Oliver Schreer

The Preparation of Electrohydrodynamic Bridges from Polar Dielectric Liquids

Horizontal and vertical liquid bridges are simple and powerful tools for exploring the interaction of high intensity electric fields (8-20 kV/cm) and polar dielectric liquids. These bridges are unique from capillary bridges in that they exhibit extensibility beyond a few millimeters, have complex bi-directional mass transfer patterns, and emit non-Planck infrared radiation. A number of common solvents can form such bridges as well as low conductivity solutions and colloidal suspensions. The macroscopic behavior is governed by electrohydrodynamics and provides a means of studying fluid flow phenomena without the presence of rigid walls. Prior to the onset of a liquid bridge several important phenomena can be observed including advancing meniscus height (electrowetting), bulk fluid circulation (the Sumoto effect), and the ejection of charged droplets (electrospray). The interaction between surface, polarization, and displacement forces can be directly examined by varying applied voltage and bridge length. The electric field, assisted by gravity, stabilizes the liquid bridge against Rayleigh-Plateau instabilities. Construction of basic apparatus for both vertical and horizontal orientation along with operational examples, including thermographic images, for three liquids (e.g., water, DMSO, and glycerol) is presented.

Real-time image processing and fusion for a new high-speed dual-band infrared camera

A dual-band infrared camera system based on a dual-band quantum well infrared photodetector (QWIP) has been developed for acquiring images from both the mid-wavelength (MWIR) and long-wavelength (LWIR) infrared spectral band. The system delivers exactly pixel-registered simultaneously acquired images. It has the advantage that appropriate signal and image processing permit to exploit differences in the characteristics of those bands. Thus, the camera reveals more information than a single-band camera. It helps distinguishing between targets and decoys and has the ability to defeat many IR countermeasures such as smoke, camouflage and flares. Furthermore, the system permits to identify materials (e.g. glass, asphalt, slate, etc.), to distinguish sun reflections from hot objects and to visualize hot exhaust gases. Furthermore, dedicated software for processing and exploitation in real-time extends the application domain of the camera system. One component corrects the images and allows for overlays with complementary colors such that differences become apparent. Another software component aims at a robust estimation of transformation parameters of consecutive images in the image stream for image registration purposes. This feature stabilizes the images also under rugged conditions and it allows for the automatic stitching of the image stream to construct large mosaic images. Mosaic images facilitate the inspection of large objects and scenarios and create a better overview for human observers. In addition, image based MTI (moving target indication) also for the case of a moving camera is under development. This component aims at surveillance applications and could also be used for camouflage assessment of moving targets.

Dual-band camera system with advanced image processing capability

A dual-band IR camera system based on a dual-band QWIP focal plane array in 384x288x2 format was developed. The camera delivers exactly pixel-registered simultaneously acquired images and exhibits an excellent NETD of <30 mK at an integration time of less than 10 ms. It is equipped with Camera Link and Gigabit Ethernet data interface and is connected to and operated from a personal computer. The camera is equipped with a special dual-band, dual-field-of-view lens (14.6 degree and 2.8 degree diagonal FOV). Radiometric calibration was performed for real quantitative comparison of MWIR and LWIR radiant power. The system uses special software to extract and visualize the - often quite small - differences of MWIR and LWIR images. The software corrects and processes the images and permits to overlay them with complementary colors such that differences become apparent and can easily be perceived. As a special feature, the system has advanced software for real-time image processing of dynamic scenes. It has an image stabilization feature which compensates for the movement of the camera sensor relative to the scene observed. It also has a powerful image registration capability for automatic stitching of live images to create large mosaic images. The camera system was tested with different scenes and under different weather conditions. It delivers large-format sharp images which reveal a lot of details which would not be perceptible with a single-band IR camera. It permits to identify materials (e.g. glass, asphalt, slate, etc.), to distinguish sun reflections from hot objects and to visualize hot exhaust gases.

Inspection of laser-seam welds in automobile manufacturing

Recent developments in infrared camera technology, testing methods and data processing algorithms have brought significant progress for high resolution spatial and temporal analysis of thermal radiation. Together with industry standard automation technology and specific infrared image data processing it became possible to non destructively inspect laser welded seams and other types of joints using heat flux analysis subsequent to active thermal excitation. High thermal diffusion coefficients of the usually metallic samples under test make the availability of high-speed infrared cameras as a key hardware component indispensable. Since high-speed infrared cameras with frame rates of at least 500 Hz have become available for commercial applications, non-destructive testing systems with a new class of performance were designed, manufactured, and implemented at industrial sites. Heat flux analysis as a new and robust method of non-destructive testing has been implemented for various types of equipment, ranging from off-line tools for laboratory use to automated robot based systems enabling fast and operator-free in-line inspection. Depending on environment, implementation surroundings, and geometry of objects to be inspected, different types of pulsed or continuous operating heat sources (e.g. flash light, laser, ...) are selected. Due to its outstanding industrial relevance some examples of non-destructive testing of laser welded seams in automobile manufacturing are shown.

Real-time processing and hard disk storage of high-bandwidth IR FPA data streams

This article presents strategies, implementations and applications of handling infrared FPA data streams at high data rates on most recent standard PCs. Those data streams require maximum data throughput of modern PCs. Real-time non-uniformity correction (gain and offset correction) of those high speed infrared FPA data streams will be discussed. The performance of PC based systems for Real-Time data Acquisition and data Hard Disk Storage (RT-AHDS) will be described in more detail. Some of the Thermosensorik systems for use in research and development, as well as in in-line testing systems in industry for various applications will be presented. This paper describes some of the demanding tasks for the PC based concept, as well as some major advantages.

Multispectral high-speed midwave infrared imaging system

For evaluation of the possibilities and potentials of multispectral infrared imaging a filter wheel camera system was developed. The camera is designed for high speed operation permitting acquisition of subsequent MWIR spectral images in short time. Potential applications of a multispectral camera are temperature measurement, gas and fire visualisation. Some experiments were performed to validate the applicability of the camera system.

Resolution enhancement of infrared imaging by triggered image acquisition with ultrashort integration time

Infrared cameras are sometimes not fast or sensitive enough when short events with low temperature dynamics have to be measured. Thermal imaging systems sensitive at 3micrometers - 5micrometers usually operate with integration times of 1 ms and more for room temperature scene measurements. Thus very short events with low dynamics cannot be resolved with sufficient temporal and thermal resolution. Advanced measurement techniques which make use of triggering, summing or even lock-in must be used then. We present an infrared imaging system, based on a high quantum efficiency 384x288 pixel HgCdTe FPA detector, for temperature measurements of gasoline sprays ejected out of injection nozzles for automobile motors. The temperature distribution of the gasoline jet while ejected out of a injection nozzle (the process is finished after 2 ms) is urged to be known with high accuracy at high temporal and spatial resolution. With highly advanced instrumentation we are able to measure with both high temporal and temperature resolution. The system described here helps automotive engineers to better understand and improve the combustion process in modern motors.