Terahertz Metamaterial Absorber Research Articles

High Degree Simplification and Tunable absorption features of Terahertz metamaterial absorber

High Degree Simplification and Tunable absorption features of Terahertz metamaterial absorber

Deep neural network-enabled dual-functional wideband absorbers

The increasing interest in switchable and tunable wideband perfect absorbers for applications such as modulation, energy harvesting, and spectroscopy has significantly driven research efforts. In this study, we present a dual-function terahertz (THz) metamaterial absorber supported by deep neural networks (DNN). This absorber achieves dual-wideband perfect absorption through the use of graphene and vanadium dioxide (VO₂), enabling both switching and tuning functionalities. Simulation results show that, in the insulating phase of VO₂, a high-frequency wideband absorption ranging from 9.31 to 9.77 THz is achieved, with an absorption rate exceeding 90%. In contrast, in the metallic phase of VO₂, a full-band wideband absorption above 90% is observed from 8.44 to 9.75 THz. The corresponding fractional bandwidths are 61.3% and 174.6%, respectively. Additionally, electrical tuning of graphene’s Fermi level from 0.01 to 1 eV enables continuous modulation of absorption intensity between 48 and 100%. The absorber also exhibits polarization insensitivity to TE and TM waves due to its symmetric design and broad incidence angle. This design holds significant potential for various THz applications, including switching, electromagnetic shielding, stealth technology, filtering, and sensing.

An adaptive assisted method based on MOPSO for THz MMA effective designing

Abstract To address the high time cost and low efficiency of traditional terahertz metamaterial absorber design, an adaptive method based on multi-objective particle swarm optimization was proposed. First, we presented a symmetric absorber of a four-split-ring resonator with a cross-shaped top layer. The structural parameters were optimized by the particle swarm optimization and multi-objective particle swarm optimization algorithms. The simulation results indicated that the multi-objective particle swarm optimization rapidly obtained geometric parameters that balance the high absorptivity and high quality factors. This method quickly identified a symmetric structure with absorptivity greater than 99% and quality factor of 377.45 at 1.584 THz. Additionally, the asymmetric structure achieved near-perfect absorption at 1.585 THz with a Q value of 281.32. By studying the electric field distribution and the surface current distribution, the physical mechanism of the absorber designed has been explained. This adaptive assisted method based on multi-objective particle swarm optimization can efficiently design metamaterial absorbers and offer an artificial intelligence strategy for terahertz functional device design.

Design and optimization of a polarization-insensitive terahertz metamaterial absorber for sensing applications

This study presents dual-band Terahertz (THz) metamaterial absorbers (MA) designed with square resonators for sensing applications. The absorber is made up of a plasmonic ring resonator, a middle polyimide layer, and a lower metal plate, which enhances its absorption capabilities. The position of annular strips and patch units is strategically adjusted to tune and optimize the absorber’s performance precisely. The proposed metamaterial (MA) consistently absorbs over 99 % within the frequency range from 1.4 to 2.8 THz at 1.6 THz for peak-1 and 2.3 THz for peak-2. The peaks labeled as ‘f1’ and ‘f2’ have a spectral width of 0.02 THz and high-quality factors (Q-factors) of 23 for peak-1 and 29 for peak-2, respectively. This makes them remarkably sensitive to variations in the environmental refractive index (RI). It is important to observe that the refractive index of most samples falls within the range of 1.0–2.0, highlighting the potential applications of this sensor.

Theoretical study of a triple-band tunable terahertz metamaterial absorber with polarization insensitive and high refractive index sensing based on bulk Dirac semimetal

In this paper, a triple-band metamaterial absorber in the terahertz frequencies is proposed, and its refractive index sensing characteristics are analyzed, where the bulk Dirac semimetal (BDS) periodic array is on top of a photonic crystal slab backed with a metal ground plane. The simulation results show that the absorber achieves three perfect absorption peaks in the range of 3.4–5.2 THz, whose absorption rates are over 96%, and a maximum quality factor (Q) of 74.1. The designed absorber exhibits excellent polarization insensitivity and dynamic tunability; further, the tuning of the Fermi energy level of BDS enables the dynamic adjustment of absorption frequencies and absorption rates of these peaks. By analyzing the distributions of the electromagnetic field and different structural parameters, it is revealed that the absorber mainly dissipates the electromagnetic wave through coupled resonance and localized surface plasmon resonance (LSPR) effects to achieve perfect absorption. Further, the metamaterial absorber shows the capacity to detect analytes with varying refractive indices, and the absorber has a maximum sensitivity S of 405 GHz/RIU with high detection accuracy. This work provides novel design options for triple-band terahertz metamaterial absorbers and their potential applications in refractive index sensing.

