Nonlinear Shear Waves in Relaxing Media

Friday, January 26, 2018
4:00 pm in ETC 4.150

John M. Cormack
Applied Research Laboratories
The University of Texas at Austin
http://www.arlut.utexas.edu

Soft materials such as rubbers, polymers, and tissue exhibit low shear-wave speeds, facilitating the generation of shear waves with large acoustic Mach numbers that propagate very slowly, on the order of meters per second, exhibiting waveform distortion and even shock formation within a few centimeters from the source. In addition to finite-amplitude effects that result from cubic nonlinearity, plane shear wave propagation in these materials is subject to frequency-dependent attenuation and dispersion that result from viscoelastic effects. Stress relaxation is a simple model for viscoelasticity that has been observed in measurements of soft rubbers and biomaterials in the frequency range of interest. A model is presented that describes plane shear waves in a relaxing material, accounting for cubic nonlinearity as well as the attenuation and dispersion associated with relaxation. For both progressive and standing waves, analytical solutions of the model equations are derived and supplemented with numerical simulations in order to investigate the interaction of, and competition between, nonlinear and viscoelastic effects in shear wave motion.

Advanced Pattern Recognition Techniques for Wave-Based
Structural Health Monitoring of Metallic Panels

Friday, February 2, 2018
4:00 p.m. in ETC 4.150

Arvin Ebrahimkhanlou
Department of Civil, Architectural and Environmental Engineering
The University of Texas at Austin
http://www.caee.utexas.edu/civil

The increasing age of aerospace and naval structures, such as airplanes and marine vessels, and the desire to reduce the downtime associated with their regular maintenance operations have all sparked interests into structural health monitoring (SHM) methods. One of the promising SHM approaches for such structures is based on guided ultrasonic waves generated and received by a network of low-profile piezoelectric transducers. Despite the significant development of such SHM systems, very few have been implemented in real structures. One major reason for this lack of acceptance is the potential for these systems to emit false positives, which means falsely detecting structural damage while no damage exists. Many of such false positives are due to the multiple reflections of the interrogating waves from structural and geometrical features, such as boundaries, stiffeners, and fasteners. These reflections, if not properly considered, often falsely appear as damage. In the light of these considerations, the ultimate objective of this research is to design, implement, and validate a novel probabilistic framework to enhance the accuracy and the capabilities of guided ultrasonic wave-based techniques for the SHM of metallic panels. In particular, the focus will be on analyzing the patterns of edge-reflected guided-ultrasonic reverberations in thin metallic plate-like structures, which are ubiquitous in marine and aerospace industries. The uniqueness of the framework resides in the development of a data processing method that leverages the reverberation patterns of guided ultrasonic waves to more accurately find the location of damage while using fewer transducers than the current algorithms.

Focused Ultrasound for Targeted and Noninvasive Therapies

Thursday, February 8, 2018
3:30 p.m. in BME 3.204

Dr. Jan Kubanek
Department of Neurobiology and Radiology
Stanford University School of Medicine
http://med.stanford.edu

The future of effective therapies lies in approaches that specifically target aberrant tissue while being applied remotely, in an incisionless manner. Focused ultrasound has emerged as a unique theranostic modality that combines depth penetration and sharp focus, within which it can exert mechanical or thermal effects. The modality begins to be used for noninvasive stimulation of excitable cells and for targeted drug delivery. The ability of ultrasound to remotely stimulate excitable cells has far-reaching implications for treatments of disorders of the nervous system. I have pursued this direction under a K99/R00 grant from the NIH. I will present our recent findings regarding the biophysical mechanism using which ultrasound stimulates excitable cells, show how that knowledge informs the design of stimulation protocols, and demonstrate an application of the method in noninvasive stimulation of neurons in specific brain regions in behaving primates. I will also introduce our future directions. In addition to stimulation of excitable cells, we will use focused ultrasound to uncage drugs from nanoparticle carriers, and develop systems to deliver ultrasound into specific brain regions in awake behaving animals and humans.

