Brian H. Houston

United States Naval Research Laboratory, Washington, Washington, D.C., United States

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Publications (160)281.18 Total impact

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    ABSTRACT: This paper discusses progress made on the design of an acoustic velocity sensor. An analytic model was developed for the frequency response of a slender cantilever rod forced by the pressure gradient and particle velocity associated with an acoustic wave propagating in a fluid. The model, validated with acoustic response measurements in air, was used to design cantilever sensors, which respond predominately to acoustic particle velocity. One such design utilizes a short cantilever formed from a 125 μm silica glass fiber immersed in a viscous fill fluid whose lateral tip displacement is detected using a multi-fiber optical probe. This velocity sensor is predicted to be able to detect fairly low acoustic sound levels in water. Progress has been made in instrumenting a large pool at NRL to allow accurate propagating acoustic wave response measurements in water of these new velocity sensors down to frequencies below 5 Hz. Measurements made in this facility on various cantilever sensors will be presented and discussed. [Work supported by ONR.]
    No preview · Article · Sep 2015 · The Journal of the Acoustical Society of America
  • Bernard R. Matis · Brian H. Houston · Jeffrey W. Baldwin
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    ABSTRACT: We present room temperature electronic and magnetotransport measurements of polycrystalline graphene, grown by chemical vapor deposition, on a SiO2 dielectric. The measured graphene devices are intentionally spatially inhomogeneous such that the length of the sample is much greater (>1000 times) than the average grain size. At magnetic field B=0T the electronic transport is well described by a diffusive transport model with contributions from grain boundary scattering significantly larger in the high charge carrier density limit. We find the largest percent change in the magnetoresistivity occurs at the film's Dirac point where the magnetotransport is largely dependent upon charge disorder. Away from the Dirac point we find a modified expression for the charge carrier density dependence of the magnetoresistivity with respect to the case of single-crystal graphene.
    No preview · Article · May 2015 · Physical Review B
  • Angie Sarkissian · Saikat Dey · Brian H. Houston · Joseph A. Bucaro
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    ABSTRACT: Scattering results are presented for targets of various shapes buried in elastic sediment with a plane wave incident from air above. The STARS3D finite element program recently extended to layered, elastic sediments is used to compute the displacement field just below the interface. Evidence of the presence of Rayleigh waves is observed in the elastic sediment and an algorithm based on the Rayleigh waves subtracts the contribution of the Rayleigh waves to simplify the resultant scattering pattern. Results are presented for scatterers buried in uniform elastic media as well as layered media. [This work was supported by ONR.]
    No preview · Article · Oct 2014 · The Journal of the Acoustical Society of America
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    ABSTRACT: Broadband laboratory and at-sea measurements systems have been built by NRL to quantify the acoustic target strength of objects sitting on or in the bottom of littoral environments. Over the past decade, these measurements and the subsequent modeling of the target strength have helped to develop an understanding of how the environment, especially near the bottom interface, impacts the structural acoustic response of a variety of objects. In this talk we will present a set of laboratory, at-sea rail and AUV based back scatter, forward scatter, and propagation measurements with subsequent analysis to understand the impact of the littoral environment. Simple targets such as spheres, along with UXO targets will be discussed. The analysis will be focused on quantifying the changes to target strength as a result of being near the bottom interface. In addition to the traditional backscatter or monosatic target strength, we focus upon efforts to investigate the multi-static scattering from targets. [Work supported by ONR.]
    No preview · Article · Oct 2014 · The Journal of the Acoustical Society of America
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    ABSTRACT: Strategies for the automated detection and classification of underwater unexploded ordnance (UXO), based upon structural acoustics derived features, are currently being transitioned to autonomous underwater vehicle based sonar systems. The foundation for this transition arose, in part, from extensive laboratory investigations conducted at the Naval Research Laboratory. We discuss the evolution of structural acoustic based methodologies, including research into understanding the free-field scattering response of UXO and the coupling of these objects, under varying stages of burial, to water-saturated sediments. In addition to providing a physics-based understanding of the mechanisms contributing to the scattering response of objects positioned near the sediment–water interface, this research supports the validation of three-dimensional finite-element-based models for large-scale structural–acoustics problems. These efforts have recently culminated with the successful classification of a variety of buried UXO targets using a numerically trained relevance vector machine (RVM) classifier and the discrimination of these targets, under various burial orientations, from several objects representing both natural and manmade clutter. We conclude that this demonstration supports the transition of structural acoustic processing methodologies to maritime sonar systems for the classification of challenging UXO targets. [Work supported by ONR and SERDP.]
