Terahertz metamaterial sensor for controlling resonant frequency based on polarization angle

Abstract

The invention provides a terahertz metamaterial sensor for controlling resonant frequency based on a polarization angle, and the unit structure of the terahertz metamaterial sensor is a typical two-layer structure which is composed of a top gold metal resonant layer and a bottom silicon dielectric substrate layer in sequence from top to bottom. The top metal layer comprises four rod-shaped structures which are equal in width and unequal in length, the rod-shaped structures are arranged in a descending order according to the length and are coupled at a geometric center at a 45-degree rotation interval, and the coupling center and the center of the silicon dielectric layer are jointly aligned with an incident wave axis. Through the change of the incident wave polarization angle from 0 degree to 90 degrees, the sensor can realize frequency selection in the range of 0.79 THz to 0.91 THz, and a new solution is provided for solving the problems that the resonant frequency is difficult to regulate and control and the structure is complex in a terahertz metamaterial sensor.

Description

Technical Field

[0001] The present invention relates to a terahertz frequency band sensing technology, and in particular to a terahertz metamaterial sensor based on polarization angle manipulation of resonant frequency. Background Art

[0002] Terahertz waves, which lie between microwaves and infrared in the electromagnetic spectrum, have frequencies ranging from 0.1 to 10 THz, corresponding to wavelengths of approximately 30 microns to 3 millimeters. They bridge the "terahertz gap" between traditional electronics and optical technologies and have become a research hotspot in recent years. Terahertz waves, with their resonance with biomacromolecules and excellent safety, offer unique advantages in industrial applications such as biomedical diagnostics, material identification, and security testing. However, the low power of terahertz light sources, the strong absorption of terahertz waves by water, and the fact that many test objects are typically in aqueous solutions limit the application of terahertz technology in direct detection of trace samples. Furthermore, most chiral molecules exhibit identical absorption peaks in specific frequency bands, making direct identification of these molecules difficult through terahertz spectroscopy. Metamaterials—artificially designed and constructed electromagnetic materials or structures—possess unique physical properties, such as a negative refractive index and a negative dielectric constant, and are highly sensitive to changes in the dielectric material attached to their surfaces. The use of metamaterial resonant local fields can enhance the interaction between samples and terahertz waves, promote the practical application of terahertz technology in the field of biological detection, and improve the identification effect of unknown substances.

[0003] In traditional metal or dielectric metasurface materials and structures, once fabricated, the metasurface exhibits an isolated narrowband resonant peak distribution, and its optical properties are fixed, resulting in extremely limited information about detected frequency shifts or amplitude changes. Sensing is more effective when the characteristic spectrum of a molecule corresponds to the metamaterial's sensing resonance, and the substances being detected often share the same resonant frequency. Therefore, achieving frequency tunability in the metasurface's excitation resonance has become an urgent challenge. To address this issue, researchers domestically and internationally have proposed resonance multiplexing methods based on multi-pixel or angle manipulation. For example, these methods achieve spectral resonant frequency tunability by combining multiple metasurfaces or manipulating the incident angle between 0 and 60 degrees. However, multi-pixel approaches typically require the fabrication and assembly of a complex array of micro-nanostructures, while angle-multiplexing metasurfaces often require complex configurations of angle manipulation and deflection devices. Researchers have incorporated active materials such as graphene into metamaterials and manipulated the graphene Fermi level with voltage to achieve resonant frequency selection, but this increases the difficulty and research cost of metamaterial fabrication. In view of the limitations of the above methods, a frequency-selective metamaterial sensor with convenient frequency control, low structural complexity and low cost has important research significance. Summary of the Invention

[0004] In light of the aforementioned shortcomings of terahertz metamaterial sensors, the present invention provides a terahertz metamaterial sensor based on polarization angle manipulation of resonant frequency, designed to address the shortcomings of current technologies. The sensor comprises the following structure: a dielectric substrate with a specific relative permittivity and one or more metal resonators.

[0005] One or more metal resonators are located on the top layer and contact the upper end of the dielectric substrate with a certain relative dielectric constant.

[0006] The metal resonator is composed of four rod-shaped structures of different lengths and the same width, which are coupled in sequence at the center of the rods at a rotation angle of 45 degrees.

[0007] Optionally, the substrate includes a substrate formed of silicon material.

[0008] Optionally, the top metal resonator is made of gold.

[0009] Optionally, the lengths of the metal rods are 72 μm, 63 μm, 54 μm, and 45 μm, respectively, the width is 5 μm, and the thickness is 0.2 μm, and they are coupled at the center position in descending order of length.

