Ryszard J. Pryputniewicz

Measurement Of Vibration Patterns Using Electro-Optic Holography

This paper describes the use of an Electro-Optic Holography system for measuring vibration patterns on diffusely reflecting objects. The system provides a high-quality display of fringes for identifying modal frequencies and setting vibration levels after which image brightness data can be transferred to a host computer. A bias vibration is introduced into the illumination beam to shift the 0 fringes so that fringe shift algorithms can be used to determine vibration amplitude. Using this approach, high spatial density displacement fields for vibrating objects were obtained directly form the time-average interferograms recorded by the Electro-Optic Holography system. These results show good correlation with the reconstructions from the holograms and with the vibration characteristics predicted by the Finite Element Methods.

Holographic microscope for measuring displacements of vibrating microbeams using time-averaged, electro-optic holography

An optical microscope, utilizing the principles of time- averaged hologram interferometry, is described for microelectrome- chanical systems (MEMS) applications. MEMS are devices fabricated via techniques such as microphotolithography to create miniature actua- tors and sensors. Many of these sensors are currently deployed in auto- motive applications which rely on, or depend on, the dynamic behavior of the sensor, e.g., airbag sensors, ride monitoring suspensions sensors, etc. Typical dimensions of current MEMS devices are measured in mi- crometers, a small fraction of the diameter of a human hair, and the current trend is to further decrease the size of MEMS devices to submi- crometer dimensions. However, the smaller MEMS become, the more challenging it is to measure with accuracy the dynamic characteristics of these devices. An electro-optic holographic microscope (EOHM) for the purpose of studying the dynamic behavior of MEMS type devices is de- scribed. Additionally, by performing phase measurements within an EOHM image, object displacements are determined as illustrated by rep- resentative examples. With the EOHM, devices with surface sizes rang- ing from approximately 353400 to 5318 mm are studied while undergo- ing resonant vibrations at frequencies as high as 2 MHz.

Absolute Shape Measurements Using High-Resolution Optoelectronic Holography Methods

Characterization of surface shape and deformation is of pri- mary importance in a number of testing and metrology applications re- lated to the functionality, performance, and integrity of components. In this paper, a unique, compact, and versatile state-of-the-art fiber-optic- based optoelectronic holography (OEH) methodology is described. This description addresses apparatus and analysis algorithms, especially de- veloped to perform measurements of both absolute surface shape and deformation. The OEH can be arranged in multiple configurations, which include the three-camera, three-illumination, and in-plane speckle corre- lation setups. With the OEH apparatus and analysis algorithms, absolute shape measurements can be made, using present setup, with a spatial resolution and accuracy of better than 30 and 10 mm, respectively, for volumes characterized by a 300-mm length. Optimizing the experimental setup and incorporating equipment, as it becomes available, having su- perior capabilities to the ones utilized in the present investigations can further increase resolution and accuracy in the measurements. The par- ticular feature of this methodology is its capability to export the measure- ments data directly into CAD environments for subsequent processing, analysis, and definition of CAD/CAE models.

Hybrid computational and experimental approach for the study and optimization of mechanical components

Increased demands on the performance and efficiency of me- chanical components impose challenges on their engineering design and optimization, especially when new and more demanding applica- tions must be developed in relatively short periods of time while satisfy- ing design objectives, as well as cost and manufacturability. In addition, reliability and durability must be taken into consideration. As a conse- quence, effective quantitative methodologies, computational and experi- mental, should be applied in the study and optimization of mechanical components. Computational investigations enable parametric studies and the determination of critical engineering design conditions, while ex- perimental investigations, especially those using optical techniques, pro- vide qualitative and quantitative information on the actual response of the structure of interest to the applied load and boundary conditions. We discuss a hybrid experimental and computational approach for investiga- tion and optimization of mechanical components. The approach is based on analytical, computational, and experimental solutions (ACES) meth- odologies in the form of computational, noninvasive optical techniques, and fringe prediction (FP) analysis tools. Practical application of the hy- brid approach is illustrated with representative examples that demon- strate the viability of the approach as an effective engineering tool for analysis and optimization.

Hybrid approach to deformation analysis

Current trends in development of components, structures, and systems place unprecedented requirements on their designers. To satisfy these demands, new, highly efficient materials and structural designs are being employed and integrated utilization of the most sophisticated technologies is being made. This paper addresses some of the pertinent issues relating to this integration and explores how to take advantage of the analytical, computational, and experimental solution methodologies in relation to a given problem. More specifically, a hybrid approach to deformation analysis is described, based on recent developments in merging, or unifying, of the finite element method with experimental methodologies, and especially with optical metrology. This approach emphasizes the analogy between the methodologies used and employs them to obtain solutions that may not have been otherwise obtainable, to ease the existing solution procedures, or to attain improvements in the results. The paper begins with an introduction to the methodologies used, continues with a discussion of the analytical fundamentals, and concludes with a presentation of representative results.

