In Pursuit of Wave Control: Flexural Wave Scattering from Boundaries with Time-Modulated Impedance

Friday, April 17, 2026, 4:00 p.m. Central Time

Kayla N. Cecil
Applied Research Laboratories
Walker Department of Mechanical Engineering
The University of Texas at Austin

Acoustic and elastic materials with space- and time-varying properties offer novel ways to control wave propagation and scattering. This talk starts with a brief overview of acoustic metamaterials and wave behavior in spatiotemporally modulated media, followed by the motivation to study scattering from boundaries with spatiotemporally modulated impedance. This is followed by an introduction to the building blocks associated with this research: (i) a semi-analytical model of forced time-harmonic motion of a single degree-of-freedom system with time-modulated parameters and (ii) an introduction to flexural wave propagation in Euler-Bernoulli beams and reflection at impedance boundaries. Time modulated boundaries are then represented using lumped-parameter spring-mass models with time-varying spring constants. This approach provides an excellent approximation of conventional boundary conditions (free, pinned, clamped, …) as well as locally resonant metasurface structures, both of which can be extended to include the effects of time-varying spring constants. Results are presented for cases of a non-resonant boundary with one modulated spring—translational or rotational—while keeping the second spring invariant in time. The resulting scattered fields contain energy at the incident wave frequency and at frequencies that are up- and down-shifted from the incident wave due to the time-modulation. This result indicates that the frequency content of the scattered field can be controlled through the modulation of translational or rotational stiffness at the beam termination. This systematic approach allows us to explore the design space of time-varying boundaries for flexural wave systems, providing a new pathway for advanced wave manipulation in elastic structures.

Separating Measurement Noise from Property Variation in Acoustic Piezoelectric Materials

Friday, April 10, 2026, 4:00 p.m. Central Time

Dr. Nathan P. Geib
Applied Research Laboratories
The University of Texas at Austin
https://www.arlut.utexas.edu/

Commercial off-the-shelf (COTS) piezoelectric elements are widely used in acoustical systems, but reported material properties often vary due to part-to-part differences and measurement system effects. This work examines variability in the characterization of COTS piezoelectric parts with simple geometry, emphasizing separation of true part variation from measurement effects. Ten nominally identical parts were characterized using repeated measurements of geometry, mass, density, electrical impedance, and piezoelectric charge coefficient, d₃₃. Measurements were performed by two operators with minimal procedural guidance to assess repeatability and reproducibility. ANOVA-based Gage Repeatability and Reproducibility (Gage R&R) methods were used to evaluate contributions from part variation, operator effects, and measurement repeatability. Results show that measurement performance depends on both parameter and method. Mass measurements exhibit negligible error relative to part variation, while dimensional measurements are limited by resolution. Direct d₃₃ measurements using a Berlincourt-type meter show substantial variability due to repeatability and operator effects. Impedance-based measurements demonstrate improved repeatability, with resonance and antiresonance frequencies clearly distinguishable. Computed d₃₃ values extracted from impedance measurements correlate strongly with direct measurements but include a systematic offset. After correcting this bias, remaining differences fall within measurement uncertainty, suggesting impedance-based methods provide a more precise approach for estimating d₃₃.

Transcranial Photoacoustic Tomography: Imaging the Brain with Light and Sound

Friday, April 3, 2026, 4:00 p.m. Central Time

Professor Umberto Villa
Department of Biomedical Engineering
Oden Institute for Computational Engineering and Sciences
The University of Texas at Austin
https://bme.utexas.edu/person/umberto-villa/

Transcranial Photoacoustic Computed Tomography (t-PACT) holds significant promise for non-invasive functional neuroimaging. However, its practical utility is fundamentally limited by the complex acoustic aberrations introduced by the human skull, which distort the reconstructed images and degrade spatial resolution. Existing reconstruction methods often struggle to mitigate these aberrations without accurate, subject-specific acoustic modeling. In this talk, we present a comprehensive framework for the stochastic generation of realistic, three-dimensional (3D) Numerical Head Phantoms to support the development and validation of advanced image reconstruction methods specifically designed to compensate for these skull-induced aberrations. Using this framework, we develop a learning-based image restoration method ensuring high-fidelity recovery of the initial pressure distribution even in the presence of inevitable inaccuracies in estimated skull properties. Remarkably, the learning method was trained using only computer simulation data and successfully applied to experimental data acquired through an ex-vivo human skull. Future efforts will focus on translating these techniques to in-vivo settings, particularly addressing the dynamic range challenges associated with external illumination geometries.

