Terahertz metasurface sensor based on lattice mode regulation and control

Abstract

The invention discloses a metasurface sensor based on lattice mode regulation and control. The metasurface sensor comprises a quartz substrate and an asymmetric double-U-shaped aluminum ring array structure on the quartz substrate. An intrinsic formant is split into a quasi-BIC peak and an intrinsic peak by changing a terahertz wave incident angle (0-45 degrees) to excite a lattice mode; when a to-be-detected object with the thickness of 1-3 microns is coated under the incident angle of 42 degrees, the refractive index response is enhanced by utilizing the inhibition effect of a lattice mode aiming at a BIC peak, and trace detection with the sensitivity of 0.5556-1.0991 RIU is realized. The sensor has remarkable advantages in the field of biomolecule and polymer detection.

Description

Technical Field

[0001] This invention relates to the field of terahertz sensing technology, specifically a metasurface sensor that achieves high-sensitivity detection by modulating quasi-BIC resonance through lattice mode. Background Technology

[0002] The lattice mode, also known as the Rayleigh-Wood anomaly, originates from the combined effect of collective oscillations of periodic structural units and Bragg scattering. Its frequency is modulated by both the lattice period and the incident angle. This mode suppresses radiation loss through a dual mechanism of coupled interference between symmetry-protected continuous-domain bound states and the Fano-Friedrich-Wintgen mode, enabling ultra-high quality factor characteristics.

[0003] A metasurface is an artificially designed two-dimensional subwavelength structure array composed of periodically arranged nanoscale units, capable of precisely controlling the phase, amplitude, and polarization characteristics of electromagnetic waves. Its sensor operating principle is based on the localized field enhancement effect or resonant mode change: when the analyte interacts with the metasurface, it causes a localized change in refractive index or a shift in electromagnetic response. High-sensitivity detection is achieved by monitoring the shift or intensity change of the resonance peak in the reflected or transmitted spectra.

[0004] In applications, metasurface sensors exhibit significant advantages, such as enabling single-molecule-level virus detection in the biomedical field (e.g., HIV detection limit of 1×10⁻⁶). 6 It can be used for particle / ml imaging and early cancer imaging; accurately identify methane concentration (sensitivity 0.004 THz / %) or microplastic pollution in environmental monitoring; and support non-contact displacement measurement and hazardous gas early warning in industrial scenarios, improving the accuracy and reliability of automated equipment.

[0005] Currently, metasurface sensors rarely utilize sensing methods that employ lattice mode modulation. Based on the significant advantages of lattice modes in exciting high-Q resonances and enhancing the ability of waves to interact with matter, this metasurface sensor based on lattice film modulation was designed. Summary of the Invention

[0006] The purpose of this invention is to provide a metasurface sensor that can efficiently utilize the modulation effect of excitation and suppression of BIC peaks in lattice mode alignment for high-sensitivity sensing.

[0007] The objective of this invention is achieved as follows:

[0008] A metasurface sensor based on lattice mode modulation is characterized by comprising a substrate layer, an asymmetric double U-shaped array structure, and a sample to be tested. The asymmetric double U-shaped array is arranged on top of the substrate according to certain parameters, and the sample to be tested is coated on the substrate, co-located with the asymmetric double U-shaped array on the same surface. The substrate of the designed metasurface is made of high-purity silicon dioxide (SiO2), with periodic P in the X direction. x =255um, period P in the Y direction y =127.5um, P x Twice P y The width W of the U-shaped ring is 8 μm, the length L is 90 μm, and the distance between two U-shaped rings is d. x =15um, with the midpoint of the spacing D as the reference, the distance from the midpoint of the substrate in the X direction is 28.75um, the substrate thickness d=50um, the aluminum metal layer thickness d1=0.2um, and the thickness of the test object is H. The dielectric constant of quartz is 3.82, and the conductivity of aluminum is... .

[0009] The lattice mode resonance frequencies satisfy the following relationship:

[0010] Where (i,j) represents the order of the lattice mode, P is the period of the unit cell structure, θ is the incident angle of the terahertz wave, and is the effective dielectric constant of the metal-dielectric interface.

[0011] As the angle increases, the lattice mode gradually redshifts, and the originally single intrinsic peak is stimulated to split into a quasi-BIC peak on the left and an intrinsic peak on the right. The quality factor of the quasi-BIC peak reaches its maximum at θ=35°. As the incident angle gradually increases, the quasi-BIC peak on the left is suppressed, the linewidth increases, and the Q value decreases. The sensor is coated with a sample layer at θ=42°, with the sample thickness ranging from 1-3 μm and the refractive index ranging from 1.1-1.9.

[0012] This angle-dependent characteristic allows for continuous shifts in lattice mode resonant frequencies by dynamically adjusting the incident angle, thus covering a wide spectral range. The core principle of lattice mode-induced quasi-BIC peaks lies in the transformation of radiatively leaky continuous-domain modes into locally bound states when the periodic structure satisfies specific phase-matching conditions. This occurs when the lattice period P and the incident terahertz wavelength satisfy the Rayleigh-Wood condition. At that time, the reciprocal lattice vector With obliquely incident wave vector component Momentum compensation leads to mode degeneracy at the Brillouin zone boundary. At this point, the collective oscillations of the lattice units localize the electromagnetic energy through constructive interference, causing the radiation channels to close and forming quasi-continuous bound states with high quality factors, which manifest as sharp resonance peaks.