A miniaturized dual band terahertz metamaterial based absorber as a biosensor for non-melanoma skin cancer diognostic

Early diagnosis of Non-melanoma skin cancers (NMSCs) is most important for successful treatment of the disease.The detection of NMSCs involves visual inspection or invasive method of detection by skin biopsy. Recently, terahertz spectroscopy has come into limelight for detection of biomarkers in low terahertz (THz) region in between 0.1 – 10 THz which will be in resonance with the biomolecules. This work entails in designing a microscale THz metamaterial absorber for discriminating the attributes between Non-melanoma skin cancerous skin and normal skin. The proposed absorber is composed of space filling curved aluminum layer over a polymide substrate. The absorber culminates its absorbance peak of 99.8 % at 0.503 THz and 99.5 % at 1.076 THz, revealing its dual band trait. Moreover, variation of refractive index of the medium from 1.3 to 1.4 shows shift in absorption peak with a sensitivity of 95.76 GHz/RIU and 100 GHz/RIU for first and second band respectively.

Ultra-broadband terahertz metamaterial absorber based on a hollow vanadium dioxide circular-truncated cone resonator

Terahertz (THz) broadband metamaterial absorbers with high absorptivity have been of great interest due to their potential applications. However, their limited bandwidth severely hinders their further development and wide applications. To address this issue and achieve ultra-broadband and strong absorption properties at THz frequencies, we present an ultra-broadband THz perfect metamaterial absorber using a hollow vanadium dioxide (VO2) circular-truncated cone array and a VO2 film supported by an Au ground plane. Simulated results show that the absorptivity of the absorber reaches more than 90% in the frequency range of 0.31–10 THz at normal incidence with a relative absorption bandwidth of 188%. At the same time, the average absorptivity in the frequency range reaches 99.2%. The physical origin of broadband perfect absorption has been elucidated by impedance matching theory and wave interference theory, respectively. The electric field distribution is further discussed to explore the physical mechanism of this absorber. Additionally, it also has the characteristics of polarization insensitivity and wide incidence angle stability. The proposed absorber can have many promising applications in the THz region, such as thermal imaging, thermal detection, and cloaking.

A perfect absorber based on a VO2-tunable Fabry–Perot cavity: an analysis of periodic oscillation absorption characteristics

Terahertz metamaterial absorbers (TMAs) have garnered significant attention as vital electromagnetic wave-absorbing devices. In this study, we designed a terahertz metamaterial absorber (TMA) utilizing an asymmetric Fabry–Perot nanocavity comprising vanadium dioxide (VO2), gold (Au), and polyimide. The TMA exhibits five perfect absorption peaks within 0.1 THz to 10 THz, with an absorption rate exceeding 97%, peaking at 99%. The absorption rate oscillates periodically between 0 and 1, and its oscillating absorption peak can be determined by f m ( fm=(2m+1)c0/(4tε2 ), while tunability of the absorption rate between 15% and 97% is achievable by adjusting the conductivity of (VO2) (2×102∼2×105S/m). The physical mechanism of the absorption peak was analyzed by simulation and compared with theoretical analysis. The results show that the absorption peak of the absorber’s absorptivity can be insensitive to polarization and has a wide absorption angle of 80% up to 40◦ or more. Importantly, the thickness of the absorber (VO2) layer can be calculated from the desired absorption frequency and dielectric constant of the interlayer medium, d=ε0/μ0/σ , thus reducing the need for redesigning different resonant layer patterns. This work provides a new perspective on terahertz absorber design.

