Page 87 - ITU Journal, Future and evolving technologies - Volume 1 (2020), Issue 1, Inaugural issue

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

cluded. set of element states, through the use of numerical
It is clariﬁed, that the middleware operations are one- simulations.
time only, i.e., once the database containing the behav-
ior proﬁle of a metasurface is complete, it can be used The experimental evaluation of the exported conﬁg-
in any application setting in the real world by any tile uration through physical measurement of a meta-
of the same type. material prototype. Notably, the presented soft-
ware has been veriﬁed experimentally, and a full
6. SOFTWARE IMPLEMENTATION report can be found online [20].
AND EVALUATION
The ﬁnal storing of all conﬁguration parameters
Employing the concepts of the previous sections, we into the conﬁguration DB to complete the function
developed a complete Java implementation of the de- optimization process.
scribed software. The software is subdivided into two
integral modules: i) an implementation of the metama- In this context, Fig. 11(a) depicts all the individual steps
terial API that handles the communication and alloca- in separate panels. If a new conﬁguration is to be de-
tion of existing conﬁgurations and ii) the Metamaterial ﬁned for a tile already present in the conﬁguration DB,
Middleware that populates the conﬁguration DB with then, the ﬁrst step can be skipped. Alternatively, the
new data (new tiles, conﬁgurations, and functionalities). user must input all essential parameters of the unit cell
The Metamaterial Middleware incorporates a full GUI structure, i.e. the number and type of all variables that
environment, guiding the user through a step-by-step correspond to the sum of reconﬁgurable metamaterial
process to produce new conﬁgurations. It utilizes all elements. The deﬁnition of a new conﬁguration begins
available theoretical and computational tools for the ac- with the parameterization of the desired functionality
curate characterization of a metamaterial tile. Further- (Fig. 11(a.2)). The current implementation supports
more, it oﬀers direct access to the conﬁguration DB, plane wave or point source inputs (for far- and near-ﬁeld
manually, via a custom-made Structured Query Lan- energy sources) and a set of output options correspond-
guage (SQL) manager or through the automated pro- ing to all basic metamaterial functionalities, discussed
cess following a successful metamaterial characteriza- in Section 2. Here, we select a beam splitting operation
tion. Through this process, all the necessary data re- and proceed to the ﬁrst main step of the characteriza-
lated to a newly produced conﬁguration become explic- tion process.
itly available to the API. The analytical evaluation of the energy scattering pro-
A microwave metasurface was selected to demonstrate ﬁle is performed in the software locally and in real time.
the capabilities of the developed concepts and methods During this step, the Metamaterial Middleware calcu-
for software-tunable metamaterials. We adapted the de- lates the proper scattered ﬁeld response of the imping-
sign of [37], where a set of RF diodes can be employed to ing wave, for each unit cell at the N × M tile, via either
toggle the reﬂection-phase of each cell between 16 states. the analytical methods of Section 5 or through an op-
We numerically extracted the response of the metasur- timization process. The scattered ﬁelds are evaluated
face (i.e., its scattering pattern), and ﬁnally used the for each unit cell as a double complex variable (A 1 e iφ 1
developed software to demonstrate how the metasurface and A 2 e iφ 2 , magnitude and phase of the reﬂected TE
response can be controlled. For the practical demonstra- and TM polarizations, respectively), a process physi-
tion of the developed software in the same measurement cally correct under the condition that the unit cell is
environment (anechoic chamber) with a simpler, 1-bit a subwavelength entity. This simply implies that the
metasurface hardware, we redirect the reader to [20,30], input of the “physical size” ﬁeld in Fig. 11(a.1) must
since the hardware manufacturing topic is quite exten- comply with this speciﬁcation or a warning message will
sive and clearly beyond the software aspects that con- appear. In our example, the selected tile consists of bi-
stitute the focus of this paper. nary elements (D stands for diodes), which may only
In the following, we list and comprehensively describe control the phase of the co-polarized scattered ﬁeld (φ 1
the steps undertaken during a optimization process, as term). By clicking the “View suggested” button, we an-
seen through the GUI environment of the Metamaterial alytically calculate and display φ 0 − φ 1 (φ 0 is the phase
Middleware. In summary, this process involves: of the incoming wavefront), which should give an indi-
cation of the diode states at the metamaterial. Alterna-
The deﬁnition of a new unit cell structure and tile
tively, a similar result can be extracted by launching the
array (if required).
metaheuristic optimizer, either via a blind optimization
process (all-0 initial solution) or an assisted optimiza-
The parameterization of a new functionality.
tion, using the analytically evaluated proﬁle as an ini-
The analytical evaluation of the scattering proﬁle tial solution. The latter practice leads to more reﬁned
on the metamaterial for the selected functionality. results, over an analytical evaluation, by considering the
ﬁnite size of the tile and the non-inﬁnitesimal size of the
The association of the metamaterial proﬁle to the unit cell.

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