Acoustics Seminars

The Prediction and Reduction of Jet Noise from Tactical Fighter Aircraft

Friday, April 26, 2013 4:00 p.m. in ETC 4.150

Professor Philip J. Morris
Department of Aerospace Engineering
The Pennsylvania State University
http://www2.aero.psu.edu/morris/

The noise generated by modern tactical fighter aircraft can cause noise-induced hearing loss in personnel located near the aircraft and annoyance in communities surrounding military bases. This is a special problem for the Navy as both landing and takeoff involve high power engine settings and personnel on a carrier deck are located very close to the aircraft. The jet noise generated by the hot supersonic jet exhausts involves two source mechanisms. The dominant noise is turbulent mixing noise generated by the supersonic convection of the large turbulent structures in the jet exhaust. This generates the highest levels and radiates in the downstream arc. The interaction of the turbulence with shock cells in the jet plume results in broadband shock-associated noise. This is important at larger angles to the jet downstream axis. This talk will describe different ways to predict these two noise sources and their radiation. Broadband shock-associated noise is predicted on the basis of an acoustic analogy and steady Reynolds averaged Navier-Stokes simulations. The mixing noise is predicted using unsteady Navier-Stokes simulations coupled to an acoustic analogy for wave extrapolation to a far field observer. Finally, a new method to reduce the strength of these jet noise sources is described. Results of simulations and experiments to demonstrate the effectiveness of this noise reduction method will be given.

Acoustics from High-Speed Jets with Crackle

Friday, April 26, 2013 1:00 p.m. in ACES 4.304

Woutijn J. Baars
Department of Aerospace Engineering
The University of Texas at Austin
http://www.ae.utexas.edu/
A scaling model based on the Gol’dberg number is proposed for predicting the presence of cumulative nonlinear distortions in acoustic waveforms produced by high speed jets. Two acoustic length scales, the shock formation distance and the absorption length are expressed in terms of jet exit parameters. This approach allows one to compute the degree of cumulative nonlinear distortion in full-scale scenarios, from laboratory-scale observations, or vice versa. Surveys of the acoustic pressure waveforms emitted by a laboratory-scale, shock free and unheated Mach 3 jet are used to support model predictions. These acoustic waveforms are acquired on a planar grid in an acoustically treated and range-restricted environment. Various statistical metrics are employed to examine the degree of local and cumulative nonlinearity in the measured waveforms. This includes skewness, kurtosis, the number of zero crossings in the waveform, a wave steepening factor, the Morfey-Howell nonlinearity indicator and an application of the generalized Burgers’ equation.

Based on findings of the model and the spatial topography of the metrics, it is concluded that cumulative nonlinear steepening effects are absent in the current data set. This implies that acoustic shock-structures in the waveforms are generated by local mechanisms in, or in close vicinity to, the jet’s hydrodynamic region. Furthermore, these shock-structures induce the crackle noise component. The research aims to quantify crackle in a temporal and spectral fashion, and is motivated by the fact that (1) it is perceived as the most annoying component of jet noise, (2) no unique measures of crackle exist, and (3) significant reductions in jet noise will be achieved when crackle can be controlled. A detection algorithm is introduced which isolates the shock-structures in the temporal waveform that are responsible for crackle. Ensemble-averages of the identified waveform sections are employed to gain an in-depth understanding of these structures. Moreover, PDF’s of the temporal intermittence of these shocks reveal modal trends and show evidence that crackling shock-structures are present in groups of multiple shocks. A spectral measure of crackle is considered by using wavelet-based time-frequency analyses. The increase in sound energy is computed by considering the global pressure spectra and the ones that represent the spectral behavior during instances of crackle. This energy-based metric is postulated to be an appropriate metric for the level of crackle.

