Liquid-enhanced sensing system and measurement method based on bowtie-type metal aperture terahertz metamaterial

Abstract

The present application relates to a kind of liquid enhanced sensing system and measurement method based on bow-tie type metal aperture terahertz metamaterials.The system includes terahertz transmitter, sensing device, terahertz detector and post-processing system.The sensing device is composed of bow-tie type metal aperture terahertz metamaterials and liquid sample cell.Terahertz transmitter and terahertz detector are respectively arranged above and below the sensing device for transmitting and receiving terahertz signals.The post-processing system is connected with the terahertz detector to process and display the received terahertz signals in real time.The measurement method of the system is as follows: detecting the terahertz signal of empty liquid sample cell, detecting the terahertz signal of bow-tie type metal aperture terahertz metamaterials with different configurations without loading or loading liquid sample to be measured, and calculating the sensitivity of bow-tie type metal aperture terahertz metamaterials with different configurations.The system is easy to operate, has excellent performance, high sensing sensitivity, and can support terahertz sensing detection of different liquids.

Description

Technical Field

[0001] The present invention relates to the field of terahertz sensing technology, and in particular to a liquid-enhanced sensing system and a measurement method based on a bowtie-type metal aperture terahertz metamaterial. Background Art

[0002] Metamaterials are composite structures composed of periodically arranged subwavelength metaatoms. They are designed to efficiently manipulate and tailor light to enable a variety of groundbreaking applications, including negative refraction, superlenses, holographic imaging, communications, and biochemical sensing. They compress electromagnetic fields in time and space by stimulating localized surface plasmon resonances. The localized field enhancement properties of metamaterials facilitate the interaction between analytes and electromagnetic waves, addressing the limitations of low absorption cross-sections caused by the mismatch between terahertz wavelengths and molecular scales. This unique property has led to significant interest and rapid development in the field of terahertz biosensing.

[0003] Most existing terahertz metamaterials are based on metal patch structures—periodic arrays of metal microstructures fabricated on a substrate. Due to substrate effects, these metamaterials reduce the overlap between the near-field and the analyte, severely limiting the utilization of the excited electric field and, consequently, limiting sensing sensitivity. Furthermore, water's strong absorption of terahertz waves restricts the application of terahertz sensors for liquid detection. Therefore, developing highly sensitive terahertz metamaterials that can also detect liquids remains a major challenge for the practical application of terahertz sensing. Summary of the Invention

[0004] The purpose of the present invention is to address the shortcomings of the existing technology and provide a liquid-enhanced sensing system and measurement method based on bowtie-type metal aperture terahertz metamaterial, which is easy to operate, has excellent performance, high sensing sensitivity, and can support terahertz sensing detection of different liquids.

[0005] To achieve the above-mentioned objectives, the technical solution of the present invention is: a liquid-enhanced sensing system based on a bowtie-type metal aperture terahertz metamaterial, comprising a terahertz emitter, a sensing device, a terahertz detector and a post-processing system. The sensing device comprises a bowtie-type metal aperture terahertz metamaterial and a liquid sample pool. The terahertz emitter and the terahertz detector are respectively arranged above and below the sensing device for transmitting and receiving terahertz signals. The post-processing system is connected to the terahertz detector to process and display the received terahertz signals in real time.

[0006] In one embodiment of the present invention, the bowtie-type metal aperture terahertz metamaterial is composed of two wedge-shaped triangles and a wedge-shaped connecting rod, whose unit periods are 150 and 200 μm, the triangle length is 82 μm, the height is 45 μm, the connecting rod length is 20 μm, and the width of the upper and lower surfaces of the connecting rod has three configurations, namely 14 μm and 3 μm, 20 μm and 9 μm, and 23 μm and 12 μm. The width is the main factor affecting the sensing performance of the metamaterial.

[0007] In one embodiment of the present invention, the bowtie-shaped metal aperture terahertz metamaterial is used as a carrier to excite localized surface plasmon resonance. It is processed on a 20μm aluminum film using ultrafast femtosecond laser processing technology. Connecting rods of different widths are achieved by adjusting the pulse energy of the femtosecond laser to 10mW, 80mW, and 100mW.

[0008] In one embodiment of the present invention, the liquid sample cell is composed of a nut, a liquid sample cell body, a terahertz window, and a gasket.

[0009] In one embodiment of the present invention, the sensing device places a bowtie-shaped metal aperture terahertz metamaterial between two washers, clamps it with a terahertz window, and then assembles it into a liquid sample cell body and tightens it with a nut.

