Article
Optics
Jun Peng, Jin Leng, Duo Cao, Xiaoyong He, Fangting Lin, Feng Liu
Summary: The tunable propagation characteristics of metamaterial absorbers based on asymmetric graphene ellipses in the THz region were investigated, showing distinct absorption peaks and modulated Fano resonance. By replacing the metal substrate with a uniform graphene layer, a bidirectional THz MMA was achieved, demonstrating absorption and reflective modulation properties. These results contribute to the design of tunable THz devices like filters, absorbers, and modulators.
Review
Materials Science, Multidisciplinary
Chuanxin Chen, Minqi Chai, Meihua Jin, Tao He
Summary: Terahertz metamaterial absorbers (TMAs) efficiently absorb electromagnetic waves in the range of 0.1-10 THz, achieving perfect absorption and broad band absorption. Their ultra-thin design and tunable electromagnetic properties make them highly valuable in communication, imaging, detection, and security inspection applications.
ADVANCED MATERIALS TECHNOLOGIES
(2022)
Article
Chemistry, Multidisciplinary
Tong Xie, Dingbo Chen, Huiping Yang, Yanhong Xu, Zhenrong Zhang, Junbo Yang
Summary: This paper introduces a metasurface Terahertz absorber based on graphene geometry resonator fractal technology, achieving ultra-wideband absorption and dynamic tuning. By incorporating different fractal layers, the absorber shows high absorption and insensitivity to the polarization angle.
Article
Materials Science, Multidisciplinary
BaoJing Hu, Ming Huang, Li Yang, Jinyan Zhao
Summary: A terahertz dual-tunable polarization-independent metamaterial absorber based on hybrid gold-graphene-strontium titanate (STO)-vanadium dioxide (VO2) configuration is proposed. The absorber achieves an absorption rate of 98.3% at 0.2 THz, and the absorption frequency and rate can be dual-tuned by adjusting the chemical potential of graphene and the temperature of STO and VO2. The theoretical analysis using coupled mode theory and impedance matching theory provides insights into the absorber's performance, and the changes in absorption spectra when modifying the depth of STO and VO2 layers are discussed.
OPTICAL MATERIALS EXPRESS
(2023)
Article
Optics
Pei-Jung Wu, Wei-Cheng Tsai, Chan-Shan Yang
Summary: In this study, an electrically tunable multi-band terahertz (THz) metamaterial filter based on graphene and multiple-square-loop structures was designed. The structure consists of multiple metal square loops of different sizes, which correspond to different THz frequencies, achieving the expected efficacy of a multi-band wave filter. By sweeping external voltages, the capability of the high-sensitivity THz filter can be modulated from single-band to multi-band filtering by changing graphene's Fermi levels. This hybrid THz wave filter study shows promise for the development of selecting channels in THz and 6G communications.
Article
Materials Science, Multidisciplinary
Meisam Esfandiyari, Ali Lalbakhsh, Saughar Jarchi, Mohsen Ghaffari-Miab, Hamideh Noori Mahtaj, Roy B. V. B. Simorangkir
Summary: This paper presents a novel tunable graphene-based bandstop filter/antenna-sensor. The structure combines filtering and high-gain radiation performance. The conductivity of graphene and its structural parameters are studied to optimize the component performance.
MATERIALS & DESIGN
(2022)
Article
Optics
Zhongmin Liu, Liang Guo, Qingmao Zhang
Summary: The study introduces a novel approach for designing and analyzing graphene metasurface-based terahertz absorbers with desired central frequency and fractional bandwidth. By using the same configuration of a single layer of graphene ribbons deposited on a metal-backed dielectric film, both narrowband and broadband absorbers are designed effectively. The proposed method shows great potential for terahertz imaging, sensing, and filtering applications.
Article
Optics
Yong Gang Zhang, Zhen Wei Feng, Lan Ju Liang, Hai Yun Yao, Ya Ru Wang, Liang Xu, Xin Yan, Wei Liu
Summary: A perfect metamaterial absorber based on strontium titanate and bulk Dirac semimetals is proposed in this study. The absorptions at 1.227 and 1.552 THz were 99.74% and 99.99%, respectively, when the temperature of strontium titanate was 300K. The sensitivities for transverse magnetic (TM) and transverse electric (TE) waves were 0.95 and 1.22 GHz/K, and 0.76 GHz/K, respectively. By modulating TE and TM waves through a bulk Dirac semimetal, the absorber achieved high modulation depths and extinction ratios at different frequencies. It shows promising applications in temperature sensing and switching devices.