[0010] Optionally, the thickness of the substrate is 30 μm, and the relative dielectric constant of the medium is ε=11.9.

[0011] As described above, the present invention proposes a highly sensitive terahertz metamaterial sensor with adjustable resonant frequency. This sensor consists of a two-layer structure: a substrate and one or more metal resonators. The one or more metal resonators are located on the top layer and contact the upper end of a dielectric substrate with a specific relative dielectric constant. The metal resonators are formed by coupling four metal rods of varying lengths, uniform widths, and thicknesses at their geometric centers. The metal structure and the bottom substrate form a metal resonator-substrate structure, enabling the formation of a highly sensitive absorption-type sensor capable of manipulating the resonant frequency using polarization angle, thereby addressing the difficulties in resonant frequency control and high processing costs associated with terahertz metamaterial sensors. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below based on specific embodiments of the present invention in conjunction with the accompanying drawings, wherein:

[0013] Figure 1 This is a schematic structural diagram of a terahertz metamaterial sensor with adjustable resonant frequency provided by the present invention;

[0014] Figure 2 These are all absorption curves of the terahertz metamaterial sensor with adjustable resonant frequency provided by the present invention as the polarization angle changes from 0 degrees to 90 degrees by 10 degrees;

[0015] Figure 3 This is a surface current diagram and an equivalent circuit diagram of the terahertz metamaterial sensor with adjustable resonant frequency provided by the present invention when the polarization angle is 0 degrees;

[0016] Figure 4 The figure is a sensing curve diagram of the terahertz metamaterial sensor with adjustable resonant frequency provided by the present invention when objects to be measured with different refractive indices are placed at a polarization angle of 0 degrees. DETAILED DESCRIPTION

[0017] In order to clearly explain the purpose and technical advantages of the present invention, the specific implementation methods are now described in conjunction with the accompanying drawings. Through core data such as diagrams, structural characteristics and absorption curves, the technical details and innovative points of the embodiments are systematically displayed, which facilitates readers to form an intuitive understanding of the sensor performance from a principle level. It should be noted that the device structure, proportional relationship and dimensional parameters presented in the accompanying drawings are all based on the theoretical design framework. The actual production requires parameter optimization based on micro-nano processing technology, material properties and detection requirements. Among them, the microstructure size, periodic arrangement mode, metal resonance layer thickness and other parameters of the metamaterial unit can be flexibly adjusted without departing from the core objectives of the present invention.

[0018] The present invention proposes a terahertz metamaterial sensor based on polarization angle manipulation of resonant frequency, wherein the unit structure is a typical two-layer structure, which consists of a bottom dielectric layer and a top metal pattern layer from bottom to top; the metal layer is coupled at the geometric center of the rod by four rod-like structures of different lengths and the same width, and the coupling method is to couple in sequence from long to short at a rotation angle of 45 degrees, and the material is gold; the bottom dielectric layer is formed by silicon material, and its geometric center coincides with the geometric center of the rod on the axis of the incident wave, and its relative dielectric constant is ε=11.9. The material exhibits stable physical properties in the terahertz frequency band and is less affected by ambient temperature changes, thereby ensuring the detection stability of the sensor under complex working conditions. The overall structural diagram of the sensor is shown in the figure below. Figure 1 shown.

[0019] In the present invention, the lengths of the selected metal rods are 72 μm, 63 μm, 54 μm, and 45 μm, respectively, and the width is 5 μm; the bottom dielectric layer has a thickness of 30 μm, and the period is a cube of 80 μm.

[0020] The terahertz metamaterial sensor can change the resonant frequency of the absorption peak based on the change of the polarization angle of the incident wave, which allows the sensor to manipulate the change of the resonant frequency by means of the polarization angle. Under the preset dimensions of the present invention, the absorption curve of the metamaterial device as the polarization angle changes from 0 degrees to 90 degrees by 10 degrees is as follows: Figure 2As shown in FIG. 1 , when the polarization angle increases by 10 degrees, the resonant frequency of the terahertz metamaterial sensor increases significantly (blue shifts). The polarization angle can be used to select the sensor to resonate at a suitable frequency.

