Terahertz Metamaterial Research Articles

An advanced deep learning-driven Terahertz metamaterial sensor for distinguishing different red wines

Terahertz time-domain spectroscopy (THz-TDS) encounters two issues in the detection field, which refer to the detection target for solid samples caused by the strong absorption of water and the large content target substance led by the low sensitivity. Fortunately, terahertz metamaterial (THz-MM) that can carry liquid samples and amplify signals solves the above problems well. In addition, the THz-MM can achieve the detection of trace substances through the resonance peak shift generated by designing suitable structures. However, since most researchers focus on designing complex structures rather than analyzing data, deep learning (DL) that can mine new features from original features and construct decision models is used to research the rich information in THz-MM sensor data. In the current research, a flexible transmissive THz-MM in the shape of a circle (‘O’ shape) was designed by depositing the gold on the polyimide substrate. Firstly, the structures referring to substrate thickness (ST), metal thickness (MT) and ring width (RW) were optimized, and the performances referring to principle, stability and sensitivity were evaluated. Next, the best THz-MM (ST: 16 µm, MT: 0.2 µm, RW: 6 µm) was prepared and characterized from morphology, thickness and consistency. Then, different concentrations of anthocyanins (R2: 0.9982) and tannic acid (R2: 0.9736) were successfully predicted by combining the resonance peak shifts. Finally, resonance peak descriptors were constructed and combined with DL referring to a fully connected neural network (FCNN) model to successfully identify different varieties of red wines (Precision: 91.11 %; Recall: 90.74 %, F1-score: 90.83 %; Accuracy: 90.74 %). Overall, the current research presents an advanced DL-driven THz-MM sensor, which promotes the process of THz-TDS technology in the food detection field

Ultrathin Flexible Terahertz Metamaterial Absorber With High Sensitivity for Bending Strain Sensing

Ultrathin Flexible Terahertz Metamaterial Absorber With High Sensitivity for Bending Strain Sensing

Metamaterial Sensing of Cyanobacteria Using THz Thermal Curve Analysis.

In this study, we perform thermal curve analyses based on terahertz (THz) metamaterials for the label-free sensing of cyanobacteria. In the presence of bacterial films, significant frequency shifts occur at the metamaterial resonance, but these shifts become saturated at a certain thickness owing to the limited sensing volume of the metamaterial. The saturation value was used to determine the dielectric constants of various cyanobacteria, which are crucial for dielectric sensing. For label-free identification, we performed thermal curve analysis of THz metamaterials coated with cyanobacteria. The resonant frequency of the cyanobacteria-coated metasensor changed with temperature. The differential thermal curves (DTC) obtained from temperature-dependent resonance exhibited peaks unique to individual cyanobacteria, which helped identify individual species. Interestingly, despite being classified as Gram negative, cyanobacteria exhibit DTC profiles similar to those of Gram-positive bacteria, likely due to their unique extracellular structures. DTC analysis can reveal unique characteristics of various cyanobacteria that are not easily accessible by conventional approaches.

Inverse Design of Multistructured Terahertz Metamaterial Sensors Based on Improved Conditional Generative Network.

The terahertz (THz) metamaterial sensor design is typically complex and requires substantial expertise in physics. To simplify this process, we propose a novel reverse design model based on an improved conditional generative adversarial network that integrates self-attention generative adversarial network and Wasserstein generative adversarial network (WGAN) networks, and is referred to as the self-attention conditional Wasserstein GAN (SACW-GAN) model. By using the target response of the sensor as the input to the generator network, and incorporating labeling information, an attention mechanism, and the Wasserstein distance, we achieve effective reverse design of THz metamaterial sensors. The simulation results demonstrate the model's high performance, with spectral and image accuracies of 95% and 97%, respectively. This deep learning approach offers new perspectives and methodologies for the reverse design and application of THz metamaterial sensors, significantly advancing the field.