[0010] In one embodiment of the present invention, the terahertz window is made of TPX with a thickness of 1 mm and a diameter of 25 mm; and the gasket is made of plastic with a thickness of 10 μm and a diameter of 25 mm.

[0011] The present invention also provides a measurement method for the liquid-enhanced sensing system based on the bowtie-type metal aperture terahertz metamaterial described above, comprising the following steps:

[0012] Step S1: placing an empty liquid sample cell between the terahertz emitter and the terahertz detector, and detecting the terahertz signal obtained by the optical path detection as a reference signal r;

[0013] Step S2: Integrate the bowtie-shaped metal aperture terahertz metamaterial into the liquid sample pool and fix it between the terahertz emitter and the terahertz detector. At this time, the terahertz signal obtained by the optical path detection is the sample signal s1.

[0014] Step S3: Using the overall liquid-enhanced sensing system as a carrier, the sample to be tested is loaded into the liquid sample cell integrated with the bowtie-shaped metal aperture terahertz metamaterial, and the excess liquid is squeezed out by tightening the nut. The terahertz signal obtained by the optical path detection is the sample signal s2;

[0015] Step S4, replacing the bowtie-shaped metal aperture terahertz metamaterial with a different configuration, and repeating steps S2-S3;

[0016] Step S5, using the obtained reference signal r, sample signals s1 and s2, the normalized sensitivity of the bowtie-shaped metal aperture terahertz metamaterial in different configurations is calculated in the post-processing system.

[0017] In an embodiment of the present application, the step S5 of calculating the normalized sensitivity of the bowtie-shaped metal aperture terahertz metamaterial specifically includes:

[0018] Step S51, the detected terahertz time-domain pulse signals r, s1 and s2 are converted into terahertz frequency-domain amplitude spectrum signals through fast Fourier transform;

[0019] Step S52, the transmittance spectrum of the sample signals s1 and s2 is calculated respectively by using a transmittance spectrum calculation formula, and the resonant frequency of the sample is obtained;

[0020] Step S53, the sensitivity of the bowtie-shaped metal aperture terahertz metamaterial is calculated by using a normalized sensitivity calculation formula;

[0021] Step S54, steps S51-S53 are repeated to calculate the normalized sensitivity of the bowtie-shaped metal aperture terahertz metamaterial in different configurations.

[0022] In an embodiment of the present application, the transmittance spectrum calculation formula in step S52 is:

[0023]

[0024] Wherein, E s (ω) and E r (ω) are the terahertz frequency-domain amplitude spectrum of the sample signals s1 and s2 and the reference signal r respectively.

[0025] In an embodiment of the present application, the normalized sensitivity calculation formula in step S53 is:

[0026]

[0027] Wherein, f s1 is the resonant frequency of the sample signal s1, f s2 is the resonant frequency of the sample signal s2, and n is the refractive index of the sample to be measured.

[0028] Compared with the existing technology, the present invention has the following beneficial effects: The present invention provides a liquid-enhanced sensing system and measurement method based on bowtie-type metal aperture terahertz metamaterials. The system uses bowtie-type metal aperture terahertz metamaterials as a carrier, and based on the extraordinary light transmission phenomenon, it eliminates the substrate effect, so that the excited electric field is fully utilized, and the interaction with the sample to be measured is enhanced. In addition, by adjusting the second pulse energy of the femtosecond laser, a smaller connecting rod metamaterial structure is achieved, thereby greatly improving the electric field enhancement and significantly improving the sensitivity. In addition, the liquid sample to be measured is loaded with the metamaterial integrated into the liquid sample pool to achieve control of the liquid thickness, thereby greatly alleviating the strong absorption of terahertz waves by polar liquids and realizing the detection of liquid samples. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a schematic diagram of the system structure of an embodiment of the present invention;

[0030] Figure 2 2 is a schematic structural diagram of a bowtie-type metal aperture terahertz metamaterial according to an embodiment of the present invention;

[0031] Figure 3 2 is a schematic diagram of a unit structure of a bowtie-type metal aperture terahertz metamaterial according to an embodiment of the present invention;

[0032] Figure 4 is a physical diagram of a liquid sample pool in an embodiment of the present invention;

[0033] Figure 5 is the transmittance spectrum of the performance test in the embodiment of the present invention;

[0034] Figure 6 is a normalized sensor sensitivity diagram in an embodiment of the present invention.

