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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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/.
–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.
–The research described in this Acoustics Lay Language Paper may not have yet been peer reviewed–
The 2023 train derailment that occurred in East Palestine, OH, brought attention to the limitations of the detectors currently used in the industry. Typically, the health of train bearings is monitored intermittently through wayside temperature detection systems that can be as far as 40 miles apart. Nonetheless, catastrophic bearing failure is often sudden and develops rapidly. Current wayside detection systems are reactive in nature and depend on significant temperature increases above ambient. Thus, when these systems are triggered, train operators rarely have enough time to react before a derailment occurs, as it did in East Palestine, OH. Multiple comprehensive studies have shown that the temperature difference between healthy and faulty bearings is not statistically meaningful until the onset of catastrophic failure. Thus, temperature alone is an insufficient metric for health monitoring.
Video 1. Vibration and noise emitted from train bearings.
Over the past two decades, we have demonstrated vibration-based solutions for wireless onboard condition monitoring of train components to address this problem. Early stages of bearing failure are reliably detected via vibrations and acoustics signatures, as shown in Video 1, which can also be used to determine the severity and location of failure. This is accomplished in three levels of analysis where Level 1 determines the bearing condition based on the vibration levels within the bearing as compared to a maximum vibration threshold for healthy bearings. In Level 2, the vibration signature is analyzed to identify the defective component within the bearing, and Level 3 estimates the size of the defect based on a developed correlation that relates the vibration levels to defect size.
To demonstrate this process, Figure 1 provides the vibration and temperature profiles for two bearings. Examining the vibration profile, the vibration levels within bearing R7 exceed the maximum threshold for healthy bearings 730 hours into the test, thus indicating a defective bearing. At the same time, the operating temperature of that bearing never exceeded the normal operating range, which would suggest that the bearing is healthy. Upon teardown and visual inspection, we found severe damage to the bearing components at the raceways, as pictured in Figure 2. Despite severe damage all around the bearing inner ring (cone), the operating temperature did not indicate any abnormal behavior.
Figure 1: Vibration and temperature profiles of two railroad bearings showcasing how vibration levels within the bearings can indicate the development of defects while operating temperature does not exhibit any abnormal behavior.
Figure 2: Picture of the damage that developed within bearing R7 (refer to Figure 1). Interestingly, the bearing inner ring (cone) had severe damage and a crack that the vibration levels picked up but not the operating temperature.
We believe that vibration-based sensors can provide proactive monitoring of bearing conditions affording rail operators ample time to detect the onset of bearing failure and schedule non-disruptive maintenance. Our work aims to continue to optimize these new methods and help the rail industry deploy these technologies to advance rail safety and efficiency. Moreover, this research program has had an extraordinary transformative impact from the local to the national level by training hundreds of engineers from underrepresented backgrounds and positioning them for success in industry, government, and higher education.
–The research described in this Acoustics Lay Language Paper may not have yet been peer reviewed–
On Saturday, July 13, 2024, thousands of supporters attended an outdoor rally held by presidential candidate Donald J. Trump at the Butler Farm Show grounds in Butler, Pennsylvania. Shortly after Mr. Trump began speaking, gunshots rang out. Several individuals in the crowd were seriously wounded and killed.
While the gunfire was clearly audible to thousands at the scene—and soon millions online—many significant details of the incident could only be discerned by the science of audio forensic analysis. More than two dozen mobile phone videos from rally attendees provided an unprecedented amount of relevant audio information for quick forensic analysis. Audio forensic science identified a total of ten gunshots: eight shots from a single location later determined to be the perpetrator’s perch, and two shots from law enforcement rifles.
In our era of rapid spread of speculative rumors on the internet, the science of audio forensics was critically important in quickly documenting and confirming the actual circumstances from the Trump rally scene.
Where did the shots come from?
Individuals near the stage described hearing pop pop pop noises that they reported to be “small-arms fire.” However, scientific audio forensic examination of the audio picked up by the podium microphones immediately revealed that the gunshot sounds were not small-arms fire as the earwitnesses had reported, but instead showed the characteristic sounds of supersonic bullets from a rifle.
When a bullet travels faster than sound, it creates a small sonic boom that moves with the bullet as it travels down range. A microphone near the bullet’s path will pick up the “crack” of the bullet passing by, and then a fraction of a second later, the familiar “bang” of the gun’s muzzle blast arrives at the microphone (see Figure 1).
Figure 1: Sketch depicting the position of the supersonic bullet’s shock wave and the firearm’s muzzle blast.
