Terahertz sensor and method of using the same

Abstract

The present invention discloses a terahertz sensor, which includes a periodic array of multiple resonance units, wherein any resonance unit includes a metal resonance layer, a dielectric layer, and a metal reflection layer stacked in sequence from top to bottom, wherein the metal resonance layer includes an outer ring and an inner ring with concentric centers, the outer ring is provided with a first opening, the inner ring is provided with a second opening, and the first opening and the second opening are connected radially. The present invention is a terahertz metamaterial sensor based on a double-opening metal ring, which can enhance the local electromagnetic field intensity and increase the interaction between the terahertz wave and the sample. When performing label-free detection on biological samples, the terahertz sensor structure of the present invention has excellent performance indicators such as perfect absorption peak, high Q value and sensitivity, and adjustable resonance frequency.

Description

Technical Field

[0001] The present invention relates to the field of terahertz detection technology, and more specifically, to a terahertz sensor and a method for using the same. Background Art

[0002] Terahertz (THz) waves are electromagnetic waves with a frequency higher than microwaves and lower than visible light, ranging from 0.1 to 10 THz (1 THz = 10 12 Hz) frequency range, with a wavelength of 3 to 0.03 mm. The vibration frequency of many biological macromolecules is in the terahertz band, and their unique fingerprint spectrum has strong advantages in identification and detection. Terahertz waves can penetrate many non-polar materials and detect the internal information of substances. In addition, the photon energy of terahertz waves is only one millionth of that of X-rays, which will not damage the internal components of the substance being tested and can be used for non-destructive testing. At present, terahertz time-domain spectroscopy (THz-TDS) technology has achieved certain research results in the identification of Chinese herbal medicines, drugs, additives, etc., and has become the main means of material classification and identification and has been widely used. In response to the problems of large noise and weak signals in spectral data caused by system or environmental factors, many scholars have established models for qualitative and quantitative analysis through machine learning, deep learning and other methods, but the detection of trace biological samples and the identification of similar fingerprint spectra are still challenging.

[0003] With the development of micro-nano processing technology, the emergence of metamaterials (MMs) has made up for the hard problems of terahertz time-domain spectroscopy technology to a certain extent. Metamaterials are artificially designed electromagnetic composite materials composed of periodic subwavelength unit structures, which have special physical properties that natural materials cannot achieve, such as negative refractive index and inverse Doppler effect. Terahertz metamaterial biosensors are label-free affinity sensors that can enhance the local electromagnetic field intensity and are extremely sensitive to changes in the dielectric constant of the surrounding environment, providing a new idea for the detection of trace biological samples.

[0004] Existing terahertz sensors generally have the problem of low detection sensitivity in spectral detection technology. Summary of the invention

[0005] An object of the present invention is to solve at least the above problems and to provide at least the advantages which will be described hereinafter.

[0006] Another object of the present invention is to provide a method for using a terahertz sensor machine, which overcomes the technical problem of low detection sensitivity of traditional spectral detection methods and realizes the detection of trace or trace biological samples.

[0007] In order to achieve these purposes and other advantages according to the present invention, a terahertz sensor is provided, which includes a periodic array of multiple resonance units, and any resonance unit includes a metal resonance layer, a dielectric layer and a metal reflection layer stacked in sequence from top to bottom, wherein the metal resonance layer includes an outer ring and an inner ring with concentric centers, a first opening is provided on the outer ring, and a second opening is provided on the inner ring, and the first opening and the second opening are connected in a radial direction.

[0008] Preferably, in the terahertz sensor, the dielectric layer and the metal reflective layer are both cubic structures, and the horizontal cross-sections of the dielectric layer and the metal reflective layer are square structures of consistent size; the centers of the horizontal cross-sections of the dielectric layer and the metal reflective layer coincide with the center of the inner ring.

[0009] Preferably, in the terahertz sensor, the thickness t of the outer ring and the inner ring in the vertical direction are both 0.2 μm; the diameter r1 of the outer ring is 18 to 35 μm, the width w1 is 1 to 4 μm, and the width g1 of the first opening is 1 to 10 μm; the diameter r2 of the inner ring is 8 to 15 μm, the width w2 is 1 to 4 μm, and the width g2 of the second opening is 1 to 10 μm;

[0010] The side length of the square structure of the horizontal cross section of the dielectric layer and the metal reflective layer is 70-200 μm; the thickness h of the dielectric layer is 10-50 μm, and the thickness t1 of the metal reflective layer is 0.5 μm.

