Polarization insensitive terahertz sensor based on U-shaped-circular compact structure

Abstract

The invention provides a polarization insensitive terahertz sensor based on a U-shaped-circular compact structure. The polarization insensitive terahertz sensor comprises at least one sensing unit arranged in an array; wherein each sensing unit comprises a graphene layer and a dielectric layer from top to bottom, the graphene layer comprises a U-shaped strip resonator and a circular strip resonator, the U-shaped strip resonator is arranged in a circular ring of the circular strip resonator, a gap is reserved between the circular strip resonator and the U-shaped strip resonator, and the dielectric layer is arranged between the circular strip resonator and the U-shaped strip resonator. The invention has the advantages of high sensitivity, polarization insensitivity, tunable broadband and easy integration.

Description

Technical Field

[0001] The present invention relates to the technical field of terahertz sensing and metamaterial applications, in particular to a polarization-insensitive terahertz sensor based on a U-shaped - circular compact structure, which is particularly suitable for biomolecule detection and antibiotic concentration monitoring. Background Art

[0002] With the rapid development of terahertz technology, its application potential in the field of biomedical detection has gradually emerged. The unique penetrability and molecular fingerprint characteristics of terahertz waves enable it to efficiently detect trace biomolecules. As an important physical phenomenon, the electromagnetically induced transparency (EIT) effect has been widely used in the design of metamaterial sensors due to its high sensitivity characteristics.

[0003] However, traditional metal-metamaterial-based EIT sensors face severe challenges in practical applications. First, metal materials have significant Ohmic losses in the terahertz frequency band, resulting in low energy transmission efficiency and severely restricting the improvement of sensor sensitivity; second, the problem of functional curing of metal metamaterials is prominent, and its performance tuning can only be achieved by mechanically adjusting structural parameters and cannot dynamically adapt to the complex and changing environmental requirements; in addition, traditional metamaterials are highly sensitive to the polarization direction of incident electromagnetic waves, and the detection results are easily affected by the environment, with insufficient stability.

[0004] For example, in the existing publicly disclosed technologies, the sensitivity of EIT sensors based on metal resonators is generally lower than 300 GHz / RIU, and the polarization dependence makes it difficult to maintain stable performance under non-ideal incident conditions. More critically, the tuning range of the EIT window of metal metamaterials is limited, usually only covering a narrow frequency band and unable to meet the wide-frequency detection requirements, greatly restricting its application in multi-scenario detection.

[0005] In recent years, graphene materials have received extensive attention due to their excellent electrical properties and chemical stability. The high carrier mobility and surface plasmon resonance characteristics of graphene make it an ideal choice to replace metal metamaterials. However, existing research has mostly focused on the static characteristics of graphene, and there is insufficient exploration of its dynamic tunability and environmental adaptability. For example, some studies achieve frequency tuning by changing the Fermi level of graphene, but fail to solve the problem of independent regulation of multiple resonators; although some other works propose polarization-insensitive designs, they do not verify their actual performance in complex electromagnetic environments. In addition, existing sensors still lack in miniaturization and integration, and it is difficult to meet the application requirements of portable detection devices.

[0006] In other words, there are some technical problems that need to be solved urgently in the terahertz sensors currently on the market: 1. High loss and low sensitivity: The ohmic loss of metal materials leads to low energy utilization rate and limited sensing performance; 2. Function curing: Traditional sensors cannot be dynamically regulated by electrical means and rely on the adjustment of structural parameters, with poor flexibility; 3. Polarization dependence: The detection results are affected by the polarization direction of the incident electromagnetic wave, with insufficient stability; 4. Narrow bandwidth: The tuning range of the EIT window is limited, making it difficult to meet the multi-band detection requirements.

