Skip to main content

Researchers make sound waves travel in one direction only, with implications for electromagnetic wave technology!


 


Researchers at ETH Zurich have managed to make sound waves travel only in one direction. In the future, this method could also be used in technical applications with electromagnetic waves.



Water, light and sound waves usually propagate in the same way forward as in a backward direction. As a consequence, when we are speaking to someone standing some distance away from us, that person can hear us as well as we can hear them. This is useful when having a conversation, but in some technical applications one would prefer the waves to be able to travel only in one direction—for instance, in order to avoid unwanted reflections of light or microwaves.


Ten years ago, researchers succeeded in suppressing sound wave propagation in the backward direction; however, this also attenuated the waves traveling forwards.


A team of researchers at ETH Zurich led by Nicolas Noiray, professor for Combustion, Acoustics and Flow Physics, in collaboration with Romain Fleury at EPFL, has now developed a method for preventing sound waves from traveling backward without deteriorating their propagation in the forward direction.


In the future, this method, which has recently been published in Nature Communications, could also be applied to electromagnetic waves.


The basis of this one-way street for sound waves are self-oscillations, in which a dynamical system periodically repeats its behavior. "I've actually spent a good part of my career preventing such phenomena," says Noiray.


Among other things, he studies how self-sustaining thermo-acoustic oscillations can arise from the interplay between sound waves and flames in the combustion chamber of an aircraft engine, which can lead to dangerous vibrations. In the worst case, these vibrations can destroy the engine.



Harmless and useful self-oscillations

Noiray had the idea to use harmless self-sustaining aero-acoustic oscillations in order to allow sound waves to pass only in one direction and without any losses through a so-called circulator. In his scheme, the unavoidable attenuation of the sound waves is compensated by the self-oscillations in the circulator synchronizing with the incoming waves, which allows them to gain energy from those oscillations.


The circulator itself was supposed to consist of a disk-shaped cavity through which swirling air is blown from one side through an opening in its center. For a specific combination of blowing speed and intensity of the swirl, a whistling sound is thus created in the cavity.


"In contrast to ordinary whistles, in which sound is created by a standing wave in the cavity, in this new whistle it results from a spinning wave," explains Tiemo Pedergnana, a former doctoral student in Noiray's group and lead author of the study.


From the idea to the experiment, it took a while. First, Noiray and his co-workers investigated the fluid mechanics of the spinning wave whistle, and then added three acoustic waveguides to it, which are arranged in a triangular shape along the edge of the circulator.


Sound waves that are fed in through the first waveguide can leave the circulator through the second waveguide. However, a wave entering through the second waveguide cannot exit "backwards" through the first waveguide, but can do so through the third waveguide.


Over several years, the ETH researchers developed and theoretically modeled the various parts of the circulator; now, finally, they could experimentally demonstrate that their loss-compensation approach works. They sent a sound wave with a frequency of around 800 Hertz (roughly the high g of a soprano) through the first waveguide and measured how well it was transmitted to the second and third waveguides.


As expected, the sound wave didn't make it to the third waveguide. From the second waveguide (in the "forward" direction), however, a sound wave emerged that was even stronger than the one originally sent in.


"This concept of loss-compensated non-reciprocal wave propagation is, in our view, an important result that can also be transferred to other systems," says Noiray. He sees his sound wave circulator mainly as a powerful toy model for the general approach of wave manipulation using synchronized self-oscillations that can, for instance, be applied to metamaterials for electromagnetic waves.


In this way, microwaves in radar systems could be guided better, and so-called topological circuits could be realized, with which signals can be routed in future communications systems.

#OliverMorsch , #ETHZurich #PhysicsGeneral

#PhysicsSoftMatter

Comments

Popular posts from this blog

How to Conduct Audience Research For SEO:A Simplified Guide!

To excel in SEO, understanding what your audience searches for and why is crucial. Audience research unveils the intent behind search queries, helping you align strategies with user needs. This approach can uncover search behaviors, map audience intent, and identify SEO opportunities, even with limited resources. Traditional Audience Research: Methods and Challenges Traditional audience research focuses on demographic, psychographic, and behavioral insights to build audience personas. It often involves: Surveys: To gather customer feedback. Focus Groups and Interviews: To understand audience preferences and behaviors. However, as advertising pioneer David Ogilvy noted, traditional research can be flawed because people often don’t act as they say. Tools like Similarweb, Audiense, and Brandwatch can assist in audience segmentation but may not fully capture search behavior or intent. A Better Approach: Audience Research for SEO SEO-focused audience research analyzes search behavior to unc...

How Often Should You Blog? A Guide to Ideal Posting Frequency

Blogging consistently is key to keeping your audience engaged and growing your reach. However, just having a blog isn’t enough. To attract traffic, establish your brand, or generate leads, you need a steady flow of fresh, valuable content. But how often should you post to get results? Here’s the answer: there’s no universal number of posts per week that’s perfect for every blog. Finding your ideal blogging frequency depends on your niche, audience size, content quality, and your goals. Here’s how to determine what’s right for you. --- Key Factors for Deciding Blog Frequency 1. Goals and Audience Define your primary goal: brand awareness, thought leadership, or sales? Different goals may require different paces. Understand your audience’s preferences. A tech guide blog may thrive with in-depth, less frequent posts, while a news blog benefits from regular updates. 2. Blog Age and Maturity Newer blogs need frequent, high-quality posts to establish a presence. As the blog matures and gains...

The Man Who Invented The "Psychopath"?

The Man Who Invented the “Psychopath”? Hervey Cleckley, an influential psychiatrist, is often credited with shaping modern understandings of psychopathy, even though his original intent was to help rather than stigmatize those affected. His 1941 work, The Mask of Sanity, was pivotal, as it introduced the concept of the psychopath as a specific personality type with 16 distinct traits. Cleckley described individuals who seemed outwardly rational but exhibited shallow emotions, lacked empathy, and engaged in destructive behaviors, though often without malice. Cleckley’s perspective was initially sympathetic; he saw these individuals as “forgotten” by psychiatry—people who needed understanding and treatment. However, as psychopathy entered the public lexicon, the term was quickly associated with malice, violence, and even inhumanity. Cleckley’s nuanced portrait of the psychopath was adapted by later researchers like Robert Hare, who created the widely used Psychopathy Checklist, a t...