Development of a Terahertz Metamaterial Micro-Biosensor for Ultrasensitive Multispectral Detection of Early Stage Cervical Cancer

Development of a Terahertz Metamaterial Micro-Biosensor for Ultrasensitive Multispectral Detection of Early Stage Cervical Cancer

Graphene‑vanadium dioxide ultra-wideband dual regulated absorber

In this paper, we propose a novel tunable THZ absorber consisting of a patterned graphene layer and a metal plate separated by a vanadium dioxide dielectric layer. The absorbent has a simple structure, is easy to make graphene patterns, and has a dual regulatory function. The ability to double regulate comes from the fact that the state of vanadium dioxide changes with the temperature between the insulating phase and the metal phase, resulting in a change in its conductivity. When vanadium dioxide is in the insulating phase, the total reflection characteristics of the absorber are >7 THz, and when vanadium dioxide is in the metallic phase, the absorber achieves near-perfect absorption in the ultra-wideband range of 3 THz to 12.4 THz (9.4 THz). Local surface plasmon resonance explains the perfect absorption. Compared with previous absorbers, our proposed absorbers are not only simple in structure, the graphene pattern is also easy to process, but also have double adjustment and perfect absorption in the ultra-wideband range, are not sensitive to polarized light, and have large tolerances for the Angle of incident. The further development and enrichment of terahertz metamaterials and metasurface devices will also have beneficial implications for terahertz wave applications in sensing, communications, and radar. Due to their significant application value in stealth, detection, and communication, metamaterial absorbers have become a research hotspot in the field of metamaterials.

Recent Developments and Prospects of Electromagnetically Active Metamaterials in Biosensing

This paper provides an overview of the progress of research on electromagnetically active metamaterials in the field of biosensing, especially the potential of terahertz metamaterials for biosensor applications. Electromagnetically active metamaterials exhibit a negative refractive index and perfect absorption through their special structure, and their electromagnetic behavior is affected by their structure and geometry, which is different from traditional materials. The article reviews the application of terahertz technology for the bio-detection of cancer cells and apoptotic processes using periodic metal arrays by terahertz biosensors, demonstrating the advantages of terahertz biosensors, such as high sensitivity and detection without labeling. This paper presents a comprehensive overview of the advancements in research concerning electromagnetically active metamaterials within the domain of biosensing, with a particular emphasis on the potential applications of terahertz metamaterials in biosensor technology. Electromagnetically active metamaterials are characterized by their negative refractive index and perfect absorption, which arise from their distinctive structural properties. The electromagnetic behavior of these materials is significantly influenced by their design and geometry, setting them apart from conventional materials. The article examines the utilization of terahertz technology for the bio-detection of cancer cells and apoptotic processes tunability, employing periodic metal arrays in terahertz biosensors. It underscores the advantages of terahertz biosensors, which include high sensitivity and the capability to detect biological entities without the necessity for labeling. Terahertz metamaterial biosensors are promising for protein, virus, and cancer cell detection. This paper also explores the design and application of chiral metamaterials, especially indium tin oxide-based mid-infrared chiral metamaterials, to solve the problem of the large size of traditional materials and investigates their circular dichroism. Looking ahead, electromagnetically active metamaterials, especially terahertz metamaterials, are expected to improve resolving power and sensitivity, reduce costs, and expand the applications of biosensors in the biomedical field. The applications and research of these sensors will continue to advance with the advancement of micro and nanoprocessing technologies.

Conductively coupled terahertz metamaterials with dual functions of electromagnetically induced transparent and Fano effects for sensing applications

A terahertz metamaterial structure consisting of two U-shaped split-ring resonators and a horizontal cut-line resonator is designed for realizing the electromagnetically induced transparency (EIT) effect and the Fano resonance effect. The genesis of the EIT and Fano resonance bifunctionality is illustrated by combining the near-field distribution analysis of transparent windows and transmission dips. Interestingly, the bifunctional dual-band transparency effect could transform into a single-functional single-band transparency effect when we change the position of the square metal sheet in the vertical direction of the composited terahertz metamaterial structure. In addition, based on the high-quality factor of Fano resonance response, the proposed bifunctional terahertz metamaterial device has good refractive index sensing sensitivity. These results indicate that our proposed terahertz metamaterial can provide guidance for the design of subsequent multifunctional and integrated metamaterials and optoelectronic devices.

