Simón Montoya-Bedoya – simonmontoyabedoya@gmail.com
Bluesky: @simontoyabe.bsky.social
Instagram: @simontoyabe
Walker Department of Mechanical Engineering, The University of Texas at Austin, Austin, Texas, 78712-1591, United States
Prof. Michael R. Haberman (Walker Department of Mechanical Engineering, The University of Texas at Austin)
Other contributors to the research:
Donal P. Finegan (National Laboratory of the Rockies, Golden, CO, US)
Hadi Khani (Texas Materials Institute, The University of Texas at Austin)
Ofodike Ezekoye (Walker Mechanical Engineering Department, The University of Texas at Austin)
–The research described in this Acoustics Lay Language Paper may not have yet been peer reviewed–
Have you noticed how heavily our current society depends on batteries? Batteries are used everywhere, from powering your phone to electrifying mobility, and energy storage to mitigate the intermittent nature of renewable energy sources like wind and sun. This increased demand for lithium-ion batteries (LIBs) has led to the exploration of new technologies with improved attributes such as safer operation or improved lifetime. For example, silicon solid-state batteries (Si-SSB) are promising because silicon as an anode material offers a higher specific capacity (~3500 mAh/g) than graphite (~300 mAh/g) used in conventional LIBs. They are also potentially safer to operate due to the use of a solid electrolyte rather than the flammable liquid electrolyte used in conventional LIBs.
However, Si-SSBs come with their own challenges associated with the avoidance of a liquid electrolyte, primarily the requirement to maintain reliable interfacial contact between all the solid layers for lithium-ion movement. Si-SSBs are therefore more brittle and more prone to contact loss and fracture.
Another challenge in studying the intricate mechanical changes that arise from the electrochemical processes in the battery is that we are “blind” to them, in other words, we cannot see inside batteries while they are operating. That’s why, just as a doctor uses ultrasound to monitor a beating heart, we can use ultrasonic waves to monitor batteries without opening them, as represented by the cartoon in Fig. 1. The key to understanding what changes within the batteries is having information about how the movement of lithium ions alters its mechanical properties. When lithium ions migrate during charging and discharging, they cause swelling, internal stresses, and sometimes fracture within the battery structure. These mechanical changes can significantly affect the propagation of ultrasonic waves through the material. This is specifically true for the silicon anode, where silicon forms alloys with the lithium ions, rather than the lithium ions becoming embedded in the molecular structure as occurs in conventional batteries. These electrochemical changes lead to large volumetric and mechanical changes. Thus, SSBs are a compelling technology to explore using ultrasound using ultrasonic signals observables, such as shifts in the time of flight (TOF) of the wave through the battery, or changes in how sound is absorbed or scattered. These “acoustic fingerprints” can potentially help us gain more insights into degradation in these next-generation (“next-gen”) batteries and therefore improve the technology for more widespread use in commercial products.
Figure 1. Analogy of the usage of ultrasonic waves for battery diagnostics, similar to how a doctor would use ultrasonics to monitor heart health. [Image generated with AI using Google NanoBanana Pro]
We aim to extend the use of ultrasonic testing methods for next-gen batteries and investigate opportunities and challenges associated with evaluating this new technology. In this work, we investigated both contact-based and immersion ultrasonic testing to monitor changes in the mechanical properties of Si-SSBs under cycle-induced aging.
In general, our experiments showed an overall stiffness reduction with aging as indicated by the increase in ultrasonic wave TOF (see Fig 2a). Further, we observed an overall reduction of transmitted energy with increased cycling. These two findings may be associated with the accumulation of damage at layer interfaces associated with the creation of solid-gas interfaces and/or debonding between layers. Finally, ultrasonic imaging using immersion testing provided information regarding the distribution and evolution of damage in space as these next-gen batteries are aged (see Fig 2b).
By refining these techniques to evaluate next-gen battery technologies, we will develop more sensitive methods to determine when something is wrong before it’s too late. In a world increasingly dependent on safe and reliable energy storage, the ability to “listen” to batteries might be precisely what we need to power the clean energy revolution.
Figure 2. Evolution of cell stiffness during aging. a) Stiffness of the SSB, normalized to its initial value, plotted against discharge capacity for both charged (blue) and discharged (red) states. With representative ultrasonic images from transmitted signals at two states of the SSB: b.1) pristine before cycling, and b.2) after 40 cycles of aging. We observed a significant reduction in transmission in the middle region of the SSB. Warmer colors indicate higher transmission, and dashed outlines mark the active cell region.
–The research described in this Acoustics Lay Language Paper may not have yet been peer reviewed–
Have you ever wanted to listen to the voices of plants when they need water? If you use our method, you can.