A Novel Fabrication Process for Capacitive Micromachined Ultrasonic Transducers

Friday, February 9, 2018
4:00 p.m. in ETC 4.150

Sam Hord
Department of Mechanical Engineering
The University of Texas at Austin

A novel fabrication method for producing capacitive micromachined ultrasonic transducers (CMUTs) is presented. The process uses conductive silicon on insulator (SOI) substrates to produce an unstressed transducer diaphragm. By etching release holes through the device layer and selectively removing the underlying buffered oxide (BOX) layer, an ultrasonic transducer can be made using only two photolithography steps. The process is described in detail, including models predicting the modal behavior and the collapse voltage of the device. The acoustical behavior of a perforated plate over a sealed cavity is modeled using mechano-acoustical circuit analysis. The device is found to produce sound despite the perforations so long as the holes are sufficiently small and the frequency of operation is sufficiently high. A pitch-catch measurement verifies the transduction of the device. To the author’s knowledge, this is the simplest method for CMUT fabrication to date.

Damage and Stress Monitoring in Structures Using Guided Waves

Friday, February 16, 2018
4:00 p.m. in ETC 4.150

Brennan Dubuc
Department of Civil, Architectural, and Environmental Engineering
The University of Texas at Austin
http://www.caee.utexas.edu/civil

There is a fundamental need to detect and characterize damage in a wide variety of civil, aerospace, and naval structures. These include prestressing/post-tensioning strands, pipelines, and aerospace/naval panels. To fulfill this need, structural health monitoring (SHM) methods have developed continually over the past decades. In order to move toward automation and faster inspection in SHM, guided ultrasonic waves (GUWs) that are influenced by the shape of a structure may be exploited. Two main topics of using GUWs are addressed in this work: (1) damage monitoring; and (2) stress monitoring. Damage monitoring involves extracting information from GUW signals, in order to infer the presence of damage in a structure. Similarly, stress monitoring infers the presence of stress, which also has implications for the health of a structure. This work presents damage monitoring for crack and impact detection in panels, corrosion and crack detection in pipelines, and corrosion detection in strands. In particular, signal processing techniques are developed to interpret damage signatures, using tools such as sparse reconstruction. In addition to their damage sensitivity, GUWs are also sensitive to the stresses present in structures. Stress variations can therefore be falsely interpreted as damage evolution, so it is important to compensate for the presence of stress. Although stress sensitivity presents a challenge for damage monitoring, it may also be leveraged to perform the stress monitoring necessary in certain structures. For instance, stress monitoring is the primary tool used to predict fatigue life in aerospace components. Stress is a source of nonlinearity in GUWs, for which the theory of acoustoelasticity was developed. In this work, advancements in acoustoelasticity are presented for the purposes of stress compensation and stress monitoring in panels and strands. These topics can lead toward the development of a multipurpose GUW system for damage and stress monitoring.

Underwater Sound Propagation Over the Chukchi Sea Continental Slope

Tuesday, February 20, 2018
10:00 a.m. in ARL Auditorium

Dr. Ying-Tsong Lin
Applied Ocean Physics & Engineering
Woods Hole Oceanographic Institute
http://www.whoi.edu

In the Canada Basin and Chukchi Sea regions, a vertical sound duct can be formed between the Pacific Summer Water Layer on the top and the Atlantic Water Layer on the bottom, providing an acoustic pathway connecting the deep basin and the shallow shelf over the Chukchi Sea continental slope. Previous studies have shown that the shelfbreak circulation (specifically upwelling), the sub-mesoscale eddies spun off the shelfbreak jet, and the ice coverage are the three major causes of the temporal and spatial variability of the Pacific Summer Water Layer in the region. In this talk, a numerical study of sound propagation variability over the Chukchi Sea shelfbreak and slope using the Parabolic-Equation (PE) approximation method along with an idealized ocean circulation model will be presented. The acoustic data over the northern Chukchi Sea shelfbreak collected during the Canada Basin Acoustic Propagation Experiment will be examined and compared with the numerical simulations.