    No preview · Article · Oct 2014 · The Journal of the Acoustical Society of America
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    ABSTRACT: For targets near the sediment–fluid interface, the scattering response is fundamentally influenced by the characterization of the sediment in the model. We show that if the model consists of a three-dimensional elastic sediment with acoustic fluid on top, then the use of perfectly matched-layer (PML) approximation for the truncation of the infinite exterior domain for scattering applications has fundamental problems and gives erroneous results. We present a novel formulation using the an interior-transmission representation of the scattering problem where the exterior truncation with PML does not induce errors in the result. Numerical examples will be presented to verify the application of this formulation to scattering from elastic targets near a fluid–sediment interface.
    No preview · Article · Oct 2014 · The Journal of the Acoustical Society of America
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    ABSTRACT: We present research on detection and classification of underwater targets buried in a saturated sediment using structural acoustic features. These efforts involve simulations using NRL’s STARS3D structural acoustics code and measurements in the NRL free-field and sediment pool facilities, off the coast of Duck, NC, and off the Coast of Panama City, FL. The measurements in the sediment pool demonstrated RVM classifiers trained using numerical data on two features—target strength correlation and elastic highlight image symmetry. Measurements off the coast of Duck were inconclusive owing to tropical storms resulting in a damaged projector. Extensive measurements were then carried out in 60 ft. of water in the Gulf using BOSS, an autonomous underwater vehicle with 40 receivers on its wings. The target field consisted of nine simulant-filled UXO and two false targets buried in the sediment and twenty proud targets. The AUV collected scattering data during north/south, east/west, and diagonal flights. We discuss the data analyzed so far from which we have extracted 3-D images and acoustic color constructs for 18 of the targets and demonstrated UXO/false target separation using a high dimensional acoustic color feature. Finally, we present related work involving targets buried in non-saturated elastic sediments. [This work is supported by ONR and SERDP.]
    No preview · Article · Oct 2014 · The Journal of the Acoustical Society of America
  • Angie Sarkissian · Saikat Dey · Brian H Houston · Joseph A Bucaro
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    ABSTRACT: Scattering results are presented for the case of cylindrical steel targets buried in elastic sediment with sound incident from the air above. The STARS3D finite element program recently extended to layered, elastic sediments is used to compute the scattering and the resulting normal displacement at the interface since the specific focus here is detection by systems which rely on monitoring the acoustic displacements or displacement-related entities at the fluid-sediment interface. Results are compared for the scattered field produced by the cylinder buried in layered elastic sediment versus in fluid sediment and for the scattered field of a buried cylindrical shell versus a buried solid cylinder. [This work was supported by ONR.].
    No preview · Article · Apr 2014 · The Journal of the Acoustical Society of America
  • Bernard R. Matis · Brian H. Houston · Jeffrey W. Baldwin
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    ABSTRACT: We study the electronic transport properties of graphene with covalently bonded hydrogen impurities. Our measurements reveal low-energy resonant scattering processes within the transport for each charge carrier type. The observed resonances exhibit a strong energy dependence and are accompanied by a sharp increase in the scattering cross section. The ability to observe the scattering resonances was found to depend on the amount of disorder introduced into the graphene through the bonding of hydrogen. The results are shown to be in agreement with a theory regarding low-energy resonant scattering off a short-range impurity in graphene that takes into account both intravalley and intervalley scattering. Theory dictates that the observed resonances are the result of the formation of quasibound states of the Dirac fermions in graphene due to a divergence in one or more of the scattering lengths for the short-range hydrogen impurity potential. We anticipate our experimental results to have implications in graphene valley physics as well as graphene chemical modification, scattering, and localization theories.
    No preview · Article · Aug 2013 · Physical Review B
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    ABSTRACT: We report using chemical functionalization to control local carrier type and density in graphene. Low frequency transport measurements demonstrate independent carrier types and densities within adjacent graphene and hydrogenated graphene regions. Measurements of the Hall coefficient confirm that the charge carriers change sign about the charge neutrality point, that the graphene carrier density retains its linear dependence on a back gate voltage, and that the hydrogenated graphene carrier density deviates from a linear relationship. Transport measurements across the bipolar interface reveal an increasing interface resistance for higher hydrogen concentrations and a source of constant resistance for lower hydrogen concentrations.