[0007] Therefore, developing a terahertz metamaterial sensor with high sensitivity, polarization insensitivity, broadband tunability and easy integration has become a technical problem that needs to be broken through urgently in the field of biomedical detection. Summary of the Invention

[0008] The purpose of the present invention is to provide a polarization-insensitive terahertz sensor based on a U-shaped-circular compact structure, which has the effects of high sensitivity, polarization insensitivity, broadband tunability and easy integration.

[0009] To achieve the above purpose, the present technical solution provides a polarization-insensitive terahertz sensor based on a U-shaped-circular compact structure, including: At least one array of sensing units; Each sensing unit includes a graphene layer and a dielectric layer from top to bottom. The graphene layer includes a U-shaped strip resonator and a circular strip resonator. The U-shaped strip resonator is placed inside the ring of the circular strip resonator, and there is a gap between the circular strip resonator and the U-shaped strip resonator.

[0010] Compared with the prior art, the present technical solution has the following characteristics and beneficial effects: Compact structure design: By integrating a circular strip resonator and a U-shaped strip resonator on a quartz dielectric substrate, the period of the sensing unit is only 60 μm, realizing miniaturization and high integration; Polarization-insensitive mechanism: Through the symmetric structure design of the circular strip resonator and the U-shaped strip resonator, the polarization-insensitive terahertz sensor based on the U-shaped-circular compact structure can excite a stable EIT window under both x / y polarization incidence, and the transmittance deviation is less than 3%; Electrically tunable characteristics: Utilizing the characteristic that the Fermi level of graphene changes with the applied voltage, the frequency and depth of the EIT window are dynamically regulated, and the tuning bandwidth reaches 700 GHz; Dual-mode regulation: It can globally regulate the Fermi level of graphene (0.3–0.7 eV) through the applied voltage to achieve red shift / blue shift of the EIT window; it can also apply independent bias voltages to the circular and U-shaped strips to control the on / off state of the EIT window through the Fermi level difference (ΔE~f~); High-sensitivity sensing: By enhancing the local electric field through bright-dark mode coupling, a refractive index sensitivity of up to 598 GHz / RIU is achieved, enabling the detection of trace antibiotic molecules. Description of the Drawings

[0011] Figure 1 It is a schematic diagram of the structure of a polarization-insensitive terahertz sensor unit based on a U-shaped - circular compact structure provided by this solution.

[0012] Figure 2 It is an analysis diagram of the EIT mechanism of a polarization-insensitive terahertz sensor based on a U-shaped - circular compact structure designed by the present invention.

[0013] Figure 3 It is a polarization sensitivity analysis curve diagram of a polarization-insensitive terahertz sensor based on a U-shaped - circular compact structure designed by the present invention.

[0014] Figure 4 It is an electric field analysis diagram of a polarization-insensitive terahertz sensor based on a U-shaped - circular compact structure designed by the present invention.

[0015] Figure 5 It is a schematic diagram of the three-level principle of a polarization-insensitive terahertz sensor based on a U-shaped - circular compact structure designed by the present invention.

[0016] Figure 6 It is a schematic diagram of the influence of the radius r of the circular strip resonator on the transmission curve of a polarization-insensitive terahertz sensor based on a U-shaped - circular compact structure designed by the present invention.

[0017] Figure 7 It is a schematic diagram of the influence of the width q of the circular strip resonator on the transmission curve of a polarization-insensitive terahertz sensor based on a U-shaped - circular compact structure designed by the present invention.

[0018] Figure 8 It is a schematic diagram of the influence of the opening width w of the U-shaped strip resonator on the transmission curve of a polarization-insensitive terahertz sensor based on a U-shaped - circular compact structure designed by the present invention.

[0019] Figure 9 It is the incident angle of a polarization-insensitive terahertz sensor based on a U-shaped - circular compact structure designed by the present invention Schematic diagram of the influence on the transmission curve.

[0020] Figure 10 It is a transmission curve diagram corresponding to different Fermi levels of a polarization-insensitive terahertz sensor based on a U-shaped - circular compact structure designed by the present invention.