Acoustic Sensing in Extreme Environments: Piezoelectric PMUT Transducers and HEMT Electronics for Operation above 800°C

Friday, March 27, 2026, 4:00 p.m. Central Time

Zihuan Liu
Chandra Family Department of Electrical and Computer Engineering
The University of Texas at Austin
https://www.ece.utexas.edu/

Acoustic measurement in environments above 500°C remains largely intractable—conventional piezoelectric materials such as PZT lose their properties well below such temperatures, and standard electronics fail even sooner. This work presents a complete acoustic sensor system designed for extreme-temperature operation, targeting applications including hypersonic flight vehicles, geothermal energy, and rocket engines. We systematically evaluated piezoelectric materials using a figure-of-merit that accounts for dielectric loss at elevated temperatures, identifying lithium niobate (LiNbO₃) and aluminum nitride (AlN) as leading candidates: LiNbO₃ for its high Curie temperature and strong electromechanical coupling, and AlN for its thermal stability. Both materials were developed into piezoelectric micromachined ultrasonic transducer (PMUT) architectures, addressing substrate impedance mismatch, bonding material stability, and packaging-induced mechanical constraints. LiNbO₃ and AlN PMUTs demonstrated stable acoustic operation above 800°C and 900°C, respectively, validated through laser Doppler vibrometry and acoustic measurements. In parallel, high-electron-mobility transistors (HEMTs) were characterized, maintaining an on/off ratio greater than 1,000× at approximately 700°C. This work establishes a systematic path—from material selection through transducer fabrication to electronics integration—toward a field-deployable acoustic sensor for environments where no such technology currently exists.

Approaching Piezoelectric Terahertz Acoustics

Friday, March 13, 2026, 4:00 p.m. Central Time

Jack P. Kramer
Chandra Family Department of Electrical and Computer Engineering
The University of Texas at Austin
https://www.ece.utexas.edu/

Piezoelectric acoustic resonators are critical building blocks for modern cellular communication systems, where they compose radio frequency filters. Despite widespread adoption below 6 GHz, scaling these devices to frequencies exceeding 10 GHz has proved challenging due to material and design limitations. These limits hinder the electrical to mechanical coupling and resonator quality factors, both critical metrics for RF filters. In this talk, we will discuss how so-called periodically poled piezoelectric films help to address these challenges and have enabled acoustic resonators from tens of GHz to above 100 GHz, into the sub-THz. We will discuss how these advancements have enabled tens of GHz filters that could be critical components as modern communication systems push to higher frequencies. We will also highlight some emerging challenges that these resonators face as the acoustic wavelengths approach the spacing of tens of atoms.

The Development of the Túngara Frog Larynx and the Sounds it Produces: Shut Up and Grow Up

Friday, February 27, 2026, 4:00 p.m. Central Time

Professor Michael J. Ryan
Department of Integrative Biology
The University of Texas at Austin
and
Smithsonian Tropical Research Institute
Gamboa, Panama
https://sites.utexas.edu/the-ryan-lab/

Most species of frogs rely on loud and conspicuous mating calls used by males to attract females for the purpose of mating. We understand many aspects of this communication system: its role in speciation and sexual selection; how the environment does or does not influence its evolution; and how the auditory system decodes and perceives this acoustic signal. Less is known about the function and development of the voice production system, especially the larynx. We describe the ontogeny of laryngeal morphology in both sexes, use ablation experiments and bound graph models to understand its inner workings, and identify a zone of silence in which males could call but they don’t. Ongoing studies ask why this is so.

On the Spectral Homogenization of Wave Motion in Periodic Continua and Origami-Inspired Structures

Friday, February 20, 2026, 4:00 p.m. Central Time

Professor Othman Oudghiri-Idrissi
Fariborz Maseeh Department of Civil, Architectural, and Environmental Engineering
The University of Texas at Austin
https://caee.utexas.edu/person/othman-oudghiri-idrissi/

We establish a comprehensive analytical framework for dynamic homogenization of wave motion at arbitrary frequency in (i) perforated periodic continua and (ii) origami-inspired periodic structures modeled using a bar-and-hinge paradigm. For a prescribed spectral content of an applied body force, the activated Bloch eigenstates are identified and classified according to the multiplicity of the participating energy levels. Near an isolated dispersion surface, projection onto the dominant Bloch mode yields an effective field equation with a homogenized source term, providing leading- and second-order approximations of both macroscopic (mean) and microscopic wave motion. When multiple dispersion surfaces are activated, coupled zeroth- and first-order effective systems are derived, accommodating spectral configurations including Dirac points, avoided crossings, and near-degenerate clusters. In the absence of forcing, the resulting formulation reduces to a low-order algebraic eigenvalue problem that accurately captures the local geometry of clustered dispersion branches. The framework is validated by comparing asymptotic dispersion predictions with direct numerical simulations and is applied to two-dimensional Kagome lattices with Neumann exclusions, square lattices with Dirichlet obstacles, Miura-ori sheets, and one-dimensional Miura tubes. Results demonstrate accurate approximation of both dispersion characteristics and body-force-induced waveforms, resolving effective and microstructural dynamics with comparable fidelity.

