Adjustable electromagnetic absorption device based on interdigital electrode-hydrogel composite structure

Abstract

The invention relates to a hydrogel-based wave-absorbing material regulated and controlled through electrochemistry, and belongs to the technical field of flexible electronic and electromagnetic functional materials. The adjustable electromagnetic absorption device based on the interdigital electrode-hydrogel composite structure comprises a metal reflecting layer, a conductive hydrogel layer arranged on the metal reflecting layer and an interdigital electrode pattern constructed on the surface of hydrogel. The conductive hydrogel is doped with graphene oxide and multivalent metal ions, so that the conductivity and polarization capability of the conductive hydrogel are enhanced; the electrode pattern is made of a copper nano material, and a periodic interdigital structure is formed on the surface of the hydrogel by using an ultrasonic spraying technology. A low-voltage electric field is loaded through an electrode, the complex dielectric constant (real part and loss) of the hydrogel is regulated and controlled, and the absorption performance of incident electromagnetic waves is dynamically adjusted. Compared with a traditional wave-absorbing structure, the wave-absorbing structure has good flexibility, light weight and electronic speed control response capability, is suitable for the fields of flexible electronics, wearable equipment, electromagnetic shielding and the like, and has wide application prospects.

Description

Technical Field

[0001] This invention relates to hydrogel-based microwave absorbing materials that utilize electrochemical regulation, belonging to the field of flexible electronic and electromagnetic functional materials technology. Background Technology

[0002] With the rapid popularization of wireless communication, radar systems, and high-frequency electronic equipment, the dense distribution of electromagnetic waves in the environment has become an issue that cannot be ignored. Especially in cities, transportation hubs, and industrial sites, electromagnetic interference accumulates, easily leading to communication distortion, equipment malfunctions, and even potential health risks. To address electromagnetic pollution, researchers have developed various absorbing materials and structures, including composite systems based on magnetic materials, carbon-based materials, and dielectric loss materials. These materials, by controlling their dielectric parameters and permeability, achieve effective absorption and energy dissipation of incident electromagnetic waves, and are widely used in communication base stations, aerospace, and military radar. In recent years, the introduction of metamaterials and frequency selective surfaces (FSS) and other artificial structures has further propelled the development of absorbing performance towards lightweight, wideband, and high-efficiency directions.

[0003] However, most current microwave absorbing materials and structures remain static systems. Their dielectric constant, loss mechanism, and impedance matching state are essentially fixed after fabrication, making real-time adjustment impossible based on external electromagnetic environment, operating frequency changes, or actual operating conditions. This lack of parameter adjustability makes it difficult to meet the dynamic absorption performance requirements of multi-frequency communication, intelligent stealth, and reconfigurable electronic systems. To achieve a certain degree of controllability, existing research has attempted to adjust the dielectric properties of hydrogel-based microwave absorbing materials by introducing conductive fillers (such as carbon materials and metal nanowires), changing water content, or applying mechanical strain. However, these methods essentially still rely on passive changes in material structure or composition, resulting in limited controllability, slow response speeds, and difficulty in achieving reversible, continuous, and precise microwave absorption tuning. Therefore, they are insufficient to meet the requirements of "real-time," "on-demand," and "controllable" modulation in practical applications. Against this backdrop, a key advantage of hydrogels truly emerges—their internal migratory ion system and highly electric field-sensitive three-dimensional network structure. When an external electric field or electrochemical bias is applied, ion redistribution, enhanced local polarization, and reversible reconstruction of the network structure occur in the hydrogel, leading to significant changes in dielectric constant, conductivity, and loss factor. This internal tunability driven by electrochemical processes makes it possible to construct a "electric stimulation-dielectric tuning-wave absorption response" chain.

[0004] This patent develops a novel hydrogel electromagnetic control structure that is simple in structure, flexible in regulation, fast in response, and easy to fabricate, in order to meet the application requirements of flexibility, low power consumption, and high integration. Specifically, it combines interdigital electrodes with an electroresponsive hydrogel to create a novel microwave absorbing structure. Researchers combine an electrode structure with a specific geometric design with the hydrogel, and use an external electric field to achieve real-time regulation of the hydrogel's electrical parameters, thereby indirectly controlling its electromagnetic response behavior. Summary of the Invention

[0005] 1. Objective of this invention

[0006] This invention aims to provide a tunable electromagnetic absorption device based on an interdigital electrode-hydrogel composite structure. By constructing a synergistic system of interdigital electrodes and electroresponsive hydrogels, active modulation of electromagnetic wave absorption performance can be achieved. This structure combines flexibility, low cost, and good electric field responsiveness, and has broad prospects for engineering applications.