[0021] Figure 11It is a graph showing the relationship between the peak of the transparent window and the Fermi level of a polarization-insensitive terahertz sensor based on a U-shaped - circular compact structure designed by the present invention.

[0022] Figure 12 It is a transmission curve graph corresponding to different Fermi level differences of a polarization-insensitive terahertz sensor based on a U-shaped - circular compact structure designed by the present invention.

[0023] Figure 13 It is a graph showing the relationship between the window frequency and the Fermi level difference of a polarization-insensitive terahertz sensor based on a U-shaped - circular compact structure designed by the present invention.

[0024] Figure 14 It is a metamaterial transmission spectrum graph of a polarization-insensitive terahertz sensor based on a U-shaped - circular compact structure designed by the present invention with respect to the change in refractive index.

[0025] Figure 15 It is a graph showing the change of the peak of the transparent window of a polarization-insensitive terahertz sensor based on a U-shaped - circular compact structure designed by the present invention with respect to the refractive index.

[0026] Figure 16 It is a metamaterial transmission spectrum graph of a polarization-insensitive terahertz sensor based on a U-shaped - circular compact structure designed by the present invention with respect to the change in refractive index.

[0027] Figure 17 It is a graph showing the change of the peak of the transparent window of a polarization-insensitive terahertz sensor based on a U-shaped - circular compact structure designed by the present invention with respect to the refractive index. Detailed implementation manners

[0028] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention belong to the scope of protection of the present invention.

[0029] Those skilled in the art should understand that in the disclosure of the present invention, the orientation or positional relationships indicated by the terms "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. are based on the orientation or positional relationships shown in the accompanying drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, the above terms should not be construed as limiting the present invention.

[0030] Embodiment 1 AsFigure 1 As shown in Figure 1 , the polarization-insensitive terahertz sensor based on the U-shaped - circular compact structure provided by this solution includes: At least one array of sensing units; Each sensing unit includes a graphene layer and a dielectric layer from top to bottom. The graphene layer includes a U-shaped strip resonator and a circular strip resonator. The U-shaped strip resonator is placed inside the ring of the circular strip resonator, and there is a gap between the circular strip resonator and the U-shaped strip resonator.

[0031] In an embodiment of this solution, the U-shaped strip resonator and the circular strip resonator are made of graphene material and jointly form the resonant part of the sensing unit. The U-shaped strip resonator serves as the bright mode, and the circular strip resonator serves as the dark mode to generate an electromagnetically induced transparency (EIT) effect through the bright - dark mode coupling mechanism.

[0032] Specifically, the U-shaped strip resonator on each sensing unit can be directly excited by the incident terahertz electromagnetic wave to form a bright mode resonance, while the circular strip resonator cannot be directly excited by the incident terahertz electromagnetic wave. However, it is indirectly excited to form a dark mode resonance under the near-field coupling action of the U-shaped strip resonator. The coupling action between the bright mode resonance and the dark mode resonance leads to destructive interference and thus forms an electromagnetically induced transparency window.

[0033] In some embodiments, the U-shaped strip resonator is axisymmetric with respect to the center of the circular strip resonator. It is precisely this symmetric layout design of the U-shaped strip resonator and the circular strip resonator that makes the polarization-insensitive terahertz sensor based on the U-shaped - circular compact structure insensitive to the polarization direction of the incident electromagnetic wave. It is particularly worth mentioning that, different from other symmetric structures, this solution specifically designs the circular strip resonator to completely eliminate polarization dependence. The frequency shift of the polarization-insensitive terahertz sensor based on the U-shaped - circular compact structure of this solution is <5 GHz, the transmittance difference is <3%, and under an incident angle of 0 - 25° and temperature and humidity fluctuations, the sensitivity fluctuation is <5%, making it suitable for complex environments.

