CONTACT or Consortium for Nanomaterials for Aerospace Commerce and Technology is a cooperative
program between the Air Force Research Laboratory and seven Texas universities focused on four research areas
in aerospace. This paper summarizes recent developments in one of those areas, sensors, for eventual use in
aircraft and spacecraft. We report direct measurement of spectrally selective absorption properties of PbSe and
PbS colloidal quantum dots (CQDs) in Si nanomembrane photonic crystal cavities on flexible plastic
polyethylene terephthalate (PET) substrates. The interaction of CQD absorption with photonic crystal Fano
resonances is presented both analytically and experimentally for use in wavelength selective sensors.
Nanotechnology is impacting the future of the military and aerospace. The increasing demands for high performance
and property-specific applications are forcing the scientific world to take novel approaches in developing programs and
accelerating output. CONTACT or Consortium for Nanomaterials for Aerospace Commerce and Technology is a cooperative nanotechnology research program in Texas building on an infrastructure that promotes collaboration between universities and transitioning to industry. The participants of the program include the US Air Force Research
Laboratory (AFRL), five campuses of the University of Texas (Brownsville, Pan American, Arlington, Austin, and
Dallas), the University of Houston, and Rice University. Through the various partnerships between the intellectual
centers and the interactions with AFRL and CONTACT's industrial associates, the program represents a model that addresses the needs of the changing and competitive technological world. Into the second year, CONTACT has expanded to twelve projects that cover four areas of research: Adaptive Coatings and Surface Engineering, Nano Energetics, Electromagnetic Sensors, and Power Generation and Storage. This paper provides an overview of the CONTACT program and its projects including the research and development of new electrorheological fluids with nanoladen suspensions and composites and the potential applications.
Nanotechnology is expected to provide the fundamental basis of the next two generations of
products and processes. Impacts for applications are already being felt in many fields, and there is
interest especially in the aerospace industry, where performance is a major driver of decisions for
applications. Four areas are receiving special emphasis in a program aimed at the Air Force's
strategic focus on materials. The emphasis includes adaptive coatings and surface engineering,
nanoenergetics, electromagnetic sensors, and power generation and storage. Seven universities in
Texas have initiated the CONTACT program of focused research including nine projects in the first
year, with plans for expansion in subsequent years. This paper discusses the focus, progress, and
plans for the second year and opportunities for industry input to the scope and content of the
research. A new model for the creation and guidance of research programs for industry is presented.
The new approach includes interaction with the aerospace industry and the Air Force that provides a
focus for the research. Results to date for the new method and for the research are presented. A
discussion of nanoengineering technology transition into the aerospace industry highlights the
mechanisms for enhancing the process and for dealing with intellectual property.
The detection of trace quantities of aromatic compounds is important to defense and security
applications, including the detection of CB agents, explosives, and other substances. These pose
threats to forces and the environment. This paper explores an approach to the detection and
identification of quantities as little as single molecules of explosives. It can in principle provide
instant warning.
Apertureless near-field scanning optical microscopy (ANSOM) is one of several promising
methods for obtaining spatial resolution below the diffraction limit at various wavelengths,
including in the terahertz regime. By scattering incident light off the junction between a probe
with a sub-wavelength tip and the surface of a sample, spatial resolution on the order of the tip
size can be obtained. For terahertz time-domain spectroscopy where the wavelength-limited
resolution is ~1 millimeter, this is a significant advantage.
In the case of a sufficiently small probe tip and a thin metallic substrate, plasmonic interaction
between the tip and sample provides an enhancement of the near-field in the junction. This
effect is dramatically enhanced for nanometer-scale metal layers, since surface plasmon states
from both sides of the film can contribute to the overall field enhancement.
We present preliminary results of THz plasmonic field enhancements, using a thin (500 nm) gold
film evaporated on glass. We observe an enhancement in the scattered THz wave, which we
attribute to the large density of plasmonic states extending throughout the THz range. This result
indicates a route to single-molecule spectroscopy at terahertz frequencies.
The flash x-ray systems developed at the University of Texas at Dallas (UTD) center around two critical subassemblies: (1) a Blumlein pulsed power source, and (2) an x-ray diode properly designed and matched to the pulse forming line. The pulse generator consists of either a single or several traxial Blumleins. For multiple lines, Blumleins are stacked in series at one end and charged in parallel and synchronously commutated with a single switching element at the other end. Extensive characterizations of these Blumlein pulsers have been performed over the past several years. Results indicate that they are capable of producing high power waveforms with risetimes and repetition rates in the range of 0.1-50 ns and 1-300 Hz, respectively, using a conventional thyratron, spark gap, or photoconductive switch. Blumlein pulsers switched by a thyratron or a spark gap have been used to drive x-ray diode loads with different characteristics and discharge geometries and high dose rates of x-rays with pulse durations in the range 3-20 ns have been obtained. In this report the technology and characteristics of these Blumlein based flash x-ray devices are reviewed. Prospects for producing ultra-fast x-ray pulses utilizing photoconductively-switched Blumlein devices are discussed.
