modulus (E) that these materials exhibit during shape change (E range of 10-4 – 10 MPa) limits their scalability, actuation stress, and load bearing. Moreover, these materials exhibit low ultimate stresses, leading to correspondingly low toughness (K) values in the range of 0.08 to 5 MJ m-3. Consequently, this results in structures with low damage tolerance. Therefore, an existing challenge for the field of 4D printing is to develop materials that can maintain their large and predictable morphing mechanism for complex shape transformation, while improving the E and K for high performance applications. Furthermore, many existing approaches rely on passive structures that necessitate the control of global conditions of the surrounding environment (e.g., hot plates, ovens, external magnets, water baths) to provide the stimulus for actuation. In this work, we tackle these challenges by introducing novel materials, ink formulations, and innovative printing techniques for multi-material Direct Ink Writing (DIW). We aim to create electrically controllable 4D printed structures that exhibit exceptional stiffness and toughness, all while preserving a large and predictable morphing mechanism for intricate shape transformations. First, we introduce multiscale heterogeneous polymer composites as a novel category of stiff, electrically controllable thermally responsive 4D printed materials. These composites consist of an epoxy matrix with an adjustable cross-link density and a plurality of isotropic and anisotropic nanoscale and microscale fillers. Leveraging this platform, we generate a set of 37 inks covering a broad range of negative and positive linear coefficients of thermal expansion. This set of inks exhibits an elastic modulus range that is four orders of magnitude greater than that of existing 4D printed materials and offers tunable electrical conductivities for simultaneous Joule heating actuation and self-sensing capabilities. Utilizing electrically controllable bilayers as building blocks, we design and print a flat geometry that changes shape into a 3D self-standing lifting robot, displaying record actuation stress and specific force when compared to other 3D printed actuators. We integrate this lifting robot with a closed-loop control system, achieving autoregulated actuation exhibiting a 4.8 % overshoot and 0.8 % undershoot, while effectively rejecting disturbances of up to 170 times the robot's weight. Furthermore, we employ our ink palette to create and 3D print planar lattice structures that transform into various self-supporting complex 3D surfaces. Ultimately, we achieve a 4D printed electrically controlled crawling robotic lattice structure, highlighting its capacity to transport loads up to 144 times its own weight. Finally, we introduced a printable PDMS adhesive that serves as synthetic fascia to hold our epoxy-based synthetic muscle together, enhancing the K of our 4D printed structures, all while maintaining high stiffness, large, predictable, and addressable actuation mechanism. Through the integration of these soft adhesive materials with high-stiffness thermally responsive epoxies via DIW, we achieved an improvement of about two orders of magnitude in the K of the resulting synthetic muscle composite, all while maintaining high stiffness and morphing mechanism. Utilizing this fabrication method, we printed an electrically controllable bilayer exhibiting damage detection and tolerance, enduring up to 7 fractures while continuing to function effectively. Furthermore, we integrated the synthetic muscle composite into our lifting robot design, setting yet again new records in specific force and actuation stress when compared to other 3D printed actuators. Notably, even after failure, the actuator maintained its operational integrity and high performance. Ultimately, we present a 4D printed lattice structure featuring the incorporation the synthetic muscle composite, showcasing a sensitive electrically responsive surface with fracture detection capabilities. To emphasize this, we subjected one of these 4D printed lattices to extreme conditions, driving a car over it. Notably, the lattice structure detected fractures and exhibited high resilience, enduring external compressive damage equivalent to 331,060 times its own weight. / 2026-05-23T00:00:00Z