Drone Acoustics at Static Thrust

Friday, March 2, 2018
4:00 pm in ETC 4.150

Dr. Charles E. Tinney
Applied Research Laboratories
The University of Texas at Austin
http://www.arlut.utexas.edu

Multirotor drones are becoming increasingly popular in both the civilian and military sectors of our society. These compact gadgets come in a variety of sizes with the smallest ones measuring less than two inches in diameter, while larger ones can be in excess of five feet. Surprisingly, very little is known about their acoustical footprint, which is becoming a topic of broad importance given that these vehicles most often operate in populated areas. Thus, a first principles understanding of the sound field produced by multirotor drones in hover is presented. Propeller diameters ranging from 8 in. to 12 in. are examined and with configurations comprising an isolated rotor, a quadcopter, and a hexacopter configuration. The drone pitch, defined as the ratio of drone diameter to rotor diameter, is the same for all multirotor configurations and is valued at 2.25. A six degree-of-freedom load cell is used to assess the aerodynamic performance of each configuration while an azimuthal array of half-inch microphones, placed between 2 and 3 hub-center diameters from the drone center, are used to assess the acoustic near-field. The analysis is performed using standard statistical metrics such as Sound Pressure Level and Overall Sound Pressure Level and is presented to demonstrate the relationship between the number of rotors, the drone rotor size and it’s aerodynamic performance (thrust) relative to the near-field acoustics.

Development and Implementation of Three-Dimensional Models for Scattering from Buried Objects

Friday, March 9, 2018
4:00 pm in ETC 4.150

Dr. Aaron Gunderson
Applied Research Laboratories
The University of Texas at Austin
http://www.arlut.utexas.edu

High fidelity modeling of acoustic scattering from objects at interfaces has profound implications for detection, classification, and recovery of objects on the seafloor. Analytical scattering solutions and approximations are few and are limited in their applicability and effectiveness. Finite element models have proven to be among the most accurate, quick, and reliable methods for predicting the scattering signature of elastic objects both in the free field and at interfaces, yet modeling capability is often limited by computational burden. Full three-dimensional finite element calculations are computationally intensive to produce, and are rarely found in published literature. Various techniques are often employed which allow the model to be solved using a two-dimensional domain, after which results are artificially extended to three dimensions by exploiting an environmental symmetry condition. These techniques have recently been used to model scattering in the time domain. For nonsymmetrical objects or environments, such techniques do not apply, and 3D models must be used. The development of a full 3D model for buried objects is currently underway. This model relies on a very small domain to reduce computational burden, and implements a fully scattered field formulation for high accuracy results. Near field results are extended to the far field through numerical determination of the two-medium Green’s function.

An Overview of Acoustics Research at the Naval Research Laboratory

Friday, March 30, 2018
1:30 pm in ETC 3.108

Dr. Brian Houston, Dr. Jeffrey Baldwin, Dr. Saikat Dey, and Dr. Zachary Waters
Acoustics Division
U.S. Naval Research Laboratory
Washington, D.C.
https://www.nrl.navy.mil/acoustics

This seminar will focus on an introduction to the Physical Acoustics Branch at the Naval Research Laboratory, which carries out a broad basic research portfolio that is vertically integrated with applications resulting in transitions that include the US Navy fleet. Current Condensed Matter research areas include Control of Phonon Transport in Thin Films and Thermoelectric materials, High-Q dielectric thin films for Q-bits and detectors, Nano-mechanical resonators and devices as well as Hydrogen in Graphene Storage for Fuel Cells. We will also introduce our applications research areas that include advanced numerical techniques for high DOF systems, Single Crystal Materials for Transduction, Fiber-Optic Acoustic Sensors, Broadband Target Scattering Physics and Structural Acoustics Sonar (Acoustic Color) for advanced detection and classification. We are also exploring Acoustic Stealth for Underwater Systems, Distributed Autonomous Systems (DAS), Buried Object Detection and Classification, and sonars integrated with Advanced Autonomy for Unmanned Underwater Vehicles (UUVs). After a summary discussion of our current research areas, we will provide a focus on up to three of the research items in the above list.

