Defence A.E.M. Schmerbauch: "Distributed actuation systems for adaptive optics: from structural modeling to design optimization"

Promotors: B. Jayawardhana, A. I. Vakis

Abstract:Deformable mirrors became indispensable elements of adaptive optics systems. We present modeling and analysis of a hysteretic deformable mirror where the facesheet interacts with a continuous layer of piezoelectric material that can be actuated distributively by a matrix of electrodes through multiplexing. A method to calculate the actuator influence functions is introduced considering the particular arrangement of electrodes. The proposed semi-analytical plate model describes the facesheet's deformation caused by a high-density array of actuators and can be used to determine the optimal pressures the actuators have to exert for achieving a desired surface deformation.

A phenomenon called electrical coupling, which arises from the design concept of this mirror, is explained and implemented in the surface fitting process. It is analyzed in detail by using a modified Miller model to describe the memory effect which is based on the ferroelectric domain switching processes. The desired butterfly memory effect in the material is obtained by modifying the saturated dipole polarization curve in the Miller model, so that we can simulate the electric field dependence of the strain in the piezoelectric material that exhibits asymmetric butterfly loops with remnant deformation through the finite-element method. The proposed method allows us to numerically investigate the electrical coupling between actuators in more detail and correspondingly understand their influence on the mirror facesheet.

Since the demands on adaptive optics are increasing to achieve high performance and meet certain requirements for accuracy and reliability with active optical systems, we propose a new actuation system and create modular actuation arrays by means of kirigami metasheets realigned in parallel and leveled in-plane. We focus on the numerical analysis of different cut patterns to couple lift-off motions within a thin, scalable sheet. A design of a modular actuation array is explained and illustrated in the context of a deformable mirror. The optimal lift-off positions within the array are calculated for this example by a proposed positioning algorithm which makes use of common methods in adaptive optics such as Zernike polynomial fitting.

Dissertation