Browsing by Author "Khalichi, Bahram"
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Item Open Access Adaptive thermal camouflage using sub-wavelength phase-change metasurfaces(Institute of Physics Publishing Ltd., 2022-12-09) Omam, Zahra Rahimian; Ghobadi, Amir; Özbay, Ekmel; Khalichi, BahramSub-wavelength metasurface designs can be used to artificially engineer the spectral thermal signature of an object. The real-time control of this emission can provide the opportunity to switch between radiative cooling (RC) and thermal camouflage functionalities. This performance could be achieved by using phase-change materials (PCMs). This paper presents a sub-wavelength dynamic metasurface design with the adaptive property. The proposed metasurface is made of vanadium dioxide (VO2) nanogratings on a silver (Ag) substrate. The design geometries are optimized in a way that both narrowband and broadband mid-infrared (MIR) emitters can be realized. At low temperatures, insulating VO2 nanogratings trigger the excitation of Fabry–Perot mode inside the grating and surface plasmon polaritons at the metal–dielectric interface with an emission peak located in the MIR region to maximize the RC performance of the design. As temperature rises, the PCM transforms into a metallic phase material and supports excitation of Wood's anomaly and localized surface plasmon resonance modes. Accordingly, the thermal signature is adaptively suppressed.Item Open Access Broadband analysis of multiscale electromagnetic problems: Novel incomplete-leaf MLFMA for potential integral equations(IEEE, 2021-06-24) Khalichi, Bahram; Ergül, Ö.; Takrimi, Manouchehr; Ertürk, Vakur B.Recently introduced incomplete tree structures for the magnetic-field integral equation are modified and used in conjunction with the mixed-form multilevel fast multipole algorithm (MLFMA) to employ a novel broadband incomplete-leaf MLFMA (IL-MLFMA) to the solution of potential integral equations (PIEs) for scattering/radiation from multiscale open and closed surfaces. This population-based algorithm deploys a nonuniform clustering that enables to use deep levels safely and, when necessary, without compromising the accuracy resulting in an improved efficiency and a significant reduction for the memory requirements (order of magnitudes), while the error is controllable. The superiority of the algorithm is demonstrated in several canonical and real-life multiscale geometries.Item Open Access Broadband solutions of potential integral equations with NSPWMLFMA(IEEE, 2019-06) Khalichi, Bahram; Ergül, Ö.; Ertürk, Vakur B.In this communication, a mixed-form multilevel fast multipole algorithm (MLFMA) is combined with the recently introduced potential integral equations (PIEs), also called as the A-φ system, to obtain an efficient and accurate broadband solver that can be used for the solution of electromagnetic scattering from perfectly conducting surfaces over a wide frequency range including low frequencies. The mixed-form MLFMA uses the nondirective stable planewave MLFMA (NSPWMLFMA) at low frequencies and the conventional MLFMA at middle/high frequencies. Various numerical examples are presented to assess the validity, efficiency, and accuracy of the developed solver.Item Open Access Correction to: Active tuning from narrowband to broadband absorbers using a sub-wavelength VO2 embedded layer(Springer, 2021-02-04) Osgouei, Ataollah Kalantari; Hajian, Hodjat; Khalichi, Bahram; Serebryannikov, Andriy E.; Ghobadi, Amir; Özbay, EkmelMetamaterial perfect absorbers (MPAs) with dynamic thermal tuning features are able to control the absorption performance of the resonances, providing diverse applications spanning from optical switches and filters to modulators. In this paper, we propose an MPA with diverse functionalities enabled by vanadium dioxide (VO2) embedded in a metal-dielectric plasmonic structure. For the initial design purpose, a silicon (Si) nanograting on a silver (Ag) mirror is proposed to have multiple resonant responses in the near infrared (NIR) region. Then, the insertion of a thin VO2 layer at the right position enables the design to act as an on/off switch and resonance tuner. In the insulator phase of VO2, in which the permittivity data of VO2 is similar to that of Si, a double strong resonant behavior is achieved within the NIR region. By increasing the temperature, the state of VO2 transforms from insulator to metallic so that the absorption bands turn into three distinct resonant peaks with close spectral positions. Upon this transformation, a new resonance emerges and the existing resonance features experience blue/red shifts in the spectral domain. The superposition of these peaks makes the overall absorption bandwidth broad. Although Si has a small thermo-optic coefficient, owing to strong light