Materials of the future: they sense, compute and actuate. A review
Smart materials are the matter of the future – a review published yesterday in the journal Science says. Engineered artificial materials which can sense, compute and actuate are getting more and more common and we are just barely scratching the surface of the things one day they could do.
Nature is full of complex biological systems which tightly integrate sensing, actuation and computation capabilities. Examples include extraordinary changes in shape and appearance, adaptive load support and high-dynamic-range tactile sensing – just to mention a few. “We looked at organisms like the cuttlefish, which change their appearance depending on their environment, and the banyan tree, which grows above-ground roots to support the increasing weight of the trunk and we asked what it would take to engineer such systems” – said Nikolaus Correll, assistant professor of computer science at the University of Colorado Boulder. Inspired by these remarkable systems, we have often envisioned the day when artificial materials will become what has always just been ‘the stuff of science fiction’. Airplane wings and vehicles capable of adapting their aerodynamic profile to the environment, clothes with adaptive camouflage capabilities, bridges and civil structures which could repair themselves or robotic skin and prosthetics with hyper-sensitivity.
Already twice, first with the advent of fast digital electronics in the 1970s, and then with the development of microelectromechanical systems in the 1990s, the dream of realizing this “programmable matter” seemed at arm’s reach. It is however only now that this dream is starting to become reality. Advances in manufacturing, combined with the miniaturization of electronics that has brought us to carry, in a pocket, smartphones with the power of a desktop computer, is enabling a new class of so-called “robotic” materials. They transcend classical matter by integrating sensors, actuators and even microprocessors which allow them to function autonomously and could be programmed to change dynamically certain properties in response to specific stimuli. For instance, “the human sensory system automatically filters out things like the feeling of clothing rubbing on the skin” – Correll says. “An artificial skin with possibly thousands of sensors could do the same thing and only report to a central ‘brain’ if it touches something new”.
While we are getting ‘closer’ to widely-available “robotic” materials we are not there yet. Manufacturing techniques for these materials of the future remains a challenge. “Right now, we’re able to make these things in the lab on a much larger scale, but we can’t scale them down” – Correll comments. “The same is true for nano- and micro-scale manufacturing, which can’t be scaled up to things like a building façade”. Interestingly, the challenge also involves our educational system, as fundamental advances in the field can only come from the tight integration of several disciplines such as both material and computer sciences. “We expose engineering students to both materials and computing, no matter what their background is” – Correl says.
Regarding this crucial aspect we are still quite far behind. Advances are currently being made mainly in individual disciplines. For instance, progress has been made in composite materials that integrate sensing and actuation (e.g. shape-changing airfoils), as well as in their manufacturing. In parallel, computer science has developed distributed algorithms to collect, process and act upon huge volumes of data. In recent years, manufacturing has been revolutionized by three-dimensional (3D) printing as well as by creating complex structures from unfolding or stretching patterned 2D composites. Finally, robotics and controls have made advances in controlling robots with multiple actuators, continuum dynamics and large numbers of distributed sensors. Unfortunately, only a limited number of systems have taken full advantage from these advances to create materials that tightly integrate sensing, computation, actuation and communication in a way that allows them to be mass-produced cheaply and readily.
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