Biomedical Applications of Acoustics

Friday, April 19, 2013 4:00 p.m. in ETC 4.150

Dr. Armen Sarvazyan
Artann Laboratories, Inc.
www.artannlabs.com

In this presentation, a wide range of topics related to biomedical applications of acoustics, ranging from diagnostic imaging and biosensors to ultrasound-enhanced drug delivery and time-reversed acoustics, will be demonstrated. For example, Artann Laboratories has developed a family of ultrasonic devices for assessment of bone health and diagnosis of diseases of the skeletal system. The fundamental difference between Bone UltraSonic Scanner™ (BUSS) developed in Artann and existing bone ultrasonometers lies in the use of multiple modes of acoustic waves generated in a wide frequency range thus resulting in multiparametric characterization of bone conditions. In addition to osteoporosis, BUSS could be used in pediatric bone growth monitoring, drug-induced bone deterioration, assessment of bone health in sports medicine, monitoring condition of skeletal system of astronauts during long-term space missions, and veterinary medicine. Another ultrasonic technology developed in Artann is related to monitoring body hydration level which is critical in maintaining both physical and cognitive health. Body water weight loss—dehydration—impairs abilities and can lead to severe health problems, even death. The Hydration Monitor (HM) is based on correlation of tissue molecular composition and acoustic properties. Specifically, the ultrasound velocity in the soft tissue is a linear function of the tissue water content. Because muscle provides the largest body reservoir for water, the assessment of water imbalance is conducted by measuring speed of ultrasound in muscle. A prototype of HM was extensively tested in animal tissues in vitro, and in human studies involving adult patients with lower limb edemas and athletes during acute dehydration and rehydration. One of the hottest areas in medical imaging is tissue elastography. Two recent volumes of Current Medical Imaging Reviews (Specials issues on hot topics) were devoted to Elasticity Imaging (EI), which is an area of major activities in Artann. Artann developed several modalities of EI, licensed them to several companies and holds about 20 USA patents related to EI. One of such EI technologies licensed to a French company SSI is Shear Wave Elasticity Imaging (SWEI) – a method of tissue elasticity assessment and visualization.  In SWEI, the radiation force of focused ultrasound remotely induces localized shear waves, which are visualized by ultrasonic or MRI methods in order to assess tissue elasticity. Several other innovative projects of Artann, such as medical and industrial applications of the Time Reversal Acoustics and Ultrasound Particle Agglutination method for the detection of human immunodeficiency virus (HIV) antibody in body fluids, will be presented. The presentation will conclude with the discussion of current and future trends in these and other biomedical acoustic technologies.

Gigahertz Opto-Acoustics using Guided-Wave Nanophotonics

Friday, April 12, 2013 4:00 p.m. in ETC 4.150

Professor Zheng Wang
Department of Electrical & Computer Engineering
The University of Texas at Austin
www.ece.utexas.edu/

Coherent acoustic waves at ultrahigh frequencies (5‑100GHz) promise a wide range of on-chip applications, from microwave signal buffering/processing to nano‑imaging. We produce such ultrahigh frequency acoustic waves using guided‑wave nanophotonic structures that strongly couple optical signals with acoustic signals. We explore nano‑structures capable of maximizing coherent acoustic phonon generation through a combination of radiation pressure and electrostriction. Experimental observation of such opto‑acoustic effects in silicon waveguides, manifests as stimulated Brillouin scattering, producing radically enhanced and tailorable third order nonlinearities.

The Acoustics of Multiphase Materials in the Shallow Water Ocean Environment

Friday, March 29, 2013 4:00 p.m. in ETC 4.150

Professor Preston S. Wilson
Applied Research Laboratories
Department of Mechanical Engineering
The University of Texas at Austin
http://www.arlut.utexas.edu/

The shallow water ocean environment can be quite complicated acoustically, in part due to the abundance of multiphase materials, such as air bubbles in water near the ocean surface, water‑saturated granular sediments, gas-bearing sediments and gas-bearing vegetation on the ocean bottom, and swim bladder fish in the water column.  Successful operation of sonar in this environment requires knowledge of the acoustic properties of these materials.  The basic physics of sound propagation in these materials will be discussed and results from a variety of laboratory and field experiments will be presented.  The success and failure of various models that attempt to predict the acoustic behavior of these materials will also be discussed.  Finally, a proof-of-concept sonar system will be described that exploits the nonlinear acoustic properties of bubbly liquids to distinguish bubble clouds from more rigid targets. [Work supported by ONR and ARL:UT IR&D.]

