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Preliminary Exam Presentation



This presentation was given to my PhD advisory committee in May 2010

This presentation was given to my PhD advisory committee in May 2010



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Preliminary Exam Presentation Preliminary Exam Presentation Presentation Transcript

  • Glenwood Garner SIAMES Research Group North Carolina State University Linear & Nonlinear Acoustic Modeling for Standoff Analysis Ph.D. Preliminary Examination May 20, 2010 10:00 am, MRC 463 ERL Anechoic Chamber Audio Spotlight Polytec PDV-100 JIEDDO
  • Presentation Overview
    • Motivations, Objectives
    • Original Contributions
      • Third-Order Nonlinear Scattering
      • Fractional Calculus Spatial Power Law Model
      • Switched Tone Probing
      • Shear Wave Elasticity Imaging (SWEI)
    • Future Work
  • Linear & Nonlinear Acoustic Modeling for Standoff Analysis Table of Contents (abridged)
    • Introduction
      • Overview
      • Original Contributions
      • Dissertation Outline
      • Published Works
    • Literature Review
      • Linear Acoustic Theory
      • Nonlinear Acoustic Theory
      • Piston Radiators
      • Sound Scattering
      • Fractional Power Law Theory
      • Acoustic Fluid-Solid Interaction
      • Transient Effects
      • Shear Wave Elasticity Theory
    • Third-Order Sound Scattering
      • Second Harmonic Characterization
      • Receiver Characterization
      • Numerical Techniques
      • Measurement
      • Results & Analysis
    • Fractional Diffusion Acoustic Piston Radiation
      • Finite Difference Method
      • Derivation of Spatial Power Law Dependence
      • Measurements
      • Results & Analysis
    • Switched Tone Transient Analysis
      • Long-Tail Transients
      • Log-Decrement Linear Metrology
      • Nonlinear Switched-Tone Model
      • Switched-Tone Measurement
      • Results & Analysis
    • Standoff Shear Wave Elasticity Imaging
      • Comparison Between Contacting & Non-contacting Methods
      • Application
      • Measurements
      • Image Processing
      • Results & Analysis
    • Conclusion & Future Work
  • Standoff Acoustic Analysis: Motivations 24,000 people killed or injured annually by over 100 million worldwide landmines, unexploded ordnance, and IEDs.
    • Human Prodders
    • Dogs
    • Metal Detectors
    • Infrared
    • Neutron Backscatter
    • Millimeter Wave Detection
    • Ground Penetrating Radar
    • Acoustics
    Lives endangered High false alarm rate Intolerant to soil moister/dielectric constant Better for detecting AT mines Mechanical effects, limited jamming, shielding, spoofing Gros (1998) Can we used acoustics to probe our environment for abnormalities? Mazzaro (2009)
  • Standoff Acoustic Analysis: Motivations Two-tone probing has been demonstrated in finding AP & AT mines. http://www.acoustics.org/press/154th/fillinger.html
    • Current Technology Drawbacks
    • Requires ground shakers…or
    • Large amplitude loudspeakers
    • Not a standoff technique
    • Inherent nonlinearity of air
    • Acoustic beam spreading
    • Research Objectives
    • Develop third-order nonlinear air model
    • Model thermal diffusion of piston sound beam
    • Explore nonlinear probing techniques
    • Adapt current techniques to standoff applications.
    Donskoy (2002), Korman (2004), Sabatier (2003)
  • Standoff Acoustic Analysis: Original Contributions
    • Developed third-order nonlinear air model, demonstrated use of cascaded second-order systems.
    • Demonstrated improved directivity of third-order nonlinear parametric array.
    • Fractional calculus spatial power law model for piston beams.
    • Evaluation of long-tail transients in geologic materials
    • Use of switched tones to generate third-order intermodulation.
    • Standoff application of shear wave elasticity imaging (SWEI) to locate inhomogeneities in targets.
