A reflective terahertz metamaterial dual-frequency sensor

Abstract

The application discloses a reflective terahertz metamaterial dual-frequency sensor, and belongs to the technical field of terahertz metamaterial devices, and comprises, from top to bottom, a metamaterial metal layer, an insulating dielectric layer and a metal reflection layer; the metamaterial metal layer comprises metamaterial units arranged periodically in an array, the metamaterial unit is a micro resonant structure composed of two resonant subunits, an equivalent LC resonant circuit with a multi-capacitance structure is constructed, and two effective working modes are formed. The application adopts the above-mentioned reflective terahertz metamaterial dual-frequency sensor, has simple structure and low manufacturing cost, effectively reduces the working frequency by using the multi-capacitance structure, forms a multi-mode working characteristic, increases stability, has excellent thin film sensing potential, and greatly increases the usability of existing terahertz sensors.

Description

Technical Field

[0001] This invention relates to the field of terahertz metamaterial device technology, and in particular to a reflective terahertz metamaterial dual-frequency sensor. Background Technology

[0002] In current technologies, optical sensors are increasingly being used in fields such as biosensing, solution detection, object imaging, and security detection. Compared to traditional destructive testing methods, label-free detection, spearheaded by terahertz technology, offers numerous advantages, including no sampling required, non-destructive nature, low cost, and real-time performance. Furthermore, the resonant frequencies of most biological solutions and samples lie in the terahertz band, making terahertz biosensors increasingly attractive for research. Terahertz refers to a high-frequency band with wavelengths between 30 and 3000 micrometers. As the last unexplored frequency band, the development of terahertz technology has been limited by various factors, such as the lack of suitable high-performance testing platforms, the difficulty in finding natural materials that generate electromagnetic responses in the terahertz band, and limitations imposed by MEMS microfabrication errors. Therefore, the application of terahertz as a sensor still requires further exploration. Previous studies using the standing wave effect of terahertz spectra generated by bovine thymus (CT) DNA samples have demonstrated that terahertz has significant spectral recognition characteristics for biological materials.

[0003] Metamaterials are artificial, subwavelength, periodically arranged oscillators with negative refractive indices. Micrometer-scale metamaterial units resonate strongly with terahertz waves of specific frequencies, forming terahertz metamaterial sensors (TMS). The combination with terahertz waves has brought new heights in the sensitivity and accuracy of biosensors. Their strong frequency selectivity and environmental sensitivity give them great potential as sensors. In recent years, research on terahertz metamaterial sensors has made significant progress.

[0004] However, existing terahertz sensors have many shortcomings: 1. Existing sensors cannot simultaneously achieve high Q value, high sensitivity, and high Fom value.

[0005] 2. Sensors operating in a single mode have insufficient measurement redundancy and are prone to large errors.

[0006] 3. High-sensitivity terahertz sensors are difficult to manufacture, and their frequencies are too high, exceeding the frequency limit of the test platform. Summary of the Invention

[0007] The purpose of this invention is to provide a reflective terahertz metamaterial dual-frequency sensor with a simple structure and low manufacturing cost. It effectively reduces the operating frequency by utilizing a multi-capacitor structure, forms multi-mode operating characteristics, increases stability, and has excellent thin-film sensing potential, greatly increasing the usability of existing terahertz sensors.

[0008] To achieve the above objectives, the present invention provides a reflective terahertz metamaterial dual-frequency sensor, comprising, from top to bottom, a metamaterial metal layer, an insulating dielectric layer, and a metal reflective layer; the metamaterial metal layer comprises metamaterial units arranged in a periodic array, wherein each metamaterial unit is a micro-resonant structure composed of two resonator units.

[0009] Preferably, each of the resonator units consists of an open resonant half-ring and three oscillators.

[0010] Preferably, the oscillators of the two resonator units are distributed at the center and opening of the resonant half-ring, forming three gaps of different sizes; wherein, the gaps on the left and right sides are of equal width, and the gap in the middle is twice the width of the gaps on the two sides, thus forming two equivalent capacitances with different capacitance values, resulting in different resonant frequencies.

[0011] Preferably, the two resonator units have the same structure and are symmetrically distributed vertically and horizontally.

[0012] Preferably, the linewidths of the resonant half-ring and the oscillator of the resonator unit are equal.

[0013] Preferably, the branch lengths of the four oscillators on the left and right sides of the two resonator units are the same.

[0014] Preferably, the outer diameter of the resonant half-ring is less than half that of the insulating dielectric layer.