Modeling of Microfluidic Acoustophoretic Motion of Cells and Particles for Identification of Vibro-Acoustic Properties

Friday, March 8, 2013 4:00 p.m. in ETC 4.150

Professor Yong-Joe Kim
Department of Mechanical Engineering
Texas A&M University
http://www.mengr.tamu.edu/

Microfluidic, acoustophoretic cell/particle separation has gained significant interest recently. In order to analyze the motion of cells/particles in the acoustophoretic separation, a one-dimensional (1-D) analytical model in a “static” fluid medium has been widely used, while the effects of acoustic streaming, viscous boundary layers, and 2‑D and 3‑D geometries are usually not considered. Therefore, it is not sufficient to accurately predict the cell/particle motion. Thus, a numerical modeling procedure for analyzing the acoustophoretic microparticle motion in microfluidic channels is presented to include the aforementioned effects.  Here, the mass and momentum conservation equations and the state equation are decomposed into zeroth‑, first‑, and second‑order governing equations by using a perturbation method.  Then, zeroth‑, first‑, and second‑order acoustic fields are calculated by applying a sixth‑order finite difference method to the decomposed governing equations.  The acoustophoretic force calculated by integrating the acoustic pressure over the surface of a rigid microparticle along with viscous drag force is then applied to the Newton’s equation of motion to analyze the acoustophoretic motion of the microparticle.  Since the acoustophoretic motion depends on the vibro-acoustic properties (e.g., density, compressibility, and size) of particles/cells, the vibro-acoustic properties can be estimated by optimally fitting the experimental and simulated trajectories. The properties obtained from experimental results with polystyrene beads and cancer cells show good agreement with the data reported in literature.

Micromachined Piezoelectric Energy Harvesters

Friday, March 1, 2013 4:00 p.m. in ETC 4.150

Donghwan Kim
Department of Electrical & Computer Engineering
The University of Texas at Austin
http://www.ece.utexas.edu/

Small-scale piezoelectric energy harvesters (PEH) have been the subject of recent investigations.  Previously the power output of MEMS PEHs was considered too small to operate a sensor, but advances in lowering the power demands of small, unattended sensors make PEHs attractive as a power source.  The opportunity to create a maintenance-free remote sensor network is attractive for many applications, including intrusion detection systems and structural health monitoring.  Fundamentally, a PEH utilizes ambient vibration input so that the piezoelectric element on the harvester deforms and produces power.  This technique is most effective near the PEH’s fundamental resonance frequency due to large mechanical deformations.  As one might expect, power output is also proportional to resonance quality factor Q.  Cantilever geometries are popular for this reason.  Designing for maximum power capture at resonance by using high‑Q resonant devices comes at the expense of reducing the PEH’s effectiveness off-resonance.  To overcome this, a broad‑band harvester innovation is proposed.  This presentation will include microfabrication of single-mode piezoelectric cantilever test structures comprised of 20‑µm‑thick silicon beams with bulk silicon tip masses.  The beams are fabricated with 1‑µm‑thick lead zirconate titanate (PZT) films along their top surface.  Testing results are also presented and include demonstration of impedance matching and theoretical maximum power capture.  A discussion of preliminary design considerations for upcoming broadband harvesters is also included.

Modeling Acoustic Scattering and Propagation with Elastic Bottoms Using Finite Elements

Friday, February 15, 2013 4:00 p.m. in ETC 4.150

Dr. Marcia J. Isakson and Dr. Nicholas P. Chotiros
Applied Research Laboratories
The University of Texas at Austin
http://www.arlut.utexas.edu

Acoustic interaction with the ocean bottom is a critical part of understanding propagation in shallow water environments. However, most ocean propagation models consider the seafloor as flat or use approximations to determine the effects of scattering from the rough interface. Each of these approximations has a range of validity which is generally unknown for layered or elastic bottom types with realistic roughness conditions. Elastic bottoms present a unique challenge since scattering from rocky or hard bottoms often produces an interface wave which is not captured in many of the approximations. Finite element analysis provides a useful benchmark for these models since it approaches an exact solution to the Helmholtz equation as the discretization density increases. In this study, finite element models will be compared with perturbation theory and the Kirchhoff approximation for rough elastic bottoms. These results will be used to compute reflection and backscattering coefficients for areas with rocky seafloors.

