Plasmonic antennas based on rectangular graphene nanoribbons with controlled polarization of terahertz and infrared radiation
- Authors: Makeeva G.S.1
-
Affiliations:
- Penza State University
- Issue: Vol 27, No 3 (2024)
- Pages: 81-90
- Section: Original Study Articles
- URL: https://journals.ssau.ru/pwp/article/view/27290
- DOI: https://doi.org/10.18469/1810-3189.2024.27.3.81-90
- ID: 27290
Cite item
Abstract
Background. To develop new terahertz wireless communication systems with high throughput and transmission speeds, such as 6G and above, effective control of the polarization direction of emitted terahertz waves is necessary, but most methods are technologically complex and expensive. The implementation of terahertz antennas and devices based on 2D materials such as graphene solves the problem associated with developing effective control. Aim. Study of the possibility of controlling the polarization of terahertz and IR radiation of plasmonic antennas based on rectangular graphene nanoribbons by changing the chemical potential (application of an external electric field). Methods. This important scientific problem related to the design of terahertz antennas can largely be solved by simulation using the electrodynamic simulation program CST MWS 2023. Results. Plasmon terahertz antennas based on rectangular graphene nanoribbons were chosen as the object of analysis and the possibility of emitting waves of two orthogonal polarizations was shown. Methods have been identified for controlling the polarization of terahertz and IR radiation from such antennas, based on the selection of operating frequencies corresponding to the resonances of the modes of surface plasmon-polaritons, and the application of metallization to the dielectric substrate. Conclusion. The ability to control the polarization of terahertz and IR radiation makes it possible to create both new elements of plasmonic antenna arrays and new communication technologies, including future 6G networks.
Full Text
Introduction
New wireless communication standards such as 6G require higher bandwidth than current technologies can provide. The terahertz (THz) frequency band is highly promising for high-speed wireless communication networks [1] because it can significantly boost transmission rates compared to ultrahigh-frequency (UHF) bands, especially in 6G Wi-Fi networks [2].
Two-dimensional (2D) materials such as graphene play a crucial role in efficient polarization control in THz devices and antennas. With its unique optoelectronic properties and high doping potential, graphene has become key material in plasmonic antennas [3–7] and THz polarizers [8–11]. It exhibits high carrier mobility and consistently absorbs light across wavelengths. Graphene properties can be tuned by adjusting its chemical potential (Fermi level) via electrical gating and chemical doping. Graphene is chemically and structurally stable owing to the strong covalent bonds among carbon atoms, which enable it to support long-lived and tunable plasmon resonances when excited by THz and infrared (IR) radiation [3].
Graphene analogs of standard metal antennas exhibit better emitting properties [4–7]. This is largely attributed to graphene’s excellent surface conductivity, which is highly responsive to changes in chemical potential when a bias voltage is applied [12]. Such dynamic conductivity control is expected to support operations at terabit-per-second speeds [3].
New THz, ultra-high-performance, and ultra-precise communication systems require efficient control of the polarization direction of the emitted waves. However, most available methods are complex and expensive [2].
The ST MWS and HFSS simulation software packages can solve important problems related to the design of microwave devices, antennas, and phased antenna arrays [13; 14].
This study uses the CST Microwave Studio electromagnetic simulation system to investigate how the polarization of terahertz and IR radiation emitted by plasmonic antennas made of rectangular graphene nanoribbons can be controlled. This control can be achieved by changing the chemical potential by applying an external electric field.
Simulation of plasmonic antenna behavior in a rectangular graphene nanoribbon excited by s- and p-polarized TEM wave under chemical potential change
Fig. 1 illustrates the CST MWS 2023 [15] models of excitation of a plasmonic antenna with a rectangular graphene nanoribbon can be excited by a normally incident TEM wave. In these models, the wave is either s-polarized (Fig. 1, a) or p-polarized (Fig. 1, b) using a waveguide port. The antenna model features a rectangular graphene nanoribbon with dimensions of length (l) and width (w) (Fig. 1) installed on a dielectric substrate made of silicon dioxide (SiO2), characterized by a dielectric constant
Fig. 1. Excitation of a plasmonic antenna with a rectangular graphene nanoribbon using a waveguide port: a – s-polarized and b – p-polarized TEM. Simulated in CST MWS 2023
Рис. 1. Модели возбуждения плазмонной антенны на основе прямоугольной графеновой наноленты TEM-волной s-поляризации (а) и p-поляризации (б) с помощью волноводного порта в программном комплексе CST MWS 2023
Fig. 1 also depicts the orientation of the incident TEM wave’s electric field strength vector E relative to the graphene nanoribbon. For an s-polarized wave, vector E is oriented along the wide side of the graphene nanoribbon (Fig. 1, a), whereas for a p-polarized wave, vector E aligns with the narrow side (Fig. 1, b).
We used the models presented in Fig. 1 to address the electrodynamic problem using CST Microwave Studio 2023 employing finite integration in the time domain [3].
We calculated an element of the scattering matrix for a graphene plasmonic antenna excited by s- and p-polarized TEM waves across the THz, far-IR, and mid-IR ranges, considering different values of the graphene’s chemical potential
Fig. 1 also depicts the orientation of the incident TEM wave’s electric field strength vector E relative to the graphene nanoribbon. For an s-polarized wave, vector E is oriented along the wide side of the graphene nanoribbon (Fig. 1, a), whereas for a p-polarized wave, vector E aligns with the narrow side (Fig. 1, b).
