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Papers by zahra atlasbaf

IEEE Microwave and Wireless Components Letters, 2017

A three-step unconditionally stable locally 1-D approach is proposed, representing a dispersive a... more A three-step unconditionally stable locally 1-D approach is proposed, representing a dispersive anisotropic magnetized plasma medium. The accuracy and stability of the method are verified through simulation of wave propagation in a microwave cavity partially filled with a plasma slab. Finally, Faraday rotation across a plasma slab is simulated by the proposed method.

Comb-like behavior of the multilayered graphene wrapped nanotubes in multiple scattering channels is investigated and utilized to design a structure for simultaneous super-scattering and super-cloaking. The underlying physics of the proposed structure is studied quantitatively by geometric interp..., 2019

Comb-like behavior of the multilayered graphene wrapped nanotubes in multiple scattering channels... more Comb-like behavior of the multilayered graphene wrapped nanotubes in multiple scattering channels is investigated and utilized to design a structure for simultaneous super-scattering and super-cloaking. The underlying physics of the proposed structure is studied quantitatively by geometric interpretation through the associated planar structure based on the Bohr model and Foster's theorem. We observed that due to the presence of multiple dispersion bands in the planar counterpart, each cylindrical scattering Mie coefficient fulfills the resonance and invisibility conditions multiple times, depending on the selected number of layers. By refining the material and geometric parameters for the specified number of layers, resonances and zeros of the first two scattering terms are coincided simultaneously to observe super-scattering and super-cloaking, respectively. The proposed structure has lots of degrees of freedom to control the response in the operating frequency.

Journal of Electromagnetic Waves and Applications, 2008

In this paper, we present a new planar waveguide-fed ultra wideband (UWB) antenna. This antenna i... more In this paper, we present a new planar waveguide-fed ultra wideband (UWB) antenna. This antenna is designed for 50 Ω feed on a loss less glass as a substrate. The impedance bandwidth with VSWR < 2 is from about 4.4 GHz to more than 12 GHz in simulation results but from 3.8 GHz to about 11.5 GHz in measurement. This Antenna also has a directional gain pattern. Other important features of this antenna are its high gain and directivity as well as its easy shape to design. The reliable full wave simulation analysis by HFSS and CST Microwave Studio show that this novel structure can easily realize a good linear variation for the sweep gain as well as high directivity within a controllable bandwidth.

electromagnetics, 2011

This article presents a new miniaturized reconfigurable slotted microstrip patch antenna with def... more This article presents a new miniaturized reconfigurable slotted microstrip patch antenna with defected ground structure. The antenna operates in two different frequency bands with polarization pattern diversity and broad radiation characteristics. The size reduction of this antenna is more than 34% in comparison to a conventional rectangular patch antenna for two frequency bands. Details of the experimental results are presented and discussed.

IEEE Antennas and Wireless Propagation Letters, 2020

Two compact ultrawideband antennas with different values of fidelity factors are introduced in th... more Two compact ultrawideband antennas with different values of fidelity factors are introduced in this letter to study the impact of the fidelity factor on the tumor detection of microwave imaging systems. The design procedures are based on achieving the largest possible bandwidth. Antenna 1 (Ant. 1) and Antenna 2 (Ant. 2) have an overall size of 20 × 28 mm 2 and 16 × 22 mm 2 , respectively. Two arrays of the proposed antenna are utilized for breast cancer detection. Two 12-element arrays of the antennas are located around a breast tissue model in two scenarios. The results show the promising performance of Ant. 2, which has a higher fidelity factor in detecting a 4 mm tumor. The investigation was also carried out on a clinical tumor model, and Ant. 2 successfully detected it.

Electromagnetics, 2011

This article presents a new miniaturized reconfigurable slotted microstrip patch antenna with def... more This article presents a new miniaturized reconfigurable slotted microstrip patch antenna with defected ground structure. The antenna operates in two different frequency bands with polarization pattern diversity and broad radiation characteristics. The size reduction of this antenna is more than 34% in comparison to a conventional rectangular patch antenna for two frequency bands. Details of the experimental results are presented and discussed.

