A terahertz metamaterial sensor with concave quasi-continuum bound states

Abstract

The present invention relates to a concave quasi-continuous domain bound state terahertz metamaterial sensor, which has a number of periodic array units in the horizontal and vertical directions. The array units are composed of a metal metasurface, a dielectric layer, and a metal backplane with a depth greater than the skin depth of the incident wave from top to bottom. The metal metasurface consists of two parts, one of which is a cylindrical structure with a double fan-shaped opening, and the other is a closed resonant ring. The opening angle of the left side of the double fan-shaped opening is unequal to the opening angle of the right side. The cylindrical structure with the double fan-shaped opening is located within the closed resonant ring, and part of the volume of the cylindrical structure is embedded in the dielectric layer. The constructed sensor generates two resonance peaks under the excitation of a vertically incident terahertz wave, respectively at 3.44THz and 3.51THz, with a maximum quality factor Q value of 3096. The present invention innovatively constructs a disk structure with unequal opening angles on the left and right sides to achieve quasi-BIC resonance, with the advantages of high refractive index sensitivity, good linearity, simple structure and easy processing.

Description

Technical Field

[0001] The present invention belongs to the field of sensing technology in the terahertz frequency band, and relates to a terahertz metamaterial sensor of a concave quasi-continuous bound state (BIC). Background Art

[0002] Terahertz waves, also known as the "rays of life," refer to electromagnetic waves with a frequency range of 0.1THz to 10THz. Terahertz biochemical detection technology boasts the unique advantages of high penetration and high safety, and holds broad application prospects in the life and health fields.

[0003] Metamaterials are a class of artificial materials with special structures and properties. Their structures at the microscopic scale are carefully designed to exhibit special properties that natural materials do not possess. The advantage of metamaterials is that by adjusting the structure, size and distribution of artificial units, the electromagnetic parameters of the material can be effectively controlled, thereby obtaining a variety of novel electromagnetic properties. With the continuous deepening of metasurface research, existing metasurface functional devices are facing greater and greater challenges, and people have an increasing demand for high-quality factor (Q value) resonance and ultra-strong electromagnetic field localization. To address this problem, solutions including Fano resonance and localized plasma have been proposed. Due to the limitations of their own design principles, the quality factor and field localization enhancement of the resonator achieved based on the above design are relatively limited, and the sensing achieved is concentrated at a single frequency.

[0004] Bound states in the continuum (BIC) are waves that remain localized and coexist with continuous radiation waves that can carry away energy. Although BIC was originally proposed in quantum mechanics, it is a universal wave phenomenon and has been observed in electromagnetic waves, sound waves in air, water waves, and elastic waves in solids. In practice, it is difficult to achieve ideal BIC using metasurfaces due to multiple limitations such as material loss, device size constraints, and processing defects. Generally, the application requirements are met by converting the ideal BIC into a quasi-BIC mode with a finite high Q value. Metasurface sensors with high Q values ​​based on quasi-BIC have considerable application potential in ultrasensitive biochemical sensing. Summary of the Invention

[0005] The present invention aims to provide a terahertz metamaterial sensor based on a concave quasi-continuum bound state (BIC), aiming to address the low quality factor, low detection sensitivity, and poor linearity of existing terahertz sensors. The sensor is applied to transformer oil insulation testing. The sensor exhibits distinct response characteristics for transformer oils of varying types and degrees of thermal aging, enabling differentiation and detection of the type and degree of aging of the transformer insulation oil.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A concave quasi-continuous domain bound state terahertz metamaterial sensor is composed of multiple cube-structured array units periodically arranged in the x and y directions. Each array unit is composed of a metal metasurface, a dielectric layer and a metal backplate with a depth greater than the skin depth of the incident wave from top to bottom.

[0008] The present invention is also characterized in that:

[0009] The metal metasurface consists of two parts: a cylindrical structure with a dual-sector opening and a closed resonant ring. The cylindrical structure with the dual-sector opening is located within the closed resonant ring. Part of the cylindrical structure with the dual-sector opening is embedded in the dielectric layer. The dual-sector opening is symmetrical about the y-axis, with an opening angle α on the right side ranging from 5° to 30° and an opening angle β on the left side ranging from 15° to 45°.

[0010] The lengths L of the dielectric layer, the metal back plate and the closed resonant ring in the x direction and in the y direction are all 50 μm to 200 μm.