[0013] Increasing the incident angle θ further disrupts the phase-matching condition, leading to quasi-BIC peak suppression. The underlying physical reason lies in the incident wave vector component... As θ increases, it surpasses the reciprocal lattice vector G, breaking the degeneracy of the Brillouin zone boundary. When At that time, the phase difference of the scattered waves from adjacent lattice units accumulates to This magnitude induces destructive interference, causing the originally localized electromagnetic field energy to recouple into the free-space radiation channel, resulting in a sharp drop in the Q value of the resonance peak. Simultaneously, the frequency relationship... This indicates that increasing θ significantly raises the resonant frequency, causing the characteristic peak to deviate from the design band, ultimately manifesting as a decrease in resonant intensity and a broadening or even disappearance of the spectral line. This angle-dependent characteristic provides the sensor with the freedom to dynamically tune.

[0014] The transmission spectrum after coating the analyte was obtained at an incident angle of 42°. The amplitude value A of the quasi-BIC peak was extracted, and the fitting equation A=1.19438-0.5556n was obtained by simple linear fitting. The slope -0.5556 is the sensitivity of the sensor when coated with analyte H=1um. The correlation coefficient can reach R2=0.9905.

[0015] By further increasing the thickness of the analyte, at H=2µm, when the amplitude decreases to its minimum value, the refractive index is in the range of 1.1-1.54, achieving a refractive index sensing sensitivity of 0.8695. At H=3µm, when the amplitude decreases to its minimum value, the refractive index is in the range of 1.1-1.42, achieving a refractive index sensing sensitivity of 1.0991. Attached Figure Description

[0016] Figure 1 The diagram shows the structure of the metasurface sensor, where a) is the overall structure of the metasurface sensor; b) is the front view of a single transmission control unit of the metasurface sensor after the substance to be measured is coated; and c) is the top view of a single transmission control unit of the metasurface sensor.

[0017] Figure 2 The following are the transmission spectra and fitting function graphs of the metasurface sensor: a) is the transmission spectrum of the metasurface sensor at 0°, 35°, and 45°; b) is the spectrum of the metasurface sensor when a 1µm thick sample is deposited at an incident angle of 42° at n=1.1-1.9; c) is the amplitude variation graph and fitting function graph for different sample thicknesses. Detailed Implementation

[0018] The present invention will be further illustrated below with reference to specific embodiments.

[0019] The specific implementation of the metasurface sensor described in this invention is achieved using the frequency domain solver of the electromagnetic simulation software CST Studio Suite. The sensor structure comprises a quartz substrate with a dielectric constant ε = 3.82, and an asymmetric double-U-shaped aluminum ring array periodically arranged on the surface with a conductivity σ = 3.56 × 10⁻⁶. 7 S / m. The element structure has a period P in the x-direction. x =255μm, y-direction period P y =127.5μm, satisfying P x =2P y The relationship is as follows: U-shaped ring width W = 8μm, length L = 90μm, and the distance between the two rings d. x =15μm, its geometric center is offset by 28.75μm relative to the center of the substrate along the x-axis. The quartz substrate thickness d=50μm, and the aluminum layer thickness d1=0.2μm. The simulation settings use unit periodic boundary conditions (x, y directions) and open space boundary conditions (z direction), and the excitation source is a plane terahertz wave.

[0020] Depend on Figure 2 As shown in Figure a, at an incident angle θ = 0°, the lattice mode frequency is far from the resonance band, and the transmission spectrum shows only a single intrinsic resonance peak. As the incident angle increases, the lattice mode undergoes a redshift, and the intrinsic peak differentiates into a quasi-BIC peak on the left and an intrinsic peak on the right at θ = 35°. At this point, the quality factor of the quasi-BIC peak reaches its maximum value. The physical mechanism of this is due to the interaction between the reciprocal lattice vector G = 2π / P and the oblique incident wave vector component K. x =K0sinθ momentum matching: when When the Rayleigh-Wood condition is satisfied, the degeneracy of the Brillouin zone boundary induces constructive interference, which transforms the radiation continuum into a locally bound state and significantly suppresses radiation loss.

[0021] Depend on Figure 2 As shown in Figure a, further increasing the incident angle to θ = 45° disrupts the phase-matching condition of the lattice mode (Kx > G), leading to a π-phase difference in the scattered waves from adjacent lattice units. This induces destructive interference, causing the quasi-BIC peak energy to recouple into the free-space radiation channel. At this point, the quasi-BIC peak is significantly suppressed, the linewidth increases, and the Q value decreases. A 42° incident angle is selected as the sensing operating point. A layer of the analyte (refractive index n = 1.1–1.9) with a thickness of H = 1 μm is coated on the sensor surface. The interaction between the analyte and the local electromagnetic field causes a change in the effective dielectric constant. (The text continues with further details about the interaction between the analyte and the local electromagnetic field, which are not directly related to the preceding paragraph.) Figure 2 As shown in b, with the increase of n, the previously suppressed quasi-BIC peak linewidth gradually narrows and the Q value increases, while the transmission amplitude A systematically decreases. This phenomenon confirms that the change in the refractive index of the analyte can counteract the interference of lattice mode alignment with BIC and reactivate its high-Q characteristics.

