Terahertz metamaterial design of rod-shaped and S-shaped composite mirror image structure

Abstract

The invention requests to protect a terahertz metamaterial design of a rod-shaped and S-shaped composite mirror image structure, the terahertz metamaterial is composed of a rod-shaped composite S shape and a mirror image structure thereof, and a unit structure is a typical two-layer structure and sequentially comprises an intermediate dielectric layer and a metal pattern layer from bottom to top; and the metal pattern layer comprises a long metal sheet with an opening at the lower end, a short metal sheet, an S-shaped metal sheet and a long metal sheet with an opening at the middle end from left to right. The mirror image structure metal pattern layer comprises a long metal sheet with an opening in the middle end, an S-shaped metal sheet, a short metal sheet and a long metal sheet with an opening in the lower end from left to right.

Description

Technical Field

[0001] The present invention relates to the technical field of terahertz spectroscopy detection, and specifically, it is an invention of a terahertz metamaterial design with a rod-shaped and "S"-shaped composite mirror structure, belonging to the field of terahertz metamaterials. Background Art

[0002] Terahertz waves are located in the intersection region of photonics and electronics in the electromagnetic spectrum, with their frequency band covering between microwaves and infrared waves, specifically referring to electromagnetic radiation with a frequency range of 0.1 - 10 THz. This band has strong penetration ability, significant absorption effect, weak photon energy characteristics, as well as non-ionizing and non-invasive properties. These characteristics enable terahertz biosensing technology to ensure the safety of operators while supporting non-destructive and repeated detection of biological samples. On this basis, it is significantly feasible to use terahertz for label-free detection of biological macromolecules. The basis lies in that the vibration modes of most biological molecules, the crystal photon vibrations, and the weak intermolecular forces (such as hydrogen bonds and van der Waals forces) generated by the skeletal vibrations are all distributed in the terahertz frequency band, and the terahertz spectrum with both amplitude and phase information can accurately obtain the dielectric parameters and attenuation characteristics of substances in the terahertz region. By analyzing the signal evolution after the interaction between terahertz waves and biological macromolecule samples, important information such as their component composition and structural characteristics can be effectively extracted. Based on the molecular-specific terahertz fingerprint spectrum and its amplitude, this technology can achieve qualitative and quantitative analysis of biomedical macromolecules. The sensing technology with terahertz radiation as the signal carrier has become an important branch of the terahertz application system, showing significant advantages in the field of material information perception, especially in the direction of biomedical molecule detection and analysis.

[0003] However, the wavelength of terahertz waves from 30 μm to 3000 μm is significantly larger than the physical scale of typical biological samples (such as biological molecules like viruses and bacteria), which limits the detection sensitivity of terahertz biosensing. Therefore, the terahertz wave resonance effect of trace biological samples can be enhanced through metamaterial design to improve sensing performances such as sensitivity.

[0004] Metamaterials are artificial materials that can flexibly achieve the desired resonance characteristics under the excitation of electromagnetic waves by customizing materials and designing resonance unit structures in the metamaterials. Specifically, by adjusting the sub-wavelength meta-atomic structure, precise regulation of the electromagnetic parameters (dielectric constant and magnetic permeability) of the metamaterials can be achieved.

[0005] As a two-dimensional planar extension of metamaterials, metasurfaces break through the physical limitations of three-dimensional nanostructure manufacturing. By constructing structured patterns on a two-dimensional substrate, metasurfaces not only inherit the electromagnetic regulation ability of metamaterials but also have a more compact physical size. This characteristic strongly promotes the research and development process of micro-optical biosensors and portable bioimaging devices.

[0006] Therefore, terahertz metamaterial sensors can achieve high-sensitivity, high-efficiency, and trace-level sensing, and have great application potential in the fields of biomedicine, non-destructive testing, food, and agriculture. Summary of the Invention

[0007] The present invention proposes a design of a terahertz metamaterial with a rod-shaped and "S"-shaped composite mirror structure. The unit structure is a typical two-layer structure, which is successively an intermediate dielectric layer and a metal pattern layer from bottom to top. The metal pattern layer from left to right is a long metal sheet with a lower end opening, a short metal sheet, an "S"-shaped metal sheet, and a long metal sheet with a middle end opening. The metal pattern layer of its mirror structure from left to right is a long metal sheet with a middle end opening, an "S"-shaped metal sheet, a short metal sheet, and a long metal sheet with a lower end opening.

[0008] This sensor realizes local electromagnetic field enhancement based on the inductance-capacitance (LC) oscillation circuit mode. In this design, the metal structure can be equivalent to an inductance element, and the adjacent metal gap can be regarded as a capacitor. When the electric field vector direction of the incident electromagnetic wave is parallel to the gap, the LC resonance mechanism can be effectively excited. Its resonance frequency is determined by the formula and thus the resonance frequency of the device can be precisely tuned by adjusting parameters such as the length of the metal rod and the opening width:

[0009] Increasing the rod length (L) will increase the inductance and lower the resonance frequency (red shift).

