Browsing by Subject "Acoustics"
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Item Acoustic characterization of encapsulated microbubbles at seismic frequencies(2013-12) Schoen, Scott Joseph, Jr.; Hamilton, Mark F.Encapsulated microbubbles, whose diameters are on the order of microns, are widely used to provide acoustic contrast in biomedical applications. But well below the resonance frequencies of these microbubbles, any acoustic contrast is due solely to their relatively high compressibility compared to the surrounding medium. To estimate how well microbubbles may function as acoustic contrast agents in applications such as borehole logging or underground flow mapping, it must be determined how they behave both at atmospheric and down-well conditions, and how their presence affects the bulk acoustic properties of the surrounding medium, most crucially its specific acoustic impedance. Resonance tube experiments were performed on several varieties of acoustic contrast agents to determine their compressibility as a function of pressure and temperature, and the results are used to estimate the effect on sound propagation when they are introduced into rock formations.Item Acoustics in the Klebanoff-Saric Wind Tunnel: Background Identification, Forcing, and Active Control(2012-07-16) Kuester, MatthewLow disturbance wind tunnels, such as the Klebanoff?Saric Wind Tunnel (KSWT), offer an ideal environment to study boundary layer transition. In particular, the leading-edge receptivity of sound can be measured by creating acoustic disturbances that interact with the leading edge of a model to create Tollmien?Schlichting Waves. The magnitude and composition (sound, turbulence) of the background disturbances can affect these experiments, so the background disturbances should be minimized and documented thoroughly. The purpose of this thesis is to document the background acoustic signature of the KSWT and describe infrastructure upgrades for acoustic receptivity experiments. The measurements presented in this thesis will support future receptivity measurements in the KSWT. Microphone measurements revealed several important acoustic features in the tunnel. Cross correlations showed that two sources of low-frequency unsteadiness (the extended diffuser and corner two) create large pressure fluctuations that dominate the pressure spectrum. Directional separation of waves in the test section revealed that motor and blade passing noise travels primarily upstream into the test section. Finally, the acoustic treatments in the plenum are effective at removing sound from the tunnel. A wall of speakers was installed in the plenum to enable acoustic receptivity experiments. The speakers create both the primary downstream traveling waves and reflected upstream traveling waves in the test section. An adaptive closed loop control system was installed to reduce the amplitude of the reflected waves during acoustic forcing. Although the performance of the control system is frequency dependent, the technique was implemented successfully. The reduction in the diffuser reflection will increase the quality of future acoustic receptivity experiments in the KSWT.Item Analysis of air-coupled system for exciting and sensing stress waves in concrete(2014-05) Tsai, Yi-Te; Zhu, JinyingNondestructive testing (NDT) plays a more important role today in evaluating structural integrity of civil infrastructure. Impact-echo method (IE) is an effective stress wave based NDT method for locating defects in concrete structures. However, the contact requirement between sensor and concrete surface significantly limits the test speed and wide application of this method to large-scale structures such as bridges. Recent studies show the feasibility of air-coupled sensing, which eliminates the contact requirement and thus accelerates IE test. To further improve the test speed, a fully non-contact IE test using air-coupled sensing and excitation is investigated in this dissertation. This dissertation provides the theoretical basis required for developing an effective air-coupled IE method. For air-coupled sensing, 2D numerical simulations are first conducted to study the wave propagation in the air-solid system during IE tests. Visualized wavefield indicates that parabolic reflectors can effectively enhance the IE signal strength by focusing airborne IE waves to an air-coupled sensor. To maximize signal amplification, an analytical solution for the focused axial pressure response of a parabolic reflector with incident plane waves is derived. This solution is used to determine the reflector geometry that gives the highest focusing gain. For air-coupled excitation, a focused spark source with an ellipsoidal reflector is employed to excite stress waves in concrete. Numerical simulations and available nonlinear computer code (KZKTexas) are employed