[0015] Preferably, the insulating dielectric layer is a resin layer with stable chemical and physical properties produced by spin coating, leveling and solidification of negative photoresist, with a dielectric constant of 3.2 and a loss tangent of 0.005.

[0016] Preferably, the thickness of the metamaterial metal layer is the same as the thickness of the metal reflective layer, and the thickness of the metal reflective layer is greater than its skin effect depth.

[0017] Preferably, both the metamaterial metal layer and the metal reflective layer are made of gold.

[0018] Therefore, the advantages of the present invention, which employs the above-mentioned reflective terahertz metamaterial dual-frequency sensor compared with the prior art, are as follows: (1) Compared with existing destructive testing technologies, terahertz nondestructive testing has advantages such as real-time performance, low cost, and non-destructive sample handling.

[0019] (2) Compared with existing microfluidic terahertz metamaterial sensors, the complexity of the test platform is reduced. The dehydration detection greatly weakens the absorption effect of water on terahertz waves. The interaction between the solute film and the metamaterial metal pattern structure generates local strong resonance, which constrains the incident electric field and improves the performance of the terahertz metamaterial sensor to a usable level.

[0020] (3) Compared with existing evaporative reflective terahertz metamaterial sensors, the original dual-resonant ring structure has been changed to construct a novel planar equivalent LC circuit multi-capacitor structure, forming two effective high-sensitivity operating modes. When the analyte is at or near a certain resonance peak, and the attenuation is so great that it cannot be detected, the second resonance peak can be used for detection. In normal detection, the second peak can also be used for comparison and error correction, which greatly improves the effectiveness and reliability of the sensor detection.

[0021] (4) Compared with the new reflective graphene metamaterial sensor, the operating frequency is reduced, the metal is more suitable for processing and testing, and the chemical stability is better.

[0022] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the metamaterial unit of the present invention; Figure 2 This is a schematic diagram of the sensing method and unit array of the present invention; Figure 3 This is a schematic diagram of the refractive index curve variation of the metamaterial sensor of the present invention; Figure 4 This is a comparison diagram of return loss modeling of the metamaterial unit CST and the equivalent LC circuit of this invention; Figure 5 These are top and side views of the electric field distribution of the metamaterial unit of the present invention under two working modes; Figure 6 This is the equivalent LC resonant circuit diagram of the metamaterial unit of this invention; Figure 7 This is a fitting curve of the frequency shift uniformity of the metamaterial sensor of the present invention; Figure 8 This is a schematic diagram of the thickness curve variation of the metamaterial unit of the present invention. Detailed Implementation

[0024] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0025] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "first," "second," and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0026] Example 1 like Figure 1 As shown, the high-performance terahertz metamaterial dual-frequency sensor of the present invention comprises, from top to bottom, a metamaterial metal layer, an insulating dielectric layer, and a metal reflective layer. The metamaterial metal layer is located on the upper surface of the insulating dielectric layer, and the metal reflective layer is located on the lower surface of the insulating dielectric layer.

[0027] The metamaterial metallic layer comprises metamaterial units arranged in a periodic array. Each metamaterial unit is a micro-resonant structure composed of two resonator units. Each resonator unit consists of an open resonant half-ring and three oscillators.

[0028] The two resonator units have identical structures and are symmetrically distributed vertically and horizontally. The oscillators of both units are located at the center and opening of the resonant half-ring, forming three gaps of different sizes. The left and right gaps are of equal width, while the middle gap is twice the width of the two side gaps, creating two equivalent capacitances with different values ​​and resulting in different resonant frequencies. The linewidth of the resonant half-ring and oscillators in each resonator unit is equal, and the stub lengths of the four oscillators on the left and right sides of both units are the same.

[0029] In the metamaterial unit, the outer diameter of the resonant semi-ring is less than half that of the insulating dielectric layer. The insulating dielectric layer uses Microchem's 2000 series negative photoresist. After spin coating, leveling, and solidification, a chemically and physically stable resin layer is produced, with a dielectric constant of 3.2 and a loss tangent of 0.005.

[0030] The thickness of the metamaterial metal layer is the same as the thickness of the metal reflective layer, and the thickness of the metal reflective layer is greater than its skin effect depth. Furthermore, the material in both the metamaterial metal layer and the metal reflective layer is gold.