[0010] Increasing the opening width (g) will decrease the capacitance and raise the resonance frequency (blue shift).

[0011] Increasing the rod width (w) will decrease the inductance and increase the fringe capacitance, resulting in a complex change in frequency.

[0012] In addition, the surface current distribution diagram at the resonance frequency shows that the incident terahertz wave can synchronously excite multiple homogeneous LC resonance units on the sensor surface. The finally observed resonance peak is actually the macroscopic manifestation of the cooperative coupling of these resonance units.

[0013] In the resonant state, a circumferential surface current (such as in the counterclockwise direction) will form in the slit region, causing charge accumulation at the opening and generating a significantly enhanced electromagnetic field distribution. The enhanced local electric field is extremely sensitive to changes in the dielectric properties of the slit region. When analyte molecules are adsorbed at the slit position, even a slight perturbation in their refractive index will significantly change the resonance characteristics of the device, manifested as an observable shift in the position of the resonance peak, thereby realizing the detection function at the molecular level. This design improves the sensitivity.

[0014] This design aims to propose a new metasurface structure to improve the sensitivity. Brief Description of the Drawings

[0015] To make the content of the present invention easier to be clearly understood, the following further details the present invention in combination with the specific embodiments of the present invention and the accompanying drawings, wherein

[0016] Figure 1 are the structural diagrams of the rod-shaped and "S"-shaped composite structure and its mirror image structure.

[0017] Figure 2 are the resonance peaks of the rod-shaped and "S"-shaped composite structure and its mirror image structure. It can be seen that the two have almost the same resonance peaks.

[0018] Figure 3 are the surface current distributions and equivalent circuits of the rod-shaped and "S"-shaped composite structure and its mirror image structure at the frequency point of 0.8462 THz.

[0019] Figure 4 are the surface current distributions of the rod-shaped and "S"-shaped composite structure and its mirror image structure at the frequency point of 1.1954 THz.

[0020] Figure 5 are the surface current distributions of the rod-shaped and "S"-shaped composite structure and its mirror image structure at the frequency point of 1.3052 THz.

[0021] Figure 6 are the surface current distributions of the rod-shaped and "S"-shaped composite structure and its mirror image structure at the frequency point of 1.433 THz.

[0022] Figure 7 are the surface current distributions of the rod-shaped and "S"-shaped composite structure and its mirror image structure at the frequency point of 1.5878 THz. Specific Embodiments

[0023] The following will clearly and detailedly describe the technical solutions in the embodiments of the present invention in combination with the accompanying drawings in the embodiments of the present invention. The described embodiments are only a part of the embodiments of the present invention.

[0024] The present invention proposes a terahertz metamaterial design of a rod-shaped and "S"-shaped composite mirror image structure, wherein the unit structure is a typical two-layer structure, which is successively a middle dielectric layer and a metal pattern layer from bottom to top; the metal pattern layer is successively a lower-end open long metal sheet, a short metal sheet, an "S"-shaped metal sheet, and a middle-end open long metal sheet from left to right. The metal pattern layer of its mirror image structure is successively a middle-end open long metal sheet, an "S"-shaped metal sheet, a short metal sheet, and a lower-end open long metal sheet from left to right.

[0025] Among them, the thickness of the metal pattern layer is 0.2 μm, and the metal material is gold. The middle dielectric layer uses silicon, and its thickness is 30 μm.

[0026] The width of the metal sheet at the lower end of the leftmost side of the metal pattern layer is 4 μm, the length of the upper metal sheet is 39 μm, the opening length is 6 μm, and the length of the lower metal sheet is 6 μm. The width of the second metal sheet from the left is 4 μm and the length is 40 μm. The length of the outer metal sheet of the "2"-shaped metal sheet is 20 μm, the length of the inner metal sheet is 15 μm, and the width of the metal sheet is 5 μm. The width of the metal sheet with an opening in the middle of the rightmost side is 4 μm, the length of the upper metal sheet is 19 μm, the opening length is 10 μm, and the length of the lower metal sheet is 22 μm. The top view of each polarization conversion unit is rectangular, with a length (y direction) of 51 μm and a width (x direction) of 48 μm. The rod-shaped composite "S"-shaped mirror metal pattern layer is the mirror image of the rod-shaped composite "S"-shaped metal pattern layer.

[0027] The technical solution of the present invention to solve the above technical problems is: using CST simulation and then fabricating the device.

