A frequency-swept liquid metal tunable metamaterial absorber

Abstract

The present invention discloses a frequency-sweeping liquid metal tunable metamaterial absorber, comprising a base layer, a microfluidic layer, and an absorbing layer, which are sequentially arranged from bottom to top. The absorbing layer comprises a plurality of absorbing units distributed in an array, each absorbing unit having an inverted truncated cone-shaped cavity provided therein, and each cavity is filled with liquid metal. The microfluidic layer comprises a plurality of support columns, each of which is positioned between the absorbing unit and the base layer. A panel is provided on the outer edge of the microfluidic layer. Compared with the prior art, the frequency-sweeping liquid metal tunable metamaterial absorber of the present invention has the characteristics of real-time response, frequency-sweeping continuous tunability, polarization insensitivity, and stability over a wide incident angle.

Description

Technical Field

[0001] The present invention belongs to the technical field of microwave device engineering, and in particular relates to a frequency-sweeping liquid metal tunable metamaterial absorber. Background Art

[0002] Microwaves are electromagnetic waves operating in the 300MHz-300GHz range. They are used in everyday mobile phone communications, wireless LANs, satellite communications, and military radar. However, with the widespread use of electromagnetic waves, electromagnetic pollution has become increasingly important. The thermal and non-thermal effects of electromagnetic radiation can trigger autonomic nervous system disorders and increase the risk of tissue cell lesions and cancer. Electromagnetic radiation can also cause electromagnetic compatibility issues. In modern warfare, the ability to effectively protect and conceal the electromagnetic signature of equipment determines its survival. Therefore, the research on electromagnetic wave absorbing materials is not only crucial to the stability of national defense but also impacts the healthy and sustainable development of society and the economy.

[0003] Metamaterials are artificial composite structures or materials that possess extraordinary physical properties not possessed by natural materials. Through systematic structural design at key physical scales, certain extraordinary physical phenomena that defy natural laws can be achieved, such as negative magnetic permeability, negative dielectric constant, negative refraction, and the inverse Doppler effect. In 2008, Landy et al. first designed a "perfect absorbing metamaterial" that achieves near-100% absorption of electromagnetic waves. Currently, metamaterials absorb electromagnetic waves across the entire frequency range, from gigahertz to visible light. Compared to traditional absorbing materials, metamaterials offer advantages such as high absorption, thinness, and light weight. Furthermore, metamaterials can control the effective absorption frequency through simple structural design, making them an ideal next-generation absorbing material.

[0004] While metamaterial absorbers (MMAs) have been extensively studied and applied in microwave absorption, a limitation of passive MMAs is that their structures typically correspond to a single response frequency. Changes in the operational mission require structural redesign. Consequently, each MMA is tailored to specific operating conditions, significantly limiting its applications. However, reconfigurable technologies can be used to achieve dynamically tunable functionality by incorporating active materials / elements into traditional passive MMAs. Various active materials / elements have been reported, such as liquid crystals, active lumped elements, and phase-change materials. These materials tune the response frequency by controlling optical, electrical, thermal, and mechanical changes. Optical, electrical, and thermal tuning essentially involves the alteration of a material's physical properties (free carrier density, band gap, or crystal equivalence) by an external magnetic field. Meanwhile, mechanical tuning primarily involves the reconfiguration of the resonant structure (which offers greater tunability but is also limited by the material's stiffness). Liquids can flow in arbitrary forms, and their electromagnetic response can be easily tuned when designed as metastructures. Liquid metals, due to their dual properties of fluidity and metallicity, have applications in stretchable electronics, flexible robotics, and microfluidic sensors. Compared to the limited reconfiguration of solid resonant unit cell structures, liquid metal resonant structures can be flexibly reconfigured into different complex forms through pre-designed microfluidic channels, making liquid metals suitable for fabricating tunable MM absorbers. Changing the filling state of the liquid metal in the channel can switch between absorption and transport.

[0005] Upon inquiry, it was found that the currently disclosed existing technologies that are highly relevant to microfluidics and metamaterial absorbers mostly switch the absorption frequency band by changing the resonance pattern, or by replacing the fluid medium to achieve the change of the absorption frequency band. They have the characteristics of long response time and discontinuous absorption frequency band.

