A multi-parameter sensing evaluation method based on multi-resonance peak terahertz metamaterials

Abstract

The present invention relates to the field of terahertz technology, and in particular to a multi-parameter sensing evaluation method based on multi-resonance peak terahertz metamaterials. First, two structures are set up, both of which are asymmetric open single-ring and triple-ring structures made of aluminum on a silicon substrate through a micromachining process. Then, the formation mechanism and sensing effect of each resonance peak of the two structures are analyzed using FDTD. Sensing experiments of vitamin B6 and the reaction of vitamin B6 with protein are carried out using the two structures. Finally, the quality factor of each resonance peak is used as a weighting coefficient to obtain comprehensive evaluation parameters of the multi-resonance peak metamaterial sensor. It is further proposed to scan the structure with the measured medium in a two-dimensional plane to obtain parameters such as the comprehensive factor, dielectric constant, and coupling factor between the medium and structure and the terahertz wave at each point in the plane. This method can comprehensively evaluate the sensing performance and promote the practical application of terahertz metamaterial sensing.

Description

Technical Field

[0001] The present invention relates to the field of terahertz technology, and in particular to a multi-parameter sensing evaluation method based on multi-resonance peak terahertz metamaterial. Background Art

[0002] Due to its low power consumption and resonant properties with many polar biomacromolecules, terahertz waves offer unique advantages in material detection, particularly in biomedical diagnostics, security imaging, and other fields. However, the lack of efficient terahertz emission sources and detectors, as well as the strong absorption of terahertz waves by water, hinders the direct detection of terahertz waves in trace samples.

[0003] Metamaterials are structures composed of artificially designed subwavelength structural units that exhibit electromagnetic properties not found in natural materials. The unique properties of metamaterials are primarily manifested through their resonant response to incident electromagnetic waves. At their resonant frequencies, metamaterials are highly sensitive to the properties of the surrounding material (such as refractive index and thickness). This unique property enables metamaterials to offer new opportunities for chemical and biomedical sensing applications. Different resonant modes of metamaterials produce different sensing effects. For example, LC resonance, magnetic resonance, Fano resonance, electromagnetically induced transparency (EMI) coupled with bright and dark modes, and ring dipole modes exhibit distinct sensing effects. Metamaterials with multiple resonant peaks and those influenced by polarization extend the sensing capabilities of metamaterials. However, research on these sensing effects has largely limited itself to describing and comparing the sensing phenomena at different resonant peaks. These studies fail to incorporate the combined effects of terahertz waves, biomolecular forces, and the metamaterial's resonant localized field. Furthermore, they fail to evaluate the sensing effects of metamaterials with multiple resonance peaks or under different polarization modes, making it difficult to highlight the advantages of these metamaterial sensors. Summary of the Invention

[0004] The purpose of the present invention is to provide a multi-parameter sensing evaluation method based on multi-resonance peak terahertz metamaterials, which improves the situation in which the existing metamaterial sensing effect evaluation is limited to the description and comparison of sensing phenomena of different resonance peaks. It comprehensively combines the sensing effects of the metamaterial under multi-peak resonance or different polarization modes for evaluation, thereby obtaining a more comprehensive evaluation of the sensing effect.

[0005] To achieve the above objectives, the present invention provides a multi-parameter sensing evaluation method based on multi-resonance peak terahertz metamaterials, comprising the following steps:

[0006] Step 1: Construct single-ring structure and three-ring structure;

[0007] Step 2: Performing resonance mechanism and sensing analysis on the single-ring structure and the triple-ring structure respectively;

[0008] Step 3: Conduct solution reaction sensing experiment;

[0009] Step 4: Use the quality factor of each resonance peak in step 2 and step 3 as the weighting coefficient to calculate and compare the sensing effects of different structures;

[0010] Step 5: Obtain the comprehensive sensing factor, refractive index and coupling coefficient of the single-ring structure and the triple-ring structure to obtain a comprehensive evaluation effect.

[0011] The single-ring structure and the three-ring structure are both asymmetric open structures made of aluminum on a silicon substrate through a micromachining process. The single-ring structure is a regular hexagonal structure, which is formed by rotating one side of a regular hexagon 60 degrees along the center and connecting them end to end, with an opening at a specified distance from the center.

[0012] The three-ring structure is composed of three concentric rings, and the outer ring and the middle ring have openings at a specified distance from the center of the circle.

[0013] Wherein, vertical incidence of terahertz waves is used in both the sensing analysis and the solution reaction sensing experiment.

[0014] In the process of performing resonance mechanism and sensing analysis on the single-ring structure and the triple-ring structure respectively, the parameters and variation relationships of the single-ring structure and the triple-ring structure in TE and TM modes are recorded respectively.

[0015] In the process of the solution reaction sensing experiment, a reaction solution is used to form a thin film on the surface of the single-ring structure and the triple-ring structure, and then a terahertz time domain system is used to measure and obtain corresponding parameters for analysis.

[0016] The reaction solution includes 0.1 mg / μl B6 solution, 0.2 mg / μl B6 solution, 0.1 mg / μl B6 and 0.167 mg / ul BSA reactant, and 0.2 mg / μl B6 solution and 0.167 mg / ul BSA reactant.

[0017] The comprehensive sensing factor, the refractive index and the coupling coefficient are respectively acquired by scanning the medium areas of the single-ring structure and the triple-ring structure point by point.