We focused on changes in the acoustic frequency characteristics of the leaf after we stopped watering. Currently, we are developing a method to evaluate leaf water content through its acoustic response for plant-human communication.
Figure1. Proposed method for evaluating leaf water content through its acoustic response
In this study, we confirmed that leaf natural frequency showed complex behavior with losing water content. Despite this complexity, we demonstrated the estimation of its frequency change using an equation based on the circular diaphragm theory.
Our research steps were conducted in the following order: I. Measurement of leaf natural frequency, II. Estimation of leaf natural frequency, and III. Comparison of measured and estimated values.
First, in “I. Measurement of leaf natural frequency,” we obtained the acoustic frequency characteristics of the leaf under non-irrigation conditions by vibrating the leaf using a bone-conduction transducer. The results showed that the natural frequency showed non-monotonic and complex changes over time as leaf water content decreased. Based on the leaf Young’s modulus and thickness measured simultaneously as physical parameters, we confirmed that the complex changes in natural frequency were due to independent changes in these physical parameters.
Next, in “II. Estimation of leaf natural frequency,” we derived an estimation equation by applying a first-order approximation to the circular diaphragm theory to clarify the leaf vibration behavior under non-irrigation conditions. The estimated values were calculated by substituting the measured physical parameters into the estimation equation.
Figure 2. Estimation equation to estimate leaf natural frequency
Finally, in “III. Comparison of measured and estimated values,” we compared the measured natural frequency in step I with the estimated natural frequency in step II using correlation coefficients. The results showed that the estimated values showed high correlation coefficients with the measured values (0.66–0.83). We concluded that the estimated equation based on the circular diaphragm theory can be applied to leaf vibration.
Figure 3. Comparison of measured and estimated leaf natural frequency changes under stopped watering
Through this study, we investigated the relationship between the leaf vibration characteristics and water content, and we clarified this relationship as a preliminary step. Based on these findings, we aim to establish a quantitative measurement method for evaluating leaf water content using its acoustic response.
Once this proposed method is established, we will be able to hear the voices of leaves when they are thirsty.
–The research described in this Acoustics Lay Language Paper may not have yet been peer reviewed–
Imagine sitting in a shared office or hospital room and hearing a message clearly while the people beside you hear almost nothing. Our research shows a way to draw a tiny “bubble” of sound in mid-air—what we call an audible enclave—without using headphones and without filling the whole room with noise. The idea is to start with ultrasound, which is far above what humans can hear, and then make ordinary sound appear only where we want it.
At first glance, readers might think this is the well-known parametric array loudspeaker (PAL), often marketed as an “audio spotlight.” A traditional PAL shoots a narrow ultrasonic beam that slowly converts into audible sound along the entire beam path. That gives strong directionality and long reach, but the audible sound exists wherever the beam travels, like a thin, far-reaching flashlight of audio. By contrast, our system keeps the propagation path essentially inaudible and creates audible sound only inside a small spot. We form two carefully shaped ultrasonic beams that bend around obstacles, such as a person’s head, and meet on the far side. Only in that tiny overlap region does the air’s nonlinearity “mix” the ultrasound and produce normal audio—music, speech, or alerts—right where we place it. Step inside the spot and you hear it; step a few centimeters away and it fades.
In experiments, we produced a palm-sized enclave more than a foot from the source and even behind an obstacle, using a compact emitter roughly the size of a dinner plate. Because the audible conversion is confined to the overlap region, the approach is quiet along the curving paths of the beams and practical in everyday spaces. We also showed that the enclave covers key parts of the speech band, so voices sound intelligible and natural in ordinary rooms rather than only in special lab setups.
This capability could potentially enable private voice prompts in cars or airplanes, confidential bedside communication in hospitals, and personal listening zones in open offices or public kiosks—without headphones and without broadcasting to bystanders. The beams can be bent and steered, so the audible spot appears where needed and avoids where it is not. We are actively improving the system‘s demodulation efficiency and refining the audio quality it delivers.
Schematic depicting the remote creation of an audible enclave. Image adapted from author’s original paper.
Demonstration of the remote creation of an audible enclave. Video adapted from author’s original paper.
Hala Abualsaud – habualsa@ucsd.edu LinkedIn: linkedin.com/in/hala-abualsaud ECE, University of California San Diego San Diego, California 92130 United States
Peter Gerstoft – pgerstoft@ucsd.edu. ECE, University of California San Diego San Diego, California 92130 United States
Popular version of 2aCA7 – Acoustic Simultaneous Localization and Mapping for Drone Navigation in Complex Environments Presented at the 188th ASA Meeting Read the abstract at https://doi.org/10.1121/10.0037541
–The research described in this Acoustics Lay Language Paper may not have yet been peer reviewed–
When drones fly indoors, inside warehouses, tunnels, or disaster zones, they can’t rely on GPS or cameras to know where they are. Instead, we propose something different: a drone that “listens” to its surroundings to navigate and map the environment.
