–The research described in this Acoustics Lay Language Paper may not have yet been peer reviewed–
Imagine a world where treating cancer doesn’t mean enduring invasive surgeries, long hospital stays, or intense side effects. Many researchers around the globe are working tirelessly to make that vision a reality. One approach could be ultrasound. Ultrasound has traditionally been associated with imaging, such as during pregnancy or heart examinations. Over the past few decades, however, scientists have reimagined its role in medicine, exploring ultrasound as a therapeutic tool to treat various diseases, including cancer. Histotripsy takes this idea to new heights. By directing focused ultrasound waves right into a tumor, we can quickly disrupt and break down cancer cells by forming tiny bubbles. When these bubbles collapse, they can collapse at speeds of several hundred meters per second, approaching speeds of a supersonic aircraft. Due to the focused nature of the device, it can protect nearby healthy cells. In fact, histotripsy is already FDA to treat certain cancers, such as liver cancer, and has shown tremendous success.
Yet, its application for colon cancer or lung cancer have yet to be fully explored. To target these cancers, a smaller device had to be developed. In fact, the device diameter is about half that of a penny (Figure 1). This would allow our device to be used with an endoscope, which means doctors can reach the tumor inside the body without needing to make big cuts.
This prototype device was recently studied in our lab. To explore the initial effectiveness of the device, lung and colon cancer cells were rapidly treated (2 minutes or less of treatment time). In fact, we were able to kill over 60% of the cells in sample (Figure 2). This highlights the versatility of the histotripsy device in treating various cancers and underscores its promising potential for a range of applications in cancer therapy. With continued research and development, this innovative technology may help improve cancer treatment and offer new hope to those affected by this disease.
–The research described in this Acoustics Lay Language Paper may not have yet been peer reviewed–
Consider a black hole in outer space, where gravity is so strong that not even light waves can escape. Now, imagine a device here on Earth that can slow sound waves so much that they cannot escape. Scientists call this intriguing phenomenon an “acoustic black hole” (ABH). An ABH structure can trap sound waves and produce a unique environment for acoustic measurement and manipulation.
How can a structure be designed to trap sound in this way? The acoustic black hole effect is achieved by altering the way sound travels down a duct. Traditional ABHs are based upon the pioneering research of Mironov and Pislyakov (2002) that used specific shapes to guide sound waves, such as rings with inner radii that vary down the length of the duct. However, in this work, the approach is different: varying the mechanical impedance of the duct walls themselves (see Figure 1). Mechanical impedance refers to how much a structure resists motion when sound waves press against it. By engineering an impedance profile—essentially, the way the walls respond to sound throughout the duct—researchers can create a situation where sound waves decrease in speed as they travel through the duct. A gradual reduction in speed effectively simulates the event horizon of a black hole, causing the sound waves to be trapped and significantly attenuated (see Figure 2).
Figure 1. A sound wave enters a duct where the walls are stiffer at the entrance and softer at the base. As the wave moves through the duct, it slows down due to the changing properties of the walls.
To better understand this phenomenon, the researchers derived and solved governing equations using two methods. First, they used a mathematical technique called the WKB approximation, which helps find approximate solutions to wave equations. Second, they used numerical simulation, which involves using computers to model complex systems. The solutions they obtained from these approaches revealed that specific impedance profiles could effectively decelerate and absorb acoustic waves, resulting in very little reflection or transmission of sound.
To verify their findings, the researchers employed a sophisticated program called Sierra/SD. This program uses a fully coupled structural-acoustic finite element algorithm. In brief, this algorithm allows researchers to create a computer model of any design they want and test how it responds to any sound source. This tool allows for detailed simulations of how sound interacts with various structures and provides a robust framework for testing theoretical predictions.
Overall, this research not only enhances understanding of the acoustic black hole effect, but also paves the way for the development of innovative acoustic materials and devices. By using the principles of ABH, these advancements could lead to improved noise control and enhanced manipulation of sound waves, with potential applications in various fields such as engineering, architecture, and environmental science.