confinement in the ultrasmall gaps, a substantial tuning can be achieved within the Si nanogratings. Therefore, the proposed hybrid design can provide multi-resonance tunable features to cover a broad range and can be a promising strategy for the design of linearly thermal-tunable and broadband MPAs. Owing to the proposed double tuning feature, the resonance wavelengths exhibits great sensitivity to temperature, covering a broad wavelength range. Overall, the proposed design strategy demonstrates diverse functionalities enabled by the integration of a thin VO2 layer with plasmonic absorbers.Item Open Access Diode like high-contrast asymmetric transmission of linearly polarized waves based on plasmon-tunneling effect coupling to electromagnetic radiation modes(Institute of Physics Publishing Ltd., 2021-06-25) Khalichi, Bahram; Ghobadi, Amir; Osgouei, Ataollah Kalantari; Özbay, EkmelWe present a narrow-band optical diode with a high-contrast forward-to-backward ratio at the near-infrared region. The design has a forward transmission of approximately $88\% $, and a backward one of less than $3\% $, yielding a contrast ratio of greater than $14.5\,$ dB at a wavelength of $1550\,$ nm. The structure is composed of a one-dimensional diffraction grating on top of a dielectric slab waveguide, both of which are made of silicon nitride (Si3N4), and all together are placed over a silver (Ag) thin film embedded on a dielectric substrate. Utilizing a dielectric-based diffraction grating waveguide on a thin silver layer leads to the simultaneous excitation of two surface plasmon modes known as long- and short-range surface plasmon polaritons (SPPs) at both interfaces of the metallic layer. The plasmon-tunneling effect, which is the result of the coupling of SPPs excited at the upper interface of the metallic layer to the radiation modes, provides a high asymmetric transmission (AT) property. The spectral response of the proposed high-contrast AT device is verified using both rigorous coupled-wave analysis as an analytical approach and finite difference time domain as a numerical one.Item 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, EkmelIn 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.Item Open Access Fast and efficient solutions of multiscale electromagnetic problems(2020-09) Khalichi, BahramFrequency-domain surface integral equations (SIEs) used together with the method of moments (MoM), and/or its accelerated versions, such as the multilevel fast multipole algorithm (MLFMA), are usually the most promising choices in solving electromagnetic problems including perfect electric conductors (PEC). However, the electric-field integral equation (EFIE) (as one of the most popular SIEs) is susceptible to the well-known low-frequency (LF) breakdown problem, which prohibits its use at low frequencies and/or dense discretizations. Although the magnetic-field integral equation (MFIE) is less affected from the LF-breakdown, it is usually criticized for being less accurate, and being applicable only to closed surfaces. In addition, the conventional MLFMA which enables the solution of electrically large problems with an extremely large number of unknowns by reducing the computational complexity for memory requirements and CPU time suffers from the LF breakdown when applied to the geometries with electrically small features. We proposed a mixed-form MLFMA and incorporated it with the recently introduced potential integral equations (PIEs), which are immune to the LF-breakdown problem, to obtain an efficient and accurate broadband solver to analyze electromagnetic scattering/radiation problems from PEC surfaces over a wide frequency range. The mixed-form MLFMA uses the conventional MLFMA at middle/high frequencies and the nondirective stable plane wave MLFMA (NSPWMLFMA) at low frequencies (i.e., electrically small boxes). We demonstrated that the proposed algorithm is accurate enough to be applied for both open and closed surfaces. In addition, we modified and utilized incomplete tree structures in conjunction with the mixed-form MLFMA to have a novel broadband incomplete-leaf (IL) MLFMA (IL-MLFMA) for the fast and accurate solution of multiscale scattering/radiation problems using PIEs. The proposed method is capable of handling multiscale electromagnetic problems containing fine geometrical details in their structures. The algorithm is population based and deploys a nonuniform clustering that enables to use deep levels safely and, when necessary, without compromising the accuracy, and hence the error is controllable. As a result, by using the proposed IL-MLFMA for PIEs (i) the efficiency is improved and (ii) the memory requirements are significantly reduced (order of magnitude) while the accuracy is maintained.Item Open Access Highly one-way electromagnetic wave