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How topological acoustics can help us better understand a warming climate

By Mark Brodie
Published: Wednesday, February 28, 2024 - 11:53am
Updated: Wednesday, February 28, 2024 - 11:57am

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The University of Arizona last year received a $30 million grant from the National Science Foundation. It’ll use the money to create a new center called New Frontiers of Sound.

The project will bring together scientists from eight other schools around the country, including Cal Tech, UCLA and Georgia Tech, in the area of topological acoustics.

Pierre Deymier is a professor in the Department of Material Science and Engineering at the University of Arizona and director of New Frontiers of Sound. The Show talked with him about what topological acoustics entails.

Headshot of Pierre Deymier
Mark Koenig/University of Arizona
Pierre Deymier

Interview highlights

PIERRE DEYMEIR: So it's a very difficult concept to grasp. But the first thing before we talk about topological acoustics, we need to define what is the geometry of sound. And once we define the geometry of sound, then I can introduce the notion of topological acoustic, if it's OK with you.

So, so basically the geometry of sound is looking at an attribute of soundwaves — which is in space and not in time. We're familiar with sound as being related to frequency. We hear high pitch sound, high frequency sound. We can talk about low tone sound, which are low frequency.

So that is in the time domain. But what we're talking about here in terms of the geometry of sound is in the spatial domain. So you can imagine a room, let's say, with all kinds of stuff in that room. We have a speaker phone. And what it's doing is it  has a given frequency, and then it's generating some soundwaves. And at some point, we're familiar with the notion of saying then the sound is filling the room. So basically, there is a now a landscape of sound in that room. We call it also the soundscape. And when we talk about the geometry of sound, I talk about the geometrical attribute of sound or the landscape of sound inside the room in terms of the intensity of the sound inside that room.

Of course, this intensity of this map depends on the the configuration of the room and what's in the room itself, as well as the frequency and the loudspeaker that is used for generating the sound.

And am I right to assume that if you have this room, and you have sound that is filling that room, if you add something to it or take something away — let's say you put a sofa in that room or take, take it away — that alters that soundscape, because there's one more or one less thing for that sound to bounce off of?

DEYMEIR: Yes, of course. It's going to change that landscape. And eventually in our center, we're going to use these soundscapes as a way of monitoring changes in the room or, effectively, we're more interested in changes in the environment as we monitor those changes through acoustic waves.

How do you go about trying to monitor that?

DEYMEIR: So, so this, this part of the project is, is as follows: If I tweak the frequency. So let's say I change the frequency of the source of sound. There may be the possibility of what we call flipping the soundscape. Which means, you know, you may have that sense. Also you have in the room, you think about the soundscape, you have part of the room which may be more quiet than another part of the room. There may be a part which is loud, a part which is more quiet. So basically that describes the landscape or the soundscape of that room.

It's ... like a topography of ... a mountainous area where you have mountains and you have valleys. Now, when we turn and change the frequency of that sound, there may be a flipping of the soundscapes. Regions where which were loud may become regions which are quiet and regions which are quiet may become loud. So we can use this change as a way of monitoring change in the environment. And if there is a change in the environment — let's say someone moves the sofa by a little bit — and then you can detect a very large change in your soundscape for a very small change in the environment.

Laser Ultrasonic Testing Equipment
Mark Koenig/University of Arizona
Laser ultrasonic testing equipment.

This kind of research has great use in technology and in computing fields. Can you explain what the relationship is between, what it is that you're studying and how it, how it might be used in computing or tech?

DEYMEIR: So, so if we continue talking about this sensing, we're going to, the center, the New Frontiers of Sound Center, is going to use this notion of topological acoustic sensing to detect changes in the permafrost, effectively the throwing of permafrost in Alaska or in the Arctic regions. We know that frost is, is a frozen part of the ground in Arctic regions. And what happens if the climate is warming, then this ground, is or the permafrost is thawing, and that is changing the ground, and then you have a dramatic effect on infrastructure like roads or buildings.

So what we're going to use is not soundwave but seismic wave — which are effectively soundwave but of very low frequency — as a way of monitoring changes in the ground because the seismic wave leave in the ground when the permafrost is thawing. So we can use this sensing technology as a way of warning people that there are changes taking place and that may impact infrastructure.

So that's one of the potential applications. The other potential application is in computing, you mentioned computing. So we can explore ways of using topological acoustic waves as a means of developing approaches to do quantum like computing. You've heard about quantum computing, we can use this analogy to use acoustic wave to do similar computations.

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