[0011] Preferably, in the terahertz sensor, the diameter r1 of the outer ring is 18 μm, the width w1 is 2 μm, and the width g1 of the first opening is 4 μm; the diameter r2 of the inner ring is 10 μm, the width w2 is 3 μm, and the width g2 of the second opening is 4 μm.

[0012] Preferably, in the terahertz sensor, the side length of the square structure of the horizontal cross section of the dielectric layer and the metal reflective layer is 80 μm; and the thickness h of the dielectric layer is 20 μm.

[0013] Preferably, in the terahertz sensor, the material of the dielectric layer is high-resistance silicon or fused quartz or polyimide or polytetrafluoroethylene or polyethylene.

[0014] Preferably, in the terahertz sensor, the material of the dielectric layer is polytetrafluoroethylene.

[0015] Preferably, in the terahertz sensor, the outer ring, the inner ring and the metal reflective layer are all made of gold, silver or copper.

[0016] Preferably, in the terahertz sensor, the outer ring, the inner ring and the metal reflective layer are all made of gold.

[0017] The present invention also provides a method for using the terahertz sensor, which comprises the following steps:

[0018] Step 1: Clean and dry the terahertz sensor for later use;

[0019] Step 2: Turn on the terahertz time-domain spectroscopy system, adjust the optical path, fill with nitrogen, reduce the humidity to below 3%, scan the air until the spectral signal is stable, obtain the reference signal spectral data Reference, and then place the terahertz sensor on the card slot for scanning to obtain the empty sensor spectral data Sample0;

[0020] Step 3, preparing a plurality of test sample solutions, wherein the plurality of test sample solutions are solutions prepared by mixing the sample mixture in equal proportions;

[0021] Step 4: Use a pipette to drop the test sample solution onto the surface of the terahertz sensor and dry it at 40°;

[0022] Step 5: Under the same conditions as in step 2, use the terahertz time-domain spectroscopy system to scan the terahertz sensor covering the sample obtained in step 4, and take the average value of the spectral data of multiple scans as the sample signal spectral data Sample1; clean the sensor and dry it;

[0023] Step 6, repeat steps 4 to 5, and record the sample signal spectrum data Sample 2, Sample 3, ... Sample n corresponding to all the test solutions;

[0024] Step 7: Import the reference signal spectral data Reference and the empty sensor spectral data Sample0, sample signal spectral data Sample1, Sample2, Sample3, ... Sample n into origin 2018, perform fast Fourier transform on them to obtain frequency domain spectrum, and use Calculate the reflectance of the sample, where E sample is the signal intensity corresponding to the spectral data of each sample, E reference is the signal strength of the air, and then the absorption rate corresponding to each sample is calculated by A=1-R, and the absorption characteristic curve of each test sample in the frequency band of 0.7~2.5THz is plotted;

[0025] Step 8: Analyze the frequency shift of the absorption characteristic curve of each test sample and establish a relationship model between the frequency shift change and the test sample.

[0026] The present invention includes at least the following beneficial effects: the present invention is a terahertz metamaterial sensor based on a double-open metal ring, which can enhance the local electromagnetic field strength and increase the interaction between the terahertz wave and the sample. When performing label-free detection on biological samples, the terahertz sensor structure of the present invention has excellent performance indicators such as perfect absorption peak, high Q value and sensitivity, and adjustable resonant frequency.