New Test Methodology for Static and Dynamic Shape Measurements of Microelectromechanical Systems

Characterization of surface shape and deformation is of primary importance in a number of testing and metrology applications related to the functionality, performance, and integrity of components. In this paper, a unique, compact, and versatile state-of-the-art fiber-optic-based optoelectronic holography (OEH) methodology is described. This description addresses apparatus and analysis algorithms, especially developed to perform measurements of both absolute surface shape and deformation. The OEH can be arranged in multiple configurations, which include the three-camera, three-illumination, and in-plane speckle correlation setups. With the OEH apparatus and analysis algorithms, absolute shape measurements can be made, using present setup, with a spatial resolution and accuracy of better than 30 and 10 ␮m, respectively, for volumes characterized by a 300-mm length. Optimizing the experimental setup and incorporating equipment, as it becomes available, having superior capabilities to the ones utilized in the present investigations can further increase resolution and accuracy in the measurements. The particular feature of this methodology is its capability to export the measurements data directly into CAD environments for subsequent processing, analysis, and definition of CAD/CAE models.

Optoelectronic characterization of shape and deformation of MEMS accelerometers used in transportation applications

Recent technological trends based on miniaturization of mechanical, electromechanical, and photonic devices have led to the development of microelectromechanical systems (MEMS). Effective development of MEMS requires the synergism of advanced design, analysis, and fabrication methodologies, with quantitative metrology techniques for characterization of their performance, reliability, and integrity. We describe optoelectronic techniques for measuring, with submicrometer accuracy, shape and changes in states of deformation of MEMS accelerometers used in transportation applications. Using the display and data modes of the described optoelectronic techniques, it is possible to characterize MEMS. This characterization is performed during static and dynamic modes of operation of MEMS. To assure high accuracy of measurements, overlapping regions, i.e., tiles, of MEMS are analyzed and the data (tiles) are patched together to represent the entire component. Preliminary results indicate that the MEMS accelerometer considered in this study deforms 1.48 μm, under the loading conditions used, which represents nearly 50% of its functional dimension in the direction of deformation.

Heterodyne Holography Applications in Studies of Small Components

Heterodyne hologram interferometry was used to study load-deformation characteristics of computer microcomponents that were surface mounted on a printed circuit board. The board was assembled as a cantilever plate and subjected to cyclic flexure loading according to industry standards. The flexure loading was sinusoidal at 0.1 cps with an amplitude of 1.25 mm (0.050 in.) at the tip of the board. Double-exposure heterodyne holograms were recorded under a number of conditions specified by the magnitude of deflection at the boards tip and the number of accumulated flexure cycles. Data obtained during reconstruction of heterodyne holograms were used to compute displacements and strains along the leads connecting the component to the printed circuit board. The experimental results show that lead displacements were on the order of 1.2 um, while strains were up to 0.054%. The results obtained in this study will be used as input to finite element models of computer microcomponents.

Time average holography in vibration analysis

This paper deals with the quantitative interpretation of time-average holograms of vibrating objects. It is shown that the images obtained during reconstruction of such holograms are modulated by a system of fringes described by the square of the zero-order Bessel function of the first kind. A procedure for quantitative interpretation of these fringes is described and illustrated with examples. The experimental results, obtained directly from the time-average holograms, show good agreement with the exact solution of the differential equation of motion based on the beam theory and with the mode shapes determined by the finite element modeling of the vibrating beam.

Novel optoelectronic methodology for testing of MOEMS

Continued demands for delivery of high performance micro-optoelectromechanical systems (MOEMS) place unprecedented requirements on methods used in their development and operation. Metrology is a major and inseparable part of these methods. Optoelectronic methodology is an essential field of metrology. Due to its scalability, optoelectronic methodology is particularly suitable for testing of MOEMS where measurements must be made with ever increasing accuracy and precision. This was particularly evident during the last few years, characterized by miniaturization of devices, when requirements for measurements have rapidly increased as the emerging technologies introduced new products, especially, optical MEMS. In this paper, a novel optoelectronic methodology for testing of MOEMS is described and its applications are illustrated with representative examples. These examples demonstrate capability to measure submicron deformations of various components of the micromirror device, under operating conditions, and show viability of the optoelectronic methodology for testing of MOEMS.