Design, simulation, and experimental realization of a high-sensitivity polarization-independent electromagnetically induced transparent terahertz metamaterials.

Electromagnetically induced transparency (EIT) originating from quantum physics can lead to a very narrow-band transparent window, which is sensitive to minor environmental changes. The rational construction of highly sensitive EIT metamaterials facilitates its wide sensing application in the terahertz (THz) range. In this work, we designed what we believe to be a novel polarization-independent EIT terahertz metamaterial sensor composed of four symmetrical Chinese Taichi-like rings and a crossed-shaped structure. The Taichi-like rings excite a high-quality planar toroidal dipole resonator and simultaneously crossed-shaped structure induces electric dipole resonance. The EIT effect is realized by the two strongly coupled resonators. The sensor shows higher sensing characteristics for the ultrathin analyte and refractive index than that of the two resonance models alone. The refractive index sensitivity reaches a maximum value of 331.3 GHz/RIU at a saturated thickness of 10 µm. The sensitivities are higher than that of most reported sensors at the same resonance frequency (range from 0.49 THz to 2.77 THz) and with the same analyte thickness (range from 2 µm to 15 µm). We experimentally fabricated the sensor and demonstrated its fascinating EIT effect. Our results pave the way for the design ideas of new polarization-insensitive and high-performance tuned EIT sensors in the THz band.

Graphene metamaterial (GMM) based dual mode, tunable, and broadband THz absorber with triple circular split ring structure

In this study we investigated a novel approach to designing a graphene metamaterial (GMM) based terahertz (THz) absorber with dual-mode functionality, tunability, and broadband absorption capabilities. The study leverages the unique properties of graphene, a material known for its exceptional electronic and optical characteristics, combined with metamaterials to achieve efficient THz absorption. Here we performed extensive simulation on four different types of configurations and found the optimized structure has the highest bandwidth of 3.8 THz and absorption over 90 %. The absorber is designed to operate in two distinct modes, enhancing its versatility for different applications in the THz spectrum. Moreover, the tunability of the absorber is a significant feature, allowing for dynamic adjustment of the absorption frequency, which is crucial for applications in THz imaging, sensing, and communication systems. The broadband nature of the absorber ensures effective performance over a wide range of frequencies, addressing the need for flexible and high-performance devices in emerging THz technologies. This work represents a significant advancement in the field of THz metamaterials, with potential implications for the development of next-generation THz devices.

Enhanced the sensing sensitivity of the metamaterial absorbers with patterned convex graphene in the terahertz

Abstract In this paper, a patterned graphene metamaterial terahertz absorber is theoretically designed. The proposed absorber consists of a gold layer, a dielectric layer of SiO2, and graphene. The sensing sensitivity of the proposed absorber is simulated for the absence and presence of a square convex nanostructure, trapezoidal convex nanostructure, and rounded convex nanostructure. The sensitivity comparison between convex and absent convex nanostructures is studied, compared to no convex nanostructure, the simulated results show that the sensing sensitivity can be improved with the convex nanostructures, it is found that the absorber has two obvious absorption peaks, and it is insensitive to TE and TM polarization, and the maximum sensitivity corresponding to low-frequency and high-frequency modes is 0.911 THz RIU−1 and 1.561 THz RIU−1, respectively. Our work will play an important role in improving the sensing sensitivity of the graphene metamaterial absorber. Meanwhile, it can also greatly promote the application of biological sensing, modulation, integrated photodetectors, frequency selectors, sensors, filters and so on.

Rapid Determination of Rivaroxaban by Using Terahertz Metamaterial Biosensor

Rapid Determination of Rivaroxaban by Using Terahertz Metamaterial Biosensor

Microelectromechanical System-Based Reconfigurable Terahertz Metamaterial for Polarization Filter, Switch, and Logic Modulator Applications.