[0027] Other advantages, objectives and features of the present invention will be embodied in part through the following description, and in part will be understood by those skilled in the art through study and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 A top view of the unit resonance of the present invention;

[0029] Figure 2 It is a structural schematic diagram of the unit resonance of the present invention;

[0030] Figure 3 Schematic diagram of the structure of the terahertz sensor of the present invention

[0031] Figure 4 This is a schematic diagram of the working principle structure of the terahertz time-domain spectroscopy system of the present invention;

[0032] Figure 5 The absorption characteristic curves corresponding to turpentine, glycerin and olive oil as covering materials of the present invention;

[0033] Figure 6 is a graph of absorption characteristics corresponding to the terahertz sensor of the present invention when the analyte is not covered;

[0034] Figure 7 This is the electric field distribution diagram of the terahertz sensor of the present invention at the resonant frequency point;

[0035] Figure 8 is a current distribution diagram of the terahertz sensor of the present invention at the resonant frequency point;

[0036] Fig. 9 is the absorption characteristic curve of the resonant unit substructure of the present invention;

[0037] Fig.10 This is a graph showing absorption characteristics of the terahertz sensor of the present invention at different cover thicknesses;

[0038] Fig.11 This is a result diagram of the frequency shift of the terahertz sensor of the present invention changing with the cover thickness;

[0039] Fig.12 This is the absorption characteristic curve of the terahertz sensor of the present invention under samples with different refractive indices

[0040] Fig.13This is a result diagram of the frequency shift of the terahertz sensor of the present invention as the refractive index changes.

[0041] Explanation of the reference numerals: 11 - outer ring 12 - inner ring 2 - dielectric layer 3 - metal reflective layer. DETAILED DESCRIPTION

[0042] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments so that those skilled in the art can implement the invention with reference to the description.

[0043] It should be understood that the terms such as “having”, “including” and “comprising” used in the present application do not exclude the existence or addition of one or more other elements or combinations thereof.

[0044] It should be noted that the experimental methods described in the following embodiments are conventional methods unless otherwise specified, and the reagents and materials can be obtained from commercial channels unless otherwise specified.

[0045] In the description of the present invention, the terms "lateral", "longitudinal", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside" and "outside" etc. to indicate directions or positional relationships are based on the directions or positional relationships shown in the accompanying drawings and are only for the convenience of describing the present invention and simplifying the description. They do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore should not be understood as a limitation on the present invention.

[0046] like Figures 1 to 3 As shown, the present invention provides a terahertz sensor, which includes a periodic array of multiple resonance units, and any resonance unit includes a metal resonance layer, a dielectric layer 2 and a metal reflection layer 3 stacked in sequence from top to bottom, wherein the metal resonance layer includes an outer ring 11 and an inner ring 12 with concentric centers, a first opening is provided on the outer ring, and a second opening is provided on the inner ring, and the first opening and the second opening are connected radially.

[0047] In the above technical scheme, the present invention provides a sensor of absorber type, whose resonance unit is a "sandwich" structure composed of a metal resonance layer, a dielectric layer and a metal reflection layer. Two concentric open circular rings are arranged on a dielectric substrate with a relative dielectric constant of a certain value, and a metal reflection layer is arranged at the bottom of the dielectric substrate. When the terahertz wave is vertically incident on the upper surface of the sensor of the present invention, LC resonance is excited to generate two perfect absorption peaks with a high Q value, which can be used for high-sensitivity detection and identification of trace or trace biological samples. The present invention can not only be used for rapid and high-sensitivity detection of trace or trace biological samples, but also can be used to prepare absorber functional devices. The present invention is a terahertz metamaterial sensor based on double open metal rings, which can enhance the local electromagnetic field intensity and increase the interaction between the terahertz wave and the sample. When performing label-free detection on biological samples, the terahertz sensor structure of the present invention has excellent performance indicators such as perfect absorption peak, high Q value and sensitivity, and adjustable resonance frequency.

[0048] The resonant units with the same structural size are arranged in an N×N periodic array to form a terahertz metamaterial biosensor with a square structure of about 1 cm on a side. There is no spacing between any two adjacent terahertz sensors, such as Figure 3 As shown; in the terahertz frequency band, since the sub-wavelength unit structure size has reached the micron level, the ordinary exposure and stripping process is difficult to ensure the preparation of high-quality terahertz metamaterial sensors. Therefore, it is proposed to use an ultraviolet exposure system and a double-layer glue development method to form a bottom cross-section that is conducive to stripping; preferably, 120×120 resonant units are arranged in a periodic array to form a terahertz sensor with a square structure with a side length of about 1 cm.

