Thomas Hierl

Infrared imaging of buried heat sources and material nonuniformities

Using a recently developed PtSi IR focal plane array imaging system, ZAE Bayern develops new IR measurement techniques for industrial and medical applications. In this paper we present three examples for the analysis of material nonuniformities and a buried heat source. A new method for detecting the surface moisture of porous solids has been developed. The water content at the surface is determined by using an infrared filter tuned to the water-specific spectral line at (lambda) equals 2.92 micrometer. With a numerical simulation of the water transport we determined the effective diffusion coefficient. Surface temperature transients are recorded after a short infrared irradiation excitation at a frame rate of 50 Hz to localize voids or blisters in solid materials. The method is tested for a glass substrate. The analysis is in quantitative agreement with the test configuration. Furthermore we show that it is possible to localize leaks in heat pipelines a few meters below the earth surface by dynamical infrared imaging techniques.

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.

Thermal infrared microscopy (TIM) with sub-10-μm spatial resolution

We present thermal IR microscopy systems suitable for a spatial resolution below 10micrometers . This resolution close to the fundamental limit is achieved using high resolution FPA - IR cameras, a high speed microscopy optic and acquisition of multiple frames which are shuffled by software in real time. Some fundamental consideration to gain insight into the task of thermal microscopy are briefed. The minimum resolvable temperature and the noise equivalent temperature difference both are a function of thermal diffusivity i.e. material properties, integration time and optics. The basic relationships are explained using numerical modeling. Based on our considerations and knowledge we developed different TIM-Systems, each having specific advantages and are therefore more or less suitable for certain applications. A high spatial temperature or thermal resolution is necessary for different materials under investigation. Examples demonstrate the unique capabilities of the innovative systems and give a glance of the various technical applications of TIM systems.

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.

Defect localization in CuInSe2 solar modules by thermal infrared microscopy

In this paper the IR Microscopy Thermosensoric Defect Localization method ((mu) -TDL) is presented. This technique is based on a novel IR microscopy lens which permits to take IR images with a spatial resolution of better than 10 micrometer, which is close to the theoretical limit. The (mu) -TDL method is demonstrated on defective CuInSe2 solar modules consisting of several solar cells serially interconnected and having solar efficiencies considerably below the average. By using the accurate localization of the defects by the (mu) -TDL method further investigations were performed and the origin for the defect was found. The (mu) -TDL method is also applicable to solar cells and modules consisting of other materials, such as amorphous Si or CdTe. The (mu) TDL method is suitable for the solar module development as well as for non- destructive production control.

Ultrathin Ir3Si4 silicide films for infrared detection

A novel silicide phase Ir3Si4 suitable for medium wave infrared (MWIR, (lambda) equals 3 micrometer - 5 micrometer) detection was prepared and characterized. Iridium is deposited on p-Si(100) substrates at various temperatures in the range from 420 degrees Celsius to 485 degrees Celsius under ultrahigh vacuum conditions. The metallic phase is formed by interdiffusion and reaction of Ir and Si. The phase is identified to Ir3Si4 by Rutherford backscattering spectrometry. Ir3Si4 films thinner than 10 nm show Schottky barrier heights as low as (Phi) Ph equals 165 meV for photoemission into the Si valence band. Dark current densities are measured to jR less than 1 (DOT) 10-9 A cm-2 (at reverse bias 5 V and detector operation temperature 50 K). The infrared test detectors exhibit responsivities (lambda equals 4 micrometer) of up to 20 mA W-1 at 5 V. The temperature resolution of the test detectors -- front illuminated and without antireflection coating and optical resonator -- is improved to a noise equivalent temperature difference NETD300K approximately equals 53 mK (at 50 Hz) compared to 75 mK of equivalent test detectors fabricated by common HV-PtSi deposition.

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.

Evaluation of infrared focal-plane-array detectors

Several staring infrared focal plane arrays differing in size and in detector material are investigated. The temporal noise and the correctability, c, defined as the ratio of the spatial inhomogeneity to the temporal noise, are determined in order to quantify the temporal-noise-equivalent temperature difference and the inhomogeneity-equivalent temperature difference, after various correction procedures, Additionally another figure of merit, the long-term stability time, τ lts , which indicates the transient degradation of the correctability of a focal-plane-array detector is measured. This time quantifies the duration after a nonuniformity correction during which the spatial noise increases to values higher than that of the temporal noise.

Localization of methane distributions by spectrally tuned infrared imaging

We present a novel method, the Gas Imaging (GIm) method, developed for the localization of gas distributions in the atmosphere. The method is suitable for the detection of a gases which exhibit at least one absorption line in the IR spectral range. In this paper the GIm method is demonstrated for methane released into the atmosphere from leaks along natural gas pipelines. Methane distributions in the atmosphere around the leaky pipeline are detected and visualized by spectrally tuned IR imaging. In contrast to conventional techniques which utilize laser radiation sources or scanning, we irradiate the overall region under investigation by 1 kW halogen lamps. The scene background is subtracted by a real-time computer evaluation of the image. The methane gas emitted from the leak creates a flickering cloud in the image which is easily recognized. Methane concentrations as low as 0.03 percent by volume are visible. The method was successfully tested under realistic conditions on a buried pipeline by a natural gas provider.