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Title: Speckle in Active Millimeter-Wave and Terahertz Imaging and Spectroscopy

Abstract

Wideband millimeter-wave imaging techniques and systems have been developed at PNNL for concealed weapon detection and other applications. These techniques evolved from single-frequency millimeter-wave holographic imaging methods to wideband three-dimensional planar and cylindrical techniques and systems. The single-frequency holographic method was derived from optical and ultrasonic holography techniques. Speckle is highly significant in this case, and is caused by constructive and destructive interference from multiple scattering locations or depths within a single resolution cell. The wideband three-dimensional techniques developed at PNNL significantly reduce the speckle effect through the use of high depth resolution obtained from the wide bandwidth of the illumination. For these techniques, speckle can still be significant in some cases and affect image quality. In this paper, we explore the situations in which speckle occurs and it's relationship to lateral and depth resolution. This will be accomplished through numerical simulation and demonstrated in actual imaging results. Speckle may also play a significant role in altering reflection spectra in wideband terahertz spectra. Reflection from rough surfaces will generate speckle, which will result in significant variation in the reflection spectrum as measured over very wide bandwidths. This effect may make if difficult to interpret spectral absorption features from general reflectancemore » data. In this paper, physical optics numerical simulation techniques will be used to model the reflection from arbitrary random surfaces and explore the effect of the surface on the reflection spectra and reconstructed image. Laboratory imaging and numerical modeling results in the millimeter-wave through the terahertz frequency ranges are presented.« less

Authors:
; ;
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
989064
Report Number(s):
PNNL-SA-54201
TRN: US201019%%181
DOE Contract Number:
AC05-76RL01830
Resource Type:
Conference
Resource Relation:
Conference: Passive Millimeter-Wave Imaging Technology X, 6548:Paper No. 654809
Country of Publication:
United States
Language:
English
Subject:
47 OTHER INSTRUMENTATION; HOLOGRAPHY; SPECTROSCOPY; WEAPONS; DETECTION; IMAGES; NOISE; RESOLUTION; COMPUTERIZED SIMULATION; SURFACES; ROUGHNESS; REFLECTION; Millimeter Waves; Cylindrical Imaging; Imaging; Holography; Personnel Surveillance; Screening

Citation Formats

Sheen, David M., McMakin, Douglas L., and Hall, Thomas E. Speckle in Active Millimeter-Wave and Terahertz Imaging and Spectroscopy. United States: N. p., 2007. Web. doi:10.1117/12.721323.
Sheen, David M., McMakin, Douglas L., & Hall, Thomas E. Speckle in Active Millimeter-Wave and Terahertz Imaging and Spectroscopy. United States. doi:10.1117/12.721323.
Sheen, David M., McMakin, Douglas L., and Hall, Thomas E. Sun . "Speckle in Active Millimeter-Wave and Terahertz Imaging and Spectroscopy". United States. doi:10.1117/12.721323.
@article{osti_989064,
title = {Speckle in Active Millimeter-Wave and Terahertz Imaging and Spectroscopy},
author = {Sheen, David M. and McMakin, Douglas L. and Hall, Thomas E.},
abstractNote = {Wideband millimeter-wave imaging techniques and systems have been developed at PNNL for concealed weapon detection and other applications. These techniques evolved from single-frequency millimeter-wave holographic imaging methods to wideband three-dimensional planar and cylindrical techniques and systems. The single-frequency holographic method was derived from optical and ultrasonic holography techniques. Speckle is highly significant in this case, and is caused by constructive and destructive interference from multiple scattering locations or depths within a single resolution cell. The wideband three-dimensional techniques developed at PNNL significantly reduce the speckle effect through the use of high depth resolution obtained from the wide bandwidth of the illumination. For these techniques, speckle can still be significant in some cases and affect image quality. In this paper, we explore the situations in which speckle occurs and it's relationship to lateral and depth resolution. This will be accomplished through numerical simulation and demonstrated in actual imaging results. Speckle may also play a significant role in altering reflection spectra in wideband terahertz spectra. Reflection from rough surfaces will generate speckle, which will result in significant variation in the reflection spectrum as measured over very wide bandwidths. This effect may make if difficult to interpret spectral absorption features from general reflectance data. In this paper, physical optics numerical simulation techniques will be used to model the reflection from arbitrary random surfaces and explore the effect of the surface on the reflection spectra and reconstructed image. Laboratory imaging and numerical modeling results in the millimeter-wave through the terahertz frequency ranges are presented.},
doi = {10.1117/12.721323},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Sun Apr 01 00:00:00 EDT 2007},
month = {Sun Apr 01 00:00:00 EDT 2007}
}

Conference:
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  • Active imaging at millimeter and sub-millimeter wavelengths has been developed for security applications including concealed weapon detection. The physical properties that affect imaging performance are discussed along with a review of the current state-of-the-art and future potential for security imaging systems.
  • Consideration is given to quasi-optical power combining techniques, state-of-the-art demonstrated performance, and system issues as they apply to endoatmospheric homing seeker insertion. Quasi-optical power combining is based on combining microwave and millimeter-wave solid-state device power in space through the use of antennas and lenses. It is concluded that quasi-optical power combining meets the severe electrical requirements and packaging constraints of active MMW seekers for endoatmospheric hit-to-kill missiles. The approach provides the possibility of wafer-scale integration of major components for low cost production and offers high reliability. Critical issues include thermal loading and system integration, which must be resolved before themore » quasi-optical power combining technology will be applied to an active MMW seeker. 18 refs.« less
  • Emerging mm-wave and high-speed fiber-optic applications will demand signal and network instrumentation with bandwidths beyond 100 GHz. We have developed nonlinear transmission line (NLTL) pulse generators and NLTL-based sampling circuits with bandwidths exceeding 500 GHz. For on-wafer S-parameter and waveform measurements, we have constructed active probes incorporating an NLTL-based network analyzer (NWA) IC and rugged, low-loss quartz coplanar-waveguide probe tips. The NWA IC itself consists of an NLTL stimulus signal generator and a NLTL-gated directional sampling circuit used to separately measure the incident and reflected waves. Measurements are made with a pulsed (NLTL) stimulus signal with frequency information obtained bymore » Fourier transformation. On-wafer measurements have been demonstrated to 200 GHz.« less
  • Active and passive radiometric imaging techniques have been used at 1.4- and 3-mm wavelengths (220 and 100 GHz) to evaluate their potential use in detecting concealed objects. An evaluation of the techniques includes a particular study of their potential in detecting shielded nuclear materials and explosives carried covertly by personnel. We have previously reported images of metal objects and nuclear shielding materials that were detected when concealed under clothing. These images appear with the human body as background. Detection of contraband by radiometric imaging techniques depends upon the differences in emissivity and reflectivity of the contraband relative to human tissue.more » Explosives, unlike metals and metal composites, generally have high emissivities and low reflectivities that closely approximate those of human tissue making explosives difficult to detect. Samples of several common types of explosives (TNT, Detasheet, C4, and several types of water gels) have been examined at the 1.4- and 3-mm wavelengths using active and passive radiometric techniques.« less
  • Abstract not provided.