[0049] In another technical solution, the terahertz sensor, the dielectric layer and the metal reflective layer are both cubic structures, and the horizontal cross-sections of the dielectric layer and the metal reflective layer are square structures of the same size; the centers of the horizontal cross-sections of the dielectric layer and the metal reflective layer coincide with the center of the inner ring. The two open rings of the metal resonance layer of the present invention are concentrically arranged and located in the middle of the dielectric layer, and a sensor with a symmetrical and regular structure is arranged, which can further achieve matching of the terahertz sensor with the free space impedance, thereby achieving perfect absorption of terahertz waves and enhancing the local electromagnetic field strength.

[0050] In another technical solution, in the terahertz sensor, the thickness t of the outer ring and the inner ring in the vertical direction are both 0.2 μm; the diameter r1 of the outer ring is 18 to 35 μm, the width w1 is 1 to 4 μm, and the width g1 of the first opening is 1 to 10 μm; the diameter r2 of the inner ring is 8 to 15 μm, the width w2 is 1 to 4 μm, and the width g2 of the second opening is 1 to 10 μm;

[0051] The side length of the square structure of the horizontal cross section of the dielectric layer and the metal reflective layer is 70-200 μm; the thickness h of the dielectric layer is 10-50 μm, and the thickness t1 of the metal reflective layer is 0.5 μm.

[0052] In order to avoid diffraction and refraction of radiation, the structural size of the terahertz sensor provided by the present invention is much smaller than the wavelength of 1.2 mm corresponding to 2.5 THz.

[0053] In another technical solution, in the terahertz sensor, the diameter r1 of the outer ring is 18 μm, the width w1 is 2 μm, and the width g1 of the first opening is 4 μm; the diameter r2 of the inner ring is 10 μm, the width w2 is 3 μm, and the width g2 of the second opening is 4 μm.

[0054] In another technical solution, in the terahertz sensor, the side length P of the square structure of the horizontal cross section of the dielectric layer and the metal reflective layer is 80 μm; the thickness h of the dielectric layer is 20 μm. The present invention selects appropriate unit structure parameters (see Table 1 for details) to further improve sensor performance.

[0055] Table 1 Geometric parameters of unit structure

[0056]

[0057] In another technical solution, in the terahertz sensor, the material of the dielectric layer is high-resistance silicon or fused quartz or polyimide or polytetrafluoroethylene or polyethylene. The dielectric layer between the metal resonance layer and the metal reflection layer can be made of rigid materials, such as high-resistance silicon, fused quartz, etc., or flexible materials, such as polyimide, polytetrafluoroethylene, polyethylene, etc.

[0058] In another technical solution, the material of the dielectric layer of the terahertz sensor is polytetrafluoroethylene. Since flexible materials have the advantages of high sensitivity, small dielectric constant, and easy bending, the present invention selects flexible material polytetrafluoroethylene as the dielectric layer material to obtain a high-performance sensor. The dielectric layer made of polytetrafluoroethylene is harmless to biological substances and can improve the detection limit, which is crucial in early disease detection, pesticide residues in agricultural products, and mycotoxin detection.

[0059] In another technical solution, in the terahertz sensor, the outer ring, the inner ring and the metal reflective layer are all made of gold, silver or copper. The metal material of the present invention is selected from one of gold, silver, copper and other metals, because the better the metal conductivity, the stronger the resonance.

[0060] In another technical solution, in the terahertz sensor, the outer ring, the inner ring and the metal reflective layer are all made of gold, preferably gold, whose electrical conductivity σ=4.561e+007S / m.

[0061] The present invention also provides a method for using the terahertz sensor, which comprises the following steps:

[0062] Step 1: Clean and dry the terahertz sensor for later use;

[0063] Step 2: Turn on the terahertz time-domain spectroscopy system, adjust the optical path, fill with nitrogen, reduce the humidity to below 3%, scan the air until the spectral signal is stable, obtain the reference signal spectral data Reference, and then place the terahertz sensor on the card slot for scanning to obtain the empty sensor spectral data Sample0;

[0064] Step 3, preparing a plurality of test sample solutions, wherein the plurality of test sample solutions are solutions prepared by mixing the sample mixture in equal proportions;

[0065] Step 4: Use a pipette to drop the test sample solution onto the surface of the terahertz sensor and dry it at 40°;

