Terahertz metal metasurface sensor based on bound states in the continuum

Abstract

The application discloses a terahertz metal super surface sensor based on a bound state in a continuum, which comprises a plurality of square metal super surface units arranged periodically and identically, wherein the metal super surface unit comprises a dielectric layer at the bottom, the dielectric layer is covered with a metal resonator layer, and the metal resonator layer is composed of a large resonant ring and a small resonant ring. When there is a to-be-measured object on the super surface, the resonant frequency of the transmission spectrum of the super surface will be shifted correspondingly, and the property of the to-be-measured object can be obtained by detecting the degree of the shift of the resonant frequency.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of terahertz metasurfaces, and particularly relates to a terahertz metal metasurface sensor based on bound states in the continuum. BACKGROUND

[0002] Terahertz waves are electromagnetic waves with a frequency of 0.1-10 THz, between microwaves and infrared light. In recent years, terahertz waves have shown great potential in the fields of security inspection, detection, sensing, communication, etc. However, natural materials are difficult to produce effective electromagnetic responses in the terahertz band, which hinders the research in the fields of developing terahertz functional devices and effectively manipulating terahertz waves, and limits the application and development of the technology.

[0003] As an artificial electromagnetic structure, the resonance response of a metasurface is easily affected by the surrounding dielectric environment, which can be used for sensing and detecting the measured object. Not only can the composition of the measured object be distinguished, but also the thickness and mixing ratio of the mixed measured object can be measured. The sensitivity of the metasurface sensor is determined by the optimization of the structure design, material selection and detection method of the metasurface, and therefore, the design of a high-sensitivity metasurface in the terahertz band is particularly important for terahertz applications. However, it is difficult for traditional metasurfaces to achieve ultra-high sensitivity.

[0004] The concept of "bound states in the continuum" (BIC) describes an ideal physical system with zero radiation loss, which can coexist with continuous radiation waves. When a metasurface is used to realize an ideal BIC mode resonance, the incident electromagnetic wave at the resonance frequency will be perfectly bound, and the disappearance of the radiation loss makes the resonance of the metasurface have infinitely high quality factor (Q value) and corresponding infinite lifetime. However, ideal BIC is not observable in the electromagnetic spectrum, so when designing functional devices based on BIC, the parameters corresponding to quasi-BIC (quasi-BIC) resonance mode with limited high Q value are usually designed as the device structure parameters. SUMMARY

[0005] The purpose of the present application is to provide a terahertz metal metasurface sensor based on bound states in the continuum. When there is a measured object on the metasurface, the resonance frequency of the transmission spectrum will shift accordingly, and by detecting the degree of frequency shift of the resonance frequency, the properties of the added measured object can be obtained.

[0006] The technical solution adopted by the present application is a terahertz metal metasurface sensor based on bound states in the continuum, which is composed of a plurality of square metal metasurface units arranged periodically, and each metal metasurface unit includes a dielectric layer at the bottom, a metal resonator layer covering the dielectric layer, and the metal resonator layer is composed of a large resonator ring and a small resonator ring.

[0007] The application is also characterized in that

[0008] The large resonant ring in the metal resonator layer is composed of a metal resonant ring A and a metal resonant ring B, the inner and outer contours of the metal resonant ring A and the metal resonant ring B are both half-rectangular shapes, and the metal resonant ring A and the metal resonant ring B are symmetrically arranged to jointly form a square large resonant ring.

[0009] The spacing between the port of the metal resonant ring A and the port of the metal resonant ring B is 15-5 μm, the line width of the port of the metal resonant ring A and the port of the metal resonant ring B is 10-5 μm, and the outer contour side length of the large resonant ring composed of the port of the metal resonant ring A and the port of the metal resonant ring B is 210-190 μm, and the top surface is a plane.

[0010] The small resonant ring in the metal resonator layer is located inside the large resonant ring, the small resonant ring is composed of a metal resonant ring C and a metal resonant ring D, the contours of the metal resonant ring C and the metal resonant ring D are both C shapes, and the metal resonant ring C and the metal resonant ring D are symmetrically arranged to jointly form a small resonant ring with a square outer contour.

[0011] The outer contour line distance of the small resonant ring to the inner contour line of the large resonant ring is 45-30 μm, and the distance from the outer contour of the large resonant ring to the edge of the metal super surface unit is 30-10 μm.

[0012] The line width of the metal resonant ring C and the metal resonant ring D is both 20-15 μm, the spacing of the two ends of the opening of the metal resonant ring C is 15-5 μm, the spacing of the two ends of the opening of the metal resonant ring D is 15-5 μm, the spacing between the metal resonant ring C and the metal resonant ring D is 20-10 μm, and the outer contour side length of the small resonant ring is both 130-120 μm, and the top surface is a plane.

