| 1. |
- Eskandari, Hossein, et al.
(author)
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Design of an Impedance-Matched Horn Antenna with Enhanced Directivity Using Conformal Transformation Optics
- 2020
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In: 2020 14th European Conference on Antennas and Propagation (EuCAP). - : Institute of Electrical and Electronics Engineers (IEEE).
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Conference paper (peer-reviewed)abstract
- In this work, conformal transformation optics is employed to enhance the directivity of a horn antenna. The phase error at the horn's aperture is mitigated using a dielectric graded-index lens designed by the conformal transformation. The design not only leads to a negligible phase error at the aperture but also has an excellent impedance match to the vacuum. Simulation results show that for a typical horn antenna with length and aperture width equal to ten wavelengths, our method can enhance the directivity more than 5 dB.
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| 2. |
- Eskandari, Hossein, et al.
(author)
-
Design of Nonmagnetic All-mode Waveguide Coupler with Perfect Transmission Using Transformation Optics
- 2019
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In: 13th European Conference on Antennas and Propagation, EuCAP 2019. - : Institute of Electrical and Electronics Engineers (IEEE). - 9788890701887
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Conference paper (peer-reviewed)abstract
- Using the transformation optics method together with the basic properties of Maxwell equations, a compact nonmagnetic waveguide coupler is designed that can ideally couple all TMn modes. Two compression functions are proposed to provide a perfect smooth transition between the waveguides. This coupler can be used to guide and compress a vacuumfilled waveguide to a smaller waveguide with a predefined higher dielectric constant inside. The design method is validated by simulated examples using COMSOL Multiphysics.
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| 3. |
- Eskandari, Hossein, et al.
(author)
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Elliptical generalized Maxwell fish-eye lens using conformal mapping
- 2019
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In: New Journal of Physics. - : Institute of Physics Publishing (IOPP). - 1367-2630. ; 21
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Journal article (peer-reviewed)abstract
- A circular graded index lens is conformally transformed to an elliptical shape using a closed-form transformation. The proposed transformation is then employed to compress a Maxwell fish-eye and its generalized version. Since the transformation is conformal, the electromagnetic properties of the device are perfectly preserved after the transformation with fully isotropic and dielectric-only materials. Ray-tracing and full-wave simulations are carried out for several cases to verify the functionality of the optically transformed lenses in geometrical optics and wave optics regimes.
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| 4. |
- Eskandari, Hossein, et al.
(author)
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Extended two dimensional transformation optics for reflection suppression
- 2019
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In: The 10th International Conference on Metamaterials, Photonic Crystals and Plasmonics, META 2019. - : META Conference. ; , s. 1383-1384
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Conference paper (peer-reviewed)abstract
- Here, we demonstrate that by extending the common twodimensional (2D) transformation optics (TO) to the third dimension in an engineered fashion, it is possible to eliminate unwanted reflections from the device boundaries in cases where the compression or expansion of the space makes the ideal transmission of the power impossible in the common formulation. The feasibility of the proposed idea is demonstrated by an example simulated in COMSOL.
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| 5. |
- Eskandari, Hossein, et al.
(author)
-
H-plane horn antenna with enhanced directivity using conformal transformation optics
- 2021
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In: Scientific Reports. - : Springer Nature. - 2045-2322. ; 11:1
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Journal article (peer-reviewed)abstract
- Conformal transformation optics is employed to enhance an H-plane horn's directivity by designing a graded-index all-dielectric lens. The transformation is applied so that the phase error at the aperture is gradually eliminated inside the lens, leading to a low-profile high-gain lens antenna. The physical space shape is modified such that singular index values are avoided, and the optical path inside the lens is rescaled to eliminate superluminal regions. A prototype of the lens is fabricated using three-dimensional printing. The measurement results show that the realized gain of an H-plane horn antenna can be improved by 1.5-2.4 dB compared to a reference H-plane horn.
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| 6. |
- Eskandari, Hossein, et al.
(author)
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Transformation optics for perfect two-dimensional non-magnetic all-mode waveguide couplers
- 2019
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In: Optical Materials Express. - : OPTICAL SOC AMER. - 2159-3930 .- 2159-3930. ; 9:3, s. 1320-1332
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Journal article (peer-reviewed)abstract
- Here, we demonstrate that transformation optics can be used to produce 2-D non-magnetic waveguide couplers with no reflections. Our approach consists of using a scaling function for reflection suppression and introducing an auxiliary function in the transformation optics formulation to achieve a non-magnetic medium for coupling the TM polarization. To demonstrate the potential of this method, two non-magnetic waveguide couplers are designed. The first one satisfies the Brewster angle condition for any arbitrary incidence angle (TMn modes), extending the performance of couplers previously reported in the literature that only operate for TEM (TM0 mode), i.e. waves with normal incidence. Our method can be applied to match any given dielectric constant. Our results demonstrate that for a given mode (angle), we achieve a perfect match to a defined dielectric constant. The second design removes the dependence of the reflectionless condition to the incident angle at the boundary. Hence, this coupler works for all incident angles (TMn modes). It is used to compress all the modes into a region with a higher predefined refractive index.
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| 7. |
- Khoun Jahan, Hossein, et al.
(author)
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A Limited Common-Mode Current Switched-Capacitor Multilevel Inverter Topology and Its Performance and Lifetime Evaluation in Grid-Connected Photovoltaic Applications
- 2021
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In: Energies. - : MDPI AG. - 1996-1073. ; 14:7
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Journal article (peer-reviewed)abstract
- In this paper, a switched-capacitor multilevel inverter with voltage boosting and common-mode-voltage reduction capabilities is put forth. The proposed inverter is synthesized with one-half bridge and several switched-capacitor cells. Due to the voltage boosting and common-mode current reduction features, the proposed multilevel inverter is suitable for grid-connected PV applications. In addition, an analytical lifetime evaluation based on mission profile of the proposed inverter has been presented to derive lifetime distribution of semiconductors. Whereas in the proposed inverter, any components failure can bring the whole system to a shutdown. The series reliability model is used to estimate the lifetime of the overall system. The performance of the suggested multilevel inverter in grid-connected applications is verified through the simulation results using the grid-tied model in Matlab/Simulink. Moreover, the viability and feasibility of the presented inverter are proven by using a one kW lab-scaled prototype.
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