Wave-absorbing material based on dynamic regulation of shape memory alloy and method for preparing graphene capacitor layer

Abstract

The application discloses a wave-absorbing material based on dynamic regulation of shape memory alloy and a method for preparing a graphene capacitor layer, and the material comprises superposed shielding layers, a first shape memory material, a graphene capacitor layer, a second shape memory material and a dielectric material, wherein a subwavelength structure wave-absorbing layer is embedded in the dielectric material; the first shape memory material is connected with the shielding layers and the graphene capacitor layer at two ends respectively, and the second shape memory material is connected with the graphene capacitor layer and the subwavelength structure wave-absorbing layer at two ends respectively; the equivalent square resistance of the graphene capacitor layer can be regulated by applying voltage; and the stretching lengths of the first shape memory material and the second shape memory material can be controlled by applying voltage at two ends of the first shape memory material and the second shape memory material respectively. The application can flexibly switch the working state, adjust the wave-absorbing frequency band and amplitude in real time, has simple structure, strong designability, good adjustable effect on incident electromagnetic waves and can meet the increasingly complex electromagnetic environment requirements.

Description

Technical Field

[0001] This invention relates to the field of electromagnetic wave absorption, and particularly to an absorbing material based on dynamic control of shape memory alloy and a method for preparing a graphene capacitor layer. The absorbing material is a dynamically controllable subwavelength structure absorbing material based on a combination of shape memory alloy and graphene. Background Technology

[0002] In recent years, microwave absorbing materials have attracted widespread attention due to their unique electromagnetic absorption properties, becoming a research hotspot both domestically and internationally. Unlike conventional coated microwave absorbing materials, the absorption effect of subwavelength structural materials on electromagnetic waves mainly depends on their unit structure design. Currently, subwavelength structural microwave absorbing materials mainly operate in a static mode, meaning that once the structure is designed and fabricated, its absorption characteristics are fixed and cannot be dynamically changed to adapt to complex and changing electromagnetic environments. To overcome this limitation, dynamically tunable microwave absorbing materials have emerged. In the microwave field, there are two main methods for dynamic absorption control: one is to load integrated components, such as PIN diodes and varactor diodes, into the subwavelength structural material, and to dynamically control the absorption amplitude or frequency response of the incident electromagnetic wave by changing the bias voltage applied to the integrated component. The other approach is to use two-dimensional materials, such as liquid crystals and ferroelectric materials. However, dynamic absorption control methods based on the above approaches still have many bottlenecks to overcome, such as narrow operating bandwidth, small control range, and limited functionality. Therefore, it is necessary and urgent to design a multifunctional absorbing material with broadband, adjustable frequency, and controllable amplitude to adapt to the increasingly complex electromagnetic environment. Summary of the Invention

[0003] To address the aforementioned issues, the inventors designed a dynamically tunable subwavelength structure absorbing material based on shape memory alloys and graphene as the main materials. The introduction of shape memory material allows for changes in the thickness of the subwavelength structure absorbing material. By combining the subwavelength structure absorbing layer with the graphene capacitor layer, broadband RCS reduction is achieved. Furthermore, by controlling the voltage applied to the graphene capacitor layer and the shape memory material, the absorption amplitude and frequency band can be altered, enabling broadband tunable absorption.

[0004] A microwave absorbing material based on dynamic control of shape memory alloy comprises a stacked shielding layer, a first shape memory material, a graphene capacitor layer, a second shape memory material, and a dielectric material, wherein a subwavelength structure absorbing layer is embedded in the dielectric material; the first shape memory material is connected to the shielding layer and the graphene capacitor layer at both ends, and the second shape memory material is connected to the graphene capacitor layer and the subwavelength structure absorbing layer at both ends.

[0005] The graphene capacitor layer can have its equivalent sheet resistance adjusted by applying voltage; the expansion and contraction lengths of the first shape memory material and the second shape memory material can be controlled by applying voltages to their respective ends.

