Riad Yahiaoui

Experimental demonstration of ultrasensitive sensing with terahertz metamaterial absorbers: A comparison with the metasurfaces

Planar metasurfaces and plasmonic resonators have shown great promise for sensing applications across the electromagnetic domain ranging from the microwaves to the optical frequencies. However, these sensors suffer from lower figure of merit and sensitivity due to the radiative and the non-radiative loss channels in the plasmonic metamaterial systems. We demonstrate a metamaterial absorber based ultrasensitive sensing scheme at the terahertz frequencies with significantly enhanced sensitivity and an order of magnitude higher figure of merit compared to planar metasurfaces. Magnetic and electric resonant field enhancement in the impedance matched absorber cavity enables stronger interaction with the dielectric analyte. This finding opens up opportunities for perfect metamaterial absorbers to be applied as efficient sensors in the finger print region of the electromagnetic spectrum with several organic, explosive, and bio-molecules that have unique spectral signature at the terahertz frequencies.

Multispectral terahertz sensing with highly flexible ultrathin metamaterial absorber

We report the simulation, fabrication, and experimental characterization of a multichannel metamaterial absorber with the aim to be used as a label-free sensing platform in the terahertz regime. The topology of the investigated resonators deposited on a thin flexible polymer by means of optical lithography is capable of supporting multiple resonances over a broad frequency range due to the individual contribution of each sub-element of the unit cell. In order to explore the performance of the chosen structure in terms of sensing phenomenon, the reflection feature is monitored upon variation of the refractive index and the thickness of the analyte. We achieve numerically maximum frequency sensitivity of about 139.2 GHz/refractive index unit. Measurements carried out using terahertz time-domain spectroscopy show good agreement with the numerical predictions. The results are very promising, suggesting a potential use of the metamaterial absorber in wide variety of multispectral terahertz sensing applications.

Resonant magnetic response of TiO2 microspheres at terahertz frequencies

Spray-drying technique is used to fabricate spherical microparticles out of dissolved TiO2 nanoparticles. We show both experimentally and through numerical calculations that the microspheres support a Mie resonance, leading to an effective magnetic response. For this purpose, nearly single layers of microspheres were prepared and characterized by time-domain terahertz spectroscopy. We developed an experimental approach allowing simultaneous measurement of complex transmittance and reflectance of a thin layer, which in turn enables evaluation of its effective dielectric permittivity and effective magnetic permeability. Numerical finite-element-method calculations of the electromagnetic response show that the prepared microparticles are suitable for preparing a metamaterial with negative effective magnetic permeability.

Trapping waves with terahertz metamaterial absorber based on isotropic Mie resonators.

Quasi-monodisperse dielectric particles organized in a periodic hexagonal network on an aluminum surface are exploited numerically and experimentally as a single-layered near-perfect absorber in the terahertz regime. Of particular interest are titanium dioxide (TiO(2)) microspheres because of their large dielectric permittivity and isotropic shape leading to Mie resonances with insensitive polarization. Absorption higher than 80% at normal incidence covering two distinct ranges of frequencies is demonstrated experimentally. Furthermore, the performance of the metamaterial absorber is kept over a wide range of incident angles.

Terahertz Plasmonic Structure With Enhanced Sensing Capabilities

We have designed, fabricated, and experimentally verified a highly sensitive plasmonic sensing device in the terahertz frequency range. For a proof of concept of the sensing phenomenon, we have chosen the so-called fishnet structure based on circular hole array insensitive to the polarization of the incident wave. We employ the localized resonance associated with the cutoff frequency (electric plasma frequency) of the hole array to investigate its sensing capability. A thin-film overlayer deposited on the surface of the metallic apertures causes an amplitude modulation and a shift in the resonant frequency of the terahertz transmission. The frequency shift and the amplitude modulation were investigated as a function of the refractive index and the thickness of the overlayer for determining the sensing potential of the proposed structure. Measurements carried out using terahertz time-domain spectroscopy show good agreement with the numerical predictions. The results we obtained indicate that the proposed device could be very promising for enhancing the sensing capabilities of the refractive index changes involved in bio-applications, for instance.