[0011] The thickness t1 of the metal back plate is 1 μm to 2 μm, the material is aluminum, and the electrical conductivity ε=3.56e+007S / m.

[0012] The thickness t2 of the dielectric layer is 10 μm to 30 μm, and the material used is silicon.

[0013] The material of the columnar structure with double fan-shaped openings is aluminum, with an electrical conductivity of ε=3.56e+007S / m and a thickness t3 of 5μm to 10μm, of which a thickness t4 of 1μm to 3μm is embedded in the dielectric layer.

[0014] The radius r of the columnar structure with double fan-shaped openings is 15 μm to 25 μm.

[0015] The closed resonant ring has a width h of 2 μm to 5 μm and a thickness t5 of 1 μm to 4 μm.

[0016] The present invention also provides an application of a terahertz metamaterial sensor in transformer oil insulation detection, specifically comprising: applying transformer insulation oil of a specified thickness to the surface of the metamaterial sensor, incidenting a terahertz wave into the metamaterial sensor, and performing absorption sensing simulation analysis of the terahertz metamaterial absorber by detecting and analyzing the refractive index change of the transformer insulation oil, thereby distinguishing the type and aging degree of the transformer insulation oil based on the absorption spectra at different resonant frequencies;

[0017] The beneficial effect of the present invention is that a terahertz metamaterial sensor with a concave quasi-continuous domain bound state (BIC) has a novel structure and does not require complex structural units or multi-layer metamaterial stacking. It has strong stability and is not easily oxidized or corroded. It also innovatively adopts a structure with unequal opening angles, breaking the symmetry of the structure, and can achieve a quasi-BIC mode when a TE wave or a TM wave is incident. This concave quasi-continuous domain bound state (BIC) terahertz metamaterial sensor can achieve resonance with a quality factor of more than 3000 in the terahertz frequency band, and can also be tuned to achieve two narrowband strong resonance peaks in the terahertz range, effectively solving the problems of low quality factor and poor sensitivity of existing terahertz sensors. This sensor is also used in the insulation detection of transformer oil to distinguish the type and aging degree of transformer insulating oil.

[0018] Other advantages, objects, and features of the present invention will be described in part in the following description and, in part, will be apparent to those skilled in the art upon examination of the following description or may be learned from practice of the present invention. The objects and other advantages of the present invention may be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below with reference to the accompanying drawings, in which:

[0020] Figure 1 Schematic diagram of the three-dimensional structure of a unit cell of a concave quasi-continuum bound state (BIC) terahertz metamaterial sensor provided by an embodiment of the present invention. (1) is the dielectric layer, (2) is the metal backplane, (3) is the closed resonant ring, and (4) is a cylindrical structure with double fan-shaped openings.

[0021] Figure 2 A top view of a unit cell of a concave quasi-continuum bound state (BIC) terahertz metamaterial sensor provided by an embodiment of the present invention. r is the radius of the cylindrical structure with dual fan-shaped openings, α is the right opening angle, β is the left opening angle, h is the width of the closed resonant ring, and L is the length of the dielectric layer, metal backplate, and closed resonant ring in the x- and y-directions.

[0022] Figure 3 A side view of a unit cell of a concave quasi-continuum bound-state (BIC) terahertz metamaterial sensor provided by an embodiment of the present invention. t1 is the thickness of the metal backplate, t2 is the thickness of the dielectric layer, t3 is the thickness of the double-sector open cylinder, t4 is the thickness of the double-sector open cylinder embedded in the dielectric layer, and t5 is the thickness of the closed resonant ring.

[0023] Figure 4The relationship between the frequency change of the low-frequency resonance peak and the refractive index of the object to be measured under the condition of vertical incidence of terahertz waves in a terahertz metamaterial sensor of a concave quasi-continuum bound state (BIC) provided by an embodiment of the present invention;

[0024] Figure 5 The relationship between the frequency change of the high-frequency resonance peak and the refractive index of the object to be measured under the condition of vertical incidence of terahertz waves in a terahertz metamaterial sensor of a concave quasi-continuum bound state (BIC) provided by an embodiment of the present invention;

[0025] Figure 6 The linear fitting results of the high-frequency resonance peak and low-frequency resonance peak corresponding to different refractive indices of the object under test for a terahertz metamaterial sensor with a concave quasi-continuum bound state (BIC) provided by an embodiment of the present invention under the condition of vertical incidence of terahertz waves;

[0026] Figure 7 This is a graph showing the response of different types of transformer insulating oil added to a concave quasi-continuum bound state (BIC) terahertz metamaterial sensor provided by an embodiment of the present invention, simulating FR3 natural synthetic ester insulating oil, dimethyl silicone oil insulating oil, and mineral oil insulating oil in the terahertz frequency band.