[0066] Step 5: Under the same conditions as in step 2, use the terahertz time-domain spectroscopy system to scan the terahertz sensor covering the sample obtained in step 4, and take the average value of the spectral data of multiple scans as the sample signal spectral data Sample1; clean the sensor and dry it;

[0067] Step 6, repeat steps 4 to 5, and record the sample signal spectrum data Sample 2, Sample 3, ... Sample n corresponding to all the test solutions;

[0068] Step 7: Import the reference signal spectral data Reference and the empty sensor spectral data Sample0, sample signal spectral data Sample1, Sample2, Sample3, ... Sample n into origin 2018, perform fast Fourier transform on them to obtain frequency domain spectrum, and use Calculate the reflectance of the sample, where E sample is the signal intensity corresponding to the spectral data of each sample, E reference is the signal strength of the empty sensor, and then the absorption rate corresponding to each sample is calculated by A=1-R, and the absorption characteristic curve of each test sample in the frequency band of 0.7~2.5THz is plotted;

[0069] Step 8: Analyze the frequency shift of the absorption characteristic curve of each test sample and establish a relationship model between the frequency shift change and the test sample.

[0070] Since each sample has different physical properties, different test samples have different corresponding refractive indices, which causes the resonance peak of the terahertz sensor to shift in frequency. Different test samples can be detected based on the frequency shift change.

[0071] The high quality factor resonance and local field distribution are achieved through structural design, which is beneficial to detect small changes in dielectric constant and reduce the amount of sample. Figure 4 As shown, the fiber laser pulse is split into two beams by a beam splitter, the stronger one is the pump light, and the weaker one is the detection light. The pump light generates a terahertz pulse through the photoconductive antenna, and the pulse signal reflected by the sample and the detection light pass through the terahertz detector on the same line to obtain the change of the terahertz electric field intensity with time, and the reflection spectrum is obtained by fast Fourier transform.

[0072] Taking turpentine with a refractive index of n=1.4721, glycerol with a refractive index of n=1.473, and olive oil with a refractive index of n=1.4763 as test samples, the method for using the terahertz sensor of the present invention is further described as follows:

[0073] Turpentine, glycerin and olive oil were covered on the terahertz sensor respectively, with a covering thickness of 10 μm. Scanning was performed under the conditions of step 2, and the absorption curve was plotted as follows: Figure 5 As shown, Figure 5 a is the characteristic curve of the three test samples at low frequency f1. Figure 5 b is the characteristic curve of the three test samples at high frequency f1. It can be seen that the greater the refractive index of the analyte, the more obvious the red shift phenomenon. The peaks at low frequencies are 0.92236THz, 0.92214THz, and 0.92104THz, respectively. The peaks at high frequencies correspond to 1.9042THz, 1.9024THz, and 1.9006THz, respectively. The frequency shift of f2 is larger than that of f1, and the absorption characteristics of the analyte can also be clearly analyzed at low frequencies. This is because the slight change of the analyte on the sensor surface causes the change of the dielectric constant of the sensor surface. C sensor The corresponding change causes the resonant frequency to change, so its change can be observed through the absorption characteristic curve. The sensor designed in this application can distinguish a refractive index difference of at least 0.01. The simulation detection experiment results prove that the present invention can detect the analyte according to the absorption characteristic curve, effectively increase the molecular absorption cross section, and show good sensing detection capabilities. It has potential application value in the field of food adulteration and high-sensitivity detection of trace or trace biological samples.

[0074] 1. Simulation analysis

[0075] The present invention uses the three-dimensional electromagnetic field simulation software CST 2020 to simulate and analyze the designed terahertz sensor, and uses the frequency domain solver based on the finite integral method (FIT) to calculate the absorptivity of the absorber, electric field current distribution and other parameters. The terahertz wave is incident vertically on the upper surface of the metamaterial structure, and the polarization direction is along the x-axis, that is, the electric field E is along the y-direction, and the magnetic field H is along the x-direction. In addition, periodic boundary conditions unit cell are set in the x and y directions, and open boundary conditions open (add space) are set in the z direction.