to investigate the reflector geometry that gives the highest stress wave excitation in solids. An acoustical muffler that works with the focused spark source is proposed to decrease the spark-induced noise level. The effect of source receiver spacing on received IE signals is studied. Simulated wavefield demonstrates that the mode shape of IE surface displacement distribution along the radial direction matches the Bessel function of the first kind (J0). Numerical 3D simulation results show the relation between focused IE signals and source receiver spacings, and indicate the spacing should be minimized to obtain better focused IE signal strength. Air-coupled IE test using through transmission setup is also investigated.Item A comparison of models for a piezoelectric 31-mode segmented cylindrical transducer(2013-12) Joseph, Nicholas John; Wilson, Preston S.; Haberman, Michael R.Piezoelectric transducers with cylindrical geometry are often designed to operate in a radial “breathing” mode. In order to tune their performance in a cost effective way, cylinders can be constructed of alternating active (piezoelectric) and inactive (non-piezoelectric) staves. Existing lumped parameter models for such a ring are based on effective piezoelectric properties of the composite ring which reduce the system to a single degree of freedom corresponding to the breathing motion. Unfortunately, if the length of the staves is a sufficiently large percentage of the circumference, the transducer may demonstrate a detrimental higher frequency resonance within the desired bandwidth of operation even when all staves are uniformly excited by an electrical field. This parasitic resonance results from bending motion of the staves associated with stiffness and mass discontinuities of the constituent material properties and can significantly decrease the radiated acoustic pressure and generate distortion of the radiated acoustic waveform. This work presents a multiple-degree-of-freedom lumped parameter model that captures both the breathing and bending resonances of the transducer and provides a more accurate prediction of its effective coupling coefficient. Results are compared with a one-degree-of-freedom model, finite element models, and experimental data. Modifications to account for internal volumes, nonlinearities, and other effects are also presented and discussed.Item Design and testing of sub-wavelength panels for underwater acoustic isolation(2015-08) Hicks, Ashley Jean; Wilson, Preston S.; Haberman, Michael R.Underwater sound isolation is an important area of research for both environmental and military applications. This work explores present research in airborne thin panel acoustic metamaterials and underwater acoustic isolation using encapsulated bubbles. These ideas are combined in the design of sub-wavelength, free-standing underwater panels for acoustic isolation. This work investigates the resonance of cylindrical air cavities in water with at aspect ratios. The spherical resonance approximation proposed by Minnaert for gas bubbles in water is shown to provide a good approximation of the resonance frequency of cylindrical inclusions. Panels with cylindrical inclusions are developed and tested in the 500 Hz to 1.3 kHz range and the 2 kHz to 5 kHz range. Panels with a void fraction of 1.3% and non-dimensional kT value of 0.02 to 0.07 show a frequency averaged insertion loss of 3 dB to 8 dB. Additionally, it is shown that an increase in void fraction yields an increase in panel isolation capability. It is the hope that this and future work in the area of sub-wavelength panels will improve the underwater environment for marine life and underwater naval applications.Item Development of a pneumatic infrasound generator(2014-05) Gorhum, Justin Daniel; Hamilton, Mark F.; Muir, Thomas Gustave, 1938-This thesis details the experimental development of a pneumatic infrasound generator, the purpose of which is for calibration, testing, and research. The source was an assembly of an air reservoir, a motor, and a rotor/stator pair, in the context of a siren. A rotating ball valve acted as the rotor/stator and modulated the compressed air from the reservoir as it vented into the atmosphere. The ball valve cross sectional area as a function of time varied as a triangular waveform, which in practice caused the infrasonic waveforms to be effectively sinusoidal. This thesis opens with a brief motivation for the creation of the source, in addition to previously developed infrasound generators and an overview of wind noise. The apparatus construction is then described. A theory is developed that describes the acoustic radiation from the infrasound generator as the superposition of a monopole and a dipole. Flow visualization, propagation, frequency response, reservoir volume, directivity, and jet velocity experimental setups and results