A surface plasmon resonance terahertz sensor

Abstract

The present invention relates to a terahertz sensor based on surface plasmon resonance, belonging to the field of terahertz sensing technology. The present invention comprehensively considers the reasonable layout and parameter optimization of the dielectric layer, bottom metal plate, and resonator unit to achieve high-sensitivity, high-selectivity, and fast-response sensing performance. The present invention is composed of a periodic array of ring resonators and butterfly resonators, forming a novel integrated sensor. The butterfly resonator is arranged in the middle of four metal ellipses, which can enhance the interaction between electromagnetic waves and substances, thereby improving the sensor performance. Plasma resonance is introduced into the reflection spectrum and a red shift occurs during transverse stretching, achieving high sensitivity and excellent robustness. Moreover, by optimizing the electromagnetic field distribution, the response ability of the sensor to specific frequencies or refractive indices is enhanced, and it can more accurately detect tiny refractive index changes, thereby improving its sensitivity.

Description

Technical Field

[0001] The present invention relates to the technical field of terahertz sensing, and specifically to a terahertz sensor based on surface plasmon resonance. Background Art

[0002] The terahertz band is a band between mid-infrared and microwave that has not been fully developed in the spectrum and is called the "terahertz gap". It has great scientific significance and application prospects in physics, materials science, life science, astronomy, information and national defense technology, etc. Due to the important academic significance and application value of the terahertz band, in recent years, terahertz physics, devices and applications have become one of the hottest frontier research fields in the world.

[0003] Surface plasmon resonance technology is a technology developed in the 1990s that can sensitively measure the change of the dielectric function of the object to be measured. This technology has very wide applications in physics, chemistry and biology, especially in real-time monitoring of the interaction of biological macromolecules. After more than 20 years of development, surface plasmon resonance biosensors have become an important research tool in the fields of life science and pharmacy.

[0004] Through the study of terahertz spectra, it is found that many biological macromolecules have characteristic peaks in the terahertz band. At present, the spectral analysis of biological macromolecules mainly uses terahertz time-domain spectrometers. An analysis of the interaction process of biological macromolecules requires a terahertz sensor that can monitor in real time. Since the refractive index of a common prism in the terahertz band is relatively low, the total reflection structure of the common prism applicable to existing surface plasmon resonance sensors is not applicable in the terahertz band.

[0005] Therefore, developing a new type of terahertz sensor that can dynamically adjust the resonant frequency and has high stability and sensitivity is of great significance for promoting the development of terahertz sensing technology. Summary of the Invention

[0006] The purpose of the present invention is to provide a terahertz sensor based on surface plasmon resonance to solve the problems raised in the above background art.

[0007] To achieve the above purpose, the present invention provides the following technical solutions:

[0008] A terahertz sensor based on surface plasmon resonance, comprising:

[0009] A base material layer, which is a double-sided polished polymer flexible base for supporting and stabilizing the entire sensor structure;

[0010] A dielectric layer, which is located above the base material layer,

[0011] The bottom metal plate is disposed above the dielectric layer. The bottom metal plate serves as a reflection layer for total reflection of incident terahertz waves. It is composed of a number of resonator units, and each resonator unit is composed of a periodic array of a ring resonator and a butterfly resonator.

[0012] The ring resonator includes four metal ellipses. The four metal ellipses form a matrix and are inclined inward. The butterfly resonator is disposed in the middle of the four metal ellipses. The butterfly resonator includes an isosceles triangular metal that is vertically mirrored.

[0013] The range of the included angle θ between the major axis of the metal ellipse and the vertical direction is 4 - 12°.

[0014] The calculation method of the co - resonance frequency of the resonator unit is as follows:

[0015]

[0016] Further, the materials of the bottom metal plate, the metal ellipse, and the isosceles triangular metal are gold.

[0017] Further, the thickness of the base material layer is 500 - 600 μm.

[0018] Further, the distance g between the two isosceles triangular metals is 1 - 2 μm, and the base L of the isosceles triangular metal is 8 - 10 μm.

[0019] Further, the horizontal length E of a single metal ellipse is 20 - 28 μm.

[0020] Further, the thickness of the metal ellipse and the isosceles triangular metal is 0.2 - 0.4 μm.