[0018] The present invention provides a multi-parameter sensing evaluation method based on multi-resonance peak terahertz metamaterials. First, two structures are set up, both of which are asymmetric open single-ring and triple-ring structures made of aluminum on a silicon substrate through a micromachining process. Then, the formation mechanism and sensing effect of each resonance peak of the two structures are analyzed using FDTD. Sensing experiments of vitamin B6 and the reaction of vitamin B6 with protein are carried out using the two structures. Finally, the quality factor of each resonance peak is used as a weighting coefficient to obtain comprehensive evaluation parameters of the multi-resonance peak metamaterial sensor. It is further proposed to scan the structure with the measured medium in a two-dimensional plane to obtain the comprehensive factor, dielectric constant, and coupling coefficient of the medium and structure with terahertz waves at each point in the plane. This method can comprehensively evaluate the sensing parameters and promote the practical application of terahertz metamaterial sensing. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other technical inspirations can be obtained based on these drawings without paying any creative work.

[0020] Figure 1 It is a flow chart of a multi-parameter sensing evaluation method based on multi-resonance peak terahertz metamaterial of the present invention.

[0021] Figure 2 Schematic diagram of the monocyclic structure of the present invention.

[0022] Figure 2 (a) is a micrograph of a single ring structure.

[0023] Figure 2 (b) is a schematic diagram of the structure of a single ring.

[0024] Figure 2 (c) is the simulated transmission spectrum of the single-ring structure in TE and TM modes.

[0025] Figure 2 (d) is the surface current distribution diagram of the resonance peak f1 of the single ring structure in TE polarization mode.

[0026] Figure 2 (e) is the surface current distribution diagram of the resonance peak f2 of the single ring structure under TE polarization mode.

[0027] Figure 2 (f) is the surface current distribution diagram of the resonance peak f of the single ring structure in TM polarization mode.

[0028] Figure 3This is a general schematic diagram of the single-ring structure sensing theory analysis of the present invention.

[0029] Figure 3 (a) is the transmission spectrum of the TE mode single ring structure as the medium thickness changes.

[0030] Figure 3 (b) is a graph showing the relationship between the frequency shift of the TE mode resonance and the thickness of the dielectric layer.

[0031] Figure 3 (c) is the transmission spectrum of the TE mode single-ring structure as the dielectric constant changes.

[0032] Figure 3 (d) is a graph showing the relationship between the frequency shift of TE mode resonance and the dielectric constant of the medium.

[0033] Figure 3 (e) is the transmission spectrum of the TM mode single ring structure as the thickness of the medium changes.

[0034] Figure 3 (f) is a graph showing the relationship between the frequency shift of the TM mode resonance and the dielectric thickness.

[0035] Figure 3 (g) is the transmission spectrum of the TM mode single ring structure as the dielectric constant changes.

[0036] Figure 3 (h) is a graph showing the relationship between the frequency shift of the TM mode resonance and the dielectric constant of the medium.

[0037] Figure 4 This is the transmission spectrum of the single ring structure after being attached to the solution in the present invention.

[0038] Figure 4 (a) is the transmission spectrum of TE mode.

[0039] Figure 4 (b) is a graph showing the relationship between the frequency shift of the TE mode resonance and the solution concentration.

[0040] Figure 4 (c) is the transmission spectrum of TM mode.

[0041] Figure 4 (d) is a graph showing the relationship between the frequency shift of the TM mode resonance and the solution concentration.

[0042] Figure 5 It is a general schematic diagram of the three-ring structure of the present invention.

[0043] Figure 5 (a) is a micrograph of the three-ring structure.

[0044] Figure 5 (b) is a schematic structural diagram of the three-ring structure.

[0045] Figure 5 (c) is the simulated transmission spectrum of the three-ring structure in TE and TM modes.

[0046] Figure 5 (d) is the surface current distribution diagram of the resonance peak f1 of the three-ring structure in TE polarization mode.

[0047] Figure 5 (e) is the surface current distribution diagram of the resonance peak f2 of the three-ring structure under TE polarization mode.

[0048] Figure 5 (f) is the surface current distribution diagram of the resonance peak f3 of the three-ring structure under TE polarization mode.

[0049] Figure 5 (g) is the surface current distribution diagram of the resonance peak f4 of the three-ring structure in TE polarization mode.

[0050] Figure 5 (h) is the surface current distribution diagram of the resonance peak f of the three-ring structure in TM polarization mode.

[0051] Figure 6 This is a schematic diagram of the overall analysis of the three-ring structure sensing theory of the present invention.

[0052] Figure 6 (a) is the transmission spectrum of the TE mode three-ring structure as the thickness changes.

[0053] Figure 6 (b) is a graph showing the relationship between the frequency shift of the TE mode resonance (f1 to f4) and the thickness of the dielectric layer.

[0054] Figure 6 (c) is the transmission spectrum of the TE mode three-ring structure as the dielectric constant changes.

[0055] Figure 6 (d) is a graph showing the relationship between the frequency shift of the TE mode resonance (f1 to f4) and the dielectric constant of the medium.

[0056] Figure 6 (e) is the transmission spectrum of the TM mode three-ring structure as the thickness of the medium changes.

[0057] Figure 6 (f) is a graph showing the relationship between the frequency shift of the TM mode resonance and the dielectric thickness.

[0058] Figure 6 (g) is the transmission spectrum of the TM mode three-ring structure as the dielectric constant changes.

[0059] Figure 6 (h) is a graph showing the relationship between the frequency shift of the TM mode resonance and the dielectric constant of the medium.

[0060] Figure 7 This is a collection of transmission spectra of the three-ring structure attached to the solution in the present invention.

[0061] Figure 7 (a) is the transmission spectrum of TE mode.