We used the models presented in Fig. 1 to address the electrodynamic problem using CST Microwave Studio 2023 employing finite integration in the time domain [3].
We calculated an element of the scattering matrix
Fig. 2 displays the frequency responses of the scattering matrix element
Fig. 2. Frequency responses of the scattering matrix element
Рис. 2. Частотные зависимости элемента матрицы рассеяния
The simulation results (Fig. 2) indicate that frequency shifts and the minima of the transmission coefficient
For an s-polarized excitation TEM wave, in which the surface electric current resonates along the wide side of the rectangular graphene nanoribbon, longitudinal plasmon resonance occurs [11]. In this case, the first resonant frequency
The table lists the estimated scattering matrix element
Table. Calculated values of the scattering matrix element
Таблица. Расчетные значения элемента матрицы рассеяния
| | S11, dB | | S11, dB | | S11, dB |
0,3 | 3,652 | –8,18936 | 7,747 | –7,22564 | 8,967 | –2,00709 |
0,7 | 5,563 | –13,68034 | 11,803 | –12,09588 | 13,636 | –4,0221 |
1 | 6,616 | –16,14356 | 14,104 | –14,39928 | 16,288 | –5,40395 |
Simulation of THz and IR radiation polarization control for plasmonic antennas with rectangular graphene nanoribbons
Fig. 3 illustrates the simulation results from CST MWS 2023. We modeled the directivity pattern (DP) of a plasmonic graphene antenna on a dielectric substrate and examined the distribution of the surface electric current density vector
Fig. 3. DP of a plasmonic antenna with a rectangular graphene nanoribbon on a dielectric substrate at resonance frequencies
Рис. 3. ДН плазмонной антенны на основе прямоугольной графеновой наноленты на диэлектрической подложке на резонансных частотах
Fig. 3 – 3.1–3.3, a–c illustrate how the frequency of a plasmonic graphene antenna can be tuned, or frequency-swept, at resonant frequencies
At the resonant frequencies of the main SPP mode, excited by an s-polarized TEM wave, a resonance of the electric current is generated by the standing SPP half-wave along the wide side of the rectangular nanoribbon [11]. This results in a half-wave distribution of the surface electric current
As the chemical potential
For comparison, Fig. 4 presents the simulated DP of a plasmonic antenna with a rectangular graphene nanoribbon on a metalized dielectric substrate, maintaining identical dimensions
Fig. 4. DP of a plasmonic antenna with a rectangular graphene nanoribbon on a metalized dielectric substrate excited by an s-polarized TEM at the resonant frequency corresponding to the main SPP mode
Рис. 4. ДН плазмонной антенны на основе прямоугольной графеновой наноленты на металлизированной диэлектрической подложке при s-поляризации возбуждающей TEM-волны на резонансной частоте основной моды ППП
The comparison of the DPs for plasmonic antennas containing rectangular graphene nanoribbons on dielectric substrates (Fig. 3 – 3.3) and metalized substrates (Fig. 4) substrates at resonant frequencies
Plasmonic antennas containing rectangular graphene nanoribbons on dielectric and metalized substrates emit THz waves with two orthogonal polarizations. This means that by applying metallization to the dielectric substrate, we can control the polarization of the THz radiation.
Fig. 5 presents the simulation results from CST MWS 2023, showing the DP of a plasmonic graphene antenna on a dielectric substrate. It also depicts the distribution of the surface electric current density vector
Fig. 5. TDP of a plasmonic antenna containing a rectangular graphene nanoribbon on a dielectric substrate at the resonance frequencies
Рис. 5. ДН плазмонной антенны на основе прямоугольной графеновой наноленты на диэлектрической подложке на резонансных частотах
Fig. 5 – 5.1–5.3, a-c demonstrate the capability of tuning the operating frequency of a plasmonic graphene antenna (frequency scanning), allowing it to scan from the THz range to the far and mid-IR ranges. This frequency tuning is achieved at resonant frequencies
At the resonant frequencies of the main SPP mode, excited by an s-polarized wave, a resonance of the electric current is generated by the standing SPP half-wave along the wide side of the rectangular nanoribbon [11]. This results in a half-wave distribution of the surface electric current
The comparison of the DPs at the resonance frequencies of the main SPP mode
A plasmonic antenna with rectangular graphene nanoribbons on a dielectric substrate can emit waves with two orthogonal polarizations. This happens when the resonance frequency shifts from the SPP mode
Conclusion
The simulation results reveal that plasmonic antennas with rectangular graphene nanoribbons can emit THz/IR waves with two orthogonal polarizations. We identified methods to control the polarization of these waves by selecting signal frequencies that align with the plasmon resonances of SPP modes and through metallization of the dielectric substrate.
This ability to control THz/IR radiation enables the creation of both new plasmonic antenna array elements [18] and new communication technologies, including future 6G networks [2]. These advancements will support energy-efficient communication, enable cognitive radio networks that can intelligently change channels, and facilitate in-band full-duplex technology that can double the bandwidth [2].
About the authors
Galina S. Makeeva
Penza State University
Author for correspondence.
Email: galina.makeeva@gmail.com
Doctor of Physical and Mathematical Sciences, Professor of the Department of Radio Engineering and Radioelectronic Systems
Russian Federation, 40, Krasnaya Street, Penza, 440026References
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