Eugene R. Koehl

Passive millimeter-wave imaging with compressive sensing

Abstract. Passive millimeter-wave (PMMW) imagers using a single radiometer, called single pixel imagers, employ raster scanning to produce images. A serious drawback of such a single pixel imaging system is the long acquisition time needed to produce a high-fidelity image, arising from two factors: (a) the time to scan the whole scene pixel by pixel and (b) the integration time for each pixel to achieve adequate signal to noise ratio. Recently, compressive sensing (CS) has been developed for single-pixel optical cameras to significantly reduce the imaging time and at the same time produce high-fidelity images by exploiting the sparsity of the data in some transform domain. While the efficacy of CS has been established for single-pixel optical systems, its application to PMMW imaging is not straightforward due to its (a) longer wavelength by three to four orders of magnitude that suffers high diffraction losses at finite size spatial waveform modulators and (b) weaker radiation intensity, for example, by eight orders of magnitude less than that of infrared. We present the development and implementation of a CS technique for PMMW imagers and shows a factor-of-ten increase in imaging speed.

Passive Millimeter-Wave Dual-Polarization Imagers

We have developed two passive millimeter-wave imagers for terrestrial remote sensing: one is an integrated imaging and spectroscopy system in the 146-154-GHz range with 16 channels of 500-MHz bandwidth each, and the other is a single-channel dual-polarized imaging radiometer in the 70-100-GHz range. The imaging in both systems is implemented through translation of a 15-cm Gaussian dielectric imaging lens. We compared the outdoor images of objects such as car, vegetation, sky, and ground by both the systems under various weather conditions, including clear, cloudy, and rainy times. A ray-tracing simulation with radiative transfer equation was used to quantify the polarization diversity of the acquired images.

Millimeter wave detection of nuclear radiation: An alternative detection mechanism

We present a nuclear radiation detection mechanism using millimeter waves as an alternative to conventional detection. It is based on the concept that nuclear radiation causes ionization of air and that if we place a dielectric material near the radiation source, it acts as a charge accumulator of the air ions. We have found that millimeter waves can interrogate the charge cloud on the dielectric material remotely. This concept was tested with a standoff millimeter wave system by monitoring the charge levels on a cardboard tube placed in an x-ray beam.

Passive Millimeter Wave Imaging and Spectroscopy System for Terrestrial Remote Sensing

We have built a passive millimeter wave imaging and spectroscopy system with a 15-channel filter bank in the 146-154 GHz band for terrestrial remote sensing. We had built the spectroscopy system first and have now retrofitted an imaging element to it as a single pixel imager. The imaging element consisted of a 15-cm-diameter imaging lens fed to a corrugated scalar horn. Image acquisition is carried out by scanning the lens with a 2-axis translation stage. A LabVIEW-based software program integrates the imaging and spectroscopy systems with online display of spectroscopic information while the system scans each pixel position. The software also allows for integrating the image intensity of all 15 channels to increase the signal-to-noise ratio by a factor of ~4 relative to single channel image. The integrated imaging and spectroscopy system produces essentially 4-D data in which spatial data are along 2 dimensions, spectral data are in the 3rd dimension, and time is the 4th dimension. The system performance was tested by collecting imaging and spectral data with a 7.5-cm-diameter and 1m long gas cell in which test chemicals were introduced against a liquid nitrogen background.

Nuclear Radiation-Induced Atmospheric Air Breakdown in a Spark Gap

We have investigated the effect of pre-ionization by a radioactive -ray source on the atmospheric air breakdown conditions in a high-voltage spark gap. A standoff millimeter-wave (mmW) system was used to monitor the breakdown properties. A decrease in breakdown threshold was observed with an increase of radiation dose. We attribute this to a space charge-controlled electron diffusion process in a cloud of radiation-induced ion species of both polarities. The space charge-dependent diffusion coefficient was determined from the measurement data. In addition, we found that the breakdown process shows random spikes with Poisson-like statistical feature. These findings portend the feasibility of remote detection of nuclear radiation using high-power mmWs.