IEEE Antennas and Wireless Propagation Letters, 2020

Two compact ultrawideband antennas with different values of fidelity factors are introduced in th... more Two compact ultrawideband antennas with different values of fidelity factors are introduced in this letter to study the impact of the fidelity factor on the tumor detection of microwave imaging systems. The design procedures are based on achieving the largest possible bandwidth. Antenna 1 (Ant. 1) and Antenna 2 (Ant. 2) have an overall size of 20 × 28 mm 2 and 16 × 22 mm 2 , respectively. Two arrays of the proposed antenna are utilized for breast cancer detection. Two 12-element arrays of the antennas are located around a breast tissue model in two scenarios. The results show the promising performance of Ant. 2, which has a higher fidelity factor in detecting a 4 mm tumor. The investigation was also carried out on a clinical tumor model, and Ant. 2 successfully detected it.

Scientific Reports, 2023

The concept of connected and capacitively coupled dipoles in a planar array, which improves wideb... more The concept of connected and capacitively coupled dipoles in a planar array, which improves wideband performance, is investigated. A long wire with multiple feeds acts as an array in connected arrays, whereas a capacitively coupled array uses capacitors between array elements. Both approaches attempt to approximate the current sheet of Wheeler. Using spectral Green's function, the array active impedance is calculated. The impedance mismatch of a connected/capacitively coupled dipole array is less than that of an array of unconnected dipoles of the same size. Both direct and capacitive connections can be used to design a wideband array antenna with a ground plane, although capacitive coupling performs better than a direct connection. This fact resulted from numerous analytical studies using infinite dipole array scan (active) impedance endorsed by full-wave simulations using CST MWS. The maximum mismatch losses over the frequency band for different source (reference) impedances are used to find the best solution at the broadside. The average reflected power over all scan angles is applied, for the scan performance, and then, the maximum average mismatch loss over the frequency band is investigated. INDEX TERMS Array active impedance, array scan impedance, connected array, tightly-coupled array, wideband array antenna.

Optics Express, Dec 6, 2019

In this paper, a 3D sub-wavelength graphene-coated nano-disk dimer (GDD) is proposed for multi-fr... more In this paper, a 3D sub-wavelength graphene-coated nano-disk dimer (GDD) is proposed for multi-frequency giant near-field enhancement. We observed that the dual-band operation originates from the excitation of hybridized localized surface plasmons on top and bottom faces of the disks along with the mutual coupling from the adjacent particle. Due to the sub-wavelength nature of the disks, the excited localized surface plasmons on the sidewalls are weak but they still can affect the dual operating bands. On the other hand, the strength and resonance frequency of the enhanced fields can be simply modulated by tuning the relative distances of 2D graphene disks on top and bottom faces. Adjustable dual-band performance is hardly attainable using simplified 2D graphene disks, however, it naturally comes out through modal hybridization in the subwavelength 3D structure containing multiple resonant units. Our suggested configuration has better optical properties than its noble metal counterparts because of its higher field enhancement and lower ohmic losses. Moreover, the electromagnetic response is reconfigurable by varying the bias voltage. The influence of graphene quality, chemical potential, and dimer gap size on the electric field enhancement and the resonance frequency of the surface plasmons are investigated, as well. To further improve its performance, a double negative metamaterial core is considered. This mechanism of the performance improvement by the core material is feasible thanks to the 3D nature of the structure. Two possible applications of the presented design are in Surface-Enhanced Raman Spectroscopy (SERS) and optical absorbers.

In this paper; a planar Artificial Magnetic Conductor (AMC) constituted of a metallic grating on ... more In this paper; a planar Artificial Magnetic Conductor (AMC) constituted of a metallic grating on a periodic anisotropic substrate is proposed. The characteristics of this structure are investigated with a full-wave computational technique which utilizes the dyadic Green's function computed by means of an equivalent transmission line (TL) model in the spectral domain. The obtained Green's function is used in an integral equation for the surface electric current on the metallic grating. The integral equation is then solved using the Method of Moments (MoM) with appropriate basis and test functions. With the help of the proposed semi-analytical method, different periodic structures on various substrates are analyzed. To verify the computed results, they are compared with previously published ones. Finally, the phase response of the introduced periodic structure is calculated as a function of the optic axis direction of the anisotropic region within the substrate. It is shown that the proposed metallic grating on the periodic anisotropic substrate can perform as a low-profile and broadband planar AMC at lower frequencies.