transmission based on outcoupling of surface plasmon polaritons to radiation modes(Institute of Electrical and Electronics Engineers, 2022-09-21) Khalichi, Bahram; Omam, Zahra Rahimian; Osgouei, Ataollah Kalantari; Ghobadi, Amir; Özbay, EkmelUnidirectional transmission of electromagnetic waves has attracted great interest due to its wide modern optical applications. This study theoretically demonstrates a one-way transmissive optical device with a high-contrast forward-to-backward ratio at the near-infrared region. The polarization-independent optical diode-like mechanism is designed using a metasurface diffraction grating configuration with symmetry breaking property along the wave propagation in which the working principle is based on the excitation of surface plasmon modes at the interfaces of thin metallic interlayer and their coupling to the radiation modes.Item 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, EkmelTraditional 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.Item Open Access Mid-infrared adaptive thermal camouflage using a phase-change material coupled dielectric nanoantenna(Institute of Physics Publishing Ltd., 2021-04-23) Buhara, Ebru; Ghobadi, Amir; Khalichi, Bahram; Kocer, Hasan; Özbay, EkmelRecently, camouflage technology has attracted researchers' attention in a large variety of thermal applications. As a special phase change material (PCM), vanadium dioxide (VO2) is an excellent candidate for the studies conducted on thermal camouflage technology. VO2 has a transition from the insulator phase to the metal phase with the increase of the temperature. With regards to this unique feature, VO2 can contribute dynamic properties to the camouflage design. In this paper, a PCM–dielectric based metamaterial mid-infrared adaptive thermal camouflage nanoantenna is designed to perfectly mimic the atmospheric windows. The adaptive property of the proposed structure is obtained by using an ultrathin VO2 interlayer embedded within the grating. The spectral responses of the structure are computed using the finite difference time domain method, and the invisibility of the structure is proved using power calculations in the different mid-infrared regions.Item Open Access Multi-band light-matter interaction in hBN-based metasurface absorber(Institute of Electrical and Electronics Engineers, 2022-09-28) Omam, Zahra Rahimian; Khalichi, Bahram; Osgouei, Ataollah Kalantari; Ghobadi, Amir; Özbay, EkmelThis paper presents a multi-band metamaterial-based absorber using phononic two-dimensional (2D) material. The structure consists of a top hexagonal boron nitride (hBN) layer on an aluminum nanograting structure deposited on a dielectric slab waveguide and a thick metallic reflector forming an MIM (metal-insulator-metal) configuration. The proposed absorber exhibits a hyperbolic phonon polariton (HPPs) in hBN, surface plasmon (SP) modes in the spacer (ZnTe: zinc telluride), and Fabry-Perot resonances in the MIM configuration, resulting in five sharp, high absorption peaks in the mid-infrared (MIR) spectral range. The proposed multi-band absorber can be utilized in various applications, ranging from optical detection devices to multispectral thermoelectric volt.Item Open Access Nano shell impact on Huygens’ metasurface dipolar resonances and optical response(Optica, 2021-09) Kocer, Hasan; Işık, Halil; Durna, Yılmaz; Khalichi, Bahram; Kurta, Hamza; Özbay, EkmelDue to several advantages over conventional devices for the control of electromagnetic (EM) radiation, the demand for metasurface utilization based on artificially engineered micro and nanostructures is boosted, especially in new generation devices. Among the metasurfaces family, there has been a growing interest in Huygens’ metasur faces that are easy to fabricate due to their lower aspect ratio compared to their counterparts and also provide alternative electromagnetic radiation control by tuning the dipolar electric and magnetic resonances. In this study, an all-dielectric Huygens’ metasurface consisting of the high-refractive-index nano shells embedded in the low-refractive-index environment is designed and extensively investigated numerically and analytically in the near infrared spectrum. By simply tuning the nano shell inner radius, the effects on the dipolar resonances are unveiled specific to the proposed design. To assess the EM wave interactions in the designed Huygens’ metasurface, an ana lytical model based on the coupled discrete dipole approach is applied for selected distinct cases of the designed metasurface. It is shown that the spectral position of the dipolar resonances can be detuned or tuned simultaneously depending on the structural parameter of the meta-atoms arranged in a periodic array. This study sheds light on the physics and abilities of the nano shell