[0076] The absorption spectrum of the terahertz sensor of the present invention when there is no covering is as follows: Figure 6 As shown in the figure, it can be seen that the designed metamaterial absorber has two nearly perfect absorption peaks at f1 and f2. The absorption rate calculation formula is A(ω)=1-R(ω)-T(ω), where R(ω) represents the reflectivity, and its value is equal to |S 11 | 2 , T(ω) represents the transmittance, and its value is equal to |S 21 | 2 Since the metal bottom plate is much larger than the skin depth of the terahertz wave in the metal, the terahertz wave is fully reflected and the transmittance is negligible. The absorption rate at the resonant frequency of the present invention reaches more than 99.9%. The quality factor Q represents the resonance characteristics of the sensor. Its size is related to both resolution and sensitivity. Generally speaking, the higher the Q value, the smaller the dielectric loss of the structure, the narrower and sharper the resonance peak, and the higher the resolution and sensitivity. It can be seen that the Q values ​​are 21.9 and 32.1 respectively.

[0077] 2. Mechanism analysis

[0078] To further explain the dual-band ( Figure 6 The resonance mechanism of the metamaterial absorber sensor (f1 and f2) is simulated to study the electric field and current distribution at the resonance frequency. The results are shown in Figure 7 and Figure 8 As shown, Figure 7 It shows that in f1( Figure 7 a is the electric field distribution at f1) and f2 ( Figure 7 b is the electric field distribution at f2) At all frequencies, the electric field is confined to the opening of the ring, and the electric field strength in the inner ring is stronger; Figure 8 It shows that at both frequencies f1 and f2, there is current mainly distributed on the two metal open rings and flows in the direction indicated by the arrows. Figure 8 a is the surface current distribution at f1; Figure 8 b is the surface current distribution at f2; Figure 8 c is the bottom plate current distribution at f1; Figure 8d is the current distribution of the bottom plate at f2. The ring can be regarded as an inductor L, and the opening can be regarded as a capacitor C. According to the principle of equivalent circuit, the electric field is generated because the induced charge generated by the incident wave gathers at the opening, and the current is generated due to the movement of the charge. This is a typical LC resonance. At the same time, the direction of the current in the metal bottom plate is opposite to the direction of the surface current. There is also a magnetic resonance between the two, and the response is weak. The resonance of this sensor can be equivalent to the superposition effect of LC resonance, such as Fig. 9 As shown, the resonant frequency can be approximated as Among them, the equivalent inductance is related to the geometric parameters of the sensor. After the parameters are determined, the equivalent inductance of the metal open ring generally does not change. The equivalent capacitance of the sensor is related to the equivalent capacitance of the opening and the equivalent capacitance of the surrounding dielectric environment. The empty sensor is only related to the equivalent capacitance of the opening.

[0079] If the biological analyte is coated on the surface of the terahertz sensor (metamaterial absorber sensor) of the present invention, a new capacitor C sensor As the surrounding dielectric constant and analyte thickness change, C sensor The value of will change, the equivalent capacitance of the metamaterial sensor will change, and the resonance frequency will change regularly with the dielectric constant and thickness of the surface medium, so that the biological characteristics of the surface material can be analyzed. Therefore, the terahertz sensor provided by the present invention can be used for sensing and detecting biological samples.

[0080] 3. Analysis of different coverage thicknesses of analytes with the same refractive index

[0081] In order to study the influence of the thickness of the analyte to be measured on the performance of the sensor, an analyte with a refractive index of n=1.68 was selected, and the analyte was covered on the surface of the terahertz sensor of the present invention for simulation analysis. During the analysis, a blank terahertz sensor not covered with the analyte was selected as a reference. The absorption characteristic curve corresponding to the change of the analyte covering thickness h1 from 2μm to 30μm is shown in the figure below. Fig.10 As shown, the resonance frequency shows a red shift phenomenon, and the relationship between the frequency shift and the thickness of the object to be measured is as follows Fig.11 As shown, as the thickness of the analyte increases, the frequency shift increases continuously, and the growth rate gradually approaches saturation. This is because the incident wave will excite the current on the sensor surface to oscillate. The greater the distance, the faster the oscillation decays. Therefore, the thickness of the analyte to be measured is preferably 10μm.

