In the world of research, technological innovation and industry, metamaterials are gathering more and more interest, thanks to their unique characteristics and the wide range of applications in which they can be used.
From 6G antennas to aerospace applications, i metamateriali promise to enter many technological sectors of the future. Various industrial sectors are interested, as well as investment funds, attracted by the potential of these particular materials. Just recently, in the United States the investment company MetaVC Partners raised 62 million dollars to create a fund dedicated to financing startups active in this area. According to Lux Research, the market for metamaterial devices will grow to $10.7 billion in 2030.
Already today they are being adopted for high-performance and energy-efficient products in the fields of information technology, optical and electromagnetic imaging, wireless communications and sensor technology.
Then there is the world of energy which is looking with great interest at this class of materials for energy harvesting (thermoelectric and solar) and storage solutions, as well as for making
wireless power transfer and energy conversion systems. This is illustrated by the University of Exeter, which has launched a research and innovation center dedicated to these artificially structured materials. Because this is what it is about: specific man-made materials, which highlight extraordinary electromagnetic properties not available in nature. Their properties are literally engineered by manipulating their physical structure. This, in addition to making them significantly different from natural materials, helps to attract the extreme interest of the scientific and industrial world for their potential applications. These engineered materials allow us to go beyond (the Greek prefix “meta” means this) the classical mechanisms according to which waves and matter interact, allowing us to design devices in which light and sound seem to ‘disobey’ conventional rules.
Takeaway
What are Metamaterials? These are materials engineered on the millimeter, micrometer or nanometer scale to control the interaction between electromagnetic waves and matter. Although their origins are traced back to the Indian physicist and botanist Jagdish Chandra Bose at the end of the nineteenth century, it is in the twentieth century that their characteristics begin to be outlined. In a 1968 article, the Russian physicist Victor Veselago theoretically conceived the existence of a material artificial with negative refractive index. What is special about this discovery? At least one, fundamental: it is one property That it is not found in nature. However, this metamaterial was only created and experimentally tested in 2000 by US physicists David R. Smith of Duke University and Sheldon Schultz of the University of California, San Diego.
Metamaterials offer other significant potential for numerous applications due to their unique acoustic, electromagnetic, optical and mechanical properties. «With metamaterials, for example, it is possible to create planar rather than concave or convex optical devices. The interest that has been focused on them is also due to the fact that the manufacturing technologies are very similar to those used to produce integrated circuits», says Giuliano Manara, professor and expert in Electromagnetic Fields at the Department of Information Engineering of the University of Pisa, where he is active in research in the electronics and telecommunications sector and where he is dedicated to the study of new wireless technologies for the creation of tracking and monitoring systems. The professor himself is heavily involved, together with his research team, in the FoReLab project, in which he deals with smart material devices.
Metamaterials can be optical, acoustic, mechanical and the real and potential fields of application are very vast. «The fundamental aspect is that, by implementing particular metamaterials, particular electromagnetic responses can be obtained, not found in materials found in nature: this opens up an important front for research and for the development of new products», Manara points out. There are already active startups on optical applications capable of attracting strong interest. For example, the American company Metalenz, active on metasurfaces (particular two-dimensional metamaterials), raised 30 million in funding last year, after having already obtained more than 47 million from investors.
The field of telecommunications is one of the fields where the strategic interest of research is most concentrated: the team of the Pisan university where Manara operates is particularly focused on these aspects. In particular, he is working on the development of smart antennas and Intelligent Reflecting Surfaces (IRS). «Our research work focuses on the development of particular metamaterials and metasurfaces that will have an important impact on the development of 6G. In this regard, we plan to create intelligent antennas and reflective surfaces». What is meant by intelligent? An intelligent base radio antenna can radiate an electromagnetic beam which, instead of covering a cell entirely, can be electronically controlled and directed only towards a possible user present inside the cell itself. This reduces the energy required to establish the link. Similarly, an intelligent reflective surface can understand where the user is and reflect the beam in a precise and targeted direction, rather than in a fixed direction. «Today this possibility seems like science fiction and in some respects it is. However, forty years ago, at the dawn of mobile telephony, almost no one would have foreseen that in 2020 we would be able to count on mobile and ubiquitous connectivity, which allows us to work almost anywhere with PCs and smartphones».
Still on the subject of antennas, the team where the telecommunications teacher works is also developing special ones we found, structural casing containers, resistant to bad weather, designed to protect an antenna. “Our research focuses on the realization of this envelope with metamaterials capable not only of allowing the undisturbed passage of radio waves, but of rejecting other unwanted waves or of manipulating the properties of the radiated field”.
The use of artificial intelligence
For the development of metamaterials it is possible to apply artificial intelligence techniques. For example, scientists from the University of Amsterdam, the AMOLF research institute and Utrecht University have demonstrated the potential of convolutional neural networks to design complex mechanical metamaterials. In their article, published in Physical Review Letters, the research team illustrated how they tested the ability offered by AI to predict the properties of these specific materials.
«Artificial intelligence is a very important tool with enormous resolving power. We too employ stochastic and evolutionary algorithms: in particular we have used the genetic algorithms and the particle swarm optimisation (bio-inspired optimization algorithms) to explore the space of useful solutions and identify not only the best solution, but also a series of sub-optimal solutions for the development of metamaterials or metasurfaces aimed at specific needs or to highlight interesting alternatives.
Metamaterials constitute one of the most promising frontiers of research, as can also be seen from the examples already seen. Among the many aspects that are being looked at with interest are the medical-health and biotechnological ones. For example, the use of metasurfaces conforming to different districts of the human body can optimize the penetration of the electromagnetic field into biological tissues for diagnosis, monitoring or for therapeutic procedures based on radiofrequency and/or microwave hyperthermia. «A field of exploration on which we intend to focus attention concerns the creation of eco-friendly sensors, for example using specific printing inks for electromagnetic tags (labels) based on RFID (Radio Frequency IDentification) technology, which do not contain electronics (chipless RFID tags) – concludes Manara -. Completely biodegradable, they can be used for various applications, including precision agriculture in particular: it is possible to imagine their application on plants to collect important parameters on their health. In the creation of these biodegradable devices and sensors, we are also adopting additive manufacturing techniques for 3D RFID tags. But the most interesting aspect is that these are just some conceivable applications, and we can let our imagination run wild to explore new fields and devices».
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