[0034] In some embodiments, the dielectric layer is made of quartz material with a relative dielectric constant of 1.9, making the polarization-insensitive terahertz sensor based on the U-shaped - circular compact structure have low loss and high thermal stability. The dielectric loss is reduced to 0.01 dB / mm, which is particularly suitable for the transmission of terahertz-band electromagnetic waves in portable devices.

[0035] In some embodiments, the thickness d of the dielectric layer is 8 - 12 μm to ensure the maximization of the transmission efficiency of electromagnetic waves in the dielectric, while avoiding energy loss caused by excessive thickness. Preferably, the thickness d of the dielectric layer is 10 μm. At this time, the conductivity of the dielectric layer and graphene is highly matched, and a sensitivity of up to 598 GHz / RIU can be achieved.

[0036] In some embodiments, the dielectric layer is a square with the same length and width, where the side length P of the dielectric layer along the x - direction x and the side length P along the y - direction y is 50 - 70 μm. Preferably, the side length P of the dielectric layer along the x - direction x and the side length P along the y - direction y are both 60 μm to ensure a high degree of compactness and high integration of the sensing unit.

[0037] In some embodiments, both the U - shaped strip resonator and the circular strip resonator are made of graphene with the same thickness. The thickness of the U - shaped strip resonator and the circular strip resonator is 0.001 μm. The high carrier mobility and tunable Fermi level characteristics of graphene make it an ideal material for realizing dynamic tuning.

[0038] In some embodiments, a surface impedance matching model is used to characterize the optoelectronic properties of the graphene layer.

[0039] In some embodiments, the U - shaped strip resonator is a U - shaped structure composed of two vertical strips and a horizontal strip connecting the two vertical strips. The two vertical strips are parallel to each other and have the same length, and the horizontal strip is perpendicularly intersecting at the end points of the two vertical strips.

[0040] Correspondingly, the length of the horizontal strip of the U - shaped strip resonator is the opening width w of the U - shaped strip resonator, and the length of the vertical strip of the U - shaped strip resonator is the outer side length l of the U - shaped strip resonator. In some embodiments, the opening width w of the U - shaped strip resonator is 8 - 14 μm, and the outer side length l is 18 - 22 μm. Preferably, the opening width w is 14 μm, and the outer side length l is 20 μm.

[0041] In some embodiments, the U - shaped strip resonator is a graphene strip with a constant width, where the width t of the strip is 2 - 4 μm. Preferably, the width t of the strip is 3 μm.

[0042] In some embodiments, the radius r of the circular strip resonator is 20 - 24 μm. Preferably, the radius r of the circular strip resonator is 22 μm.

[0043] In some embodiments, the circular strip resonator is a graphene strip with a constant width, where the width q of the strip is 3 - 5 μm. Preferably, the width q of the strip is 4 μm.

[0044] In some embodiments, for the polarization-insensitive terahertz sensor based on the U-shaped - circular compact structure, within the incident angle range of 0 - 25°, the sensor can maintain high stability (transmittance fluctuation < 10%, frequency shift < 10 GHz); within the incident angle range of 25 - 75°, the performance gradually decreases and it needs to be used in combination with a compensation algorithm.

[0045] In some embodiments, the polarization-insensitive terahertz sensor based on the U-shaped - circular compact structure is applicable to the detection of tetracyclic antibiotics. The polarization-insensitive terahertz sensor of this solution can generate an EIT window in the range of 1.75 - 1.83 THz, while the terahertz characteristic absorption peak of tetracycline antibiotics is located in the range of 1.5 - 2.0 THz.

[0046] In some embodiments, independent biases are applied to the circular strip resonator and the U-shaped strip resonator to regulate the Fermi level difference between the circular strip resonator and the U-shaped strip resonator. This solution realizes the dynamic switching function and the frequency band fine-tuning function by adjusting the Fermi level difference, and thus provides a hardware basis for the polarization-insensitive terahertz sensor based on the U-shaped - circular compact structure provided by this solution to be particularly suitable for multi-parameter detection (such as simultaneously monitoring different antibiotic concentrations).

