Concave quasi-continuous domain bound state terahertz metamaterial sensor

Abstract

The invention relates to a concave quasi-continuous domain bound state terahertz metamaterial sensor, the sensor is provided with a plurality of periodic array units in horizontal and vertical directions, and each array unit is composed of a metal metasurface, a dielectric layer and a metal back plate from top to bottom, and the depth of the metal back plate is larger than that of an incident wave skin; wherein the metal metasurface is composed of two parts, one part is a cylindrical structure with a double-fan-shaped opening, the other part is a closed resonant ring, the left opening angle of the double-fan-shaped opening is not equal to the right opening angle of the double-fan-shaped opening, the cylindrical structure with the double-fan-shaped opening is located in the closed resonant ring, and a part of the cylindrical structure is embedded in the dielectric layer. The constructed sensor generates two harmonic peaks under excitation of vertical incidence terahertz waves, the two harmonic peaks are respectively located at 3.44 THz and 3.51 THz, and the highest quality factor Q value reaches 3096. According to the invention, a disc structure with unequal opening angles on the left and right sides is innovatively constructed, quasi-BIC resonance is realized, and the quasi-BIC resonator has the advantages of high refractive index sensitivity, good linearity, simple structure, easy processing and the like.

Description

Technical Field

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

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

[0003] Metamaterials are a type 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 have. 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 increasing 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. Limited by the design principles themselves, 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 ideal BIC is converted into a quasi-BIC mode with a finite high Q value to meet application requirements. Metasurface sensors with high Q values ​​based on quasi-BIC have considerable application potential in ultrasensitive biochemical sensing. Summary of the invention

[0005] The purpose of the present invention is to provide a terahertz metamaterial sensor of concave quasi-continuum bound state (BIC), aiming to solve the problems of low quality factor, low detection sensitivity, poor linearity, etc. of existing terahertz sensors. It is applied to transformer oil insulation detection. The sensor will show different response characteristics on transformer oils of different types and thermal aging degrees, and can distinguish and detect the type and aging degree of 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, the sensor is composed of a plurality of cube-structured array units periodically arranged in the x-direction and the y-direction, each of the array units is composed of a metal metasurface, a dielectric layer and a metal back plate 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, one part is a cylindrical structure with a double fan-shaped opening, and the other part is a closed resonant ring. The cylindrical structure with the double fan-shaped opening is located in the closed resonant ring. Part of the volume of the cylindrical structure with the double fan-shaped opening is embedded in the dielectric layer. The double fan-shaped opening is symmetrical about the y-axis, the right opening angle α is 5° to 30°, and the left opening angle β is 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, which specifically includes: applying transformer insulation oil of a specified thickness to the surface of the metamaterial sensor, incident terahertz waves on the metamaterial sensor, performing absorption sensing simulation analysis of the terahertz metamaterial absorber by detecting and analyzing the refractive index change of the transformer insulation oil, and then distinguishing the type and aging degree of the transformer insulation oil according to the absorption spectra of different resonant frequencies;

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

[0018] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can 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 in conjunction with the accompanying drawings, wherein:

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

[0021] Figure 2 A top view of a unit 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 columnar structure with double 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, the metal back plate, and the closed resonant ring in the x direction and the length in the y direction.

[0022] Figure 3 A side view of a unit 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 back plate, t2 is the thickness of the dielectric layer, t3 is the thickness of the double-sector open column, t4 is the thickness of the double-sector open column 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 in a terahertz metamaterial sensor of a concave quasi-continuum bound state (BIC) provided by an embodiment of the present invention under the condition of vertical incidence of terahertz waves;

[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 in a terahertz metamaterial sensor of a concave quasi-continuum bound state (BIC) provided by an embodiment of the present invention under the condition of vertical incidence of terahertz waves;

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

[0026] Figure 7 A concave quasi-continuum bound state (BIC) terahertz metamaterial sensor provided by an embodiment of the present invention is added with different types of transformer insulating oils to simulate the response curves of 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 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 only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