[0022] Extract the relationship data between the quasi-BIC peak amplitude value A and the refractive index n. Figure 2 c), the equation is obtained by fitting a linear regression: A = 1.19438 − 0.5556n Slope S = -0.5556RIU ⁻¹ The sensitivity was measured, with a correlation coefficient R² = 0.9905. Further increasing the analyte thickness to H = 2 μm, the amplitude showed a significant decreasing trend in the range of n = 1.1–1.54, and the fitting sensitivity improved to 0.8695 RIU. ⁻¹ When H=3μm, the sensitivity reaches 1.0991RIU in the range of n=1.1–1.42. ⁻¹ It should be noted that the amplitude tends to saturate after the refractive index exceeds the critical value (n>1.54 when H=2μm, n>1.42 when H=3μm), indicating that the sensing dynamic range is constrained by thickness. This phenomenon is attributed to the fact that increasing the thickness of the analyte enhances the depth of electromagnetic field-matter interaction, but an excessively thick analyte will lead to excessive dissipation of evanescent field energy, limiting the effective detection range.

[0023] In this implementation, the lattice mode modulation mechanism achieves a dual function through dynamic adjustment of the incident angle: firstly, it excites high-Q quasi-BIC states at θ=35°, providing sharp spectral characteristics for sensing; secondly, it utilizes the lattice mode suppression effect at θ=42° to construct an amplitude response window sensitive to the refractive index. Combined with the design of an asymmetric double-U structure, a RIU of 0.5556–1.0991 is achieved within the analyte thickness range of 1–3 μm and refractive index range of 1.1–1.9. ⁻¹ The adjustable sensitivity of this sensor provides a novel detection method for trace biomolecules and polymers. Experiments have verified that the sensor overcomes the linear range limitation of traditional resonant displacement sensing through the synergistic regulation of lattice mode and quasi-BIC coupling, opening up a new path for terahertz trace detection.

Claims

1. A metasurface sensor based on lattice mode modulation, characterized in that: It includes a substrate, an asymmetric double U-shaped array structure, and a sample to be tested. The asymmetric double U-shaped array is placed on the substrate according to certain parameters, and the sample to be tested is coated on the substrate and is on the same surface as the asymmetric double U-shaped array. The substrate of the designed metasurface is made of high-purity silicon dioxide (SiO2), with periodic P-type polarization in the X-direction. x =255um, period P in the Y direction y =127.5um, P x Twice P y The width W of the U-shaped ring is 8 μm, the length L is 90 μm, and the distance between two U-shaped rings is d. x =15um, with the midpoint of the spacing D as the reference, the distance from the midpoint of the substrate in the X direction is 28.75um, the substrate thickness d=50um, the aluminum metal layer thickness d1=0.2um, and the thickness of the test object is H. The dielectric constant of quartz is 3.82, and the conductivity of aluminum is... .

2. The sensor according to claim 1, characterized in that: The lattice mode resonance frequencies satisfy the following relationship:

3. Where (i,j) represents the order of the lattice mode, P is the period of the unit structure, θ is the incident angle of the terahertz wave, and is the effective dielectric constant of the metal-dielectric interface.

4. The sensor according to claim 2, characterized in that: As the angle increases, the lattice mode gradually redshifts, and the originally single intrinsic peak is stimulated to split into a quasi-BIC peak on the left and an intrinsic peak on the right. The quality factor of the quasi-BIC peak reaches its maximum at θ=35°. As the incident angle gradually increases, the quasi-BIC peak on the left is suppressed, the linewidth increases, and the Q value decreases. The sensor is coated with a sample layer at θ=42°, with the sample thickness ranging from 1-3 μm and the refractive index ranging from 1.1-1.

9.

5. The detection method according to claim 3, comprising: The transmission spectrum after coating the analyte was obtained at an incident angle of 42°. The amplitude value A of the quasi-BIC peak was extracted, and the fitting equation A=1.19438-0.5556n was obtained by simple linear fitting. The slope -0.5556 is the sensitivity of the sensor when coated with analyte H=1um. The correlation coefficient can reach R2=0.9905.

6. The method according to claim 4, characterized in that: By further increasing the thickness of the analyte, at H=2µm, when the amplitude decreases to its minimum value, the refractive index is in the range of 1.1-1.54, achieving a refractive index sensing sensitivity of 0.8695. At H=3µm, when the amplitude decreases to its minimum value, the refractive index is in the range of 1.1-1.42, achieving a refractive index sensing sensitivity of 1.0991.

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