[0021] Further, the L is the equivalent inductance and C is the equivalent capacitance.

[0022] Further, the distance between the long - side width S and the short - side width W of the rectangular lattice formed by the four metal ellipses as a matrix is 110 - 130 μm, and the center distance d between the two metal ellipses is d = W / 1.5.

[0023] Further, the material of the dielectric layer is polytetrafluoroethylene.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] The surface plasmon resonance terahertz sensor structure of the present invention comprehensively considers the reasonable layout and parameter optimization of the dielectric layer, the bottom metal plate, and the resonator unit to achieve high - sensitivity, high - selectivity, and fast - response sensing performance.

[0026] The present invention is composed of a periodic array of ring resonators and butterfly resonators to form a new integrated sensor. The butterfly resonator is arranged in the middle of four metal ellipses, which can enhance the interaction between electromagnetic waves and matter, thereby improving the sensor performance, introducing plasma resonance in the reflection spectrum, and producing a red shift during lateral stretching, thereby achieving high sensitivity and excellent robustness. By optimizing the electromagnetic field distribution, the sensor's response ability to specific frequencies or refractive indices is enhanced, and tiny refractive index changes can be detected more accurately, thereby improving its sensitivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The schematic diagram is a structural diagram of a surface plasmon resonance terahertz sensor of the present invention.

[0028] Figure 2 It is a top view of the present invention.

[0029] Figure 3 It is the transmission spectrum of the present invention.

[0030] Figure 4 This is a test result curve diagram of different values of θ of the present invention.

[0031] Figure 5 This is the transmission spectrum of the present invention with different distance values and L values.

[0032] List of reference numerals: base material layer 1; adhesive layer 2; metal QBIC metasurface layer 3; resonator unit 4; upper ring chain resonator 5; lower ring chain resonator 6; first gap 7; second gap 8; protective layer 9; anti-reflection layer 10; dielectric isolation layer 11; functional film 12. DETAILED DESCRIPTION

[0033] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] It should be noted that the illustrations provided by the high-sensitivity terahertz sensor of the present invention only illustrate the basic concept of the present invention, rather than the specific dimensional data of the actual physical object. In actual production, specific analysis should be carried out in combination with actual production difficulties and other issues. This specification only provides a structure, ratio, size, etc., which are only used to cooperate with the specification to explain the present invention. In order to enable practitioners in the technical field to better understand and learn the present invention, it is hereby stated that the above-mentioned technical solutions, specific implementation methods, structural designs, and preparation technologies, etc., are not limiting conditions for the implementation of the present invention. This explanation should not be construed as a substantial limitation of technical details. Without affecting the effects that the present invention can produce and the purposes that can be achieved, any adjustment of the structure, modification of the proportional relationship, or change in size can be applied to the technical scope of the present invention. The core of the present invention lies in improving the sensitivity of the terahertz sensor. For achieving this goal, the flexibility of technical implementation is crucial. Therefore, for technicians, the structure can be modified or parameters can be adjusted according to actual needs to meet the requirements of specific application scenarios. This flexibility ensures the applicability and universality of the present invention, enabling various relevant technicians to better understand, apply, and promote the technical content of the present invention.

[0035] As Figures 1 to 5 shown,

[0036] Example 1

[0037] This example specifically describes the construction process of a surface plasmon resonance terahertz sensor, in which the parameters of each layer are precisely controlled according to the design requirements.

[0038] Substrate material layer 1, the substrate material layer 1 is a double-sided polished polymer flexible substrate, which is used to support and stabilize the entire sensor structure; the substrate material layer 1 is selected as a polymer flexible substrate. Through precise processing technology, its thickness is ensured to be 500 μm to ensure the stability and support of the structure. The selection of this thickness is based on the low-loss characteristics and good mechanical stability in the terahertz frequency band. A thicker substrate can provide stronger support force to ensure the stability of the entire sensor structure in a complex environment. At the same time, it also ensures that terahertz waves can efficiently penetrate the substrate and interact with the bottom metal plate 3.