We developed a new system called acSLAM (acoustic Simultaneous Localization and Mapping) that uses sound to guide a drone in 3D space. Our drone carries three microphone arrays, arranged in triangles, along with a motion sensor called an IMU (inertial measurement unit). As the drone moves, it records sounds and small changes in movement. Using this information, it estimates its own position and finds where multiple sound sources are located at the same time.
To handle the complexity of real 3D motion (where rotations can easily become unstable), we represent the drone’s orientation using quaternions – a way of describing rotation that avoids problems like gimbal lock, where the drone would otherwise lose its sense of direction. Quaternions work better than traditional methods because they keep track of rotation smoothly and consistently, even during fast or complex motion. They don’t get tripped up by tricky angles or repeated turns, which helps the drone stay accurately oriented as it moves through 3D space.
Our system works by first listening for where sounds are coming from (their angle of arrival) and measuring time differences (time difference of arrival) between microphones. Combining these clues with the drone’s movement, acSLAM builds a map of where sounds are in the room, like where people are talking or where machines are running.
We use advanced filtering methods (particle filters for the drone’s movement and Extended Kalman filters for the sound sources) to make sense of noisy real-world data. The system updates itself every step of the way, refining the drone’s position and improving the map as it gathers more information.
In testing, we found that using multiple sound observations, instead of relying on just one dramatically improved the drone’s ability to localize itself and map sources accurately. Even when the drone made sharp turns or accelerated quickly, the system stayed reliable.
This approach has exciting applications: drones could someday explore collapsed buildings, find survivors after disasters, or inspect underground spaces — all by listening carefully to their environment, without needing light, cameras, or external signals.
In short, we taught a drone not just to hear but to think about what it hears, and fly smarter because of it.
MELVILLE, N.Y., Nov. 20, 2024 – While camping is a great opportunity to unplug and connect with nature, it’s hard not to rely on some sort of technology—cellphones, radios, lanterns, and portable chargers are all useful tools to bring along while exploring the wilderness. Research by Lixian Guo at the University of Canterbury may make it possible to keep all those devices powered with another piece of equipment you’re likely to bring with you while exploring the great outdoors: camping stoves.
Guo’s work focuses on using the excess heat produced by camping stoves to create a thermoacoustic engine (TAE). TAEs convert thermal energy into acoustic energy. This acoustic energy can then be transformed into mechanical or electrical energy. When optimized, these engines can generate power ranging from tens to thousands of watts, depending on their size.
A diagram of the thermoacoustic engine proposed in Guo’s research. Credit: Lixian Guo
Guo will present work on a mathematical model of a portable outdoor waste heat-driven engine Wednesday, Nov. 20, at 10:40 a.m., ET as part of the virtual 187th Meeting of the Acoustical Society of America, running Nov. 18-22, 2024.
The researchers’ work includes simulations and analyses of experimental data from waste heat produced by common camping gas stoves, aiming to design a compact outdoor TAE capable of efficiently collecting waste heat.
Guo has emphasized the versatility of this technology.
“We have considered its potential for camping, backpacking, and emergency situations, as it can operate with any heat source, including residual heat from combustion or solar energy.”
The ultimate aim of this research is to establish a foundation for more efficient energy conversion devices, with significant applications in aviation, marine engineering, and industrial waste heat recovery. By effectively harnessing waste heat, TAEs can play a vital role in promoting sustainable energy practices across different sectors.
Guo acknowledges the challenges inherent in this research but views it as a chance to expand upon their work.
“Naturally, there are challenges in this research, particularly concerning stability and energy loss. These challenges also present opportunities for deeper exploration.”
As researchers continue to refine thermoacoustic technology, the implications for energy efficiency and sustainability are profound, offering exciting possibilities for the future.
“In the 1990s, the Los Alamos National Laboratory in the United States conducted many fascinating studies on thermoacoustic engines, using them to recover waste heat from ships to power refrigeration systems for storing ice cream. I hope my research can lay the foundation for the development of more efficient energy conversion devices in the future,” Guo said.
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LAY LANGUAGE PAPERS ASA will also share dozens of lay language papers about topics covered at the conference. Lay language papers are summaries (300-500 words) of presentations written by scientists for a general audience. They will be accompanied by photos, audio, and video. Learn more at https://acoustics.org/lay-language-papers/.
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ABOUT THE ACOUSTICAL SOCIETY OF AMERICA The Acoustical Society of America is the premier international scientific society in acoustics devoted to the science and technology of sound. Its 7,000 members worldwide represent a broad spectrum of the study of acoustics. ASA publications include The Journal of the Acoustical Society of America (the world’s leading journal on acoustics), JASA Express Letters, Proceedings of Meetings on Acoustics, Acoustics Today magazine, books, and standards on acoustics. The society also holds two major scientific meetings each year. See https://acousticalsociety.org/.