[0031] like Figure 2As shown, a solution of a specific refractive index and homogenized concentration is dropped onto the surface of a metamaterial sensor formed by periodically arranged metamaterial units using a pipette. After natural drying or high-temperature evaporation, a solute layer of a specific thickness remains, controlled during solution preparation. An incident terahertz wave is incident vertically from above, illuminating the sensor, passing through the solute film, the metamaterial metal layer, the insulating dielectric layer, and finally undergoing total reflection through the metal reflective layer. Depending on the testing platform, assuming both operating modes function normally, the maximum incident angle deviation is ±8°, providing a certain degree of stability and robustness for the measurement. Large incident angles can cause high-frequency resonance peak splitting, affecting the measurement results.

[0032] like Figure 3 As shown in the diagram, the refractive index curve illustrates the effect of the solute dielectric constant changing from 1 to 4 (i.e., the refractive index changing from 1 to 2) on the redshift of the dual-mode resonance peak of the sensor proposed in this invention at a fixed thickness of 12 micrometers. When n=1.4, mode one achieved the highest absorbance of 99.97%, and when n=2, mode two achieved the highest absorbance of 99.83%, a significant improvement compared to the unloaded state. This indicates that the loading of the analyte enhances the frequency selectivity of the sensor and achieves a higher QF. Good consistency is observed in the frequency shift sensitivity within the refractive index range of 1-2, encompassing the refractive indices of common solutes. High-frequency noise can be filtered using algorithms. Expanding the interaction between the analyte and the sensor is the correct way to improve sensor sensitivity. Our designed metamaterial sensor effectively confines the electric field above and below the metamaterial. Absorbance, as an important definition of a bio-optical sensor, is expressed by the following formula: Where S11(ω) is the reflection coefficient at frequency ω, and S21(ω) represents the transmission coefficient at frequency ω. Since terahertz waves can hardly penetrate the metal reflective layer, the absorptivity of the reflective metamaterial sensor is defined as... . Figure 3 The absorption rate directly reflects the sensor's resonant peak frequency and quality factor.

[0033] like Figure 4 As shown, after the analyte is loaded, the surface electric field is significantly enhanced, and the electric field is mainly distributed in the gap between the oscillators on both sides of the resonator unit. When the metamaterial unit is working, the terahertz wave propagating vertically from above causes the metamaterial unit to resonate at 2.30 THz. At this time, the analyte film and the sensor itself together form a narrowband selective absorber, and more of the electric field is distributed in the analyte solute film, which reconstructs the electromagnetic properties of the sensor and creates a strong constraint on the surface electric field.

[0034] like Figure 5As shown, the metamaterial element model of the present invention under no-load conditions was simulated using ADS. Figure 5 Comparison of simulation results for return loss in the range of 1.5-3.5THz.

[0035] like Figure 6 As shown, the low-frequency resonance is formed by the coupling of capacitance C and inductance L between the metamaterials, creating an equivalent LC resonant circuit. The resonant frequency can be expressed by the following formula: in It is the vacuum permittivity. V is the volume change. Where is the dielectric constant of the material, and E(v) is the total electric field space confined by the resonance. This formula shows that as the dielectric constant of the material increases, the capacitance of the equivalent LC circuit increases, leading to a redshift of the resonant frequency. The final optimized equivalent two-dimensional circuit has capacitances of C1=C3=0.0107pF, C2=0.0245pF, and inductance of L1=L2=4.5×10⁻⁴nH. When C1 and C3 increase to 0.019pF, and C2 increases to 0.043pF, the redshift of S11 is consistent with the behavior when the refractive index changes from 1 to 2, and the high-frequency resonant point becomes sharper, perfectly matching the two simulation results. When we simultaneously increase the capacitances of C1 and C3, both Mode 1 and Mode 2 redshift synchronously. When only the capacitance of C3 is increased, the low-frequency Mode 1 remains unchanged, while the high-frequency Mode 2 redshifts. Therefore, the redshift in Mode 1 is considered to be the result of increasing C1 and C3, while the redshift in Mode 2 is considered to be the result of the superposition of increasing the capacitances C1, C2, and C3. Thus, the constructed Mode 2 has higher sensitivity than Mode 1.

[0036] like Figure 7 As shown, when the dielectric constant of the analyte film changes from 1 to 4, the low-frequency absorption peak on the left shifts by 560 GHz, while the high-frequency peak on the right shifts by 800 GHz. Simultaneously, the absorption peaks within the full refractive index detection range are all greater than 97%, indicating almost complete absorption. This surpasses most existing terahertz metamaterial sensors, providing ample redundancy for practical fabrication. This demonstrates that the designed metamaterial unit exhibits high frequency shift uniformity within the refractive index range of conventional analytes, possessing excellent sensing characteristics. Calculations show that the sensor's Fom values ​​are 6.7 and 28.8, respectively, representing a significant improvement over previous terahertz metamaterial sensors.

