Richard Baraniuk: Squid skin inspires camouflage
Richard Baraniuk believes the animal kingdom has a lot to teach, not just to scientists who are looking to understand, but also to engineers who are looking to create. Baraniuk, a professor of electrical and computer engineering at Rice University, is helping to develop new materials for defense purposes – inspired by the skin of sea creatures, such as squid, that can camouflage themselves underwater. This interview is part of a special EarthSky series, Biomimicry: Nature of Innovation, produced in partnership with Fast Company and sponsored by Dow.
Tell us about the project called “squid skin”
First, we want to understand how squid and other cephalopods do such a remarkable job of camouflaging themselves against the background of a sea environment. They’re able to blend in perfectly with the background and almost disappear. We’re trying to understand the basic science of how they’re capable of it and what the mechanisms are.
We want to understand it both from the sensing side of things – how they perceive the light environment around them – and from an actuation side of things. In other words, how they actually control organs inside their skin in order to reflect and absorb light of all different wavelengths. And then we want to understand it from a neural perspective, how they have a control system that enables the sensing to drive this actuation so that they can blend into the background.
From this basic science understanding, we’re then trying to engineer a synthetic squid skin that will replace the eyes with cameras and other kinds of light sensors, replace the skin with a metamaterial – modern materials that have very powerful light reflecting and absorbing capabilities based on nanotechnology that can also reflect and absorb light at all kinds of wavelengths – and finally, create sophisticated computer algorithms that can tune the skin so that the skin will be able to, just like the squid, camouflage itself and blend perfectly into the background.
Make the connection for us of what scientists are attempting to learn and apply from sea creatures that camouflage.
There are really three basic scientific goals. On the sensing side, we want to understand how squid and other cephalopods can sense this extremely complex light field that surrounds them in a sea environment. Anytime you dive under the sea and look around, you see – it’s extremely complicated. There are reflections off of the surface, reflections off the bottom, and light coming from all directions. In order to camouflage itself, a squid has to be able to sense all of its light field.
We’re just starting to scratch the surface of understanding of the sensing systems. We know that squid and other cephalopods have very high-acuity eyes, and they’re able to see a lot about their environment in a way analogous to how humans see. But they have even more. They can sense the polarization of light, which is extremely useful for understanding light that’s been reflected off different objects, light that is upwelling from further down in the sea. They’re capable of seeing better in that respect than humans.
The other element that’s extremely exciting from both a scientific and engineering side of view is that our collaborator, Roger Hanlon of Woods Hole Oceanographic Institution, has discovered that a large class of cephalopods actually have light sensors distributed throughout their skin. So you can actually think of the entire body of a squid being like a gigantic camera that can sense light from all kinds of different directions, above the squid, below the squid, and at all sides. And so we believe from the sensing side of things, it’s really the combination of the eyes and these distributed light sensors that are providing the ability to blend into the background.
The second basic research question is about the actuation mechanism. How can squid and other cephalopods actually change their color, change their reflectivity, their luminosity? This is the part of the project that’s the most well-understood. Scientists over the past few decades have been able to find that cephalopods have organs inside their skin called chromatophores, iridophores, and leucophores. These three organs are able to absorb light and reflect light at different frequencies, so change color. The chromatophores are able to absorb light at a lot of different frequencies, for example, so they can change color. The iridophores are able to reflect light at different frequencies. And the leucophores are able to diffuse light. And so with this arsenal of these three different elements, they can make an incredible different array of patterns to match the background of their sea environment.
The third really interesting basic science question is around the nervous system aspect. How does the squid or other cephalopod integrate all this information from these distributed light sensors, from their eyes, process that information, and then control the actuators – the chromatophores, iridophores, and leucophores – so that they blend in, not just with the color of that background but with the very subtle light variations that you get underwater?
We understand these materials could be used to camouflage vessels used in defense – like submarines. Tell us about that.
Once you understand the basic principles and architecture that a squid uses to camouflage itself, we can imagine engineering a synthetic skin that replaces, for example, the light sensors in the skin and the eyes of the squid with cameras, with distributed light sensing systems. We can replace the skin with some kind of metamaterials, technology that can reflect and refract and diffuse light of different wavelengths. And we can replace the central nervous system with a computer that is able to analyze background textures and control these actuators.
If we can do this, we can imagine building underwater vehicles, for example, that are covered with this metamaterial skin that operate in very much the same fashion that a squid would in order to camouflage itself. They can become virtually invisible under the sea.