Theoretical investigation of enhanced terahertz metamaterial absorber integrated with blocked-impurity-band detector

Blocked-impurity-band (BIB) device becomes a prevalent terahertz detection technology, but its overall optical performance, such as quantum efficiency, is constrained by the thickness of the absorption layer. Metamaterial absorbers can effectively concentrate and absorb terahertz waves at a subwavelength scale, and their ultra-thin thickness facilitates device integration. A multi-band metamaterial absorber is developed and simulated tailored for the working band of Ge-doped BIB detectors. The design is founded on a three-layer structure with Ti rectangular resonator, Ge dielectric layer, and Ti reflective layer. This configuration achieves two absorption peaks at 74.16 μm and 92.09 μm, with optical absorption reaching 95.66% and 97.29%, respectively. The operating wavelength can be regulated by altering the geometric parameters of the rectangular resonator, and it exhibits angle-insensitive properties under small-angle incidence. These findings enhance the application of BIB detectors in terahertz detection technology, potentially improving their performance in deep space exploration.

A cross-shaped terahertz metamaterial absorber for brain cancer detection.

The article presents, for the first time, a terahertz metamaterial absorber (TMA) designed in the shape of a cross consisting of four orthogonally positioned horn-shaped patches in succession, to detect brain cancer cells. The design exhibits the property of mu-negative material, indicating magnetic resonance. The proposed TMA has achieved an impressive absorption rate of 99.43% at 2.334 THz and a high Q-factor of 47.15. The sensing capability has been investigated by altering the refractive index of the surrounding medium in the range of 1.3 to 1.48, resulting in a sensitivity of 0.502 THz/RIU. The proposed TMA exhibits complete polarization insensitivity, highlighting this as one of its advantageous features. The adequate sensing capability of the proposed TMA in differentiating normal and cancerous brain cells makes it a viable candidate for an early and efficient brain cancer detector. This research can be the foundation for future research on using THz radiation for brain cancer detection.

Dual-narrowband terahertz metamaterial absorber based on all-metal vertical ring array for enhanced sensing application

In this paper, a novel design of a dual-narrowband metamaterial absorber (MMA) was proposed for using as a high-performance refractive index (RI) sensor in the terahertz (THz) region. The proposed MMA is based on a vertical-ring-shaped (VRS) structure gold film array. Through numerical simulation, it was found that the MMA can achieve high absorption levels of 99.8% and 94.6% at 1.723 THz and 2.457 THz, respectively, which are consistent with the values obtained using coupling mode theory (CMT). The MMA also exhibits high Q-factor values of about 27.35 and 102.38, respectively, which are close to the CMT values of 29.94 and 98.34. The dual-band strong absorption of the MMA is attributed to the guided modes of the critical coupling resonance, and the absorption properties can be adjusted by changing the geometrical parameters of the unit-cell structure. The proposed MMA has a narrowband and a higher Q-factor, making it suitable for RI sensing, with a sensitivity of about 1.66 and 1.88 THz RIU−1, and a figure-of-merit (FOM) of about 259.4 and 659.7 RIU−1, respectively. These findings open up new opportunities for the development of highly efficient MMAs, which have potential applications in biochemical sensing and detection in the THz region.

Five narrow bands terahertz metamaterial absorber based on metal and Dirac semi-metal for high sensitivity refractive index sensing

A five narrow bands terahertz metamaterial absorber based on metal and Dirac semi-metal for high sensitivity refractive index sensing is designed in this paper. The absorber is a traditional sandwich structure. And the most remarkable difference is that two hybrid materials (metal and Dirac semi-metal) are used in the top layer. The numerical results show five absorption peaks can be achieved at 5.527, 5.759, 7.247, 9.257 and 10.186 THz, among which the perfect absorption achieve at 5.759, 7.247 and 10.186 THz, respectively. The physical mechanism of the proposed absorber is analyzed qualitatively and quantitatively by electric field distributions and couple-mode theory. In addition, the sensing application of the proposed absorber is also studied. The sensitivity of the sensing band can reach up to 3.89 THz/RIU by computation. Finally, we design a specific application scenario to ensure the accuracy of the absorber in application through calculation. We believe that the absorber we designed will shine brilliantly in the fields of thermal imaging, thermal radiation and photothermal detection.

