Publications

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As engineering challenges grow in the ever shrinking world of nano-design, methods of making dynamic measurements of these materials and systems will become important. Electron microscopes have imaged these extremely small samples for years, but are incapable of measuring dynamic events. A means of measuring these nano-scale dynamic events is envisioned by converting an electron microscope into a Doppler velocimeter. This idea proceeds from the analogous concept of laser Doppler velocimetry. However, the obvious solution of using a laser to probe at the nano-scale is not feasible because the diffraction limit of light is orders of magnitude larger than the samples of interest. This paper investigates the theoretical underpinnings of using electron beams for Doppler measurements. Potential issues and their solutions, including electron beam coherence and interference will be presented. If answers to these problems can be found, the invention of the Doppler electron velocimeter could yield a completely new measurement concept at atomistic scales.

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As engineering challenges grow in the ever-shrinking world of nano-design, methods of making dynamic measurements of nano-materials and systems become more important. The Doppler electron velocimeter (DEV) is a new measurement concept motivated by the increasing importance of nano-dynamics. Nano-dynamics is defined in this context as any phenomenon that causes a dynamically changing phase in an electron beam, and includes traditional mechanical motion, as well as additional phenomena including changing magnetic and electric fields. The DEV is only a theoretical device at this point. Lastly, this article highlights the importance of pursuing nano-dynamics and presents a case that the electron microscope and its associated optics are a viable test bed to develop this new measurement tool.

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Measurement of dynamic events at the nano-scale is currently impossible. This paper presents the theoretical underpinnings of a method for making these measurements using electron microscopes. Building on the work of Moellenstedt and Lichte who demonstrated Doppler shifting of an electron beam with a moving electron mirror, further work is proposed to perfect and utilize this concept in dynamic measurements. Specifically, using the concept of ''fringe-counting'' with the current principles of transmission electron holography, an extension of these methods to dynamic measurements is proposed. A presentation of the theory of Doppler electron wave shifting is given, starting from the development of the de Broglie wave, up through the equations describing interference effects and Doppler shifting in electron waves. A mathematical demonstration that Doppler shifting is identical to the conceptually easier to understand idea of counting moving fringes is given by analogy to optical interferometry. Finally, potential developmental experiments and uses of a Doppler electron microscope are discussed.

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This paper outlines a model for a corner-supported, thin, rectangular bimorph actuated by a two-dimensional array of segmented, orthotropic PVDF laminates; it investigates the realization and measurement of such a bimorph. First, a model is derived to determine the deflected shape of an orthotropic laminate for a given distribution of voltages over the actuator array. Then, boundary conditions are realized in a laboratory setup to approach the theoretical corner-supported boundary condition. Finally, deflection measurements of actuated orthotropic PVDF laminates are performed with Electronic Speckle Pattern Interferometry and are compared to the model results. Copyright © 2005 by ASME.

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