Terahertz Metamaterial Sensor Research Articles

High-Q factor terahertz metamaterial sensor based on quasi-BIC

In this paper, we proposed a terahertz (THz) metamaterial sensor, which consists of an array with two mirrored double split ring resonators (DSRRs) in one unit cell deposited on a lossless polyimide substrate. The THz spectral response show that when the two DSRRs in one unit cell are mirror symmetric and center symmetric simultaneously, two types of symmetry-protected bound states in the continuum (BICs) can be generated with the incident polarization unchanged. When the gaps are on the short or long arms of DSRRs, different modes of BIC can be observed. By breaking the symmetry of the structure with the gaps deviating from the center line of the DSRRs, quasi-BICs can be achieved, which can provide high Q-factors for our designed THz metamaterial sensor. The performance of the sensor is also evaluated, which has the characteristics of high Q-factor, high sensitivity, and high linearity. The integration of quasi-BIC and THz sensing technology will help solve the problems faced in the design of ultra-high Q-factor THz sensors and further expand the applications of terahertz technology.

Multi-parameter terahertz metamaterial sensors based on single-layer quarter ring patterns

A terahertz metamaterial sensor based on a single-layer quarter ring pattern is proposed to realize the simultaneous measurement of temperature, refractive index, and other parameters through a metasurface consisting of a patterned quarter ring gold layer and a silicon substrate. Field finite element numerical simulations were performed to analyse the transmission and reflection spectra. A two-parameter sensor combined with electric field distribution was realized using multiple peaks, thus revealing the physical mechanisms of the interaction in metamaterial structures. In addition, the effect of each geometrical parameter on the sensor performance is also simultaneously analysed to verify the optimal selection of structural parameters. On this basis, the sensors are theoretically analysed at different incidence and polarization angles, and the results show that the transmittance is not sensitive to the polarization angle. The simulation results show that the transmittance at the resonant frequencies of 0.48 THz, 0.64 THz, 0.79 THz and 1.04 THz are 93.7 %, 79.1 %, 38.4 % and 50.8 %, respectively, and the refractive index sensitivities at the resonant frequencies are 6.84 GHz/RIU, 7.42 GHz/RIU, 8.22 GHz/RIU and 32.11 GHz/RIU, and quality factor Q of 6.76, 9.63, 15.51 and 26.28, respectively. The devices proposed in this study are simple in structure, easy to fabricate, easy to miniaturize and can be integrated for sensitivity, multi-parameter sensors. They can be functionally designed for chemical and biological sensing and other important applications.

Dual-band terahertz metamaterial sensor and its sensing capacity enhanced with a central-relief design.

In this paper, a dual-band terahertz metamaterial sensor based on aluminum and silicon is proposed and simulated. The aluminum surface, which is deposited on a silicon substrate, is made of a C-shaped frame resonator, a rectangular beam, and a cross. The device is insensitive to the change of incident angle in the range of 0°-30°, which shows the great transmission stability of the sensor. By examining the resonance frequency shift, it is shown that 98.3 and 237.5GHz/RIU refractive index sensitivity can be obtained near 1.76 and 2.404THz transmission dips of the proposed structure, respectively. The two dips can be used to sense analytes in different refractive index ranges, respectively. For Dip 1 at 1.76THz, the range is 1.0-1.6. For Dip 2 at 2.404THz, the range is 1.6-2.0. Different from traditional multi-band metamaterial sensors, two dips generated by the proposed device can measure continuous and non-multiplexed refractive index ranges, respectively. Because the resonance frequencies of matters are different, such a characteristic enables the device to measure different types of analyte using the appropriate resonant peak. A central-relief design is then proposed based on perturbation theory to further improve its sensing performance. The aluminum cross is covered by polyimide, which can interfere with the scattering field on the metal surface and affect the transmission results. For both transmission dips, the optimized structure realizes higher sensitivities of 111.7GHz/RIU and 262.5GHz/RIU, respectively. More significantly, the optimized structure also has the characteristic of a wide and non-multiplexed refractive index range. In addition, the effects of analyte thickness and polyimide layer thickness on sensor performance are also discussed. The proposed structure opens up new prospects in the design of multiple-band terahertz metamaterial sensors. It can also meet the sensing needs of biomedical, environmental monitoring, and industrial manufacturing.

