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183 results on '"Hoff, Brad W."'

2. A reflective mm-wave photonic limiter

Author

Kononchuk, Rodion, Suwunnarat, Suwun, Hilario, Martin S., Baros, Anthony E., Hoff, Brad W., Vasilyev, Vladimir, Vitebskiy, Ilya, Kottos, Tsampikos, and Chabanov, Andrey A.

Subjects
Physics - Applied Physics, Physics - Optics
Abstract

Millimeter wave (mm-wave) communications and radar receivers capable of processing small signals must be protected from high-power signals, which can damage sensitive receiver components. Many of these systems arguably can be protected by using photonic limiting techniques, in addition to electronic limiting circuits in receiver front-ends. Here we demonstrate, experimentally and numerically, a free-space, reflective mm-wave limiter based on a multilayer structure involving a nanolayer of vanadium dioxide (VO2), experiencing a thermal insulator-to-metal transition. The multilayer acts as a variable reflector, controlled by the input power. At low input power levels, VO2 remains dielectric, and the multilayer exhibits resonant transmittance. When the input power exceeds a threshold level, the emerging metallic phase renders the multilayer highly reflective while dissipating a small portion of the input power without damage to the limiter. In the case of a Gaussian beam, the limiter has a nearly constant output above the limiting threshold input., Comment: 18 pages, 6 figures, 3 supplementary figures and 1 supplementary table

Published
2020
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4. Computational Characterization of a Composite Ceramic Block for a Millimeter Wave Heat Exchanger

Author

Kumi, Petra, Venne, Jonathan S., Yakovlev, Vadim V., Hilario, Martin S., Hoff, Brad W., Rittersdorf, Ian M., Bock, Hans Georg, Series Editor, de Hoog, Frank, Series Editor, Friedman, Avner, Series Editor, Gupta, Arvind, Series Editor, Nachbin, André, Series Editor, Ozawa, Tohru, Series Editor, Pulleyblank, William R., Series Editor, Rusten, Torgeir, Series Editor, Santosa, Fadil, Series Editor, Seo, Jin Keun, Series Editor, Tornberg, Anna-Karin, Series Editor, Nicosia, Giuseppe, editor, and Romano, Vittorio, editor

Published
2020
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11. A reflective millimeter-wave photonic limiter

Author

Kononchuk, Rodion, primary, Suwunnarat, Suwun, additional, Hilario, Martin S., additional, Baros, Anthony E., additional, Hoff, Brad W., additional, Vasilyev, Vladimir, additional, Vitebskiy, Ilya, additional, Kottos, Tsampikos, additional, and Chabanov, Andrey A., additional

Published
2022
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13. Observed Reductions in the Infectivity of Bioaerosols Containing Bovine Coronavirus Under Repetitively Pulsed RF Exposure

Author

Hoff, Brad W., primary, Cohick, Zane W., additional, Tilley, Burt S., additional, Luginsland, John W., additional, Revelli, David, additional, Cox, Jason, additional, Irshad, Hammad, additional, Snider, Amanda, additional, Arndt, Ariel, additional, Ibey, Bennett L., additional, Enderich, Daniel A., additional, Thomas, Robert J., additional, McConaha, Jeremy W., additional, Franzi, Matthew A., additional, Roach, William P., additional, and Shiffler, Donald A., additional

Published
2022
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14. High Temperature W-band Complex Permittivity Measurements of Thermally Cycled Ceramic-Metal Composites: AlN:Mo with 0.25 vol% to 4.0 vol% Mo from 25 °C to 1000 °C in Air

Author

Cohick, Zane W, primary, Schaub, Samuel C., additional, Hoff, Brad W., additional, Dynys, Frederick W., additional, Baros, Anthony E., additional, Telmer, Maxwell, additional, Orozco, Haylie, additional, Grudt, Rachael O., additional, Hayden, Steven C., additional, Rittersdorf, Ian M., additional, and Savrun, Ender, additional

Published
2021
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15. Magnetic priming at the cathode of a relativistic magnetron

Author

Hoff, Brad W., Gilgenbach, Ronald M., Jordan, N.M., Lau, Y.Y., Cruz, Edward J., French, David M., Gomez, Matthew R., Zier, Jacob C., Spencer, Thomas A., and Price, David

Subjects
Microwaves -- Properties, Magnetrons -- Design and construction, Magnetism -- Evaluation, Business, Chemistry, Electronics, Electronics and electrical industries
Abstract

Experiments have been performed in testing magnetic priming at the cathode of a relativistic magnetron to study the effects on high-power microwave performance. Magnetic priming consists of N/2 azimuthal magnetic perturbations applied to an N-cavity magnetron for rapid generation of the desired number of electron spokes for the [pi]-mode. Magnetic perturbations were imposed by utilizing three high-permeability nickel-iron wires embedded beneath the emission region of the cathode, spaced 120[degrees] apart. Magnetic priming was demonstrated to increase the percentage of [pi]-mode shots by 15% over the baseline case. Mean peak power for [pi]-mode shots was found to be higher in the magnetically primed case by almost a factor of two. Increases in mean microwave pulsewidth were also observed in the magnetically primed case when compared to the unprimed case (66-ns primed versus 50-ns unprimed). Magnetron starting current for the magnetically primed [pi]-mode exhibited a reduction to 69% of the unprimed baseline starting current. Index Terms--High power microwaves, magnetron, mode competition, priming, startup.