Non-Contact Acoustic Excitation and Sensing for Nondestructive Testing of Concrete Structures

Friday, February 8, 2013 4:00 p.m. in ETC 4.150

Professor Jinying Zhu and Xiaowei Dai
Department of Civil, Architectural and Environmental Engineering
The University of Texas at Austin
http://www.caee.utexas.edu

Air‑coupled sensing has shown great potential for rapid nondestructive sensing and scanning of concrete infrastructure. However, the current air‑coupled sensing method has two limitations: (1) the air‑couple sensor (a microphone) has low sensitivity, which results in low signal‑to‑noise ratio (SNR) for testing in the field and (2) a mechanical contact impact source is needed to excite elastic waves in concrete. In this presentation, we present a fully air-coupled acoustic excitation and sensing system to address these challenges. To improve the SNR, a parabolic reflector is used to focus the incident plane wave radiated from the concrete specimen, and a microphone located at the focal point of reflector receives the amplified signals. An analytical solution has been derived to optimize the geometry of the reflector for this purpose. Experimental studies and finite element simulations validate the improved sensitivity and SNR. To realize non‑contact excitation, an acoustic spark source with an ellipsoidal reflector has been proposed to excite wave motion in concrete. Analogous to shock wave lithotripter devices, the spark is located at the near focus and generates an outgoing wave that is then focused at the far focus of the reflector which is aligned at the air-concrete interface. Applications of the air-coupled system for Rayleigh wave, zero‑group velocity Lamb wave (impact‑echo) and through‑transmission tests on a concrete slab are presented.

Recent Advancements in Research and Commercialization of Tethered Encapsulated Bubbles for Low-Frequency Underwater Noise Abatement

Friday, February 1, 2013 4:00 p.m. in ETC 4.150

Dr. Kevin M. Lee
Applied Research Laboratories
The University of Texas at Austin
http://www.arlut.utexas.edu/
and
Dr. Mark S. Wochner
AdBm Technologies, LLC
http://adbmtech.com

Arrays of large encapsulated bubbles have been shown to be very effective at reducing underwater sound radiated from various sources.  These arrays provide noise reduction using the combined effects of bubble resonance attenuation and acoustic impedance mismatching and have been used to treat both sources of noise and to protect receiving areas from external noise. Recent research efforts at UT concerning the acoustics of large encapsulated bubbles and their use in reducing underwater noise will be presented.  Measurements of encapsulated bubble resonance frequencies and attenuation were made and compared with various bubbly liquid effective medium models for the purpose of determining which models are best suited for designing future systems.  Additionally, experiments were conducted in which encapsulated bubble arrays were used to reduce underwater noise from both continuous and impulsive noise sources. The research has also resulted in a UT spin-off company, AdBm Technologies, which was formed in 2012 and is currently commercializing the technology as well as sponsoring UT research aimed at developing prototype noise abatement systems. The process of technology commercialization at UT and the transition from idea to salable product will be detailed.

Seabed Properties from Acoustic Reflection Measurement: An experiment in the Mediterranean

Friday, January 25, 2013 4:00 p.m. in ETC 4.150

Nicholas P. Chotiros and Marcia J. Isakson
Applied Research Laboratories
The University of Texas at Austin
http://www.arlut.utexas.edu/

The seabed is often modeled as a fluid, visco-elastic solid, or water-saturated poro-elastic material. Using experimental measurements from a sandy seabed, it is shown that the poro-elastic model can fit the measured reflection data better than the other models. Roughness scattering had a significant effect on the measurements requiring a more sophisticated roughness model than Eckart scattering. Reflection loss and roughness measurements were taken at the Experimental Validation of Acoustic Models experiment in 2006 (EVA-06), off the Isola d’Elba, Italy, in collaboration with the NATO Undersea Research Centre. The magnitude and phase of the reflection loss were measured at frequencies from 5 to 80 kHz and grazing angles from 7 to 77 degrees. Approximately 1500 samples were taken at each angle. The roughness was measured with a laser profiler. The measurements were compared with model predictions. The material is based on [M. J. Isakson, N. P. Chotiros, R. A. Yarbrough, and J. N. Piper, “Quantifying the effects of roughness scattering on reflection loss measurements,” J. Acoust. Soc. Am., Vol. 132, pp.  3687-3697, 2012].

