Ahigh-performance digital imaging system has been assembled to provide enhanced capabilities for characterizing materials and processes. Highspeed imaging is needed for observation and analysis of such fast dynamic processes as impact fracture (including ballistically induced fracture) in advanced composite materials, dynamic deformation of materials, and hydrodynamic instabilities in jets. Because these dynamic processes occur at diverse temporal and spatial scales, there is a need for an imaging system that can operate at correspondingly diverse frame rates, spatial resolutions, and magnifications, and that is capable of recording various numbers of image frames.

A thorough market search led to the conclusion that no single commercially available electronic camera can satisfy all of the diverse requirements. Therefore, it was decided to satisfy the requirements by building the present high-performance digital imaging system as a combination of three commercially available electronic camera systems that have overlapping resolution, recording-rate, record-length, sensitivity, and other performance characteristics. The resulting assembly is a unique, state-of-the-art, ultrahighresolution/ speed imaging system for quantitative observation and analysis of dynamic processes.

High-spatial-resolution digital imaging at a rate of a million or more frames per second is needed for the analysis of many dynamic processes. Market research revealed that only rotating-mirror charge-coupled-device (CCD) camera systems can satisfy these requirements. The specific commercially available system chosen to satisfy these requirements was a Cordin Model 550 24 high-resolution rotatingmirror CCD camera system, which contains 24 cameras synchronized for imaging at a rate as high as 1.5 million frames per second. The rotating mirror and associated optics distribute incoming light to the cameras in sequence, and the exposure time and recording rate are electronically controlled in accordance with the rotation. Pictures having resolution and dynamic range superior to those recorded by use of a multichannel-plate image intensifier and having exposure times as short as hundreds of nanoseconds can be taken by use of this system.

A capability of imaging at 10 million or more frames per second is needed for ballistic impact experiments. The commercial system chosen to satisfy this requirement was a Cordin Model 214-8 image-intensified gated CCD camera system. In a camera system of this type, an optical subsystem divides the image across multiple channels, thus yielding temporal resolution, at some loss in spatial resolution and sensitivity. Individual channels are activated in sequence to record a series of images separated by very short time intervals. The Model 214-8 system records 8 frames at a minimum interframe and exposure time of 25 nanoseconds.

A digital camera system capable of making 1,000-frame or longer movies of moving objects at rates greater than 1,000 frames per second and spatial resolutions of at least 1,000 pixels along each axis is needed for visualization and analysis of electrospinning processes. Also needed are software that supports making of video recordings and software for performing two- and threedimensional particle-velocity and -trajectory analyses. The Redlake MotionXtra HG 100K high- speed color complementary metal oxide semiconductor (CMOS) camera system was found to satisfy these requirements and, accordingly, was incorporated into the present system. A control computer for this camera was acquired separately.

This work was done by Y. Dzenis and R. Feng of the University of Nebraska for the Air Force Research Laboratory. For more information, download the Technical Support Package (free white paper) at www.defensetechbriefs.com/tsp under the Physical Sciences category. AFRL-0029


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Imaging System for Characterizing Materials and Processes

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This article first appeared in the August, 2007 issue of Defense Tech Briefs Magazine.

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