Sylvia Gebhardt

Bio: Sylvia Gebhardt is an academic researcher. The author has contributed to research in topics: Adaptive optics & Deformable mirror. The author has an hindex of 3, co-authored 3 publications receiving 42 citations.

Modular bimorph mirrors for adaptive optics

Abstract: This paper examines the possibility of constructing deformable mirrors for adaptive optics with a large number of degrees of freedom from silicon wafers with bimorph piezoelectric actuation. The mirror may be used on its own, or as a segment of a larger mirror. The typical size of one segment is 100 to 200 mm; the production process relies on silicon wafers and thick film piezoelectric material deposition technology; it is able to lead to an actuation pitch of the order of 5 mm, and the manufacturing costs appear to grow only slowly with the number of degrees of freedom in the adaptive optics.

Large lightweight segmented mirrors for adaptive optics

Abstract: This paper examines the possibility of constructing deformable mirrors for adaptive optics with a large number of degrees of freedom, by assembling segmented silicon mirrors with bimorph piezoelectric actuation. The production process relies on silicon wafers and thick film PZT deposition technology; it is able to lead to an actuation pitch of the order of 5 mm, and the manufacturing costs appear to grow only slowly (linearly or less) with the number of degrees of freedom in the adaptive optics.

Advances in deployable structures and surfaces for large apertures in space

Abstract: Large apertures in space have applications for telecommunications, Earth observation and scientific missions. This paper reviews advances in mechanical architectures and technologies for large deployable apertures for space antennas and telescopes. Two complementary approaches are described to address this challenge: the deployment of structures based on quasi-rigid members and highly flexible structures. Regarding the first approach, deployable articulated structures are classified in terms of their kinematics as 3D or planar linkages in multiple variants, resulting in different architectures of radial, peripheral or modular constructions. A dedicated discussion on the number of degrees of freedom and constraints addresses the deployment reliability and thermo-elastic stability of large elastic structures in the presence of thermal gradients. This aspect has been identified as a design driver for new developments of peripheral ring and modular structures. Meanwhile, other design drivers are maintained, such as the optimization of mass and stiffness, overall accuracy and stability, and pragmatic aspects including controlled industrial development and a commitment to operators’ needs. Furthermore, reflecting surface technologies and concepts are addressed with a view to the future, presenting advances in technical solutions for increasing apertures and reducing areal mass densities to affordable levels for future missions. Highly flexible materials capable of producing ultra-stable shells are described with reference to the state of the art and new developments. These concepts may enable large deployable surfaces for antennas and telescopes, as well as innovative optical concepts such as photon sieves. Shape adjustment and shape control of these surfaces are described in terms of available technologies and future needs, particularly for the reconfiguration of telecommunications antennas. In summary, the two complementary approaches described and reviewed cover the domain of present and foreseeable space applications. Recent European developments are discussed within a global context and a critical review of the state of the art and recent advances taking into account the reliability and structural stability as design drivers.

Design and manufacturing rules for maximizing the performance of polycrystalline piezoelectric bending actuators

Abstract: Increasing the energy and power density of piezoelectric actuators is very important for any weight-sensitive application, and is especially crucial for enabling autonomy in micro/milli-scale robots and devices utilizing this technology. This is achieved by maximizing the mechanical flexural strength and electrical dielectric strength through the use of laser-induced melting or polishing, insulating edge coating, and crack-arresting features, combined with features for rigid ground attachments to maximize force output. Manufacturing techniques have also been developed to enable mass customization, in which sheets of material are pre-stacked to form a laminate from which nearly arbitrary planar actuator designs can be fabricated using only laser cutting. These techniques have led to a 70% increase in energy density and an increase in mean lifetime of at least 15× compared to prior manufacturing methods. In addition, measurements have revealed a doubling of the piezoelectric coefficient when operating at the high fields necessary to achieve maximal energy densities, along with an increase in the Young's modulus at the high compressive strains encountered—these two effects help to explain the higher performance of our actuators as compared to that predicted by linear models.

Actuator patterns for unimorph and bimorph deformable mirrors

Abstract: The actuator pattern of an adaptive mirror determines the amplitudes and the fidelities of the mirror deformations that can be achieved In this study, we analyze and compare different electrode patterns of piezoelectric unimorph deformable mirrors using a numerical finite element model The analysis allows us to determine the optimum actuator pattern, and it is also applicable to bimorph mirrors The model is verified by comparing its predictions with experimental results of our prototype of a novel unimorph deformable mirror

Double drive modes unimorph deformable mirror for low-cost adaptive optics

Abstract: This paper reports the development and characterization of a low-cost thin unimorph deformable mirror (DM) driven by positive voltage. The developed DM consists of both an inner actuator array and an outer ring actuator, which works two drive modes: the inner actuator array is used for aberration correction, while the outer ring actuator is used to generate an overall defocus bias. An analytical model based on the theory of plates and shells is studied for predicting the behavior of the developed DM. Measurement results indicate that dual direction maximum defocus deformations of the developed DM are −14.3 and 14.9 μm, respectively, and the resonant frequency is 1.8 kHz. The root-mean-square deformation of the mirror surface after correction is better than λ/20 for λ=633 nm. The replication of Zernike mode shapes up to the fifth order demonstrates that this developed DM is satisfactory for low-order aberration correction.

Adaptive Optics Systems

Abstract: This chapter presents an overview of adaptive optics (AO) systems, including a brief summary of their development history and their importance in high-resolution imaging systems. The first section of this chapter introduces the basic optical concepts of wavefronts and aberrations. The operating principle of AO systems and the primary components of these systems are then presented. Covered in the last section is a review of retinal imaging AO systems, including a brief review of the history of ophthalmic imaging systems and the requirements and challenges to their practical implementation using AO systems.