[0082] 4. Analysis of analytes with different refractive indices

[0083] The thickness and dielectric constant of the analyte to be measured on the sensor surface will affect the frequency shift and intensity of the absorption characteristic curve. After optimizing and determining the unit structure parameters of the sensor, the response characteristics of the sensor to the analyte are further studied. The coverage thickness of the analyte on the surface of the terahertz sensor is determined to be 10μm. Analytes with different refractive indices are covered on the terahertz sensor respectively, and the corresponding absorption characteristic curves are simulated and drawn. During the analysis process, a blank terahertz sensor without analyte coverage is selected as a reference; the analysis results are shown in Figure 2. Fig.12 and Fig.13 As shown, Fig.12 When the refractive index n of the analyte changes from 1.1 to 1.9, the two resonance peaks show a significant red shift. This is because the dielectric constant around the sensor has changed significantly. The metamaterial sensor reflects this change in the change of the resonance curve. The degree of frequency shift caused by the change of the refractive index of the two resonance frequencies is shown in the curve Fig.13 As shown, Δf2 is significantly greater than Δf1. After linear fitting, the refractive index sensitivities of f1 and f2 are 314.6 GHz / RIU and 682.7 GHz / RIU, respectively, and the FOM values ​​are 6.4 and 9.6, respectively. The refractive index of many substances is distributed within this range, and the sensor can be used for the detection of cancer tissues, pesticide residues, etc. The number of devices and processing scales described here are used to simplify the description of the present invention. The application, modification and variation of the present invention will be obvious to those skilled in the art.

[0084] Compared with the structures of other articles, the sensor structure designed in this application has certain improvements in sensitivity, quality factor, stability, and degree of electromagnetic wave modulation. The design is based on comprehensive consideration of sensor performance indicators, and the vibration frequency of many biological macromolecules is within this frequency band, which is conducive to later detection. The metal open ring is a typical artificial structural unit proposed by Pendry, which is more suitable for microwave-millimeter wave-terahertz frequency band. In order to facilitate later production and practical application, this application designs the sensor for use in biomedicine, non-destructive testing and other fields, so as to achieve the requirements of national safety standards and prevent diseases in advance. Single-peak terahertz metamaterial sensors still occupy the mainstream position. Since each sample has different electromagnetic response characteristics to the resonant frequency, the research on multi-peak metamaterials is of great significance in biological detection. First of all, the sensor designed in this application uses flexible material PTFE as the substrate material. Flexible materials have the advantages of high sensitivity and small dielectric constant, and high-performance sensors can be obtained. In the process of designing the sensor, the reasons for the changes in various parameters are explained from a theoretical level, and the physical laws therein are explored to achieve high-performance sensor design, as follows:

[0085] ① Choose the right material to avoid the serious disadvantages of traditional rigid substrate materials such as large dielectric constant. The flexible material PTFE has the advantages of low dielectric constant, stable performance, easy bending, etc. It is harmless to biological substances and can improve the detection limit. It is crucial in early disease detection, pesticide residues in agricultural products and mycotoxins. In addition, this application analyzes the mechanism of the influence of different substrates on sensors. Among the current mainstream materials, PTFE material has the best performance for the sensor designed in this application.

[0086] ② One of the goals of this application is to realize an absorber sensor with dual-band perfect absorption. Two resonance peaks are generated within a range of high signal-to-noise ratio of the terahertz spectrometer, achieving near-perfect absorption of terahertz waves, and the performance indicators are improved. At the same time, this application also analyzes the physical mechanism of resonance. By using multi-band sensors for sample detection, the electromagnetic responses of different samples at two resonance frequencies can be studied, laying a theoretical foundation for classifying and identifying samples.

[0087] ③ Regarding the parameters of the sensor, this application analyzes and optimizes them from the physical level. First, the opening position of the metal ring is analyzed. This application finds that when the inner ring moves and the inner and outer rings rotate, it shows a certain regular change, and the absorption peak intensity, position and half-peak width change greatly. There is even only one resonant frequency due to excessive coupling. These factors will cause the sensor performance to change to some extent; the resonant structure parameters are the second factor considered in this application. This application studies the influence of radius, line width, and opening gap and uses the equivalent circuit physical mechanism to analyze the cause. Selecting appropriate parameters can improve sensor performance. The unit structure period has a small effect and the substrate thickness has a large effect; in addition, this application compares transmission sensors. In terms of electromagnetic wave modulation and performance indicators, absorption sensors are slightly better.