Published
2008

16. Radio frequency priming of a long-pulse relativistic magnetron

Author

White, William M., Gilgenbach, Ronald M., Jones, Michael C., Neculaes, V. Bogdan, Lau, Yue Ying, Pengvanich, P., Jordan, Nicholas M.C., Hoff, Brad W., Edgar, Ryan, Spencer, Thomas A., and Price, David

Subjects
Magnetrons -- Research, Microwaves -- Research, Electron beams -- Research, Business, Chemistry, Electronics, Electronics and electrical industries
Abstract

Rapid startup, increased pulsewidth, and mode locking of magnetrons have been explored experimentally on a relativistic magnetron by radio frequency (RF) priming. Experiments utilize a -300 kV, 2-8 kA, 300-500-ns electron beam to drive a Titan six-vane relativistic magnetron (5-100 MW output power in each of the three waveguides). The RF priming source is a 100-kW pulsed magnetron operating at 1.27-1.32 GHz. Tuning stubs are utilized in the Titan structure to adjust the frequency of the relativistic magnetron to match that of the priming source. Experiments are performed on rising sun as well as standard anode configurations. Magnetron start-oscillation time, pulsewidth, and [pi]-mode locking are compared with RF priming versus the unprimed case. The results show significant reductions in microwave output delay and mode competition even when Adler's Relation is not satisfied. Index Terms--High-power microwaves, magnetrons, priming, pulse shortening.

Published
2006

17. Nonlinear transmission line-driven apparatus for short-pulse microwave exposure of aerosolized pathogens

Author

Enderich, Daniel A., primary, Hoff, Brad W., additional, Geiler, Michael, additional, Geiler, Anton, additional, Ottesen, Casey, additional, Cohick, Zane W., additional, McConaha, Jeremy W., additional, Pohle, Hugh H., additional, Franzi, Matthew A., additional, Lepell, P. David, additional, Montoya, Thomas, additional, Schrock, James A., additional, Luginsland, John W., additional, Revelli, David, additional, Cox, Jason, additional, and Irshad, Hammad, additional

Published
2021
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18. Magnetic perturbation effects on noise and startup in DC-operating oven magnetrons

Author

Neculaes, V. Bogdan, Hidaka, Y., Bosman, Herman L., Jones, Michael C., Pengvanich, P., Gilgenbach, Ronald M., Jordan, N.M., Lau, Y. Y., White, William M., Luginsland, John W., and Hoff, Brad W.

Subjects
Microwaves -- Research, Noise generators (Electronics) -- Research, Magnetrons -- Research, Perturbation (Mathematics) -- Analysis, Business, Electronics, Electronics and electrical industries
Abstract

The study presents an experiment that adds five perturbing magnets on each of two existing magnets of the magnetron, restoring the axial symmetry of the magnetic field, while maintaining the five-fold azimuthal magnetic field symmetry. The results revealed that the noise close to the carrier is reduced by up to 20 dB, while the sidebands are not completely eliminated for medium and high currents.

Published
2005

19. Magnetic priming effects on noise, startup, and mode competition in magnetrons

Author

Neculaes, V. Bogdan, Jones, Michael C., Gilgenbach, Ronald M., Lau, Y.Y., Luginsland, John W., Hoff, Brad W., White, William, M., Jordan, N.M., Pengvanich, P., Hidaka, Y., and Bosman, Herman L.

Subjects
Magnetism -- Research, Microwaves -- Research, Business, Chemistry, Electronics, Electronics and electrical industries
Abstract

Azimuthally varying axial magnetic fields have been utilized to perform 'magnetic priming' of magnetrons for rapid startup, low noise, and mode control. An overview of the latest magnetic priming experimental and simulation results are presented in this paper. Magnetic priming experiments in dc-operating microwave oven magnetrons show sideband elimination, even with the cathode heater turned off. Simulations using three three-dimensional (3-D) improved concurrent electromagnetic particle-in-cell (ICEPIC) codes with two different computational algorithms recover the oven magnetron experimental results obtained with magnetic priming including fast mode growth, rapid spoke formation, and the tendency toward lower noise operation. A new, axially symmetric, azimuthally varying magnetic field geometry for oven magnetrons is explored and preliminary results are reported. Simulations using two-dimensional (2-D) MAGIC code for the University of Michigan/Titan relativistic magnetron show that the oscillation startup time can be dramatically decreased (almost by a factor of 3) and mode competition can be suppressed with magnetic priming. Index Terms--High-power microwaves, magnetron, microwave noise, mode competition.