You could take this further, take it out of the water. We should be able to cover vehicles in a similar kind of metamaterials squid skin, and be able to make vehicles disappear, so that people wouldn’t be able to see a car or a truck sitting in a field, for example. Moving even beyond that, beyond usual light frequencies, into things like radio frequencies or acoustic frequencies, you could imagine building vehicles on the ground or even airplanes that are virtually invisible to radar. So you could imagine an entire new array of stealth-type vehicles that are invisible to prying eyes.
We understand that this work could also aid in the imaging capacity of underwater vessels. Tell us about that.
Cephalopods not only have a centralized sensing system for light – an eye that you could imagine replacing with a digital camera – but also have light sensors distributed throughout their body. So in some sense their entire body is like a giant camera of distributed light sensors. We’re just starting to understand that we can use this distributed light sensing concept to enable radically new ways to image, to be able to see underwater, not only at visible wavelengths, like light, but also potentially using acoustic wavelengths to be able to use sonar-like probing systems. Imagine vehicles that are not only able to blend into their background, but are also better able to understand their background, other targets within the background, fish swimming around, other submarines, things like that.
What are some other ways this project will impact the world outside of the lab?
There’s tremendous opportunity for application of some of these new engineered solutions. The first, on the metamaterials side, the actual “skin” side – metamaterials are extremely promising for building new kinds of display technologies. Imagine very low-cost flexible displays that can be used for computers, for other kinds of reading-type displays. Imagine very large panels – an entire wall of your house that is a gigantic TV screen.
On the light-sensing side of things, there’s this idea that squid use distributed light-sensing to understand their environment. We can apply those kind of ideas eventually to build massive distributed camera systems. Imagine wallpaper that you put up in your house that covers an entire wall that is able to perform 3D reconstruction of everything inside the room and everything moving around the room, which would be tremendously useful in the future for virtual reality kind of systems, for security applications, for surveillance-kind of applications.
On the nervous system side, the better that we understand how cephalopods and squid actually integrate, fuse the information from the sensors and use it to control the actuators, this is enabling us to design radically new kinds of texture and seeing synthesis techniques, which could enable new kinds of computer graphics and computer-generated movies and games technologies, and also texture analysis – techniques, for example, for recognizing people in scenes or vehicles in scenes. All of these ideas are coming out of the better understanding of how cephalopods sense and then blend themselves into the background.
Can we go back to the “squid skin” itself for a minute? How does it compare to real squid skin? Break how this works down for us.
The engineered squid skin that we’re creating is directly inspired from of our basic science understanding of how a cephalopod senses light, integrates it, and blends itself into the background.
In our engineered skin, we have digital cameras to replace the eyes. We have light-sensitive diodes embedded in the skin that are able to sense light coming from all directions around the skin. Then we have the actual skin itself, that can change colors. And there, we are taking the light actuation organs of the cephalopod, the chromatophores, the iridophores, the leucophores, and we’re engineering what are called metamaterials to mimic their properties. Metamaterials are modern materials that have a very powerful light reflecting and absorbing capabilities. These are made, for example, nano-sized glass balls, and covering them with very fine, thin sheets of gold or other kinds of matter so that we can selectively absorb or reflect light of different frequencies.
The third element of the skin is mimicking the central nervous system of the cephalopod. And here, we’re employing sophisticated computer algorithms to take the information coming in from the distributed light sensors and the cameras, to understand the background texture of the objects that we’re trying to blend into, and then to generate electrical control signals that are then used to control the metamaterials so that they absorb and reflect light at just the right frequencies so that the skin blends in with its background.
What are your thoughts on biomimicry – learning how nature does things and applying that knowledge to human problems?
I believe the animal kingdom has a lot to teach, not just scientists who are looking to understand, but also engineers who are looking to create.
The thing that amazes me about the biomimicry field in general is that the more that we understand about how animals work and process information, for example, the more we learn that they actually have, over time – thanks to evolution – adopted optimal or near optimal solutions, the best possible way to solve a problem.
A great example from some earlier work that I’ve done in my career is bats, who fly around in the dark hunting moths. And they actually use sonar. They use echolocation. The thing that is astounding is that the bat actually uses a mathematically optimal waveform that it shouts out in order to find both the location of moths and how fast they’re flying so that they can catch the most in a night.
I think that in engineering, we have just begun to create systems that are approaching the complexity of biological systems. If you look at, for example, the world’s most complicated systems, things like the space shuttle with millions of parts, once we move into the animal kingdom, we’re talking about systems with billions, trillions of parts. In order to make headway in this, I think we’re going to have to adopt some of the strategies that we can learn from biology.