[0088] ④ In terms of sensing performance analysis, this application proves the advantages of the sensor designed in this application by comparing the refractive index sensitivity of two substrate materials, and fully considers the influence of the electromagnetic wave incident angle, azimuth angle and errors in the manufacturing process during the detection process, proving that the sensor designed in this application has high stability.

[0089] ⑤ This application verifies the actual detection effect of the sensor through the dielectric properties of existing samples under the terahertz time-domain spectrum. For different samples, the sensor can identify the refractive index change of 0.01. Compared with the traditional tablet pressing detection, it has greatly improved both in reducing the amount of sample used and in low-content detection. Compared with the current terahertz sensors, its frequency selection characteristics are stronger (high quality factor) and its sensitivity is improved.

[0090] Although the embodiments of the present invention have been disclosed as above, they are not limited to the applications listed in the specification and the implementation modes, and they can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to the specific details and the illustrations shown and described herein.

Claims

1. A terahertz sensor, characterized in that: A periodic array comprising a plurality of resonant units, wherein any resonant unit comprises a metal resonant layer, a dielectric layer and a metal reflective layer stacked in sequence from top to bottom, wherein the metal resonant layer comprises an outer ring and an inner ring with the same center, the outer ring is provided with a first opening, the inner ring is provided with a second opening, and the first opening and the second opening are connected in a radial direction; The dielectric layer and the metal reflective layer are both cubic structures, and the horizontal cross-sections of the dielectric layer and the metal reflective layer are square structures with the same size; the centers of the horizontal cross-sections of the dielectric layer and the metal reflective layer coincide with the center of the inner ring; The diameter r1 of the outer ring is 18 μm, the width w1 is 2 μm, and the width g1 of the first opening is 4 μm; the diameter r2 of the inner ring is 10 μm, the width w2 is 3 μm, and the width g2 of the second opening is 4 μm; The side length of the square structure of the horizontal cross section of the dielectric layer and the metal reflective layer is 80 μm; the thickness h of the dielectric layer is 20 μm; The material of the dielectric layer is polytetrafluoroethylene; The outer ring, the inner ring and the metal reflective layer are all made of gold; The method for using the terahertz sensor comprises the following steps: Step 1: Clean and dry the terahertz sensor for later use; Step 2: Turn on the terahertz time-domain spectroscopy system, adjust the optical path, fill with nitrogen, reduce the humidity to below 3%, scan the air until the spectral signal is stable, obtain the reference signal spectral data Reference, and then place the terahertz sensor on the card slot for scanning to obtain the empty sensor spectral data Sample0; Step 3, preparing a plurality of test sample solutions, wherein the plurality of test sample solutions are solutions prepared by mixing the sample mixture in equal proportions; Step 4: Use a pipette to drop the test sample solution onto the surface of the terahertz sensor and dry it at 40°; Step 5: Under the same conditions as in step 2, use the terahertz time-domain spectroscopy system to scan the terahertz sensor covering the sample obtained in step 4, and take the average value of the spectral data of multiple scans as the sample signal spectral data Sample1; clean the sensor and dry it; Step 6: Repeat steps 4 to 5 to record the sample signal spectrum data Sample 2, Sample 3, ... Sample n corresponding to all test solutions; Step 7: Import the reference signal spectral data Reference and the empty sensor spectral data Sample0, sample signal spectral data Sample1, Sample2, Sample3, ... Sample n into origin 2018, perform fast Fourier transform on them to obtain frequency domain spectrum, and use R = Calculate the reflectance of the sample, where E sample is the signal intensity corresponding to the spectral data of each sample, E reference is the signal strength of air, and then the absorption rate corresponding to each sample is calculated by A = 1-R, and the absorption characteristic curve of each test sample in the frequency band of 0.7~2.5THz is plotted; Step 8: Analyze the frequency shift of the absorption characteristic curve of each test sample and establish a relationship model between the frequency shift change and the test sample.

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