Physicists Discover a Remarkable New Type of Sound Wave

Sound Vortex

Sound vortex generation enabled by the spin-orbit interaction in real space. Credit: Wang, S., Zhang, G., Wang, X. et al. / DOI number: 10.1038/s41467-021-26375-9

Can you imagine sound travels in the same way as light does? A research team at City University of Hong Kong (CityU) discovered a new type of sound wave: the airborne sound wave vibrates transversely and carries both spin and orbital angular momentum like light does. The findings shattered scientists’ previous beliefs about the sound wave, opening an avenue to the development of novel applications in acoustic communications, acoustic sensing, and imaging.

The research was initiated and co-led by Dr. Wang Shubo, Assistant Professor in the Department of Physics at CityU, and conducted in collaboration with scientists from Hong Kong Baptist University (HKBU) and the Hong Kong University of Science and Technology (HKUST). It was published in Nature Communications, titled “Spin-orbit interactions of transverse sound.”

Beyond the conventional understanding of sound wave

The physics textbooks tell us there are two kinds of waves. In transverse waves like light, the vibrations are perpendicular to the direction of wave propagation. In longitudinal waves like sound, the vibrations are parallel to the direction of wave propagation. But the latest discovery by scientists from CityU changes this understanding of sound waves.

Meta-Atom and Transverse Sound

Illustration of the “meta-atom” and transverse sound. Credit: Wang, S., Zhang, G., Wang, X. et al. / DOI number: 10.1038/s41467-021-26375-9

“If you speak to a physicist about airborne transverse sound, s/he would think you are a layman without training in university physics because textbooks say that airborne sound (i.e., sound propagating in the air) is a longitudinal wave,” said Dr. Wang. “While the airborne sound is a longitudinal wave in usual cases, we demonstrated for the first time that it can be a transverse wave under certain conditions. And we investigated its spin-orbit interactions (an important property only exists in transverse waves), i.e. the coupling between two types of angular momentum. The finding provides new degrees of freedom for sound manipulations.”

The absence of shear force in the air, or fluids, is the reason why sound is a longitudinal wave, Dr. Wang explained. He had been exploring if it is possible to realize transverse sound, which requires shear force. Then he conceived the idea that synthetic shear force may arise if the air is discretized into “meta-atoms,” i.e. volumetric air confined in small resonators with size much smaller than the wavelength. The collective motion of these air “meta-atoms” can give rise to a transverse sound on the macroscopic scale.

Conception and realization of “micropolar metamaterial”

He ingeniously designed a type of artificial material called “micropolar metamaterial” to implement this idea, which appears like a complex network of resonators. Air is confined inside these mutually connected resonators, forming the “meta-atoms”. The metamaterial is hard enough so that only the air inside can vibrate and support sound propagation. The theoretical calculations showed that the collective motion of these air “meta-atoms” indeed produces the shear force, which gives rise to the transverse sound with spin-orbit interactions inside this metamaterial. This theory was verified by experiments conducted by Dr. Ma Guancong’s group in HKBU.

Negative Refraction

Negative refraction induced by the spin-orbit interaction in momentum space. Credit: Wang, S., Zhang, G., Wang, X. et al. / DOI number: 10.1038/s41467-021-26375-9

Moreover, the research team discovered that air behaves like an elastic material inside the micropolar metamaterial and thus supports transverse sound with both spin and orbital angular momentum. Using this metamaterial, they demonstrated two types of spin-orbit interactions of sound for the first time. One is the momentum-space spin-orbit interaction which gives rise to negative refraction of the transverse sound, meaning that sound bends in the opposite directions when passing through an interface. Another one is the real-space spin-orbit interaction which generates sound vortices under the excitation of the transverse sound.

The findings demonstrated that airborne sound, or sound in fluids, can be a transverse wave and carry full vector properties such as spin angular momentum the same as light does. It provides new perspectives and functionalities for sound manipulations beyond the conventional scalar degree of freedom.

Wang Shubo Team

Dr Wang Shubo from City University of Hong Kong (first from right) and his research team. Ms Tong Qing (second from left) is a co-author of the paper. Credit: City University of Hong Kong

“This is just a precursor. We anticipate more explorations of the intriguing properties of the transverse sound,” Dr. Wang said. “In future, by manipulating these extra vector properties, scientists may be able to encode more data into the transverse sound to break the bottleneck of traditional acoustic communication by normal sound waves.”