are described next. The outcomes of the research are subsequently discussed, including a brief overview of a scaled up model of the infrasound generator.Item Diagnosis of Fracture Flow Conditions with Acoustic Sensing(2014-07-10) Martinez, RobertoDistributed acoustic sensing (DAS) is an emerging technology in hydraulic fracture diagnosis. Current uses of DAS systems have been limited to qualitative analysis that pinpoint noise sources, such as injection into formation or production from a fracture. Identification of noise verifies that injection or production is happening and its sound intensities at the different locations give a relative indication as to which locations took more fluid or produced more fluid post-treatment. Signal processing techniques and quantitative analysis are used to measure flow rates in a simulated fractured well. Production into a 5-? inch OD well was simulated by injecting fluid through packed bed of 16/30 mesh, 20/40 mesh and 30/50 mesh proppant. Gas was injected at varying rates into the fracture and into the well. The noise produced from production was recorded with a hydrophone. The acoustic signal was transformed from the time domain to the frequency domain through a fast Fourier transform (FFT) for analysis. The experimental results showed that the frequency of sound and its intensity were crucial in determining the amount of fluid being produced. The sound level of the peak frequencies were found to be linearly related to the flow rate. The results verified that sound alone can be used to measure flow rate through a proppant packed fracture and perforation tunnel. Incorporation of this technique into current DAS systems can give a real time value for injection rates during hydraulic fracture treatments and for production rates from post treatment measurements.Item Direct measurement of effective medium properties of model fish schools(2014-05) Dolder, Craig Nealon; Wilson, Preston S.The scattering and attenuation caused by fish schools has been extensively studied for applications in fisheries management and naval sonar. The literature contains extensive in situ measurements of scattering by fish schools, however significant uncertainties exist with respect to characterizing the size, quantity, and distribution of fish within the schools, that confounds accurate measurement-model comparison. Hence there is a need for application of measurement techniques that can more precisely characterize the acoustic properties of fish schools and the variations intrinsic to live subjects in continual motion. To begin to address this deficiency, measurements of the sound speed through collections of live fish were conducted in a laboratory setting. The species chosen for measurement were zebrafish (Danio rerio). The sound speed was investigated using a resonator technique which yielded inferences of the phase speed within the fish school though measurements of the resonances of a one-dimensional waveguide. The waveguide was calibrated to compensate for finite wall impedance and for finite reflections from the ends of the waveguide. Fish densities were investigated ranging from 8.6 to 1.7 fish lengths per mean free path. Measurements agree well with a predictive model that is based on shell-free spherical bubbles, which indicates that the phase speed is not significantly affected by the fish flesh or swimbladder morphology for the species studied. The variation in phase speed due to individual fish motion within the model school was measured to be up to ± 5.6 %. This indicates that precise knowledge of the fish position is required to achieve greater model accuracy. To compliment the phase speed measurements, the attenuation through a cloud of encapsulated bubbles was evaluated through insertion loss measurements. Multiple arrangements of balloons of radius 4.68 cm were used to surround a projector. The insertion loss measurements indicated an amplification of around 10 dB at frequencies below the individual balloon resonance frequency and an insertion loss of around 40 dB above the individual balloon resonance frequency. Analytical modeling of the bubble collection predicted both the amplification and loss effect, but failed to accurately predict the level of amplification and insertion loss. Effective medium models and full scattering models (requiring knowledge of bubble size and position) were evaluated for a model fish school. The two models agree for forward scattering for all frequencies except those immediately around the individual bubble resonance frequency. Back scattered results agree at low frequencies, however as soon as the wavelength becomes smaller than four mean free paths between fish the models diverge. Ramifications of these findings and potential future research directions are discussed.Item End-effects regime study in full-scale and laboratory scale