Hydrophobic terahertz metamaterial absorber sensor for renal cancer detection application

In this paper, a hydrophobic terahertz (THz) metamaterial absorber sensor aiming to detect renal cancer cells is proposed. The absorption properties, physical mechanism, structural parameters, sensing properties, and wettability of the sensor are theoretically investigated using the full-vector finite element method. The results indicate that the sensitivity (S), quality factor (Q) and figure of merit (FOM) for A-mode and B-mode are 180.46 GHz/RIU, 1128.23, 226.59 and 211.33 GHz/RIU, 1103.54, 246.59, respectively. The Q-factor and FOM are higher than those of the current sensors. The device can accurately differentiate between cancerous and normal cells in renal tissue. Additionally, the sensor possesses self-cleaning and self-protection capabilities due to the hydrophobic layer of polytetrafluoroethylene (PTFE). This provides a solid foundation for the repeated use and cost reduction of the sensor. Given these advantages, the proposed sensor has potential application value in the field of bio-detection and sensing.

Modelling and analysis of a triple-band metamaterial absorber for early-stage cervical cancer HeLa cell detection

The paper introduces a unique design and analysis of a terahertz metamaterial absorber (MMA) that can be used for early detection of cervical cancer by employing microwave imaging techniques. Computer Simulation Technology (CST) is used to design and analyze the proposed absorber. The MMA operates in the frequency range of 6–8 THz and can absorb energy in three specific spectral bands: 6.606 THz, 6.824 THz, and 7.426 THz, with absorption peaks of 99.75 %, 99.87 %, and 99.73 % correspondingly. The working principle of the absorber is described using the impedance matching and interference theory. The electric field (E), magnetic field (H), and surface current of the MMA are also examined. Finally, detecting cancerous HeLa cells is also being investigated by analyzing the E-field and H-field using microwave imaging. The suggested biosensor features a high-quality factor of 494.3, a frequency shifts per refractive index of 1.08 THz/RIU, and a figure of merit (FOM) of 42. The suggested MMA-based sensor has numerous advantages and can be utilized for early-stage cervical cancer detection.

MEMS reconfigurable terahertz meta-absorber with polarization-dependent and sensing characteristics

This study presents and demonstrates a design of a micro-electro-mechanical system (MEMS) reconfigurable terahertz (THz) metamaterial absorber (TMA) that shows tunable free spectra range with a maximum value as 166 GHz in transverse magnetic mode and switchable resonance from 1.24 THz to 1.53 THz. The unit structure of TMA consists of two movable rectangular resonators aside and an x-shaped resonator at the center comprising two c-shaped resonators connected upside down. The material configuration of TMA is typical of the metal–insulator-metal sandwich configuration. That is a bottom Au layer preventing the penetration of the THz wave, a dielectric SiO2 layer to accommodate and absorb the incident wave, and a patterned Au structure array to select the resonant frequency. The electromagnetic response of TMA could be flexibly modulated when the structure is reconfigured by changing the gaps between x-shaped resonators and rectangular resonators based on the MEMS platform. Meanwhile, owing to the asymmetry of resonant structure, the electromagnetic response of TMA could be tuned from single-, dual-, triple- quad-resonances by varying the polarization state of incidence. Furthermore, the sensitivity of TMA is explored and demonstrated with remarkable linearity under a variation of the surrounding environment refractive index from 1.0 to 2.0. The feasibility of TMA is validated as the experimental absorption spectra are well meet the simulation results. The above results indicate the proposed TMA possesses great potential applications in multiple resonance switches, polarization switches, and highly efficient environmental sensors.

Theoretical simulation of a dual-band and dual-broadband terahertz metamaterial absorber using two asymmetric rectangular rings

Theoretical simulation of a dual-band and dual-broadband terahertz metamaterial absorber using two asymmetric rectangular rings

Tunable ultra-broadband terahertz metamaterial absorber enabled by high-order resonances of single square VO2 patch

Tunable ultra-broadband terahertz metamaterial absorber enabled by high-order resonances of single square VO2 patch

Temperature and refractive index sensor based on perfect absorber in InSb double rectangular ring resonator metamaterials