NDE Technology for Ceramic Composites

Installation of gas turbine components made of ceramic matrix composite (CMC) materials, which have limited test bed data bases, can put test engines at risk. Further, changes in properties of the materials of these components have been shown to occur with exposure. Risks to the engine can be mitigated through the application of proper nondestructive inspection methods. Further, while still under development, proper application of certain nondestructive evaluation (NDE) technologies seem likely to be able to provide data that can be correlated to retained strength or other properties of these composite materials. If sufficient data were available informed decisions could be made regarding reuse, repair or replace with appropriate NDE. Over the past fourteen years, Argonne National Laboratory (ANL), has been developing various NDE methods specifically for CMC materials. These NDE technologies include: infrared based thermal imaging, air-coupled ultrasonic approaches, high spatial resolution x-ray computed tomography and more recently optical coherence tomography and guided plate waves. This paper will review the developments of these NDE technologies and will provide results with collaboration from engine and laboratory materials tests.Copyright

Development of nondestructive evaluation methods for hot gas filters

AbstractRigid ceramic hot gas candle filters are currently under development for high-temperature hot gas particulate cleanup in advanced coal-based power systems. The ceramic materials for these filters include monolithics (usually non-oxides), oxide and non-oxide fiber-reinforced composites, and recrystallized silicon carbide. A concern of end users in using these types of filters, where over 3000 may be used in a single installation, is the lack of a data base on which to base decisions for reusing, replacing or predicting remaining life during plant shutdowns. One method to improve confidence of usage is to develop nondestructive evaluation (NDE) technology to provide surveillance methods for determination of the extent of damage or of life-limiting characteristics such as thermal fatigue, oxidation, damage from ash bridging such as localized cracking, damage from local burning, and elongation at elevated temperatures. Although in situ NDE methods would be desirable in order to avoid disassembly of th...

Determining thermal diffusivity and defect attributes in ceramic matrix composites by infrared imaging

Ceramic matrix composites are being developed for numerous high temperature applications, including rotors and combustors for advanced turbine engines, heat exchanger and hot-gas filters for coal gasification plants. Among the materials of interest are silicon-carbide-fiber- reinforced-silicon-carbide (SiC(f)/SiC), silicon-carbide-fiber-reinforced-silicon-nitride (SiC(f)/Si3N4), aluminum-oxide-reinforced-alumina (Al2O3(f)/Al2O3, etc. In the manufacturing of these ceramic composites, the conditions of the fiber/matrix interface are critical to the mechanical and thermal behavior of the component. Defects such as delaminations and non-uniform porosity can directly affect the performance. A nondestructive evaluation (NDE) method, developed at Argonne National Laboratory has proved beneficial in analyzing as-processed conditions and defect detection created during manufacturing. This NDE method uses infrared thermal imaging for full-field quantitative measurement of the distribution of thermal diffusivity in large components. Intensity transform algorithms have been used for contrast enhancement of the output image. Nonuniformity correction and automatic gain control are used to dynamically optimize video contrast and brightness, providing additional resolution in the acquired images. Digital filtering, interpolation, and least-squares-estimation techniques have been incorporated for noise reduction and data acquisition. The Argonne NDE system has been utilized to determine thermal shock damage, density variations, and variations in fiber coating in a full array of test specimens.

Microwave Remote Sensing of Ionized Air

We present observations of microwave scattering from ambient room air ionized with a negative ion generator. The frequency dependence of the radar cross section of ionized air was measured from 26.5 to 40 GHz (Ka-band) in a bistatic mode with an Agilent PNA-X series (model N5245A) vector network analyzer. A detailed calibration scheme is provided to minimize the effect of the stray background field and system frequency response on the target reflection. The feasibility of detecting the microwave reflection from ionized air portends many potential applications such as remote sensing of atmospheric ionization and remote detection of radioactive ionization of air.

Conceptual Design of a Pilot-Scale Pyroprocessing Facility

Abstract Argonne National Laboratory and Merrick & Company developed the conceptual design of a pilot-scale (100 T/year) pyroprocessing facility for the treatment of used fuel generated by commercial light water reactors and subsequent treatment of waste streams generated during the process. The primary purpose of this study was to perform sufficient engineering for the pilot facility conceptual design so that credible capital and operating cost estimates could be developed. Initial safety, safeguards, and security assessments were also completed to provide a detailed evaluation in these areas that can significantly affect both capital and operating costs. Electrorefining-based pyroprocessing resulted in a compact hot-cell facility with few process equipment systems. The process equipment and support systems were estimated to cost