Distributed actuation systems for adaptive optics: from structural modeling to design optimization

Deformable mirrors are active optical systems used for wavefront control and correction of optical aberrations in many imaging and non-imaging applications such as microscopy, three-dimensional imaging, and medical or industrial applications. Their surface can be deformed by actuator arrays that are mounted below the reflective top-layer. While the performance increases as the density of actuators increases, scaling of the current mirror designs to the needed capabilities remains challenging. Well-engineered mirrors have actuator numbers ranging from 100 to 6000, but new concepts aim to achieve much denser arrays. A recently presented concept of a hysteretic deformable mirror features an actuator array of more than 16000 individually addressable locations, realized by 2D memory actuators utilizing piezoelectric hysteresis for stable shape configurations. A mechanical model has been proposed for describing the deformation of the reflective surface and predicting the accuracy of the mirror, while detailed multiphysics simulations were performed to investigate the behavior of the actuators in an array. Although this concept presents one possibility to achieve a high number of actuators with a design that relies on long-lasting technical components, we have also researched novel ways to realize new approaches for actuation systems. Kirigami actuators, whose mechanisms are grounded on geometrical cut patterns, can also open up the way for modular arrays used for deformable mirrors that will require a lightweight design

Electrical coupling analysis of 2D time-multiplexing memory actuators exhibiting asymmetric butterfly hysteresis

We present the modeling and analysis of electrical coupling in a hysteretic deformable mirror with 2D memory piezoac- tuators, which are made of a purposely-designed piezomaterial sandwiched between electrodes arranged crosswise and actuated by a multiplexing approach. Using a modified Miller model to describe the memory effect which is based on the ferroelectric domain switching processes, the proposed framework is used to 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 desired butterfly memory effect in the material is obtained by modifying the saturated dipole polarization curve in the Miller model. The proposed method allows us to numerically investigate the electrical coupling between actuators in more detail and correspondingly understand their influence to the mirror facesheet

Modular kirigami arrays for distributed actuation systems in adaptive optics

The demands on adaptive optics are increasing to achieve high performance and meet the requirements for accuracy and reliability with these systems. At present, common technologies for actuator arrays are highly developed and designed in complex arrangements leading to bulky devices. In this work, we propose a novel approach for designing modular actuation arrays by means of kirigami metasheets realigned in parallel and leveled in-plane. The study focuses 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. The algorithm is validated by several simulations calculating the membrane deflection, and the overall concept is discussed

Gärqualität und Schimmelpilzwachstum in Silagen in Abhängigkeit von Lagerungsdichte und äußerem Luftabschluß