[0062] Figure 7 (b) is a graph showing the relationship between the frequency shift of the TE mode resonance (f1 to f4) and the solution concentration.

[0063] Figure 7 (c) is the transmission spectrum of TM mode.

[0064] Figure 7 (d) is a graph showing the relationship between the frequency shift of the TM mode resonance and the solution concentration.

[0065] Figure 8 This is a comparison diagram of the repeatability of the transmission spectra of the single-ring structure and the three-ring structure in the present invention. DETAILED DESCRIPTION

[0066] The following describes the implementation process of the present invention in detail, and examples of the implementation are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and are not to be construed as limiting the present invention.

[0067] See also Figure 1 The present invention proposes a multi-parameter sensing evaluation method based on multi-resonance peak terahertz metamaterials, comprising the following steps:

[0068] S1: Construction of single-ring and triple-ring structures;

[0069] S2: performing resonance mechanism and sensing analysis on the single-ring structure and the triple-ring structure respectively;

[0070] S3: perform solution reaction sensing experiments;

[0071] S4: using the quality factors of the resonance peaks in step S2 and step S3 as weighting coefficients to calculate parameters such as the comprehensive factor, and comparing the sensing effects of different structures;

[0072] S5: Obtaining the comprehensive sensing factor, refractive index and coupling coefficient of the single-ring structure and the triple-ring structure to obtain a comprehensive evaluation effect.

[0073] Both the single-ring structure and the triple-ring structure are asymmetric open structures made of aluminum on a silicon substrate through a micromachining process. The single-ring structure is a regular hexagonal structure, which is formed by rotating one side of a regular hexagon 60 degrees along the center and connecting them end to end, with an opening at a specified distance from the center.

[0074] The three-ring structure is composed of three concentric rings, and the outer ring and the middle ring have openings at a specified distance from the center of the circle.

[0075] The sensing analysis and the solution reaction sensing experiment both use vertical incidence of terahertz waves.

[0076] During the process of performing resonance mechanism and sensing analysis on the single-ring structure and the triple-ring structure, the parameters and variation relationships of the single-ring structure and the triple-ring structure in TE and TM modes are recorded respectively.

[0077] The comprehensive sensing factor, the refractive index, and the coupling coefficient are respectively acquired by scanning the medium areas of the single-ring structure and the triple-ring structure point by point.

[0078] The present invention is further described below with reference to specific embodiments and simulation experiments:

[0079] 1. Single Split Ring (hereinafter referred to as SSR)

[0080] 1.1. Formation mechanism of SSR structure and its resonance peak

[0081] like Figure 2 As shown, the single-ring SSR is a regular hexagonal structure, formed by rotating one side of the hexagon 60 degrees around its center and connecting them end to end. The structure is open at a distance d from the center. The structure was optimized and simulated using the electromagnetic simulation software CST MicrowaveStudio. Electromagnetic waves were incident perpendicularly along the z-axis on the SRR under TE and TM mode conditions. The boundary conditions in the x and y directions were set to the unit cell boundaries, and the z direction was open space. Figure 2 (a) is a micrograph of SRR fabricated on a 500 μm thick silicon substrate using surface micromachining technology. Figure 2 (b) Schematic diagram of the structure of a single open ring, where the period numbers in the x and y directions are 80 μm and 90 μm, respectively. The specific dimensions after optimization are shown in Table 1.

[0082] Table 1. Structural parameters of SSR (unit: μm)

[0083] <![CDATA[R1]]> <![CDATA[R2]]> d l g 30 25 16 36 5

[0084] The structure was simulated and analyzed using CST software. The dielectric constant of the substrate material high-conductivity silicon was set to 11.9, the structural material was aluminum with a thickness of 200 nm, and the conductivity was set to 3.56×10 7When the terahertz wave is incident vertically on the SRR surface, in the TE polarization mode, that is, the polarization direction is parallel to the line connecting the centers of the openings (along the y-axis), the transmission spectrum is obtained as follows: Figure 2 As shown by the solid line in (c), there are two resonance peaks with frequencies of f1 = 0.45 THz and f2 = 0.95 THz respectively. The simulated transmission spectrum in the TM polarization mode is shown in Figure 2 As shown by the dotted line in (c), there is only one resonance peak frequency f = 0.95THz. The formation mechanism of each resonance peak is analyzed using surface current, as shown in Figure 2 (df) shows the surface current distribution of each resonance peak in the TE mode and TM mode. Driven by the external electric field, the surface current flows on the metal ring along the direction indicated by the arrow. The ring can be regarded as an inductor, and the opening can be regarded as a capacitor

[15] . In the TE mode, the surface current at the resonance frequency f1 can be regarded as an LC oscillation, and the surface current at f2 can be regarded as a dipole oscillation. In the TM mode, the surface current at the resonance peak can be regarded as a dipole oscillation, because the surface current at the resonance peak f2 in the TE mode and the surface current at the resonance peak f in the TM mode are both dipole oscillations with basically the same length, so their resonance frequencies are the same.