[0007] 2. Key Technical Points of the Invention

[0008] To achieve the above objectives, the present invention provides a tunable electromagnetic absorption device based on an interdigitated electrode-hydrogel composite structure, characterized in that it comprises:

[0009] (1) An interdigitated electrode array is disposed on the upper surface of the structure as an electric field application unit to generate a spatially controllable electric field in the hydrogel layer;

[0010] (2) A hydrogel layer is disposed below the electrode as a dielectric response unit, whose ionic conductivity and dielectric constant undergo reversible changes under the action of the electric field;

[0011] (3) A metal reflective layer is set at the bottom of the structure as an electromagnetic wave reflective unit to block electromagnetic wave transmission and enhance absorption performance.

[0012] This invention applies an electric field to the hydrogel layer using interdigitated electrodes, causing changes in ion migration or distribution within the hydrogel. This forms an electrical bilayer structure at the electrode / hydrogel interface, significantly affecting the hydrogel's conductivity and polarization characteristics, and consequently leading to controllable adjustment of its complex dielectric constant (including the real part and loss). Under the influence of electromagnetic waves, the overall input impedance of the structure changes with the dielectric properties of the hydrogel, thereby achieving dynamic control of performance parameters such as absorption frequency and absorption intensity.

[0013] The present invention also provides a method for fabricating the aforementioned tunable hydrogel-based microwave absorbing device, characterized by comprising the following steps:

[0014] a) Preparation of hydrogel layer

[0015] A. Acrylamide (AAm) is added to deionized water at a mass percentage of 10 wt%, and crosslinking agent N,N'-methylenebisacrylamide (MBAA) 0.1 wt% and initiator ammonium persulfate (APS) 0.3 wt% are added. Stir thoroughly to form a homogeneous solution.

[0016] B. Disperse Fe3O4 and GO powder in water at a set mass ratio, and then sonicate to form a uniform composite dispersion. Add the prepared dispersion to the above liquid and stir evenly. If necessary, further sonicate to assist dispersion so that the functional nanomaterials are evenly distributed in the solution.

[0017] C. Inject the mixed solution into the mold, place it in an oven, and heat it at 60°C to induce a polymerization and cross-linking reaction. After the reaction is complete, demold the mold to obtain a composite hydrogel material with microwave absorption properties.

[0018] b) Fabrication of the metal reflective layer

[0019] The preferred metal layer is copper or aluminum foil with a thickness of 0.1 mm. The cross-linked conductive hydrogel is removed, cut to a size that matches the metal reflective layer, and fixed with a biocompatible adhesive to ensure tight contact and interface stability.

[0020] c) Fabrication of interdigitated electrode arrays

[0021] Interdigitated metal electrode patterns were formed on the surface of a conductive hydrogel using ultrasonic spraying. First, high-purity copper nanoparticles were dispersed in ethanol, with a stabilizer added to prevent agglomeration, forming a uniform spray suspension. Then, the prepared solution was loaded into an ultrasonic spraying system, where the liquid was atomized into micron-sized droplets by high-frequency vibration (typically 20–120 kHz) of a piezoelectric transducer. Using ultrasonic spraying equipment (atomization frequency 120 kHz, nozzle-to-substrate distance approximately 3 cm), after path setup, multiple reciprocating sprays were performed at a speed of 10 mm / s to control the electrode thickness to approximately 18–20 mm. The interdigitated fingers are 10-15 mm wide. After curing, the electrode pattern bonds tightly to the hydrogel surface, forming a stable contact interface to ensure uniform electric field loading and stable response.

[0022] The present invention provides an tunable microwave absorbing composite structure based on conductive hydrogel, which has a novel structure, reasonable configuration, and good flexibility and electromagnetic response capability. Attached Figure Description Figure 1 This is a schematic diagram of a tunable electromagnetic absorption device based on an interdigital electrode-hydrogel composite structure. By introducing copper material to fabricate patternable interdigital electrodes, the electric field distribution inside the hydrogel can be effectively controlled, thereby changing its dielectric parameters and dynamically adjusting the electromagnetic absorption performance of the structure.

[0023] This structure achieves microwave absorption performance while exhibiting good deformability, low processing temperature, and biocompatibility, making it suitable for applications such as flexible electronics, wearable devices, and intelligent electromagnetic shielding. Compared with traditional metal / dielectric microwave absorption structures, it has advantages such as being lightweight, tunable, and highly integrated, and its fabrication method is simple and highly scalable.