Optics Letters, May 2, 2022

In this Letter, we discuss a novel, to the best of our knowledge, approach for designing passive ... more In this Letter, we discuss a novel, to the best of our knowledge, approach for designing passive nanoantennas with maximum forward and almost-zero backward scattering. The proposed approach is based on the use of high-index dielectric spheres supporting dipolar magnetic resonances, which are coated by ultra-thin surface impedance coatings. It is shown that, by properly engineering the radius of the coat and its surface reactance, it is possible to introduce an additional electric dipolar resonance and to make this overlap with the magnetic one sustained by the high-index dielectric sphere. A realistic design that is based on graphene and works in the low-THz range is also proposed and verified with full-wave simulations. Compared to earlier techniques based on the combination of multipoles or on the use of ellipsoidal particles, the proposed one is quite robust toward realistic ohmic losses and preserves the isotropic behavior of the nanoantenna.

IntechOpen eBooks, Mar 14, 2023

Plasmonics, Jan 9, 2022

In this paper, shell-shaped truncated pyramidal unit cells have been used in the design of solar ... more In this paper, shell-shaped truncated pyramidal unit cells have been used in the design of solar cells. The shells are formed by manganese (Mn) transition metal which has very similar constitutive parameters to those of the ideal metal, leading to a compact geometry. To exhibit the potential of Mn material in the solar absorber design, the plasmonic nature of the material is exhibited and the attenuation constant of the illuminating wave is calculated. The outstanding feature of our proposed absorber is its ultra-broad bandwidth, covering the whole solar spectrum with an efficiency above 97%. Ultra broad bandwidth is the consequence of gradual impedance matching thanks to the selected element and transmission elimination using a metallic substrate. Moreover, the utilization of a thin shell along with a hollow element leads to a lightweight device, absorbing the lower band of the spectrum more efficiently. The absorber also covers the ultraviolet region beyond the solar spectrum. The polarization insensitive absorption enhancement is maintained up to the wide incident angles around 60°. The proposed device can be fabricated with current fabrication technologies.

International Journal of Rf and Microwave Computer-aided Engineering, May 27, 2022

Journal of Electromagnetic Waves and Applications, Oct 21, 2020

In this paper, an assembly of substrate mediated graphene-coated cylindrical nano-rods is propose... more In this paper, an assembly of substrate mediated graphene-coated cylindrical nano-rods is proposed as an efficient broadband absorber. Initially, a square lattice of isolated graphene-based particles is considered and a single-band perfect optical absorber is obtained. Then, the possibility of absorption spectrum modulation using the lattice periodicity is illustrated. Moreover, it is exhibited that the performance is stable concerning any polarization state and incident angle up to around 60°. The absorption mechanism relies on the excitation of localized surface plasmon resonances (LSPRs) of various orders on the different sections of the unit cell. Later, the particles are connected through optimized bridges to enhance the operating bandwidth. The bridges also offer the opportunity for the real-time tunability of the absorption spectrum by the electrostatic scheme. The attained absorption band regarding the efficiency of 90% is extended to a 15.43 THz span (18.57-34 THz) using a geometrically simple structure.

Optics Express, Jun 1, 2020

In this paper, a second-order fractal oligomer constructed by graphene-coated cylindrical nano-ro... more In this paper, a second-order fractal oligomer constructed by graphene-coated cylindrical nano-rods is proposed as the unit cell of a wideband optical absorber. Nano-rods have resided on a dielectric substrate with a thick metallic mirror. The fractional bandwidth of the designed structure is 88.67% for the absorption above 90%. Broadband absorption originates from the cooperative excitation of localized surface plasmon resonances (LSPRs) of the bottom, top, and lateral surfaces of the rods, engineered by the geometrical parameters through the fractal concept. Designed full absorber has an acceptable performance concerning the incident angles up to around 35° and it is polarization insensitive. Moreover, broadband absorption can be altered to multi-band performance in the same spectrum with the desired number of frequency bands. This feature is obtained by manipulating the substrate thickness to excite multiple orders of Fabry-Perot cavity resonances. Our proposed structure has potential applications in various optical devices such as filters, sensors, and modulators.

