On Designing Compliant Actuators Based On Dielectric Elastomers

Dielectric Elastomers (DE) are incompressible dielectrics which can experience deviatoric (isochoric) finite deformations in response to applied large electric fields. Thanks to the strong electro-mechanical coupling, DE intrinsically offer great potentialities for conceiving novel solid-state mechatronic devices, in particular linear actuators, which are more integrated, lightweight, economic, silent, resilient and disposable than equivalent devices based on traditional technologies. Such systems may have a huge impact in applications where the traditional technology does not allow coping with the limits of weight or encumbrance, and with problems involving interaction with humans or unknown environments. Fields such as medicine, domotic, entertainment, aerospace and transportation may profit. For actuation usage, DE are typically shaped in thin films coated with compliant electrodes on both sides and piled one on the other to form a multilayered DE. DE-based Linear Actuators (DELA) are entirely constituted by polymeric materials and their overall performance is highly influenced by several interacting factors; firstly by the electromechanical properties of the film, secondly by the mechanical properties and geometry of the polymeric frame designed to support the film, and finally by the driving circuits and activation strategies. In the last decade, much effort has been focused in the devolvement of analytical and numerical models that could explain and predict the hyperelastic behavior of different types of DE materials. Nevertheless, at present, the use of DELA is limited. The main reasons are 1) the lack of quantitative and qualitative models of the actuator as a whole system 2) the lack of a simple and reliable design methodology. In this thesis, a new point of view in the study of DELA is presented which takes into account the interaction between the DE film and the film supporting frame. Hyperelastic models of the DE film are reported which are capable of modeling the DE and the compliant electrodes. The supporting frames are analyzed and designed as compliant mechanisms using pseudo-rigid body models and subsequent finite element analysis. A new design methodology is reported which optimize the actuator performances allowing to specifically choose its inherent stiffness. As a particular case, the methodology focuses on the design of constant force actuators. This class of actuators are an example of how the force control could be highly simplified. Three new DE actuator concepts are proposed which highlight the goodness of the proposed method.

Optical Microring Resonators based on ion-implanted LiNbO3 ridge waveguides

The growing interest for Integrated Optics for sensing, telecommunications and even electronics is driving research to find solutions to the new challenges issued by a more and more fast, connected and smart world. This thesis deals with the design, the fabrication and the characterisation of the first prototypes of Microring Resonators realised using ion implanted Lithium Niobate (LiNbO3) ridge waveguides. Optical Resonator is one among the most important devices for all tasks described above. LiNbO3 is the substrate commonly used to fabricate optical modulators thanks to its electro-optic characteristics. Since it is produced in high quantity, good quality and large wafers its price is low compared to other electro-optic substrate. We propose to use ion implantation as fabrication technology because in the other way standard optical waveguides realised in LiNbO3 by Proton Exchange (PE) or metal diffusion do not allow small bending radii, which are necessary to keep the circuit footprint small. We will show in fact that this approach allows to fabricate waveguides on Lithium Niobate that are better than PE or metal diffused waveguides as it allows smaller size devices and tailoring of the refractive index profile controlling the implantation parameters. Moreover, we will show that the ridge technology based on enhanced etching rate via ion implantation produces a waveguide with roughness lower than a dry etched one. Finally it has been assessed a complete technological process for fabrication of Microring Resonator devices in Lithium Niobate by ion implantation and the first prototypes have been produced.

Advanced SPM studies on the growth of ultrathin films of organic semiconductors at metal and dielectric interfaces

Many studies on the morphology, molecular orientation, device performance, substrate nature and growth parameter dependence have been carried out since the proposal of Sexithiophene (6T) for organic electronics [ ] However, these studies were mostly performed on films thicker than 20nm and without specifically addressing the relationship between morphology and molecular orientation within the nano and micro structures of ultrathin films of 0-3 monolayers. In 2004, the observation that in OFETs only the first few monolayers at the interface in contact with the gate insulator contribute to the charge transport [ ], underlined the importance to study submonolayer films and their evolution up to a few monolayers of thickness with appropriate experimental techniques. We present here a detailed Non-contact Atomic Force Microscopy and Scanning Tunneling Microscopy study on various substrates aiming at the investigation of growth mechanisms. Most reported similar studies are performed on ideal metals in UHV. However it is important to investigate the details of organic film growth on less ideal and even technological surfaces and device testpatterns. The present work addresses the growth of ultra thin organic films in-situ and quasi real-time by NC-AFM. An organic effusion cell is installed to evaporate the organic material directly onto the SPM sample scanning stage.

Numerical analysis of Dielectric Barrier Discharge

A numerical investigation of dielectric barrier discharge aimed to simulate the electro hydro dynamic interaction is presented. A discharge drift diffusive model according to the Townsend avalanche is described and used to duplicate the plasma kinetics of a DBD actuator. The discharge characteristics dependence upon dielectric material and applied voltage are simulated and the EHD force field according to a simplified approach is presented and discussed. The coupling of DBD results with a fluid dynamic code is also shown. Finally, a new non invasive diagnostic technique for EHD interaction based on Schlieren imaging is computationally validated.