Page 78 - ITU Journal, Future and evolving technologies - Volume 1 (2020), Issue 1, Inaugural issue

ITU Journal on Future and Evolving Technologies, Volume 1 (2020), Issue 1

tion, which has not been proposed before. Additionally,
our paper focuses more on the networking approaches
for metamaterials, which has only been treated in our
previous work [8], and only for the EM case. Finally,
the work of Chen et al. [27] also advocates for the use
of metamaterial in any physical domain for distributed
energy harvesting, e.g., in a smart house or a city. How-
ever, software enablers and networking considerations
are not discussed or solved in [27]. Moreover, the energy
manipulation type is restricted to harvesting which can
be viewed as a subset of our proposed IoMMT potential.

Metamaterials: Principles of Operation, Classi-
fication and Supported Functionalities

A conceptual metamaterial is illustrated in Fig. 5 [3].
Basically, a metamaterial consists of periodically re-
peated meta-atoms arranged in a 3D grid layout, with
Fig. 4 – Energy manipulation domains of artificial materials: the metasurfaces being a sub-case. In particular, unit
(a) Electromagnetic [20] (b) Mechanical [21] (c) Acoustic [22] (d)
Thermoelectric [23]. cells comprise passive and tunable parts, required in
reconfigurable metamaterials as well as optional inte-
munications [7, 15–19], offering substantially increased grated sensory circuits, which can extract information
bandwidth and security between two communicating of the incident energy wave. Furthermore, tunable parts
parties. are crucial for metamaterials, as they enable reconfig-
The potential stemming from interconnected metama- urability and switching between different functions. For
terials has begun to be studied only recently [8]. The illustration, in EM metamaterials at microwave frequen-
perspective networking architecture and protocols [7,8], cies, the tunable parts embedded inside the unit cells
metamaterial control latency models [24], and smart en- can be voltage-controlled resistors (varistors) and/or ca-
vironment orchestration issues have been recently stud- pacitors (varactors), micro-electromechanical switches
ied for the EM case [25,26]. (MEMS), to name a few [3,19].
Notably, a similarly named concept, i.e., the Internet On the other hand, in mechanical and acoustic meta-
of NanoThings [9], was recently proposed to refer to materials, the tunable parts can be micro-springs with
materials with embedded, nano-sized computing and a tunable elasticity rate [28, 29]. The meta-atoms may
communicating elements. In general, these materials also form larger groups, called super-atoms or super-
are derived from miniaturizing electronic elements and cells, repeated in specific patterns that can serve more
placing them over or embedding them into fabrics and complex functionalities, as discussed later in this paper.
gadgets, to increase their application-layer capabilities. Lastly, the software-defined metamaterials include a
For instance, this could make a glass window become gateway [7], i.e., an on-board computer, whose main
a giant, self-powered touchpad for another IoT device. tasks are to: i) power the whole device and ii) control
Originally. the concept of software-defined metasurfaces (get/set) the state of the embedded tunable elements,
wa based on the nano-IoT as the actuation/control en- iii) interoperate with the embedded sensors, and iv)
abler [17]. Nano-devices can indeed act as the con- interconnect with the outside world, using well-known
trollers governing the state of the active cells, offer- legacy networks and protocol stacks (e.g. Ethernet).
ing manufacturing versatility and extreme energy effi- The relative size of a meta-atom compared to the wave-
ciency. Nonetheless, until nano-IoT becomes a main- length of the excitation (impinging wave) defines the en-
stream technology, other approaches can be adopted ergy manipulation precision and efficiency of a metama-
for manufacturing software-defined metasurfaces, as re- terial. For example, EM metasurfaces share many com-
ported in the related physics-oriented literature [6]. It is mon attributes with classic antenna-arrays and reflect-
also noted that nano-IoT as a general concept is about arrays. Antenna arrays can be viewed as independently
embedding nano-sized computers into materials in order operating antennas, being very effective for coarse beam
to augment the penetration level of applications (e.g., steering as a whole. Reflect-arrays typically consist of
sense structural, temperature, humidity changes within smaller elements (still subwavelength), permitting more
a material, rather than just over it, etc.), and not specif- fine-grained beam steering and a very coarse polariza-
ically to control the energy propagation within them. tion control. Metamaterials comprise orders of magni-
In contrast, our work refers specifically to the case of tude smaller meta-atoms, and may also include tunable
metamaterials and the capabilities they offer for the ma- elements and sensors. Their meta-atoms are generally
nipulation of energy across physical domains. Moreover, considered tiny with regard to the exciting wavelength,
our paper introduces the software enablers for this direc- hence allowing full control over the form of the departing

58 © International Telecommunication Union, 2020