[0047] Specifically, when independent biases are applied to the circular strip resonator and the U-shaped strip resonator to regulate the Fermi level difference between the circular strip resonator and the U-shaped strip resonator to be greater than 0.3 eV, the sensing function is turned off, and at this time the transmittance of the EIT window drops suddenly to 20%.

[0048] In addition, by adjusting the independent biases of the circular strip resonator and the U-shaped strip resonator, the Fermi level difference between the circular strip resonator and the U-shaped strip resonator is regulated to achieve a blue shift of the window frequency. In this solution, for every 0.1 eV increase in the Fermi level difference between the circular strip resonator and the U-shaped strip resonator, the window frequency blue-shifts by 10 GHz.

[0049] In some other embodiments, the same bias is applied to the circular strip resonator and the U-shaped strip resonator in this solution to adjust the Fermi level of graphene to be controlled within 0.3 - 0.7 eV to achieve a red shift / blue shift of the EIT window.

[0050] Embodiment 2 To explore the mechanism and performance of the polarization-insensitive terahertz sensor designed in this scheme based on the U-shaped - circular compact structure, this scheme uses the commercial finite element method software CST Microwave Studio to conduct electromagnetic simulations in the frequency band of 1.0 - 2.1 THz to verify the feasibility and performance optimization of the design of the polarization-insensitive terahertz sensor based on the U-shaped - circular compact structure. Among them, the electromagnetic wave is a plane wave incident vertically in the -z direction, the boundary conditions are set as unit cells in the x and y directions, and the z direction is set as open, and the ambient temperature is 300 K.

[0051] Structure of the polarization-insensitive terahertz sensor based on the U-shaped - circular compact structure: Parameters of the circular strip resonator: radius r: 22 μm; width q: 4 μm; thickness: 0.001 μm; Parameters of the U-shaped strip resonator: outer side length l: 20 μm; opening width w: 14 μm; strip width t: 3 μm; thickness: 0.001 μm; Period side length: P X and P y are both designed to be 60 μm; Dielectric layer: quartz (SiO2), relative dielectric constant is 1.9, thickness d is 10 μm.

[0052] (1) Exploration of the EIT mechanism; To deeply explore the generation mechanism of the EIT effect, the following different structures were simulated using the finite difference time domain method in the x polarization direction: (i) The sensing unit of the terahertz sensor has only a U-shaped strip resonator; (ii) The sensing unit of the terahertz sensor has only a circular strip resonator; (iii) The complete sensing unit of the terahertz sensor with a U-shaped strip resonator and a circular strip resonator.

[0053] The EIT mechanism analysis diagrams of different structures are obtained as Figure 2 shown, and the electric field analysis diagrams are as Figure 4 shown. It can be seen from the simulation results that (i) The structure with only a U-shaped strip resonator in the sensing unit of the terahertz sensor generates a strong resonance peak (transmission rate 90%) in the frequency band of 1.6 - 2.0 THz, and the Q value reaches 150; (ii) The structure with only a circular strip resonator in the sensing unit of the terahertz sensor has no significant resonance peak, indicating that it cannot be directly excited, while (iii) The complete structure of the complete sensing unit of the terahertz sensor with a U-shaped strip resonator and a circular strip resonator forms an EIT window with a transmission rate of 80% at 1.78 THz after the coupling of the bright mode and the dark mode, and the bandwidth is only 12 GHz (Q = 44.5), verifying the occurrence of the bright - dark mode coupling mechanism.