From the Trump rally, audio forensic analysis of the first audible shots in the podium microphone recording showed the “crack” sound due to the supersonic bullet passing the microphone, followed by the “bang” sound of the firearm’s muzzle blast. Only a small fraction of a second separated the “crack” and the “bang” for each audible shot, but the audio forensic measurement of those tiny time intervals (see Figure 2) was sufficient to estimate that the shooter was 130 meters from the microphone—a little more than the length of a football field away. The acoustic calculation prediction was soon confirmed when the body of the presumed perpetrator was found on a nearby rooftop, precisely that distance away from the podium.
Figure 2: Stereo audio waveform and spectrogram from podium microphone recording showing the first three shots (A, B, C), with manual annotation.
How many shots were fired?
The availability of nearly two dozen video and audio recordings of the gunfire from bystanders at locations all around the venue offered a remarkable audio forensic opportunity, and our audio forensic analysis identified a total of ten gunshots, labeled A-J in Figure 3.
Figure 3: User-generated mobile phone recording from a location near the sniper’s position, showing the ten audible gunshots.
The audio forensic analysis revealed that the first eight shots (labeled A-H) came from the identified perpetrator’s location, because all the available recordings gave the same time sequence between each of those first eight shots. This audio forensic finding was confirmed later when officials released evidence that eight spent shell casings had been recovered from the perpetrator’s location on the rooftop
Comparing the multiple audio recordings, the two additional audible shots (I and J) did not come from the perpetrator’s location, but from two different locations. Audio forensic analysis placed shot “I” as coming from a location northeast of the podium. Matching the audio forensic analysis, officials later confirmed that shot “I” came from a law enforcement officer firing toward the perpetrator from the ground northeast of the podium. The final audible shot “J” came from a location south of the podium. Again, consistent with the audio forensic analysis, officials confirmed that shot “J” was the fatal shot at the perpetrator by a Secret Service counter-sniper located on the roof of a building southeast of the podium.
Analysis of sounds from the Trump rally accurately described the location and characteristics of the audible gunfire, and helped limit the spread of rumors and speculation after the incident. While the unique audio forensic viewpoint cannot answer every question, this incident demonstrated that many significant details of timing, sound identification, and geometric orientation can be discerned and documented using the science of audio forensic analysis.
Please feel free to contact the author for more information.
–The research described in this Acoustics Lay Language Paper may not have yet been peer reviewed–
Exciters are devices that can be stuck to just about anything in order to make a speaker. Many DIY speaker makers wonder what material is going to sound the best for their product or home speaker project. The sound of an exciter-based plate speaker depends on many things. These include the plate materials, size, shape, and where the exciter is attached. The fact that there are so many factors that control the sound makes it difficult to directly compare the sound of materials. For example, a plastic and aluminum plate of the same size and thickness will have completely different frequency ranges when set up as speakers. In this paper, a method is proposed to calculate the required shape and size of any set of materials so that speakers made from them will have the same loudness and frequency range and the effect of the materials on the speaker sound can be easily compared.
Equations derived in the paper demonstrate that the vibrations and volumes of plates made from different materials will match when they have the same length-to-width ratio and weight (volume times density). Three different materials (Foam poster board, plastic, and aluminum) were chosen for comparison in this paper because they are commonly used by DIY makers to create speakers. Figure 1 shows the simulated relative loudness over a range of audio frequencies for three different materials (foam poster board, plastic, and aluminum) with the same length-to-width ratio and weight. The loudness graphs mostly overlap, but the volumes diverge at high frequencies because the ring shape of the exciter interacts differently with each material. This effect can be mitigated by using a smaller exciter.
Figure 1 – Simulated speaker loudness using three different materials with matching length-to-width ratios and weights.
Simulated plate responses are then compared with experimentally measured loudness results using actual plates made from plastic, aluminum, and foam poster board. These comparisons shown in Figure 2 allow us to identify whether there are any material-specific deviations from the simulated response that would lend each material its unique “sound.”
Figure 2 – Simulated vs. experimentally measured plate loudness for three different materials.
The plastic and aluminum plates match their simulations closely. The aluminum plate has sharper peaks than the plastic plate, indicating a more “hollow” sound. The foam poster board does not match its simulation well, showing that this material adds a distinctive “color” to the sound at mid-range and high audio frequencies.
Applying this method to additional materials that DIY speaker builders use like wood, cardboard, and foam insulation can shed light on their unique “sounds” as well.