Published
2005

20. Observed Reductions in the Infectivity of Bioaerosols Containing Bovine Coronavirus Under Repetitively Pulsed RF Exposure

Author

Hoff, Brad W., Cohick, Zane W., Tilley, Burt S., Luginsland, John W., Revelli, David, Cox, Jason, Irshad, Hammad, Snider, Amanda, Arndt, Ariel, Ibey, Bennett L., Enderich, Daniel A., Thomas, Robert J., McConaha, Jeremy W., Franzi, Matthew A., Roach, William P., and Shiffler, Donald A.

Abstract

Objective: The purpose of the present study is to investigate the inactivation of bioaerosols containing Bovine Coronavirus, BCoV, under repetitively pulsed radio frequency (RF) electromagnetic exposure. Methods: These experiments were performed in a waveguide containing a flowing aerosol stream and were limited to a single RF waveform: ∼2 μs square envelope, 5.6 GHz, 4.8 kHz repetition rate. Aerosol streams were exposed to RF electric field amplitudes in the range of 41.9 +/−6.2 kV/m. Under laminar flow conditions, 75% of the total collected aerosol stream spends 0.85 seconds or less in the RF exposure region. Results: Application of the RF waveform changed mean survival rate of the aerosolized BCoV by −0.58 decades (roughly a 74% reduction) and impacted the variance and standard deviation of the experimental results, with the RF exposure data showing an 800% increase in variance and 196% increase in standard deviation over the control results. Experimental results were compared to those from an analytic electromagnetic-heating inactivation model. Conclusion: The comparison indicated the feasibility that the observed reduction in BCoV survival rate might be due to a combination of thermal effects and non-thermal electric field effects. Significance: Developing better insight into the mechanisms of inactivation is important for understanding the potential limits of efficacy for this method. Additionally, these results contribute an important baseline for the impact of electromagnetic fields on aerosolized pathogens.

Published
2023
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21. Apparatus for controlled microwave exposure of aerosolized pathogens

Author

Hoff, Brad W., primary, McConaha, Jeremy W., additional, Cohick, Zane W., additional, Franzi, Matthew A., additional, Enderich, Daniel A., additional, Revelli, David, additional, Cox, Jason, additional, Irshad, Hammad, additional, Pohle, Hugh H., additional, Schmitt-Sody, Andreas, additional, Schaub, Samuel C., additional, Baros, Anthony E., additional, Lewis, Naomi C., additional, Luginsland, John W., additional, Lanagan, Michael T., additional, and Perini, Steven, additional

Published
2021
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28. Brazed carbon fiber fabric field emission cathode

Author

Hoff, Brad W., primary, Beeson, Sterling, additional, Simon, David, additional, Tang, Wilkin, additional, Smith, Ronald, additional, Exelby, Steven C., additional, Jordan, Nicholas M., additional, Sayir, Ali, additional, Gilgenbach, Ronald M., additional, Lepell, P. David, additional, and Montoya, Tom, additional

Published
2020
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29. High temperature W-band complex permittivity measurements of thermally cycled ceramic-metal composites: AlN:Mo with 0.25 to 4.0 vol% Mo from 25 °C to 1000 °C in air.

Author

Cohick, Zane W, Schaub, Samuel C, Hoff, Brad W, Dynys, Frederick W, Baros, Anthony E, Telmer, Maxwell, Orozco, Haylie, Grudt, Rachael O, Hayden, Steven C, Rittersdorf, Ian M, and Savrun, Ender

Subjects
HIGH temperatures, PYROMETRY, PERMITTIVITY measurement, DIELECTRIC properties, ALUMINUM nitride, THERMOCYCLING, MOLYBDENUM
Abstract

An apparatus for measuring the W-band (75â€"110 GHz) complex permittivity of dielectrics at 1000 °C was developed. This apparatus allows for measurements at approximately twice the temperature of previously published high temperature free-space measurement systems while maintaining similar precision. Challenges were addressed related to high temperature measurements, including temperature uniformity, the accuracy of temperature measurements, and preventing temperature related changes to mm-wave measurement systems. The details of complex permittivity extraction from the measured S-parameters are discussed. Sources of error related to permittivity measurement and mathematical models were identified and are discussed in detail herein. Thermally-cycled, mm-wave absorbing, aluminum nitride ceramic composites containing varying levels of molybdenum additives were measured over the range of 25 °Câ€"1000 °C. These measurements were compared to the same composites before thermal cycling. It was found that ceramic composites are largely stable after thermal cycling in terms of dielectric properties despite the presence of visible surface modifications. [ABSTRACT FROM AUTHOR]

Published
2022
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41. Harmonic-frequency locking in planar magnetrons

Author

Packard, Drew A., primary, Greening, Geoffrey B., additional, Jordan, Nicholas M., additional, Exelby, Steven C., additional, Wong, Patrick Y., additional, Lau, Y.Y., additional, Gilgenbach, Ronald M., additional, Hoff, Brad W., additional, and Hammond, Jason F., additional

Published
2018
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