[0024] 3. Embodiments of the present invention

[0025] The following describes embodiments of the method of the present invention:

[0026] Example 1

[0027] A tunable electromagnetic absorption device based on an interdigitated electrode-hydrogel composite structure is fabricated as follows:

[0028] In this embodiment, firstly, 10 wt% of acrylamide monomer, 0.1 wt% of crosslinking agent N,N'-methylenebisacrylamide (MBAA), and 0.3 wt% of initiator ammonium persulfate (APS) were added to deionized water and stirred with a magnetic stirrer for 30 min until clear. Then, 0.4 wt% of graphene oxide (GO) and 1.0 wt% of Fe3O4 were mixed in deionized water and ultrasonically treated to form a uniform composite dispersion. This dispersion was then mixed with the above liquid, injected into a mold, and polymerized in a 60°C oven for 4 h to form a soft, 3 mm thick hydrogel. The resulting hydrogel was soaked in deionized water for 24 h to remove impurities, cut into 200 mm × 200 mm rectangular blocks, and laminated with copper foil of the same size as a reflective substrate. Subsequently, copper nanomaterials were deposited on the surface of the hydrogel using ultrasonic spraying technology to form an interdigitated electrode pattern, with an interdigitation width of 10 mm and a spacing of 5 mm. The total length covers the effective area of ​​the hydrogel. After spraying, it is dried at room temperature for 2 hours to ensure good electrode adhesion and the formation of a stable conductive path, ultimately obtaining an interdigitated hydrogel-based microwave absorbing device.

[0029] Example 2

[0030] A tunable electromagnetic absorption device based on an interdigitated electrode-hydrogel composite structure is fabricated as follows:

[0031] In this embodiment, firstly, 10 wt% of acrylamide monomer, 0.1 wt% of crosslinking agent N,N'-methylenebisacrylamide (MBAA), and 0.3 wt% of initiator ammonium persulfate (APS) were added to deionized water and stirred with a magnetic stirrer for 30 min until clear. Then, 0.4 wt% of graphene oxide (GO) and 1.0 wt% of Fe3O4 were mixed in deionized water and ultrasonically treated to form a uniform composite dispersion. This dispersion was then mixed with the above liquid, injected into a mold, and polymerized in a 60°C oven for 4 h to form a soft, 3 mm thick hydrogel. The resulting hydrogel was soaked in deionized water for 24 h to remove impurities, cut into 200 mm × 200 mm rectangular blocks, and laminated with copper foil of the same size as a reflective substrate. Subsequently, copper nanomaterials were deposited on the surface of the hydrogel using ultrasonic spraying technology to form an interdigitated electrode pattern with an interdigitation width of 15. The spacing is 5 The total length covers the effective area of ​​the hydrogel. After spraying, it is dried at room temperature for 2 hours to ensure good electrode adhesion and the formation of a stable conductive path, ultimately obtaining an interdigitated hydrogel-based microwave absorbing device.

[0032] Example 3

[0033] A tunable electromagnetic absorption device based on an interdigitated electrode-hydrogel composite structure is fabricated as follows:

[0034] In this embodiment, firstly, 10 wt% of acrylamide monomer, 0.1 wt% of crosslinking agent N,N'-methylenebisacrylamide (MBAA), and 0.3 wt% of initiator ammonium persulfate (APS) were added to deionized water and stirred with a magnetic stirrer for 30 min until clear. Then, 0.4 wt% of graphene oxide (GO) and 1.0 wt% of Fe3O4 were mixed in deionized water and ultrasonically treated to form a uniform composite dispersion. This dispersion was then mixed with the above liquid, injected into a mold, and polymerized in a 60°C oven for 4 h to form a soft, 3 mm thick hydrogel. The resulting hydrogel was soaked in deionized water for 24 h to remove impurities, cut into 200 mm × 200 mm rectangular blocks, and laminated with copper foil of the same size as a reflective substrate. Subsequently, copper nanomaterials were deposited on the surface of the hydrogel using ultrasonic spraying technology to form an interdigitated electrode pattern with an interdigitation width of 10 mm. The spacing is 10. The total length covers the effective area of ​​the hydrogel. After spraying, it is dried at room temperature for 2 hours to ensure good electrode adhesion and the formation of a stable conductive path, ultimately obtaining an interdigitated hydrogel-based microwave absorbing device.