[0035] In the figure: 1-THz emitter; 2-Incident THz pulse; 3-Nut; 4-Liquid sample cell body; 5-THz window; 6-Gasket; 7-Bow tie type metal aperture THz metamaterial; 701-Connecting rod; 702-Triangle; 8-Liquid sample to be tested; 9-Transmitted THz pulse; 10-THz detector; 11-Post-processing system. DETAILED DESCRIPTION

[0036] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings.

[0037] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present application belongs.

[0038] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application; as used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form, and it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or their combinations.

[0039] like Figure 1 As shown, this embodiment provides a liquid-enhanced sensing system based on a bowtie-type metal aperture terahertz metamaterial, including a terahertz transmitter, a sensing device, a terahertz detector and a post-processing system. The sensing device is composed of a bowtie-type metal aperture terahertz metamaterial 7 and a liquid sample pool. The terahertz transmitter 1 and the terahertz detector 10 are respectively arranged above and below the sensing device for transmitting and receiving terahertz signals. The post-processing system 11 is connected to the terahertz detector 10 to process and display the received terahertz signals in real time.

[0040] like Figure 2 、 3 As shown, in this embodiment, the bowtie-type metal aperture terahertz metamaterial is composed of two wedge-shaped triangles 702 and a wedge-shaped connecting rod 701, whose unit periods are 150 and 200 μm, the length of the triangle is 82 μm, the height is 45 μm, the length of the connecting rod is 20 μm, and the width of the upper and lower surfaces of the connecting rod has three configurations, namely 14 μm and 3 μm, 20 μm and 9 μm, and 23 μm and 12 μm. The width is the main factor affecting the sensing performance of the metamaterial.

[0041] In this embodiment, the bowtie-shaped metal aperture terahertz metamaterial is used as a carrier to excite localized surface plasmon resonance. It is processed on a 20μm aluminum film using ultrafast femtosecond laser processing technology. Connecting rods 701 of different widths are achieved by adjusting the pulse energy of the femtosecond laser to 10mW, 80mW, and 100mW.

[0042] like Figure 1 、 4 As shown, in this embodiment, the liquid sample cell is composed of a nut 3, a liquid sample cell body 4, a terahertz window 5 and a gasket 6; the sensing device is composed of a bowtie-shaped metal aperture terahertz metamaterial 7 placed between two gaskets 6, then clamped with the terahertz window 5, and then assembled into the body and tightened with a nut 4; the terahertz window 5 is composed of TPX with a thickness of 1 mm and a diameter of 25 mm; the gasket 6 is composed of plastic with a thickness of 10 μm and a diameter of 25 mm.

[0043] When performing liquid sample sensing, a bowtie-shaped metal aperture terahertz metamaterial 7 is used as a carrier and integrated into a liquid sample cell consisting of a nut 3, a liquid sample cell body 4, a terahertz window 5, and a gasket 6. The bowtie-shaped metal aperture terahertz metamaterial 7 is then fixed between a terahertz emitter 1 to be activated and a terahertz detector 10. The terahertz emitter 1 and the terahertz detector 9 are then activated, and an incident terahertz pulse 2 is emitted. The terahertz wave reacts on the surface of the bowtie-shaped metal aperture terahertz metamaterial 7 by transmission, and then exits through the terahertz window 5. Finally, the detected transmitted terahertz pulse 8 sample signal is transmitted to a terahertz signal post-processing system 11 to obtain a sample signal s1. The liquid sample 8 to be tested is then loaded onto the surface of the bowtie-shaped metal aperture terahertz metamaterial integrated into the liquid sample cell. The excess liquid sample is squeezed out by tightening the nut 3. The above process is repeated to obtain a sample signal s2. Finally, the normalized sensitivity of the metamaterial is calculated. The above process is performed on bowtie-shaped metal aperture terahertz metamaterials with different connecting rod sizes. The measurement method of the system specifically includes the following steps:

[0044] Step S1: placing an empty liquid sample cell between the terahertz emitter and the detector. At this time, the terahertz signal obtained by the optical path detection is the reference signal r;

[0045] Step S2: Integrate the bowtie-shaped metal aperture terahertz metamaterial into the liquid sample pool and fix it between the terahertz emitter and the detector. At this time, the terahertz signal obtained by the optical path detection is the sample signal s1;

[0046] Step S3: Using the sensor system as a carrier, the sample to be tested is loaded into the liquid sample cell integrated with the metamaterial, and the nut is tightened to squeeze out excess liquid. The terahertz signal obtained by the optical path detection is the sample signal s2;

[0047] Step S4, replacing the bowtie-shaped metal aperture terahertz metamaterial with a different configuration, and repeating steps S2-S3;

[0048] Step S5: using the obtained reference signal r and sample signals s1 and s2 in a post-processing system, calculate the normalized sensitivity of bowtie-shaped metal aperture terahertz metamaterials with different configurations.