  • Standoff Acoustic Analysis: Publications Glenwood Garner, Jonathan Wilkerson, Michael M. Skeen, Daniel F. Patrick, Ryan D. Hodges, Ryan D. Schimizzi, Saket R. Vora, Zhi-Peng Feng, Kevin G. Gard, and Michael. B. Steer “ Acoustic-RF Anechoic Chamber Construction and Evaluation” Radio & Wireless Symposium, Orlando, FL, 2008. Glenwood Garner III, Jonathan Wilkerson, Michael M. Skeen, Daniel F. Patrick, Hamid Krim, Kevin G. Gard, and Michael B. Steer “ Use of Acoustic Parametric Arrays for Standoff Analysis and Detection” Government Microcircuit Applications Conf., Las Vegas, NV, 2008. Glenwood Garner III, Marcus Wagnborg, and Michael B. Steer “ Standoff Acoustical Analysis of Natural and Manmade Objects” Government Microcircuit Applications Conf., Orlando, FL, 2009. Glen Garner, Jonathan Wilkerson, and Michael B. Steer “ Third-Order Distortion of Sound Fields” Government Microcircuit Applications Conf., Reno, NV, 2010 Glenwood Garner,and Michael Steer “ Nonlinear Propagation of Sound in Air” IEEE Transactions on Geoscience and Remote Sensing (unpublished) Conference Journal
  • Third-Order Nonlinear Scattering: Overview *Taken from: http://spie.org/Images/Graphics/Newsroom/Imported/0569/0569_fig1.jpg When two sound beams (plane waves) interact at angle θ , phase interference produces Moiré bands*. Westervelt (1957) Lighthill (1952) c : sound speed p : pressure (total, scattered, incident) ρ : density a : transmitter radius q : simple source density
  • Third-Order Nonlinear Scattering: Overview Ingard & Pridmore-Brown (1956) Muir & Willette (1972) Lauvstad &Tjotta (1962) Garner & Steer (2010) r 0 / r =1 Lockwood, Muir, & Blackstock (1972)
  • Third-Order Nonlinear Scattering: Distortion Transmitter and receiver nonlinearity must be characterized in all nonlinear measurements. p = 90 dB, r = 2m, f = 40kHz a = 0.22 m a = 0.016 m IM3 Power sweep for 55kHz & 65 kHz input frequencies, with & without acoustic attenuator (melamine foam) over microphone
  • Third-Order Nonlinear Scattering: Measurement
    • l = 2 meters
    • θ = 20º
    • f 1 = 55 kHz, f 2 = 65 kHz
    • p 1 ≈ p 2 ≈ 125 dB SPL
    • r 0 = 7 meters
    • Independent signal generators and amplifiers to eliminate electrical intermodulation.
    • Conducted outside to prevent standing waves
    • Absorber used to mitigate side lobe interaction.
  • Third-Order Nonlinear Scattering: Measured Fields Very good agreement between measured and theoretical IM3. Scattered third-order 3 dB beam widths of 1.7 degrees. To be included in 1 st journal paper ( IEEE GRS ), demonstrate directivity of third-order nonlinear air model.
    • Westervelt (1963), second-order scattering (red)
    • f 1 = 64 kHz, f 2 = 66 kHz
    • p 1 = p 2 = 111 dB SPL
    • a = 0.1 meters
    • ~18 º beam width
    Third-Order Nonlinear Scattering: Directivity
    • Third-order scattering (black)
    • f 1 = 33 kHz, f 2 = 64 kHz
    • p 1 = p 2 = 127 dB SPL
    • a = 0.1 meters
    • ~1.7 º beam width
    At 2 kHz, you get a significant gain in directivity with third-order scattering compared to second-order scattering
  • Fractional Diffusion Model: Overview Used to model long-tail effects (stretched exponentials), power-law attenuation, and fractal geometries. Blackstock (2000), Zemanek (1971)
  • Fractional Diffusion Model: Overview Fractional order element, Schiessel (1995)
    • Fractional derivatives produce memory effects
    • Allow for smooth transistion between diffusive and wave phenomenon.
    • Good at capturing derivatives of varying scale.
