Acoustic Engineering Advances

A breakthrough in audio engineering has been achieved by a team of researchers led by yun jing a professor at Penn State University. They have pioneered the concept of "audible enclaves," allowing for private listening without the need for headphones. By emitting two nonlinear ultrasonic beams, these audible enclaves create localized pockets of sound zones. In these enclaves, individuals can hear sound while others nearby cannot, even in enclosed spaces like vehicles or directly in front of the audio source. Published in the Proceedings of the National Academy of Sciences on March 17, the study details how this innovative technology precisely narrows where sound is perceived, offering a unique listening experience at the intersection point of the ultrasonic beams. https://lnkd.in/gyYyuFww

How Scientists Created a Unidirectional Path for Sound That Could Transform Wave Technology Researchers break sound wave reciprocity, opening new possibilities for advanced communication and sensing systems. Overview: Scientists have successfully created a unidirectional path for sound waves, breaking the fundamental principle of reciprocity—the symmetrical propagation of sound between sender and receiver. This breakthrough could revolutionize acoustic technologies, including sonar systems, noise-canceling devices, and communication networks. By restricting sound waves to travel in one direction, researchers have addressed a long-standing limitation in wave-based technologies. What Is Reciprocity in Sound Waves? • Bidirectional Nature: In standard acoustic systems, sound waves travel symmetrically between two points. If Person A can hear Person B, the reverse is also true. • The Challenge: Reciprocity can cause signal reflections and interference, limiting the performance of communication and sensing systems. • Non-Reciprocal Sound Waves: By breaking reciprocity, scientists can control sound propagation, allowing it to move in only one direction while preventing backflow or unwanted reflections. How Researchers Broke Sound Reciprocity: • Acoustic Metamaterials: Scientists used specialized materials designed to manipulate sound wave propagation. • Asymmetrical Structures: These materials were engineered to allow sound waves to move freely in one direction while blocking them in the opposite direction. • Dynamic Modulation: Researchers applied external stimuli, like magnetic fields or electronic signals, to guide sound waves selectively along a predetermined path. Why This Breakthrough Matters: 1. Improved Communication Systems: Non-reciprocal sound wave paths reduce signal loss and interference, enhancing the efficiency of acoustic communication networks. 2. Advanced Noise Control: Devices can now block unwanted sound reflections, improving the performance of noise-canceling technologies. 3. Enhanced Sonar and Ultrasound: Medical imaging and underwater sonar systems can achieve clearer, more accurate signal reception without disruptive backscatter. 4. Energy Efficiency: Unidirectional sound systems minimize energy loss caused by reflections, making devices more efficient. Applications of Unidirectional Sound Technology: • Sonar Systems: Enhanced underwater detection and mapping with reduced interference. • Medical Imaging (Ultrasound): Clearer imaging results by eliminating signal distortions caused by bidirectional sound waves. • Acoustic Communication Devices: Improved audio clarity in smart devices, hearing aids, and home assistant technologies. • Noise-Canceling Infrastructure: Better soundproofing in buildings, vehicles, and public spaces.

SYMMETRY-PROTECTED ACOUSTIC "GHOST TUNNELS" DUALITY Acoustic metamaterials continue to expand the fundamental limits of wave manipulation. A recent Physical Review Letters study reports a striking demonstration of boundary‑selective wave transport: an engineered acoustic structure that behaves simultaneously as a near‑perfect waveguide and an acoustically invisible medium, depending solely on the direction of incidence. This dual behavior—termed a symmetry‑protected acoustic “ghost tunnel”—is enabled by precise control of dispersion, impedance, and nonsymmorphic symmetry within a subwavelength metamaterial lattice. Conventional acoustic waveguides confine sound through rigid boundaries that reflect waves inward. While effective for guided propagation, these same boundaries scatter any external waves approaching from the side, creating unavoidable crosstalk in multi‑channel acoustic systems. The ghost tunnel overcomes this limitation by embedding two distinct effective media within a single physical structure, each selectively excited by different boundary conditions. The metamaterial consists of a 2D array of 3D‑printed unit cells, each containing paired air cavities connected by coiled channels. This geometry slows acoustic propagation and enables a zero‑index response at the operating frequency (2.8 kHz), allowing sound entering through the tunnel ends to propagate with negligible phase accumulation and near‑unity transmission. Simultaneously, the structure is engineered to be impedance‑matched to air, so that waves incident on the lateral boundaries experience no reflective interface and pass through as if the tunnel were absent. This duality arises from symmetry‑protected dispersion branches. The zero‑index branch supports tightly confined, phase‑free transport along the tunnel axis, while a separate air‑matched branch governs lateral incidence. Conservation of the tangential wavevector ensures that waves entering from different boundaries couple exclusively to their respective branches, preventing cross‑interaction. The result is a single metamaterial that functions as both a perfect acoustic guide and a perfect acoustic ghost. Experiments confirm both regimes: end‑fire excitation yields high‑fidelity guided transport, while side incidence produces undistorted transmission through the structure. This boundary‑dependent effective‑medium behavior represents a conceptual advance in acoustic metamaterials, enabling waveguiding and cloaking functionalities that traditionally require separate components. The implications are broad. Ghost‑tunnel architectures could significantly reduce crosstalk in sonar arrays, acoustic circuits, and multi‑channel sensing environments. Moreover, the underlying symmetry‑engineered mechanism is general and may translate to electromagnetic, photonic, and electronic wave systems, offering a versatile framework for multiplexed, non‑interfering wave transport. #DOI: 10.1103/9y6g-42nm