Of primary importance to the design and application of adaptive structures is a modeling method to allow for performance prediction and parametric optimization of the integrated system. The statics-based modeling approaches have been applied to model piezoelectric (PZT) actuator-driven adaptive structures. The dynamic interaction between the actuators and their host structures has been ignored, and the system energy conversion can’t be predicted. As a matter of fact, PZT actuator-driven smart structures are complex electromechanical coupling systems in which electrical energy is converted into mechanical energy and vice-versa. The actuator outputs and the system energy conversion are dominated by the complex electro-mechanical impedance of the system. The entire actuator/substrate system can thus be essentially represented by a coupled impedance-based system model. This research presents such an impedance-based electro-dynamics analytical method and the experimental investigation for integrated PZT/substrate systems. When compared with the conventional static models, the system modeling method has revealed the physical essence and the interconnections among the intelligent elements and supporting structures. The frequency-dependent behaviors of the actuator and the dynamic response of the integrated system are accurately predicted. The theoretical model was developed for generic PZT actuator-driven active structures. The actuation force was evaluated as a result of the dynamic interaction between the actuator and the host structure. The model was then extended to include the electrical parameters of the PZT actuator such that the power flow and consumption of the integrated system can be predicted. The system dissipative power was then treated as the equivalent generation source to evaluate a temperature rise and thermal damage of the actuator. To examine the utility and generality of the system modeling method, the developed model was applied to typical two-dimensional structures such as thin plates and thin shells, and to one-dimensional structures such as the circular rings and beams. The design-related mechanical and thermal stress characteristics of the actuators were also specifically investigated. In addition to the theoretical work, experiments were conducted. The PZT actuator-driven simply-supported plate was built and tested. The velocity response of the integrated plate and the dynamic strain of the PZT actuators were measured. The coupled electromechanical admittance of the real system was also directly measured using an impedance analyzer. The predicted solutions agree with the experimental results in all of the tested cases, verifying the theoretical model. / Ph. D.

Induced strain actuators have been integrated with conventional structural materials to serve as energy input devices or actuating elements in many engineering applications implementing intelligent material systems and structures concepts. In order to use the actuation mechanism produced by the integrated induced strain actuators efficiently, the mechanics of the mechanical interaction between the actuator and the host substructure must be understood and modeled accurately. A refined analytical model has been developed based on the plane stress formulation of the theory of elasticity for a surfacebonded induced strain actuator/beam substructure system. Closed-form solutions of the induced stress field were obtained in an approximate manner using the principle of stationary complementary energy. The model has also been extended to include the presence of adhesive bonding layers and applied external loads. The results of the current model were compared with those obtained by finite element analysis and the pin-force and Euler-Bernoulli models. It was shown that the current model is capable of describing the edge effects of the actuator on actuation force/moment transfer and interfacial shear and peeling stress distributions that the existing analytical models fail to describe. Good agreement was obtained between the current model and the finite element analysis in terms of predicting actuation force/moment transfer. The interfacial shear stress distribution obtained by the current model satisfies stress-free boundary conditions at the ends of the actuator, which the finite element model is not able to satisfy. The current model correctly describes the transfer of the actuation mechanism and the resulting interfacial stress distributions; thus, it can be used in designing integrated induced strain actuator/substructure systems. Moreover, a new induced strain actuator configuration, which includes inactive edges on the ends of the actuators, has been proposed to alleviate the intensity of the interfacial stresses. The effectiveness of the actuator on the interfacial stress alleviation was verified by the current analytical model and finite element analysis. It was shown that the proposed actuator configuration can significantly alleviate intensive interfacial shear and peeling stresses without sacrificing the effectiveness of the actuation mechanism. The chances of interfacial failure of the integrated structural system, fatigue failure in particular, can thus be reduced. / Ph. D.