Article
Materials Science, Multidisciplinary
Rong Cheng, Yuxiu Zhou, Xinghua Wu, Qingkai Wang, Jianqiang Liu
Summary: With promising applications in various fields, mechanically tunable THz absorbers based on overlapping graphene nanoribbon arrays have been developed. By adjusting the horizontal position of the upper cover plate, the frequencies of the absorption peaks can be widely tuned. The proposed absorber provides a reference for tunable THz absorbers that can be applied in different fields.
RESULTS IN PHYSICS
(2023)
Article
Chemistry, Physical
Haonan Qi, Bin Tang
Summary: In this paper, a switchable and tunable functional metamaterial device based on hybrid graphene-vanadium dioxide (VO2) is proposed. By utilizing the metal-insulator transition properties of VO2, the proposed metamaterials can switch between tunable circular dichroism (CD) and dual-band perfect absorption in the terahertz region. The operation mechanism behind the phenomena can be explained by utilizing the electric field distribution and the coupled mode theory. The proposed switchable and tunable metamaterial provides a platform for designing versatile functional devices in the terahertz region.
PHYSICAL CHEMISTRY CHEMICAL PHYSICS
(2023)
Article
Materials Science, Multidisciplinary
Jiali Wu, Xin Yan, Xueguang Yuan, Yangan Zhang, Xia Zhang
Summary: The dual-tunable broadband terahertz absorber based on graphene and strontium titanate achieves ultra-wide bandwidth and high absorption rate through adjustments of Fermi energy and temperature. It is insensitive to incident angles and maintains stable performance, showing great potential for applications in tunable broadband terahertz absorbers.
RESULTS IN PHYSICS
(2021)
Article
Optics
Limei Qi, MingJing Wu, Xiaojun Han
Summary: In this study, a method to generate tunable THz radiation using a graphene metasurface is proposed. The frequency, amplitude, and direction of the radiation can be controlled by varying the chemical potential of the graphene. Several new phenomena are observed, including the resonance frequency matching and the inverse relationship between radiation magnitude and reflection magnitude.
Article
Chemistry, Physical
P. Upender, Amarjit Kumar
Summary: This paper proposes a design of a cylindrical dielectric resonator antenna (CDRA) and rectangular dielectric resonator (RDR) slab combination for terahertz (THz) applications, providing multi-band response and circular polarization characteristics at different frequencies. The CP tuning is achieved by varying the antenna's graphene potential, allowing for both RHCP and LHCP behavior at different resonant frequencies. Incorporating a rectangular slab with CDRA known as CPDRA, the antenna achieves impressive performance metrics such as maximum gain, radiation efficiency, impedance bandwidth, and axial ratio bandwidth. The use of graphene material for antenna tunability makes this Quad band CP DRA unique and suitable for THz applications.
Article
Materials Science, Multidisciplinary
Jifan Yin, Ranjan Singh, Min Chen, Lijuan Xie
Summary: Introduces a carbon nanotube-based electrically tunable THz absorber with high electrical tunability and polarization selectivity. The experimental results show that the absorber has an absorbance of up to 99% in the range of 0.2 THz to 1.6 THz. The proposed absorber has a simple fabrication method and can promote THz applications in various fields.
Article
Materials Science, Multidisciplinary
Yu-Shan Chen, Yu-Yao Cheng, Dan Meng, Ke-Wei You, Yue Liu, Yong-Chang Wu, Jing Liu
Summary: We present an ultrasensitive refractive-index sensor using a patterned graphene dual-band absorber in the terahertz band. The structure exhibits two perfect absorption peaks in the 1-9 THz band with theoretical absorptions of 99.4%. The positions of the absorption peaks can be adjusted using the applied bias voltage based on the properties of graphene. The proposed structure shows high symmetry, making it insensitive to polarization and incident angle variations.
DIAMOND AND RELATED MATERIALS
(2023)
Article
Nanoscience & Nanotechnology
Xuchen Wang, Mohammad S. S. Mirmoosa, Sergei A. A. Tretyakov
Summary: This paper theoretically elucidates the effect of temporal discontinuities of effective parameters on the propagation of reactive metasurface surface waves. It shows that by switching the surface reactance value, the velocity of surface waves can be fully controlled, and the power of reflected and transmitted waves can be amplified. It also demonstrates that switching a boundary from supporting transverse-electric polarization to only allowing transverse-magnetic polarization freezes and converts the propagating surface wave to a static magnetic-field distribution. Furthermore, temporal jumps of the boundary reactance couple free-space propagating waves to the surface wave, similar to a spatial prism. These intriguing phenomena enable the generation and control of surface waves.
Article
Physics, Applied
J. A. Alvarez-Sanchis, B. Vidal, S. A. Tretyakov, A. Diaz-Rubio
Summary: By controlling geometric parameters, the quality factor of all-dielectric metasurfaces can be adjusted and designed theoretically for improved performance as sensors in the THz band. However, material losses significantly limit the resonances' quality factor, leading to the proposal of all-dielectric metasurfaces as an alternative to metal-dielectric structures. In this study, the effect of losses on all-dielectric metasurfaces is examined using realistic materials, and their sensing performance is compared with nanostructures supporting extraordinary optical transmission. The results highlight the limitations of all-dielectric metasurfaces and the superiority of structures with extraordinary optical transmission.