Figure 2. An illustration of a sound wave vanishing in an acoustic black hole structure. The ABH effect is seen from the wavefronts becoming closer together (slower sound speed) and lower in amplitude (lower peaks, higher troughs) at the right end.
Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA-0003525.
Brendan Smith – brendan.smith@dal.ca
Twitter: @bsmithacoustics
Instagram: @brendanthehuman
Dalhousie University, Department of Oceanography, Halifax, Nova Scotia, B3H 4R2, Canada
–The research described in this Acoustics Lay Language Paper may not have yet been peer reviewed–
The Main Endeavour Hydrothermal Vent Field (MEF) is located on the Juan de Fuca Ridge in the Northeast Pacific Ocean. This ridge is a seafloor spreading center, where tectonic plates pull apart and new oceanic crust is formed as magma upwells from beneath the earth’s surface. This movement of the earth’s crust causes cracks to form, allowing seawater to penetrate downwards towards the magma below, where it circulates and eventually resurfaces into the ocean at temperatures over 300 degrees Celsius. Uniquely adapted organisms thrive at these sites, surviving from energy provided not by the sun, but by the heat and chemical composition of the vent fluid.
Figure 1: Black-smoker hydrothermal vent chimney at the Main Endeavour Hydrothermal Vent Field (Image courtesy of Ocean Networks Canada)
Long term measurements of hydrothermal vent activity are of scientific interest. However, the high temperatures and caustic chemical characteristics make it challenging to place probes directly in the vent flow. For this reason, passive acoustics (listening) can be a useful tool for hydrothermal vent monitoring, because the hydrophones (underwater microphones) can be located a safe distance from the vent fluid. Ocean Networks Canada have had a hydrophone at MEF continuously recording for over 5 years, and for the past year, a 4-element hydrophone array has been recording at this location.
The motion of the tectonic plates in these regions causes a lot of seismic activity, such as earthquakes. On March 6, 2024, a large ~4.1 magnitude earthquake was recorded at MEF, and earthquake rates were the highest observed since 2005. This earthquake was recorded on the hydrophone array and can be seen in the spectrogram in Figure 2.
Figure 2: Spectrogram of ~4.1 magnitude earthquake at MEF
Figure 3 shows differences in the soundscape at Endeavour before, during, and after the earthquake. The changes after the earthquake persist more than 1-week following the event. The duration and higher frequency components of the changes in the soundscape suggest sources other than seismicity.
Figure 3: Acoustic spectra before, during, and after the earthquake at MEF
The hydrophone array also provides us with the opportunity to gain further insights. For example, surface wind/wave-generated noise is a predominant source of ambient sound in the ocean, and the coherence, or spatial relationship between multiple hydrophone elements in the presence of this sound source, is well known. We can compare the measured coherence with the expected (modeled) coherence to explore any deviations, which could be attributed to hydrothermal vent activity. In Figure 4 we see differences between the measurements and model below 1 kHz (outlined by black boxes), suggesting the influence of hydrothermal vent sounds on the local soundscape.
Figure 4: Measured and modeled acoustic vertical coherence at MEF
In conclusion, passive acoustic monitoring can be used to monitor changes in hydrothermal vent fields in response to seismic activity. This earthquake provided a test case to prepare for a more major seismic event, which is expected to occur at Endeavour in the coming years. Passive acoustic monitoring will be an important tool to document vent field activity during this future event.
–The research described in this Acoustics Lay Language Paper may not have yet been peer reviewed–
Impact of sound on aquatic animals
Human-generated sound, called ‘anthropogenic sound,’ is now widely recognized as an environmental stressor. It affects aquatic life in both marine and freshwater habitats. Over the last few decades, policy makers, animal welfare communities, behavioural biologists and environmental managers have been increasingly interested in understanding how man-made sound may lead to negative consequences on both terrestrial and underwater animals. Aquatic animals can be negatively affected by anthropogenic sound in many ways. For example anthropogenic sound can mask biologically relevant sounds, cause attentional shifts, affect foraging performance and interfere in communications in aquatic animals among taxa. Therefore, we need to understand how anthropogenic sound may affect individuals, to eventually be able to assess the impact of anthropogenic sound on populations, communities, and ecosystems.