[0027] Figure 8 In a concave quasi-continuum bound state (BIC) terahertz metamaterial sensor provided by an embodiment of the present invention, vegetable insulating oils with different degrees of thermal aging are added to simulate the response curves of unaged and differently aged FR3 vegetable insulating oils in the terahertz frequency band. DETAILED DESCRIPTION

[0028] The following describes the embodiments of the present invention by means of specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic illustrations of the basic concept of the present invention, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0029] Among them, the accompanying drawings are only for illustrative purposes and represent only schematic diagrams rather than actual pictures, and should not be understood as limiting the present invention. In order to better illustrate the embodiments of the present invention, some parts of the accompanying drawings may be omitted, enlarged or reduced, and do not represent the dimensions of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions may be omitted in the accompanying drawings.

[0030] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if there are terms such as "upper", "lower", "left", "right", "front", "back", etc. indicating directions or positional relationships, they are based on the directions or positional relationships shown in the drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operate in a specific direction. Therefore, the terms describing the positional relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0031] See also Figures 1 to 8 , which is a terahertz metamaterial sensor with a concave quasi-continuum bound state (BIC).

[0032] Example 1

[0033] This embodiment describes in detail a concave quasi-continuum bound state (BIC) terahertz metamaterial sensor proposed by the present invention.

[0034] like Figure 1 As shown, the concave quasi-continuum bound state (BIC) terahertz metamaterial sensor in this embodiment consists of a periodically arranged array of several units. Each unit is composed, from top to bottom, of a metal metasurface, a dielectric layer, and a metal backplane with a depth greater than the skin depth of the incident wave. The metal metasurface consists of two parts: a cylindrical structure with a dual-sector opening and a closed resonant ring. The cylindrical structure with the dual-sector opening is located within the closed resonant ring. Part of the volume of the cylindrical structure with the dual-sector opening is embedded in the dielectric layer.

[0035] In this embodiment, a sensor array consisting of several sensing units is defined as having its length in the x-direction and its width in the y-direction. The openings of all array units are oriented parallel to and oriented in the x-direction, and the vertical axes of all array units are oriented in the y-direction. All sensor array units are periodically arranged along the x- and y-directions, resulting in a metamaterial sensor operating in the 2.91-3.51 THz band.

[0036] Preferably, if Figure 2 As shown, in this embodiment, the lengths of the dielectric layer, metal backplate and closed resonant ring of a single array unit in the x-direction and y-direction are denoted as L, which ranges from 50 μm to 200 μm, preferably 100 μm; the width of the closed resonant ring of a single array unit is denoted as h, which ranges from 2 μm to 5 μm, preferably 4 μm.

[0037] Preferably, the radius of the double-fan-shaped opening columnar structure of a single array unit in this embodiment is denoted as r, which ranges from 15 μm to 25 μm, and is preferably 20 μm; the double-fan-shaped opening of a single array unit is symmetrical about the y-direction axis, the right opening angle is denoted as α, which ranges from 5° to 30°, and is preferably 15°, and the left opening angle is denoted as β, which ranges from 15° to 45°, and is preferably 25°.

[0038] Preferably, if Figure 3 As shown, in this embodiment, the thickness of the metal backplate of a single array unit is t1, which ranges from 1 μm to 2 μm, preferably 1 μm; the thickness of the dielectric layer of a single array unit is t2, which ranges from 10 μm to 30 μm, preferably 30 μm.

[0039] Preferably, in this embodiment, the thickness of the double-fan-shaped open cylindrical structure of a single array unit is recorded as t3, which ranges from 5 μm to 10 μm, and is preferably 7 μm; the thickness of the double-fan-shaped open cylindrical structure of a single array unit embedded in the dielectric layer is recorded as t4, which ranges from 1 μm to 3 μm, and is preferably 2 μm; the thickness of the closed resonant ring of a single array unit is recorded as t5, which ranges from 1 μm to 4 μm, and is preferably 2 μm.