Scientific Reports

Since the recent on-demand applications need more sophisticated circuits and subsystems, componen... more Since the recent on-demand applications need more sophisticated circuits and subsystems, components with configurable capabilities attract attention more than before in commercial systems, specifically the fifth generation (5G). Power dividers play a crucial role in 5G phased array systems, and their role becomes more significant if the output powers ratio is adjustable. Here, we suggest a design methodology by which planar power splitters with arbitrary output power levels can be designed in light of very simple perturbations, i.e., vias. Through our design procedure, we find an optimized pattern for hybrid vias-some of them are made of PEC, and others are dielectric, e.g., air, high-permittivity materials. Thanks to deep neural networks, we demonstrate that this technique can be employed to design power splitters whose output ports have different amplitudes. In light of the proposed method, we fabricated and measured a 4-way power divider realizing Chebyshev coefficients for sidel...

Optics Express, 2021

Due to the increasing interest in emerging applications of graphene or other 2D material-based de... more Due to the increasing interest in emerging applications of graphene or other 2D material-based devices in photonics, a powerful, fast and accurate tool for the analysis of such structures is really in need. In this paper, the semi-analytical method of lines (MoL) is generalized for the diffraction analysis of tunable graphene-based plasmonic devices possessing three dimensional periodicity. We employ Floquet’s theorem to handle analytically propagation of waves in the periodicity of the graphene-dielectric arrays in the direction of the layers stacking. This makes the method very effective in terms of computational time and memory consumption. To validate its efficiency and accuracy, the method is applied to plasmonic devices formed by alternating patterned graphene sheets and dielectric layers. Direct comparison with results available in literature and those obtained by a commercial software exhibits their full consistency.

International Journal of Microwave and Wireless Technologies, 2019

A novel dual-polarization, single-layer reflectarray has been designed and manufactured to operat... more A novel dual-polarization, single-layer reflectarray has been designed and manufactured to operate at receive (20 GHz) and transmit (30 GHz) frequencies for Ka-band terminal antennas. The reflectarray unit cell is composed of several types of resonant elements printed on the upper side of a conductor-backed substrate, which are designed to produce a collimated beam at 20 and 30 GHz in dual polarization. Cross-shaped loops are used to provide the required phases at 20 GHz, while crossed dipoles and modified truncated rings are used to control the phasing at 30 GHz. The resonant lengths of the proposed elements have been adjusted cell by cell by means of a two-dimensional interpolation method to achieve the required phase shift at each frequency. Two different feeds have been used to illuminate the reflectarray at 20 and 30 GHz. The measured gain is 28.02 dBi at 20 GHz and 32.14 dBi at 30 GHz. The measurement results show that the radiation patterns of the designed single-layer reflec...

International Journal of Applied Electromagnetics and Mechanics, 2013

In this paper two novel left-handed composite metamaterials consisting of SRRs, wire and single s... more In this paper two novel left-handed composite metamaterials consisting of SRRs, wire and single sided S-shaped resonators are proposed. One of them is a reduced-size resonator which uses superposition hypothesis to achieve adjacent reso- nances for a much broader negative refraction passband. The other is a modified planar structure with improved electromagnetic coupling and reduced electrical size. Both structures are truly matched to free space in almost whole left-handed frequency band. It will be shown that these metamaterials are robust to the fabrication errors of misalignment printing on both sides of the substrate. The superior performance of these structures are investigated numerically and experimentally and compared with the other split ring resonators. Wedge shape simulation and experimental results confirm the left-handed passband.

IEEE Microwave and Wireless Components Letters, 2017

A three-step unconditionally stable locally 1-D approach is proposed, representing a dispersive a... more A three-step unconditionally stable locally 1-D approach is proposed, representing a dispersive anisotropic magnetized plasma medium. The accuracy and stability of the method are verified through simulation of wave propagation in a microwave cavity partially filled with a plasma slab. Finally, Faraday rotation across a plasma slab is simulated by the proposed method.

Comb-like behavior of the multilayered graphene wrapped nanotubes in multiple scattering channels is investigated and utilized to design a structure for simultaneous super-scattering and super-cloaking. The underlying physics of the proposed structure is studied quantitatively by geometric interp..., 2019

Comb-like behavior of the multilayered graphene wrapped nanotubes in multiple scattering channels... more Comb-like behavior of the multilayered graphene wrapped nanotubes in multiple scattering channels is investigated and utilized to design a structure for simultaneous super-scattering and super-cloaking. The underlying physics of the proposed structure is studied quantitatively by geometric interpretation through the associated planar structure based on the Bohr model and Foster's theorem. We observed that due to the presence of multiple dispersion bands in the planar counterpart, each cylindrical scattering Mie coefficient fulfills the resonance and invisibility conditions multiple times, depending on the selected number of layers. By refining the material and geometric parameters for the specified number of layers, resonances and zeros of the first two scattering terms are coincided simultaneously to observe super-scattering and super-cloaking, respectively. The proposed structure has lots of degrees of freedom to control the response in the operating frequency.