Many crustaceans and fish species have been artificially introduced to confined areas for different purposes. Crustaceans and fish are being used in laboratory conditions for scientific research, in aquaria and zoos for entertainment, as well as in aquaculture facilities (e.g., cages, races, pens) for breeding, restocking and harvesting around the world. As a result, aquatic animals in captivity may be continuously exposed to a variety of sound sources. Although there are relatively well-documented studies exploring anthropogenic sound effects on aquatic animals across taxa in the Global North Countries, this field of research is less developed in the Global South Countries. Moreover, policy makers have already set regulations for marine environments to safeguard a so-called good environmental status, but there are no agreements yet for freshwater habitats. This means freshwater crustaceans and fishes in a diversity of waterbody types are more or less exposed to man-made sound without any incentive to control impact and without any protection by law.
Sound exposure studies
To better understand how sound affects aquatic animals, I conducted several sound exposure studies on captive fish and crustaceans. In my experimental studies, I explored how anthropogenic sound affects captive fish (e.g., zebrafish and guppy) and crustaceans (red cherry shrimp). Figure 1 illustrates behavioral changes in red cherry shrimp when exposed to different sound levels, showing how they react to sound stress.
I examined various sound exposure treatments to provide insights that may be useful for future explorations for indoor and outdoor sound impact studies as well as for assessing animal welfare and productivity in captive situations. For example, I explored short-term behavioural parameters, which are indicators of sound-related stress, disturbance and deterrence. My findings may also raise awareness for sound levels in laboratories and the potential effect on reliability for fish as a model species for medical and pharmaceutical studies. As a follow-up step of my PhD research, I also explored the complexity of sound fields in indoor fish tanks by selecting a different set-up for each study, which makes behavioural analyses and direct comparisons not only relevant within each study, but also provides insight into the role of fish tank acoustics on ‘natural’ and experimental exposure conditions. Several behavioural states are likely to reflect considerable changes in underlying physiology, which would be interesting and feasible to investigate for more long-term consequences, but this was beyond the scope of the current step of my research lab priorities.
Development of bioacoustics in Iran and future directions
This research study is a pioneering effort in a relatively new field in Iran. This research is important because Iran has a broad range of coastlines with The Caspian Sea, The Persian Gulf and Oman Sea and there are quite diverse habitats and fragile ecosystems in these aquatic areas (See figure 2). However, yet there are large gaps in our knowledge of effects of anthropogenic sound on aquatic animals in Iran. Further studies are needed to assess anthropogenic sound impacts on aquatic animals and the potential cascading effects at the community level of the aquatic environment in Iran. This research, a series of experiments, lays the groundwork for future bioacoustics studies in Iran and other countries in the West Asia. I call, therefore, for more grounded laboratory-based and field based empirical research of global collaborations and high quality data collection towards open science in bioacoustics.
Figure 2. An overview of the geographical location of Iran’s aquatic habitats (yellow circles); The Caspian Sea in the north of Iran and The Persian Gulf and The Gulf of Oman/Oman Sea. Image courtesy of: https://www.google.com/maps
Acknowledgments
Finally, I am very grateful to my graduate M.Sc. students: Reza Mohsenpour, Sasan Azarm-Karnagh, Marziyeh Amini Fard for their excellent collaborations in behavioural studies and high quality data collection at the Fisheries Department, Faculty of Natural Resources, University of Guilan, Sowmeh Sara, Iran. I established and set up my research lab in 2016 and actively recruit enthusiastic undergraduate and graduate students by organizing workshops, seminars, mini research projects and relevant course material to develop this field of academic research in Iran. Hereby I would like to thank Hans Slabbekoorn my PhD supervisor at Leiden University who have helped and supported me to develop my underwater bioacoustics lab in my home country, Iran.
Selected references:
Azarm-Karnagh, S., López Greco, L., & Shafiei Sabet, S. (2024). Anthropogenic noise impacts on invertebrates: case of freshwater red cherry shrimp (Neocaridina davidi). In The Effects of Noise on Aquatic Life: Principles and Practical Considerations (pp. 1-12). Cham: Springer International Publishing.