Characterization of Sound Power Level Spectra Produced by HVAC Chillers with Double Helical Rotary Screw Compressors

Friday, April 6, 2018
4:00 pm in ETC 4.150

Daniel A. Hemme
BAi, LLC
Austin, Texas
https://www.baiaustin.com

Heating, ventilating, and air conditioning (HVAC) chiller units with double helical rotary screw compressors, or screw chillers, have been in common use since the mid-to-late 1980s. Sound level data for this type of equipment is generally available through the manufacturer on a broadband (often A-weighted) or octave-band basis. However, screw chillers produce sound spectra with prominent narrow-band components that are not adequately described by broad-band or octave-band data. The object of the study discussed in this presentation was to take the first steps towards developing empirical correlations that yield typical sound power level (PWL) spectra for air- and water-cooled screw chillers under specified operating conditions, similar to the equations which have been developed for many other types of mechanical and industrial equipment. PWL was determined on a one-third-octave-band basis for several local screw chillers, most under multiple operating conditions, using the two-surface method. Preliminary empirical correlations were developed to describe the PWL spectra produced by air- and water-cooled screw chillers. The utility of the empirical correlations to the architectural acoustical consultant is demonstrated in this presentation, with examples. The main job functions of an architectural acoustical consultant include providing advice regarding room acoustics, sound isolation, and noise control, as well as sound reinforcement and audio-visual systems design. The role of the architectural acoustical consultant in the building design process, and in the investigation and remediation of acoustical deficiencies in occupied buildings, will also be discussed.

Dynamic Pressure Sensors for Hypersonic Flow Measurement

Friday, April 13, 2018
4:00 p.m. in ETC 4.150

Yoonho Seo
Department of Mechanical Engineering
The University of Texas at Austin
http://www.me.utexas.edu

This presentation will focus on the research and development of an acoustic pressure
sensor designed for hypersonic flow measurement. Hypersonic flows (normally more
than 5 times the speed of sound, Mach 5) are characterized by shocks, laminar-toturbulent
transitions, elevated temperature, and high-frequency turbulence with small
(sub–1 mm) characteristic length scales. Non-invasive pressure measurements at the
walls of such flows allow useful diagnostics to predict the characteristics of the flow
and are desired by the hypersonic community. The desired sensor specifications are
as follows: operation up to 1,000 K temperature, 1.0 MHz bandwidth, and sensing
elements spanning less than 500 µm. The chosen embodiment is a piezoelectric sensor
employing aluminum nitride as the piezoelectric material. The preliminary prototypes
have been constructed and tested. These sensors are comprised of four diaphragms
with 500 µm diameter and 2 µm thickness. The results of pressure measurement under
Mach 2.3 flow in a wind tunnel will be presented alongside the rigorous performance
characterization of these sensors, the exploration of an array embodiment to enable
pressure gradient measurements, and sensor design and characterization.

An Adaptive Discontinuous Petrov Galerkin Method for
High Frequency Time-Harmonic Wave Propagation Problems

Friday, April 20, 2018
4:00 pm in ETC 4.150

Socratis Petrides
The Institute for Computational Engineering and Sciences
The University of Texas at Austin
https://www.ices.utexas.edu

The goal of this work is to develop an efficient and robust method for the simulation of high frequency wave propagation problems. The first part of the talk will focus on the description of the Discontinuous Petrov Galerkin (DPG) method and its attractive features, i.e, different variational formulations, unconditional discrete stability and automatic hp-adaptivity. As a model problem, we simulate a high frequency Gaussian beam in two and three space dimensions. In the second part of the talk, we outline the construction of a new iterative solution scheme, for the solution of the DPG linear system. This new solver works hand in glove with the adaptive procedure by constructing a two-grid solver using the adaptive meshes. We demonstrate this technology on the solution of the linear acoustics problem in two space dimensions. Our results show convergence in terms of iterations at a rate independent of the mesh and the wavenumber. We conclude the talk with a discussion of ongoing work to extend the solver in the multi-grid setting for problems in three space dimensions.

Environmental Noise from Underwater Explosions and the Impact of the Seabed on the Received Levels

Friday, April 27, 2018
10:30 a.m. in ARL Auditorium

Alexander G. Soloway
Applied Physics Laboratory
University of Washington
http://www.apl.washington.edu

In the following work measurements of underwater explosions from three experimental sites will be presented and compared. The goals of this work will be to present the measurements of small underwater explosions (charges weighing between 0.5 kg and 20 kg) with an emphasis on the metrics commonly used to describe environmental noise including the peak pressure and the SEL. These data will be provided within the context of the measurement environments, the seabed in particular, so that they can be more effectively utilized by both researchers and policy makers for studying environmental noise and in the development of mitigation measures to protect marine life from harmful noise levels.