Terahertz metamolecules deposited on thin flexible polymer: design, fabrication and experimental characterization

Metamolecules deposited on thin dielectric film using standard optical lithography have been investigated numerically and experimentally in the terahertz regime. The topology of the proposed metamolecules is able to achieve a multiple–band frequency response over a broad frequency range. The analysis of the spectral response of the investigated metamaterial reveals that such a feature arises from coupling effects between its individual constituents. The successful demonstration of a THz flexible metamaterial may open up new perspectives towards achieving complex electromagnetic functions involving non-planar metamaterials with simple design and fabrication.

Towards left-handed metamaterials using single-size dielectric resonators: The case of TiO2-disks at millimeter wavelengths

We report a strong magnetic activity using an all-dielectric metamaterial based on Mie resonances, designed to work at millimeter wavelengths over the 30–70 GHz band. A good agreement was achieved between numerical simulations and experiment in the case of one meta-layer based on TiO2-disks, manufactured using a simple bottom-up approach. We also demonstrate through numerical simulations a negative refractive index within the same investigated metamaterial made of high dielectric permittivity single-size pellets. Choosing the suitable aspect-ratio of the metamaterial building blocks, a broadband magnetic response and a left-handed behavior are simultaneously obtained. This is a promising step towards innovative and complex electromagnetic functions, involving cheap and easy made metamaterials for millimeter wave applications.

Active control and switching of broadband electromagnetically induced transparency in symmetric metadevices

Electromagnetically induced transparency (EIT) arises from coupling between the bright and dark mode resonances that typically involve subwavelength structures with broken symmetry, which results in an extremely sharp transparency band. Here, we demonstrate a tunable broadband EIT effect in a symmetry preserved metamaterial structure at the terahertz frequencies. Alongside, we also envisage a photo-active EIT effect in a hybrid metal-semiconductor metamaterial, where the transparency window can be dynamically switched by shining near-infrared light beam. A robust coupled oscillator model explains the coupling mechanism in the proposed design, which shows a good agreement with the observed results on tunable broadband transparency effect. Such active, switchable, and broadband metadevices could have applications in delay bandwidth management, terahertz filtering, and slow light effects.

Broadband polarization-independent wide-angle and reconfigurable phase transition hybrid metamaterial absorber

We report the simulation, fabrication, and experimental characterization of a single-layer broadband, polarization-insensitive and wide-angle near perfect metamaterial absorber (MA) in the microwave regime. The topology of the resonators is chosen in such a way that is capable of supporting simultaneously multiple plasmon resonances at adjacent frequencies, which lead to a broadband operation of the MA. Absorption larger than 80% at normal incidence covering a broad frequency range (between 7.4 GHz and 10.4 GHz) is demonstrated experimentally and through numerical simulations. Furthermore, the performance of the metamaterial absorber is kept constant up to an incident angle of 30°, for both TE and TM-polarizations. In addition, a hybrid model of the MA is proposed and implemented numerically in order to dynamically tune the absorption window. The hybrid MA is controlled by incorporating vanadium dioxide (VO2) temperature-driven metal-insulator phase transition material, which enables the transition from b...

Integrated active mixing and biosensing using low frequency vibrating mixer and Love-wave sensor for real time detection of antibody binding event

The development of lab-on-chip devices is expected to dramatically change biochemical analyses, allowing for a notable increase of processing quality and throughput, provided the induced chemical reactions are well controlled. In this work, we investigate the impact of local acoustic mixing to promote or accelerate such biochemical reactions, such as antibody grafting on activated surfaces. During microarray building, the spotting mode leads to low efficiency in the ligand grafting and heterogeneities which limits its performances. To improve the transfer rate, we induce a hydrodynamic flow in the spotted droplet to disrupt the steady state during antibody grafting. To prove that acoustic mixing increases the antibody transfer rate to the biochip surface, we have used a Love-wave sensor allowing for real-time monitoring of the biological reaction for different operating conditions (with or without mixing). An analysis of the impact of the proposed mixing on grafting kinetics is proposed and finally checked in the case of antibody-antigen combination.