Azarm-Karnagh, S., López Greco, L., & Shafiei Sabet, S. (2023). Annoying noise: effect of anthropogenic underwater noise on the movement and feeding performance in the red cherry shrimp, Neocaridina davidi. Frontiers in Ecology and Evolution, 11, 1091314.
Shafiei Sabet, S., Karnagh, S. A., & Azbari, F. Z. (2019). Experimental test of sound and light exposure on water flea swimming behaviour. In Proceedings of Meetings on Acoustics (Vol. 37, No. 1). AIP Publishing.
Radford, A. N., Kerridge, E., & Simpson, S. D. (2014). Acoustic communication in a noisy world: can fish compete with anthropogenic noise?. Behavioral Ecology, 25(5), 1022-1030.
Slabbekoorn, H., Bouton, N., van Opzeeland, I., Coers, A., ten Cate, C., & Popper, A. N. (2010). A noisy spring: the impact of globally rising underwater sound levels on fish. Trends in ecology & evolution, 25(7), 419-427.
Popper, A. N., & Hastings, M. C. (2009). The effects of anthropogenic sources of sound on fishes. Journal of fish biology, 75(3), 455-489.
–The research described in this Acoustics Lay Language Paper may not have yet been peer reviewed–
In a noisy world, capturing clear audio from specific directions can be a game-changer. Imagine a system that can zero in on a target sound, even amid background noise. This is the goal of Target Directional Sound Extraction (TDSE), a process designed to isolate sounds from a particular direction, while filtering out unwanted noise.
Our team has developed an innovative TDSE system that combines Digital Signal Processing (DSP) and deep learning. Traditional sound extraction relies on signal processing, but it struggles when multiple sounds come from various directions or when using fewer microphones. Deep learning can help, but it sometimes results in distorted audio. By integrating DSP-based spatial filtering with a deep neural network (DNN), our system extracts clear target audio with minimal interference, even with limited microphones.
The system relies on spatial filtering techniques like beamforming and blocking. Beamforming serves as a signal estimator, enhancing sounds from the target direction, while blocking acts as a noise estimator, suppressing sounds from the target direction and leaving other unwanted noises intact. Using a deep learning model, our system processes spatial features and sound embeddings (unique characteristics of the target sound), yielding clear, isolated audio. In our tests, this method improved sound quality by 3-9 dB and performed well with different microphone setups, even those not used during training.
TDSE could transform various industries, from virtual meetings to entertainment, by enhancing audio clarity in real time. Our system’s design offers flexibility, making it adaptable for real-world applications where clear directional audio is crucial.
This approach is an exciting step toward more robust, adaptive audio processing systems, allowing users to capture target sounds even in challenging environments.
Figure 1. A sound wave enters a duct where the walls are stiffer at the entrance and softer at the base. As the wave moves through the duct, it slows down due to the changing properties of the walls.
Figure 2. An illustration of a sound wave vanishing in an acoustic black hole structure. The ABH effect is seen from the wavefronts becoming closer together (slower sound speed) and lower in amplitude (lower peaks, higher troughs) at the right end.
Figure 1: Black-smoker hydrothermal vent chimney at the Main Endeavour Hydrothermal Vent Field (Image courtesy of Ocean Networks Canada)
Figure 2: Spectrogram of ~4.1 magnitude earthquake at MEF
Figure 3: Acoustic spectra before, during, and after the earthquake at MEF
Figure 4: Measured and modeled acoustic vertical coherence at MEF
Figure 1. Behavioral changes of the freshwater red cherry shrimp in response to an underwater speaker. Behavioral responsiveness of shrimp when exposed to acoustic stimuli was categorized as movement activity impacts and feeding activity impacts (Image courtesy of: Azarm-Karnagh et al., 2023; © 2024 Springer Nature).
Figure 2. An overview of the geographical location of Iran’s aquatic habitats (yellow circles); The Caspian Sea in the north of Iran and The Persian Gulf and The Gulf of Oman/Oman Sea. Image courtesy of: 