[0037] like Figure 8 As shown, mode 1 is insensitive to analyte thickness, while mode 2 exhibits a redshift of the absorption peak as the analyte thickness increases. With a frequency shift sensitivity of 20 GHz / μm, relatively stable results can still be obtained in the low-frequency mode even with imprecise solute thickness control. In the high-frequency mode, the position of the absorption peak indicates the current solute film thickness, thus enabling the designed sensor to serve two different purposes.

[0038] In this embodiment, each metamaterial unit has an outer contour dimension of 87µm*87µm. Each metamaterial unit includes two identical resonator units, and the outer diameter of the circle containing the resonator units is 37µm. In this embodiment, all six oscillator branches and two semicircular rings have the same linewidth of 3µm, with smaller gaps on both sides (2.5µm) and larger gaps in the middle (5µm). In this example, based on the actual MEMS fabrication capabilities, the thickness A of the upper metamaterial metal layer is selected as 0.4µm, and the thickness of the middle insulating layer is preferably 7.5µm. A suitable insulating layer thickness better matches the refractive index range of common analyte films, confining the electric field to the upper surface of the metamaterial and enhancing the Fom value of the sensor.

[0039] In this embodiment, a terahertz metamaterial dual-frequency sensor containing 110*110 units is designed. Under no-load conditions, it operates at two frequency points: 2.30THz and 3.18THz. When the thickness of the solute analyte is 12 micrometers, the sensor's low-frequency sensitivity reaches a maximum of 560GHz / RIU, and the sensor's high-frequency sensitivity reaches a maximum of 800GHz / RIU (the analyte thickness includes the thickness of the metamaterial metal layer, and the thickness ranges overlap spatially). The analyte and the sensor itself constitute the resonator of the sensor, which is a major advantage of thin-film sensing compared to microfluidic chip sensors.

[0040] Therefore, the reflective terahertz metamaterial dual-frequency sensor described in this embodiment of the invention employs a multi-capacitor structure to construct two perfectly absorbed resonant peaks, elucidating the design and implementation principle of narrowband resonance. Mode 1 sensitivity reaches 560 GHz / RIU with a QF of 27.8, while Mode 2 sensitivity reaches 800 GHz / RIU with a QF of 86.3. Simulation results show that the maximum absorption rate of both modes exceeds 99.5%, and the two modes exhibit different characteristics in response to changes in analyte thickness. Circuit modeling using ADS yields good matching results. This design demonstrates high structural feasibility and has broad application prospects in fields such as biosensing, security detection, and medicine.

[0041] Therefore, the present invention employs the above-mentioned reflective terahertz metamaterial dual-frequency sensor, which has a simple structure and low manufacturing cost. It effectively reduces the operating frequency by utilizing a multi-capacitor structure, forms multi-mode operating characteristics, increases stability, and has excellent thin-film sensing potential, greatly increasing the usability of existing terahertz sensors.

[0042] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A reflective terahertz metamaterial dual-frequency sensor, characterized in that: From top to bottom, it includes a metamaterial metal layer, an insulating dielectric layer, and a metal reflective layer; the metamaterial metal layer includes metamaterial units arranged in an array periodically, and each metamaterial unit is a micro-resonant structure composed of two resonator units; Each of the aforementioned resonator units consists of an open resonant half-ring and three oscillators; The oscillators of the two resonator units are distributed at the center and opening of the resonant half-ring, forming three gaps of different sizes; the gaps on the left and right sides are of equal width, and the gap in the middle is twice the width of the gaps on the two sides. The two resonator units have identical structures and are symmetrically distributed vertically and horizontally. The linewidths of the resonant half-ring and the oscillator of the resonator unit are equal. The branch lengths of the four oscillators on the left and right sides of the two resonator units are the same; The outer diameter of the resonant half-ring is less than half that of the insulating dielectric layer.

2. The reflective terahertz metamaterial dual-frequency sensor according to claim 1, characterized in that: The insulating dielectric layer is a resin layer with stable chemical and physical properties produced by spin coating, leveling and solidification of negative photoresist. Its dielectric constant is 3.2 and its loss tangent is 0.

005.

3. The reflective terahertz metamaterial dual-frequency sensor according to claim 1, characterized in that: The thickness of the metamaterial metal layer is the same as the thickness of the metal reflective layer, and the thickness of the metal reflective layer is greater than its skin effect depth.

4. The reflective terahertz metamaterial dual-frequency sensor according to claim 1, characterized in that: Both the metamaterial metal layer and the metal reflective layer are made of gold.

Images