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Displaying 526 - 550 of 1560

A Two-Dimensional Terahertz Imaging System Using Hot Electron Bolometer

May 10, 2006
Author(s)
Dazhen Gu, Eyal Gerecht, Fernando Rodriquez Morales, Sigfrid Yngvesson
We present first results with a two-dimensional(2D)scanning, terahertz passive heterodyne imaging system currently under development. The imager is based on a phonon-cooled quasi-optically coupled HEB mixer integrated with an InP MMIC IF low-noise

Near-Field Imaging of High Frequency Magnetic Fields with Calorimetric Cantilevers Probes

April 21, 2006
Author(s)
Simone Lee, Y. C. Lee, Thomas Mitchell (Mitch) Wallis, John M. Moreland, Pavel Kabos
Calorimetric probes for near-field imaging of high-frequency (1-20 GHz) magnetic fields were fabricated by depositing patterned metal structures on micromachined, dielectric multilayer cantilevers. In the presence of high-frequency magnetic fields, the

Chip scale atomic magnetometers

April 19, 2006
Author(s)
John M. Moreland, John Kitching, Peter D. Schwindt, Svenja A. Knappe, Li-Anne Liew, V Shah, V Gerginov, Ying-Ju Wang, Leo W. Hollberg
We are developing a new class of sensors based on atoms confined in micro-fabricated enclosures. Recent work at the National Institute of Standards and Technology (NIST) has lead to a prototype chip scale atomic clock (CSAC) with remarkable operating

Large-angle magnetization dynamics measured by time-resolved ferromagnetic resonance

March 30, 2006
Author(s)
Thomas Gerrits, Michael Schneider, Anthony B. Kos, Thomas J. Silva
A time-resolved ferromagnetic resonance technique was used to investigate the nonlinear magnetization dynamics of a 10 nm thin Permalloy TM film in response to a sequence of large-amplitude field pulses. The magnetic field pulse sequence was set at a

Radio Communications for Emergency Responders in Large Public Buildings: Comparing Analog and Digital Modulation

March 7, 2006
Author(s)
Catherine A. Remley, Marc Rutschlin, Dylan F. Williams, Robert T. Johnk, Galen H. Koepke, Christopher L. Holloway, Mike G. Worrell, Andy MacFarlane
To assess in-building radio coverage, in 2004 the City of Phoenix Fire Department carried out extensive testing of their radio systems. They deployed firefighters in standard configurations in a variety of buildings, and rated on a scale of 1 to 5 the

Precision Measurement Method for Cryogenic Amplifier Noise Temperatures Below 5 K

March 1, 2006
Author(s)
James P. Randa, Eyal Gerecht, Dazhen Gu, Robert L. Billinger
We report precision measurements of the effective input noise temperature of a cryogenic (liquid helium temperature) MMIC amplifier at the amplifier reference planes within the cryostat. A method is given for characterizing and removing the effect of the

Phenomenology of Passive Broadband Terahertz Images

February 15, 2006
Author(s)
Charles Dietlein, A. Luukanen, Francois Meyer, Zoya Popovic, Erich N. Grossman
Images acquired by a 105-mK noise equivalent temperature difference (NETD) scanned single-pixel broadband 0.1-1 THz passive system are analyzed with two specific parameters of interest in mind. First, the minimum system noise level for clothing feature

Terahertz circular variable filters

February 15, 2006
Author(s)
Erich N. Grossman, Charles Dietlein, A. Luukanen
We describe a novel class of millimeter-wave and terahertz monochrometers based on adiabatically tuned frequency-selective surfaces. They are analogous to the circular-variable filters commonly used in the infrared for low to moderate resolution

Requirements for an Effective Reverberation Chamber: Unloaded or Loaded

February 1, 2006
Author(s)
Christopher L. Holloway, David A. Hill, Galen H. Koepke, John M. Ladbury
In this paper we present two versions of a threshold metric for the purpose of accessing the effectiveness of a reverberation chamber. One metric is based on the chamber quality factor (Q), and the other is based on the volume of the loaded reverberation

Surface oxidation of Permalloy thin films

January 24, 2006
Author(s)
M. R. Fitzsimmons, Thomas J. Silva, T. M. Crawford
The chemical and magnetic structures of oxides on the surface of Permalloy Ni 81Fe 19 films were investigated as functions of annealing time with x-ray and polarized neutron reflectometry. For annealing times of less than one hour, the oxide consisted of a

Enhanced ferromagnetic damping in Permalloy/Cu bilayers

January 18, 2006
Author(s)
Thomas Gerrits, Michael Schneider, Thomas J. Silva
We have investigated the enhancement of ferromagnetic damping for thin Permalloy (Ni 80Fe 20) films grown with Cu capping layers of variable thickness (5-1000nm). The measurements were performed with a pulsed inductive microwave magnetometer in the

Effect of tensile strain on grain connectivity and flux pinning in Bi 2 Sr 2 Ca 2 Cu 3 O x tapes

January 17, 2006
Author(s)
Daniel C. van der Laan, John (Jack) W. Ekin, Hans J. van Eck, M Dhalle, Bennie ten Haken, Michael W. Davidson, Justin Schwartz
The grain-to-grain connectivity in Bi 2Sr 2Ca 2Cu 3O x tapes is still poorly understood, even though they have been commercially available in long lengths for several years. This letter explains the effects of tensile strain on the grain-to-grain

Covariance-Based Uncertainty Analysis of the NIST Electrooptic Sampling System

January 1, 2006
Author(s)
Dylan F. Williams, Arkadiusz C. Lewandowski, Tracy S. Clement, C. M. Wang, Paul D. Hale, Juanita M. Morgan, Darryl A. Keenan, Andrew Dienstfrey
We develop a covariance matrix describing the uncertainty of mismatch-corrected measurements performed on the National Institute of Standards and Technology's electro-optic sampling system. This description offers a general way of describing the

Tailored Nanoscale Contrast Agents for Magnetic Resonance Imaging

December 30, 2005
Author(s)
Alexander J. Barker, Brant Cage, Stephen E. Russek, Ruchira Garg, R Shandas, Conrad Stoldt
Two potential molecular imaging vectors are investigated for material properties and magnetic resonance imaging (MRI) contrast improvement. Monodisperse magnetite (Fe 3O 4) nanocrystals ranging in size from 7 to 22 nm are solvothermally synthesized by

Dependence of magnetization dynamics on magnetostriction in NiFe alloys

December 23, 2005
Author(s)
Roberto Bonin, Michael Schneider, Thomas J. Silva, John P. Nibarger
We present a quantitative, systematic study of the effect of magnetostriction on the dynamical properties in NiFe alloys. Both the ferromagnetic resonance frequency and the damping times are correlated to the magnetostriction. In addition, we find that the
Displaying 526 - 550 of 1560