[0006] In order to solve the problems existing in the existing absorbing metamaterial technology, the present invention provides a microfluidic-based swept-frequency liquid metal tunable metamaterial absorber with the characteristics of real-time response, swept-frequency continuous adjustment, polarization insensitivity, and wide incident angle stability. Summary of the Invention

[0007] The purpose of the present invention is to provide a frequency-sweeping liquid metal tunable metamaterial absorber with the characteristics of real-time response, frequency-sweeping continuous tunability, polarization insensitivity, and wide incident angle stability.

[0008] To achieve the above-mentioned objectives, the technical solution adopted by the present invention is: a frequency-sweeping liquid metal tunable metamaterial absorber, comprising a base layer, a microfluidic layer and an absorbing layer arranged in sequence from bottom to top, wherein the absorbing layer comprises a plurality of absorbing units distributed in an array, each of the absorbing units is provided with an inverted truncated cone-shaped cavity inside, and each of the absorbing units is filled with liquid metal, the microfluidic layer comprises a plurality of support columns, each of the support columns is abutted between the absorbing unit and the base layer, and a panel is provided on the outer edge of the microfluidic layer.

[0009] When the swept-frequency liquid metal tunable metamaterial absorber of the present invention is in operation, liquid metal is pumped into the microfluidic pipe by a microfluidic pump and first fills the microfluidic layer to form a reflective backing. At this time, the electromagnetic waves are reflected. The purpose of this step is to prove that the absorbing ability comes from the absorbing layer and eliminate the influence of other layers. As the microfluidic layer is filled, the liquid metal enters the inverted cone in the absorbing unit of the absorbing layer, and the absorbing performance appears at this time. The filling amount of liquid metal can be changed through microfluidic technology, and converted into liquid level height according to the model size.

[0010] Preferably, the thickness of the base layer is 4-6 mm, the thickness of the microfluidic layer is 4-6 mm, and the thickness of the absorbing layer is 2-4 mm.

[0011] Preferably, the cross-sectional diameter of each microfluidic column is 1-2 mm.

[0012] Preferably, the cross section of each of the wave absorbing units is a rectangle with a side length of 12 mm*13 mm.

[0013] Preferably, the base layer, the wave absorbing layer and the microfluidic layer are all made of photosensitive resin.

[0014] Preferably, the liquid metal is a gallium-indium-tin alloy, and in the gallium-indium-tin alloy, the mass percentage of gallium is 68-69%, the mass percentage of indium is 21-22%, and the balance is tin.

[0015] Preferably, the method for preparing the gallium indium tin alloy comprises the following steps:

[0016] S1. Place metallic gallium in a sealed flask according to the ratio, and heat it in a water bath to 50°C to obtain liquid metallic gallium;

[0017] S2. Then put indium and tin into a glass container containing liquid metal gallium, and stir with a glass rod for 2 hours under argon protection until indium and tin are completely dissolved into liquid and mixed evenly, and keep warm at 50°C for 10 minutes to obtain gallium indium tin alloy.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] 1. The frequency-swept liquid metal tunable metamaterial absorber of the present invention has the characteristics of real-time response, frequency-swept continuous tunability, polarization insensitivity, and wide-incident-angle stability;

[0020] 2. The frequency-sweeping liquid metal tunable metamaterial absorber of the present invention is entirely made of photosensitive resin material and manufactured by photocuring, which has high precision, is easy to form, and has a short processing cycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a schematic structural diagram of the frequency-sweepable liquid metal tunable metamaterial absorber of the present invention;

[0022] Figure 2 Schematic diagram of the liquid metal filling state of the frequency-swept liquid metal tunable metamaterial absorber according to Example 1 of the present invention;

[0023] Figure 3 This is a physical picture of the liquid metal filling state of the swept-frequency liquid metal tunable metamaterial absorber according to Example 1 of the present invention;

[0024] Figure 4 The effect of the liquid level on the absorption rate in the swept-frequency liquid metal tunable metamaterial absorber of Example 1 of the present invention;

[0025] Figure 5 The absorption rates of the swept-frequency liquid metal tunable metamaterial absorber according to Example 2 of the present invention at different incident angles for TE waves and TM waves when the liquid metal level is 3 mm. DETAILED DESCRIPTION

[0026] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0027] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any intermediate value within a stated value or stated range and any other stated value or intermediate value within the stated range is also encompassed by the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0028] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The present description and examples are intended to be illustrative only.

[0029] like Figure 1As shown, an embodiment of the present invention provides a frequency-sweeping liquid metal tunable metamaterial absorber, comprising a base layer, a microfluidic layer, and an absorbing layer arranged in sequence from bottom to top. The absorbing layer comprises a plurality of absorbing units distributed in an array, each absorbing unit having an inverted truncated cone-shaped cavity provided therein, and each cavity is filled with liquid metal. The microfluidic layer comprises a plurality of support columns, each support column being positioned between the absorbing unit and the base layer, and a panel is provided on the outer edge of the microfluidic layer.