ETS-Lindgren Acoustic Research Laboratory and Factory Tour

Saturday, December 8, 2012 1:00 p.m. at ETS-Lindgren

Dr. Douglas F. Winker
ETS-Lindgren
1301 Arrow Point Drive
Cedar Park, Texas
http://www.ets-lindgren.com/Acoustics

In 2002, ETS-Lindgren acquired Acoustic Systems of Austin, Texas, and in doing so, expanded their test and measurement capabilities to include the Acoustic Systems Acoustical Research Facility on Saint Elmo Road in South Austin. The latter had existed to serve outside clients and as a research and development branch for Acoustic Systems for most of its 30-year history. In 2008, the acoustic testing facility in South Austin was closed and the existing ETS-Lindgren Test and Measurement facilities in Cedar Park were expanded to include new world-class acoustic test chambers. Testing equipment, procedures, software, and quality systems of the old laboratory were all upgraded and implemented at the new Acoustic Research Laboratory. Reaccreditation in all test methods was completed in October 2008. The facility includes several state-of-the-art chambers for acoustic test services, including a hemi-anechoic chamber and two reverberation chambers, impedance tubes and supporting acoustic test equipment and software. The laboratory offers product noise emission testing and structural/architectural acoustic testing. See one of the attachments to this announcement for technical information on the facilities.

The tour is expected to last approximately two hours. Meet at the entrance to ETS-Lindgren on the south side of the building at the address provided above. Preceding the tour, starting at 12:30 p.m., there will be an Amy’s Ice Creams social sponsored by the Austin Student Chapter of the Acoustical Society of America. All are invited. If you need a ride, contact Mustafa Abbassi (mustafa_abbasi@utexas.edu), who is organizing a carpool that will depart from the loading dock behind ETC at noon. Also contact Mustafa if you cannot get to ETC on Saturday and need to be picked up.

Turbulence as a Source of Jet Noise

Thursday, December 6, 2012 3:30 p.m. in WRW 113

Professor Jonathan B. Freund
Department of Mechanical Science and Engineering
Department of Aerospace Engineering
University of Illinois at Urbana-Champaign
http://jbfreund.mechse.illinois.edu

We will review the underlying theory for how turbulence makes sound and use that to motivate detailed simulation-based investigation of jet noise mechanisms. High-fidelity sub-sonic noise prediction is particularly elusive because the wavenumber-frequency makeup of the turbulence is such that it does not directly couple with propagating wave equation solutions.  This will be illustrated with a model two-dimensional mixing layer, which is perturbed into a quiet state based upon an adjoint-based optimization procedure. The potential for extension of this approach to engineering applications is discussed, including preliminary examples. Higher-speed jet noise is, in a sense, simpler because in this case the turbulence directly couples with the sound. However, the radiation is so strong that its generation and propagation involves important nonlinearity, which complicates its description. Recent high-speed-flow simulations will show some of the key features of these mechanisms.

Modeling the Generation and Propagation of Radially-Polarized Shear Waves in Tissue-Like Media

Friday, November 30, 2012 4:00 p.m. in ETC 4.150

Kyle S. Spratt
Applied Research Laboratories and Department of Mechanical Engineering
The University of Texas at Austin
http://www.arlut.utexas.edu/
http://www.me.utexas.edu/

In the past decade there has been an increasing interest in the optics literature regarding the unique characteristics of focused, radially-polarized light beams. Of particular interest is the existence of a longitudinal component to the electric field in the focal region of the beam, of comparable amplitude to the radial component and yet with a smaller beamwidth [cf. Q. Zhan, Adv. Opt. Photon. 1, 1-57 (2009)]. In the linear approximation there exists a direct analogy between these light beams and radially-polarized shear wave beams in incompressible elastic media, and hence we may interpret the results found in the optics literature as applying to low-frequency shear waves propagating through tissue-like media. Unlike a plane shear wave, such a radially-polarized beam is predicted to generate a significant second harmonic when propagating nonlinearly through a tissue-like medium, and we present an analytic solution for the second harmonic generated by a focused, radially-polarized shear wave beam with Gaussian amplitude shading. Lastly we consider the possibility of generating radially-polarized beams in an elastic half-space using a piston source pushing on the bounding surface of the solid.  Using an angular spectrum approach to model such a source, we demonstrate how the near-incompressibility of tissue-like media, and the Poisson effect that takes place directly below such a piston source, can be exploited to generate a radially-polarized shear wave beam.