[0085] 1.2 SSR sensing theory analysis

[0086] The thickness and dielectric constant of the metamaterial surface medium affect the frequency shift and amplitude of the transmission spectrum, which can be used to identify materials. According to the effective medium theory, the refractive index and thickness of the medium affect the transmission of electromagnetic waves. First, the refractive index is fixed and the simulation analysis of the effect of the surface medium thickness on the transmission spectrum is carried out. μ r =1, then numerically Assume that the refractive index of the dielectric layer is n = 2, that is, ε r =4, change the medium thickness t value, use CST to perform parameter scanning on the medium thickness, and obtain the frequency shift at different thicknesses, such as Figure 3 (a) and 3(e). Previous studies have shown that when the thickness is greater than 5μm, the resonant frequency shift remains almost constant as the dielectric layer thickness increases, and the loss increases with increasing thickness, so the dielectric should not be too thick. Taking t = 5μm, the effect of the dielectric constant on the SRR transmission spectrum is simulated and analyzed, as shown in Figure 3 (c) and Figure 3 (g). When the dielectric constant ε of the covering medium is increased r or the thickness of the medium t, will lead to an increase in coupling capacitance, the resonant frequency will decrease and produce a red shift, such as Figure 3 shown.

[0087] The frequency shift is calculated by subtracting the frequency measured after different solutions are attached to the sensor surface and dried from the frequency at each resonance when there is no medium on the sensor surface. In order to further determine the relationship between the thickness and dielectric constant change of the medium attached to the sensor surface and the resonant frequency shift, the origin is used for fitting, such as Figure 3 (b), (d), (f), and (h). Using the transmission curve of a sensor without any material attached as a reference, the effect of thickness changes on the TE and TM mode resonant frequencies is compared. When the dielectric thickness increases to 5μm, the TM mode resonance shifts by 40GHz, and the frequency shifts of the TE mode resonances f1 and f2 are 26GHz and 35GHz, respectively. This indicates that the increase in dielectric thickness causes a slightly larger frequency shift in the TM mode resonance than in the TE mode resonance. For a fixed dielectric thickness, the frequency shift of each resonance increases as the dielectric constant of the covering material increases. When the dielectric constant increases to 4, the TM mode resonance shifts by 41GHz, and the frequency shifts of the TE mode resonances f1 and f2 are 26GHz and 31GHz, respectively. Similar to the effect of dielectric thickness on SSR sensing, the increase in dielectric constant causes a slightly larger shift in the TM mode resonance than in the TE mode resonance.

[0088] The sensor's sensitivity, S, is expressed as the frequency shift of the sensor's central resonant frequency or the change in transmitted intensity per unit refractive index change. Its expression is: S = Δf / Δn, where Δf is the frequency shift of the resonant peak position and Δn is the refractive index change. The unit of sensitivity is THz / RIU (Refractive Index Unit). The TE mode's high-frequency sensing sensitivity (31 THz / RIU) is greater than its low-frequency sensing sensitivity (26 THz / RIU), while the TM mode's sensitivity (41 THz / RIU) is greater than the TE mode's. TM mode resonance is formed by two dipole resonances, and TE mode's high-frequency resonance is also formed by two dipole resonances. The polarization direction affects the different equivalent capacitances at the metal ring opening, resulting in different sensing effects. The surface current in the SSR structure's TE mode low-frequency resonance can be viewed as an LC resonance. The change in the equivalent capacitance of the LC oscillation caused by the embedded dielectric is less significant than the change in the dipole equivalent capacitance in the TE mode high-frequency resonance. Therefore, the frequency shift of the SSR's TE mode high-frequency resonance is greater than that of the low-frequency resonance.

[0089] 1.3. Solution reaction sensing experiment of SSR

[0090] (1) Materials and instruments

[0091] B6 (content 99%, product number S13026) was purchased from Shanghai Yuanye Biotechnology Co., Ltd. The experimental instrument was a CCT-1800 terahertz time-domain spectrometer produced by Shenzhen Terahertz Technology Innovation Institute Huaxun Ark, with a spectrum range of 0.05-5 THz.

[0092] (2) Preparation of solution

[0093] Accurately weigh 20 mg and 40 mg of vitamin B6 sample respectively and dissolve them in 200 μl of deionized water, shake well to obtain 0.1 mg / μl and 0.2 mg / μl VB6 solutions; weigh 50 mg of BSA and dissolve it in 300 μl of deionized water, shake well to obtain 0.167 mg / ul BSA solution; use a pipette to take 10 ul of vitamin B6 and 10 ul of BSA solution respectively, mix them in a test tube, shake well and react for 10 minutes to obtain the VB6 and BSA reaction solution.

[0094] (3) Experimental methods

[0095] A 5μl drop of the test solution was taken out with a pipette and dropped onto the surface of the sensor SSR. The sensor was then placed in a constant temperature box (the temperature of the constant temperature box was maintained at around 40°C to ensure the invariance of the measured medium). After about 10 minutes, a thin film was formed on the sensor surface. The terahertz time-domain system was then used for measurement to obtain the terahertz transmission spectrum of the B6 vitamin and the reaction between B6 and BSA.

[0096] (4) Experimental analysis of the reaction between vitamin B6 and BSA using the sensor SRR

[0097] Figure 4 The following are the transmission spectra of 0.1mg / μl B6 solution, 0.1mg / μl B6 and 0.167mg / ul BSA reaction product, and 0.2mg / μl B6 solution and 0.167mg / ul BSA reaction product attached to the sensor SSR. Figure 4 It can be seen that the transmission amplitude of each resonance peak of the sensor has changed differently after the addition of these substances, and the TE mode resonance peak (f1 and f2) and TM mode resonance peak f TM Different degrees of red shift occurred: Using the transmission spectrum of 0.1 mg / μl B6 as a reference, the resonance peaks of the two concentrations of vitamin B6 and BSA reactants exhibited different red shifts, indicating that vitamin B6 alters the conformation of BSA, i.e., the composition of the solution itself. The refractive index of the vitamin B6 and BSA reactants differs from that of the pure B6, resulting in different responses to electromagnetic waves when coated on the SSR surface. This results in different frequency shifts in the transmission spectrum resonance peaks, which is related to the properties of the substances themselves and the sensitivity of the SRR sensor.