Thrilled to share our Nature Electronics paper that creates sound bubbles with AI-powered hearables. Paper: https://rdcu.be/d0bYE Videos and code: https://lnkd.in/ghS4XAAE Imagine having the ability to create a sound bubble where all speakers within the bubble are audible, but speakers and noise outside are suppressed. For example, envision a scenario where a person desires to eliminate all the noise in a restaurant but effortlessly tunes in to the conversation at their table. While noise-canceling headphones can suppress sounds around the wearer, they cannot perceive distance or selectively program acoustic scenes based on speaker distances. The distance perception of the human auditory system is also limited, and although we can determine the angular direction of a sound source, estimating distance is more challenging. We developed real-time neural networks that create sound bubbles with adjustable radii of 1–2 meters. We introduced the first dataset of audio recordings capturing head-related reflections and reverberations by distance in real-world. Finally, we built hardware integrating a noise-canceling headset with six microphones, powered by our real-time acoustic bubble network on a Raspberry Pi. We demo various applications including mobility, with speakers entering the bubble, multiple overlapping speakers and no speakers within the bubble. Taking a step back, this addresses the cocktail party problem has been a long-standing challenge for headsets, hearing aids and now smart glasses. Tuochao Chen, Malek Itani, Sefik Emre Eskimez,Takuya Yoshioka

Low-frequency sound waves can do more than shake the room, they can stop fires in their tracks. Researchers at George Mason University have developed a revolutionary sound wave fire extinguisher that disrupts combustion using low-frequency pressure waves (30-60 Hz) instead of traditional chemicals or water. How It Works: Fire needs heat, fuel, and oxygen to sustain combustion. Instead of blowing air (which adds oxygen), low-frequency sound waves create oscillating pressure zones, disrupting the boundary layer of oxygen around the flames. This separates oxygen from the fuel source, effectively snuffing out the fire. Technical Insights: Frequencies in the bass range (30-60 Hz) work best for displacing oxygen. Resonant acoustic waves cause air molecules to vibrate rapidly, interfering with combustion. Unlike CO₂ or foam-based extinguishers, this method leaves no residue and is environmentally friendly. Potential Applications: Kitchen and household fires (safe, non-toxic suppression) Data centers and electrical fires (no water damage) Aerospace & microgravity environments where traditional extinguishers are impractical This innovation could change how we fight fires, no chemicals, no mess, just precision engineered acoustics. Looks like DJs can’t "burn the stage" anymore... literally:)