[0035] Example 4

[0036] A tunable electromagnetic absorption device based on an interdigitated electrode-hydrogel composite structure is fabricated as follows:

[0037] In this embodiment, firstly, 10 wt% of monomeric acrylamide, 0.1 wt% of crosslinking agent N,N'-methylenebisacrylamide (MBAA), and 0.3 wt% of initiator ammonium persulfate (APS) were added to deionized water and stirred with a magnetic stirrer for 30 min until clear. Then, 0.8 wt% of graphene oxide (GO) and 1.0 wt% of Fe3O4 were mixed in deionized water and ultrasonically treated to form a uniform composite dispersion. This dispersion was then mixed with the above liquid, injected into a mold, and polymerized in a 60°C oven for 4 h to form a soft, 3 mm thick hydrogel. The resulting hydrogel was soaked in deionized water for 24 h to remove impurities, cut into 200 mm × 200 mm rectangular blocks, and laminated with copper foil of the same size as a reflective substrate. Subsequently, copper nanomaterials were deposited on the surface of the hydrogel using ultrasonic spraying technology to form an interdigitated electrode pattern with an interdigitation width of 10 mm. The spacing is 5 The total length covers the effective area of ​​the hydrogel. After spraying, it is dried at room temperature for 2 hours to ensure good electrode adhesion and the formation of a stable conductive path, ultimately obtaining an interdigitated hydrogel-based microwave absorbing device.

[0038] Example 5

[0039] A tunable electromagnetic absorption device based on an interdigitated electrode-hydrogel composite structure is fabricated as follows:

[0040] In this embodiment, firstly, 10 wt% of acrylamide monomer, 0.1 wt% of crosslinking agent N,N'-methylenebisacrylamide (MBAA), and 0.3 wt% of initiator ammonium persulfate (APS) were added to deionized water and stirred with a magnetic stirrer for 30 min until clear. Then, 0.4 wt% of graphene oxide (GO) and 1.5 wt% of Fe3O4 were mixed in deionized water and ultrasonically treated to form a uniform composite dispersion. This dispersion was then mixed with the above liquid, injected into a mold, and polymerized in a 60°C oven for 4 h to form a soft, 3 mm thick hydrogel. The resulting hydrogel was soaked in deionized water for 24 h to remove impurities, cut into 200 mm × 200 mm rectangular blocks, and laminated with copper foil of the same size as a reflective substrate. Subsequently, copper nanomaterials were deposited on the surface of the hydrogel using ultrasonic spraying technology to form an interdigitated electrode pattern with an interdigitation width of 10 mm. The spacing is 5 The total length covers the effective area of ​​the hydrogel. After spraying, it is dried at room temperature for 2 hours to ensure good electrode adhesion and the formation of a stable conductive path, ultimately obtaining an interdigitated hydrogel-based microwave absorbing device.

[0041] Example 6

[0042] A tunable electromagnetic absorption device based on an interdigitated electrode-hydrogel composite structure is fabricated as follows:

[0043] In this embodiment, firstly, 10 wt% of acrylamide monomer, 0.1 wt% of crosslinking agent N,N'-methylenebisacrylamide (MBAA), and 0.3 wt% of initiator ammonium persulfate (APS) were added to deionized water and stirred with a magnetic stirrer for 30 min until clear. Then, 0.4 wt% of graphene oxide (GO) and 1.0 wt% of Fe3O4 were mixed in deionized water and ultrasonically treated to form a uniform composite dispersion. This dispersion was then mixed with the above liquid, injected into a mold, and polymerized in a 60°C oven for 4 h to form a soft, 2 mm thick hydrogel. The resulting hydrogel was soaked in deionized water for 24 h to remove impurities, cut into 200 mm × 200 mm rectangular blocks, and laminated with copper foil of the same size as a reflective substrate. Subsequently, copper nanomaterials were deposited on the surface of the hydrogel using ultrasonic spraying technology to form an interdigitated electrode pattern with an interdigitation width of 10 mm. The spacing is 5 The total length covers the effective area of ​​the hydrogel. After spraying, it is dried at room temperature for 2 hours to ensure good electrode adhesion and the formation of a stable conductive path, ultimately obtaining an interdigitated hydrogel-based microwave absorbing device.