[0028] 1. Design simulation and structure optimization

[0029] Theoretical modeling: Based on the target frequency band of 0.2 - 2 THz, design the metasurface unit structure, optimize the structure parameters through the electromagnetic simulation software CST, and achieve a specific resonance response. Obtain the S parameters, simulate the interaction between terahertz waves and the metasurface, and verify whether the electromagnetic properties such as dielectric constant and permeability meet the sensing requirements.

[0030] 2. The device can be fabricated through mature surface micro-nano processing technology. This technology can precisely control the geometric parameters of the structure, making the edges of the device smooth and the contour clear, so as to ensure that the actual performance of the device is as close as possible to the theoretical results.

[0031] The processing steps are as follows:

[0032] (1) Spin-coat a photoresist layer uniformly on the surface of the silicon substrate and dry it thoroughly;

[0033] (2) Subsequently, precisely align the mask with the substrate, and perform ultraviolet light exposure on the photoresist through the mask (the hollowed-out area of which corresponds to the shape of the target structure). After development, a visible micro-structure pattern can be presented;

[0034] (3) Deposit a metal thin film on the entire area using the metal evaporation process;

[0035] (4) Finally, strip the excess photoresist and synchronously remove the metal layer attached to the photoresist, leaving only the metal pattern structure required by the design.

[0036] The above embodiments should be understood as being only used to illustrate the present invention and not to limit the protection scope of the present invention. After reading the content recorded in the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent changes and modifications also fall within the scope defined by the claims of the present invention.

Claims

1. A terahertz metasurface design, characterized in that: The rod-shaped composite "S" shape and its mirror image structure together realize the detection of chiral substances.

2. The terahertz metasurface design according to claim 1, characterized in that: The rod-shaped composite "S"-shaped metasurface structure is composed of M×M polarization conversion units periodically arranged in the same horizontal plane, wherein the polarization conversion units sequentially comprise an intermediate dielectric layer (1) and a metal pattern layer (2) from bottom to top (along the z direction); wherein the intermediate dielectric layer (1) is used to form resonance with the metal pattern layer (1) for incident terahertz waves.

3. The terahertz metasurface design according to claim 2, characterized in that: The intermediate dielectric layer (1) is made of silicon.

4. The terahertz metasurface design according to claim 2, characterized in that: The thickness of the intermediate dielectric layer (1) is 30 μm.

5. The terahertz metasurface design according to claim 2, characterized in that: The metal pattern layer (2) comprises, from left to right, a long metal sheet with an opening at the lower end, a short metal sheet, an "S"-shaped metal sheet, and a long metal sheet with an opening at the middle end.

6. The terahertz metasurface design according to claim 2, characterized in that: The metal material of the metal pattern layer (2) is gold.

7. The terahertz metasurface design according to claim 2, characterized in that: The thickness of the metal pattern layer (2) is 0.2 μm.

8. The terahertz metasurface design according to claim 2, characterized in that: The width of the metal sheet at the leftmost lower opening of the metal pattern layer (2) is 4 μm, the length of the upper metal sheet is 39 μm, the length of the opening is 6 μm, and the length of the lower metal sheet is 6 μm.

9. The terahertz metasurface design according to claim 2, characterized in that: The second metal sheet from the left of the metal pattern layer (2) has a width of 4 μm and a length of 40 μm.

10. The terahertz metasurface design according to claim 2, characterized in that: The outer metal sheet of the "S"-shaped metal sheet in the metal pattern layer (2) is 20 μm long, the inner metal sheet is 15 μm long, and the width of the metal sheet is 5 μm.

11. The terahertz metasurface design according to claim 2, characterized in that: The width of the metal sheet at the rightmost middle opening of the metal pattern layer (2) is 4 μm, the length of the upper metal sheet is 19 μm, the length of the opening is 10 μm, and the length of the lower metal sheet is 22 μm.

12. The terahertz metasurface design according to claim 2, characterized in that: The top view of each polarization conversion unit is rectangular, with a length (y direction) of 51 μm and a width (x direction) of 48 μm.

13. The terahertz metasurface design according to claim 1, characterized in that: The rod-shaped composite "S"-shaped mirror structure is composed of M×M polarization conversion units periodically arranged in the same horizontal plane, wherein the polarization conversion unit comprises an intermediate dielectric layer (3) and a metal pattern layer (4) from bottom to top (along the z direction); the rod-shaped composite "S"-shaped mirror structure metal pattern layer (4) is a mirror image of the rod-shaped composite "S"-shaped metal pattern layer (2). The metal pattern layer (2) has a thickness of 0.2 μm and is made of gold.

14. The terahertz metasurface design according to claim 13, characterized in that: The intermediate dielectric layer (3) is made of silicon and has a thickness of 30 μm.

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