Our new article titled “Enhancing Acoustic Performance of Refrigerator Compressors through Muffler Modeling and Optimizing via Discharge Pressure” was just published in International Journal of Refrigeration. To enhance the acoustic performance of refrigerator compressors, it is essential to minimize undesirable vibrations and noise emissions. A crucial factor in this endeavor is the optimization of the compressor's gas flow path, focusing on noise generation. This article investigates the enhancement of acoustic performance in compressors through the optimization of muffler designs within the gas flow path. 1D Transfer Matrix Method (TMM) was used to model Transmission Loss (TL) of suction and discharge mufflers, with results validated against Finite Element Method (FEM) simulations. Pressure pulsation data from the discharge line were analyzed using Welch method, which informed the optimization of a two-chamber discharge muffler through custom optimization algorithms: Genetic Algorithm (GA) and Interior Point Method (IPM). These methodologies targeted specific frequencies, while adhering to predefined design constraints. Furthermore, the results of this study provide insights into the interplay between pressure pulsation dynamics and noise emissions, contributing to compressor acoustics-efficient muffler designs. This article evaluates TMM for modelling complex geometries, specifically suction mufflers at low to mid-range frequencies. TMM accurately predicted discharge muffler performance, even at higher frequencies. Optimizations led to significant improvements in acoustic performance, with GA outperforming IPM in both accuracy and efficiency. Experimental validation conducted in a full anechoic room (FAR) confirmed that the optimized muffler design achieved a reduction in overall Sound Power Level (SWL). These optimized designs not only led to a significant decrease in noise but also reinforced the established correlation between pressure pulsations and corresponding acoustic emissions, highlighting advanced modelling and optimization. I would like to thank my doctoral assistant N. Onur Çatak, and Ergin Arslan from Beko Global Central R&D for their dedicated work and contributions. We acknowledge Beko Global for supporting this research. Free access to the full article is provided at the link below through November 19, 2025: https://lnkd.in/dETB9dBQ #refrigerator #compressor #noise #muffler #geneticalgorithm #optimization #powerspecturm #soundpowerlevel

Sound That Shapes the Sea: How Acoustic Waves Are Transforming Ocean Innovation What if we could shape ocean waves using sound—without touching the water, without engines, and without chemicals? Recent breakthroughs in marine acoustofluidics have shown that sound can be used to precisely control wave formations on the ocean’s surface. By adjusting frequency, phase, and amplitude, scientists can generate acoustic fields that create, amplify, or guide wave patterns with stunning accuracy. This is not just a visual phenomenon—it’s a tool that enables non-contact manipulation of surface materials, from pollutants to floating sensors. This technology opens new possibilities for oil spill response, marine debris harvesting, and even energy optimization, by directing wave motion where and when it’s needed most. It also holds promise for aquaculture, oceanic biotech, and autonomous marine operations, allowing systems to work with the sea instead of fighting against it. As an expert in underwater and coastal systems, I see this as a major leap forward for the Blue Economy. It combines elegance with efficiency—bringing physics, engineering, and sustainability into one seamless innovation. We’re entering a new era where acoustics become a clean force for marine control and environmental intelligence. The next wave of maritime technology is silent—but powerful. Let’s talk if you’re ready to surf it. #BlueTech #Ocean #Innovation #Marine #Engineering #AcousticControl #CleanOceans #BlueEconomy #EnvironmentalTech #FutureOfTheSea

A few days ago I mentioned that I was working on a small experimental platform for underwater acoustic and digital signal processing. Today I would like to introduce it: ❇️ PASLAB : Programmable Acoustic Signal Laboratory. ▶️ PASLAB is a multidisciplinary bench-top development platform designed for hardware-validated acoustic and signal-processing experiments. ▶️ It combines low-noise analog front-end design, controlled waveform and noise generation, measurement of transducer characteristics, analog self-noise observation, embedded configurability, DSP-oriented experimentation, and Qt-based scenario control within a single practical system. ▶️ The system was designed with a strong focus on real-world behavior, where analog noise, gain stages, and hardware limitations are treated as first-class design constraints. ▶️ Controlled Signal and Noise Injection : PASLAB also supports controlled noise injection, allowing programmable signal-to-noise ratio(SNR) experiments to evaluate detection algorithms under repeatable laboratory conditions. ▶️ The platform can emulate a programmable acoustic channel in a Qt-based scenario by combining acoustic signal generation, attenuation, and controlled noise injection (SL, TL, NL, TVR, RVS, TS, etc.) ❇️ PASLAB – What can be done with it? ▶️ Arbitrary waveform generation (rectangular, hann, hamming, blackman, burst, chirp(FM), coded, noise, ping) ▶️ It includes a controllable noise injection and attenuation stage that allows experiments under different SNR conditions.. ▶️ Scenario based Underwater Acoustic Communication ▶️ Scenario based Acoustic Target Detection ▶️ Detecting weak signals buried in noise ▶️ Testing DSP algorithms under controlled conditions (FFT, THD, windowing, energy det., matched filtering, FIR, IIR, SNR , processing gain etc.) ▶️ Transducer Behavior and Matching (BVD Model) ▶️ Transducer Matching & Power Transfer & Estimates Preamplifier Input Impedance ▶️ Measuring analog chain noise floor and dynamic range ▶️ Recording and Replaying real signals under different conditions using SRAM/FRAM ▶️ Detection Algorithms   • Matched Filter   • Energy Detection   • Envelope Detection   • FFT-based Detection   • Adaptive Threshold (CFAR concepts) The images provide the system architecture, signal chain overview, capability summary, and HW design criteria. Note :  In the design of this platform, engineering is not about being 10 out of 10 in one field, but about being 8 out of 10 across several fields at the same time. BTW Passive filters, low noise buffers.. are not shown in the block diagram. The system is currently under development. More results and experiments will be shared once the first hardware tests are completed. #signalprocessing #acoustics #embedded #electronics #instrumentation