Passive trapping of biomolecules in hotspots with all-dielectric terahertz metamaterials

Electromagnetic metamaterials feature the capability of squeezing photons into hotspot regions of high intensity near-field enhancement for strong light-matter interaction, underpinning the next generation of emerging biosensors. However, randomly dispersed biomolecules around the hotspots lead to weak interactions. Here, we demonstrate an all-silicon dielectric terahertz metamaterial sensor design capable of passively trapping biomoleculars into the resonant cavities confined with powerful electric field. Specifically, multiple controllable high-quality factor resonances driven by bound states in the continuum (BIC) are realized by employing longitudinal symmetry breaking. The dielectric metamaterial sensor with nearly 15.2 experimental figure-of-merit enabling qualitative and quantitative identification of different amino acids by delivering biomolecules to the hotspots for strong light-matter interactions. It is envisioned that the presented strategy will enlighten high-performance meta-sensors design from microwaves to visible frequencies, and serve as a potential platform for microfluidic sensing, biomolecular capture, and sorting devices.

Detection of Trace Dibutyl Phthalate Based on Multiresonant Terahertz Metamaterial Sensor

Detection of Trace Dibutyl Phthalate Based on Multiresonant Terahertz Metamaterial Sensor

Design and application of terahertz metamaterial sensor based on bull’s-eye-shaped resonator in detection of hexadecane

Hexadecane, as a kind of typical nonpolar molecule, plays a crucial role in the preparation of reverse micellar solutions, which have been proved to be a suitable tool to overcome water absorption in THz region. In this work, a bull’s-eye-shaped metamaterial sensor is designed, fabricated and used to detect hexadecane by using terahertz spectroscopy. The refraction index and the thickness of the analyte deposited on the resonator were analyzed and discussed by simulating. Then we test whether the combination of the sensor with hexadecane could improve the sensitivity, and verify the sensing properties of the bull's-eye-shaped metamaterial, achieving a frequency shift of approximately 0.14 THz. This approach paves the way for future quantitative detection and qualitative identification of cells or other hydrated substances, offering a neoteric pathway in sensing field.

Using Mirror-based Terahertz Metamaterial Sensor to Chiral Identification and Detection of D-/L- Serine

Using Mirror-based Terahertz Metamaterial Sensor to Chiral Identification and Detection of D-/L- Serine

A Terahertz Metamaterial Sensor Based on Dual Resonant Mode and Enhancement of Sensing Performance

A Terahertz Metamaterial Sensor Based on Dual Resonant Mode and Enhancement of Sensing Performance

A dual-band terahertz metamaterial sensor with high Q-factor and sensitivity

A dual-band terahertz metamaterial sensor with high Q-factor and sensitivity

Terahertz Metamaterial Sensor Based on Electromagnetic Induced Transparency

A graphene-based terahertz electromagnetically induced transparency (EIT) metamaterial sensor is proposed and studied. The sensor is made up of two bright modes: a graphene strip resonator and a 7-shape resonator. In a terahertz metamaterial sensor based on EIT, the metamaterial structure is designed to have two resonant modes that are coupled through a common resonator. When terahertz radiation hits the metamaterial, the two resonant modes interact, creating a window of transparency in the transmission spectrum. It illuminated that the physical mechanism of the EIT effect lay in the recombination effect of the conductive resonators. By changing the carrier relaxation lifetime or the Fermi energy of the graphene, the amplitude or the location of the EIT window could be actively tuned. The terahertz metamaterial sensors based on EIT have the potential to provide highly accurate and sensitive measurements in a wide range of fields and could lead to important advances in medical diagnostics.