    Full-text · Article · Mar 2013 · Applied Physics Letters
  • Angie Sarkissian · Brian Houston · Joseph Bucaro · Larry Kraus
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    ABSTRACT: A near-field to far-field projection algorithm is applied to a structure in the free-field case and generalized to a buried scatterer. The method of superposition is applied where the scattered field produced by the target may be approximated by the field produced by a number of point sources placed near the target. The source strengths are determined by requiring the field they produce to satisfy boundary conditions on the measurement surface. In the free-field case, the expression of the Green's function is simple. In the buried case, the two-domain Green's function may be expressed as an integral over special functions. Once the source strengths are determined, the far-field is computed as a superposition of the fields produced by the individual sources. The algorithm is tested on numerically generated data.
    No preview · Article · Feb 2013 · The Journal of the Acoustical Society of America
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    ABSTRACT: Using a finite element-based structural acoustics code, simulations were carried out for the acoustic scattering from an unexploded ordnance rocket buried in the sediment under 3 m of water. The simulation treated 90 rocket burial angles in steps of 2°. The simulations were used to train a generative relevance vector machine (RVM) algorithm for identifying rockets buried at unknown angles in an actual water/sediment environment. The trained RVM algorithm was successfully tested on scattering measurements made in a sediment pool facility for six buried targets including the rocket at 90°, 120°, and 150°, a boulder, a cinderblock, and a cinderblock rolled 45° about its long axis.
    No preview · Article · Dec 2012 · The Journal of the Acoustical Society of America
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    ABSTRACT: In this article, we review our efforts to continuously tune mechanical and thermal properties in multilayer chemically modified graphene (CMG) films. An alteration of the graphene lattice by functional groups, by defects created during reduction, or by defect re-crystallization is used to control CMG mechanical and thermal properties. We attribute a notable increase in Young's modulus and film strength to an emerging network of sp2–sp3 crosslinks established between graphene layers. Control over the film stress and strength enabled us to dramatically improve the performance of radio frequency CMG resonators by fine tuning the fabrication process.
    No preview · Article · Nov 2012 · Solid State Communications
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    ABSTRACT: We report a method to introduce direct bonding between graphene platelets that enables the transformation of a multilayer chemically modified graphene (CMG) film from a "paper mache-like" structure into a stiff, high strength material. On the basis of chemical/defect manipulation and recrystallization, this technique allows wide-range engineering of mechanical properties (stiffness, strength, density, and built-in stress) in ultrathin CMG films. A dramatic increase in the Young's modulus (up to 800 GPa) and enhanced strength (sustainable stress ≥1 GPa) due to cross-linking, in combination with high tensile stress, produced high-performance (quality factor of 31,000 at room temperature) radio frequency nanomechanical resonators. The ability to fine-tune intraplatelet mechanical properties through chemical modification and to locally activate direct carbon-carbon bonding within carbon-based nanomaterials will transform these systems into true "materials-by-design" for nanomechanics.
    No preview · Article · Jul 2012 · Nano Letters
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    ABSTRACT: Near-field acoustic holography reconstruction of the acoustic field at the surface of an arbitrarily shaped radiating structure from pressure measurements at a nearby conformal surface is obtained from the solution of a boundary integral equation. This integral equation is discretized using the equivalent source method and transformed into a matrix system that can be solved using iterative regularization methods that counteract the effect of noise on the measurements. This work considers the case when the resultant matrix system is so large that it cannot be explicitly formed and iterative methods of solution cannot be directly implemented. In this case the method of surface decomposition is proposed, where the measurement surface is divided into smaller nonoverlapping subsurfaces. Each subsurface is used to form a smaller matrix system that is solved and the result joined together to generate a global solution to the original matrix system. Numerically generated data are used to study the use of subsurface extensions to increase the continuity of the global solution, and investigate the size of the subsurfaces, as well as the distance between the measurement and the vibrating surface. Finally a vibrating ship hull structure is considered as a physical example to apply and validate the proposed methodology.
    Full-text · Article · Jul 2012 · The Journal of the Acoustical Society of America