structure as a Huygens’ metasurface for the potential applications of metasurface-based light–matter interaction including imaging and sensing.Item 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, EkmelOptical 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.Item Open Access Polarization insensitive phase change material-based nanoantenna array for thermally tunable infrared applications(Institute of Electrical and Electronics Engineers, 2022-09-21) Khalichi, Bahram; Omam, Zahra Rahimian; Osgouei, Ataollah Kalantari; Ghobadi, Amir; Özbay, EkmelThermal radiation management is an emerging application of metamaterials owing to their exotic electromagnetic radiative properties. Herein, a thermally tunable phase change material-based nanoantenna array is reported to manipulate electromagnetic waves for potential applications in radiative cooling and multispectral camouflage from thermal infrared detectors. The simulation results show that the proposed nanoantenna array possesses high reflectance exceeding at least 60% within the 3−5 µm and 8−12 µm wavelength ranges, indicating low thermal emissivity, while the reflectance value increases as the temperature rises. Additionally, the wavelength-selective nanoantenna emitter operates with high absorption and therefore emission within the non-atmospheric window (5−8 µm). The thermally tuning feature leads to further controlling the absorption and, therefore, the emission performance of the nanoantenna and corresponding infrared signatures detected by thermal cameras.Item Open Access A spectrally selective gap surface-plasmon-based nanoantenna emitter compatible with multiple thermal infrared applications(Institute of Physics Publishing Ltd., 2021-08-20) Osgouei, Ataollah Kalantari; Ghobadi, Amir; Khalichi, Bahram; Özbay, EkmelWavelength-selective nanoantenna emitters have attracted considerable attention due to their widespread applications ranging from thermal radiation management to thermophotovoltaics. In this paper, we design a wavelength-selective nanoantenna emitter based on the excitation of gap-surface plasmon modes using a metal–insulator–metal configuration (silicon dioxide (SiO2) sandwiched between silver (Ag) layers) for satisfying multiple infrared applications. The proposed design, which is called design I, realizes triple narrowband perfect absorptions at the resonance wavelengths of 1524nm,2279nm, and 6000nm, which perfectly match the atmospheric absorption bands while maintaining relatively low emissivity in the atmospheric transparency windows of 3-5 µm and 8-12 µm. Later, the functionality of design I is extended, which is called design II, to include a broadband absorption at the near-infrared region to minimize the solar irradiation reflection from the nanoantenna emitter. Finally, single- and three-layer graphene are introduced to provide a real-time tuning of the infrared signature of the proposed nanoantenna emitter (design II). It is also demonstrated that the three-layer graphene structure can suppress an undesired absorption resonance wavelength related to the intrinsic vibrational modes (optical phonons) of the SiO2 layer by 53.19% compared to 25.53% for the single-layer one. The spectral analysis of design I is validated using both analytical and numerical approaches where the numerical simulation domain is extended for the analysis of design II. The thermal characteristic analyses of design I and design II (without/with graphene layers) reveal that infrared signatures of the blackbody radiation are significantly reduced for the whole wavelength spectrum at least by 96% and 91% within a wide temperature ranging from room temperature to 500K, respectively.Item Open Access A Transmissive all-dielectric metasurface-based nanoantenna array for selectively manipulation of thermal radiation(Institute of Electrical and Electronics Engineers, 2022-09-21) Khalichi, Bahram; Omam, Zahra Rahimian; Osgouei, Ataollah Kalantari; Ghobadi, Amir; Özbay, EkmelIn this study, a wavelength-selective thermal nanoantenna emitter based on metamaterial design with heat radiation signature management and radiative cooling property is proposed. The design can be considered as a multifunctional window by reducing the heat signature and releasing the heat energy within the non-atmospheric window. The approach relies on the indium tin oxide cubic-shaped unit cell coated on a flexible and transparent substrate (polystyrene). The spectral behaviors of the proposed structure are obtained using the finite difference time domain method, where the power calculation model is utilized to demonstrate the radiative cooling efficiency and low power detection on infrared cameras.Item Open Access Uncovering the non-radiative thermal characteristics of a passive radiative cooler under real operating conditions(Institute