An Introduction to the Theory of Predicting Noise from Turbulence with a Historical Perspective

Friday, August 31, 2018
4:00 pm in ETC 4.150

Professor Steven A. E. Miller
Department of Mechanical and Aerospace Engineering
University of Florida
http://www.mae.ufl.edu/people/sae-miller

The prediction of noise from turbulence continues to be a curious problem in fluid dynamics over the course of many decades. Acoustic analogies represent an exact rearrangement of the equations of motion for the purpose of noise prediction. We review major developments in the theories of Lighthill, Ffowcs-Williams, Lilley, and Tam and their associated historical motivation. The limitations of these models are identified and resolved through a new approach. The mathematics of the approach are described. The new capability is illustrated through the prediction of noise from isotropic turbulence and from a high-speed jet flow. The implications of the new model and associated future research will be outlined. Finally, a short description of other research endeavors within the group will be presented.

Exploring the Modern Arctic Soundscape

Friday, September 7, 2018
4:00 pm in ETC 4.150

Dr. Jason D. Sagers and Dr. Megan S. Ballard
Applied Research Laboratories
The University of Texas at Austin
http://www.arlut.utexas.edu/

The Pacific Arctic Region has experienced recent decadal changes in atmospheric conditions, seasonal sea-ice coverage, and seawater temperature. The pace of these environmental changes, particularly the rapid decline in sea-ice extent, has given rise to the phrase “the modern Arctic” to differentiate from the Arctic conditions of only 40 years ago.  Scientific observations of the region seek to understand the magnitude, extent, and impact of these changes on regional and global scales.

From October 2016 to October 2017, the Canada Basin Acoustic Propagation Experiment (CANAPE) was conducted in an area extending from the Chukchi Shelf into the Beaufort Sea to understand the changing soundscape and to explore the use of acoustic signals as a remote sensing tool in the modern Arctic.  As part of a multi-institutional research collaboration, scientists from the Applied Research Laboratories deployed passive acoustic receivers on the Chukchi Shelf to monitor the ambient noise field and to receive acoustic transmissions from moored, low- and mid-frequency acoustic sources.  During the recovery cruise, ARL scientists also deployed the Acoustic Coring System to collect seabed samples and to make in-situ measurements of seabed properties.

This talk presents initial results from four areas of ongoing data analysis:  1) statistics of the ambient noise field on the Chukchi shelf; 2) temporal variability of low-frequency, long-range acoustic propagation; 3) in-situ observations of seabed properties; and 4) acoustic inference of seabed properties using opportunistic noise sources.  These analyses contribute to understanding the larger spatiotemporal complexities of the Arctic acoustic environment.

Introduction to Vortex Sound Theory and Application to the Prediction of Vortex Pairing Noise

Friday, September 14, 2018
4:00 p.m. in ETC 2.136

Professor Christophe Schram
Aeronautics and Aerospace Department
Environmental and Applied Fluid Dynamics Department
von Karman Institute for Fluid Dynamics
Brussels, Belgium

The aeroacoustic analogy proposed by Lighthill in the 1950s provides a theoretical framework that has made possible the successful prediction of the noise emitted by free turbulent flows in numerous instances. Yet, the form taken by the equivalent source term of this analogy (involving the Reynolds stress tensor) is causing some numerical difficulties in some cases, related to the relatively large spatial spreading of the apparent source field, extending to relatively quiet regions of the flow. Vortex Sound Theory (VST) proposes a reformulation of the aeroacoustic analogy in which the source term involves the vorticity, which leads to a much more concentrated distribution of equivalent sources in most flows. In addition, in some cases this formulation permits the recurrent imposition of physical assumptions that considerably reinforce the numerical robustness of the noise prediction. Those concepts are illustrated through the application of a so-called conservative formulation of Powell/Möhring VST to an academic vortex interaction: the leapfrogging and merging of two vortex rings. It is demonstrated that the conservative VST formulation enables an accurate prediction of the noise emitted by this mechanism, even when an experimental description of the flow field—inherently contaminated by measurement errors—is used as input.