[0013] The two openings formed by the metal resonant ring C and the metal resonant ring D are collinear with the two openings formed by the port of the metal resonant ring A and the port of the metal resonant ring B.

[0014] The thickness of the large resonant ring and the small resonant ring of the metal resonator layer is both 100-200 nm, the dielectric constant of the dielectric layer is 3.5, the loss tangent of the dielectric layer is δ=0.005, and the thickness of the dielectric layer is 5-10 μm.

[0015] The period of the metal super surface unit is 230-250 μm, and the working frequency of the metal super surface unit is 0.57-0.63 THz.

[0016] The beneficial effect of the present application is that the terahertz metal super surface sensor based on the bound state in the continuum, which is composed of a metal resonator layer and a dielectric layer, is simple in structure and convenient to process; the super surface can produce quasi-BIC mode resonance with a resonance frequency of 0.59 THz and a Q value of 31.9, and the sensitivity can reach 0.11 THz / RIU. The metal resonator layer 1 of the super surface forms quasi-Friedrech-Wintgen BIC mode resonance through the coupling effect between the dipole mode resonance and the capacitance-inductance (LC) mode resonance produced by the two resonant rings, and the resonance frequency, resonance strength and quality factor thereof can be regulated by changing the geometric structure of the metal super surface unit 7; the terahertz metal super surface sensor based on the bound state in the continuum proposed by the present application is composed of a metal resonator layer 1 and a dielectric backing layer 2, and can be used for detecting the dielectric constant, thickness and corresponding changes of trace substances. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is a three-dimensional view of the metal super surface sensor unit structure based on the bound state in the continuum of the present application;

[0018] Figure 2 is a top view of the unit structure of the present application;

[0019] Figure 3 is a schematic diagram of the overall structure of the present application;

[0020] Figure 4 is a schematic diagram of the reflection spectrum when detecting different test objects of the present application;

[0021] Figure 5 is a schematic diagram of the sensitivity change when detecting different test objects of the present application.

[0022] In the figure, 1. metal resonator layer, 2. dielectric layer, 3. metal resonant ring A, 4. metal resonant ring B, 5. metal resonant ring C, 6. metal resonant ring D, 7. metal super surface unit. DETAILED DESCRIPTION

[0023] The present application will be described in detail below in combination with the drawings and specific embodiments.

[0024] The terahertz metal super surface sensor based on the bound state in the continuum of the present application has a structure as shown in Figure 1 、 Figure 2 , which includes a plurality of square metal super surface units 7 arranged periodically and having the same structure, wherein the metal super surface unit 7 includes a bottom dielectric layer 2, and the dielectric layer 2 is covered with a metal resonator layer 1, and the metal resonator layer 1 is composed of a large resonant ring and a small resonant ring.

[0025] In combination with Figure 2 、 Figure 3The large resonant ring in the metal resonator layer 1 is composed of a metal resonant ring A3 and a metal resonant ring B4, the inner and outer contours of the metal resonant ring A3 and the metal resonant ring B4 are both half-rectangular, and the metal resonant ring A3 and the metal resonant ring B4 are symmetrically arranged to jointly form a square large resonant ring.

[0026] The distance between the port of the metal resonant ring A3 and the port of the metal resonant ring B4 is 15-5 μm, the line width of the metal resonant ring A3 and the metal resonant ring B4 is 10-5 μm, the outer contour side length of the large resonant ring composed of the metal resonant ring A3 and the metal resonant ring B4 is 210-190 μm, and the top surface is a plane.

[0027] The small resonant ring in the metal resonator layer 1 is located inside the large resonant ring, the small resonant ring is composed of a metal resonant ring C5 and a metal resonant ring D6, the contours of the metal resonant ring C5 and the metal resonant ring D6 are both C-shaped, and the metal resonant ring C5 and the metal resonant ring D6 are symmetrically arranged to jointly form a small resonant ring with a square outer contour.

[0028] The distance between the outer contour line of the small resonant ring and the inner contour line of the large resonant ring is 45-30 μm, and the distance from the outer contour of the large resonant ring to the edge of the metal metasurface unit 7 is 30-10 μm.

[0029] The line width of the metal resonant ring C5 and the metal resonant ring D6 is both 20-15 μm, the distance between the two ends of the opening of the metal resonant ring C5 is 15-5 μm, the distance between the two ends of the opening of the metal resonant ring D6 is 15-5 μm, the distance between the metal resonant ring C5 and the metal resonant ring D6 is 20-10 μm, the outer contour side length of the small resonant ring is 130-120 μm, and the top surface is a plane.

[0030] The two openings formed by the metal resonant ring C5 and the metal resonant ring D6 and the two openings formed by the port of the metal resonant ring A3 and the port of the metal resonant ring B4 are collinear.