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

[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 the terms "upper", "lower", "left", "right", "front", "rear", etc. indicate the orientation or position relationship, they are based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the terms describing the position 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 terahertz metamaterial sensor of the concave quasi-continuum bound state (BIC) in this embodiment is composed of a number of array units arranged periodically, and each unit is composed of a metal metasurface, a dielectric layer and a metal backplane larger than the skin depth of the incident wave from top to bottom. The metal metasurface is composed of two parts, one part is a cylindrical structure with a double fan-shaped opening, and the other part is a closed resonant ring. The cylindrical structure with a double fan-shaped opening is located in the closed resonant ring. Part of the volume of the cylindrical structure with a double fan-shaped opening is embedded in the dielectric layer.

[0035] In this embodiment, the length direction of the sensor array composed of a plurality of sensor units is defined as the x direction, and the width direction is defined as the y direction. The openings of all array units point to the x direction and are parallel to the x direction, and the vertical axes of all array units point to the y direction. All sensor array units are periodically arranged along the x and y directions, and the working band of the metamaterial sensor finally formed is 2.91 to 3.51 THz.

[0036] Preferably, if Figure 2 As shown, in this embodiment, the lengths of the dielectric layer, the metal back plate and the closed resonant ring of a single array unit in the x-direction and the 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 by r, which ranges from 15μm to 25μm, and is preferably 20μm; the double-fan-shaped opening of a single array unit is symmetrical about the y-direction axis, the right opening angle is denoted by α, which ranges from 5° to 30°, and is preferably 15°, and the left opening angle is denoted by 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 back plate 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 columnar structure of a single array unit is recorded as t3, which ranges from 5μm to 10μm, and is preferably 7μm; the thickness of the double-fan-shaped open columnar structure of a single array unit embedded in the dielectric layer is recorded as t4, which ranges from 1μm to 3μm, and is preferably 2μm; the thickness of the closed resonant ring of a single array unit is recorded as t5, which ranges from 1μm to 4μm, and is preferably 2μm.

[0040] Preferably, the top metal layer and the bottom metal backplane are both metal Al with lossy characteristics, and its conductivity in the terahertz band is ε=3.56e+007S / m. Its good conductivity and magnetism can control the resonant frequency and coupling characteristics of the sensor, thereby improving the detection sensitivity of the sensor 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, so it can accurately capture tiny changes related to the object to be measured, which is particularly important for terahertz band metamaterial sensors that require high-precision measurements.

[0042] like Figure 4 and Figure 5 As shown in Figure 1, 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 change trend of the high-frequency resonance peak shows that the resonance frequency shows an obvious red shift phenomenon with the increase of the refractive index. The response curve is obtained by simulation with CST software. The simulation frequency range is 2.91~3.51THz. The plane wave is incident vertically into the unit structure, the electric field is parallel to the x-axis, a fully matched layer is used along the z-direction, and periodic boundary conditions are used along the x- and y-directions.

[0043] like Figure 6As shown, 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 resonance peak, and FWHM is the peak width at half the height of the resonance peak. From this, it can be calculated that the quality factor corresponding to the high resonance peak of the metamaterial sensor invented in this embodiment is Q1 = 3095.56, and the quality factor corresponding to the low resonance peak is Q2 = 539.918. According to the calculation results, the sensor has a high quality factor Q, reflecting strong frequency selectivity.

[0045] Usually, 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 the resonance, and Δn is the unit refractive index change. It can be calculated that the sensitivity corresponding to the high resonance peak of the metamaterial sensor invented in this embodiment is S1=745GHz / RIU, and the sensitivity corresponding to the low resonance peak is S2=395GHz / RIU, which has a high sensitivity. It can be seen that the present invention has good sensing performance.