[0006] Furthermore, both the first shape memory material and the second shape memory material are chromium-nickel shape memory alloy wires, and are respectively coated with insulating varnish and conductive layer from the inside to the outside; when voltage is applied, the positive and negative terminals of the power supply are directly connected to the conductive layer at both ends of the first shape memory material and the second shape memory material.

[0007] Furthermore, both the first shape memory material and the second shape memory material have a helical structure.

[0008] Furthermore, the shielding layer includes one of a metal plate, aluminum foil, or carbon fiber composite material, which has a radar wave shielding effect.

[0009] Furthermore, the dielectric material is one of foam, fiber-reinforced composite materials, or ceramics, which supports and protects the subwavelength structure absorbing layer.

[0010] Furthermore, the graphene capacitor layer has a multilayer structure, including a resistive film, an electrolyte layer, and graphene; electrodes are respectively disposed on the resistive film and the graphene, and are connected to an external circuit through the electrodes. The electrolyte layer is sandwiched between the resistive film and the graphene.

[0011] Furthermore, periodically arranged through holes are processed on the graphene, and the control range of the equivalent sheet resistance of the graphene capacitor layer can be adjusted by adjusting the size of the through holes; the electrolyte layer is made by using a porous polyethylene film as a carrier and fully impregnating it with an ionic liquid.

[0012] Furthermore, the substrate of the subwavelength structure absorbing layer is a polyimide film, and the subwavelength structure pattern can be one or more of the following: square, square ring, circular ring, open ring, etc., or their variations. The period of each unit structure is less than or equal to 1 / 4 of the wavelength of the maximum absorption frequency.

[0013] Another aspect of the present invention discloses a method for preparing a graphene capacitor layer based on the above-mentioned shape memory alloy dynamically controlled microwave absorbing material, comprising the following steps:

[0014] Step 1, Preparation of resistive film electrode: A single-sided adhesive conductive copper foil is attached to the edge of the conductive film for applying voltage;

[0015] Step 2, preparation of the electrolyte layer. This layer uses a porous polyethylene membrane as a carrier. The ionic liquid is evenly coated on both sides of the porous polyethylene membrane to fully impregnate it with the ionic liquid.

[0016] Step 3, Preparation of graphene electrodes: A conductive copper foil or pure gold electrode with adhesive on one side is attached to the edge of the graphene to be used as a voltage loading device;

[0017] Step 4: Assemble the graphene capacitor layer. Align and press the resistive film, electrolyte layer and graphene layer in sequence, and remove air bubbles between layers to form a sandwich-structured graphene capacitor layer.

[0018] Furthermore, in step 1, the conductive film is a polyimide thin film-based conductive film.

[0019] The beneficial effects of this invention are as follows:

[0020] (1) The present invention has a simple structure and strong controllability in processing;

[0021] (2) The subwavelength structure absorbing material proposed in this invention has strong designability, not only with ultra-wideband, but also with adjustable frequency and controllable amplitude, adapting to increasingly complex electromagnetic environments.

[0022] (3) The absorbing material proposed in this invention has the characteristic of functional reconfigurability through the change of the length of the shape memory material and the equivalent sheet resistance of the graphene capacitor layer, and can switch between absorbing and reflecting working states in real time. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of a microwave absorbing material structure based on dynamic control of shape memory alloy in Example 1;

[0024] Figure 2 This is a schematic diagram of the graphene capacitor layer structure in Example 1;

[0025] Figure 3 This is a top view of the graphene in Example 1;

[0026] Figure 4 This is a top view of the subwavelength structure absorbing layer in Example 1;

[0027] Figure 5 The curve showing the relationship between the equivalent sheet resistance of the graphene capacitor layer and the electromagnetic wave reflectivity of the absorbing material based on the dynamic control of shape memory alloy in Example 1 is shown.

