Tunable terahertz absorber

Abstract

The present invention provides a tunable terahertz absorber, comprising a substrate layer and a thin film layer fixed on the substrate layer; wherein the substrate layer is provided with a first groove and a second groove which are independent of each other, the first groove and the second groove are connected through a flow channel, a metasurface array structure is formed in the second groove, a liquid with a required dielectric constant is injected into the first groove, and the liquid flows into the second groove through the flow channel; the thin film layer is sealed on the substrate layer so that the first groove and the second groove form a closed cavity, and there is a distance between the metasurface array structure and the thin film layer. The present invention solves the problem that the absorption characteristics of the existing absorber are fixed and cannot be adjusted, and realizes the function of real-time adjustment of the absorption peak frequency and absorption rate of the terahertz absorber.

Description

Technical Field

[0001] The invention belongs to the technical field of absorber design and manufacture, and in particular relates to a tunable terahertz absorber. Background Art

[0002] The world's first 6G white paper report points out that "Terahertz key devices will be the key technology and challenge for realizing the future 6G vision". With the further application of terahertz technology in the future communication field, it is crucial to develop materials or devices that can resist or weaken terahertz radiation. Among them, metamaterial absorbers are a very important and effective device for absorbing electromagnetic waves.

[0003] The concept of a perfect metamaterial absorber was proposed in 2008, but the absorbers at that time were mainly "metal-dielectric-metal" structures, which had the disadvantages of complex structure, difficult processing, and difficulty in achieving multi-frequency or broadband absorption. Later, the emergence of all-dielectric absorbers solved the above problems. Among them, silicon has become the most widely used material for making terahertz absorbers. This is not only because silicon has excellent physical, chemical, and mechanical properties, but also because silicon with a certain doping concentration can support surface plasmon resonance in the terahertz band. To date, various silicon-based absorbers have been proposed. At present, once the metamaterial absorber is processed, its performance is fixed and cannot be adjusted, which greatly limits the application of absorbers in various scenarios. Therefore, the adjustable absorption characteristics of the absorber have become the focus of current research. Summary of the invention

[0004] The purpose of the present invention is to provide a tunable terahertz absorber to address the deficiencies of the prior art. The absorber solves the problem that the absorption characteristics of the prior absorber are fixed and cannot be adjusted, and realizes the function of real-time adjustment of the absorption peak frequency and absorption rate of the terahertz absorber.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] A tunable terahertz absorber comprises a substrate layer and a thin film layer fixed on the substrate layer; wherein:

[0007] A substrate layer, wherein a first groove and a second groove which are independent of each other are formed on the substrate layer, the first groove and the second groove are connected through a flow channel, a metasurface array structure is formed in the second groove, a liquid with a required dielectric constant is injected into the first groove, and the liquid flows into the second groove through the flow channel;

[0008] A thin film layer is sealed on the substrate layer so that the first groove and the second groove form a closed cavity, and there is a distance between the super surface array structure and the thin film layer.

[0009] Furthermore, the substrate layer is made of highly doped silicon.

[0010] Furthermore, the metasurface array structure includes a plurality of periodically arranged trapezoidal boss structures, the cross-sectional area of ​​the trapezoidal boss structures gradually decreases as approaching the thin film layer, and channels for liquid to flow through are provided between two adjacent trapezoidal boss structures.

[0011] Furthermore, the structural parameters of the metasurface array structure are 10 1 The wave absorbing characteristics of the absorber can be changed by changing its structural parameters.

[0012] Furthermore, the film layer and the substrate layer are irreversibly bonded via silicon-oxygen bonds.

[0013] Furthermore, the first groove is also connected to a hydraulic device, which extends into the first groove through a pipeline through the thin film layer and controls the volume of liquid injected into the first groove to control the height of the liquid in the first groove and the second groove, thereby adjusting the wave absorbing characteristics of the absorber.