Topographic Effects in Earthquake Ground Motions: Insights Gained from Field Studies of Frequency and Predictable Mining Seismicity

November 9, 2012 4:00 p.m. in ETC 2.136

Professor Brady R. Cox
Department of Civil, Architectural and Environmental Engineering
The University of Texas at Austin
http://www.caee.utexas.edu/technical-areas/geotechnical-engineering.html

Topographic effects, in the context of earthquake engineering, refer to a commonly recognized phenomenon that causes amplification and frequency alteration in ground motions measured in the vicinity of a topographic feature (hillsides, ridges and canyons) relative to flat ground conditions. Although it is widely recognized that topographic amplification can elevate seismic hazard, there is currently no consensus on how to reliably quantify its effects. Lack of consensus has precluded development of acceptable guidelines on how to account for this phenomenon in practice, thus leaving an important factor contributing to seismic hazard unaccounted for in building codes. This presentation details experimental work from the first phase (Phase I) of a two-phase field study aimed at investigating topographic effects using frequent, shallow and predictable seismicity induced by underground longwall coal mining. A locally-dense array of ground motion instruments was used to capture over 50 seismic events on steep, irregular topography above a coal mine in central-eastern Utah. Results from processing these ground motions indicate a regular pattern of amplification near the crest of a ridge of approximately 4 times the “base” ground motions within the frequency range of 1 – 2 Hz. The frequency range of topographic amplification is investigated relative to the shape of the 3D feature and its average shear wave velocity.

Low Frequency In Situ Sediment Dispersion Estimates in the Presence of Discrete Layers and Gradients

Thursday, November 1, 2012 3:00 p.m. in ARL Auditorium

Dr. Charles W. Holland
Applied Research Laboratory
The Pennsylvania State University
http://www.arl.psu.edu/

One of the difficulties in validating sediment models has been the lack of reliable low frequency dispersion measurements. A reflection method is presented that yields in situ dispersion without sediment disturbance over a broad range of frequencies and can explicitly disentangle frequency-dependent effects of vertical structure, e.g., layers and gradients. Measurements on the outer shelf from 300—3000 Hz show that dispersion is a strong function of depth in the sediment column. The depth and frequency-dependent results generally agree well with independent measurements on core data. Cohesive sediments in the upper few meters exhibit a nearly frequency-independent sound speed and a nearly linear frequency dependence of attenuation. In the lower part of the sediment column the sediments are more granular: the lowest layer exhibits an attenuation with a peak frequency at 1100 Hz, where its dependence below and above trends to f^2 and f^(1/2), respectively. While Biot theory predicts this dependence, its underlying physical explanation, fluid flow through interstitial pores, does not seem plausible for this sediment, due to the unreasonable permeability value required. Viscous Grain Shearing theory also predicts this dependence, but it is not known whether the parameter values are reasonable.

Radiation Forces and Torques of Acoustic Beams

Friday, October 12, 2012 4:00 p.m. in ETC 4.150

Dr. Likun Zhang
Department of Physics and Center for Nonlinear Dynamics
The University of Texas at Austin
http://chaos.utexas.edu

Acoustic beams can exert radiation forces on objects, allowing, for example, manipulation of cells in suspension, assessment of viscoelastic properties of biological tissues, and targeted drug and gene delivery. The force is related to the interaction of the object with the acoustic field because of momentum transport associated with acoustic scattering and energy absorption. Acoustic beams can also carry orbital angular momentum such as the so-called acoustic vortex beams, which are characterized by a screw phase dislocation of the wave field around its propagation axis with a magnitude null at its core. When interacting with an object, the vortex field can transfer the angular momentum to the object, and hence exert torques on the object. The talk will present recent theoretical and experimental advances on negative radiation forces by non-diffracting beams, angular momentum transport of vortex beams, and associated radiation torques on objects. The realization of these beams and their fabrication will allow innovative applications especially for the manipulation of microparticles with acoustic beams of traveling waves, such as the concepts of acoustic tractor beams for pulling the particles or acoustic spanners for noncontact rotational manipulation.