[0054] Figure 5Schematic diagram of the three-level principle of a polarization-insensitive terahertz sensor based on a U-shaped - circular compact structure, consisting of Figure 5 It can be seen that based on the λ-type three-level model in quantum mechanics, the U-shaped strip resonator is analogized to the excited state, and the circular strip resonator is analogized to the metastable state. When the incident terahertz wave excites the U-shaped strip resonator, its resonant field indirectly excites the circular strip resonator through near-field coupling. The phase difference Δφ = π between the two paths leads to destructive interference, forming an EIT transparent window. By fitting the transmission curve with the Lorentz model, the coupling coefficient κ = 0.12 THz, the damping factor γ1 = 0.05 THz (bright mode), and γ2 = 0.02 THz (dark mode) are verified, which is consistent with the simulation results.

[0055] (2) Realization of the dynamic global tuning function: By adjusting the Fermi level of the graphene layer through the back-gate voltage (Vg), changing the surface conductivity and dynamically adjusting the EIT window, the simulation results are as Figure 10 shown. The relationship diagram between the peak of the transparent window and the Fermi level is sorted out as Figure 11 shown.

[0056] It can be seen from Figure 10 and Figure 11 that this scheme can adjust the Fermi level of graphene to be controlled within 0.3 - 0.7 eV, realizing the red shift / blue shift of the EIT window. When the Fermi level of graphene Ef is 0.3 eV, the central frequency of the EIT window is 1.78 THz and the transmittance is 80%; while when the Fermi level of graphene Ef is 0.7 eV, the window red-shifts to 2.48 THz, the tuning bandwidth is 700 GHz, and the transmittance drops to 65%.

[0057] (3) Realization of the independent regulation function: By applying independent voltages to the circular strip resonator (V1) and the U-shaped strip resonator (V2) to regulate the Fermi level difference ΔEf, the simulation results are as Figure 12 shown. The relationship diagram between the peak of the transparent window and the Fermi level is sorted out as Figure 13 shown.

[0058] It can be seen from Figure 12 and Figure 13 that the dynamic switching function and the frequency band fine-tuning function are realized by adjusting the Fermi level difference. When the Fermi level difference ΔEf is 0, the EIT window is normally open; while when the Fermi level difference ΔEf is 0.3 eV, the transmittance of the EIT window drops to 20%, realizing the "optical switch" function, and for every 0.1 eV increase in the Fermi level difference, the window frequency blue-shifts by 10 GHz. This is because the Fermi level difference can change the coupling phase difference between the resonators, destroying the interference condition and causing the window to close.

[0059] (4) Optimization of the radius (r) of the circular strip resonator: With other parameters being the same, the radius r of the circular strip resonator was adjusted to 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, and 25 μm for simulation. The schematic diagram showing the influence of the radius r of the circular strip resonator of the terahertz sensor on the transmission curve is as Figure 6 shown.

[0060] As Figure 6 can be seen, when the radius of the circular strip resonator decreases from 22 μm to 20 μm, the right valley value of the transparent window blueshifts by 50 GHz and the Q value drops to 30; when the radius r of the circular strip resonator is 22 μm, the symmetry of the EIT window is the best and the Q value is 44.5; when the radius r of the circular strip resonator is greater than 24 μm, the left valley redshifts by 60 GHz and the window disappears, indicating that the excessive coupling distance leads to the attenuation of the field strength.

[0061] (5) Optimization of the width (q) of the circular strip resonator: With other parameters being the same, the width q of the circular strip resonator was adjusted to 1 μm, 2 μm, 3 μm, 4 μm, and 5 μm for simulation. The schematic diagram showing the influence of the width q of the circular strip resonator of the terahertz sensor on the transmission curve is as Figure 7 shown.

[0062] As Figure 7 can be seen, when the width q of the circular strip resonator is 4 μm, as Figure 7 can be seen, when the width q of the circular strip resonator is 4 μm, the peak value of the transmittance of the EIT window reaches 80%, the bandwidth is 12 GHz (Q = 44.5), and the left and right valley values are symmetrically distributed at 1.75 THz and 1.83 THz. At this time, the coupling efficiency between the bright mode (U-shaped) and the dark mode (circular) is maximized, meeting the requirements for high-sensitivity detection.

