Enabling an electrically tunable terahertz metasurface

In an article recently published in the journal communication materialsThe researchers discussed the ability of a graphene/gold bilayer construct to enable the electrically tunable terahertz metasurface.

Enabling an electrically tunable terahertz metasurface

Study: Electrically Tunable Terahertz Metasurface Enabled by a Graphene/Gold Bilayer Structure. Image Credit: Mathier/Shutterstock.com

Terahertz bands

Terahertz (THz) bands are perfect for next generation wireless networks. However, the lack of availability of components and technology that can operate at frequencies beyond current electronic and photonic frequencies has hampered the development of THz wireless communication systems.

Two-dimensional (2D) materials

To create electrical and photonic devices that operate at terahertz frequencies, novel materials, such as 2D materials like graphene, and device designs that include ultrafast charge carrier dynamics and capabilities are highly desirable. Selectively tunable and electrically tunable terahertz absorbers with high Q factor resonances are highly desired but hard to find for building terahertz systems. The growing interest in metamaterials and 2D materials to provide reconfigurable, tunable, and programmable functions for terahertz applications is a result of the absence of terahertz-area tunable devices.

Graphene-based metamaterials

For terahertz devices, graphene-based metamaterials have attracted a lot of interest. One of the most challenging aspects of graphene-based electronics development is fabricating graphene into scalable, usable, and functional electronic devices. To develop state-of-the-art graphene-based tunable metamaterial devices, new metamaterial architectures and production techniques are required.

Electrical modulation of terahertz waves using graphene

In this article, the authors added graphene to an overlaying graphene/gold bilayer metamaterial structure, which enabled effective electrical modulation of terahertz waves. This graphene/gold bilayer metamaterial strategy was used to design and experimentally create a 0.2 terahertz frequency-selective absorber. The proposed device maintained benchmark high-quality factor resonance performance while demonstrating 16 decibel amplitude matching at 0.2 terahertz resonance and greater than 95% broadband modulation with a bias voltage of only 6 volts.

The team addressed the poor performance of graphene metasurfaces and the lack of tunability of gold metasurfaces by preparing a bilayer metamaterial structure of gold and graphene. To test the efficacy of the proposed bilayer strategy, a highly tunable terahertz frequency selective absorber was created and tested.

The researchers illustrated the development of a graphene metamaterial-based device operating in the 0.1 to 1 terahertz communications window, where graphene was patterned throughout the complex metasurface structure, producing a high-quality reference resonance. with a Q factor of up to 19. Significant amplitude tuning of 16 decibels with a low bias of 6 volts.

The tuning mechanism was detailed along with design theory, modeling, and experimental data. A flexible, high-frequency laminated circuit board served as the basis for the device.

Tunable performance and broadband response of the metamaterial structure

The adjusted resonance went from 0.192 to 0.187 terahertz and its amplitude increased from about 18 to 25 decibels. With a range of graphene conductance from 40 to 100 millisiemens, the maximum simulated amplitude changed from -17 to -22 decibels. These values ​​were very similar to those measured experimentally and were -18 decibels at unbiased resonant amplitudes and -25 decibels at 6 volt bias.

The imaginary portion of the graphene conductivity increased marginally with the applied voltage. Although the design and modeling of the metadevice focused on the 0.2 terahertz range, higher-order resonances and broadband features were observed. There were auxiliary modes at 0.36 terahertz, 0.40 terahertz, and 0.56 terahertz. Modulation depth (MD) was 85% between 0.23 and 0.32 terahertz, 91% between 0.43 and 0.50 terahertz, and 95% above 0.72 terahertz.

Conclusions and Future Perspectives

In conclusion, this study looked at the development of a bilayer metamaterial structure in which the entire device design was overlaid on graphene and gold. The experimentally developed graphene/gold bilayer terahertz frequency selective absorber exhibited a tuning performance of more than 16 decibels with a bias voltage of only 6 volts while maintaining a reference high Q factor of 19. With the same low bias of 6 volts, the device also had broadband tuning that was greater than 95%.

The theoretical prediction of the fitability for the bilayer metamaterial design was validated by the experimental findings, which were in good agreement with those of the theoretical modelling.

The authors stated that a wide variety of terahertz devices could be easily fabricated using the proposed scalable fabrication process. They believe that new material and device technologies being advanced in this work will impact developing industries such as terahertz satellite target tracking, wireless communications, and sensing.

Reference

Squires, AD, et al. (2022) Electrically tunable terahertz metasurface enabled by a graphene/gold bilayer structure. Communication Materials 3(56). https://www.nature.com/articles/s43246-022-00279-7

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