The interaction of spin with orbital angular momentum enables unprecedented sound manipulations via its angular momentum. “The discovery may open an avenue to the development of novel applications in acoustic communications, acoustic sensing, and imaging,” he added.

Reference: “Spin-orbit interactions of transverse sound” by Shubo Wang, Guanqing Zhang, Xulong Wang, Qing Tong, Jensen Li and Guancong Ma, 21 October 2021, Nature Communications.
DOI: 10.1038/s41467-021-26375-9

Dr. Wang is the first author and the corresponding author of the paper. Dr. Ma is another corresponding author. Collaborators include Professor Li Jensen from The Hong Kong University of Science and Technology, Ms. Tong Qing, a PhD student from CityU, and other researchers from HKBU.

The work was supported by the Research Grants Council in Hong Kong and the National Natural Science Foundation of China.

24 Comments on "Physicists Discover a Remarkable New Type of Sound Wave"

  1. BibhutibhusanPatel | December 10, 2021 at 10:12 pm | Reply

    This is a fine demonstration that how in some sort nature cañ generate coversely sound and work with this,even in the human brain.

  2. Alexander Garcia | December 11, 2021 at 10:56 am | Reply

    Soon they will discover sound travels faster than light. Our thoughts are sound waves and seemingly travel faster than light.

    • No…they will not because they know and have measured to a remarkable accuracy both the speed of sound (at various altitudes because since sound propagates thru air it depends on that make it dependant on the atmospheric pressure) and the speed of light (by bouncing it off a reflector they left on the moon during the Apollo moon landings.

      For the life of me i can’t understand comments like yours. Its very basic science to know both the speed of sound and light as introductory physics teaches us these VERY IMPORTANT VALUES.

      • It’s always the condescending people who claim to know everything that know nothing. You’re clearly too wrapped up in ego to understand the implications.

    • I guess that’s why you (alone in the universe) hear thunder long before the associated flash of a lightning strike. Hmmm?

  3. Future Nobel prize

  4. Please let someone use this research to reexamine whale song recordings. We know some whale song can be heard and understood by another whale halfway around the planet.
    Imagine if there was another layer of communication data in the songs that we have been missing all along.

  5. I usually run 8 – 12,000 watts of radio equipment in my whip. Runs lower hz. Below 20 hz can be heard. Tho what’s being said here is much more – I usually can knock chit off walls without directing / focusing any certain pattern. As one pattern can sync – multiple amplified is always better.

  6. Louisa…shut the blank up you POS.

  7. “The findings demonstrated that airborne sound, or sound in fluids, can be a transverse wave and carry full vector properties such as spin angular momentum the same as light does”. This is a phenomena established by this work and demonstrates what is sometimes experienced but was difficult to explain.
    A new property of sound finds place in physics and shall provide many avenues.

  8. Themaninthemoon | December 11, 2021 at 11:19 pm | Reply

    The thought theory that sound can/could be manipulated into bring at a super subsonic level to dispel light by gravitational force, is not new, but transcending the layers into which sound, can be directionally used to outspeed a beam of light, or perhaps using quantitative beams of light to break what we call normal sound, into its various layers will be the keys to cracking the hardness of a walnut sized shell, to get to the meat of it inside, … we do know that gravity, can bend light, but we have not been able to do so, … yet have observed that gravitational power of black holes to do so, … so if we can observe it, can it be done on a level of physics which could be grasped much as a hand holding a hammer to drive a nail into a block of wood? I asked an old schoolmate of mine who I sat behind in typing class, (as I was a freshman, & he was a senior, in high school), … a question after he said he was a professor at a prestigious college, out west, … I said that if light travels the purported 185,000 mps, then would it not be possible to place a satellite in geo orbit around the planet that could capture sunlight 24/7/365, & take the power captured via the photocells, & beam that xvy amount of electrical signal to areas of the planet that needed electrical power to power pumps for irrigation, or any other type of electrical energy usages? He told me no, … I believe he is incorrect, … if I could place a small portable power station, anywhere, & get signal from a geosynchronous satellite, then I should also be able to harness said power from the light strength of the sun, … and be able to irrigate any place on earth, by directing water pumped from any location on the planet to any other place on the planet, … it is not like I would be stealing anything from someone else, as all sentient beings have access to the power of the sun, … or to create enough power generated by the sun, or to illuminate as necessary for my needs, and to provide the energy necessary for my needs, …

  9. It’s information is true but three years ago a college student also think about this sound wave but he didn’t publish there research paper because he want to exactly result in his hypothesis.