A terahertz metamaterial sensor with high-sensitivity based on electromagnetically induced transparency effect

In this study, we design an electromagnetically induced transparency (EIT) effect based on a metamaterial sensor composed of three split-ring structures in the terahertz range. The EIT transparency window appears at 1.83 THz due to the electromagnetic coupling between the three split-rings. To analyze its physical mechanism, we use the ‘two-particle’ model and obtain good consistency between the simulation and theoretical results. The simulation results also show that when the thickness of the measured object is 15 μm and the refractive index is between 1 and 1.5, the refractive index sensitivity of the sensor is as high as 423.9 GHz RIU−1, and the figure of merit value is 6.9. In addition, the sensor is used to simulate the detection and distinction of different types of microbiota. We expect that this work will pave the way for designing high-sensitivity EIT sensors in the terahertz region and promote the development of terahertz sensing and label-free detection of pathogens.

Research on highly sensitive quantitative detection of aflatoxin B2 solution based on THz metamaterial enhancement

Food such as cereal crops, oil crops and dairy products are very easy to produce highly toxic and carcinogenic aflatoxins during inappropriate storage. Therefore, it is of great significance to achieve rapid, non-destructive and highly sensitive detection of aflatoxin. A terahertz metamaterial sensor with “X” compound double-peak structure is designed based on electromagnetic theory to realize highly sensitive detection of aflatoxin B2 solution. It is found that the amplitude of the transmission peak of the terahertz transmission spectrum of aflatoxin B2 (AFB2) solution around 1.2 THz and 2.0 THz gradually decreased with the increase of the concentration of aflatoxin B2 solution, and the frequency of the transmission peak gradually shifted to high frequency with the increase of the concentration of aflatoxin B2 solution, hence a full concentration model was established. And a strategy of first classifying concentration intervals and then building a grouped quantitative model was proposed. The Limit of Detection (LOD) of the interval sub-model of low and medium concentration of aflatoxin B2 solution has been greatly improved with the LOD of the optimal grouping model was 7.28 × 10−11 mg/ml, 4.19 × 10−9 mg/ml and 1.22 × 10−7 mg/ml, respectively. This research verifies the feasibility of terahertz metamaterial sensor based on “X” composite double-peak structure combined with THz-TDS technology for highly sensitive detection of aflatoxin B2 solution. And it provides a new rapid, non-destructive and highly sensitive detection of aflatoxin in food.

Application of circuit analog optimization method in fast optimization of dynamically tunable terahertz metamaterial sensor

The simulation design of terahertz metamaterial sensors with dynamically tunable parameters typically relies on manual parameter tuning for structural optimization. However, this method is often prone to subjective factors and suffer from issues such as frequent reconstruction of simulations, high computational costs, long processing times, and suboptimal optimization results. In this paper, we propose a circuit analog optimization method (CAOM), which constructs equivalent RLC parameters to achieve a highly fitted terahertz transmission spectrum frequency obtained from CST full-wave numerical simulation. To validate the effectiveness of the proposed model, we use a typical periodic structure unit, a double-nested split ring resonator (DSRR) terahertz metamaterial sensor, as the simulation object. Both the inner and outer open resonant rings of the sensor are made of graphene, as a result, the opening size and Fermi level of the resonant rings are dynamically tunable. The results of the validation demonstrate that the adjustments of the sensor parameters can be effectively mapped by the changes of the equivalent RLC parameters. And the proposed equivalent circuit model has parameter substitutability in the simulation modeling of split ring resonator type sensors. The proposed equivalent circuit model exhibits parameter substitution in the simulation modeling of open resonant ring-type sensors. To achieve optimal sensing performance for the electromagnetically induced transparency (EIT)-like resonant peak (with a resonant frequency of f 2) of the sensor under constrained conditions, we introduce the genetic algorithm (GA) into the equivalent circuit model to enable fast optimization of the opening sizes of the inner and outer resonant rings, as well as the Fermi level of the sensor. Moreover, the accuracy of the optimization results is verified by CST simulations. Finally, the optimization results show that the optimal FOM of the EIT-like resonant peak within the given parameter range is 0.712, which is greater than that of any randomly combined parameters. This numerical result demonstrates the effectiveness of the proposed CAOM. The proposed model and optimization method have potentials to inspire further research in device design, performance optimization, theoretical modeling, etc.