Photoconductive switching of the stacked Blumlein pulsers, developed at the Univ. of Texas at Dallas (UTD), currently produces high power, nanosecond pulses with risetimes on the order of 200 ps. The device has a compact geometry and is commutated by a single GaAs photoconductive semiconductor switch (PCSS) triggered by a low power laser diode array. Filamentation of the conductivity associated with high gain GaAs switches produces such high current density that the switches are damages near the metal-semiconductor interface and the lifetime is limited. The semiconductor properties of amorphic diamond can be employed to improve the PCSS longevity by coating the switch cathode or anode areas or both. For example if the switch cathode is coated, the tunneling of electrons from amorphic diamond to GaAs during the off-state stage of PCSS operation provides pre-avalanche sites that diffuse conduction current upon switch activation. This report presents the progress toward improving the high gain switch operation and lifetime by advanced treatments with amorphic diamond coatings. A significant improvement in switch lifetime is demonstrated by testing the diamond-coated switch performance in a stacked Blumlein prototype pulser.
KEYWORDS: High power microwaves, Antennas, Dielectrics, Microwave radiation, Diodes, Picosecond phenomena, Directed energy weapons, Switches, Silicon carbide, Systems modeling
This paper describes current projects in High Power Microwave (HPM) source development within the Air Force's basic research program managed by the Air Force Office of Scientific Research and conducted at the Air Force Research Laboratory's Directed Energy Directorate and at universities throughout the U.S. and the world. Studies are proceedings along two separate paths: narrow band high power microwave tubes and ultra-wide band sources. While these two paths invoke drastically different physical mechanisms that produce microwave radiation qualitatively distinct from each other, there are many common technical challenges. The focus of this report will be the active research in the Air Force ultra-wide band program, but many of the technical improvements being sought for improved materials, high voltage breakdown mitigation, and advanced design techniques will help the entire high power microwave program. The paper concludes with a brief discussion of the future of HPM research.
This paper describes the progress made in recent years in addressing the technological challenges that must be met to achieve high power microwave sources for a variety of purposes. Efforts are underway to increase the pulse width and power of high power microwave sources. Research in narrow band sources has progressed toward the junction of high power and conventional tube technology. Ultra-wide band technology is at present focused on a number of promising avenues that will improve switching and antennas that promise to increase substantially the field strength projected at substantial range from the antenna. Efforts in both narrow band and ultra-wide band technology also seek to explore the potential for operating at increased pulse repetition frequency. This paper discusses these efforts and gives recommendations for future investment of research talent to these ends.
Presently there is a substantial effort in the US and in laboratories around the world in intense microwave source research. This paper reviews the current sate of the art and technical barriers to further progress in producing higher power and higher energy pulses of radiofrequency radiation. The paper also suggests research avenues that offer the potential for further improvements in these sources. Key recent publications and conference proceedings are cited that provide a guide to current thought and recent advances in high power microwave source research.
This paper describes progress in a cooperative research program of national scale that is focused on crucial research issues in the development of high energy microwave sources. These have many applications in the DOD and industry. The program includes participation by and cooperation among University, Industrial and Government research laboratories.
The generation of Ultra-Wide Band Pulses nanoseconds is a challenging problem that involves generating pulses with 100 pico-second rise times and voltage of 500 kV with pulse widths of the order of less than one to a few nanoseconds. A critical step involves switching high voltages with precision. The use of both gas and oil for the switching insulating medium have been accomplished with varying results. The Phillips Laboratory is pursuing both media in the gas switched Hindenburg series of pulsers and in the study of oil switches that promise good performance in compact packages. This paper reports on progress in gas switching associated with the new H-5 pulser and with the use of earlier Hindenburg pulsers to investigate the UWB properties of oil switches. We compare the design strategies and techniques of oil and gas switching in the context of pulsers of interest.
KEYWORDS: Microwave radiation, Plasma, High power microwaves, Electron beams, Plasma generation, Explosives, Pulsed power, Medium wave, Dielectrics, Oscillators
The problem of pulse shortening was raised at this conference two years ago, and in the intervening time, efforts to address the problem have been initiated. There is already some significant progress at our laboratory and at some others. This paper reviews the progress and describes the directions of research and industrial efforts underway at this time. The subject is an exciting one in view of the potential applications that would benefit from the extension of pulse length in Gigawatt class microwave tubes. The paper discusses some of the implications of success in this regard.