The terahertz (THz) metamaterials integrated with microelectromechanical systems (MEMS) have led to the realization of dynamic control in amplitude, phase, polarization, and spin angular momentum of the THz wave. In this study, we demonstrate an MEMS-based reconfigurable THz metamaterial (RTM) composed of a split ring resonator (SRR) for real-time modulation of THz wave. By gradually increasing the polarization angle of the incident THz wave, the resonant frequency of SRR switches from 0.74 to 1.16 THz, and the maximum modulation depth is more than 70%. When the MEMS-based RTM is actuated by different DC bias voltages, the polarization-dependent transmission intensity and resonant frequency of the device can be actively tuned. MEMS-based RTM shows logical function characteristics that can be used for logic modulators by performing the driving voltages and polarization states as 2-bit input signals and quantizing the transmission response as "on" and "off" states. The logic gates of "NAND" are at 0.439 THz and "AND" is at 0.732 THz. These results offer potential applications for the proposed MEMS-based RTM in tunable and reconfigurable polarization filters, optical switches, programmable logic modulators, and so on.

THz Metamaterial Sensitivity Enhancement by Reduction of Substrate's Fabry-Pérot Oscillations Using Back Plates as an Optical De-Coupler.

This work presents a new method for the enhancement of sensitivity in Terahertz (THz) spectroscopy on metamaterial (MM) in terms of its resonance frequency shift (ΔF), by attaching the dielectric back plate to the MM's silicon (Si) wafer. The dielectric back plates are designed to minimize the Fresnel reflections at the backside of the substrate, identical to a broadband antireflective (AR) plate tailored for THz. Utilizing broadband AR technology, we demonstrate the concept of decoupling MM resonance from the substrate's Fabry-Pérot (FP) oscillations. This is done by effectively coupling the THz light out of the high-permittivity substrate, resulting in the improved quality factor of the MM resonance and overall plasmonic enhancement on the metasurface. The back plate acts as a surface plasmonic enhancer to the THz MM by increasing the field intensity on the front metasurface, leading to enhancement of dielectric response (MM's ΔF). This makes the MM resonance ultrasensitive to the minor changes of particle size/concentration under test spread on the metasurface, contributing to enhanced resonance ΔF. The plate also makes the Si substrate optically lossless, enabling the full effect of MM resonance shift and increasing the resonance ΔF by 8-fold compared with MM's fabricated on conventional Si substrates. This research is backed-up with system-level CST simulations and experimental THz impedance spectroscopy of the MM. This method and chip structure is CMOS compatible having potential applications for any resonant MM fabricated on a substrate aimed to maximize dielectric sensitivity for biosensing and nanoparticle THz spectroscopy.

A bidirectional broadband multifunctional terahertz device based on vanadium dioxide

We propose a switchable and bidirectional metamaterial terahertz absorber/reflector based on vanadium dioxide. Simulation results show that the device can achieve broadband absorption and reflection by adjusting the phase state of vanadium dioxide. When the vanadium dioxide is in the insulating phase, the device can be a perfect bidirectional broadband absorber with more than 90% absorptivity under normal forward/backward TE/TM-polarized incident wave in the frequency range from 1.9 THz to 10 THz. This excellent absorption characteristic is insensitive to the polarization angle of the incident wave. When the vanadium dioxide is in the metal phase, the device achieves more than 90% reflectivity in the low-frequency range under forward/backward TE-polarized incident wave. In the high-frequency range, the device has both reflection and absorption effects on the TE-polarized wave. When vanadium dioxide is in two different phase states, the performance of device is not sensitive to the electromagnetic wave incidence angle. The change in vanadium dioxide conductivity does not affect the stable performance of the device at high (low) frequencies when used as an absorber (reflector). The proposed device has potential applications in terahertz energy harvesting, detection, sensing, optical switching, and shielding.

Label-free detection of inclusion body formation in E. coli with application of terahertz