[0098] Figure 4(b) and (d) are the fitting lines of the resonant frequency shift of the SSR sensor in TE and TM modes, respectively, with B6 attached and after the reaction of different concentrations of B6 with BSA. Specific values ​​are shown in Table 2. The experimental results show that after B6 attachment and the reaction of different concentrations of B6 with BSA, the frequency shift of the TM mode resonant peak is significantly greater than that of the TE mode resonant peaks f1 and f2. The trend of change is generally consistent with the simulation, indicating that this sensor can be used for biosensing.

[0099] Table 2 TE modes (f1 and f2) and TM modes (f3) after the reaction of 0.1 mg / μl B6, 0.1 mg / μl B6 and BSA, and 0.2 mg / μl B6 and BSA on the surface of SSR sensor TM ) frequency shift of the mode resonance peak

[0100] sample <![CDATA[Δf1 / GHz]]> <![CDATA[Δf2 / GHz]]> <![CDATA[Δf TM / GHz]]> <![CDATA[0.1mg / μlB6]]> 10 47 52 <![CDATA[0.1mg / μlB6+BSA]]> 35 58 78 <![CDATA[0.2mg / μlB6+BSA]]> 38 70 90

[0101] 2. Triple Split Ring (hereinafter referred to as TSR)

[0102] 2.1 TSR structure and resonance formation mechanism

[0103] The settings of the simulation environment and processing technology of the three-ring structure are exactly the same as those of the single-ring structure. Figure 5 The period of the three-ring structure along both the x and y directions is 80 μm. R1, R2, and R3 represent the outer diameters of the three rings from outer to inner, respectively. w1, w2, and w3 represent the widths of the three rings, respectively. d represents the distance from the center of the opening to the center of the structure, and g represents the width of the opening. The optimized dimensions are shown in Table 3.

[0104] Table 3. Main parameters of TSR structure (unit: μm)

[0105] <![CDATA[R1]]> <![CDATA[R2]]> <![CDATA[R3]]> <![CDATA[w1]]> <![CDATA[w2]]> <![CDATA[w3]]> d g 30 25 15 5 5 7 5 5

[0106] The structure was simulated and analyzed using CST software. When the terahertz wave was incident vertically on the TSR surface, the simulated transmission spectra were obtained in TE and TM polarization modes. Figure 5 As shown in (c), there are four resonance peaks in the TE mode, with frequencies f1 = 0.49 THz, f2 = 0.62 THz, f3 = 0.74 THz, and f4 = 0.99 THz; the resonance frequency of the TM mode polarization mode is f = 1.04 THz. The formation mechanism of the resonance is analyzed by using surface current. The surface current distribution of each resonance peak in the TE and TM modes is shown in Figure 5 (dh) shown.

[0107] Figure 5As shown in (d), the first absorption peak f1 of TSR is formed by the LC resonance of the outer ring. Since the current oscillates on the outer ring, the oscillation length of the dipole is long, the equivalent inductance value is large, and the resonant frequency is low. Figure 5 As shown in (e), the surface current of the resonance f2 is mainly distributed on the left side of the outer ring and the right side of the inner ring, forming an LC resonance on the inner and outer rings as a whole. Figure 5 (d) and Figure 5 (e), the length of the resonant f2 current distribution is significantly smaller than the length of the resonant f1 current distribution, i.e. Figure 5 (e) The equivalent inductance formed by the surface current is less than Figure 5 (d) The equivalent inductance, so the frequency of TSR resonance f2 is greater than the frequency of resonance f1. The current distribution of resonance f3 is as follows Figure 5 As shown in (f), the oscillating current is mainly distributed in the entire inner ring and the left side of the outer ring. The two electric dipoles in the inner ring form an LC oscillation. The oscillation direction of the electric dipole on the left side of the outer ring is the same as that of the electric dipole on the right side of the inner ring. It can be roughly regarded as the two dipoles connected in parallel and in series with the dipole on the left side of the inner ring. Figure 5 (e), Figure 5 (f) The equivalent total inductance of the resonance is reduced, so the frequency of the TSR resonance f3 is greater than the frequency of the resonance f2. Figure 5 The surface current of the resonance f4 shown in (g) is mainly distributed on both sides of the middle ring, and the oscillation direction is the same, forming two dipoles. The resonance frequency formed by the two dipoles in parallel is significantly higher than the LC resonance frequency. In the TM polarization mode, the surface current of the resonance peak is as follows Figure 5 As shown in (h), it can be regarded as a parallel connection of multiple dipoles, so the resonant frequency is relatively high.