[0030] When the swept-frequency liquid metal tunable metamaterial absorber of the present invention is in operation, liquid metal is pumped into the microfluidic pipe by a microfluidic pump and first fills the microfluidic layer to form a reflective backing. At this time, the electromagnetic waves are reflected. The purpose of this step is to prove that the absorbing ability comes from the absorbing layer and eliminate the influence of other layers. As the microfluidic layer is filled, the liquid metal enters the inverted cone in the absorbing unit of the absorbing layer, and the absorbing performance appears at this time. The filling amount of liquid metal can be changed through microfluidic technology, and converted into liquid level height according to the model size.

[0031] In a specific embodiment, the thickness of the base layer is 4-6 mm, the thickness of the microfluidic layer is 4-6 mm, and the thickness of the absorbing layer is 2-4 mm.

[0032] In a specific embodiment, the cross-sectional diameter of each microfluidic column is 1-2 mm.

[0033] In a specific embodiment, the cross section of each absorbing unit is a rectangle with a side length of 12 mm*13 mm.

[0034] In a specific embodiment, the base layer, the absorbing layer, and the microfluidic layer are all made of photosensitive resin. The swept-frequency liquid metal tunable metamaterial absorber of the present invention is entirely made of photosensitive resin and manufactured by photocuring, which has high precision, easy molding, and short processing cycle.

[0035] In a specific embodiment, the liquid metal is a gallium-indium-tin alloy, wherein the gallium content by weight is 68-69%, the indium content by weight is 21-22%, and the balance is tin. Due to its dual properties of fluidity and metallicity, liquid metal has applications in stretchable electronics, flexible robots, and microfluidic sensors. Compared to the limited reconfiguration of solid resonant unit cell structures, liquid metal resonant structures can be flexibly reconfigured into various complex forms through pre-designed microfluidic channels, making liquid metal suitable for the fabrication of tunable MM absorbers.

[0036] In a specific embodiment, the method for preparing the gallium indium tin alloy includes the following steps:

[0037] S1. Place metallic gallium in a sealed flask according to the ratio, and heat it in a water bath to 50°C to obtain liquid metallic gallium;

[0038] S2. Then put indium and tin into a glass container containing liquid metal gallium, and stir with a glass rod for 2 hours under argon protection until indium and tin are completely dissolved into liquid and mixed evenly, and keep warm at 50°C for 10 minutes to obtain gallium indium tin alloy.

[0039] The technical effects of the present invention are described below with reference to specific embodiments.

[0040] like Figure 1 As shown, since the absorption test in this experiment needs to test the reflection coefficient by the bow method, in order to ensure the accuracy of the test, the sample is required to have a certain size. An embodiment of the present invention provides a frequency-sweeping liquid metal tunable metamaterial absorber, comprising a base layer, a microfluidic layer and an absorbing layer arranged in sequence from bottom to top, the absorbing layer comprising a plurality of absorbing units distributed in an array, each absorbing unit is provided with an inverted truncated cone-shaped cavity inside, and each cavity is filled with liquid metal, the microfluidic layer comprises a plurality of support columns, each support column is between the absorbing unit and the base layer, and a panel is provided on the outer edge of the microfluidic layer. In this experiment, the frequency-sweeping liquid metal tunable metamaterial absorber The device size is designed to be 180mm*180mm*13mm, the number of its absorbing units is 15*15, the thickness of the base layer is 5mm, the thickness of the microfluidic layer is 5mm, the thickness of the absorbing layer is 3mm, the cross-sectional diameter of each microfluidic column is 2mm, the cross-sectional area of ​​each absorbing unit is a rectangle with a side length of 12mm*13mm, the base layer, the absorbing layer and the microfluidic layer are all made of photosensitive resin, the liquid metal is a gallium indium tin alloy, and the gallium mass percentage of the gallium indium tin alloy is 68-69%, the indium mass percentage is 21-22%, and the balance is tin. The preparation method of the gallium indium tin alloy comprises the following steps:

[0041] S1. Place metallic gallium in a sealed flask according to the ratio, and heat it in a water bath to 50°C to obtain liquid metallic gallium;

[0042] S2. Then put indium and tin into a glass container containing liquid metal gallium, and stir with a glass rod for 2 hours under argon protection until indium and tin are completely dissolved into liquid and mixed evenly, and keep warm at 50°C for 10 minutes to obtain gallium indium tin alloy.