[0014] Furthermore, the film layer is made of a flexible polymer material, and the wave absorbing characteristics of the wave absorber can be adjusted by adjusting the thickness of the film layer.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] 1. The present invention solves the problem that the absorption characteristics of existing absorbers are fixed and cannot be adjusted, and realizes the function of real-time adjustment of the absorption peak frequency and absorption rate of the terahertz absorber. Specifically, the present invention can not only change the absorption characteristics of the absorber by changing the thickness of the thin film layer and the structural parameters of the metasurface array structure, but also realize dynamic adjustment of the absorption characteristics by changing the liquid height between the metasurface and the thin film layer;

[0017] 2. The absorber of the present invention has a thin film layer on its surface, which can form a hydraulic cavity with the substrate to adjust the liquid height, and can also protect the metasurface array structure and increase the service life of the absorber;

[0018] 3. The absorber described in the present invention has a simple structure and is prepared by a femtosecond laser method, which is easy to process and has low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a structural schematic diagram of the wave absorber according to an embodiment of the present invention;

[0020] Figure 2 A top view of a substrate layer of the absorber according to an embodiment of the present invention;

[0021] Figure 3The relationship between the wave absorbing characteristics of the wave absorber according to the embodiment of the present invention and the liquid height;

[0022] Figure 4 The relationship between the wave absorbing characteristics of the wave absorber of the present invention and the film thickness. DETAILED DESCRIPTION

[0023] The technical solutions in the embodiments of the present invention will be described clearly and completely below in combination with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0025] The present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited thereto.

[0026] like Figure 1 As shown, the present invention provides a tunable terahertz absorber, comprising a substrate layer 2 and a thin film layer 1 fixed on the substrate layer 2. Figure 2 , a first groove 10 and a second groove 11 are formed independently of each other on the substrate layer 2, the first groove 10 and the second groove 11 are connected through a flow channel 12, a metasurface array structure 13 is formed in the second groove 11, a liquid with a required dielectric constant is injected into the first groove 10, and the liquid flows into the second groove 11 through the flow channel 12. In this embodiment, the substrate layer is 360 μm thick and the doping concentration is 6.73×10 17 cm -3 The first groove 10 and the flow channel 12 are hydraulic adjustment areas. The metasurface array structure 13 is a sub-wavelength periodic array structure, which is the absorber working area. Since the absorber works in the terahertz band, the structural parameters of the metasurface array structure 13 are 10 1 μm order of magnitude. When the terahertz wave is incident on the metasurface array structure 13 region, it is mainly divided into three parts, including reflected wave, absorbed wave and transmitted wave, and their proportions are represented by reflectivity R, absorptivity A and transmittance T respectively. Due to the existence of the metasurface array structure 13, impedance matching is achieved between the metasurface array structure region and the free space, thereby effectively reducing the reflectivity. Since the thickness of the silicon wafer is greater than the skin depth of silicon in the terahertz band, the transmittance is 0, so the absorptivity of the absorber can be expressed as A=1-R=1-|S 11 | 2 , where S 11is the input reflection coefficient, that is, the input return loss. The wave absorption principle of the absorber is: when the electromagnetic wave is incident on the metasurface array structure 13, the subwavelength structure and the free electrons of a specific concentration cause the surface of the metasurface array structure 13 to generate surface plasmon resonance, and the oscillation wave propagates along the surface direction of the metasurface array structure 13. Finally, the energy of the electromagnetic wave is converted into the energy of the electron oscillation and dissipated, thereby achieving the absorption of the electromagnetic wave.

[0027] Furthermore, the metasurface array structure 13 is obtained by processing on the bottom surface of the second groove 11 using a femtosecond laser. The metasurface array structure 13 includes a plurality of periodically arranged trapezoidal boss structures 130, the cross-sectional area of ​​the trapezoidal boss structures 130 gradually decreases as it approaches the thin film layer 1, and there is a channel for liquid to flow between two adjacent trapezoidal boss structures 130. Since it is processed using a femtosecond laser with a Gaussian beam, the obtained channel has an inverted trapezoidal structure that is "wide at the top and narrow at the bottom". The channel is formed by scanning the femtosecond laser along an "S"-shaped path multiple times, so the width and depth of the channel structure can be controlled by changing the width of the scanning path and the number of scans, thereby achieving the adjustment of the wave absorption characteristics. In addition, changing parameters such as the laser power and scanning speed can obviously also change the structural parameters of the channel.