[0108] 2.2 TSR sensing theory analysis

[0109] First, the refractive index is fixed and the effect of the surface medium thickness on the transmission spectrum is simulated and analyzed. Assuming the refractive index of the medium layer is n = 2, the CST is used to perform parameter sweeps on the medium thickness to obtain the transmission spectra of the TE mode and TM mode at different thicknesses, as shown in the following example: Figure 6 (a) and Figure 6 (e) Then, t = 5 μm is fixed and the effect of dielectric constant on the transmission spectrum of TE mode and TM mode is simulated and analyzed, as shown in the figure. Figure 6 (c) and Figure 6 (g) In order to further determine the relationship between the thickness and dielectric constant change of the medium attached to the sensor TSR surface and the resonant frequency shift, the origin is used for fitting, as shown in Figure 6Figures (b), (d), (f), and (h) show the effect of thickness changes on the TE and TM mode resonant frequencies of the TSR structure, using the transmission curve of a sensor without any material attached as a reference. When the dielectric thickness increases to 5μm, the TM mode resonance shifts by 86GHz, while the TE mode resonances f1, f2, f3, and f4 shift by 36GHz, 47GHz, 55GHz, and 61GHz, respectively. This indicates that increasing dielectric thickness on the TSR surface causes the TM mode resonance frequency shift to be significantly greater than the frequency shift of the four TE mode resonance peaks (f1 to f4). For a fixed dielectric thickness of t = 5μm, the frequency shift of each resonance increases with increasing dielectric constant of the covering material. When the dielectric constant increases to 4, the TM mode resonance shifts (66 GHz), and the TE mode resonances f1, f2, f3, and f4 shift by 46 GHz, 55 GHz, 60 GHz, and 58 GHz, respectively. Similar to the effect of dielectric thickness on SSR sensing, the increase in dielectric constant on the TSR surface causes the TM mode resonance frequency shift to be significantly greater than the frequency shift of its four TE mode resonance peaks (f1 to f4). The dielectric primarily changes the equivalent capacitance at the opening, resulting in different sensing effects for the TE and TM mode resonance peaks.

[0110] 2.3 TSR solution sensing experiment

[0111] Figure 7 The following are the transmission spectra of 0.1mg / μl B6 solution, 0.1mg / μl B6 and 0.167mg / ul BSA reaction product, and 0.2mg / μl B6 and 0.167mg / ul BSA reaction product attached to the sensor TSR. Figure 7 The addition of these substances reveals that the transmission amplitudes of the various resonance peaks in the transmission spectrum change to varying degrees, and that both the TE mode resonance peaks (f1∽f4) and the TM mode resonance peak f of the TSR undergo varying degrees of redshift. Similar to the sensing principle of a single ring, the refractive index of the vitamins and BSA reactants differs from that of the single B6, primarily causing a change in the equivalent capacitance of the gap within the structure, which in turn causes varying degrees of redshift in the frequencies of the various resonance peaks. Figure 7 (b) and (d) show the fitting lines for the TSR sensor's resonance peak frequency shifts after B6 and BSA reactants with different concentrations in the TE and TM modes, respectively. Specific values ​​are shown in Table 4. The experimental results show that after B6 and BSA reactants with different concentrations, the TM mode resonance peak frequency shift is significantly greater than the TE mode resonance peak frequency shift from f1 to f4, and the trend is consistent with the simulation.

[0112] Table 4 TE mode (f1∽f4) and TM (f TM) frequency shift of the mode resonance peak

[0113] sample <![CDATA[Δf1 / GHz]]> <![CDATA[Δf2 / GHz]]> <![CDATA[Δf3 / GHz]]> <![CDATA[Δf4 / GHz]]> <![CDATA[Δf TM / GHz]]> <![CDATA[0.1mg / μlB6]]> 0 3 32 29 81 <![CDATA[0.1mg / μlB6+BSA]]> 18 47 72 53 95 <![CDATA[0.2mg / μlB6+BSA]]> 44 55 92 66 127

[0114] 3. Comprehensive evaluation of multi-parameters of metamaterial sensors

[0115] 3.1 Comprehensive factors

[0116] Experimental observations reveal that the TE and TM mode resonance peaks of SSR and TSR sensors exhibit different sensitivity for the same medium. This is primarily due to the fact that the measured medium is embedded within the sensor, altering the metamaterial sensor's equivalent capacitance. Current research in metamaterial sensing primarily focuses on analyzing the sensing behavior of metamaterials with varying structures for a specific medium, with limited comparative analysis of the sensing performance of different metamaterials for a specific measured medium. In summary, the metamaterial sensing field lacks methods for comparing measurement results of different metamaterials for the same measured medium, or for analyzing the combined TE and TM mode resonance peaks of multi-resonant metamaterials and asymmetric metamaterials. The development of sensing performance evaluation methods will facilitate the application of metamaterial sensing.

[0117] The multiple resonance peaks of the metamaterial participate in the sensing measurement simultaneously. The sensing sensitivity of each resonance peak is different, which can be regarded as unequal precision measurements. In data measurement, "weight" represents the reliability of the measurement data, and the inverse of the square of the standard deviation is generally used as the weight. In this experiment, multiple measurements of fixed points on the metamaterial are random errors. The data accuracy of random errors is generally measured by standard deviation. In the experiment, each set of data is the average value after 50 scans. The single-ring structure and the three-ring structure were measured three times. Figure 8 The deviations between the various resonance peaks measured over multiple times are relatively small. If the inverse of the square of the experimentally obtained standard deviations of each resonance peak were used as weights, these weights would be similar, making it difficult to compare the sensing performance of different structures. Because the Q value of a metamaterial represents the sensitivity of that resonance, the Q value of each resonance peak is used as a weight to perform a weighted average of the data from different structures, obtaining the device's overall sensing factor and enabling comparison of the sensing performance of different structures.

[0118] The Q value of the resonant peak is calculated as f / FWHM, where f represents the center resonant frequency and FWHM represents the half-width at half maximum (FWHM) of the resonant frequency. Because the actual measured spectrum is affected by the data conversion method and the measurement environment, such as the medium, irregularity in the spectrum can lead to varying Q values. Using the Q value from the experimental spectrum as a weighting factor introduces instability and changes the overall factor. Therefore, the Q value of the simulated transmission spectra of the SSR and TSR structures is used as the weight for weighted calculation to obtain the overall factor. The Q values ​​of the SSR and TSR structures are shown in Table 5.