PHYSICAL REVIEW APPLIED
(2023)
Article
Physics, Applied
Hamidreza Taghvaee, Fu Liu, Ana Diaz-Rubio, Sergei Tretyakov
Summary: Breaking the diffraction limit on optical devices and achieving subwavelength focusing requires tailoring the evanescent spectrum of wave fields. This paper presents a feasible strategy based on the concepts of the perfect lens and power flow-conformal metasurfaces, allowing for subwavelength hotspot size in near-field focusing. The findings have potential applications in antennas, beam-shaping devices, nonradiative wireless power transfer systems, microscopy, and lithography.
PHYSICAL REVIEW APPLIED
(2023)
Article
Physics, Applied
M. H. Mostafa, N. Ha-Van, P. Jayathurathnage, X. Wang, G. Ptitcyn, S. A. Tretyakov
Summary: The Chu limit restricts the operational bandwidth of resonant circuits due to the size limitation of the resonator. This limitation hinders the miniaturization of antennas, as their bandwidth is inversely proportional to their size. To overcome this, we propose the use of slow time modulation of resistive elements to engineer the bandwidth of small antennas. The modulation of resistance induces a virtual impedance that can be fully controlled by modulation parameters and optimize the frequency response of a resonant circuit.
APPLIED PHYSICS LETTERS
(2023)
Article
Multidisciplinary Sciences
Xuchen Wang, Mohammad Sajjad Mirmoosa, Viktar S. Asadchy, Carsten Rockstuhl, Shanhui Fan, Sergei A. Tretyakov
Summary: Photonic time crystals are artificial materials with spatially uniform but temporally varying electromagnetic properties. This study extends the concept of photonic time crystals to two-dimensional artificial structures called metasurfaces. By designing a microwave metasurface, the researchers confirmed the existence of momentum bandgaps and exponential wave amplification, demonstrating the potential of metasurfaces as a material platform for emerging photonic space-time crystals and for amplifying surface-wave signals in wireless communications.
Article
Chemistry, Multidisciplinary
Shuomin Zhong, Xuchen Wang, Sergei A. A. Tretyakov
Summary: Conventional coherent absorption occurs only when two incident beams exhibit mirror symmetry. This study proposes a more general metasurface paradigm for coherent perfect absorption with impinging waves from arbitrary asymmetric directions. It shows theoretically and confirms experimentally that the relative amplitude of the reflected wave can be continuously tuned by changing the phase difference between the two beams, opening up promising possibilities for wave manipulation with applications in various fields.
ADVANCED FUNCTIONAL MATERIALS
(2023)
Article
Engineering, Electrical & Electronic
Grigorii Ptitcyn, Mohammad Sajjad Mirmoosa, Amirhosein Sotoodehfar, Sergei A. Tretyakov
Summary: In recent years, there has been increasing interest in using time-modulation techniques to realize new phenomena and create new applications by varying system properties. This field, which originated in the middle of the previous century, has gained revitalized attention. In this tutorial article, the authors provide a historical overview and review the basic concepts in this field. They introduce the general theory of linear time-varying systems, discuss accounting for frequency dispersion in nonstationary systems, and elucidate models of time-varying electrical circuits and materials.
IEEE ANTENNAS AND PROPAGATION MAGAZINE
(2023)
Article
Engineering, Electrical & Electronic
Sravan K. R. Vuyyuru, Risto Valkonen, Do-Hoon Kwon, Sergei A. Tretyakov
Summary: A perfect anomalous reflector is designed based on the receiving and scattering array antenna theory to optimize the scattering characteristics of a planar reflecting surface. By algebraic optimization of the load reactances, the reflection amplitudes into propagating Floquet modes can be controlled, avoiding the need for brute-force optimization via electromagnetic simulations. Numerical designs of wide-angle reflectors show that the proposed approach achieves higher reflection efficiencies compared to conventional reflectarray designs in a computationally efficient manner.
IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS
(2023)
Article
Physics, Applied
N. Ha-Van, C. R. Simovski, F. S. Cuesta, P. Jayathurathnage, S. A. Tretyakov
Summary: In conventional inductive wireless power devices, energy is transferred via reactive near fields, and radiation from transmitting and receiving coils is considered a parasitic effect that reduces power-transfer efficiency. This paper develops a dynamic theory of wireless power transfer between two small loop antennas, clarifies the role of far-field radiation, and proposes a possibility to achieve efficient wireless power transfer at large distances through radiation suppression. The analytical results are validated through simulations and measurements, offering the potential to greatly expand the distance range of compact wireless power-transfer devices.