[0021] The surface current diagram and equivalent circuit diagram of the terahertz metamaterial sensor when the polarization angle is 0 degrees are shown in the figure below. Figure 3 As shown, under the action of the incident wave, the metal rod horizontal to the electric field direction of the incident wave is regarded as an inductor, and the metal rod perpendicular to the electric field direction is regarded as a capacitor. According to the surface current diagram, it can be seen that the main current flow direction of the metal rod with an angle of 40 degrees to the electric field direction is horizontal to the electric field direction of the incident wave, which can be regarded as the inductor in the equivalent circuit. Figure 2 According to the equivalent circuit in , the resonant frequency of the sensor can be obtained as:

[0022]

[0023] When the polarization angle increases, the equivalent inductance L decreases and the equivalent capacitance C increases. Since the change in the equivalent capacitance C is much smaller than the change in the equivalent inductance L, the resonant frequency W increases significantly, resulting in a blue shift. As the polarization angle changes from 0 degrees to 90 degrees, the sensor can achieve frequency selection within the range of 0.79THz to 0.91THz, such as Figure 3 shown.

[0024] The main performance parameter of the terahertz metamaterial sensor is sensitivity S, which is an important indicator to measure the sensing performance of the sensor. The higher the sensitivity, the better the sensing performance of the sensor, and the better the resolution effect of the object to be measured. The sensitivity of the terahertz metamaterial sensor is defined as the offset of the resonant frequency when the unit refractive index changes. Its specific value can be expressed in the same formula S=Δf / Δn, where Δf is the change in the corresponding resonant frequency when the refractive index of the sensor object changes, and Δn is the change in the refractive index of the object to be measured. With the help of the simulation software CST, a 20μm thick object to be measured is placed on the sensor, and the refractive index n of the object to be measured is changed from n=1.0 to n=2.0, with an interval of 0.25 each time. When the refractive index of the object to be measured changes, the resonant frequency of the sensor redshifts. The sensitivity of the sensor is calculated by the formula, and the sensitivity is 50GHz / RIU. The sensing curve of the terahertz metamaterial sensor when objects of different refractive indices are placed at a polarization angle of 0 degrees is shown as follows. Figure 4 shown.

[0025] In summary, the present invention proposes a terahertz metamaterial sensor that uses polarization angle to control resonant frequency. Its dual-layer structure consists of a silicon dielectric base layer and a gold metal resonant layer. The metal layer comprises four rod-like structures of equal width and unequal length, arranged in descending order of length and coupled at 45-degree intervals at their geometric center. The coupling center and the center of the silicon dielectric layer are aligned with the axis of the incident wave. By varying the polarization angle of the incident wave from 0 to 90 degrees, the sensor can achieve frequency selection within the range of 0.79 THz to 0.91 THz, providing a new solution to the difficulties in resonant frequency control and structural complexity in terahertz metamaterial sensors.

[0026] The above examples are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention in any way. Any person skilled in the art may make various modifications or variations to the above examples without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or variations within the relevant technical field that do not depart from the core concepts and technical ideas disclosed in the present invention are intended to be included within the scope of the claims of the present invention.

Claims

1. A terahertz metamaterial sensor based on polarization angle manipulation of resonant frequency, characterized by: A dielectric substrate with a certain relative dielectric constant and one or more metal resonators. The one or more metal resonators are located on the top layer and contact the upper end of the dielectric layer with a certain relative dielectric constant.

2. The terahertz metamaterial sensor based on polarization angle manipulation resonant frequency according to claim 1, characterized in that: The bottom dielectric layer includes a dielectric material formed of silicon material.

3. The terahertz metamaterial sensor based on polarization angle manipulation resonant frequency according to claim 1, characterized in that: The metal resonator includes a top metal structure formed of gold material.

4. The terahertz metamaterial sensor based on polarization angle manipulation resonant frequency according to claim 1, characterized in that: The lengths of the metal rods are 72 μm, 63 μm, 54 μm, and 45 μm, respectively, with a width of 5 μm and a thickness of 0.2 μm. They are coupled at the center position in descending order of length.

5. The terahertz metamaterial sensor based on polarization angle manipulation resonant frequency according to claim 1, characterized in that: The bottom dielectric layer is 30 μm thick and the period length is 80 μm.

6. The terahertz metamaterial sensor based on polarization angle manipulation resonant frequency according to claim 1, characterized in that The device consists of two layers: a substrate and one or more metal resonators. The metal resonators are located on the top layer, contacting the upper end of a dielectric substrate with a specific relative dielectric constant. The metal resonators are formed by coupling four metal rods of varying lengths, uniform widths, and thicknesses at their geometric centers. The metal structure and the bottom substrate form a metal resonator-substrate structure, enabling the creation of a highly sensitive absorption sensor that manipulates the resonant frequency using polarization angle, thereby addressing the difficulties in resonant frequency control and high processing costs associated with terahertz metamaterial sensors.

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