[0039] Dielectric layer 2, the dielectric layer 2 is located above the substrate material layer 1 and is used to adjust the resonance frequency of the sensor and enhance its response to specific terahertz wavelengths. The dielectric layer 2 can be made of a material with a specific dielectric constant, such as polytetrafluoroethylene,

[0040] The bottom metal plate 3 is disposed above the dielectric layer 2 and is composed of a number of resonator units 4. The bottom metal plate 3 serves as a reflective layer for total reflection of incident terahertz waves, thereby increasing the Q value and sensitivity of the sensor. This design significantly improves the optical efficiency of the sensor, enabling the sensor to have higher sensitivity when detecting weak signals.

[0041] In the specific implementation of the present invention, the thickness of the bottom metal plate 3 can be a continuous gold layer, which can totally reflect terahertz waves.

[0042] Resonator unit 4: Each resonator unit 4 is composed of a periodic array of a ring resonator 5 and a butterfly resonator 6. The distance between the long side width S and the short side width W of the rectangular lattice formed by four metal ellipses 7 is 110 - 130 μm.

[0043] The ring resonator 5 includes four metal ellipses 7, which form a matrix. The four metal ellipses 7 are inclined inward. The butterfly resonator 6 is disposed in the middle of the four metal ellipses 7. The butterfly resonator 6 includes an isosceles triangular metal 8 that is vertically mirrored. In the design of the high - sensitivity terahertz sensor of the present application, the metal ellipse 7 and the isosceles triangular metal 8 are integrated to further enhance its flexibility and adaptability. These components can dynamically adjust the resonance frequency of the sensor, thereby achieving an accurate response to terahertz waves of different frequencies.

[0044] To achieve efficient terahertz wave transmission and detection, waveguide structures such as MDM waveguide structures or planar surface plasmon waveguide structures can be added. These structures can optimize the FOM (figures of merit) and sensitivity of the sensor. The waveguide supports different conduction modes, which are related to the effective medium refractive index of the waveguide. When the refractive index of the material surrounding the waveguide changes, it will cause a change in the effective medium refractive index of the waveguide, a change in the conduction mode, and a shift in the resonance peak position, so it can be used to detect the refractive index of the material.

[0045] The range of the angle θ between the major axis of the metal ellipse 7 and the vertical direction is 4 - 12°.

[0046] The calculation method of the resonance frequency of the resonator unit 4 is as follows:

[0047]

[0048] The structures of the ring resonator 5 and the butterfly resonator 6 improve the sensitivity and selectivity of the sensor and achieve a response to an external electric field by changing the propagation path of terahertz waves and enhancing the local surface plasmon mode, thereby dynamically adjusting the performance of the sensor.

[0049] Example 1, the calculation method of the resonance frequency of the ring resonator 5 is as follows:

[0050] The ring resonator 5 includes four metal ellipses 7. The four metal ellipses 7 form a matrix, and the four metal ellipses 7 are arranged to incline inward. Sensor parameters are set, and the parameters are shown in Table 1.

[0051] Table 1 Sensor parameters

[0052]

[0053] The performance of the sensor was simulated and analyzed using the full-wave electromagnetic analysis software CST Microwave Studio. When simulating, a frequency solver based on the finite integration technique (FIT) was used to calculate the transmission coefficient and electric field distribution of the sensor. The X and Y directions were set as periodic boundaries, and the Z direction was set as an open boundary. The THz wave was perpendicularly incident on the surface of the sensor. The metal layer was lossy metal gold with a conductivity σ = 4.561×107 S / m, and the dielectric constant ε of the PC substrate was 2.7.