setups(2015-12) Rojo, Raymondo Mendivil, III; Goldstein, David Benjamin, doctor of aeronautics; Tinney, Charles Edmund, 1975-; Ruf, JosephFull-scale launch data from a cluster of three rocket engines employing a Thrust Optimized Parabolic contour nozzle and hot gas was compared with a laboratory-scale representation. The laboratory setups comprised of both three-nozzle and four-nozzle cluster aerodynamically scaled for use with cold gas. The evolving free-shock separated and restricted separated shock flow states seen in the full-scale was reproduced in the laboratory as well as an end-effects regime prior to flowing full. Acoustic pressure waveforms recorded on the base of both vehicles and behind the rocket clusters are analyzed using various statistical metrics as well as time-frequency analysis, along with the influence staggered starts have on these waveforms. Wall pressure data captured near the lip of these nozzles were compared with the acoustics and analyzed for evidence of nozzle interaction. During the end-effects regime, the nozzles produced high intensity loads and steepened waveforms given by raises the overall sound pressure level, and in both the skewness and kurtosis values of the acoustic pressure time derivative. The finding reveals a 3 dB reduction in end-effect regime loads when a stagger was introduce. However, the effects of stagger had neglible influence on the skewness and kurtosis of the acoustic pressure time derivative as they rose to the same levels, thereby demonstrating the intermittence and impulsiveness of the acoustic waveforms that form during rocket engine startup.Item Extraction of blade-vortex interactions from helicopter transient maneuvering noise(2014-05) Stephenson, James Harold; Tinney, Charles Edmund, 1975-Time-frequency analysis techniques are proposed as a necessary tool for the analysis of acoustics generated by helicopter transient maneuvering flight. Such techniques are necessary as the acoustic signals related to transient maneuvers are inherently unsteady. The wavelet transform is proposed as an appropriate tool, and it is compared to the more standard short-time Fourier transform technique through an investigation using several appropriately sized interrogation windows. It is shown that the wavelet transform provides a consistent spectral representation, regardless of employed window size. The short-time Fourier transform, however, provides spectral amplitudes that are highly dependent on the size of the interrogation window, and so is not an appropriate tool for this situation. An extraction method is also proposed to investigate blade-vortex interaction noise emitted during helicopter transient maneuvering flight. The extraction method allows for the investigation of blade-vortex interactions independent of other sound sources. The method is based on filtering the spectral data calculated through the wavelet transform technique. The filter identifies blade-vortex interactions through their high amplitude, high frequency impulsive content. The filtered wavelet coefficients are then inverse transformed to create a pressure signature solely related to blade-vortex interactions. This extraction technique, along with a prescribed wake model, is applied to experimental data extracted from three separate flight maneuvers performed by a Bell 430 helicopter. The maneuvers investigated include a steady level flight, fast- and medium-speed advancing side roll maneuvers. A sensitivity analysis is performed in order to determine the optimal tuning parameters employed by the filtering technique. For the cases studied, the optimized tuning parameters were shown to be frequencies above 7 main rotor harmonics, and amplitudes stronger than 25% (−6 dB) of the energy in the main rotor harmonic. Further, it is shown that blade-vortex interactions can be accurately extracted so long as the blade-vortex interaction peak energy signal is greater or equal to the energy in the main rotor harmonic. An in-depth investigation of the changes in the blade-vortex interaction signal during transient advancing side roll maneuvers is then conducted. It is shown that the sound pressure level related to blade-vortex interactions, shifts from the advancing side, to the retreating side of the vehicle during roll entry. This shift is predicted adequately by the prescribed wake model. However, the prescribed wake model is shown to be inadequate for the prediction of blade-vortex interaction miss distance, as it does not respond to the roll rate of the vehicle. It is further shown that the sound pressure levels are positively linked to the roll rate of the vehicle. Similar sound pressure level directivities and amplitudes can be seen when vehicle roll rates are comparable. The extraction method is shown to perform admirably throughout each maneuver. One limitation with the technique