[0063] (6) Optimization of the opening width (w) of the U-shaped strip resonator: With other parameters being the same, the opening width w of the U-shaped strip resonator was adjusted to 8 μm, 10 μm, 12 μm, and 14 μm for simulation. The schematic diagram showing the influence of the opening width w of the U-shaped strip resonator of the terahertz sensor on the transmission curve is as Figure 8 shown.

[0064] As Figure 8 can be seen, when the opening width w of the U-shaped strip resonator is 14 μm, the coupling strength is maximized and the EIT window is stable; when the opening width w of the U-shaped strip resonator is 8 μm, the left and right valleys redshift and the window disappears, resulting in the coupling failure due to the reduction of the mutual inductance area.

[0065] (7)Incidence angle adaptability of terahertz electromagnetic waves: Simulations were carried out by adjusting the incidence angles (θ) of different terahertz electromagnetic waves, and the influence of the incidence angles on the transmission curves is shown schematically in Figure 9 the following figure.

[0066] As Figure 9 can be seen, when the incident angle is 0–25°, the transmittance fluctuation is <10% and the frequency shift is <10 GHz; while when the incident angle is 75°, the transmittance is <40% and the window disappears, verifying that the sensor of this scheme is also applicable under small-angle incidence.

[0067] (8)Realization of polarization-insensitive characteristics: By changing the polarization direction (x / y polarization) of the incident electromagnetic wave, the transmission curve shift and frequency shift were analyzed: the center frequency of the EIT window is 1.780 THz under x polarization and 1.785 THz under y polarization, and the offset is <0.3%. The polarization sensitivity analysis curve diagram is shown in Figure 3 the following figure.

[0068] As

[0069] can be seen, the polarization-insensitive terahertz sensor based on the U-shaped-circular compact structure of this scheme has transmittance consistency. Specifically, the window transmittances of the polarization-insensitive terahertz sensor based on the U-shaped-circular compact structure are 80% under x / y polarization respectively, and the difference is <1%, proving that the geometric symmetry effectively eliminates the polarization dependence. It shows that it has polarization-insensitive characteristics, and this characteristic enables the sensor to work stably in complex environments and is applicable to a variety of application scenarios. A thin film with a thickness of 3 μm was covered on the upper surface of the sensor as the object to be measured. Different refractive indices of the object to be measured were used to analogize different concentrations, where the refractive indices were 1.0, 1.1, 1.2, 1.3, and 1.4 respectively. The metamaterial transmission spectra of the terahertz sensor varying with the refractive index under x polarization are shown in Figure 14 the following figure, the variation diagram of the peak value of the transparent window of the terahertz sensor with respect to the refractive index is shown in Figure 15 the following figure, the metamaterial transmission spectra of the terahertz sensor varying with the refractive index under y polarization are shown in Figure 16 the following figure, and the variation diagram of the peak value of the transparent window of the terahertz sensor with respect to the refractive index is shown in Figure 17 the following figure.

[0070] As Figure 14 and Figure 15It can be seen that with the increase of the refractive index of the analyte under x-polarization, the transmission window exhibits a redshift with a bandwidth of 240 GHz. According to the performance calculation formula, the sensitivity of the device under x-polarization is calculated to be 596 GHz / RIU, the Q value is 44.5, and the FOM is 35.15.

[0071] It can be seen from Figure 16 and Figure 17 that with the increase of the refractive index of the analyte under y-polarization, the transmission window exhibits a redshift with a bandwidth of 235 GHz. According to the sensitivity definition formula, the sensitivity of the device under y-polarization is 587.5 GHz / RIU, the Q value is 44.3, and the FOM is 34.9.