Flexible terahertz Metamaterial sensor for sensitive detection of imidacloprid

In this paper, a flexible terahertz (THz) Metamaterial (MM) with high sensitivity is proposed for the detection of the pesticide imidacloprid. The MM sensor is composed of a polyimide (PI) substrate and a periodic aluminum (Al) split ring resonator array. The sensing performance of the MM is verified by both simulation and experiment. The simulation results show that the refractive index (RI) sensitivity of the proposed MM sensor is 220.7 GHz/RIU, and the figure of merit (FOM) of this MM is 1.52. Then, the sensing performance of the MM sensor is verified by using imidacloprid solutions with different concentrations. The experimental results show that the detection sensitivity of the MM sensor is 12.3 GHz/(mg/ml), and the limit of detection (LOD) is 0.0112 mg/ml. The THz MM sensor proposed in this paper is flexible, simple to make, cost-effective, highly sensitive and has a very broad application prospect in the concentration detection of pesticides such as imidacloprid.

Study on qualitative identification of aflatoxin solution based on terahertz metamaterial enhancement.

Aflatoxin is the main carcinogen that contaminates agricultural products and foods such as peanuts and corn. There are many kinds of aflatoxins, mainly including aflatoxin B1 (AFB1), aflatoxin B2 (AFB2), aflatoxin G1 (AFG1) and aflatoxin G2 (AFG2). Different types of aflatoxins have different toxicity and different levels of contamination to agricultural products as well as food. Therefore, the rapid, non-destructive and highly sensitive qualitative identification of aflatoxin species is of great significance to maintain people's life and health. The conventional terahertz detection method can only qualitatively identify the samples at the milligram level, but it is not suitable for the qualitative analysis of trace samples. In this paper, a terahertz metamaterial sensor with "X" composite double-peak structure was designed based on electromagnetic theory to investigate the feasibility of THz-TDS technology based on a metamaterial sensor for the qualitative identification of trace aflatoxin B2, G1 and G2 solutions. Firstly, the terahertz transmission spectra of eight different concentrations of aflatoxin B2, G1 and G2 were collected respectively, and then the differences of terahertz transmission spectra of different aflatoxin species were investigated. Finally, the terahertz transmission spectra of aflatoxin B2, G1 and G2 solutions were modeled and analyzed using chemometric methods. It was found that there were significant differences in the transmission peak curves of different kinds of aflatoxin. Through the comparative analysis of different models, it was concluded that the prediction accuracy of the CARS-RBF-SVM model was the highest, and the accuracy of the calibration set reached 100%. 119 out of 120 predicted samples were correctly predicted, and the prediction accuracy was 99.17%. This study verified the feasibility of qualitative identification of trace aflatoxin B2, G1 and G2 solutions by a metamaterial sensor based on the "X" composite double-peak structure combined with THz-TDS technology, and provided a theoretical basis and a new detection method for the qualitative identification of trace aflatoxins. This will facilitate the rapid, non-destructive and highly sensitive qualitative detection of different kinds of aflatoxins in food and agricultural products. At the same time, this study has important implications for promoting the qualitative detection of other trace substances.

A novel terahertz integrated sensor for liquid samples detections based on metamaterial and embedded microfluidic channels

THz metamaterial (MM) microfluidic sensors, which can be utilized for the detection of small volume liquid specimen, have attracted much attention in biosensing applications. In this paper, we propose a novel microfluidic channel embedded terahertz MM sensor, which employs split ring resonators (SRRs) and asymmetric two-gap SRRs for the detection of liquid samples. Unlike currently reported THz MM microfluidic sensors utilizing microfluidic superstrate-metal-substrate structure, our approach combines the microfluidic superstrate with substrate, by designing micro-channels underneath the gap of the SRRs within the polydimethylsiloxane substrate. It could be easily fabricated by standard photolithography techniques. The simulated results show that the performance of the sensor is dependent on the spacing angle between two gaps, the orientation of the gaps, as well as the polarization of electric fields. Furthermore, maximum Q factors of 9.5 and 44 are achieved for dipole resonance, with corresponding figure of merits of 0.63 and 2.89 RIU−1 for transmission and reflection scenarios. Thus, this concept and method not only provides sensitive biosensing for liquid-based samples, but also can be applied to other MM structures to further improve the sensitivity.