    • α = 1: Diffusion
    • α = 2: Wave Equation
    Caputo Fractional Derivative allows traditional initial & boundary conditions Agrawal (2002) Typical boundary conditions Piston source boundary conditions (extend to 3D) Can we find an efficient, fractional order solution to model thermal diffusion of piston source? Mainardi (1994), Podlubny (1999)
  • Fractional Diffusion Model: Overview Current fractional models aim to capture fractional order power-law attenuation. Begin by adding a fractional viscous loss term to wave equation Apply Fourier time/space fractional derivatives to obtain the following dispersion relation where and using the Szabo smallness approximation 40 kHz No viscosity Classical viscosity Chen (2004), Holm (2010)
  • Can a spatial fractional inverse power law be derived (similar to computing a fractional dispersion relation) to model beam spreading from baffled vibrating piston source? Fractional Diffusion Model: Method
  • Switched-Tone Probing: Overview Can the problems associated with standoff nonlinear analysis be avoided using switched tones?
    • Inherent nonlinearity of air and non-perfect collimation cause intermodulation.
    • Due to lack of spatial (velocity) dispersion, switched tones remain separated in time and no intermodulation is generated.
    • If target has long-tail “ringing”, intermodulation is generated on the target’s surface.
    • Surface velocity is measured with laser doppler vibrometer (LDV).
    f 1 f 1 f 2 f 2
  • Switched-Tone Probing: Physical Model Log Decrement Walker (2007), RF continuous excitation Mazzaro (2009), RF switched tones Parker (2005), biological tissues G Conductance per unit length η JJ -1 Inverse damping coefficient C Capacitance per unit length c JJ -1 Inverse stiffness coefficient L Inductance per unit length ρ Mass per unit volume V s Source Voltage per unit length F i Body Force per unit volume I Current v i Particle Velocity V Voltage - T J Negative Stress Auld (1990)
  • Switched-Tone Probing: Physical Model ADS Circuit Model Surface Velocity (Current) response to 25 Pa, 200 ms input signals 590 Hz 840 Hz Can you model physical resonance as an RF filter?
    • Probe a target using switched tones to characterize material type, density, composition.
    • Try using electrical diode model to capture physical nonlinearity.
    • Goal: Demonstrate on uniform samples shapes to verify this phenomenon is a material property
    • Goal: Demonstrate invariance to sample shape.
  • Switched-Tone Probing: Current Results
    • Third-order intermodulation generated by switched tones in metal, plywood, and fiberglass.
    • Did not see this response in microphone placed next to targets.
    • Need to employ windowed FFT and shorter duration tones to eliminate possibility of standing wave error & parametric effect.
    • Applied Physics Letters draft completed.
  • Shear Wave Elasticity Imaging: Overview SWIE is a linear metrology technique that relies on a localized change in stiffness to indicate an inhomogeneity. Modify the general linear shear wave equation to have piecewise Young’s modulus of elasticty. Shear waves typically excited using low frequency shaker and measured using Doppler ultrasound (contacting method). Propose using low frequency speaker (sub-woofer) and LDV to measured surface velocity/displacement (standoff method). Gao (1995), Parker (1996) – Sonoelasticity Imaging
  • Shear Wave Elasticity Imaging: Application Can we use SWEI to model and measure the vibration pattern of materials at standoff ranges? Expanded polystyrene model (Styrofoam TM ) Predicted (1,1) mode (converted to velocity) and velocity measured with LDV To do: Verify predicated amplitudes are correct, measure higher modes, measure different materials.
  • Shear Wave Elasticity Imaging: Application Can we use SWEI to detect dense objects hidden within soft targets? 580 Hz excitation, 2.2 m standoff distance Medical Imaging Standoff Detection To do: Implement inhomogeneous lossy model, determine maximum detection depths in various materials. Incredible difference in stiffness & density compensate for poor solid-air matching.
  • Standoff Acoustic Analysis: Remaining Tasks
    • Implement numerical integration for third-order scattering model?
      • 90% MATLAB code finished
      • Submit to IEEE Geosciences & Remote Sensing
    • Develop fractional diffusion model
    • Complete switched-tone probing measurements
      • Determine best time domain methods and signal processing
      • Use shorter pulses to mitigate parametric effect
      • Submit to Applied Physics Letters
    • Complete standoff SWEI measurements
      • Different materials/inhomogeneities
      • Geologic Materials/non-parallelepiped shapes
      • Submit to IEEE Geosciences & Remote Sensing