Journal of Electromagnetic Waves and Applications, 2008

In this paper, we present a new planar waveguide-fed ultra wideband (UWB) antenna. This antenna i... more In this paper, we present a new planar waveguide-fed ultra wideband (UWB) antenna. This antenna is designed for 50 Ω feed on a loss less glass as a substrate. The impedance bandwidth with VSWR < 2 is from about 4.4 GHz to more than 12 GHz in simulation results but from 3.8 GHz to about 11.5 GHz in measurement. This Antenna also has a directional gain pattern. Other important features of this antenna are its high gain and directivity as well as its easy shape to design. The reliable full wave simulation analysis by HFSS and CST Microwave Studio show that this novel structure can easily realize a good linear variation for the sweep gain as well as high directivity within a controllable bandwidth.

electromagnetics, 2011

This article presents a new miniaturized reconfigurable slotted microstrip patch antenna with def... more This article presents a new miniaturized reconfigurable slotted microstrip patch antenna with defected ground structure. The antenna operates in two different frequency bands with polarization pattern diversity and broad radiation characteristics. The size reduction of this antenna is more than 34% in comparison to a conventional rectangular patch antenna for two frequency bands. Details of the experimental results are presented and discussed.

IEEE Antennas and Wireless Propagation Letters, 2020

Two compact ultrawideband antennas with different values of fidelity factors are introduced in th... more Two compact ultrawideband antennas with different values of fidelity factors are introduced in this letter to study the impact of the fidelity factor on the tumor detection of microwave imaging systems. The design procedures are based on achieving the largest possible bandwidth. Antenna 1 (Ant. 1) and Antenna 2 (Ant. 2) have an overall size of 20 × 28 mm 2 and 16 × 22 mm 2 , respectively. Two arrays of the proposed antenna are utilized for breast cancer detection. Two 12-element arrays of the antennas are located around a breast tissue model in two scenarios. The results show the promising performance of Ant. 2, which has a higher fidelity factor in detecting a 4 mm tumor. The investigation was also carried out on a clinical tumor model, and Ant. 2 successfully detected it.

Electromagnetics, 2011

This article presents a new miniaturized reconfigurable slotted microstrip patch antenna with def... more This article presents a new miniaturized reconfigurable slotted microstrip patch antenna with defected ground structure. The antenna operates in two different frequency bands with polarization pattern diversity and broad radiation characteristics. The size reduction of this antenna is more than 34% in comparison to a conventional rectangular patch antenna for two frequency bands. Details of the experimental results are presented and discussed.

IEEE Antennas and Wireless Propagation Letters, 2020

Two compact ultrawideband antennas with different values of fidelity factors are introduced in th... more Two compact ultrawideband antennas with different values of fidelity factors are introduced in this letter to study the impact of the fidelity factor on the tumor detection of microwave imaging systems. The design procedures are based on achieving the largest possible bandwidth. Antenna 1 (Ant. 1) and Antenna 2 (Ant. 2) have an overall size of 20 × 28 mm 2 and 16 × 22 mm 2 , respectively. Two arrays of the proposed antenna are utilized for breast cancer detection. Two 12-element arrays of the antennas are located around a breast tissue model in two scenarios. The results show the promising performance of Ant. 2, which has a higher fidelity factor in detecting a 4 mm tumor. The investigation was also carried out on a clinical tumor model, and Ant. 2 successfully detected it.