[0031] The thickness of the large resonant ring and the small resonant ring of the metal resonator layer 1 is both 100-200 nm, the dielectric constant of the dielectric layer 2 is 2.8-3.5, the tangent value of the loss of the dielectric layer 2 is δ=0.002-0.005, and the thickness of the dielectric layer 2 is 5-10 μm.

[0032] The period of the metal metasurface unit 7 is 230-250 μm, and the working frequency of the metal metasurface unit 7 is 0.57-0.63 THz.

[0033] The large resonant ring and the small resonant ring are both made of metal gold.

[0034] Figure 4The resonance frequency offset degree of the application when detecting different to-be-detected objects, as can be seen from the figure, for the to-be-detected object with a constant thickness added to the surface of the metasurface, with the increase of the dielectric constant of the to-be-detected object, the transmission spectrum of the metasurface will appear frequency shift in the low frequency direction, and the correlation coefficient R is close to 1, it can be seen that there is a good linear relationship between the resonance frequency shift degree of the metasurface and the dielectric constant of the to-be-detected object, which proves that the metasurface has the potential of sensing detection.

[0035] Figure 5 The figure is a schematic diagram of the sensitivity of the application when detecting different to-be-detected objects, which changes with the thickness of the to-be-detected object. As can be seen from the figure, the sensitivity of the application increases with the increase of the thickness of the to-be-detected object, and the increase amplitude decreases with the increase of the thickness of the to-be-detected object. It can be seen that the application has a limit sensitivity corresponding to the best to-be-detected object thickness, and the order of magnitude is in the order of microns (μm), which is suitable for detecting trace substances.

Claims

1. A terahertz metallic metasurface sensor based on bound states in a continuum, characterized in that, The structure comprises a periodically arranged array of multiple identical square metal metasurface units (7). Each metal metasurface unit (7) includes a bottom dielectric layer (2) covered by a metal resonator layer (1). The metal resonator layer (1) consists of a large resonant ring and a small resonant ring. The large resonant ring in the metal resonator layer (1) is composed of a metal resonant ring A (3) and a metal resonant ring B (4). The inner and outer contours of the metal resonant ring A (3) and the metal resonant ring B (4) are both semi-rectangular. The metal resonant ring A (3) and the metal resonant ring B (4) are symmetrically arranged to form a square large resonant ring. The distance between the port of the metal resonant ring A (3) and the port of the metal resonant ring B (4) is 15~5 µm. The linewidth between the port of the metal resonant ring A (3) and the metal resonant ring B (4) is 10~5 µm. The outer contour side length of the large resonant ring formed by the port of the metal resonant ring A (3) and the metal resonant ring B (4) is 210~190. µm, and the top surface is a plane. The small resonant ring in the metal resonator layer 1 is located inside the large resonant ring. The small resonant ring is composed of metal resonant ring C (5) and metal resonant ring D (6). The outlines of metal resonant ring C (5) and metal resonant ring D (6) are both C (5) shaped. Metal resonant ring C (5) and metal resonant ring D (6) are symmetrically arranged to form a small resonant ring with a square outer outline. The line width of metal resonant ring C (5) and metal resonant ring D (6) is 20~15 µm. The distance between the two ends of the opening of metal resonant ring C (5) is 15~5 µm. The distance between the two ends of the opening of metal resonant ring D (6) is 15~5 µm. The distance between metal resonant ring C (5) and metal resonant ring D (6) is 20~10 µm. The side length of the outer outline of the small resonant ring is 130~120 µm, and the top surface is a plane.

2. The terahertz metallic metasurface sensor based on bound states in a continuum according to claim 1, characterized in that, The distance between the outer contour of the small resonant ring and the inner contour of the large resonant ring is 45~30µm; the distance between the outer contour of the large resonant ring and the edge of the metal metasurface unit (7) is 30~10µm.

3. The terahertz metallic metasurface sensor based on bound states in a continuum according to claim 2, characterized in that, The two openings formed by the metal resonant ring C (5) and the metal resonant ring D (6) and the port of the metal resonant ring A (3) and the two openings formed by the metal resonant ring B (4) are collinear.

4. The terahertz metallic metasurface sensor based on bound states in a continuum according to claim 3, characterized in that, The thickness of both the large and small resonant rings of the metal resonator layer (1) is 100~200 nm, the dielectric constant of the dielectric layer (2) is 3.5, and the loss tangent of the dielectric layer (2) is... δ =0.005, the thickness of the dielectric layer (2) is 5~10μm.

5. The terahertz metallic metasurface sensor based on bound states in a continuum according to claim 4, characterized in that, The period of the metal metasurface unit (7) is 230~250μm, and the operating frequency of the metal metasurface unit (7) is 0.57~0.63THz.

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