Abstract
We report theoretical investigations performed in the terahertz G-band, in the 228–232 GHz spectral window for a piezoelectrically-responsive ring-cone element metasurface composed of polyvinylidene fluoride (PVDF)/Silicon and PVDF/Silica glass. The choosing of this spectral window is motivated by a multitude of applications in terahertz detection and terahertz imaging, that commonly make use of this band. The uniqueness of the envisioned architecture resides in the combination between the readily-available polyvinylidene fluoride polymer and silicon/silica glass substrates, together with the introduction of an extra degree of freedom, in the form of a ring-cone architecture, and the active control of the geometric sizes through the longitudinal piezoelectric effect exhibited by the polymer. The spectral response of the metasurface is dependent on the combination between the polymer elements and the substrate, and ranges from near-zero absorption switching to a resonant behavior and significant absorption. The interaction between the electromagnetic field and the polymer-based metasurface also modifies the phase of the reflected and transmitted waves over a full range, permitting complete control of the electric field polarization. Moreover, we take advantage of the longitudinal piezoelectric effect of PVDF and analyze the spectrum shaping capability of the polymer-based metasurface. Our analysis highlights the capability of the proposed architecture to achieve complete electric field polarization control, near-zero optical switching and resonant behavior, depending on the geometries and sizes of the architecture elements resulting from construction considerations and from the externally applied voltages through the piezoelectric effect.
Highlights
Metasurfaces [1] are man-made structures consisting of repeating unit cells known as meta-atoms, which have gained notoriety relatively recently due to their property of exhibiting negative electric permittivity and magnetic permeability μ tensors at the same time [2,3,4]
In this paper, we have investigated the spectral response of a piezoelectrically-addressable polyvinylidene fluoride (PVDF) ring-cone metasurface in the terahertz G-band, in a window that is commonly used for security applications and terahertz imaging
The results show a complete control of the electric field properties and on-demand tunability via the piezoelectric effect that is exhibited by the PVDF elements
Summary
Metasurfaces [1] are man-made structures consisting of repeating unit cells known as meta-atoms, which have gained notoriety relatively recently due to their property of exhibiting negative electric permittivity and magnetic permeability μ tensors at the same time [2,3,4]. An essential part of coherent control in these application is spectral filtering and transmission/reflection switching, which is accompanied by inherent absorption This is due to the sharp discontinuities in the phase topology across the unit cell. There exists a wide range of airport scanners which are tuned for screening at a frequency f = 230 GHz, making our proposed architecture relevant for this type of application The choice of such combination of materials for this window is justified by the favorable spectral properties of the individual components in the desired spectral range, together with the piezoelectric response of the PVDF, which is able to offer enhanced addressability. The simplicity of the architecture, combined with the new degree of freedom created by the third dimension and the piezoelectric response of the PVDF make our proposed structure a viable candidate for an externally-addressable, high-quality switching device in the G-band, with a multitude of on-demand applications
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