Scientific Reports, 2023

The concept of connected and capacitively coupled dipoles in a planar array, which improves wideb... more The concept of connected and capacitively coupled dipoles in a planar array, which improves wideband performance, is investigated. A long wire with multiple feeds acts as an array in connected arrays, whereas a capacitively coupled array uses capacitors between array elements. Both approaches attempt to approximate the current sheet of Wheeler. Using spectral Green's function, the array active impedance is calculated. The impedance mismatch of a connected/capacitively coupled dipole array is less than that of an array of unconnected dipoles of the same size. Both direct and capacitive connections can be used to design a wideband array antenna with a ground plane, although capacitive coupling performs better than a direct connection. This fact resulted from numerous analytical studies using infinite dipole array scan (active) impedance endorsed by full-wave simulations using CST MWS. The maximum mismatch losses over the frequency band for different source (reference) impedances are used to find the best solution at the broadside. The average reflected power over all scan angles is applied, for the scan performance, and then, the maximum average mismatch loss over the frequency band is investigated. INDEX TERMS Array active impedance, array scan impedance, connected array, tightly-coupled array, wideband array antenna.

Optics Express, Dec 6, 2019

In this paper, a 3D sub-wavelength graphene-coated nano-disk dimer (GDD) is proposed for multi-fr... more In this paper, a 3D sub-wavelength graphene-coated nano-disk dimer (GDD) is proposed for multi-frequency giant near-field enhancement. We observed that the dual-band operation originates from the excitation of hybridized localized surface plasmons on top and bottom faces of the disks along with the mutual coupling from the adjacent particle. Due to the sub-wavelength nature of the disks, the excited localized surface plasmons on the sidewalls are weak but they still can affect the dual operating bands. On the other hand, the strength and resonance frequency of the enhanced fields can be simply modulated by tuning the relative distances of 2D graphene disks on top and bottom faces. Adjustable dual-band performance is hardly attainable using simplified 2D graphene disks, however, it naturally comes out through modal hybridization in the subwavelength 3D structure containing multiple resonant units. Our suggested configuration has better optical properties than its noble metal counterparts because of its higher field enhancement and lower ohmic losses. Moreover, the electromagnetic response is reconfigurable by varying the bias voltage. The influence of graphene quality, chemical potential, and dimer gap size on the electric field enhancement and the resonance frequency of the surface plasmons are investigated, as well. To further improve its performance, a double negative metamaterial core is considered. This mechanism of the performance improvement by the core material is feasible thanks to the 3D nature of the structure. Two possible applications of the presented design are in Surface-Enhanced Raman Spectroscopy (SERS) and optical absorbers.

In this paper; a planar Artificial Magnetic Conductor (AMC) constituted of a metallic grating on ... more In this paper; a planar Artificial Magnetic Conductor (AMC) constituted of a metallic grating on a periodic anisotropic substrate is proposed. The characteristics of this structure are investigated with a full-wave computational technique which utilizes the dyadic Green's function computed by means of an equivalent transmission line (TL) model in the spectral domain. The obtained Green's function is used in an integral equation for the surface electric current on the metallic grating. The integral equation is then solved using the Method of Moments (MoM) with appropriate basis and test functions. With the help of the proposed semi-analytical method, different periodic structures on various substrates are analyzed. To verify the computed results, they are compared with previously published ones. Finally, the phase response of the introduced periodic structure is calculated as a function of the optic axis direction of the anisotropic region within the substrate. It is shown that the proposed metallic grating on the periodic anisotropic substrate can perform as a low-profile and broadband planar AMC at lower frequencies.

Optics Letters, May 2, 2022

In this Letter, we discuss a novel, to the best of our knowledge, approach for designing passive ... more In this Letter, we discuss a novel, to the best of our knowledge, approach for designing passive nanoantennas with maximum forward and almost-zero backward scattering. The proposed approach is based on the use of high-index dielectric spheres supporting dipolar magnetic resonances, which are coated by ultra-thin surface impedance coatings. It is shown that, by properly engineering the radius of the coat and its surface reactance, it is possible to introduce an additional electric dipolar resonance and to make this overlap with the magnetic one sustained by the high-index dielectric sphere. A realistic design that is based on graphene and works in the low-THz range is also proposed and verified with full-wave simulations. Compared to earlier techniques based on the combination of multipoles or on the use of ellipsoidal particles, the proposed one is quite robust toward realistic ohmic losses and preserves the isotropic behavior of the nanoantenna.