[0119] Table 5 Q values ​​of each resonance peak of SSR and TSR

[0120] sample <![CDATA[Q(f1)]]> <![CDATA[Q(f2)]]> <![CDATA[Q(f3)]]> <![CDATA[Q(f4)]]> <![CDATA[Q(f TM )]]> SSR 14.7 26.39 23.17 TSR 17.24 15.66 16.86 17.19 24.29

[0121] If we take t=5um, n=2 as an example, we can use weighted average to calculate the comprehensive factor (CF). i represents the number of the resonance peak, Q i Represents the quality factor of resonance peak i, Δf i represents the frequency shift of the i resonance peak. The comprehensive factors for the single ring and the three ring are 33.1 and 63.8 respectively. The comprehensive factors are calculated using the experimental frequency shift. The TE mode (f1∽f4) and TM (f TM The comprehensive factors for calculating the frequency shift of the ) mode resonance peak are shown in Table 6:

[0122] Table 6 Comprehensive sensing factors (CF) of the solutions after the reaction of 0.1 mg / μl B6, 0.1 mg / μl B6 and 0.167 mg / ul BSA, and 0.2 mg / μl B6 and 0.167 mg / ul BSA on the surface of SSR and TSR sensors, respectively

[0123] sample CF(SSR) CF(TSR) <![CDATA[0.1mg / μlB6]]> 40.97 33.45 <![CDATA[0.1mg / μlB6+BSA]]> 59.9 60.04 <![CDATA[0.2mg / μlB6+BSA]]> 69.89 80.99

[0124] Table 6 shows that the CF factors of the SSR and TSR sensors increase in sequence after being coated with 0.1 mg / μl B6, 0.1 mg / μl B6 and 0.167 mg / ul BSA, and 0.2 mg / μl B6 and 0.167 mg / ul BSA reactants, respectively. This is consistent with the sensing rules of the SSR and TSR resonance peaks for the above substances. In addition, Table 6 shows that when both sensors are coated with 0.1 mg / μl B6, the CF factor of the TSR is smaller than that of the SSR. When coated with 0.1 mg / μl B6 and BSA and 0.2 mg / μl B6 and BSA reaction solutions, the CF factor of the TSR is slightly larger than that of the SSR. It can be seen that the comprehensive factor not only simplifies the expression of the multi-resonance peak sensing results, but also shows that for the measured medium with lower concentration, the sensor with fewer resonance peaks has a larger comprehensive factor and a slight advantage. For the measured medium with higher concentration, the sensor with more resonance peaks has a larger comprehensive factor as the concentration increases, and the sensing advantage is obvious.

[0125] 3.2. 3D diagram of the comprehensive sensing factor in the metamaterial plane (x, y, CF xy )

[0126] The above analysis focuses on measurements performed at a fixed point within the metamaterial sensor, a common method used for data sampling in many current metamaterial sensing applications. However, the distribution of the measured solution across the metamaterial surface, and the uniformity of the solution, makes the fixed-point measurement less representative of the measurement result. However, the concentration of the solution is still unevenly distributed across the metamaterial surface. Furthermore, the processing of the metamaterial also introduces certain errors. Furthermore, the size of the solution distribution and the number of plasmas on the metamaterial surface affect measurement accuracy. Therefore, the measurement method that uses a single region as a proxy for the entire metamaterial surface lacks certainty. Scanning the metamaterial sensing medium point by point to obtain sensing parameters within the metamaterial's two-dimensional plane can improve measurement reliability. During sampling, the area of ​​a measurement point is roughly the size of the light spot diameter (typically a circular spot of approximately 3 mm). Scanning each region within the metamaterial's plane yields a transmission spectrum for each sampling point (x, y) (x and y represent the coordinates of the sampling point within the metamaterial plane), and calculating the comprehensive factor (CF). xy , by scanning point by point, the comprehensive factors (x, y, CF xy ), it is also convenient to calculate the average value and error range of CF, providing data support for the calculation of other parameters of this sensing method.

[0127] 3.3. 3D refractive index map (x, y, n) in the metamaterial plane xy )

[0128] The transmission spectrum is obtained in the above scanning, and the dielectric constant of the scanning position can be calculated, thus obtaining a three-dimensional coordinate dielectric constant map (x, y, ε xy ). The specific calculation method is as follows: During the experiment, the time domain spectrum of the sample is obtained through the terahertz time domain system, and the frequency domain spectrum is obtained through Fourier transform. The frequency domain spectrum can obtain the transmission coefficient, which can be expressed by the following formula: Where p(w) represents the amplitude, To express the phase, use the formula To calculate the refractive index, the thickness d was measured using a three-dimensional optical microscope. The magnetic permeability μ can be regarded as 1, so the dielectric constant can be calculated by the refractive index. The three-dimensional coordinate diagram (x, y, n) of the refractive index of the corresponding area in the metamaterial plane can be obtained by point-by-point transmission spectrum. xy ), taking the 3D map of the refractive index at the corresponding point of the bare metamaterial sensor as a reference.

[0129] 3.4. 3D graph of the coupling coefficient in the metamaterial plane (x, y, n xy )

[0130] The resonance of metamaterials is sensitive to the surrounding medium. On the one hand, the localized field of electromagnetic waves at the microstructure alters their propagation. On the other hand, the medium within the microstructure also influences the transmission of electromagnetic waves. This is particularly true when measuring chiral materials using chiral structures. Whether linearly or circularly polarized, the microstructure and chiral medium alter the propagation and absorption of electromagnetic waves. This principle relationship can be expressed using the following equation.