[0028] Figure 6 The curve showing the relationship between the length of the shape memory material and the electromagnetic wave reflectivity of the microwave absorbing material dynamically controlled by the shape memory alloy in Example 1;

[0029] Figure 7 The electromagnetic wave reflectivity curve of the absorbing material under the combined effect of the equivalent sheet resistance of the graphene capacitor layer and the length of the shape memory material in Example 1 is shown. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this disclosure clearer, the following detailed description is provided in conjunction with specific embodiments and the accompanying drawings.

[0031] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. The terms “comprising,” “including,” etc., as used herein indicate the presence of the stated features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0032] It should be noted that if the embodiments of this disclosure involve directional indication, the directional indication is only used to explain the relative positional relationship and movement of the components in a specific posture. If the specific posture changes, the directional indication will also change accordingly.

[0033] Figure 1 This is a schematic diagram of the structure of the microwave absorbing material based on dynamic control of shape memory alloy in this disclosure. The microwave absorbing material includes a stacked shielding layer 100, a first shape memory material 201, a graphene capacitor layer 400, a second shape memory material 202, and a dielectric material 302. The dielectric material 302 embeds a subwavelength structure microwave absorbing layer 500. The first shape memory material 201 is connected to the shielding layer 100 and the graphene capacitor layer 400 at both ends, and the second shape memory material 202 is connected to the graphene capacitor layer 400 and the subwavelength structure microwave absorbing layer 500 at both ends.

[0034] The first shape memory material 201 is bonded to the shielding layer 100 and the graphene capacitor layer 400 at both ends using cold adhesive; the second shape memory material 202 is bonded to the graphene capacitor layer 400 and the dielectric material 302 at both ends using cold adhesive.

[0035] The equivalent sheet resistance is regulated by applying voltage to the graphene capacitor layer 400; the expansion and contraction length is controlled by applying voltage to both ends of the first shape memory material 201 and the second shape memory material 202, respectively. The shape memory material is a chromium-nickel shape memory alloy wire, with insulating varnish and conductive layers attached from the inside to the outside. When power is applied, the positive and negative terminals of the power supply are directly connected to the conductive layers at both ends.

[0036] When an external voltage is applied, the first shape memory material 201 and the second shape memory material 202 can control their length extension within a certain voltage range by applying voltage to both ends of the shape memory material. Since the spiral structure has a large deformation range, the first shape memory material 201 and the second shape memory material 202 in Example 1 are spiral structures, but they can also be other feasible structures such as line segments.

[0037] In order to have a wider adjustment band, based on the above embodiments, the minimum height and maximum height of the first shape memory material 201 and the second shape memory material 202 differ by more than 1 time.

[0038] The shielding layer 100 includes one of a metal plate, aluminum foil, or carbon fiber composite material, and has a radar wave shielding effect.

[0039] The dielectric material 302 is one of foam, fiber-reinforced composite materials, and ceramics. It has high strength and surface flatness and plays a supporting and protective role for the subwavelength structure absorbing layer 500.

[0040] Figure 2 This is a schematic diagram of the graphene capacitor layer 400 disclosed herein. The graphene capacitor layer 400 has a multilayer structure, including a resistive film 403, an electrolyte layer 402, and graphene 401. The electrolyte layer 402 is sandwiched between the resistive film 403 and the graphene 401. Electrodes are respectively disposed on the resistive film 403 and the graphene 401, and are connected to an external circuit through the electrodes. The equivalent sheet resistance of the graphene capacitor layer 400 is adjustable in the range of 50 to 1000 Ω / sq. The sheet resistance of the resistive film 403 is between 5000 and 15000 Ω / sq.

[0041] Figure 3 This is a schematic diagram of the graphene 401 structure disclosed herein. Periodically arranged through-holes are fabricated on the graphene, and the equivalent sheet resistance of the graphene capacitor layer can be adjusted by regulating the size of the through-holes. The equivalent sheet resistance of the graphene capacitor layer 400 can be controlled by adjusting the voltage applied between the graphene 401 electrode and the resistive film 403 electrode.