[0028] Furthermore, the substrate layer 2 and the thin film layer 1 are placed in an oxygen plasma cleaning machine and bombarded for 30 seconds, then taken out, and the two are immediately bonded together and pressed for a period of time, and the irreversible bonding between the thin film layer 1 and the substrate layer 2 is achieved through the silicon-oxygen bond. After bonding, the first groove 10 and the second groove 11 are both formed into a closed cavity. In order to prevent the thin film layer 1 from bonding with the super-surface array structure 13, thereby ensuring the deformability of the thin film layer 1, the top height of the super-surface array structure 13 should be lower than the top height of the side walls around the substrate layer, that is, there is a gap between the top surface of the super-surface array structure 13 and the bottom surface of the thin film layer 1. In this embodiment, the gap between the two is set to 5μm. Of course, in other embodiments, other gaps can also be set according to actual needs.

[0029] The closed cavity formed by the first groove 10 is also connected to the hydraulic device 3. The hydraulic device 3 extends into the closed cavity through a pipeline and injects a liquid with a certain dielectric constant into the closed cavity. The liquid enters the closed cavity formed by the second groove 11 from the flow channel 12. The liquid continues to be injected into the first groove 10 through the hydraulic device 3. The height of the liquid in the cavity increases. The volume of liquid to be injected can be calculated by the structural parameters of the absorber and the final liquid height. By controlling the volume of injected liquid, the liquid height can be precisely controlled to adjust the wave absorbing characteristics of the absorber. In this embodiment, the dielectric constant of the injected liquid is 2. In other embodiments, a liquid with a suitable dielectric constant is selected according to the needs. Figure 3As shown in the figure, absorbers with different liquid heights have different wave absorption characteristics, and the main change in the wave absorption characteristics lies in the change of the absorption peak frequency. In addition, the maximum absorption rate of the absorption peak will also be different.

[0030] In addition, by changing the coating parameters, the film layer 1 with different thicknesses can be prepared, and the absorber using the film layer 1 with different thicknesses will also obtain different wave absorbing properties, see Figure 4 . Figure 4 The wave absorbing characteristics of the wave absorber with thin film layers 1 of different thicknesses. It can be seen that the thickness of the thin film layer 1 will also affect the frequency of the absorption peak and the maximum absorption rate and other characteristics. Therefore, the wave absorbing characteristics of the wave absorber can also be adjusted by changing the thickness of the thin film layer 1.

[0031] The above are only preferred embodiments of the present invention, and are not intended to limit the implementation methods and protection scope of the present invention. Those skilled in the art should be aware that all solutions obtained by equivalent substitutions and obvious changes made using the contents of the specification of the present invention should be included in the protection scope of the present invention.

Claims

1. A tunable terahertz absorber, characterized in that: It includes a substrate layer and a thin film layer fixed on the substrate layer; wherein, A substrate layer, wherein a first groove and a second groove which are independent of each other are formed on the substrate layer, the first groove and the second groove are connected through a flow channel, a metasurface array structure is formed in the second groove, a liquid with a required dielectric constant is injected into the first groove, and the liquid flows into the second groove through the flow channel; A thin film layer is sealed on the substrate layer so that the first groove and the second groove form a closed cavity, and there is a distance between the super surface array structure and the thin film layer.

2. The tunable terahertz absorber according to claim 1, characterized in that: The substrate layer is made of highly doped silicon.

3. The tunable terahertz absorber according to claim 1, characterized in that: The metasurface array structure includes a plurality of periodically arranged trapezoidal boss structures, wherein the cross-sectional area of ​​the trapezoidal boss structures gradually decreases as they approach the thin film layer, and channels for liquid to flow through are provided between two adjacent trapezoidal boss structures.

4. The tunable terahertz absorber according to claim 1, characterized in that: The structural parameter of the metasurface array structure is 10 1 The wave absorbing characteristics of the absorber can be changed by changing its structural parameters.

5. The tunable terahertz absorber according to claim 1, characterized in that: The film layer and the substrate layer are irreversibly bonded via silicon-oxygen bonds.

6. The tunable terahertz absorber according to claim 1, characterized in that: The first groove is also connected to a hydraulic device, which extends into the first groove through a pipeline through the film layer and controls the height of the liquid in the first groove and the second groove by controlling the volume of the liquid injected into the first groove, thereby adjusting the wave absorbing characteristics of the absorber.

7. The tunable terahertz absorber according to claim 1, characterized in that: The film layer is made of a flexible polymer material, and the wave absorbing characteristics of the wave absorber can be adjusted by adjusting the thickness of the film layer.

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