Nonlinear Waves in Granular Crystals:
History and Current Topics

Friday, September 21, 2018
4:00 p.m. in ETC 2.136

Dr. Samuel P. Wallen
Applied Research Laboratories
The University of Texas at Austin
http://www.arlut.utexas.edu/

Ordered arrays of spherical particles in contact, often referred to as granular crystals (GCs), have been shown to exhibit rich nonlinear dynamics stemming from contact forces and hold promise as a class of mechanical wave-tailoring media. While most of the existing literature on GCs has focused on 1D nonlinear wave propagation in macro-scale systems, recent advances in self-assembly fabrication methods have enabled the study of GCs composed of microscale particles, which may have long-range order in two and three dimensions and are statically compressed by short-range adhesive forces. Recent theoretical and computational studies on 2D, pre-compressed GCs have revealed complex interplay between nonlinearity, shear interactions, and particle rotations.

This talk will provide an overview of linear and nonlinear wave phenomena in this rich and evolving field. We will begin with a discussion of dispersive waves in 1D GCs, highlighting the near-linear, weakly-nonlinear, and strongly-nonlinear regimes and illustrating connections to the classical Fermi-Pasta-Ulam problem and the Korteweg-de Vries equation. Next, we will review linear dynamics of 2D, pre-compressed GCs with emphasis on shear and rotational waves. We will conclude with a presentation of recent computational results on nonlinear waves in 2D GCs, focusing on the propagation of nonlinear bulk and surface waves from an impulsive point source at a traction-free boundary.

Acoustic Wave Propagation:
Numerical Modeling and Its Control via Acoustic Metamaterials/Metasurfaces

Thursday, September 27, 2018
4:00 p.m. in ETC 5.132

Professor Yun Jing
Department of Mechanical and Aerospace Engineering
North Carolina State University
https://www.mae.ncsu.edu/jing/

This talk will be divided into two parts. In the first part, I will talk about our recent work on numerical modeling of acoustic wave propagation at ultrasound frequencies in both homogeneous and heterogeneous media, such as biological tissue. An extended angular spectrum approach was developed for modeling nonlinear wave propagation in homogeneous media. Based on this approach, transient nonlinear acoustical holography has been investigated. A mixed-domain method and a k-space time-domain method were also developed, which are capable of modeling linear or nonlinear wave propagation in arbitrarily heterogeneous media in a computationally efficient manner. I will talk about their potential applications in biomedical ultrasound and other areas. In the second part, I will talk about our recent work on acoustic metamaterials and metasurfaces. This part will include our work on acoustic hyperbolic metamaterials, acoustic complementary metamaterials, and acoustic metasurfaces for asymmetrical sound transmission.

Infrasound Analysis Using Regional Seismo-Acoustic Array Data

Friday, October 5, 2018
4:00 p.m. in ETC 2.136

Dr. Junghyun Park
Department of Earth Sciences
Southern Methodist University
https://www.smu.edu/Dedman/Academics/Departments/EarthSciences/People/Staff/Park

Infrasound—inaudible low-frequency (<20 Hz) sound waves that propagate in the atmosphere—is generated by natural (i.e., earthquakes, volcanos, bolides, and tornados) and human activities (i.e., nuclear/chemical/mining explosions, rocket launches, and motor tests).  The development of seismo-acoustic arrays provides an opportunity to study infrasound and seismic signals from sources that couple energy to both the atmosphere and the solid Earth.  This talk provides an overview of regional infrasound monitoring that includes signal detection based on array processing, association between detections at multiple arrays, and subsequent event location.  Various applications using infrasound data on the Korean Peninsula and in the western U.S. are presented.  Knowledge of background noise and diurnal or seasonal variations in the atmosphere impacts infrasound detection and provides a basis for evaluating array performance under changing environmental conditions, as well as providing a basis for improved event locations.  Ground truth sources such as rocket motor tests and rocket body demolition on the Earth surface are used to assess temporal changes in atmospheric conditions and the consequences of these changes to infrasound detection.  These comparisons are used to assess the predictive capabilities of the current generation of time-dependent atmospheric specifications.  Results of these studies illustrate that developing infrasound technology provides a robust tool for assessing natural and anthropogenic phenomena using signals observed at regional distances.