  10. Babu G. Ranganathan | December 12, 2021 at 6:26 am | Reply

    Babu G. Ranganathan*
    (B.A. Bible/Biology)

    JUST BECAUSE SCIENCE CAN EXPLAIN how an airplane works doesn’t mean that no one designed or made the airplane. And just because science can explain how life or the universe works doesn’t mean there was no Designer and Maker behind them.

    Natural laws may explain how the order in the universe works and operates, but mere undirected natural laws cannot explain the origin of that order. Once you have a complete and living cell then the genetic code and biological machinery exist to direct the formation of more cells from raw materials such as amino acids and other chemicals, but how could life or the cell have naturally originated when no directing code and mechanisms existed in nature? Read my Internet article: HOW FORENSIC SCIENCE REFUTES ATHEISM.

    WHAT IS SCIENCE? Science simply is knowledge based on observation. No human observed the universe coming by chance or by design, by creation or by evolution. These are positions of faith. The issue is which faith the scientific evidence best supports.

    SCIENCE SHOWS THAT THE UNIVERSE CANNOT BE ETERNAL because it could not have sustained itself eternally due to the law of entropy (increasing and irreversible net energy decay, even in an open system). Even a hypothetical oscillating universe could not continue to oscillate eternally! Einstein’s General Theory of Relativity shows that space, matter, and time all are physical and all had a beginning. Space even produces particles because it’s actually something, not nothing. What about the Higgs boson (the so-called “God Particle”)? The Higgs boson, even if it existed, would not have created mass from nothing, but rather it would have converted energy into mass. Einstein showed that all matter is some form of energy. Even time had a beginning! Time is not eternal.

    The law of entropy doesn’t allow the universe to be eternal. If the universe were eternal, everything, including time (which modern science has shown is as physical as mass and space), would have become totally entropied by now and the entire universe would have ended in a uniform heat death a long, long time ago. The fact that this hasn’t happened already is powerful evidence for a beginning to the universe.

    Popular atheistic scientist Stephen Hawking admits that the universe had a beginning and came from nothing but he believes that nothing became something by a natural process yet to be discovered. That’s not rational thinking at all, and it also would be making the effect greater than its cause to say that nothing created something. The beginning had to be of supernatural origin because science teaches us from the First Law of Thermodynamics that natural laws and processes do not have the ability to bring something into existence from nothing.

    The supernatural origin of the universe cannot be proved by science but science points to a supernatural intelligence and power for the origin and order of the universe. Where did God come from? Obviously, unlike the universe, God’s nature doesn’t require a beginning.

    The disorder in the universe can be explained because of chance and random processes, but the order can be explained only because of intelligence and design.

    Gravity may explain how the order found in the precise and orderly courses of thousands of billions of stars is maintained, but gravity cannot explain the origin of that order.

    Some evolutionary astronomers believe that trillions of stars crashed into each other leaving surviving stars to find precise orderly orbits in space. Not only is this irrational, but if there was such a mass collision of stars then there would be a super mass residue of gas clouds in space to support this hypothesis. The present level of residue of gas clouds in space doesn’t support the magnitude of star deaths required for such a hypothesis. And, as already stated, the origin of stars cannot be explained by the Big Bang because of the reasons mentioned above. It’s one thing to say that stars may decay and die into random gas clouds, but it is totally different to say that gas clouds form into stars.

    Even the father of Chaos theory admitted that the “mechanisms” existing in the non-living world allow for only very rudimentary levels of order to arise spontaneously (by chance), but not the kind or level of order we find in the structures of DNA, RNA, and proteins. Yes, individual amino acids have been shown to come into existence by chance but not protein molecules which require that the various amino acids be in a precise sequence just like the letters found in a sentence.

    Some things don’t need experiment or scientific proof. In law there is a dictum called prima facie evidence. It means “evidence that speaks for itself.”

    An example of a true prima facie would be if you discovered an elaborate sand castle on the beach. You don’t have to experiment to know that it came by design and not by the chance forces of wind and water.