is identified, and a proposal to mitigate its effects is made. The limitation occurs when the main rotor harmonic energy drops below an arbitrary threshold. When this happens, a decreased spectral amplitude is required for filtering; which leads to the extraction of high frequency noise unrelated to blade-vortex interactions. It is shown, however, that this occurs only when there are no blade-vortex interactions present. Further, the resulting sound pressure level is identifiable as it is significantly less than the peak blade-vortex interaction sound pressure level. Thus the effects of this limitation are shown to be negligible.Item Impacts of Vessel Noise Perturbations on the Resident Sperm Whale Population in the Gulf of Mexico(2012-07-16) Azzara, AlysonThe Gulf of Mexico is home to two of the world?s ten busiest ports by cargo volume, the Port of New Orleans and the Port of Houston; and in 2008, these ports hosted a combined 14,000 ships, a number which is likely only to increase. Past research shows that this increase in shipping worldwide has historically lead to an increase in ambient noise level of 3-5dB per decade. Sperm whales in the Gulf of Mexico are considered a genetically distinct, resident population. They have a preference for the Louisiana-Mississippi Shelf region which directly overlaps with the entrance to the Mississippi and the Port of New Orleans. Disruptions from vessel noise could influence feeding and breeding patterns essential to the health of the stock. Data used in this analysis were collected continuously over 36 days in the summer of 2001 from bottom moored Navy Environmental Acoustic Recording System (EARS) buoys. Results showed a significant difference (P<0.05) in noise level between hours with ships passing and hours without. Metrics for 56 ship passages were analyzed to compare duration of ship passage with duration of maximum received level (MRL) during ship passage. Results of that analysis showed an average ship passage of 29 minutes with average MRL lasting 23% of the ship passage and an average increase of 40dB. Lastly, click counts were made with the Pamguard. Click counts for ship passages were completed for 35 min and 17.5 min before and after the estimated closest point of approach (CPA) for each ship. Results showed a 36% decrease in the number of detectable clicks as a ship approaches when comparing clicks detected at intervals of both 35 minutes before and 17 minutes before the CPA; additionally, 22% fewer clicks were counted 30 min after the ship than 30 min before (results significant at the P=0.01 level). These results indicate a potential change in sperm whale behavior when exposed to large class size vessel traffic (e.g. tankers and container ships) from major shipping lanes. Recommendations for addressing this issue are discussed.Item The importance of sediment roughness on the reflection coefficient for normal incidence reflections(2011-05) Hron, Joel Maurice; Isakson, Marcia J.; Ezekoye, Ofodike A.This research experimentally shows the effect of sediment roughness characteristics on the acoustic reflection coefficient. This information is useful when trying to classify various types of sediment over an area. This research was conducted in an indoor laboratory tank at Applied Research Laboratories (ARL) at the University of Texas at Austin. A single beam echo-sounder (SBES) system was developed to project and receive a wideband (3 kHz to 30 kHz) acoustic pulse. A method was developed using the system transfer function to create a custom pulse that would minimize the dynamic range over the wide frequency band. A matched filtering and data processing algorithm was developed to analyze data over the full frequency bandwidth and over smaller frequency bands. Analysis over the smaller frequency bands showed the effect of the roughness on the reflection coefficient with respect to frequency. It was found that the reflection coefficient is significantly lower at the higher frequencies (above 20 kHz) than at the lower frequenices [sic] due to off specular scattering. It was also found that the variability of the reflection coefficient was significantly higher for the rough sediment than for the smooth sediment.Item Investigation of acoustically forced non-premixed jet flames in crossflow(2011-05) Marr, Kevin Chek-Shing; Clemens, Noel T.; Ezekoye, Ofodike A.; Hall, Matthew J.; Raman, Venkat; Varghese, Philip L.The work presented here discusses the effects of strong acoustic forcing on jet flames in crossflow (JFICF) and the physical mechanisms behind theses effects. For forced non-premixed JFICF, the jet fuel flow is modulated using an acoustic speaker system, which results in a drastic decrease in flame length and soot luminosity. Forced JFICF are characterized by periodic ejections of high-momentum, deeply penetrating vortical structures, which draws