IntechOpen eBooks, Mar 14, 2023

Plasmonics, Jan 9, 2022

In this paper, shell-shaped truncated pyramidal unit cells have been used in the design of solar ... more In this paper, shell-shaped truncated pyramidal unit cells have been used in the design of solar cells. The shells are formed by manganese (Mn) transition metal which has very similar constitutive parameters to those of the ideal metal, leading to a compact geometry. To exhibit the potential of Mn material in the solar absorber design, the plasmonic nature of the material is exhibited and the attenuation constant of the illuminating wave is calculated. The outstanding feature of our proposed absorber is its ultra-broad bandwidth, covering the whole solar spectrum with an efficiency above 97%. Ultra broad bandwidth is the consequence of gradual impedance matching thanks to the selected element and transmission elimination using a metallic substrate. Moreover, the utilization of a thin shell along with a hollow element leads to a lightweight device, absorbing the lower band of the spectrum more efficiently. The absorber also covers the ultraviolet region beyond the solar spectrum. The polarization insensitive absorption enhancement is maintained up to the wide incident angles around 60°. The proposed device can be fabricated with current fabrication technologies.

International Journal of Rf and Microwave Computer-aided Engineering, May 27, 2022

Journal of Electromagnetic Waves and Applications, Oct 21, 2020

In this paper, an assembly of substrate mediated graphene-coated cylindrical nano-rods is propose... more In this paper, an assembly of substrate mediated graphene-coated cylindrical nano-rods is proposed as an efficient broadband absorber. Initially, a square lattice of isolated graphene-based particles is considered and a single-band perfect optical absorber is obtained. Then, the possibility of absorption spectrum modulation using the lattice periodicity is illustrated. Moreover, it is exhibited that the performance is stable concerning any polarization state and incident angle up to around 60°. The absorption mechanism relies on the excitation of localized surface plasmon resonances (LSPRs) of various orders on the different sections of the unit cell. Later, the particles are connected through optimized bridges to enhance the operating bandwidth. The bridges also offer the opportunity for the real-time tunability of the absorption spectrum by the electrostatic scheme. The attained absorption band regarding the efficiency of 90% is extended to a 15.43 THz span (18.57-34 THz) using a geometrically simple structure.

Optics Express, Jun 1, 2020

In this paper, a second-order fractal oligomer constructed by graphene-coated cylindrical nano-ro... more In this paper, a second-order fractal oligomer constructed by graphene-coated cylindrical nano-rods is proposed as the unit cell of a wideband optical absorber. Nano-rods have resided on a dielectric substrate with a thick metallic mirror. The fractional bandwidth of the designed structure is 88.67% for the absorption above 90%. Broadband absorption originates from the cooperative excitation of localized surface plasmon resonances (LSPRs) of the bottom, top, and lateral surfaces of the rods, engineered by the geometrical parameters through the fractal concept. Designed full absorber has an acceptable performance concerning the incident angles up to around 35° and it is polarization insensitive. Moreover, broadband absorption can be altered to multi-band performance in the same spectrum with the desired number of frequency bands. This feature is obtained by manipulating the substrate thickness to excite multiple orders of Fabry-Perot cavity resonances. Our proposed structure has potential applications in various optical devices such as filters, sensors, and modulators.

Scientific Reports

Since the recent on-demand applications need more sophisticated circuits and subsystems, componen... more Since the recent on-demand applications need more sophisticated circuits and subsystems, components with configurable capabilities attract attention more than before in commercial systems, specifically the fifth generation (5G). Power dividers play a crucial role in 5G phased array systems, and their role becomes more significant if the output powers ratio is adjustable. Here, we suggest a design methodology by which planar power splitters with arbitrary output power levels can be designed in light of very simple perturbations, i.e., vias. Through our design procedure, we find an optimized pattern for hybrid vias-some of them are made of PEC, and others are dielectric, e.g., air, high-permittivity materials. Thanks to deep neural networks, we demonstrate that this technique can be employed to design power splitters whose output ports have different amplitudes. In light of the proposed method, we fabricated and measured a 4-way power divider realizing Chebyshev coefficients for sidel...