🔥 Breaking news from the frontier of exterior computational acoustics. After years of effort, we can finally eliminate artificial absorbing layers. No more tuning damping parameters. No mysterious reflections sneaking back from your truncation boundary at a few wavelengths. Instead: An exact non-reflecting Dirichlet-to-Neumann boundary condition for time-harmonic exterior acoustics. Place the boundary on a separable surface. Apply the operator. The exterior is handled — exactly. Elegant. Clean. … Now for the part that makes me smile 😀. This idea was already over 30 years old when the poster circulated around 2010. And our group at Clemson had published on it more than 20 years ago. Researchers like Astley, Keller, Givoli, Harari, and Grote had already laid much of the groundwork. Back then, we were: • Wrapping complex 3D scatterers with spheroidal DtN boundaries • Running large-scale scattering simulations • Scaling Krylov solvers across distributed processors • Getting near-optimal parallel speedup On hardware that now belongs in a museum next to dial-up modems. So why revisit this? Because in practice, most exterior acoustic simulations still rely on: • Infinite elements • "Perfectly" matched layers • Absorbing boundary approximations They’re flexible. They’re familiar. They fit neatly into the standard “assemble local elements → solve sparse system” workflow. Exact DtN boundaries are a little different. They require separable geometries — spheres, cylinders, spheroids. And the boundary operator is non-local. That last word tends to make software developers slightly uneasy. “Wait… all the boundary nodes talk to each other?” Yes. “But our code assumes everything is local.” Also yes. Here’s the part that often gets overlooked: Inside an iterative solver, that non-local DtN contribution is just part of a matrix–vector product. It doesn’t require tearing apart the interior assembly. It doesn’t destroy sparse solution strategies. It doesn’t prevent parallel scaling. In fact, the parallel speedup data on the poster shows the DtN portion scaling cleanly across processors. The limitation wasn’t mathematical. It was architectural — and partly cultural. Users expect element-based absorbing layers. Developers design around that expectation. This isn’t a critique of PML or infinite elements. They are extremely useful and widely applicable. But it’s worth remembering: Exact non-reflecting boundaries on separable geometries are not speculative theory. They are not impractical curiosities. They were implemented. Tested. Parallelized. Published. Sometimes the “new capability” is simply something that didn’t fit comfortably inside the dominant software template of its time. And sometimes progress isn’t about inventing the next idea. It’s about revisiting a good one — and asking whether today’s hardware, solvers, and users might finally make it feel… normal. With a bit of perspective. And a bit of humor. 😊

Researchers have created a new technology that can send sound only to a specific person, even in a crowded space. Imagine listening to music or having a private conversation without headphones and without disturbing anyone nearby. This breakthrough could change the way we experience sound in public spaces, from entertainment to communication. Normally, sound waves spread out as they travel, which makes it difficult to control where the sound goes. But researchers have found a way to focus sound using ultrasound, a type of sound that is too high-pitched for humans to hear. By using two silent ultrasound beams at different frequencies, they create a new sound wave in the spot where the beams meet. This new sound is the one that can be heard, but only in that particular spot. What makes this technology even more impressive is that the ultrasound beams can bend and follow a curved path, similar to how light can bend through a lens. This allows the sound to reach a specific location, even around obstacles. The sound is silent until it reaches the target area, making it possible to deliver sound only to one person without anyone else hearing it. While this technology isn’t ready for widespread use yet, it could have huge impacts on things like personalized audio in public places, creating quiet zones, and even improving privacy in conversations. However, challenges like sound quality and energy use still need to be worked out. Research Paper 📄 https://lnkd.in/ePCNqBig