This thesis aims to provide a comprehensive reference on the effective integration of shape memory alloys into architectural design and design. Despite growing interest in SMAs for kinetic structures and adaptive facades, there is currently a fragmented understanding of how to leverage their unique properties in the built environment. Designers lack consolidated resources that map the capacities and limitations of different SMA materials and configurations with respect to functional objectives, manufacturing constraints, and performance goals. My research will gather dispersed knowledge across materials science, mechanics, and fabrication processes relevant to architectural SMAs. After conducting extensive research and different stages of prototyping, a final responsive wall piece will be designed and built that interacts with users responding to different stimuli including touch, sound, or distance. The outcome of this research on the integration of shape memory alloys (SMAs) into architectural design and construction can contribute significantly to designers and the field of architecture in several ways • Unlocking new design possibilities: • Facilitating interdisciplinary collaboration• Developing design guidelines and tools • Advancing responsive architecture• Inspiring future research and innovation / Master of Architecture / This thesis explores how new materials called Shape Memory Alloys (SMAs) can be used to make buildings more dynamic and responsive to their environment. SMAs are special because they can change shape when heated and return to their original form when cooled, much like magic metal. The research shows how SMAs can be used in architecture to create structures that move and adapt in response to changes in their surroundings. For example, building facades made with SMAs can automatically adjust to control sunlight and temperature, making buildings more energy-efficient and comfortable for people inside. A significant part of this study is a project where SMAs are used to create a wall that reacts to touch and other stimuli, bringing the wall to life in a way that interacts with people nearby. This work aims to inspire architects and designers to think beyond static structures and consider how buildings can become more interactive and environmentally friendly. Overall, this research opens up exciting possibilities for the future of building design, making our living and working spaces smarter and more in tune with our needs and the natural world.

Exploring the advancement of soft and variable impedance actuators (VIAs), the research focuses on their potential for enhancing safety and adaptability in physical human-robot interactions (pHRI). Despite the promising attributes of these technologies, their adoption in portable applications is still emerging. Addressing the challenges hindering the widespread implementation of soft actuators and VIAs, a multidisciplinary approach is employed, spanning materials science, chemistry, thermodynamics, and more. Novel compliant actuators utilizing phase-change materials and flexible thermoelectric devices are introduced, offering improved safety, adaptability, and efficiency. Thermo-active phase change soft actuators, integrating Peltier junctions, achieve precise thermal control and reversible actuation, overcoming traditional Joule heating limitations for more efficient and controlled thermal responses. The research also delves into thermal variable impedance actuators, using viscoelastic polymers like polycaprolactone (PCL) for variable stiffness and damping. This innovation enables rapid adaptation to changing load conditions, enhancing the dynamic performance of VIAs. Key contributions encompass the design of an agonist-antagonist system using thermo-active phase change materials, applications in soft robotic devices such as grippers and locomotion mechanisms, and the implementation of bidirectional heating elements within these actuators. The work also outlines the challenges encountered, such as gravity's influence on actuation and the frequency-dependent properties of PCL, setting the stage for future research directions to advance the field of soft robotics. Through these contributions, the research demonstrates practical applications of soft and variable impedance actuators in pHRI, paving the way for future innovations in soft robotics.