Seeing the World Through Their Ears: The Sensory World of Bats and
What They Can Teach Us About the Operation of the Brain

Friday, October 12, 2018
4:00 p.m. in ETC 2.136

Professor George D. Pollak
Department of Neuroscience
The University of Texas at Austin
G. D. Pollak faculty page

In this lecture I shall discuss the world of bats from the perspective of a sensory physiologist whose research is concerned with the mechanisms by which the mammalian auditory system processes and represents external features of the world.  My theme will be that what we perceive is nothing more than that which our brains construct for us from the information provided by our sensory receptors.  Which brings me to bats, because these animals “see” their world through their ears by using a form of biological sonar called echolocation.  As a sensory physiologist, I always have to wonder, “How do they do it?”  What exactly occurs in the brain to endow a species with a new ability, which in turn, provides it with an advantage for survival?  And how do the neural adaptations for echolocation co-exist with neural processes for vocal communication?  I will argue that whatever the circuits and mechanisms are that enable bats to form images of objects in their environment by listening to echoes, they are also present in humans.  I will bolster this assertion with Daniel Kish, who is blind but can echolocate almost as well as a bat by emitting clicks and listening to the echoes from nearby objects.

Using the Sound of Nuclear Power

Friday, October 19, 2018
4:00 p.m. in ETC 2.136

Professor Steven L. Garrett (Retired)
Graduate Program in Acoustics
The Pennsylvania State University
https://www.acs.psu.edu/

Motivated by the Fukushima nuclear reactor disaster in March 2011, a thermoacoustic engine that exploits the energy-rich conditions in the core of a nuclear reactor was designed and tested to telemeter core condition information to the operators without a need for external electrical power. The heat engine is self-powered and can wirelessly transmit the temperature and reactor power level by generation of a pure tone that can be detected outside the reactor. A standing-wave thermoacoustic engine with dimensions identical to an ordinary fuel rod was placed in the core of the Breazeale Nuclear Reactor on Penn State’s campus. The heat necessary to produce thermoacoustic oscillations was provided by two 10 mm long by 5 mm diameter, 7.5% enriched, ²³⁵U fuel pellets. Those pellets were contained within a stainless-steel finned heat exchanger that was fabricated by additive manufacturing (3-D printing). The (mass-controlled) resonator was suspended in the surrogate fuel rod using two six-armed leaf springs (spiders) that centered the resonator in the “slotted tube” and allowed longitudinal vibrations of the entire resonator that coupled the oscillatory momentum of the gas within the resonator to the surrounding light-water reactor coolant. A 2.0 MPa mixture of 25% argon and 75% helium provided a good trade-off between dipole radiation efficiency, resonator length, and low onset temperature differential, to produce a frequency that was high enough to be detectable above the dominant noise produced by coolant and ¹⁶N diffusion pumps. These trade-offs were optimized using the Los Alamos DeltaEC software.

Are Two Ears Better Than One?

Friday, October 26, 2018
4:00 p.m. in ETC 2.136

Professor Craig A. Champlin
Department of Communication Sciences and Disorders
The University of Texas at Austin
https://csd.utexas.edu/faculty/craig-champlin

The answer to this question is obviously yes. We know that having two ears enables localization of sound sources, enhances signal perception in noisy backgrounds and helps reduce overall listening effort. Although we understand these two-ear advantages in a general sense, how do we measure a given person’s binaural capabilities? As a clinical audiologist, I am interested in this question because I evaluate individual patients. Curiously, the standard battery of audiological tests does not typically include any binaural tests. This omission seems odd given that having trouble hearing in noise is a frequent complaint of adults seeking professional hearing assessment services. I will discuss methods we currently use in a clinical lab that provide reliable and efficient measures of binaural hearing and will pay particular attention to the measurement of speech perception in noise. I will consider the concept of “auditory stream segregation.” Sounds that arise from a specific physical location in auditory space tend to be perceived as a discrete stream and can be selectively attended to and tracked as a separate entity. To illustrate the clinical approach, I will also describe a new tool for assessing potential deficits in auditory stream segregation.