[0040] Preferably, both the top metal layer and the bottom metal backplane are made of aluminum, a lossy metal with a conductivity of ε = 3.56e+007 S / m in the terahertz band. Its excellent conductivity and magnetism can control the sensor's resonant frequency and coupling characteristics, thereby improving its detection sensitivity and reducing energy loss.

[0041] Preferably, the material of the middle dielectric layer is silicon (Si), which has a relative dielectric constant of 11.7 in the terahertz band. It is very sensitive to changes in the refractive index and thickness of the object to be measured, and can therefore accurately capture tiny changes related to the object to be measured. This is particularly important for terahertz-band metamaterial sensors that require high-precision measurements.

[0042] like Figure 4 and Figure 5 As shown in Figure 2, the sensor generates different response curves when sensing objects with different refractive indices. Figure 4 is the changing trend of the low-frequency resonance peak, Figure 5 The graph shows the variation trend of the high-frequency resonance peak. As the refractive index increases, the resonance frequency exhibits a significant redshift. The response curves were obtained using CST software simulations over a frequency range of 2.91 to 3.51 THz. A plane wave was incident perpendicularly on the unit structure, with the electric field parallel to the x-axis. A perfectly matched layer was used along the z-direction, and periodic boundary conditions were applied along the x- and y-directions.

[0043] like Figure 6As shown in the figure, the relationship between the resonant frequency of the terahertz metamaterial sensor of the concave quasi-continuum bound state (BIC) and the refractive index of the object being measured is further studied. The fitted solid line shows a good linear relationship between the two, that is, the resonant absorption frequency shift Δf is inversely proportional to the refractive index change Δn.

[0044] Generally, the quality factor Q is an indicator for evaluating the sharpness of the resonance peak, which is defined as: Where f is the frequency of the resonant peak, and FWHM is the width at half the height of the resonant peak. Based on this, we can calculate the quality factor corresponding to the high resonant peak of the metamaterial sensor invented in this embodiment to be Q1 = 3095.56, and the quality factor corresponding to the low resonant peak to be Q2 = 539.918. These calculations show that this sensor has a high quality factor Q, demonstrating strong frequency selectivity.

[0045] Generally, sensitivity S is an indicator for evaluating the resonant peak sensing performance, which is defined as The unit is GHz / RIU, where Δf is the frequency shift of resonance and Δn is the unit refractive index change. From this, it can be calculated that the sensitivity corresponding to the high resonance peak of the metamaterial sensor invented in this embodiment is S1 = 745 GHz / RIU, and the sensitivity corresponding to the low resonance peak is S2 = 395 GHz / RIU, which has high sensitivity. It can be seen that the present invention has good sensing performance.

[0046] Example 2

[0047] This embodiment provides a specific application of the terahertz metamaterial sensor with a concave quasi-continuum bound state (BIC) described in Example 1. Transformer oil of a certain thickness is applied to the surface of the metamaterial sensor, and the effect of different transformer oils on the sensor response curve is detected by incident terahertz waves.

[0048] like Figure 7 As shown, based on the source of transformer base oil, transformer oil insulation can be mainly divided into vegetable oil insulating oil, silicone oil insulating oil, mineral oil insulating oil, and synthetic ester insulating oil. In this embodiment, FR3 natural ester insulating oil, dimethyl silicone insulating oil, and mineral insulating oil were analyzed. It is known that their refractive indices at 25° are 1.533, 1.4, and 1.46, respectively. The object to be tested was placed on the metamaterial absorber sensor, and the corresponding refractive indices of different transformer oil insulations were set for simulation. As shown in the results, it can be found that the resonant frequencies of transformer oil insulations with different refractive indices have a certain degree of differentiation. In addition, as the refractive index increases, the resonant frequency decreases, and the response curves presented are also different. The present invention can distinguish different types of transformer oil insulation.

[0049] Considering that the insulating oil will deteriorate and age during the long-term operation of the transformer, Figure 8As shown in the figure, this example uses FR3 natural ester insulating oil and simulates it based on the average refractive index obtained from experiments with different degrees of thermal aging. The corresponding refractive indices for unaged FR3 natural ester insulating oil aged for 10, 20, 40, and 60 days are 1.533, 1.549, 1.554, 1.561, and 1.564, respectively. The object under test is placed on the metamaterial absorber sensor, and the corresponding refractive indices of FR3 natural ester insulating oil at different degrees of aging are set for simulation.