Elektroakustische Systeme wie Lautsprecher, die elektrische Signale in akustische Signale umwandeln, sind heute Eckpfeiler der Kommunikation. Von Mikrotreibern in Kopfhörern und Smartphones über Audiosysteme in Fahrzeugen und Wohnzimmern bis hin zu großen Beschallungsanlagen in öffentlichen Räumen, Kinos und Konzerten sowie zahlreichen technischen Anwendungen sind sie heute ein allgegenwärtiger Bestandteil des täglichen Lebens. Die gängigsten Lautsprechertechnologien basieren auf elektrodynamischen Wandlern. Seit der ersten Patentierung vor 145 Jahren wurden diese, die notwendige Leistungselektronik sowie die Methoden zur Auslegung und Systembeschreibung im Klein- und Großsignalbereich kontinuierlich weiterentwickelt. Die Forschung befasst sich aber auch ständig mit alternativen Technologien, die Vorteile gegenüber konventionellen Antrieben haben können. In diesem Zusammenhang haben dielektrische Elastomere (DE) in den letzten 25 Jahren zunehmend an Aufmerksamkeit gewonnen. Sie versprechen u.a. einen höheren Wirkungsgrad, neuartige Konstruktionen und eine erhebliche Gewichtsreduktion. Zudem können sie aus kostengünstigen Ausgangsmaterialien ohne den Einsatz von Seltenen Erden oder ferroelektrischen Materialien hergestellt werden, was die Abhängigkeit von Rohstoffimporten verringert und neue Anwendungsfelder eröffnet. Trotz sehr aktiver Forschung und Entwicklung bei Materialien, Design und Herstellung gibt es bisher nur wenige kommerziell verfügbare Aktuatoranwendungen. Eine grundlegende Voraussetzung für die Etablierung einer Technologie sind standardisierte und nachvollziehbare Methoden zur prädiktiven Systembeschreibung und zum rechnergestützten Systementwurf. Diese sind für DE in dynamischen Anwendungen noch nicht verfügbar. In dieser Arbeit wird die etablierte Entwurfsmethodik zur prädiktiven Beschreibung kleinsignaliger dynamischer Systeme mit elektromechanischen und akustischen Netzwerken auf dielektrische Elastomere erweitert. Das Kernelement ist die Ableitung der elektromechanischen Wandlermodelle für DE-Längs- und Dickenoszillatoren. Basierend auf dieser Systembeschreibung, werden Auslegungskriterien für DE-basierte Schallquellen aufgestellt. Der Fokus liegt dabei auf der praktischen Anwendbarkeit und der Generierung von technologischen Vorteilen gegenüber elektrodynamischen Wandlern. Aus diesen Kriterien werden neuartige Wandlerkonzepte in Form von rollenaktorgetriebenen Lautsprechermembranen und unimorphen Membranen entwickelt, analysiert und als Demonstratoren realisiert. Darüber hinaus wird die Leistungselektronik untersucht, auf deren Basis Schaltungen zur Durchführung messtechnischer Untersuchungen und zum Betrieb der Demonstratoren entwickelt und realisiert wurden. Ziel der Arbeit ist es, Anwendungsentwicklern mit der vorgestellten Entwurfsmethodik einen besseren Zugang zur Technologie zu ermöglichen und so zur Entwicklung von DE-basierten Schallquellen im Speziellen und dynamischen DE-Aktoren im Allgemeinen beizutragen.:1 Introduction 1 2 Fundamentals of Dielectric Elastomers 5 3 Electromechanical Network Model of Dielectric Elastomers 9 3.1 Transducer Network Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 3.1.1 Electrostatic Forces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 3.1.2 Simulative-experimental Validation . . . . . . . . . . . . . . . . . . . . . . 14 3.1.3 Mechanical Interactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 3.1.4 Determination of the Parameters at the Operating Point . . . . . . . . . 19 3.1.5 Electromechanical Transducer Model . . . . . . . . . . . . . . . . . . . . . 23 3.2 Electrical Behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 3.3 Operating Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 3.4 Mechanical Behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 4 Power Electronics 37 4.1 Fundamental Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 4.2 Alternative Concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 4.2.1 Adapted Circuit Designs for Capacitive Loads . . . . . . . . . . . . . . . . 39 4.2.2 Summing Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 4.3 Realization of Power Electronics . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 4.3.1 Coupling Capacitance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 4.3.2 Branch to Discharge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 4.3.3 Charging Resistor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 4.3.4 Additional Extensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 4.3.5 Implemented Power Electronics . . . . . . . . . . . . . . . . . . . . . . . . 46 5 Design of DE Loudspeakers 49 5.1 State of the Art . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 5.1.1 Membrane and Bubble-Loudspeakers . . . . . . . . . . . . . . . . . . . . 49 5.1.2 Annular Membrane Actuators . . . . . . . . . . . . . . . . . . . . . . . . . 52 5.1.3 Preformed Membranes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 5.1.4 Thickness Oscillators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 5.2 Fundamental Design Considerations . . . . . . . . . . . . . . . . . . . . . . . . . 55 5.3 Proposed Concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 6 DE-Roll Actuator based Loudspeaker Driver 61 6.1 Fundamentals of DERA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 6.2 Stability Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 6.3 Model Computation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 6.3.1 Fundamental Implementation . . . . . . . . . . . . . . . . . . . . . . . . . 