of Physics Publishing Ltd., 2022-12-12) Koçer, Hasan; Durna, Yılmaz; Işık, Halil; Soydan, Mahmut Can; Khalichi, Bahram; Ghobadi, Amir; Kurt, H.; Özbay, EkmelPassive radiative cooling (PasRadCool), which emits thermal energy from objects to deep cold space through atmospheric transparency, offers complementary and alternative green energy solutions for passive cooling of buildings, clothing, and renewable energy harvesting. Depending on the spectral emissive/absorptive properties of the unit under test (UUT), radiative heat exchanges occur between the UUT, atmosphere, and sun, while at the same time non-radiative heat exchange occurs. The performance of the PasRadCool is determined by the combined thermal and thermodynamic effects of both exchange mechanisms. Although the non-radiative heat exchange, which consists of conductive and convective processes to the outer surfaces of the UUT and the surrounding air fluid, is very sensitive to environmental changes, the actual performance is not fully determined since this feature is considered statically in many studies. Herein, we propose a method that reveals the non-radiative thermal characteristics of the PasRadCool under real operating conditions. With a photonic radiative cooler structure, which we manufacture as a proof of concept, we perform nighttime field test measurements in varying non-radiative thermal conditions. The proposed method extracts the time-dependent non-radiative heat transfer coefficient of the UUT as accurately as possible. We also confirm that our experimental result shows good agreement with both numerical and analytical methods. The proposed approach, which highlights the realistic thermal management of PasRadCool, is not specific to the circumstances of our study and can be applied to all PasRadCool situations with different geometry, material, and environmental conditions.Item Open Access Visible light metasurface for adaptive photodetection(Institute of Physics Publishing Ltd., 2022-10-05) Osgouei, Ataollah Kalantari; Ghobadi, Amir; Khalichi, Bahram; Sabet, Rana Asgari; Tokel, Onur; Özbay, EkmelSemiconductor-based sub-wavelength metasurfaces are promising device platforms for the realization of optically thick and electrically thin photodetectors. Strong light–matter interactions in ultrathin film regions provide an opportunity to achieve near-unity absorption in dimensions comparable with carrier diffusion length and this, in turn, leads to an efficient collection of photogenerated carriers. Moreover, the use of phase change materials can provide real-time active tuning of optical responses of metasurface-based devices. In the first part of this paper, a tunable color filtering device is demonstrated using a metasurface design made of sub-wavelength antimony trisulphide (Sb2S3) grating placed on top of a continuous silver layer. Four distinct optical states can be acquired upon (a) the changes in the incident light polarization and (b) the phase transitions of Sb2S3. Numerical simulations and theoretical modeling data show that Fabry–Perot resonances are the driving phenomena when the proposed design is normally illuminated by an electromagnetic field with transverse electric polarization. In contrast, surface plasmon resonances are excited in transverse magnetic polarization. Furthermore, it is shown that the resonance wavelengths of the proposed design can be dynamically tuned using the geometrical parameters. Later, in the second part of the paper, adaptive photodetection is designed by integrating a $5\,$ nm Sb2S3 layer as a collection layer into the structure. The proposed metasurface design provides light–matter interaction in the Sb2S3 layer and maximizes the photogenerated carriers' collection efficiency. The optically thick and electrically thin adaptive photodetection offers an opportunity to design efficient active optoelectronic and photonic devices.Item Open Access A wavelength-selective multilayer absorber for heat signature control(Institute of Electrical and Electronics Engineers, 2022-09-28) Osgouei, Ataollah Kalantari; Khalichi, Bahram; Omam, Zahra Rahimian; Ghobadi, Amir; Özbay, EkmelEngineering the thermal radiation using wavelength-selective thermal emitters is of great importance in the field of thermophotovoltaics, radiative cooling, and heat signature control. In this paper, a wavelength-selective Vanadium/Germanium (V/Ge) multilayer absorber is demonstrated. The proposed design realizes a perfect absorption at the resonance wavelength of 5870 nm, placed within the nonatmospheric window (5-8 μ m) while maintaining low absorptivity within the atmospheric windows. It is verified that the proposed emitter represents angle insensitive feature for oblique incidence up to 60° for both transverse magnetic (TM) and transverse electric (TE) polarizations.