This paper reviews the experimental research accomplished to date relating to catastrophic electromagnetic breakdown in certain media that are interesting for high voltage, short temporal pulse width pulsers. The authors begin with the classic work of Felsenthal and Proud and follow experimental results into the present day. The paper considers not only the experimental results of short pulse radio frequency breakdown but also the relationship with long pulse RF breakdown. The paper presents some recent measurements as well as reviewing the previous work performed in our laboratories and elsewhere.
KEYWORDS: Oscillators, High power microwaves, Medium wave, Magnetism, Microwave radiation, Electron beams, Pulsed power, Antennas, Plasma, Analytical research
The Magnetically Insulated Line Oscillator (MILO) is a cross field tube that has been studied analytically and experimentally by researchers in several laboratories. The tube is remarkable in that it requires no externally imposed magnetic field, but rather it can be designed to provide a sufficient self field in the relativistic electron beam to guide the electrons. The MILO can be made to operate at high power in the power range above 100 MW. It has been observed that the tube experiences a diminution in pulse width when operated at successively higher powers. This phenomenon, called variously pulse shortening or pulse tearing is also observed in conventional tubes designed for lower power. The process of conditioning commercial tubes is a costly part of the production of high power tubes for applications including particle accelerators. In the case of high power microwave tubes operating in excess of 100 MW, it presents a limitation on the energy that can be extracted from these tubes. This paper describes work performed at the Phillips Laboratory on a relatively high power MILO and discusses the phenomena that may account for this behavior.
This paper introduces a new cooperative research program of national scale that is focused on crucial research issues in the development of high energy microwave sources. These have many applications in the DOD and industry. The Air Force Office of Scientific Research (AFOSR), in coopertaion with the Phillips Laboratory, the Naval Research Laboratory, and the Army Research Laboratory, has established a tri-service research consortium to investigate novel high energy microwave sources. The program is part of the DODs 'Multidisciplinary University Research Initiative' and will be funded at a rate of $DLR3.0M per year for up to five years. All research performed under this program will be unclassified. Under its auspices, HPM scientists at nine US universities will be attacking twenty-two separate research projects under the leadership of Neville Luhmann at UC-Davis, Victor Granatstein at Maryland, Magne Kristiansen at Texas Tech, Edl Schamiloglu at New Mexico, John Nation at Cornell, Ned Birdsall at UC-Berkeley, George Caryotakis at Standord, Ronald Gilgenbach at Michigan, and Anthony Lin at UCLA. To facilitate the rapid transition of research results into the industrial community, formal collaborative subcontracts are already in place with James Benford at Physics International, Carter Armstrong at Northrop, and Glen Huffman at Varian Associates. Although this new program officially only came into existence in mid-March of this year, it builds on over a decade of microwave research efforts funded by the plasma physics office at AFOSR. It also is synergistic with the ongoing Tri-Service Vacuum Electronics Initiative led by Robert Parker of NRL as well as with the AFOSR's and Rome Laboratory's long standing Advanced Thermionic Research Initiative. An overview will be given of the broad spectrum of research objectives encompassed by NUCOMR. Areas of collaboration and technology transfer will be highlighted. The areas in which the three university consortia will conduct research are described, and the connectivity to industry and to the DOD laboratories are discussed. There are a number of critical technical barriers to reaching the desired goals for high power and high energy sources. These are discussed and the planned focus of research to resolve them is also presented.
Ultra-wideband emitters are of interest for a variety of potential applications that range from radar transmitters to communications applications. This technology is of current interest to the USAF Phillips Laboratory where theoretical and experimental efforts have been underway for a number of years. Research into the production of ultra-wideband sources at the Phillips Laboratory has been accomplished along several different technology lines. The approaches include three main thrusts: 1) very powerful hydrogen spark gap pulsers, 2) compact hydrogen gas switches in conjunction with high gain ultra-wideband antennas and, 3) solid state switched array antennas. This paper reviews the progress-to-date along these lines and identifies some pacing research obastacles that limit further improvements.
George Huttlin, Michael Bushell, D. Conrad, David Davis, K. Ebersole, Daniel Judy, P. Lezcano, Marc Litz, Nino Pereira, Brian Ruth, Douglas Weidenheimer, Forrest Agee
Work begun in 1986 is continuing on the reflex-diode oscillator mounted on one of the Aurora 10-MV 22- ci pulsers. The most recent work extracted microwaves radially into six rectangular WR-975 waveguides at the virtual cathode and into two additional arms a few meters downstream. Two of the waveguides were open-ended and radiated into an anechoic chamber. Diagnostics for radially extracted microwave energy included directional couplers card calorimeters and free-field sensors. The peak output is ''-50 3 per arm for the frequencies below 1. 0 (3Hz. Parameter variations have included the anode/cathode spacing and the positioning of a second anode foil. Dosimetry and electric field measurements were made to study beani dynamics in the drift region. Thus far the measurements suggest that our virtual cathode is weak. 1.
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