65 6.4 Construction and Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68 6.4.1 PolyPower Actuators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 VTable of Contents 6.4.2 Elastosil Actuator Manufacturing . . . . . . . . . . . . . . . . . . . . . . . . 77 6.4.3 Overview of Manufactured Actuators . . . . . . . . . . . . . . . . . . . . . 78 6.5 Measurement Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 6.5.1 Static Function Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80 6.5.2 Electrical Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 6.5.3 Dynamic Electromechanical Measurements . . . . . . . . . . . . . . . . . 83 6.6 Electromechanical Test Results and Model Updating . . . . . . . . . . . . . . . . 85 6.7 Radial Actuation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 6.8 Acoustic Extension . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 6.8.1 Acoustic Configurations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 6.8.2 Selection of loudspeaker diaphragm . . . . . . . . . . . . . . . . . . . . . 92 6.8.3 Loudspeaker in Closed Cabinet . . . . . . . . . . . . . . . . . . . . . . . . . 96 6.8.4 Loudspeaker in Vented Cabinet . . . . . . . . . . . . . . . . . . . . . . . . 98 6.8.5 Bending Wave Transducer . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 6.9 Acoustic Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 6.10 Demonstrator Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 6.11 Considerations towards Large-Signal Behaviour . . . . . . . . . . . . . . . . . . . 112 7 Dielectric Elastomer Unimorph Membrane 115 7.1 Membrane Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116 7.2 Model-based Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117 7.3 Headphones demonstrator construction . . . . . . . . . . . . . . . . . . . . . . . 119 7.4 Measurements and Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121 8 Summary and Outlook 129 Appendix 133 A ANSYS APDL simulation code for DE elementary cell model . . . . . . . . . . . . 136 B Additional comparisons of measurement and simulation data . . . . . . . . . . 138 / Electroacoustic systems such as loudspeakers, which convert electrical signals into acoustic signals, are nowadays cornerstones of communication. From microdrivers in headphones and smartphones, to audio systems in vehicles and living rooms, to large sound reinforcement systems in public spaces, cinemas and concerts, as well as numerous technical applications, they are nowadays a ubiquitous part of everyday life. The most common loudspeaker technologies are based on electrodynamic transducers. Since the first patent 145 years ago, they, the necessary power electronics as well as the methods for design and system description in the small- and large- signal range have been continuously developed. However, research is also constantly looking at alternative technologies that may have advantages over conventional drives. In this context, dielectric elastomers (DE) have gained increasing attention over the past 25 years. They promise, among other things, higher efficiency, novel designs and considerable weight reduction. Moreover, they can be manufactured from inexpensive starting materials without the use of rare-earths elements or ferroelectric materials, which reduces the dependence on raw materials imports and opens up new fields of application. Despite very active research and development of materials, designs and fabrication, there are only few commercially available actuator applications so far. A fundamental requirement for the establishment of a technology are standardized and comprehensible methods for predictive system description and for computer-aided system design. These are not yet available for DE in dynamic applications. In this work, the established design methodology for the predictive description of smallsignal dynamic systems using electromechanical and acoustic networks is being extended to dielectric elastomers. The core element is the derivation of the electromechanical transducer models for DE longitudinal and thickness oszillators. Based on this system description, design criteria for DE based sound sources are established. The focus lies on practical applicability and the generation of technological advantages compared to electrodynamic transducers. From these criteria, novel transducer concepts in the form of roll actuator driven loudspeaker diaphragms and unimorph membranes are developed, analyzed and realized as demonstrators. In addition, the power electronics are examined, on the basis of which circuits for carrying out metrological investigations and for operating the demonstrators were developed and implemented. The goal of the work is to provide application developers with better access to the technology using the presented design methodology and thus contribute to the development of DE-based sound sources in particular and dynamic DE actuators in general.:1 Introduction 1 2 Fundamentals of Dielectric Elastomers 5 3 Electromechanical Network Model of Dielectric Elastomers 9 3.1 Transducer Network Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 3.1.1 Electrostatic Forces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 3.1.2 Simulative-experimental Validation . . . . . . . . . . . . . . . . . . . . . . 