[0046] Example 2

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

[0048] like Figure 7 As shown, according to 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, etc. In this embodiment, FR3 natural ester insulating oil, dimethyl silicone insulating oil and mineral insulating oil are analyzed. It is known that their refractive indices under 25° environment correspond to 1.533, 1.4 and 1.46 respectively. The object to be tested is placed on the metamaterial absorber sensor, and the corresponding refractive indices of different transformer oil insulations are set for simulation. According to the results, it can be found that the resonant frequencies of transformer oil insulations with different refractive indices have a certain degree of differentiation, and as the refractive index increases, the resonant frequency decreases instead, and the presented response curves 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 this example, FR3 natural ester insulating oil is selected, and the simulation is performed based on the average refractive index obtained in the experiment with different degrees of thermal aging. According to the refractive indices corresponding to the unaged FR3 natural ester insulating oil and the aging FR3 natural ester insulating oil for 10 days, 20 days, 40 days and 60 days, which are 1.533, 1.549, 1.554, 1.561 and 1.564 respectively, the object to be tested is placed on the metamaterial absorber sensor, and the corresponding refractive index of the FR3 natural ester insulating oil with different degrees of aging is set for simulation.

[0050] According to the simulation results, compared with the non-aged insulating oil, the resonant frequency of the insulating oil with different aging degrees will also be smaller, showing a response curve of different resonant frequencies. This is because the more serious the aging of the insulating oil, the higher the migration rate of polar substances such as water and small molecular acids into the insulating oil, resulting in a greater polarity of the insulating oil. Therefore, the more serious the aging of the insulating oil, the stronger the absorption of terahertz waves. Therefore, these THz absorption peaks can be used as characteristic fingerprints for transformer oil insulation degradation detection. The present invention can distinguish different aging degrees of transformer oil insulation.

[0051] In summary, the terahertz metamaterial sensor of the concave quasi-continuum bound state (BIC) described in the present invention has a simple structure and superior performance, meeting the demand for cost-effectiveness in the sensor design process; and has a high quality factor and good sensitivity, which greatly improves 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 solution of the present invention rather than to limit it. 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 solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. A terahertz metamaterial sensor of concave quasi-continuum bound state, characterized in that: The sensor is composed of a plurality of cube-structured array units periodically arranged in the x-direction and the y-direction, and each of the units is composed from top to bottom of a metal super surface, a dielectric layer (1) and a metal back plate (2) greater than the skin depth of an incident wave.

2. The concave quasi-continuous domain bound state terahertz metamaterial sensor according to claim 1, characterized in that: The metal metasurface is composed of two parts, one part is a columnar structure (3) with double fan-shaped openings, 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, the right opening angle α is 5° to 30°, and the left opening angle β is 15° to 45°.

3. The concave quasi-continuous domain bound state terahertz metamaterial sensor according to claim 2, 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.

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

5. The concave quasi-continuous domain bound state terahertz metamaterial sensor according to claim 4, characterized in that: 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.

6. The concave quasi-continuous domain bound state terahertz metamaterial sensor according to claim 5, characterized in that: The thickness t2 of the dielectric layer is 10 μm to 30 μm, and the material used is silicon.

7. The concave quasi-continuous domain bound state terahertz metamaterial sensor according to claim 6, 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 t3 of 5 μm to 10 μm, of which a thickness t4 of 1 μm to 3 μm is embedded in the dielectric layer.

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

9. The concave quasi-continuous domain bound state terahertz metamaterial sensor according to claim 8, characterized in that: The closed resonant ring has a width h of 2 μm to 5 μm and a thickness t5 of 1 μm to 4 μm.

10. An application of the terahertz metamaterial sensor according to any one of claims 1 to 9 in transformer oil insulation detection, characterized in that: The same thickness of transformer oil is coated on the surface of the metamaterial sensor, and a terahertz wave is incident on the metamaterial sensor. The response curve of transformer oils with different refractive indices is simulated and analyzed by the metamaterial sensor, so that the type and aging degree of the transformer insulating oil can be distinguished; Among them, the resonant frequencies of transformer insulating oils with different refractive indices have a certain degree of distinction, 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 the unaged insulating oil, the insulation resonant frequency of different aging degrees will also be smaller, presenting absorption spectra of different resonant frequencies, and the resonant peak in the response curve can be used as a characteristic fingerprint map for transformer oil insulation degradation detection to distinguish different aging degrees of transformer oil insulation.

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