MaD TwinNet: Masker-Denoiser Architecture with Twin Networks for Monaural Sound Source Separation

Friday, November 2, 2018
4:00 p.m. in ETC 2.136

Professor Gerald Schuller
Institute for Media Technology, Technical University of Ilmenau
Fraunhofer Institute for Digital Media Technology
Ilmenau, Germany
https://www.tu-ilmenau.de/en/applied-media-systems-group/

Monaural singing voice separation task focuses on the prediction of the singing voice from a single channel music mixture signal. Current state of the art (SOTA) results in monaural singing voice separation are obtained with deep learning based methods. In this work we present a novel deep learning based method that learns long-term temporal patterns and structures of a musical piece. We build upon the recently proposed Masker-Denoiser (MaD) architecture and we enhance it with the Twin Networks, a technique to regularize a recurrent generative network using a backward running copy of the network. We evaluate our method using the Demixing Secret Dataset and we obtain an increment to signal-to-distortion ratio (SDR) of 0.37 dB and to signal-to-interference ratio (SIR) of 0.23 dB, compared to previous SOTA results.

Life After Graduation: Careers and Case Studies in Acoustics

Friday, November 16, 2018
4:00 p.m. in ETC 2.136

Dr. Douglas F. Winker
ETS-Lindgren, Inc.
Cedar Park, Texas
http://www.ets-lindgren.com

With exams and homework looming, it may not seem like it right now but one day you will graduate and have to get a job. What types of jobs are out there in acoustics? What companies are hiring acoustical engineers and why? Some of the answers to these questions may seem obvious, but oftentimes they are surprising. I know I did not follow the career path I laid out while in graduate school. I design acoustical test chambers and test solutions for companies and universities around the world. Each company and university has different requirements and usually has an acoustical engineer on staff. This talk will present multiple case studies of projects ranging from anechoic chambers to tabletop test enclosures. While each case study will feature the measurement problem and solution, particular focus will be on the engineer behind the project and the variety of careers available for acoustical engineers.

Noise Control in a Vacuum

Friday, November 30, 2018
4:00 p.m. in ETC 2.136

David A. Nelson, P.E.
Nelson Acoustics
Elgin, Texas
www.nelsonacoustical.com

Noise control recommendations for industrial equipment are ideally based on measured data or, if data is insufficient, on empirical noise emission models. How does one proceed when neither is available? A recent project presented that very dilemma. NASA’s Space Environments Complex employs two chains of powerful rotary-lobe (“Roots”) blowers to evacuate the world’s largest space simulation thermal-vacuum chamber. A vacuum of a different sort was encountered when it became apparent that noise data is scarce and that noise emission models for rotary-lobe blowers are incomplete. Moreover, the blower system is a one-of-a-kind extreme-engineering showcase that operates very infrequently. Therefore the relative contribution of inlet, discharge, and gear noise, which are critical to making recommendations, cannot be determined without running the Chamber. Naturally, the client needs noise control treatments in place before the next pump-down. This seminar will cover an overview of the Vacuum Chamber, the general function and configuration of the blowers, sound levels observed during operation, likely noise generating mechanisms (including an attempt to estimate the spectrum of a monopole source driving shock and expansion waves), as well as the recommended treatments and how they were selected.

Flush Mounted Piezoelectric Microphones for Flight Testing

Friday, December 7, 2018
4:00 p.m. in ETC 2.136

Professor Mark Sheplak
Department of Electrical and Computer Engineering
Interdisciplinary Microsystems Group
University of Florida
http://www.img.ufl.edu

To understand and mitigate the impact of noise sources on an aircraft, researchers in aeroacoustics are in need of high performance, low cost microphones to address the increasing noise restrictions on commercial aircraft. Existing commercial sensors, even with their relatively high cost, in some cases constrain the quality and type of measurements that may be achieved. This talk presents the design, fabrication and calibration developments of the first truly flush-mount piezoelectric microelectromechanical (MEMS) dynamic pressure sensor with associated packaging for aircraft fuselage arrays. Through-silicon-vias (TSVs) are incorporated into the fabrication of the sensor to eliminate front-side wire bonds and enable an overall flush surface for the packaged sensor that minimizes flow disturbance. The developed packaging method for the sensor demonstrates an overall flushness to within 10 µm, showing substantial improvement over any previously reported efforts.