[0131]

[0132] k is the coupling coefficient between the measured medium and the metamaterial. n=n0+k, n0 is the refractive index of the bare metamaterial, n is the refractive index after the medium is embedded in the microstructure, and the corresponding sample transmission spectrum is scanned and the refractive index is calculated to obtain the distribution of the refractive index in the two-dimensional plane of the terahertz metamaterial (x, y, n xy ) and the distribution of coupling coefficients (x, y, k xy ).

[0133] The present invention is based on asymmetric open single-ring (SSR) and triple-ring (TSR) structures made by two micromachining processes, and analyzes the resonance mechanism and sensing analysis in TE and TM modes. Sensing analysis after three media 0.1mg / μl B6, 0.1mg / μl B6 and BSA, and 0.2mg / μl B6 and BSA reactants are carried out respectively. Simulation and experiments show that: (1) the sensing sensitivity of the TM mode of SSR and TSR is significantly greater than the sensing sensitivity of their TE mode; (2) with the increase of medium concentration, the sensing effect of the resonance peak with high sensing sensitivity of TSR is significantly greater than the resonance peak with high sensing sensitivity of SSR. This paper uses the quality factor of the resonant peaks in the simulated transmission spectra of each structure as a weighting coefficient, combining the frequency shift of each resonant peak and its quality factor with a comprehensive factor to evaluate the sensing effects of SSR and TSR. Experiments show that this parameter can basically reflect the sensing laws of SSR and TSR, simplifying the sensing expression of multiple resonant peaks and multipolarization modes. The revelation of the sensing laws also provides a design method for terahertz metamaterial sensors. On this basis, a theoretical method is proposed to scan the metamaterial sensor point by point to obtain the comprehensive factor, refractive index, and coupling coefficient in a two-dimensional plane. This not only improves the reliability of the sensor measurement results but also deeply reveals the sensing mechanism, providing an optimization strategy for terahertz metamaterial sensing design and promoting the application of metamaterial sensors.

[0134] The above disclosure is only a preferred embodiment of the present invention, and certainly cannot be used to limit the scope of the rights of the present invention. Ordinary technicians in this field can understand that all or part of the processes of the above embodiment and equivalent changes made in accordance with the claims of the present invention are still within the scope of the invention.

Claims

1. A multi-parameter sensing evaluation method based on multi-resonance peak terahertz metamaterial, characterized in that: The following steps are involved: Step 1: Construct single-ring and triple-ring structures; Both the single-ring structure and the triple-ring structure are asymmetric open structures made of aluminum on a silicon substrate through a micromachining process. The single-ring structure is a regular hexagonal structure, which is formed by rotating one side of a regular hexagon 60 degrees along the center and connecting them end to end, with an opening at a specified distance from the center. The three-ring structure is composed of three concentric rings, and the outer ring and the middle ring have openings at a specified distance from the center of the ring; step 2: performing resonance mechanism and sensing analysis on the single ring structure and the three-ring structure respectively; Step 3: Conduct solution reaction sensing experiment; During the solution reaction sensing experiment, a reaction solution is used to form a thin film on the surface of the single-ring structure and the triple-ring structure, and then a terahertz time-domain system is used to measure and obtain corresponding parameters for analysis; The reaction solutions include 0.1 mg / μl B6 solution, 0.2 mg / μl B6 solution, 0.1 mg / μl B6 and 0.167 mg / ul BSA reactant, and 0.2 mg / μl B6 solution and 0.167 mg / ul BSA reactant; Step 4: Use the quality factor of each resonance peak in step 2 and step 3 as a weighting coefficient to compare the sensing effects of different structures; Step 5: Obtain the comprehensive sensing factor, refractive index and coupling coefficient of the single-ring structure and the triple-ring structure to obtain a comprehensive evaluation effect; The comprehensive sensing factor, the refractive index, and the coupling coefficient are obtained by scanning the medium areas of the single-ring structure and the triple-ring structure point by point respectively; The comprehensive sensing factor is to use the quality factor of the multi-resonance peak as the weighting coefficient to perform a weighted average on the frequency shift of each resonance peak. Specifically, the Q value of each resonance peak is used as the weighting coefficient to calculate the frequency shift Δf. i Perform weighted averaging, the formula is: i represents the number of the resonance peak, Q i Represents the quality factor of resonance peak i, Δf i represents the frequency shift of the i resonance peak, and n is the number of resonance peaks; The refractive index is a physical quantity that describes the effect of the medium on the propagation speed of terahertz waves. The formula is: in, represents the phase, c is the speed of light in vacuum, ω is the angular frequency of the terahertz wave, and d is the thickness of the dielectric film; The coupling coefficient reflects the interaction strength between the measured medium, metamaterial structure, and terahertz wave. The coupling coefficient is derived from the change in refractive index, and the formula is: n=n0+k Where n0 is the refractive index of the bare metamaterial, and n is the refractive index after embedding the medium in the microstructure.

2. The multi-parameter sensing evaluation method based on multi-resonance peak terahertz metamaterial according to claim 1, characterized in that: The sensing analysis and the solution reaction sensing experiment both use vertical incidence of terahertz waves.

3. The multi-parameter sensing evaluation method based on multi-resonance peak terahertz metamaterial according to claim 1, characterized in that: During the process of performing resonance mechanism and sensing analysis on the single-ring structure and the triple-ring structure, the parameters and variation relationships of the single-ring structure and the triple-ring structure in TE and TM modes are recorded respectively.

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