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    ABSTRACT: A giant negative magnetoresistance of up to 28% at 2.5 T is observed in plasma hydrogenated graphene at the charge neutrality point without any sign of saturation at 2.0 K. A detailed analysis of the gate voltage dependence demonstrates a suppression of the giant negative magnetoresistance, which is accompanied by a crossover from strong localization at low carrier concentrations to weak localization at higher carrier concentrations. Evidence of asymmetry in the electron/hole transport is found in the magnetic field traces at low temperature. The asymmetrical transport is attributed to charge transfer processes at the graphene/metal interface and demonstrates the effect of using invasive contact geometries in hydrogenated graphene devices.
    Full-text · Article · May 2012 · Physical review. B, Condensed matter
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    ABSTRACT: We study the magnetoresistance of hydrogenated graphene devices on a SiO2 substrate. A large negative magnetoresistance of up to 30% in a field of 2.5T is observed at low temperatures and at the film's charge neutrality point without any sign of saturation. A detailed analysis of the gate voltage dependence demonstrates a suppression of the large, negative magnetoresistance, which appears to be driven by a crossover from strong localization at low carrier concentrations to weak localization at higher carrier concentrations. Evidence of electron-hole symmetry breaking is found in the magnetic field traces at low temperature.
    No preview · Article · Feb 2012
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    ABSTRACT: We report shear modulus (G) and internal friction (Q(-1)) measurements of large-area monolayer graphene films grown by chemical vapor deposition on copper foil and transferred onto high-Q silicon mechanical oscillators. The shear modulus, extracted from a resonance frequency shift at 0.4 K where the apparatus is most sensitive, averages 280 GPa. This is five times larger than those of the multilayered graphene-based films measured previously. The internal friction is unmeasurable within the sensitivity of our experiment and thus bounded above by Q(-1) ≤ 3 × 10(-5), which is orders-of-magnitude smaller than that of multilayered graphene-based films. Neither annealing nor interface modification has a measurable effect on G or Q(-1). Our results on G are consistent with recent theoretical evaluations and simulations carried out in this work, showing that the shear restoring force transitions from interlayer to intralayer interactions as the film thickness approaches one monolayer.
    Full-text · Article · Jan 2012 · Nano Letters
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    ABSTRACT: We report internal friction and shear modulus measurements of several types of synthesized graphene films. They include reduced graphene oxide, chemical-vapor deposited (CVD) graphene films on thin nickel films and on copper foils. These films were transferred from their host substrate into a water bath, and re-deposited onto to a high-Q single crystal silicon mechanical double-paddle oscillator. A minimal thickness dependence of both internal friction and shear modulus was found for reduced graphene oxide films varying thickness from 4 to 90 nm and CVD graphene films on nickel from 6 to 8 nm. The shear modulus of these multilayered films averages 53 GPa. Their internal friction exhibits a temperature independent plateau below 10K. The values of the plateaus are similar for both the reduced graphene oxide films and CVD graphene films on nickel, and they are as high as the universal "glassy range" where the tunneling states dominated internal friction of amorphous solids lies. In contrast, CVD graphene films on copper foils are 90~95% single layer. The shear modulus of these single layer graphene films are about five times higher, averaging 280 GPa. Their low temperature internal friction is too small to measure within the uncertainty of our experiments. Our results demonstrate the dramatic difference in the elastic properties of multilayer and single layer graphene films.
    No preview · Article · Jan 2012 · Solid State Phenomena
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    ABSTRACT: We report the first observation of the n-type nature of hydrogenated graphene on SiO(2) and demonstrate the conversion of the majority carrier type from electrons to holes using surface doping. Density functional calculations indicate that the carrier type reversal is directly related to the magnitude of the hydrogenated graphene's work function relative to the substrate, which decreases when adsorbates such as water are present. Additionally, we show by temperature-dependent electronic transport measurements that hydrogenating graphene induces a band gap and that in the moderate temperature regime [220-375 K], the band gap has a maximum value at the charge neutrality point, is tunable with an electric field effect, and is higher for higher hydrogen coverage. The ability to control the majority charge carrier in hydrogenated graphene, in addition to opening a band gap, suggests potential for chemically modified graphene p-n junctions.
    Full-text · Article · Dec 2011 · ACS Nano

Publication Stats

1k Citations
281.18 Total Impact Points

Institutions

  • 1995-2015
    • United States Naval Research Laboratory
      • • Chemistry Division
      • • Physical Acoustics Branch
      • • Acoustics Division
      Washington, Washington, D.C., United States
  • 2011
    • United States Navy
      Monterey, California, United States
  • 2010
    • Louisiana State University
      • Department of Mechanical Engineering
      Baton Rouge, Louisiana, United States
  • 2003
    • Naval Undersea Warfare Center
      Newport, Rhode Island, United States
    • Cornell University
      Ithaca, New York, United States