Maxwell stress induced optical torque upon gold prolate nanospheroid

We study the rotational motion of objects trapped in a focused laser beam (optical tweezers). Micrometer-sized flat slabs are fabricated using two-photon photopolymerization. These objects, trapped by linearly-polarized light, tend to align parallel to the polarization plane. This alignment effect is attributed to the polarization anisotropy resulting from the object shape and we present a simple electromagnetic approach to estimate the resulting optical torque. Micro-rotors of different sizes are studied experimentally. We characterize the behavior of micro-objects when the light polarization is rotated at constant speed. Our theoretical approach gives a good prediction of how the size of micro-objects affects their rotation efficiency.

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Validierung einer optischen Drehmomentmessung*/Validation of an optical torque measurement

wt Werkstattstechnik online ◽

10.37544/1436-4980-2017-09-28 ◽

2017 ◽

Vol 107 (09) ◽

pp. 590-593

Author(s):

T. Schneider ◽

J. Wortmann ◽

B. Eilert ◽

M. Stonis ◽

L. Prof. Overmeyer

Keyword(s):

Measurement Method ◽

Rotation Angle ◽

State Of The Art ◽

Torque Sensor ◽

Torque Measurement ◽

Research Project ◽

Industrial Sectors ◽

Current State ◽

Stand Der Technik ◽

Optical Torque

Das Erfassen von Drehmomenten durch Sensoren sowie das Erzeugen von Drehmomenten stellen eine wichtige Basis für viele Industriezweige dar. Im Rahmen eines Forschungsprojektes wurde ein optisches, berührungsloses Messverfahren zur absoluten Drehwinkel- und Drehmomentmessung entwickelt. Zum Vergleich mit dem aktuellen Stand der Technik wurde ein Versuchsstand aufgebaut sowie ein Referenzdrehmomentsensor eingesetzt. Die Ergebnisse dieser Validierung werden in diesem Fachaufsatz vorgestellt.   The measurement of torque via sensors as well as the generation of torque are the basis of many industrial sectors. Within a research project an optical and non-contact measurement method to detect the absolute rotation angle and torque was developed. For comparison with the current state of the art torque sensors a test stand was built and compared to a reference torque sensor. The results of this validation are presented in the present paper.

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A numerical approach based on finite element method for the wrinkling analysis of dielectric elastomer membranes

Journal of Applied Mechanics ◽

10.1115/1.4051212 ◽

2021 ◽

pp. 1-37

Author(s):

Guoyong Mao ◽

Wei Hong ◽

Martin Kaltenbrunner ◽

Shaoxing Qu

Keyword(s):

Finite Element Method ◽

Finite Element ◽

Thickness Distribution ◽

Numerical Approach ◽

Dielectric Elastomer ◽

Equivalent Model ◽

Maxwell Stress ◽

Buckling Mode ◽

Post Buckling ◽

Element Method

Abstract Dielectric elastomer (DE) actuators are deformable capacitors capable of a muscle-like actuation when charged. When subjected to voltage, DE membranes coated with compliant electrodes may form wrinkles due to the Maxwell stress. Here, we develop a numerical approach based on the finite element method (FEM) to predict the morphology of wrinkled DE membranes mounted on a rigid frame. The approach includes two steps, I) pre-buckling and II) post-buckling. In step I, the first buckling mode of the DE membrane is investigated by substituting the Maxwell stress with thermal stress in the built-in function of the FEM platform SIMULIA Abaqus. In step II, we use this first buckling mode as an artificial geometric imperfection to conduct the post-buckling analysis. For this purpose, we develop an equivalent model to simulate the mechanical behavior of DEs. Based on our approach, the thickness distribution and the thinnest site of the wrinkled DE membranes subjected to voltage are investigated. The simulations reveal that the crests/troughs of the wrinkles are the thinnest sites around the center of the membrane and corroborate these findings experimentally. Finally, we successfully predict the wrinkles of DE membranes mounted on an isosceles right triangle frame with various sizes of wrinkles generated simultaneously. These results shed light on the fundamental understanding of wrinkled dielectric elastomers but may also trigger new applications such as programmable wrinkles for optical devices or their prevention in DE actuators.

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Crossover from positive to negative optical torque in mesoscale optical matter

Nature Communications ◽

10.1038/s41467-018-07376-7 ◽

2018 ◽

Vol 9 (1) ◽

Cited By ~ 21

Author(s):

Fei Han ◽

John A. Parker ◽

Yuval Yifat ◽

Curtis Peterson ◽

Stephen K. Gray ◽

...

Keyword(s):

Optical Torque

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Electric field induced structural change for poly(vinylidene fluoride-co-trifluoroethylene) ultrathin films studied by scanning Maxwell stress microscope

Journal of Vacuum Science & Technology B Microelectronics Processing and Phenomena ◽

10.1116/1.589765 ◽

1998 ◽

Vol 16 (1) ◽

pp. 121 ◽

Cited By ~ 14

Author(s):

Tisato Kajiyama

Keyword(s):

Structural Change ◽

Electric Field ◽

Ultrathin Films ◽

Vinylidene Fluoride ◽

Maxwell Stress ◽

Poly Vinylidene Fluoride

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A First-Principles Method of Determining Van Der Waals Forces in a Dissipative Media

ASME 2012 Third International Conference on Micro/Nanoscale Heat and Mass Transfer ◽

10.1115/mnhmt2012-75165 ◽

2012 ◽

Author(s):

Yi Zheng ◽

Arvind Narayanaswamy

Keyword(s):

Stress Tensor ◽

First Principles ◽

Van Der Waals ◽

Maxwell Stress ◽

Quantum Field ◽

Maxwell Stress Tensor ◽

Lifshitz Theory ◽

Dissipative Media ◽

Dissipative Material ◽

Vdw Force

Lifshitz theory of van der Waals (vdW) force and energy is strictly valid when the location at which the stress tensor is calculated is in vacuum. Generalization of Lifshitz theory to the case when the stress tensor is to be calculated in a dissipative material, as opposed to vacuum, is a surprisingly difficult undertaking because there is no expression for the electromagnetic stress tensor in dissipative materials. Here, we derive the expression for vdW force in planar dissipative media by calculating the Maxwell stress tensor in a fictious layer of vacuum, that is eventually made to vanish, introduced in the structure, without employing the complicated quantum field theoretic method proposed by Dzyaloshinskii, Lifshitz, and Pitaevskii. Even though this work has proven to be a corroboration of Dzyaloshinskii et al., it has thrown new light on our understanding of vdW forces and suggests that it should be possible to achieve the similar result for objects with arbitrary shapes.

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