The primary scientific objective of the proposed project is to design magnetic field-actuated MEMS (cantilever-based) reconfigurable terahertz metasurfaces and then to determine the relationship between the selected parameters of the designed metasurface on its electromagnetic properties and how the metasurface interacts with electromagnetic waves propagating in the terahertz range.
Electromagnetic waves in the terahertz frequency range (0.1-10 THz) and their interaction with different materials or propagation in a variety of settings are the topic of a large number of international scientific investigations. During the last two decades, tremendous progress has been made in this subject, including the invention of photoconductive antennas (PCA) that permit pulsed excitation and, consequently, Time Domain Spectroscopy (TDS) technology. Artificial materials - the metamaterials (MM) – are one of the most rapidly growing subjects in the terahertz spectrum at present.
A metamaterial is an artificial, man-made structure consisting of periodic or quasi-periodic arrays of sub-wavelength size unit (structural) elements that can take on the properties of non-naturally occurring materials, e.g. negative refractive index or both negative permittivity and permeability referred as double-negative structures (DNG). This opens up new possibilities for interaction with electromagnetic waves. Metasurfaces (MS) are two-dimensional versions of metamaterials. Their properties can be designed as fixed before the fabrication process or can be designed as variable
(some external excitation dependent, like light, electric current or potential, temperature, etc.). One of the possibilities to obtain the reconfigurability of MS is an application of magnetic field-driven micro-electro-mechanical systems (MFDMEMS), where the geometry of structural element is modulated using a magnetic field. Such structures are commonly utilized as light switches, micromirrors actuators and in metrology. Nevertheless, their application to tunable terahertz metasurfaces is very rare and limited.
In the proposed project the driving magnetic field vector will be freely controllable by an external excitation system. MEMS-based THz metasurface structure placed in a magnetic field that can interact in any direction will be proposed. Metasurface’s structural elements will consist of conductive and magnetic micro cantilevers serving as variable geometry. The altered geometries of structural components influence the electromagnetic properties of MS in the terahertz frequency range: transmission and reflection spectral content (changes in resonant frequencies), polarization, etc. This gives unparalleled opportunities for altering the layout of structural components and, as a result, the electromagnetic parameters of the meta-surface in the terahertz frequency band. Appropriate design of structural components (considering the aforementioned attributes) has a substantial effect on the electromagnetic properties of metasurfaces, therefore such geometries will be sought that will maximize such a change in EM properties (e.g. resonance frequency). The project will also develop the optimal methodology for the production of microcantilevers made of magnetic materials.
The project will solve the following fundamental concerns about the planned metasurface structures:
• optimization of metasurface geometries. The optimal surface will be reconfigured with the magnetic field to the greatest extent, allowing for deeper interaction with the THz wave;
• examination of the influence of selected geometrical and magnetic parameters of the designed metasurfaces on their effective ability to the desired interaction with the THz wave;
• exploration of the possibility of using other metasurface reconfiguration techniques in conjunction with the MEMS technique;
• study of the dynamics of the interaction between the metasurface and the THz wave;
• determination of the impact of continuous cyclic operation on the generated metastructure (and, as a result, its interaction with the THz wave).