[0049] The calculation of the normalized sensitivity of the bowtie metal aperture terahertz metamaterial is as follows:

[0050] Step S51, converting the detected terahertz time-domain pulse signals r, s1 and s2 into terahertz frequency-domain amplitude spectrum signals through fast Fourier transform;

[0051] Step S52: using a transmission spectrum calculation formula to calculate the transmittance spectra of the sample signals s1 and s2, thereby obtaining the resonant frequency of the sample;

[0052] Step S53: Finally, the sensitivity of the bowtie metal aperture terahertz metamaterial is calculated using the normalized sensitivity calculation formula;

[0053] Step S54 , repeating steps S51 - S53 to calculate and obtain the normalized sensitivities of bowtie-shaped metal aperture terahertz metamaterials with other different configurations.

[0054] The transmittance spectrum calculation formula is:

[0055]

[0056] Among them, E s (ω) and E r (ω) are the terahertz frequency domain amplitude spectra of the sample signals (s1, s2) and the reference signal r, respectively.

[0057] Among them, the normalized sensitivity calculation formula is:

[0058]

[0059] Among them, f s1 is the resonant frequency of the sample signal s1, f s2 is the resonant frequency of the sample signal s2, and n is the refractive index of the sample to be measured.

[0060] Performance evaluation of terahertz metamaterial sensing system:

[0061] The performance evaluation of the liquid-enhanced sensing system based on bowtie-type metal aperture terahertz metamaterial is to load liquid paraffin with nitrogen on the surface of metamaterials with different connecting rod sizes, and then integrate them into the liquid sample pool and place them at the designated position for sensing detection.

[0062] The transmission spectrum is calculated by the terahertz frequency domain amplitude spectrum of different samples to be tested, and the sensing characterization is performed according to the shift Δf of the resonance point frequency with the change Δn of the refractive index of the liquid sample to be tested.

[0063] The performance of the bowtie metal aperture terahertz metamaterial was evaluated. The performance test results of the embodiment of the present invention are as follows: Figure 5 、 6 As shown. From the experimental transmittance spectrum, it can be seen that compared with nitrogen, due to the higher refractive index and loss of liquid paraffin, its transmittance spectrum shows obvious red shift and resonance peak broadening and intensity weakening. Metamaterials with different connecting rod sizes show different sizes of red shift. These significant changes prove that the localized surface plasmon resonance supported by the bowtie metal aperture terahertz metamaterial is sensitive to changes in the surrounding dielectric environment. The normalized sensing sensitivity calculation results according to the embodiment of the present invention are shown in Figure 2. Figure 5As shown, they are 0.586RIU -1 , 0.596RIU -1 , 0.62RIU -1 The results, corresponding to different connecting rod sizes (from large to small), demonstrate that reducing the connecting rod size can enhance terahertz sensing capabilities. Furthermore, the presence of a distinct resonance profile after placing liquid paraffin on the metamaterial surface also demonstrates that integrating a liquid sample cell is an effective means of detecting liquid samples.

[0064] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any other manner. Any person skilled in the art may utilize the above-disclosed technical content to modify or modify the present invention into equivalent embodiments. However, any simple modifications, equivalent variations, and modifications to the above embodiments that do not depart from the technical content of the present invention and are based on the technical essence of the present invention remain within the scope of protection of the present invention.