Micromachined Microphones with In-Plane Directivity

Friday, October 5, 2012 4:00 p.m. in ETC 4.150

Michael Kuntzman
Department of Electrical and Computer Engineering
The University of Texas at Austin
http://www.ece.utexas.edu/
http://www.utmems.com/

Since being commercialized less than a decade ago, the microelectromechanical systems (MEMS) microphone market has seen dramatic growth, with 1 billion units shipped in 2011 and global shipments projected to reach 2.9 billion units in 2015. While low cost and robust, all current commercial MEMS microphones are omnidirectional. The signal-to-noise ratio (SNR) of MEMS microphones, while good enough for close-talking applications, is too poor to address advanced audio functionalities on the horizon. As a step towards realizing more innovative microphones that truly leverage unique design flexibility afforded by microfabrication, we will introduce piezoelectric microphones designed for in-plane figure-8 directivity. Topics will include description of the overall concept, microfabrication, and a presentation of directivity measurements on early proof-of-concept prototypes. A hybrid modeling method combining finite element analysis (FEA), modal analysis, and lumped element network modeling, which is capable of accounting for the dynamics of multiple vibration modes and multiple transduction ports, will be introduced.

Fun with Musical Acoustics

Friday, September 28, 2012 4:00 p.m. in ETC 4.150

Dr. Thomas G. Muir
Applied Research Laboratories
The University of Texas at Austin
www.arlut.utexas.edu

Musical acoustics has fascinated the intellect of man since pre-historic time, when tunes were played on flutes made from feathers and of bone, as well as lyres made from yokes, turtle shell resonators, and gut strings. Some anecdotal comments are offered on the achievements of some great philosophers, scientists and engineers in the art of organology, the study of musical instruments, which include, for example, Pythagoras (550 BC), Galileo (1638), down through Wheatstone (1828), and many others. Recently, the availability of applications (apps) on smart phones, pods, pads, tablets and laptops has offered a wide assortment of very good tools for casual, and even professional use in musical acoustics. These apps include assets such as sound level meters, FFT and octave band analyzers, as well as signal generators and more, all offering opportunities unheard of by the masters, enabling the educated user to contribute to the art, which previously required laboratory facilities. Some examples of iPhone app results are given here through an experimental study of an American reed “pump” organ, recently restored by the author. These instruments, popular in the 19th and early 20th centuries, have long provided interesting pursuits involving their acquisition, restoration, history and musicology, as well as performance. Some acoustical curiosities of the author’s instrument are described, including mechanical design, means of sound production, reeds, reed spectra, stop types, and intonation. Recordings are played to demonstrate the tonal quality of the various stops and playing options, and video sound clips of professional artists playing restored instruments are presented.

Hitting the High Notes: Integrative Biology of Acoustic Communication in Neotropical Singing Mice

Friday, September 21, 2012 4:00 p.m. in ETC 4.150

Dr. Bret Pasch
Section of Integrative Biology
The University of Texas at Austin
www.biosci.utexas.edu/ib

Many animals use long-distance acoustic signals to advertise their presence to a network of potential mates and competitors. A rich tradition of studies on acoustic communication in birds, anurans, and insects has provided important insights into disparate disciplines of biology through integration of proximate and ultimate levels of analysis. Here, we synthesize data on vocal ontogeny, hormonal control, and the adaptive function of Neotropical singing mouse (Scotinomys) vocalizations in an ecological context. Neotropical singing mice are diurnal insectivorous rodents that inhabit montane cloud forests throughout Central America. Adult males of two species commonly produce a rapid series of notes that sweep from ~ 43 to 14 kHz.  I describe how vocalizations develop from pup isolation calls, how sex differences in singing arise during puberty and are modulated by androgens, and how vocalizations are used in mate attraction and male-male aggression. Between species, interspecific communication reflects underlying dominance interactions and contributes to competitive exclusion along altitudinal gradients. Accordingly, the auditory tuning of mouse brains differs between sympatric and allopatric populations to accommodate the ecological salience of song. Altogether, Neotropical singing mice are emerging as important species that permit comparisons to communication systems in traditionally more tractable taxa.