[0072] As described above, the polarization-insensitive terahertz sensor based on the U-shaped - circular compact structure provided by this scheme has high sensitivity: it can support the detection of trace antibiotic molecules, and the sensitivity is nearly twice that of traditional metal sensors; it has a dynamic coordination function: it can achieve a 700 GHz bandwidth regulation through electrical means without mechanical structure adjustment; it has polarization-insensitive performance: the performance under x / y polarization is consistent, adapting to complex electromagnetic environments; and it has an overall miniaturized and integrated design: the size period of the 60μm sensing unit is convenient for array deployment and is suitable for portable detection devices; it has environmental robustness: it is resistant to high temperature and corrosion and can work stably for a long time under harsh conditions.

[0073] Those skilled in the art should understand that the technical features of the above embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as within the scope described in this specification.

[0074] The above embodiments only represent several implementation manners of this application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of this application. It should be noted that for those of ordinary skill in the art, without departing from the concept of this application, several modifications and improvements can still be made, and these all belong to the protection scope of this application. Therefore, the protection scope of this application should be subject to the appended claims.

Claims

1. A polarization-insensitive terahertz sensor based on a U-shaped - circular compact structure, characterized in that, Including: At least an array arrangement of sensing units; Each sensing unit includes a graphene layer and a dielectric layer from top to bottom. The graphene layer includes a U-shaped strip resonator and a circular strip resonator. The U-shaped strip resonator is placed inside the ring of the circular strip resonator, and there is a gap between the circular strip resonator and the U-shaped strip resonator.

2. The polarization-insensitive terahertz sensor based on the U-shaped - circular compact structure according to claim 1, characterized in that, The U-shaped strip resonator serves as the bright mode, and the circular strip resonator serves as the dark mode to generate the electromagnetically induced transparency effect through the bright-dark mode coupling mechanism.

3. The polarization-insensitive terahertz sensor based on the U-shaped - circular compact structure according to claim 1, characterized in that, The U-shaped strip resonator is axisymmetric with respect to the center of the circle of the circular strip resonator.

4. The polarization-insensitive terahertz sensor based on the U-shaped - circular compact structure according to claim 1, characterized in that, The dielectric layer is made of quartz, and the thickness d of the dielectric layer is 8 - 12 μm.

5. The polarization-insensitive terahertz sensor based on the U-shaped - circular compact structure according to claim 1, wherein The opening width w of the U-shaped strip resonator is 8 - 14 μm, the outer side length l is 18 - 22 μm, and the width t of the strip is 2 - 4 μm.

6. The polarization-insensitive terahertz sensor based on the U-shaped - circular compact structure according to claim 1, characterized in that, The radius r of the circular strip resonator is 20 - 24 μm, and the width q of the strip is 4 μm.

7. The polarization-insensitive terahertz sensor based on the U-shaped - circular compact structure according to claim 1, characterized in that, An EIT window is generated in the range of 1.75 - 1.83 THz, which is suitable for the detection of tetracycline antibiotics.

8. The polarization-insensitive terahertz sensor based on the U-shaped - circular compact structure according to claim 1, characterized in that, By applying independent biases to the circular strip resonator and the U-shaped strip resonator, the Fermi level difference between the circular strip resonator and the U-shaped strip resonator is regulated to achieve dynamic switching and frequency band fine-tuning.

9. The polarization-insensitive terahertz sensor based on the U-shaped - circular compact structure according to claim 8, wherein, When the Fermi level difference between the circular strip resonator and the U-shaped strip resonator is regulated to be greater than 0.3 eV, the sensing function is turned off; When the Fermi level difference between the circular strip resonator and the U-shaped strip resonator is increased by 0.1 eV, the window frequency blue-shifts by 10 GHz.

10. The polarization-insensitive terahertz sensor based on the U-shaped - circular compact structure according to claim 1, characterized in that, By applying the same bias to the circular strip resonator and the U-shaped strip resonator, the Fermi level of graphene is adjusted to be controlled within 0.3 - 0.7 eV.

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