InSb is an important semiconductor material in the field of optoelectronic devices due to its high electron and hole mobility, low effective mass, and low energy gap at room temperature. In this paper, a thermally controlled dual-band terahertz metamaterial absorber with a patterned InSb film is designed and studied. The unit cell of the proposed metamaterial is composed of combined InSb double rectangular ring resonators (DRRR) adhered on a continuous gold layer and substrate. Finite-difference-time-domain (FDTD) simulation results demonstrate that the absorption peak can reach 98.95 %, and 99.45 % at 1.499 THz and 1.592 THz when the external environment temperature is 283 K. Electric field distribution and parameter sweep indicate the two absorption peaks result from the near-field coupled linear superposition between the big square and small square resonators. The proposed absorber not only has the features of wide incident-angle stability, but also polarization insensitivity. Besides, the proposed absorber shows temperature-tunable features due to the temperature-dependent variation of the permittivity of InSb material. The InSb pattern proposed in this paper provides an alternative method for designing of dual parameters sensor in the terahertz band, the proposed dual-band absorber can function as a temperature sensor with sensitivities of about 8.6 GHz/K and 12.8 GHz/K, respectively. The proposed dual-band absorber can also be used as a refractive index sensor with sensitivities of about 1.065 THz /RIU, and 0.499 THz /RIU, respectively. Therefore, the present work provides an effective method for implementing thermally and refractive index sensors in the terahertz range.

Multi-functional and actively tunable terahertz metamaterial absorber based on graphene and vanadium dioxide composite structure

In this paper, a fabrication friendly terahertz (THz) metamaterial hybrid absorber comprised of square-shaped graphene and U-shaped vanadium dioxide is proposed and numerically analyzed. This device can be tuned dynamically to function as a wide-broadband, reduced-broadband, multi-band, or perfect single-band absorber. Switchable qualities are achieved through simultaneous tuning of the electrical properties of graphene and the phase transition properties of vanadium dioxide. The theory behind the absorption is explored using the distribution of the electric field and the theory of impedance matching. It is clear from the simulation results that the suggested structure can perform as a wide-broadband absorber for the transverse electric (TE) wave during the insulating phase of vanadium dioxide. In this case, graphene’s Fermi energy is configured to 0.7 eV, and it has a 0.1 ps relaxation time. Moreover, only changing the relaxation time to 0.5 ps enables the identical structure to perform as a multi-band absorber. On the contrary, the designed structure exhibits a reduced broadband absorption for the TE wave when the vanadium dioxide is thermally tuned to a metallic state and graphene’s Fermi energy is configured to 0 eV with a 0.1 ps relaxation time. Moreover, by inducing the metallic state in vanadium dioxide and adjusting the Fermi energy of graphene to 0.3 eV with a 0.1 ps relaxation time, the structure performs as a single-band perfect absorber. The main advantage of this work is that the proposed absorber device can be operated as a single-band, multi-band, or broadband absorber with two different bandwidths by applying external voltage and changing temperature. Additionally, for both the TE and transverse magnetic (TM) waves, the structure retains a high level of absorption until 40° of incident angle. Finally, due to its multi-functional property, simple geometric structure, and actively adjustable function, the presented structure has possible real-life applications in the terahertz frequency range.

Design of ultra-thin multi-band sub-terahertz metamaterial absorber using three concentric ring resonators with same opening direction

In this paper, an ultra-thin sub-terahertz multi-band terahertz metamaterial absorber is proposed, its cell consists of three concentric ring resonators with the same opening direction, which can realize three discrete absorption peaks in the sub-terahertz frequency domain. The absorption peaks are mainly formed when the three open circular resonators interact with each other, and the superposition of the three discrete peaks creates a three-band absorption. The physical mechanisms of three-band absorption are illustrated by the electric fields and surface current distributions of three absorption peaks. Adjustment of the absorption effect could be obtained by altering the dimensions of the cleft circular resonator. By fixing the dimensions and changing the opening direction, these resonators will couple to each other and play an important role in regulating the frequency, intensity, and number of absorption peaks. Moreover, the multi-band metamaterial structure could be combined with vanadium dioxide, a phase change material, to actively modulate the absorption. In addition, the three-band metamaterial absorber has the characteristics of polarization-sensitive and wide-angle, which has extensive applications in the domains of security detection, biomedicine and communication.