[0043] In order to achieve swept-frequency tuning absorption, liquid metal is connected to a microfluidic pump. Due to its high conductivity, when electromagnetic waves are incident on liquid metal, a large internal current will be generated in the liquid metal. At the same time, the complex electric and magnetic fields of the electromagnetic waves will generate a certain amount of current and eddy current. The electromagnetic energy is converted into heat energy through the loss of current and eddy current, providing effective absorption capacity.

[0044] After the liquid metal enters the cavity, it will form a hemispherical shape on the top of the liquid surface due to its surface tension, such as Figure 2Schematic diagram of the state. As the flow rate of liquid metal increases, the liquid level rises accordingly. Since the cavity is a truncated cone, the area of ​​the liquid level rises. For the incident electromagnetic wave, the cavity is a circular conductive pattern with a continuously increasing radius. Relatively speaking, the whole is a metamaterial with continuously changing absorbing units. The increase in the conductive pattern reduces the non-conductive area between the two absorbing units. For the equivalent circuit of the metamaterial, the capacitance increases. Since the relationship between frequency and capacitance is negatively correlated, the frequency shifts to low frequencies. Figure 3 This is an actual photo of the liquid metal filling state.

[0045] For the structural dimensions selected in this embodiment, the effect of the liquid level change on the frequency is as follows: Figure 4 As shown, from Figure 4 It can be seen that the absorption peak shifts from 18 GHz to 8 GHz, achieving real-time response swept frequency tuning.

[0046] Experimental Example 2

[0047] The only difference from Example 1 is that this example changes the excitation mode of the test antenna and the incident angle of the electromagnetic wave. The results are as follows: Figure 5 As shown, from Figure 5 It can be seen that when the liquid level is 3 mm, for TE and TM polarized waves, the position and intensity of the absorption peak do not change significantly with the change of angle θ, confirming that the metamaterial absorber has polarization insensitivity and wide incident angle characteristics.

[0048] Although the present invention is disclosed as above, the scope of protection disclosed by the present invention is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention, and these changes and modifications will fall within the scope of protection of the present invention.

Claims

1. A frequency-sweeping liquid metal tunable metamaterial absorber, characterized in that: The invention comprises a base layer, a microfluidic layer and an absorbing layer arranged in sequence from bottom to top. The absorbing layer comprises a plurality of absorbing units distributed in an array. An inverted truncated cone-shaped cavity is provided inside each of the absorbing units, and each of the cavities is filled with liquid metal. The microfluidic layer comprises a plurality of support columns, each of which is abutted between the absorbing unit and the base layer. A surrounding plate is provided on the outer edge of the microfluidic layer.

2. The frequency-swept liquid metal tunable metamaterial absorber according to claim 1, characterized in that: The thickness of the base layer is 4-6 mm, the thickness of the microfluidic layer is 4-6 mm, and the thickness of the wave absorbing layer is 2-4 mm.

3. The frequency-swept liquid metal tunable metamaterial absorber according to claim 1, characterized in that: The diameter of the cross section of each support column is 1-2 mm.

4. The frequency-swept liquid metal tunable metamaterial absorber according to claim 1, characterized in that: The cross section of each of the wave absorbing units is a rectangle with a side length of 12 mm*13 mm.

5. The frequency-swept liquid metal tunable metamaterial absorber according to claim 1, characterized in that: The base layer, the wave absorbing layer and the microfluidic layer are all made of photosensitive resin.

6. The frequency-swept liquid metal tunable metamaterial absorber according to claim 1, characterized in that: The liquid metal is a gallium-indium-tin alloy, and in the gallium-indium-tin alloy, the mass percentage of gallium is 68-69%, the mass percentage of indium is 21-22%, and the balance is tin.

7. The frequency-swept liquid metal tunable metamaterial absorber according to claim 6, characterized in that: The preparation method of the gallium indium tin alloy comprises the following steps: S1. Place metallic gallium in a sealed flask according to the ratio, and heat it in a water bath to 50°C to obtain liquid metallic gallium; S2. Then put indium and tin into a glass container containing liquid metal gallium, and stir with a glass rod for 2 hours under argon protection until indium and tin are completely dissolved into liquid and mixed evenly, and keep warm at 50°C for 10 minutes to obtain gallium indium tin alloy.

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