14 3.1.3 Mechanical Interactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 3.1.4 Determination of the Parameters at the Operating Point . . . . . . . . . 19 3.1.5 Electromechanical Transducer Model . . . . . . . . . . . . . . . . . . . . . 23 3.2 Electrical Behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 3.3 Operating Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 3.4 Mechanical Behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 4 Power Electronics 37 4.1 Fundamental Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 4.2 Alternative Concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 4.2.1 Adapted Circuit Designs for Capacitive Loads . . . . . . . . . . . . . . . . 39 4.2.2 Summing Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 4.3 Realization of Power Electronics . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 4.3.1 Coupling Capacitance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 4.3.2 Branch to Discharge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 4.3.3 Charging Resistor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 4.3.4 Additional Extensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 4.3.5 Implemented Power Electronics . . . . . . . . . . . . . . . . . . . . . . . . 46 5 Design of DE Loudspeakers 49 5.1 State of the Art . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 5.1.1 Membrane and Bubble-Loudspeakers . . . . . . . . . . . . . . . . . . . . 49 5.1.2 Annular Membrane Actuators . . . . . . . . . . . . . . . . . . . . . . . . . 52 5.1.3 Preformed Membranes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 5.1.4 Thickness Oscillators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 5.2 Fundamental Design Considerations . . . . . . . . . . . . . . . . . . . . . . . . . 55 5.3 Proposed Concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 6 DE-Roll Actuator based Loudspeaker Driver 61 6.1 Fundamentals of DERA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 6.2 Stability Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 6.3 Model Computation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 6.3.1 Fundamental Implementation . . . . . . . . . . . . . . . . . . . . . . . . . 65 6.4 Construction and Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68 6.4.1 PolyPower Actuators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 VTable of Contents 6.4.2 Elastosil Actuator Manufacturing . . . . . . . . . . . . . . . . . . . . . . . . 77 6.4.3 Overview of Manufactured Actuators . . . . . . . . . . . . . . . . . . . . . 78 6.5 Measurement Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 6.5.1 Static Function Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80 6.5.2 Electrical Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 6.5.3 Dynamic Electromechanical Measurements . . . . . . . . . . . . . . . . . 83 6.6 Electromechanical Test Results and Model Updating . . . . . . . . . . . . . . . . 85 6.7 Radial Actuation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 6.8 Acoustic Extension . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 6.8.1 Acoustic Configurations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 6.8.2 Selection of loudspeaker diaphragm . . . . . . . . . . . . . . . . . . . . . 92 6.8.3 Loudspeaker in Closed Cabinet . . . . . . . . . . . . . . . . . . . . . . . . . 96 6.8.4 Loudspeaker in Vented Cabinet . . . . . . . . . . . . . . . . . . . . . . . . 98 6.8.5 Bending Wave Transducer . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 6.9 Acoustic Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 6.10 Demonstrator Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 6.11 Considerations towards Large-Signal Behaviour . . . . . . . . . . . . . . . . . . . 112 7 Dielectric Elastomer Unimorph Membrane 115 7.1 Membrane Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116 7.2 Model-based Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117 7.3 Headphones demonstrator construction . . . . . . . . . . . . . . . . . . . . . . . 119 7.4 Measurements and Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121 8 Summary and Outlook 129 Appendix 133 A ANSYS APDL simulation code for DE elementary cell model . . . . . . . . . . . . 136 B Additional comparisons of measurement and simulation data . . . . . . . . . . 138