air into the jet nozzle and enhances mixing in the nearfield region of the jet. Mixture fraction images of the non-reacting forced jet in crossflow are obtained from acetone planar laser-induced fluorescence and show that the ejected jet fluid is effectively partially premixed. Flame luminosity images and exhaust gas measurements show that forced non-premixed JFICF exhibit similar characteristics to unforced partially-premixed JFICF. Both strong forcing and air dilution result in net reductions in NOx, but increases in CO and unburned hydrocarbons. NOx scaling analysis is presented for both forced non-premixed and unforced partially-premixed flames. Using flame volume arguments, EINOx scales with amplitude ratio for forced non- premixed flames, but does not scale with air dilution for unforced partially-premixed flames. The difference in scaling behavior is attributed to differences in flame structure. The effect of forcing on the flowfield dynamics of non-premixed JFICF is investigated using high-speed stereoscopic particle image velocimetry and luminosity imaging. The frequency spectra of the windward and lee-side flame base motions obtained from luminosity movies of the forced JFICF show a peak at the forcing frequency in the lee-side spectrum, but not on the windward-side spectrum. The lee-side flame base responds to the forcing frequency because the lee-side flame base stabilizes closer to the jet exit. The windward-side flame base does not respond to the forcing frequency because the integrated effect of the incident crossflow and vortical ejections leads to extinction of the flame base. From the PIV measurements, flowfield statistics are conditioned at the flame base. The local gas velocity at the flame base did not collapse for forced and unforced JFICF and was found to exceed 3SL. The flame propagation velocity was determined from the motion of the flame base, which is inferred from regions of evaporated seed particles in the time-resolved PIV images. The flame propagation velocity collapses for forced and unforced JFICF, which implies that the flame base is an edge flame; however, the most probable propagation velocity, approximately 2-3SL, is larger than propagation velocity predicted by edge flame theories. A possible explanation is that the flame propagation is enhanced by turbulent intensities and flame curvature.Item Low-frequency acoustic classification of methane hydrates(2010-12) Greene, Chad Allen; Wilson, Preston S.; Hamilton, Mark F.; Coffin, Richard B.Methane hydrates are naturally-occurring ice-like substances found in permafrost and in ocean sediments along continental shelves. These compounds are often the source of cold seeps—plumes which vent methane into aquatic environments, and may subsequently release the potent greenhouse gas into the atmosphere. Methane hydrates and methane gas seeps are of particular interest both for their potential as an energy source and for their possible contribution to climate change. In an effort to improve location of hydrates through the use of seismic surveys and echo-sounding technology, this work aims to describe the low-frequency (10 Hz to 10 kHz) acoustic behavior of methane gas bubbles and methane hydrates in water under simulated ocean-floor conditions of low temperatures and high pressures. Products of the experiments and analysis presented in this thesis include (a) passive acoustic techniques for measurement of gas flux from underwater seeps, (b) a modified form of Wood's model of low-frequency sound propagation through a bubbly liquid containing real gas, and (c) low-frequency measurements of bulk moduli and dissociation pressures of four natural samples of methane hydrates. Experimental procedures and results are presented, along with analytical and numerical models which support the findings.Item Methodology for the design of hydrophone acoustic baffles and supporting materials(2011-08) Embleton, Steven Thomas; Wilson, Preston S.; Haberman, Michael R.One key element of underwater transducer design is the acoustic baffle. Acoustic baffles isolate a structure, such as a submarine hull, from noise and vibration produced by the active elements of the transducer and vice versa. Baffle materials must meet many conflicting requirements such as the need to be lightweight while providing high acoustic isolation. Currently Syntactic Acoustic Damping Material (SADM) is widely used as the primary acoustic baffle material. However, SADM baffles have many undesirable characteristics such as high density, poor machinability, high lead content and depth dependent acoustical behavior. The study of baffle materials is an under-represented area of sonar design. Most sonar transducer research focuses on the electrically active materials and their response to a variety of conditions. Relatively fewer studies have been devoted to understanding the