PHYSICAL REVIEW APPLIED
(2023)
Article
Physics, Applied
G. A. Ptitcyn, M. S. Mirmoosa, S. Hrabar, S. A. Tretyakov
Summary: Temporal modulation allows dynamic control and modification of electromagnetic system response, enabling functionalities that were conventionally unachievable. By explicitly considering the time dependence of circuit or surface parameters, it becomes possible to emulate electromagnetic systems with arbitrary frequency dispersion and nonlinear properties, including non-Foster response. Proper modulation of a time-varying capacitor can mimic static inductance, capacitance, or resistance with arbitrary values, positive or negative. The stability of the system is ensured through necessary modifications of determined ideal modulation functions. A proposed invisible sensor is demonstrated using full-wave simulations, along with discussions on the stability of externally modulated systems. This study introduces an alternative paradigm of using time modulations to engineer system responses, applicable not only to electromagnetic systems but also in other branches of physics.
PHYSICAL REVIEW APPLIED
(2023)
Proceedings Paper
Engineering, Electrical & Electronic
Sergei Kosulnikov, Francisco S. Cuesta, Xuchen Wang, Ana Diaz-Rubio, Sergei Tretyakov
Summary: High-frequency wireless communications at millimeter-wave bands require directive, high-gain antennas to achieve longer communication links. Anomalously reflecting and reconfigurable intelligent surfaces can be used to ensure sufficient space coverage. This presentation discusses recent analytical estimations of link budget with the presence of such reflectors, providing simple expressions for the far field using macroscopic reflection coefficients and a generalized Friis formula. The analytical results are validated through numerical simulations of a specific realization for millimeter-wave frequency band.
2023 17TH EUROPEAN CONFERENCE ON ANTENNAS AND PROPAGATION, EUCAP
(2023)
Proceedings Paper
Engineering, Electrical & Electronic
Yongming Li, Xikui Ma, Grigorii Ptitcyn, Sergei Tretyakov
Summary: In this study, a novel method is proposed for designing anomalous reflectors using arrays of loaded strips. By assuming two different sets of induced polarization currents flowing on the surface, specular reflection can be eliminated and the reflected wave propagates towards the desired direction. Surface waves are tuned by optimizing the current distribution to obtain purely reactive loads. Additional loaded strips inserted within a lambda/2-sized cell of the structure help optimize the design, and perfect anomalous reflection is achieved. The obtained results are compared with conventional reflectarrays, demonstrating significant improvement.
2023 17TH EUROPEAN CONFERENCE ON ANTENNAS AND PROPAGATION, EUCAP
(2023)
Article
Materials Science, Multidisciplinary
F. S. Cuesta, M. S. Mirmoosa, S. A. Tretyakov
Summary: One advantage of reciprocal bianisotropic metasurfaces is their ability to produce asymmetric scattering depending on the illumination side and circular polarization. However, we demonstrate that geometrical asymmetry can be emulated using nonbianisotropic layers in coherent illumination, enabling optical control of desired asymmetric scattering and chirality effects. We illustrate this concept by emulating asymmetric scattering required for creating a 180 degrees hybrid junction for plane waves using either a bianisotropic metasurface or simple sheets with electric response under simultaneous illumination by two coherent waves.
Proceedings Paper
Engineering, Electrical & Electronic
Nam Ha-Van, Constantin R. Simovski, Francisco S. Cuesta, Prasad Jayathurathnage, Sergei A. Tretyakov
Summary: We investigate a regime of radiation suppression in wireless power transfer (WPT) between two loop antennas in free space. By optimizing load impedance and working frequency, high power transfer efficiency can be achieved due to partial compensation of the radiation resistances of both antennas. This regime is analyzed for two antenna arrangements: coaxial arrangement, where WPT is solely based on near fields, and coplanar arrangement, where both near-field and far-field power transfer mechanisms are combined. The radiation suppression regime is analyzed and visualized for both arrangements. Theoretical results are validated by simulations and experiments with two loop antennas.
2023 53RD EUROPEAN MICROWAVE CONFERENCE, EUMC
(2023)
Proceedings Paper
Engineering, Electrical & Electronic
Shamsul Arefeen Al Mahmud, Prasad Jayathurathnage, Yining Liu, Jorma Kyyra
Summary: Fast automatic identification of WPT receiver is critical for future deployment of efficient and low-cost dynamic wireless power transfer devices. This article presents a new approach for receiver identification and transmitter activation in wireless power transfer systems, enabling fast charging request and energy-saving.
2023 IEEE WIRELESS POWER TECHNOLOGY CONFERENCE AND EXPO, WPTCE
(2023)