4D Metamaterials: From Spatial to Temporal Wave Control

Friday, February 13, 2026, 4:00 p.m. Central Time

Professor Emanuele Galiffi
Chandra Family Department of Electrical and Computer Engineering
The University of Texas at Austin
https://www.emanuelegaliffi.me/

Metamaterials enable wave manipulation beyond the limits of natural materials by exploiting subwavelength spatial structuring, leading to a host of exotic wave behaviors ranging from negative refraction to cloaking, as well as applications ranging from the extreme miniaturization of optical components to nonreciprocal wave propagation. More recently, the metamaterials community has started exploring the opportunity of generalizing this paradigm to the temporal dimension, opening a new research front on 4D metamaterials. Intriguingly, causality results in time behaving as a different sort of dimension than its spatial counterparts, leading to the manipulation of the energy and frequency of waves, rather than their momentum and wave vector, resulting in a variety of opportunities for extreme wave control ranging from new amplification paradigms to unidirectional wave propagation and gain, and enabling the breaking of the conventional limitations of passive media, such as the Rozanov and Chu bandwidth for absorbers and antennas. In this talk I will provide an overview of the rising field of time-varying metamaterials, focusing on their capabilities in manipulating the energy and frequency content of waves, and how the engineering of their coherent illumination input can dramatically control our ability to exploit them to produce gain, loss and perfect frequency conversion.

The Sounds of an Ocean Eddy

Friday, January 30, 2026, 4:00 p.m. Central Time

Dr. Robert T. Taylor
Applied Research Laboratories
The University of Texas at Austin
https://www.arlut.utexas.edu/

Northern latitude ocean environments are dynamic and complex, with shortened spatial and temporal scales leading to dramatic changes in water column structure compared to more equatorial regimes. In the waters surrounding Jan Mayen Island in the Nordic Seas, eddies frequently spin off of the Norwegian Atlantic Current, further complicating the local ocean state and the associated acoustic propagation environment. The Northern Ocean Rapid Surface Evolution (NORSE) experiment, conducted between 2022 and 2023, sought to understand both the internal ocean dynamics and the corresponding impact on the underwater acoustic environment. A year-long collection of water column temperature, salinity, and flow velocity, were obtained with a suite of sensors mounted on a mooring line located on a 420 m deep ridge near Jan Mayen. To study the acoustics, ARL:UT deployed a 380 m long vertical line array mooring roughly 1 km away, providing ambient sound measurements throughout the water column. This presentation details the investigation of various acoustic sources of opportunity and their relationship to the in situ ocean environment. Inversion techniques were developed to enable continuous acoustic estimates of temperature, flow speed, and flow direction. In particular, the acoustic data reveal the passage of an anti-cyclonic eddy directly over the ridge during a two-week period. This work shows that hydrophone arrays can be used simultaneously for both ocean parameter estimation and conventional acoustic applications.

Mastering, Consulting, and Education: One Perspective on a Career in Professional Audio

Friday, January 23, 2026, 4:00 p.m. Central Time

Nick Landis
Chief Mastering Engineer
Nick Landis LLC
Austin, TX
www.nicklandis.com

What does a career in professional audio really look like? In this seminar, Nick Landis will share his journey as a mastering engineer, acoustics consultant, and educator. He will discuss his approach to projects, how he differentiates himself in a competitive market, and how his workflow has evolved over the years with new technologies. Nick will also reflect on career flow beyond mastering, including consulting on broad acoustics challenges—often collaborating with architects or guiding DIY solutions—and his experiences teaching audio production and acoustics at Austin Community College.  The talk will highlight how multiple facets of professional audio including creative process, technical problem-solving, client collaboration, and education intersect to create a sustainable career. Nick will also touch on his involvement with The Recording Academy and the Audio Engineering Society, providing perspective on professional engagement in the field. The seminar will be conversational and story-driven, with a generous Q&A session designed to foster discussion about mastering, acoustics consulting, and career development in audio.