Das Ziel der Untersuchungen war die Ermittlung der Grenzbedingungen von Lagerungsdichte und äußerer Luftabschlußgüte (Gasdurchlässigkeit des Zudeckmaterials), unter denen Schimmelpilzwachstum während der Silagelagerung eingeschränkt wird. Den Schwerpunkt bildeten 10 Praxis- und Laborsilierversuche mit extensiv erzeugtem Grünfutter, das aufgrund relativ hoher Rohfasergehalte allgemein schwer verdichtbar ist. In den Silagen wurde die Pilzkeimzahl sowie der Gehalt an Ergosterin und Roquefortin C bestimmt. Für die Analyse des Ergosteringehaltes wurde eine neue Methode entwickelt. Die Gasdurchlässigkeit von 1 - 8 Folienlagen der verwendeten Silierstretchfolie wurde radiometrisch gemessen. Im Versuchszeitraum (1995 - 1997) wurde Grünfutter von jahreszeitlich verschiedenen Aufwüchsen unter landwirtschaftlichen Praxisbedingungen einsiliert. Mit Hilfe drei verschiedener Ballenpressen wurden insgesamt 165 Silageballen mit unterschiedlichen Lagerungsdichten erzeugt. Die Folienlagenzahl und die Lagerdauer bei den Silageballen wurde gestaffelt. Hierdurch sollte der Einfluß des Luftabschlusses auf Gärqualität, Pilzbefall und Mykotoxingehalt in den Silagen untersucht werden. Im Labor wurden Einflußfaktoren wie der Trockenmassegehalt (T-Gehalt) des Siliergutes geprüft. In den Praxisversuchen trat bei einem T-Gehalt 450 g/kg bei ausreichendem Luftabschluß buttersäurefreie (£ 0,3 % T) Silagen erzielt. Hier lag offenbar ein ausreichender T-Gehalt zur Sicherung einer guten Gärqualität vor. In allen Versuchen stellte die Erhöhung der Lagerungsdichte die primäre Grundlage zur Erzeugung eines ausreichenden Luftabschlusses in den Silagen dar. Die äußere Luftabschlußgüte besaß im Vergleich dazu sekundären Charakter. Als notwendige Grenzbedingungen des Luftabschlusses zur Erzeugung einer guten Gärqualität sowie zur Einschränkung von Pilzbefall in den Silagen erwiesen sich: (1) eine Lagerungsdichte von mindestens 200-210 kg T/m³ und (2) eine maximale Gasdurchlässigkeit des Zudeckmaterials von 1,7 l/m² in 24 Stunden (6 Folienlagen der verwendeten Silierstretchfolie). Ein ausreichender Luftabschluß war die Voraussetzung für die Wirksamkeit von Silierzusätzen hinsichtlich der Einschränkung von Pilzbefall und der Verbesserung der Gärqualität in den Silagen. Die Mykotoxinbildung in den Silagen, die am Beispiel des Vorkommens von Roquefortin C (ROF) untersucht worden ist, wurde ungeachtet von Lagerungsdichte und äußerem Luftabschluß vor allem durch den T-Gehalt des Siliergutes beeinflußt. Bei einem T-Gehalt 550 g/kg wurde in den Silagen Roquefortin C nicht nachgewiesen. Die insgesamt in den Silagen gemessenen Gehalte an Roquefortin C waren mit 450 g/kg, no butyric acid (£ 0,3 % dry matter) was found in the silages with sufficient air exclusion. Here, the d-content to ensure a good fermentation quality was sufficient. In all experiments, the primary way to generate sufficient air exclusion in the silages was to increase the compactness. Compared with this, the hermetic level of covering material had secondary character. To get a sufficient fermentation quality, as well as an inhibition of mould growth in the silages, necessary boundary conditions of air exclusion were: (1) a compactness of at least 200-210 kg T/m³ and (2) a maximum permeability of the covering material of 1,7 l /m² in 24 hours (6 numbers of wraps of the used ensiling stretch film). Sufficient air exclusion was necessary for the effectiveness of the silage additives in inhibiting mould growth and improving the fermentation quality in the silages. The mycotoxin formation in the silages, investigated by measuring the occurrence of roquefortine C (ROF), was influenced mainly by the dry matter content of the ensiled material, regardless of the compactness and hermetic level of covering material. At a dry matter content of 550 g/kg, no roquefortine C was found in the silages. Summarised, the measured amounts of < 1,0 mg ROF/kg roquefortine C in the silages is considered to be relatively low. Within the actual state of knowledge of toxicology, it is not considered dangerous to feed ruminant animals with silages containing these low amounts of roquefortine C

Modeling and analysis of a hysteretic deformable mirror with electrically coupled actuators

In this paper, we present our novel concept of deformable mirror which enables a high density 2D actuation array through multiplexing. We investigate the resulting electrical coupling effect in the neighboring actuators through finite element analysis. These insights are used to consider the behavior within the least-square fitting performed to achieve wavefront error corrections

Influence functions for a hysteretic deformable mirror with a high-density 2D array of actuators

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. Moreover, a method for calculating the actuator influence functions is described considering the particular arrangement of electrodes. The results are presented in a semi-analytical model to describe the facesheet's deformation caused by a high density array of actuators, and validated in a simulation. The proposed modeling of an interconnection layout of electrodes is used to determine the optimal pressures the actuators have to exert for achieving a desired surface deformation