    If you discovered a romantic letter or message written in the sand, you don’t have to experiment to know that it was by design and not because a stick randomly carried by wind put it there. You naturally assume that an intelligent and rational being was responsible.

    It’s interesting that Carl Sagan would have acknowledged sequential radio signals in space as evidence of intelligent life sending them, but he wouldn’t acknowledge the sequential structure of molecules in DNA (the genetic code) as evidence of an intelligent Cause. Read my popular Internet article, HOW DID MY DNA MAKE ME.

    I encourage all to read my popular Internet articles:

    NATURAL LIMITS TO EVOLUTION
    HOW FORENSIC SCIENCE REFUTES ATHEISM

    Visit my latest Internet site: THE SCIENCE SUPPORTING CREATION (This site answers many arguments, both old and new, that have been used by evolutionists to support their theory)

    Author of popular Internet article, TRADITIONAL DOCTRINE OF HELL EVOLVED FROM GREEK ROOTS

    *I have given successful lectures (with question and answer period afterwards) defending creation before evolutionist science faculty and students at various colleges and universities. I’ve been privileged to be recognized in the 24th edition of Marquis “Who’s Who in The East” for my writings on religion and science.

  11. It is obvious that God’s nature does not require a beginning? Do you hear yourself right now? There is no tangible evidence that there is the existence of the supernatural.

  12. Looks like I’ll have to buy the White album again.

  13. While this is a great discovery, it’s unsurprising that sound waves formation is similar from light wave propagation, given the common wave structure’s that govern the known universe.

  14. Experimenting with a variety of audio equipment and what little knowledge I had of geometry, I discovered that I could create something like an auditory hallucination. Sounds seemed to be coming not from the audio equipment, but birthed straight out of the air giving my brain details like position and direction of something I could not visually see. I’m not a scientist nor am I even educated. I think I discovered something then that is still not yet talked about. This article may have nothing to do with what I experienced, but it sounds to me like there may be at least something here relative to my generated “auditory hallucination” experience. Sound that has position direction and force but is born straight out of the air. Like it was a product of geometry and harmony maybe. Idk. Perhaps I am just an uneducated mad tinkerer.

  15. Its interesting and it will be more interesting in future…

  16. Submarines, that’s going to be the first use by the CCP

  17. I could not work out from the article if these sounds can be heard by human ears or if they are silent to us.

  18. Rebecca Sinnamon | December 17, 2021 at 3:52 pm | Reply

    Is this why I sometimes have a high frequency interfere with my energy that it makes my ears ring… sometimes takes me a minute to get myself back to normal and if I try to talk before that I slur my words and what not… like a stroke but it’s after my ears ring .. sometimes it’s loud sometimes not .. and I believe some of us humans energies aren’t able to be contained fully inside our bodies.. so it has an outer circle around us and those people feel the extra waves or frequencies or whatever you want to call them that others wouldn’t as there’s is contained within. The new waves aren’t just passing across the others or flowing with them. They are actually cutting them out as they pass through . I don’t fully understand all of this. But I know this is how it is. Because it’s happening to me and I take notice of what and search for reason.. whatever the new wave is.. can’t be healthy for the human mind .. or it wouldn’t ‘short it out ‘ I guess is a way to explain it

  19. Rebecca Sinnamon. Yes, I know exactly what you mean. You seem to be hit by a push on energy, or walk through a beam of it focussed on a doorway or a sidewalk. After that the rough static sound ( very quiet – but if it persists for a long time it begins to seem very loud, and if too long it hurts your ears) begins. Something sharp and unnatural. The effect of the “push” is that you feel stupid for a period of time and then gradually return to “full thinking” mode. I’ve heard a few people mention this lately. I wonder what it is. Next time, take off at a quick sprint. You’ll notice you can leave the static behind you for a few seconds. Hide from it if your clever.

  20. I’m sorry, but this seems like a contrived/dubious result to me. “Meta-atoms” are a solid and sticking them all together into a matrix is an extended solid with “resonance” i.e. they too are vibrating. Perhaps I didn’t understand fully, but to me this isn’t a new type of sound wave as much as a new type of resonator that converts longitudinal wave energy into transverse energy.

  21. Daniel Nowak Janssen | January 14, 2022 at 1:08 pm | Reply

    So theoretically could it be possible to transfer electrons in those bubbles?

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