Optics Express, 2021

Due to the increasing interest in emerging applications of graphene or other 2D material-based de... more Due to the increasing interest in emerging applications of graphene or other 2D material-based devices in photonics, a powerful, fast and accurate tool for the analysis of such structures is really in need. In this paper, the semi-analytical method of lines (MoL) is generalized for the diffraction analysis of tunable graphene-based plasmonic devices possessing three dimensional periodicity. We employ Floquet’s theorem to handle analytically propagation of waves in the periodicity of the graphene-dielectric arrays in the direction of the layers stacking. This makes the method very effective in terms of computational time and memory consumption. To validate its efficiency and accuracy, the method is applied to plasmonic devices formed by alternating patterned graphene sheets and dielectric layers. Direct comparison with results available in literature and those obtained by a commercial software exhibits their full consistency.

International Journal of Microwave and Wireless Technologies, 2019

A novel dual-polarization, single-layer reflectarray has been designed and manufactured to operat... more A novel dual-polarization, single-layer reflectarray has been designed and manufactured to operate at receive (20 GHz) and transmit (30 GHz) frequencies for Ka-band terminal antennas. The reflectarray unit cell is composed of several types of resonant elements printed on the upper side of a conductor-backed substrate, which are designed to produce a collimated beam at 20 and 30 GHz in dual polarization. Cross-shaped loops are used to provide the required phases at 20 GHz, while crossed dipoles and modified truncated rings are used to control the phasing at 30 GHz. The resonant lengths of the proposed elements have been adjusted cell by cell by means of a two-dimensional interpolation method to achieve the required phase shift at each frequency. Two different feeds have been used to illuminate the reflectarray at 20 and 30 GHz. The measured gain is 28.02 dBi at 20 GHz and 32.14 dBi at 30 GHz. The measurement results show that the radiation patterns of the designed single-layer reflec...

International Journal of Applied Electromagnetics and Mechanics, 2013

In this paper two novel left-handed composite metamaterials consisting of SRRs, wire and single s... more In this paper two novel left-handed composite metamaterials consisting of SRRs, wire and single sided S-shaped resonators are proposed. One of them is a reduced-size resonator which uses superposition hypothesis to achieve adjacent reso- nances for a much broader negative refraction passband. The other is a modified planar structure with improved electromagnetic coupling and reduced electrical size. Both structures are truly matched to free space in almost whole left-handed frequency band. It will be shown that these metamaterials are robust to the fabrication errors of misalignment printing on both sides of the substrate. The superior performance of these structures are investigated numerically and experimentally and compared with the other split ring resonators. Wedge shape simulation and experimental results confirm the left-handed passband.

Intechopen, 2017

This chapter reviews the most signiicant advancements in the context of metamaterial 􀇻MTM􀇼 leaky ... more This chapter reviews the most signiicant advancements in the context of metamaterial 􀇻MTM􀇼 leaky wave antennas 􀇻LWAs􀇼. A brief review of the mechanism of leaky wave radiation along with an important class of MTMs known as composite right/left-handed 􀇻CRLH􀇼 structures is presented. Then, recent outstanding works in the area of CRLH
LWAs are reported in detail. These works include the application of electronic control, substrate integrated waveguides, dual band and wideband performance, ferrite loaded waveguides, and split-ring-resonator 􀇻SRR􀇼-based MTMs in LWAs. Also, the beneits of LWAs to design high gain active structures, relecto-directive systems, wideband duallayer
substrate integrated waveguide antennas and conformal antennas are discussed.

intechopen, 2023

There are two main approaches for developing solar cells, including photovoltaic and photothermal... more There are two main approaches for developing solar cells, including photovoltaic and photothermal technologies. Photovoltaic solar cells benefit from an active region whose performance can be improved by embedding nanoparticles with different shapes and materials. Photothermal solar cells are broadband absorbers, enabling
electromagnetic energy absorption in the solar radiation region. Since the solar spectrum is expanded from 120 to 1000 THz, the device bandwidth engineering and its efficiency enhancement through utilizing nanoparticles, multiresonance configurations, and multilayered structures are necessary. Moreover, using chemically inert materials with high thermal conductivities results in stable performance under different
environmental conditions. Thus, in this chapter, various photovoltaic and
photothermal solar cells will be discussed, emphasizing their design principles. The chapter mainly considers absorption bandwidth enlargement, absorption efficiency enhancement, and material selection considerations. In this regard, solar cells designed with plasmonic materials, transition metals, refractory metals, and carbon materials are presented. Notably, the potential of two-dimensional graphene material in the solar cell design is revealed, and a lightweight graphene-based solar cell with near-perfect coverage of the whole solar spectrum is introduced.