Claims

1. A measurement method for a liquid-enhanced sensing system based on bowtie-type metal aperture terahertz metamaterial, characterized in that: The liquid-enhanced sensing system based on a bowtie-type metal aperture terahertz metamaterial comprises a terahertz emitter, a sensing device, a terahertz detector, and a post-processing system. The sensing device comprises a bowtie-type metal aperture terahertz metamaterial and a liquid sample pool. The terahertz emitter and the terahertz detector are respectively arranged above and below the sensing device for transmitting and receiving terahertz signals. The post-processing system processes and displays the received terahertz signals in real time by connecting to the terahertz detector. The bowtie-type metal aperture terahertz metamaterial is composed of two wedge-shaped triangles and a wedge-shaped connecting rod, wherein the unit period is 150 and 200 μm, the triangle is 82 μm long and 45 μm high, the connecting rod is 20 μm long, and the width of the upper and lower surfaces of the connecting rod has three configurations, namely 14 μm and 3 μm, 20 μm and 9 μm, and 23 μm and 12 μm, respectively. The width is the main factor affecting the sensing performance of the metamaterial. The method comprises the following steps: Step S1: placing an empty liquid sample cell between the terahertz emitter and the terahertz detector, and the terahertz signal obtained by the optical path detection is the reference signal r; Step S2: Integrate the bowtie-shaped metal aperture terahertz metamaterial into the liquid sample pool and fix it between the terahertz emitter and the terahertz detector. At this time, the terahertz signal obtained by the optical path detection is the sample signal s1. Step S3: Using the overall liquid-enhanced sensing system as a carrier, the sample to be tested is loaded into the liquid sample cell integrated with the bowtie-shaped metal aperture terahertz metamaterial, and the excess liquid is squeezed out by tightening the nut. The terahertz signal obtained by the optical path detection is the sample signal s2; Step S4, replacing the bowtie-shaped metal aperture terahertz metamaterial with a different configuration, and repeating steps S2-S3; Step S5: using the obtained reference signal r and sample signals s1 and s2 in a post-processing system, calculate the normalized sensitivity of bowtie-shaped metal aperture terahertz metamaterials with different configurations.

2. The measurement method of the liquid-enhanced sensing system based on bowtie-type metal aperture terahertz metamaterial according to claim 1, characterized in that: The bowtie-shaped metal aperture terahertz metamaterial serves as a carrier for exciting localized surface plasmon resonance. It is processed on a 20μm aluminum film using ultrafast femtosecond laser processing technology. Connecting rods of different widths are achieved by adjusting the pulse energy of the femtosecond laser to 10mW, 80mW, and 100mW.

3. The measurement method of the liquid-enhanced sensing system based on bowtie-type metal aperture terahertz metamaterial according to claim 1, characterized in that: The liquid sample cell consists of a nut, a liquid sample cell body, a terahertz window and a gasket.

4. The measurement method of the liquid-enhanced sensing system based on bowtie-type metal aperture terahertz metamaterial according to claim 3, characterized in that: The sensing device places a bowtie-shaped metal aperture terahertz metamaterial between two washers, clamps it with a terahertz window, and then assembles it into a liquid sample pool body and tightens it with a nut.

5. The measurement method of the liquid-enhanced sensing system based on bowtie-type metal aperture terahertz metamaterial according to claim 3 or 4, characterized in that: The terahertz window is made of TPX with a thickness of 1 mm and a diameter of 25 mm; the gasket is made of plastic with a thickness of 10 μm and a diameter of 25 mm.

6. The measurement method of the liquid-enhanced sensing system based on bowtie-type metal aperture terahertz metamaterial according to claim 1, characterized in that: The calculation of the normalized sensitivity of the bowtie metal aperture terahertz metamaterial in step S5 is specifically as follows: Step S51, converting the detected terahertz time-domain pulse signals r, s1 and s2 into terahertz frequency-domain amplitude spectrum signals through fast Fourier transform; Step S52: using the transmission spectrum calculation formula to calculate the transmittance spectra of the sample signals s1 and s2, respectively, to obtain the resonant frequency of the sample; Step S53: Calculate the sensitivity of the bowtie metal aperture terahertz metamaterial using a normalized sensitivity calculation formula; Step S54 , repeating steps S51 - S53 to calculate and obtain the normalized sensitivity of bowtie-shaped metal aperture terahertz metamaterials with different configurations.

7. The measurement method of the liquid-enhanced sensing system based on bowtie-type metal aperture terahertz metamaterial according to claim 6, characterized in that: The transmittance spectrum calculation formula in step S52 is: Among them, E s (ω) and E r (ω) are the terahertz frequency domain amplitude spectra of the sample signals s1, s2 and the reference signal r.

8. The measurement method of the liquid-enhanced sensing system based on bowtie-type metal aperture terahertz metamaterial according to claim 6, characterized in that: The normalized sensitivity calculation formula in step S53 is: Among them, f s1 is the resonant frequency of the sample signal s1, f s2 is the resonant frequency of the sample signal s2, and n is the refractive index of the sample to be measured.

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