[0054] Since the structure of the sensor has a great influence on its performance, the unit structure parameters W and S of the sensor were optimized by the control variable method first. When W increased from 80 μm to 140 μm in steps of 10 μm, the transmission spectrum of the sensor was as shown in Figure 3 (a). It can be found that when W = 120 μm, its resonance peak is very sharp, and the Q value corresponding to the sensor is the largest. When S increased from 80 μm to 140 μm in steps of 10 μm, the transmission spectrum of the sensor was as shown in Figure 3 (b). It can be found that when S = 120 μm, the sensing is 348. When W increases, the resonance absorption peak will be redshifted. In addition, it can also be significantly redshifted. The reason is that the surface currents on the two ellipses with the closest distance between adjacent units in the X direction will repel each other. After W increases, this mutual repulsive force between charges will decrease, and the width of the surface current distribution on the ellipse will increase, ultimately resulting in an increase in the equivalent inductance L of the sensor and a redshift of the resonance frequency f. When S increases, the resonance absorption peak will be significantly blueshifted. The reason is that the surface currents on the two ellipses with the closest distance between adjacent units in the Y direction will also repel each other. After S increases, this mutual repulsive force between charges will decrease, and the length of the surface current distribution on the ellipse will increase and expand towards both ends of the ellipse. At this time, two effects will occur: 1) The equivalent inductance L of the sensor increases, and the resonance frequency f redshifts; 2) The equivalent capacitance C of the sensor decreases, and the resonance frequency f blueshifts. Since the blueshift of the resonance frequency caused by the decrease in the equivalent capacitance C is greater than the redshift of the resonance frequency caused by the increase in the equivalent inductance L, ultimately resulting in a blueshift of the resonance frequency, the distance between the long side width S and the short side width W of the rectangular lattice formed by the four metal ellipses of the present invention is 110 - 130 μm, preferably 120 μm.

[0055] As shown in Figure 4As shown, when θ increases from 0° to 12°, the position of the central resonance point f0 remains almost unchanged. While the depth of the resonance absorption peak increases, the FWHM value also continuously increases. In the experiment, when θ = 6°, the FWHM is 3.3 GHz, and the Q value of the sensor is as high as 348. It is worth noting that when θ = 0°, the resonance peak suddenly disappears.

[0056] The electric field distribution, magnetic field distribution, and surface current distribution at the frequency of the resonance absorption peak are simulated using FIT, and the results are as Figure 2 shown. It can be found that the resonance electric field energy is much greater than the magnetic field energy. The electric field distribution at the resonance point of 1.426 THz is calculated. Positive and negative charges are generated at both ends of the metal ellipse 7 under the excitation of THz waves. Electric fields are generated between one end of the four ellipses in each adjacent periodic array, forming an electric quadrupole moment. The electric quadrupole moment is a resonance model excited by the electric field oscillation formed by the same-sex charges on the diagonal of the rectangle and the adjacent opposite-sex charges. This also explains the reason for always keeping the center distance d = W / 1.5 in the simulation, that is, to prevent the generation of two resonance peaks due to different resonance distances of the electric quadrupoles excited by adjacent ellipses, thereby dispersing the resonance energy, reducing the depth of the resonance peak, and further affecting the performance of the sensor.

[0057] Example two:

[0058] Figure 2 and Figure 1 This is for the present invention, which consists of a ring resonator 5 and a butterfly resonator 6. L is the base length of the isosceles triangle, g is the gap length between the top angles of the two triangles, and E is the width of the metal ellipse 7. The CST frequency domain solver is used to optimize the simulation of the sensor. The thickness is 150 nm, the conductivity is 4.561x10 7 S / m, the substrate material layer 1 is 500 μm, and the dielectric constant is 11.9. The x and y directions are set as unit boundary conditions, and the z direction is set as an open boundary condition. The terahertz wave (E field along the y-axis direction) is vertically incident on the surface of the sensor. Since the performance of the sensor is affected by its structure, in order to quantitatively analyze the surface electromagnetic field enhancement effect, we calculate the Q / V eff of the two metasurfaces. The quality factor Q is calculated using the classical analysis method, which is defined as the ratio of the resonance frequency to the resonance full width at half maximum.

[0059] As Figure 5 shown, for the index of the ratio of the quality factor to the effective mode volume (Q / V eff ), the distance g between the two isosceles triangular metals 8 is tested. It is the transmission spectrum when g (2 μm) is fixed and L takes different values. The Q value can be calculated according to the transmission spectrum, and the V eff parameter can be calculated using Comsol software. Finally, the numerical calculation results of Q / V eff show that when L is 10 μm, Q / Veff reaches its maximum. Then, with L fixed at 10 μm, the transmission spectra for different values of g are as shown in Figure 5 (b), and the numerical calculation results for Q / V eff show that the smaller g is, the larger Q / V eff becomes.

[0060] The metal ellipse 7 enhances the overall capacitance of the present invention, enabling the capacitive microcavity to store a large amount of electromagnetic energy, which helps to improve the sensitivity of the metasurface.