A Four-Band Terahertz Metamaterial Sensor Based on Symmetric E-Shaped Structure

To realize the multi-frequency selectivity of the analyte, a novel four-band terahertz metamaterial sensor is proposed in this work. In particular, the sensor performance is analyzed theoretically and numerically within a terahertz frequency range (0.8–1.5 THz) via the finite element method. According to the results, higher-order Fano resonance is the main cause of the four narrow and sharp transmission valleys in the operating band region of the sensor, yielding high resolution with Q values up to 177. Moreover, this sensor is polarization-insensitive over a wide polarization angle range of 0° to 50°. In addition, the sensor achieves refractive index sensitivity of 200 GHz/RIU and offers FOM values of up to 26.7. The sensor proposed in this study exhibits a simple structure, frequency selection characteristics, low cost, and enhances the interaction between terahertz waves and substances, which is of great theoretical and practical significance for the development of terahertz functional devices such as sensors and filters.

Analysis of reaction between vitamin B6 and bovine serum albumin based on a terahertz metamaterial sensor.

A four-peak terahertz metamaterial sensor was used to detect the reaction between different concentrations of vitamin B6 (VB6) and bovine serum albumin (BSA), which achieves a concentration range (0.015-0.125 mg/µl) of VB6 and a maximum binding concentration (0.05 mg/µl) of VB6 and 0.0875 mg/µl BSA. To understand the combination of VB6 and BSA, the reactants between VB (VB1, VB3, and VB5) with the same concentration (0.05 mg/µl) and a BSA solution with a concentration of 0.0875 mg/µl were carried on the surface of the sensor. Experimental results show that the reactants cause the four resonance peaks of the sensor to produce the coincident redshift, which is the same as the order of their binding coefficients determined by the fluorescence method. The experimental process indicates that it is feasible to use terahertz metamaterials to detect the reaction process of organic matter.

Terahertz Metamaterial Sensor With Ultra-High Sensitivity and Tunability Based on Photosensitive Semiconductor GaAs

We proposed and demonstrated an ultra-high sensitive refractive index metamaterial sensor within terahertz region. The sensor consists of a gallium arsenide (GaAs) structure on the top, aluminum in the middle, and a polyimide as the bottom substrate. The simulation results show that such sensor has an absorption peak at 2.0 THz with the Q-factor up to 444. The sensor is very sensitive to the change of the refractive index (RI) of the surrounding medium. The metamaterial sensor with optimized structure has a sensitivity of 1.762 THz/RIU and a figure of merit (FoM) value of 392 RIU <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> , respectively. Meanwhile, both the absorption peak position and intensity of such metamaterial sensor could be adjustable. The proposed terahertz metamaterial sensor with such high sensitivity and easily tunable properties has broad application prospects in research fields including biomedical sensing, disease diagnosis, and also trace detection of hazardous substances.

Study on the Spectral Characteristics of Plant Growth Regulators Based on the Structure Difference of Terahertz Metamaterial Sensor

In this study, in order to solve the problems of low sensitivity and complex sample pretreatment in traditional detection, a method was proposed to detect plant growth regulators using terahertz combined with metamaterial sensors. Two metamaterial sensors with different structures are designed. The differences of two kinds of metamaterial sensors for detecting plant growth regulators were analyzed from three aspects of frequency domain, time domain and absorption characteristics. It is further proved that the difference of metamaterial structure will lead to the change of frequency shift, time domain waveform and absorption characteristics of measured samples, and the influence of sample concentration on the detection characteristics of the metamaterial sensor. The results show that both metamaterial sensors can effectively detect the four plant growth regulator solutions with concentrations as low as 0.05 mg/L. In terms of detection and sensing, the frequency shift, sensitivity, figure of merit value, vibration amplitude and change rate of absorption intensity of metamaterial sensor 2 are higher than each parameter of metamaterial sensor 1, which has better detection performance. However, in terms of identification between samples, metamaterial sensor 1 is more suitable for the identification of daminozide and naphthaleneacetic acid solutions, and metamaterial sensor 2 was more suitable for the detection of glyphosine and gibberellic acid solutions. It provides a new method for multi-target fusion to detect plant growth regulators with high sensitivity and high accuracy.