[0044] Example 7

[0045] A tunable electromagnetic absorption device based on an interdigitated electrode-hydrogel composite structure is fabricated as follows:

[0046] In this embodiment, firstly, 10 wt% of acrylamide monomer, 0.1 wt% of crosslinking agent N,N'-methylenebisacrylamide (MBAA), and 0.3 wt% of initiator ammonium persulfate (APS) were added to deionized water and stirred with a magnetic stirrer for 30 min until clear. Then, 0.4 wt% of graphene oxide (GO) and 1.0 wt% of Fe3O4 were mixed in deionized water and ultrasonically treated to form a uniform composite dispersion. This dispersion was then mixed with the above liquid, injected into a mold, and polymerized in a 60°C oven for 4 h to form a soft, 5 mm thick hydrogel. The resulting hydrogel was soaked in deionized water for 24 h to remove impurities, cut into 200 mm × 200 mm rectangular blocks, and laminated with copper foil of the same size as a reflective substrate. Subsequently, copper nanomaterials were deposited on the surface of the hydrogel using ultrasonic spraying technology to form an interdigitated electrode pattern with an interdigitation width of 10 mm. The spacing is 5 The total length covers the effective area of ​​the hydrogel. After spraying, it is dried at room temperature for 2 hours to ensure good electrode adhesion and the formation of a stable conductive path, ultimately obtaining an interdigitated hydrogel-based microwave absorbing device.

Claims

1. This invention provides an tunable electromagnetic absorption device based on an interdigitated electrode-hydrogel composite structure, characterized in that, include: (1) An electrode array is disposed on the upper surface of the structure as an electric field application unit to generate a spatially controllable electric field in the hydrogel layer; (2) A hydrogel layer is disposed below the electrode as a dielectric response unit, whose ionic conductivity and dielectric constant undergo reversible changes under the action of the electric field; (3) A metal reflective layer is set at the bottom of the structure as an electromagnetic wave reflective unit to block electromagnetic wave transmission and enhance absorption performance.

2. The structure according to claim 1, characterized in that, The interdigitated electrode structure consists of multiple parallel conductive strips with uniform spacing between adjacent electrodes and an appropriate electrode width and spacing to form an effective electric field in the hydrogel layer.

3. The structure according to claim 1, characterized in that, The hydrogel is a hydrogel material with ion migration ability or electronic conductivity, and the conductivity originates from ions, conductive polymers or functional nanofillers.

4. The structure according to claim 1, characterized in that, The conductive electrode is formed by spraying and the material is a metal nanomaterial, preferably a copper nanomaterial.

5. A method for fabricating the microwave absorbing device according to claim 1, characterized in that, Includes the following steps: 1) Preparation of hydrogel layer A. Acrylamide (AAm) is added to deionized water at a mass percentage of 10 wt%, and crosslinking agent N,N'-methylenebisacrylamide (MBAA) 0.1 wt% and initiator ammonium persulfate (APS) 0.3 wt% are added. Stir thoroughly to form a homogeneous solution. B. Disperse Fe3O4 and GO powder in water at a set mass ratio, and then sonicate to form a uniform composite dispersion. Add the prepared dispersion to the above liquid and stir evenly. If necessary, further sonicate to assist dispersion so that the functional nanomaterials are evenly distributed in the solution. C. Inject the mixed solution into the mold, place it in an oven, and heat it at 60°C to induce a polymerization and cross-linking reaction. After the reaction is complete, demold the mold to obtain a composite hydrogel material with microwave absorption properties. 2) Fabrication of the metal reflective layer The preferred metal layer is copper foil or aluminum foil with a thickness of 0.1 mm. The cross-linked conductive hydrogel is taken out, cut to a size that matches the metal reflective layer, and fixed with a biocompatible adhesive to ensure tight contact and interface stability. 3) Fabrication of interdigitated electrode arrays An interdigitated metal electrode pattern is formed on the surface of a conductive hydrogel by ultrasonic spraying. First, high-purity copper nanoparticles are dispersed in ethanol, and a stabilizer is added to prevent agglomeration, forming a uniform spray suspension. Then, the prepared solution is loaded into an ultrasonic spraying system, and the liquid is atomized into micron-sized droplets by high-frequency vibration (usually 20–120 kHz) of a piezoelectric transducer. Using ultrasonic spraying equipment (atomization frequency 120 kHz, nozzle-to-substrate distance of about 3 cm), after the path is set, multiple reciprocating sprays are performed at a speed of 10 mm / s, controlling the electrode thickness to be about 18–20 μm and the interdigitated width to be 10–15 mm. After the electrode pattern is cured, it is tightly bonded to the surface of the hydrogel, forming a stable contact interface, ensuring uniform electric field loading and response stability.

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