[0061] Four metal ellipses 7 enable the sensor to flexibly change the resonant frequency, produce a focusing effect, have a fast response time (within a few milliseconds), and a short recovery time. This dynamic response ability enables the sensor to adapt to the detection requirements of terahertz waves with different frequencies, improving its practicality and flexibility.

[0062] The present invention is composed of a periodic array of ring resonators 5 and bowtie resonators 6, forming a novel integrated sensor. The bowtie resonator 6 is arranged in the middle of the four metal ellipses 7, which can enhance the interaction between electromagnetic waves and substances, thereby improving the sensor performance, introducing plasma resonance in the reflection spectrum, and generating a redshift during transverse stretching, achieving high sensitivity and excellent robustness.

[0063] By changing the phase of the incident circularly polarized wave through the ring resonator 5 and the bowtie resonator 6, amplitude difference and phase (geometric phase) encoding of terahertz waves can be performed respectively, thereby realizing the splitting and deflection of terahertz beams. The ring resonator 5 and the bowtie resonator 6 can flexibly control the propagation path and intensity of terahertz waves. And by optimizing the electromagnetic field distribution, the response ability of the sensor to specific frequencies or refractive indices is enhanced, and it can also more precisely detect minute refractive index changes, thereby improving its sensitivity.

[0064] In summary, through the above data tables and their analysis, we can clearly see the superior performance of this high-sensitivity terahertz sensor in aspects such as transmission spectrum, sensitivity, selectivity, and dynamic response. These performance characteristics make the sensor have broad application prospects in fields such as biological detection and environmental monitoring.

[0065] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be encompassed within the present invention. Any reference signs in the claims should not be regarded as limiting the claimed rights.

[0066] In addition, it should be understood that although this specification is described according to embodiments, not every embodiment only contains an independent technical solution. This narrative manner of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A surface plasmon resonance terahertz sensor, characterized in that, Including: A base material layer (1), which is a double-sided polished polymer flexible substrate for supporting and stabilizing the entire sensor structure; A dielectric layer (2), which is located above the base material layer (1); A bottom metal plate (3), which is arranged above the dielectric layer (2). The bottom metal plate (3) serves as a reflection layer for total reflection of incident terahertz waves and is composed of a number of resonator units (4). Each resonator unit (4) is composed of a periodic array of a ring resonator (5) and a butterfly resonator (6); The ring resonator (5) includes four metal ellipses (7). The four metal ellipses (7) form a matrix and are arranged to be inclined inward. The butterfly resonator (6) is arranged in the middle of the four metal ellipses (7). The butterfly resonator (6) includes an isosceles triangular metal (8) that is vertically mirrored; The range of the included angle θ between the major axis of the metal ellipse (7) and the vertical direction is 4 - 12°; The calculation method of the resonance frequency of the resonator unit (4) is as follows: Wherein, L is the equivalent inductance and C is the equivalent capacitance.

2. The surface plasmon resonance terahertz sensor according to claim 1, characterized in that The materials of the bottom metal plate (3), the metal ellipse (7), and the isosceles triangular metal (8) are gold.

3. The surface plasmon resonance terahertz sensor according to claim 1, wherein The thickness of the base material layer (1) is 500 - 600 μm.

4. The surface plasmon resonance terahertz sensor according to claim 1, wherein The distance g between the two isosceles triangular metals (8) is 1 - 2 μm, and the base length L of the isosceles triangular metal (8) is 8 - 10 μm.

5. The surface plasmon resonance terahertz sensor according to claim 1, wherein The horizontal length E of a single metal ellipse (7) is 20 - 28 μm.

6. The surface plasmon resonance terahertz sensor according to claim 1, characterized in that, The thickness of the metal ellipse (7) and the isosceles triangular metal (8) is 0.2 - 0.4 μm.

7. The surface plasmon resonance terahertz sensor according to claim 6, characterized in that, The distance between the long side width S and the short side width W of the rectangular lattice formed by the four metal ellipses (7) is 110 - 130 μm. The center distance d between the two metal ellipses (7) on both sides of the isosceles triangular metal (8) is d = W / 1.

5.

8. The surface plasmon resonance terahertz sensor according to claim 1, characterized in that The material of the dielectric layer (2) is polytetrafluoroethylene.

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