effects of the supporting and baffle materials. This work considers the effects of the entire hydrophone system on the response while developing a method for aiding in proper system material selection. This was accomplished by first developing a model for a transducer's response in a variety of conditions. The response was validated with numerical finite-element models and experiments. Next, a generic model was developed that allows any number of layers with any material to be analyzed. This generic model is applied in concert with a material optimization method to aid in the selection of materials that will improve the transducer's response. The tools are finally applied to a simple real world problem to illustrate its strengths and weaknesses.Item Micromachined in-plane acoustic pressure gradient sensors(2014-05) Kuntzman, Michael Louis; Hall, Neal A.; Champlin, Craig A; Driga, Mircea D; Hamilton, Mark F; Neikirk, Dean PThis work presents the fabrication, modeling, and characterization of two first-generation acoustic in-plane pressure gradient sensors. The first is a micromachined piezoelectric microphone. The microphone structure consists of a semi-rigid beam structure that rotates about torsional pivots in response to in-plane pressure gradients across the length of the beam. The rotation of the beam structure is transduced by piezoelectric cantilevers, which deflect when the beam structure rotates. Sensors with both 10 and 20-μm-thick beam structures are presented. An analytical model and multi-mode, multi-port network model utilizing finite-element analysis for parameter extraction are presented and compared to acoustic sensitivity measurements. Directivity measurements are interpreted in terms of the multi-mode model. A noise model for the sensor and readout electronics is presented and compared to measurements. The second sensor is a capacitive sensor which is comprised of two vacuum-sealed, pistons coupled to each other by a pivoting beam. The use of a pivoting beam can, in principle, enable high rotational compliance to in-plane small-signal acoustic pressure gradients, while resisting piston collapse against large background atmospheric pressure. A design path towards vacuum-sealed, surface micromachined broadband microphones is a motivation to explore the sensor concept. Fabrication of surface micromachined prototypes is presented, followed by finite element modeling and experimental confirmation of successful vacuum-sealing. Dynamic frequency response measurements are obtained using broadband electrostatic actuation and confirm a first fundamental rocking mode near 250 kHz. Successful reception of airborne ultrasound in air at 130 kHz is also demonstrated, and followed by a discussion of design paths toward improve signal-to-noise ratio beyond that of the initial prototypes presented. A method of localizing sound sources is demonstrated using the piezoelectric sensor. The localization method utilizes the multiple-port nature of the sensor to simultaneously extract the pressure gradient and pressure magnitude components of the incoming acoustic signal. An algorithm for calculating the sound source location from the pressure gradient and pressure magnitude measurement is developed. The method is verified by acoustic measurements performed at 2 kHz.Item Micromachined Optical and Acoustic Waveguide Systems for Advance Sensing and Imaging Applications(2014-07-08) Chang, Cheng-ChungEvolving from the IC fabrication processes, micromachining technologies allow mass production of 2D or 3D microstructures, which are otherwise difficult to achieve with traditional machining techniques. In this research, novel micromachining processes have been developed to enable new micro optical and acoustic waveguide systems for advanced optical sensing and acoustic imaging applications. The investigated applications include non-invasive cancer detection inside human body, in-field soil characterization, and time-delayed and multiplexed ultrasound and photoacoustic tomography. Micromachining technology enables miniaturized optical waveguide system for efficient light transmission. The small size and light-guiding capabilities are particularly useful for optical sensing at places deep inside the human body or underground. Two micromachined optical waveguide systems were fabricated and tested. The first one was used to conduct oblique incidence diffuse reflectance spectroscopy (OIDRS) for the determination of tumor margins on human pancreas specimens. The second one was used to conduct visible-near-infrared diffuse reflectance spectroscopy (VNIR-DRS) for extracting the compositional information of soil samples. Micromachining technology also makes it possible to utilize single-crystalline silicon as a structural material for acoustic wave propagation. It enables the development of high-performance integrated