Université de Sherbrooke, Département de génie mécanique, Sherbrooke, Québec, J1K 2R1, Canada
Marc-André Guy, Département de génie mécanique, Université de Sherbrooke
Kamal Kesour, Innovation Maritime, Rimouski, QC, Canada
Jean-Christophe G.Marquis, Innovation Maritime, Rimouski, QC, Canada
Giuseppe Catapane, University of Naples Federico II, Naples, Italy
Giuseppe Petrone, University of Naples Federico II, Naples, Italy
Olivier Robin, Département de génie mécanique, Université de Sherbrooke
Popular version of 1pEA6 – Use of metamaterials to reduce underwater noise generated by ship machinery
Presented at the 186th ASA Meeting
Read the abstract at https://doi.org/10.1121/10.0026790
–The research described in this Acoustics Lay Language Paper may not have yet been peer reviewed–
The underwater noise generated by maritime traffic is the most significant source of ocean noise pollution. This pollution threatens marine biodiversity, from large marine mammals to invertebrates. At low speeds, the machinery dominates the underwater radiated noise from vessels. It also has a precise sound signature since it usually operates at a fixed rotation frequency. If you think of it, an idling vehicle produces a tonal acoustic excitation. The sound energy distribution is mainly concentrated at a few precise frequencies and multiples. Indeed, the engine rotates at a given rotation speed – in round per minutes – or frequency (divided by 60, it is the number of oscillations per second). In addition to the rotating frequency, the firing order and the number of cylinders will lead to the generation of excitation multiples of the rotating frequency. The problem is that the produced frequencies are generally low and difficult to mitigate with classical soundproofing materials requiring substantial material thickness.
This research project delves into new solutions to mitigate underwater noise pollution using innovative noise control technologies. The solution investigated in this work is structured quarter-wavelength acoustic resonators. These resonators usually absorb sound at a resonant frequency and odd harmonics, making them ideal for targeting precise frequencies and their multiples. However, the length of these resources is dictated by the wavelength corresponding to the target frequency. As for the required material thickness, this wavelength is significant at low frequencies (in air, for a frequency of 100 Hz and a speed of sound of 340 m/s, the wavelength is 3.4 m since the wavelength is the ratio of speed by frequency). The length of a quarter wavelength resonator tuned at 100 Hz is thus 0.85 m.
Fig.1. Comparison between classical and innovative soundproofing material on sound absorption, from Centre de recherche acoustique-signal-humain, Université de Sherbrooke.
Therefore, a coiled quarter wavelength resonator was considered to reduce its bulkiness, and facilitate their installation. The inspiration follows Archimedes’ spiral geometry shape, a structure easily manufactured using today’s 3D printing technologies. Experimental laboratory tests were conducted to characterize the prototypes and determine their effectiveness in absorbing sound. We also created a numerical model that allows us to quickly answer optimization questions and study the efficiency of a hybrid solution: a rock wool panel with embedded coiled resonators. We aim to combine classic and innovative solutions tom propose low weight and compact solutions to efficiently reduce underwater noise pollution!
Fig.2. Numerical model of coiled resonators embedded in rockwool, from Centre de recherche acoustique-signal-humain, Université de Sherbrooke.
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).
Figure 1: Vibration and temperature profiles of two railroad bearings showcasing how vibration levels within the bearings can indicate the development of defects while operating temperature does not exhibit any abnormal behavior.
Figure 1: Sketch depicting the position of the supersonic bullet’s shock wave and the firearm’s muzzle blast.
Figure 2: Stereo audio waveform and spectrogram from podium microphone recording showing the first three shots (A, B, C), with manual annotation.
Figure 3: User-generated mobile phone recording from a location near the sniper’s position, showing the ten audible gunshots.
Exciters are devices that can be stuck to just about anything in order to make a speaker. Many DIY speaker makers wonder what material is going to sound the best for their product or home speaker project. The sound of an exciter-based plate speaker depends on many things. These include the plate materials, size, shape, and where the exciter is attached. The fact that there are so many factors that control the sound makes it difficult to directly compare the sound of materials. For example, a plastic and aluminum plate of the same size and thickness will have completely different frequency ranges when set up as speakers. In this paper, a method is proposed to calculate the required shape and size of any set of materials so that speakers made from them will have the same loudness and frequency range and the effect of the materials on the speaker sound can be easily compared.
Figure 1 – Simulated speaker loudness using three different materials with matching length-to-width ratios and weights.
Figure 2 – Simulated vs. experimentally measured plate loudness for three different materials.
