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The strength of all-ceramic restorations depends on not only properties of basic material but also used ceramic material, substructure and upper structure connection, the thickness of crown, design, and bonding technique of restoration. The purpose of this study is to analyze the shear stress between the zirconia core and silica-based ceramic by using the finite element method. Using 20-node structural solid elements, the shear stresses were calculated with the methods of shear test and Schmitz-Schulmeyer test through 3-dimensional finite element method. The commercial software Ansys (Ansys Version 11.0, ANSYS, Inc., Canonsburg, PA 15317, USA) was used to create a three-dimensional mesh. There is no significant difference between the test methods as a result of the force applied close to the bond interface. However, when moving away from the bond interface, it is understood that there is a failure in higher tensile forces. It was determined that there was no significant difference in the results when the force to be applied in both the Shear bond Test and Schmitz-Schulmeyer tests was performed the near interface of Zirconia core-Silica based veneer ceramic

Conference Name: International Conference on Electromagnetics in Advanced Applications (ICEAA) Date of Conference: 05-09 September 2022 Engineering 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.

Conference Name: Antennas and Propagation Society International Symposium Date of conference: 10-15 July 2022 In 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.

Conference Name: Antennas and Propagation Society International Symposium Date of Conference: 10-15 July 2022 Thermal 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.

For the first time, the effect of the gate structure on the kink phenomenon in S22 of the AlGaN/GaN HEMT is investigated in this study. To provide critical understanding into the S22 kink effect, the kink effect in S22 of the AlGaN/GaN HEMTs is investigated with transistors that have various gate lengths (Lg) and gate connected field plate lengths (LgH). The HEMTs are fabricated and characterised at the same conditions, and the equivalent circuit models are used to get consistent results. The experimental results show that the gate structure can play an important role on kink effect in S22. The results present valuable information on the development of the AlGaN/GaN HEMT technology and the MMIC design regarding kink effect.

Conference Name: 6th International Conference on Competitive Materials and Technology Processes, IC-CMTP 2021 and 2nd European Conference on Silicon and Silica Based Materials, EC-SILICONF 2021 Date of Conference: 4 - 8 October 2021 The structural, mechanical, and electronic properties of Perovskite BaIrO3 and SrIrO3 compounds based on the density functional theory (DFT) have been examined in four different structures (C2/c, R-3m, P6_3/mmc and Pm-3m) and Pnma structure, respectively. The spin polarized generalized gradient approximation has been used for modeling exchange-correlation effects. As a result of spin polarized calculations, it has been observed that BaIrO3 compound showed magnetic properties in C2/c and R-3m structures, but not in Pm-3m and P6_3/mmc structures. SrIrO3 compound also shows magnetic properties in Pnma structure. The elastic constants have been calculated using the strain-stress method and the other related quantities (the bulk modulus, shear modulus, Young's modulus, Poisson's ratio, anisotropy factor, sound velocities, and Debye temperature) have also been estimated. In electronic band structure calculations, while Pm-3m and P6_3/mmc structures of NaIrO3 compound are metallic and semiconductor (Eg = 1.190 eV indirect), respectively, while C2/c and R-3m structures showing magnetic properties are metallic in spin down state and semiconductor (Eg=0.992 eV indirect and Eg=0.665 eV direct, respectively) in the spin up state. The Pmna structure in the SrIrO3 compound is a semiconductor in both spin states (Eg=0.701 eV “0.632 eV” indirect in the spin up “spin down”). © 2022 Institute of Physics Publishing. All rights reserved.

We propose a black phosphorus-silicon carbide (BP-SiC) metasurface with in-plane structural symmetry that can act as both a nearly perfect anisotropic absorber and tunable polarized source of mid-infrared (MIR) radiation. The metasurface is a periodic array of square SiC patches integrated with a BP flake at the top and separated from a bottom reflector by a BaF2 spacer. We first use analytical calculations and numerical simulations to study the hybridization of the anisotropic plasmons of BP with isotropic phonons of SiC. We also analyze the in-plane characteristics of the resulting hybrid modes of the BP/SiC heterostructure and the BP-SiC metasurface. It is then demonstrated that the proposed metasurface can serve as a nearly perfect anisotropic absorber of MIR radiation with highly selective and omnidirectional features. It is also shown that the metasurface can be used as a polarized MIR source with tunable temperature, which is determined by the thermal equilibrium between the matter and radiation. The suggested design holds promise for artificial coatings that can tune the blackbody thermal signatures, MIR sensing, and highly directional in-plane transportation of the MIR energy.

Conference Name: Proceedings of the 15th European Microwave Integrated Circuits Conference Date of Conference A new method to simulate the large-signal behaviour of GaN HEMTs is presented along with the two 15W X-band MMIC Class AB power amplifier (PA) designs using the same methodology. Proposed modeling approach is based on curve-fitting transistor performance parameters in the load impedance plane, while transistor’s behaviour in the source impedance space is calculated using a virtual source-pull technique. Good agreement with the results of two fabricated GaN PA MMICs demonstrate the accuracy of the method in simulating Pout , Gt and PAE of the amplifiers at any given compression level. This approach is distinguished from conventional modeling methods with its minimal measurement requirements, ease of model development, and generic nature while accurately predicting the large-signal response, thus is suitable to use for PA design, under the lack of a more comprehensive transistor model.

In this work, we performed a systematic study on a hybrid plasmonic system to elucidate a new insight into the mechanisms governing the fluorescent enhancement process. Our lithographically defined plasmonic nanodisks with various diameters act as receiver and transmitter nano-antennas to outcouple efficiently the photoluminescence of the coupled dye molecules. We show that the enhancement of the spontaneous emission rate arises from the superposition of three principal phenomena: (i) metal enhanced fluorescence, (ii) metal enhanced excitation and (iii) plasmon-modulated photoluminescence of the photoexcited nanostructures. Overall, the observed enhanced emission is attributed to the bi-directional near-field coupling of the fluorescent dye molecules to the localized plasmonic field of nano-antennas. We identify the role of exciton-plasmon coupling in the recombination rate of the sp-band electrons with d-band holes, resulting in the generation of particle plasmons. According to our comprehensive experimental analyses, the mismatch between the enhanced emission and the emission spectrum of the uncoupled dye molecules is attributed to the plasmon-modulated photoluminescence of the photoexcited hybrid plasmonic system. publishedVersion

In this study, AlInN/AlN high electron mobility transistor (HEMT) structure is grown on c-oriented sapphire substrate using metal organic chemical vapor deposition method. Optical properties of the structure are investigated by photoluminescence (PL) and ultraviolet (UV–Vis.) spectras. According to PL results, direct bandgap of AlN is determined around 2.80 eV. In UV–Vis. spectra it is seen that conduction of AlInN layer starts at 360 nm. Swanepoel envelope method is applied on transmission spectra and some optical properties such as refractive index (n), film thickness (t), absorption coefficient (α), and extinction coefficient (k) are determined. Forbidden energy bandgap is determined again from Tau method and it is compared with the value gained from PL spectra. This study is a rare one that presents optical properties of HEMTs using Swanepoel and Tau methods. In addition to this, it helps estimating how optical properties of HEMTs effect electrical properties.