acoustic circuits and allows direct acoustic signal processing and control. The acoustic properties and propagation inside silicon waveguides were characterized, and the acoustic signal processing using micromachined acoustic waveguide system was investigated. Based on the results, two acoustic waveguide systems were designed and constructed. The first system utilized micromachined acoustic delay lines to passively delay acoustic signal thereby reducing the required transceivers and processing electronics; while the second system employed micromachined acoustic multiplexer to actively control the transmission of acoustic signals. Both techniques are expected to provide new solutions to reduce the complexity and cost of the acoustic receiver systems in ultrasound and photoacoustic imaging.Item Modeling and prototyping of a micromachined optical microphone(2010-12) Kuntzman, Michael Louis; Hall, Neal A.; Wilson, Preston S.A microelectromechanical systems (MEMS) optical microphone that measures the interference of light resulting from its passage through a diffraction grating and reflection from a vibrating diaphragm (JASA, v. 122, no. 4, 2007) is described. In the present embodiment, both the diffractive optical element and the sensing diaphragm are micromachined on silicon. Additional system components include a semiconductor laser, photodiodes, and required readout electronics. Advantages of this optical detection technique have been demonstrated with both omni-directional microphones and biologically inspired directional microphones. In efforts to commercialize this technology for hearing-aids and other applications, a goal has been set to achieve a microphone contained in a small surface mount package (occupying 2mm x 2mm x 1mm volume), with ultra-low noise (20 dBA), and broad frequency response (20Hz–20kHz). Such a microphone would be consistent in size with the smallest MEMS microphones available today, but would have noise performance characteristic of professional-audio microphones significantly larger in size and more expensive to produce. This paper will present several unique challenges in our effort to develop the first surface mount packaged optical MEMS microphone. The package must accommodate both optical and acoustical design considerations. Dynamic models used for simulating frequency response and noise spectra of fully packaged microphones are presented and compared with measurements performed on prototypes.Item Modeling three-dimensional acoustic propagation in underwater waveguides using the longitudinally invariant finite element method(2014-08) Goldsberry, Benjamin Michael; Hamilton, Mark F.; Isakson, Marcia J.Three-dimensional acoustic propagation in shallow water waveguides is studied using the longitudinally invariant finite element method. This technique is appropriate for environments with lateral variations that occur in only one dimension. In this method, a transform is applied to the three-dimensional Helmholtz equation to remove the range-independent dimension. The finite element method is employed to solve the transformed Helmholtz equation for each out-of-plane wavenumber. Finally, the inverse transform is used to transform the pressure field back to three-dimensional spatial coordinates. Due to the oscillatory nature of the inverse transform, two integration techniques are developed. The first is a Riemann sum combined with a wavenumber sampling method that efficiently captures the essential components of the integrand. The other is a modified adaptive Clenshaw-Curtis quadrature. Three-dimensional transmission loss is computed for a Pekeris waveguide, underwater wedge, and Gaussian canyon. For each waveguide, the two integration schemes are compared in terms of accuracy and efficiency.Item Nonlinear acoustical detection of buried landmines using pulsed standoff excitation(2014-05) Copenhaver, Benjamin Joseph; Hamilton, Mark F.To help resolve certain practical issues with acoustical methods for landmine detection, experiments were performed using a pulsed, standoff source consisting of sixteen speakers mounted on a circular arc. This source, as well as a pair of 18-inch subwoofers, were used separately for acoustical excitation of the buried mine, and the response of the target site was examined as a function of source frequency, sound pressure level, and excitation signal type, with a particular focus on multitone signals. In addition, modeling was undertaken to investigate the effects of nonlinearity, including bimodular nonlinearity, on frequency generation. A numerical, time-domain solution based on a lumped-element model proposed by Donskoy et al. [J. Acoust. Soc. Am. 117, 690 (2005)] was developed and used to simulate pulsed excitation and the effects of bimodular nonlinearity, which allowed experimentally observed spectra to be compared with modeled results.