[0042] Figure 4 This is a schematic diagram of the subwavelength structure absorbing layer 500 disclosed herein. The substrate of the subwavelength structure absorbing layer 500 is a polyimide film with a sheet resistance between 20 and 500 Ω / sq. The subwavelength structure pattern can be one or more of the following: cube, square ring, circular ring, open ring, etc., or their variations, but the period of its unit structure must be less than or equal to 1 / 4 of the wavelength of the maximum absorption frequency of the subwavelength structure absorbing layer.

[0043] Based on the above embodiments, the dielectric material 302 is a quartz fiber reinforced cyanate ester composite board with a real part of dielectric constant of 3.1–3.4, a loss of 0.006, and a thickness of 0.4 mm. The subwavelength structure absorbing layer 500 has a substrate thickness of 50 μm, a unit array period of 10 mm, a subwavelength structure pattern of square pieces with a side length of 5 mm, and a subwavelength structure absorbing layer resistance of 105 Ω / sq. The graphene 401 has a thickness of 100 μm and is processed into a square ring structure by laser engraving, with a central square hole size of 5 mm and an array arrangement period of 10 mm.

[0044] By adjusting the height of the shape memory material and the 400 ohm equivalent sheet resistance of the graphene capacitor layer through electrical control, the electromagnetic wave absorption effect and absorption frequency range of the subwavelength structure absorbing material can be controlled.

[0045] Based on the above embodiments, the initial height of the shape memory material is 6mm. When a voltage of 0.6V is applied, the height of the shape memory material increases by 1mm; when a voltage of 1.2V is applied, the height of the shape memory material increases by 6mm; and when a voltage of 1.8V is applied, the height of the shape memory material increases by 8mm. The first shape memory material 201 has h1 = 4mm, and the second shape memory material 202 has h2 = 6mm.

[0046] The preparation of graphene capacitor layer 400 involves the following steps:

[0047] Step 1, Preparation of the resistive film 403 electrode: A single-sided adhesive conductive copper foil is attached to the edge of the conductive film for applying voltage;

[0048] Step 2, preparation of electrolyte layer 402. This layer uses a porous polyethylene membrane as a carrier, and the ionic liquid is evenly coated on both sides of the porous membrane to fully wet it.

[0049] Step 3, Preparation of graphene 401 electrode: A single-sided adhesive conductive copper foil or pure gold electrode is attached to the edge of the graphene to be used as a voltage loading device;

[0050] Step 4: Assembly of graphene capacitor layer 400. The resistive film 403, electrolyte layer 402 and graphene 401 are aligned and pressed together in sequence, and air bubbles between the layers are removed to form a sandwich structure graphene capacitor layer 400.

[0051] Based on the above embodiments, the conductive film in step 1 is a polyimide thin film-based conductive film with a resistance of 5000Ω / sq.

[0052] Electromagnetic simulation calculations were performed on the absorbing material in the above embodiments, and the corresponding electromagnetic wave reflectivity is as follows: Figure 5 As shown, within the 3.7-17GHz frequency band, the electromagnetic wave reflectivity can reach below -10dB, exhibiting a broadband absorption effect. As the equivalent sheet resistance of the graphene capacitor layer 400 changes, its absorption amplitude can be dynamically adjusted. When the sheet resistance of the graphene capacitor layer 400 changes from 200Ω / sq to 800Ω / sq, the reflectivity can change from -18dB to -5dB, with a maximum change range reaching -13dB.

[0053] By adjusting the bias voltage applied across the shape memory material, the height of the material can be changed. For example... Figure 6As shown, by applying voltage, the height of the first shape memory material 201 can be increased from 6mm to 10mm, and the height of the second shape memory material 202 can be increased from 4mm to 8mm. The resonant frequency of this dynamic absorbing material can be varied from 8.5-13.5GHz to achieve the effect of tuned absorption, with an absorption peak value higher than 20dB. Figure 7 This demonstrates the effect of simultaneously adjusting the 400 dB bias voltage of the graphene capacitor layer, showing that the reflectivity can be adjusted to below -5 dB. The dynamic-tunable absorbing material achieves a relative bandwidth of 128.5% in broadband absorption mode, superior to other similar designs.