[0050] Simulation results show that compared to unaged insulating oil, insulating oils with varying degrees of aging exhibit lower resonant frequencies, exhibiting response curves with varying resonant frequencies. This is because the more severely aged the insulating oil, the higher the migration rate of polar substances such as moisture and small molecule acids into the oil, resulting in a greater polarity. Consequently, the more severely aged the insulating oil, the stronger its absorption of terahertz waves. Therefore, these THz absorption peaks can serve as characteristic fingerprints for detecting transformer oil insulation degradation. This invention can distinguish between different degrees of transformer oil insulation aging.

[0051] In summary, the concave quasi-continuum bound state (BIC) terahertz metamaterial sensor described in the present invention has a simple structure and superior performance, meeting the cost-effectiveness requirements in the sensor design process; it also has a high quality factor and good sensitivity, greatly improving its sensing performance, and can distinguish transformer oil insulation of different types and degrees of thermal aging.

[0052] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions, which should all be included in the scope of the claims of the present invention.

Claims

1. A concave quasi-continuous domain bound state terahertz metamaterial sensor, characterized in that: The sensor is composed of a plurality of cube-shaped array units periodically arranged in the x-direction and the y-direction, wherein each unit is composed of a metal metasurface, a dielectric layer (1) and a metal back plate (2) having a depth greater than the skin depth of the incident wave from top to bottom; The metal metasurface consists of two parts, one part is a columnar structure (3) containing a double fan-shaped opening, and the other part is a closed resonant ring (4); The columnar structure with double fan-shaped openings is located in the closed resonant ring; Part of the volume of the columnar structure with double fan-shaped openings is embedded in the dielectric layer; The double fan-shaped opening is symmetrical about the x-axis, and the right opening angle 5°~30°, left opening angle It is 15° ~45°.

2. The concave quasi-continuous domain bound state terahertz metamaterial sensor according to claim 1, characterized in that: The array unit is a sub-wavelength structure with a wavelength of 0.1λ to 0.01λ, wherein λ is the wavelength corresponding to the lowest sensing frequency.

3. The concave quasi-continuous domain bound state terahertz metamaterial sensor according to claim 2, characterized in that: The length of the dielectric layer, the metal back plate and the closed resonant ring in the x direction and the length in the y direction Both are 50μm~200μm.

4. The concave quasi-continuous domain bound state terahertz metamaterial sensor according to claim 3, characterized in that: The thickness of the metal back plate It is 1μm~2μm, the material is aluminum, and the electrical conductivity ε=3.56e+007S / m.

5. The concave quasi-continuous domain bound state terahertz metamaterial sensor according to claim 4, characterized in that: The thickness of the dielectric layer The thickness is 10μm to 30μm, and the material used is silicon.

6. The concave quasi-continuous domain bound state terahertz metamaterial sensor according to claim 5, characterized in that: The material of the columnar structure with double fan-shaped openings is aluminum, with an electrical conductivity of ε=3.56e+007S / m and a thickness of 5μm to 10μm, of which 1μm to 3μm thickness Embedded in the dielectric layer.

7. The concave quasi-continuous domain bound state terahertz metamaterial sensor according to claim 6, characterized in that: The radius of the columnar structure with double fan-shaped openings It is 15μm~25μm.

8. The concave quasi-continuous domain bound state terahertz metamaterial sensor according to claim 7, characterized in that: The closed resonant ring width 2μm~5μm, thickness 1μm~4μm.

9. A method for transformer oil insulation detection using the terahertz metamaterial sensor according to any one of claims 1 to 8, characterized in that: The same thickness of transformer oil is applied to the surface of the metamaterial sensor, and a terahertz wave is incident on the metamaterial sensor. The response curves of transformer oils with different refractive indices are simulated and analyzed by the metamaterial sensor to distinguish the type and aging degree of the transformer insulating oil. Among them, the resonant frequencies of transformer insulating oils with different refractive indices have a certain degree of differentiation, and as the refractive index increases, the resonant frequency decreases, and the response curves presented are also different, thereby distinguishing different types of transformer oil insulation; compared with non-aged insulating oil, the resonant frequency of insulation with different aging degrees will also be smaller, presenting absorption spectra with different resonant frequencies, and the resonant peak in the response curve can be used as a characteristic fingerprint spectrum for transformer oil insulation degradation detection to distinguish different aging degrees of transformer oil insulation.

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