Browsing by Author "Rahimian Omam, Zahra"

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Open Access
Fano resonance in a dolomite phase-change multilayer design for dynamically tunable omnidirectional monochromatic thermal emission
(Optica, 2022) Rahimian Omam, Zahra; Ghobadi, Amir; Khalichi, Bahram; Özbay, Ekmel
In this Letter, we unveil the unprecedented optical phonon response of CaMg(CO3)2 (dolomite) thin film in the design of a planar ultra-narrowband mid-infrared (MIR) thermal emitter. Dolomite (DLM) is a carbonate mineral composed of calcium magnesium carbonate, which can inherently accommodate highly dispersive optical phonon modes. Utilizing strong interference in the Al-DLM bilayer, a lithography-free planar thermal emitter is realized with near-unity omnidirectional emission at a specific resonance wavelength of 7.12 µm. Further incorporation of embedded vanadium dioxide (VO2) phase change material (PCM) enables the excitation of hybrid Fano resonances with dynamic spectral tunability. The findings of this study can have multiple applications, ranging from biosensing and gas sensing to thermal emission.
Open Access
Microheater-integrated spectrally selective multiband mid-infrared nanoemitter for on-chip optical multigas sensing
(American Chemical Society, 2023-11-10) Rahimian Omam, Zahra; Ghobadi, Amir; Khalichi, Bahram; Güneş, Burak; Özbay, Ekmel
Traditional optical gas sensors often require multiple components such as broadband infrared sources, detectors, and band-pass filters to detect various target gases, resulting in bulky and expensive sensor designs. A streamlined optical gas-sensing platform utilizing a narrowband thermal emitter with a spectrally selective response, capable of accommodating various target gases, has the potential to supplant current bulky designs. Through the on-chip integration of a narrowband metamaterial perfect absorber with a microelectromechanical system (MEMS) heater, a selective infrared source emitter could be designed. In this paper, a multiband metamaterial absorber with resonance modes located at different gas absorption signatures is developed for optical multi-gas-sensing applications. The proposed nanoemitter supports penta-band light absorption through the simultaneous excitation of phononic modes (within the hexagonal boron nitride (hBN) topmost layer) and plasmonic modes (with the spectrally selective underlying metal-insulator-metal (MIM) absorber stack). It achieves five near-perfect sharp absorption resonance peaks compatible with the H2S, CH4, CO2, NO, and SO2 gas absorption signatures in the mid-infrared (MIR) spectral range. This spectrally engineered multiwavelength absorption behavior is achieved by simultaneously coupling the optical phonons (OPhs) and the plasmonic modes in the vicinity of the OPh region of hBN and by exciting plasmonic modes with the help of the spacer (ZnTe: zinc telluride) and the metallic nanogratings. Finally, this low-cost and efficient penta-band absorber is combined with a MEMS-based microheater. The microheater uses a Peano-shaped configuration to provide a highly uniform surface temperature, which is crucial for accurate and reliable gas sensing. The proposed platform demonstrates excellent potential in terms of cost-effectiveness, source-free operation, and suitability for multi-gas-sensing platforms.
Open Access
Phase-change Fano resonator for active modulation of thermal emission
(Royal Society of Chemistry, 2023-06-10) Khalichi, Bahram; Ghobadi, Amir; Kalantari Osgouei, Ataollah; Rahimian Omam, Zahra; Kocer, Hasan; Ozbay, Ekmel
Optical modulation of heat emission using spectrally selective infrared (IR) metasurface nanoantenna designs has found potential applications in various fields, including radiative cooling and thermal camouflage. While radiative cooling requires emitters to emit within atmospheric transmissive windows (mainly located at 8–14 μm), thermal camouflage structures have to operate within the non-transmissive window (5–8 μm) to hide an object from thermal imaging systems and cameras. Therefore, a passive nanoantenna structure cannot satisfy both conditions simultaneously. In this paper, we propose an adaptive nanoantenna emitter made of samarium nickelate (SmNiO3) phase change material to cover both functionalities with a single Fano resonator-based design. As the temperature rises, the thermal signature of the nanoantenna at the transmissive window is suppressed; therefore, a better camouflage performance is achieved. The dynamic tunability of switching from radiative cooling to thermal camouflage of the proposed Fano resonator-based design is quantitatively demonstrated using emissive power calculations under different conditions.
Open Access
Simple and high-sensitivity dielectric constant measurement using a high-directivity microstrip coupled-line directional coupler
(IEEE, 2022-06-23) Rahimian Omam, Zahra; Nayyeri, Vahid; Javid-Hosseini, Sayyed-Hossein; Ramahi, Omar M.
Simple methods using a microstrip coupled-line directional coupler (CLDC) are presented for dielectric constant measurements. The material under test (MUT) is placed on the coupled-line section of the coupler, and either the coupler’s coupling ( |S31| ) or its isolation level ( |S41| ) is considered as the sensor’s response. Putting different MUTs on the microstrip line leads to a change in the effective dielectric constant of the structure and consequently causing a change in the coupling coefficient. In addition, since the isolation level of a microstrip coupled-line coupler depends on the phase velocity difference between the substrate and the medium above the signal strips, putting different MUTs on the line significantly changes the isolation level. This change is significantly greater than the change in |S21| level of a microstrip line when loaded with different MUTs. Validation of the method is presented through measurements for both solid and liquid MUTs.