Additional authors:
Alexandria Podolski
William Gray
Andrew Brown
Theodore Argo
Popular version of 1pEA3 – Investigating Commercially Available Force Sensors for Bone Conduction Hearing Device Evaluation
Presented at the 187th ASA Meeting
Read the abstract at https://doi.org/10.1121/10.0035017
–The research described in this Acoustics Lay Language Paper may not have yet been peer reviewed–
Bone conduction (BC) headphones produce sound without covering the outer ears, offering an appealing alternative to conventional headphones. While BC technologies have long been used for diagnosing and treating hearing loss, consumer BC devices have become increasingly popular with a variety of claimed benefits, from safety to sound quality. However, objectively measuring BC signals – to guide improvement of device design, for example – presents several unique challenges, beginning with measurement of the BC signal itself.
Airborne audio signals, like those generated by conventional headphones, are measured using microphones; BC signals are generated by vibrating transducers pressed against the head. These vibrations are impacted by how/where and how tightly the BC headphones are positioned on the head, and other factors including individualized anatomy.
BC devices have historically been evaluated using an artificial mastoid (Figure 1 – left), a specialized (and expensive) measurement tool that was designed to simulate key properties of the tissue behind the ear, capturing the output of selected clinical BC devices under carefully controlled measurement conditions. While the artificial mastoid’s design allows for high-precision measurements, it does not account for the variety of shapes and sizes of consumer BC devices. Stakeholders ranging from manufacturers to researchers need a method to measure the effective outputs of consumer BC devices as worn by actual listeners.
Figure 1. The B&K Artificial Mastoid (left) is the standard solution for measuring BC device output. There is a need for a sensor to be placed between the BCD and human head for real-life measurements of the device’s output.
Our team, made up of collaborators at Applied Research Associates, Inc. (ARA) and the University of Washington, is working to develop a system that can be used across a wide variety of unique anatomy, BC devices, and sensor placement locations (Figure 1 – right). The goal is to use thin/flexible sensors placed directly under BC devices during use to accurately and repeatably measure the coupling of the BC device with the head (static force) and the audio-frequency vibrations produced by the device (dynamic force).
Three low-cost force sensors have been identified, shown in Figure 2, each having different underlying technologies with potential to meet the requirements necessary to characterize BC device output. The sensors have undergone preliminary testing, which revealed that all three can produce static force measurements. However, the detectable frequencies and signal quality of the dynamic force measurements varied based on the sensing design and circuitry of each sensor. The design of the Ohmite force sensing resistor (Figure 3– left) limited the quality of the measured signal. The SingleTact force sensing capacitor (Figure 3– middle) was incapable of collecting dynamic measurements for audio signals. The Honeywell FSA was limited by its circuitry and could only partially detect the desired frequency ranges.
Figure 2. Three force-sensors were evaluated; Ohmite force-sensing resistor (left), SingleTact force-sensing capacitor (middle), and Honeywell FSA (right).
Further testing and development are necessary to identify whether dynamic force measurements can be improved by utilizing different hardware for data collection or implementing different data analysis techniques. Parallel efforts are focused on streamlining the interface between the BC device and the sensors to improve listener comfort.
Figure 1. Analogy of the usage of ultrasonic waves for battery diagnostics, similar to how a doctor would use ultrasonics to monitor heart health. [Image generated with AI using Google NanoBanana Pro]
Figure 1. Analogy of the usage of ultrasonic waves for battery diagnostics, similar to how a doctor would use ultrasonics to monitor heart health. [Image generated with AI using Google NanoBanana Pro]
Figure 2. Evolution of cell stiffness during aging. a) Stiffness of the SSB, normalized to its initial value, plotted against discharge capacity for both charged (blue) and discharged (red) states. With representative ultrasonic images from transmitted signals at two states of the SSB: b.1) pristine before cycling, and b.2) after 40 cycles of aging. We observed a significant reduction in transmission in the middle region of the SSB. Warmer colors indicate higher transmission, and dashed outlines mark the active cell region.
Figure1. Proposed method for evaluating leaf water content through its acoustic response
Figure 2. Estimation equation to estimate leaf natural frequency
Figure 3. Comparison of measured and estimated leaf natural frequency changes under stopped watering
Figure 1. The B&K Artificial Mastoid (left) is the standard solution for measuring BC device output. There is a need for a sensor to be placed between the BCD and human head for real-life measurements of the device’s output.
Figure 2. Three force-sensors were evaluated; Ohmite force-sensing resistor (left), SingleTact force-sensing capacitor (middle), and Honeywell FSA (right).