Extensive production of recombinant protein is essential for use in various fields. Bacterial cells, especially the Escherichia coli (E. coli) expression system, are widely used for the production of recombinant proteins due to their advantages in time and cost. However, the formation of inclusion bodies (IBs) caused by the production of recombinant protein is a significant issue. Therefore, a precise tool for the detection of IBs is in high demand. In this study, we demonstrated a label-free and rapid sensing platform for the detection of IBs formation in E. coli using terahertz-time domain spectroscopy (THz-TDS) system and terahertz metamaterials. The detection was based on the local polarity difference between E. coli samples with induced (positive) and non-induced (negative) protein overexpression. The formation of IBs in positive samples resulted in a decrease in local polarity compared to negative samples. This local polarity difference, strongly related to intermolecular interactions, influenced THz absorption as the THz regime involves weak intermolecular vibrational modes. Experimental results showed that the THz transmittance (ΔT) and resonance frequency shift (Δf) were significantly different between positive and negative samples, confirming the effectiveness of our method. Specifically, positive samples exhibited a ΔT value of 26.57% and a Δf value of 0.12 THz, while negative samples showed a ΔT value of 31.83% and a Δf value of 0.14 THz. These results highlight the capability of our platform to detect IBs rapidly and accurately.

Terahertz metamaterials for spectrum modulation: structural design, materials and applications

Metamaterials, an artificial electromagnetic (EM) material, have exhibited unique characteristics, enabling innovations in terahertz (THz) wavefront shaping, polarization modulation, surface wave manipulation, and spectrum modulation. In this review, we focus on the advancements in THz metamaterials for spectrum modulation, emphasizing their structural design, special materials, and applications. The review discusses various structural designs, including metal-dielectric composite structures, all-metal structures, and all-dielectric structures, each offering distinct advantages for THz applications. Key special materials such as graphene, vanadium dioxide (VO2), molybdenum disulfide (MoS2), and flexible materials are highlighted for their significant contributions to enhancing the performance and functionality of THz metamaterials. The applications of THz metamaterials in EM stealth and sensing are thoroughly introduced, with a particular focus on biosensing, pesticide detection, and other sensing applications. The review emphasizes the potential of THz metamaterials in developing highly sensitive and selective sensors, as well as efficient THz absorbers and filters. Future perspectives include the continuous development of novel materials, advanced fabrication technologies, and the integration of multifunctional capabilities to further expand the applications and efficiency of THz metamaterials. These advancements are expected to drive significant progress in THz technology, impacting fields such as medical diagnostics, environmental monitoring, food safety, wireless communication, and security.

Femtosecond laser direct writing wedge metallic microcavities for terahertz sensing

Metallic resonators allow the manipulation of electromagnetic fields in subwavelength volumes for strong light-matter interaction, underpinning emerging flat-optics devices. Metamaterials designed with optimized effective mode volume (Veff) for stimulating and maximizing the utilization of high-density photons are highly desirable for sensing applications. Here, we demonstrate a bowtie-type terahertz (THz) metallic aperture metamaterial structure with low Veff for enhanced biosensing. The device leverages the inherent characteristic of the femtosecond laser fabrication process enabling wedge cavities down to 3 µm by tailoring the pulse energy, whose sensing performance is superior to trapezoidal ones. Such a substrate-free, microcavity metallic metamaterial sensor with extremely strong interactions achieves an experimentally normalized sensitivity of 0.654 RIU−1, and demonstrates the detection of L-proline down to 0.87 nmol. These findings provide new insights into the design and optimization of efficient THz metamaterials with tightly confined fields for ultrasensitive biomolecular detection.

A novel tree-slotted metamaterial terahertz antenna to diagnose breast cancer cells

A novel tree-slotted metamaterial terahertz antenna to diagnose breast cancer cells

Optical terahertz metamaterial switch controlled via high-stability CsPbBr3 microcrystals.

Dynamic control of terahertz metamaterials using thin organic perovskite active layers has been extensively researched. However, the preparation of organic perovskite devices requires strict environmental conditions, and the devices are prone to hydrolysis in air, which reduces performance. Herein, we report an optical terahertz metamaterial switch controlled via hybridization with high-stability CsPbBr3 microcrystals prepared through precipitation from a water-dimethylformamide (DMF) mixed-solution. Under light excitation, a modulation factor of 24% was achieved based on the photoelectric and photothermal effects of the CsPbBr3 microcrystals. After exposure to air for four months, the modulation factor remained essentially unchanged, demonstrating the exceptional stability of the system generated. Following the integration of CsPbBr3 microcrystals with the metamaterial, a frequency-shift of its dipole resonance and switching of Fano resonance was achieved, providing a novel approach to dynamic control of terahertz waves.