[0054] Therefore, this metasurface can switch from broadband absorption to narrowband absorption. Combined with graphene resistance control, the absorption amplitude can be controlled in both states, realizing the free switching between the two electromagnetic control functions of absorption and reflection.

[0055] Therefore, the embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above, which are merely illustrative and not restrictive. Those skilled in the art, under the guidance of the present invention, can make many modifications without departing from the spirit and scope of the claims, and all such modifications are within the protection scope of the present invention.

[0056] The parts of this invention not described in detail are well-known to those skilled in the art.

Claims

1. A microwave absorbing material based on dynamic control of shape memory alloy, characterized in that: The material comprises a stacked shielding layer (100), a first shape memory material (201), a graphene capacitor layer (400), a second shape memory material (202), and a dielectric material (302), wherein a subwavelength structure absorbing layer (500) is embedded in the dielectric material (302); the first shape memory material (201) is connected to the shielding layer (100) and the graphene capacitor layer (400) at both ends, and the second shape memory material (202) is connected to the graphene capacitor layer (400) and the subwavelength structure absorbing layer (500) at both ends. The graphene capacitor layer (400) can have its equivalent sheet resistance adjusted by applying a voltage. The expansion and contraction lengths of the first shape memory material (201) and the second shape memory material (202) are controlled by applying voltages to both ends of the first shape memory material (201) and the second shape memory material (202), respectively. The first shape memory material (201) and the second shape memory material (202) are chromium-nickel shape memory alloy wires, and are coated with insulating varnish and conductive layers from the inside to the outside. When the voltage is applied, the positive and negative terminals of the power supply are directly connected to the conductive layers at both ends of the first shape memory material (201) and the second shape memory material (202).

2. The microwave absorbing material based on dynamic control of shape memory alloy according to claim 1, characterized in that, Both the first shape memory material (201) and the second shape memory material (202) have a spiral structure.

3. The microwave absorbing material based on dynamic control of shape memory alloy according to claim 1, characterized in that, The shielding layer (100) comprises one of a metal plate, aluminum foil, or carbon fiber composite material, and has a radar wave shielding effect.

4. The microwave absorbing material based on dynamic control of shape memory alloy according to claim 1, characterized in that, The dielectric material (302) is one of foam, fiber-reinforced composite material and ceramic, which supports and protects the subwavelength structure absorbing layer (500).

5. The microwave absorbing material based on dynamic control of shape memory alloy according to claim 1, characterized in that, The graphene capacitor layer (400) has a multilayer structure, including a resistive film (403), an electrolyte layer (402), and graphene (401); the electrolyte layer (402) is sandwiched between the resistive film (403) and the graphene (401); Electrodes are respectively provided on the resistive film (403) and the graphene (401), and are connected to the external circuit through the electrodes.

6. The microwave absorbing material based on dynamic control of shape memory alloy according to claim 5, characterized in that, The graphene (401) is processed with periodically arranged through holes, and the equivalent sheet resistance of the graphene capacitor layer (400) can be adjusted by adjusting the size of the through holes. The electrolyte layer (402) is made by using a porous polyethylene membrane as a carrier and fully impregnating it with an ionic liquid.

7. The microwave absorbing material based on dynamic control of shape memory alloy according to claim 1, characterized in that, The substrate of the subwavelength structure absorbing layer (500) is a polyimide film, and the subwavelength structure pattern is one or more of the following: square, square ring, circular ring, open ring or their deformation. The period of the subwavelength structure is less than or equal to 1 / 4 of the wavelength of the maximum absorption frequency.

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