A flexible wave-absorbing resin-based composite material, a preparation method and application thereof

Abstract

The application discloses a preparation method of a flexible wave-absorbing resin-based composite material, which comprises the following steps: mixing a flexible photosensitive resin with multi-walled carbon nanotubes and spherical carbonyl iron, and performing ultrasonic treatment and mechanical stirring to obtain a flexible wave-absorbing resin-based composite slurry; and then performing light curing 3D printing to obtain the flexible wave-absorbing resin-based composite material. The application further discloses a method for preparing a multi-stage honeycomb structure flexible wave-absorber for high-frequency application based on the flexible wave-absorbing resin-based composite material. The preparation method is simple in operation, fast in forming speed and low in cost, and the prepared multi-stage honeycomb structure flexible wave-absorber has excellent wave-absorbing performance, and even at a high bending angle (150°), the multi-stage honeycomb structure flexible wave-absorber still has low reflection loss. In addition, the material has the advantages of high flexible deformation, self-recovery and no crease damage in repeated bending, greatly improves the environmental adaptability, and can be applied in the fields of intelligent wearable functional devices, intelligent electronics or intelligent driving and the like.

Description

Technical Field

[0001] This invention relates to the field of composite material technology, and in particular to a flexible microwave absorbing resin-based composite material, its preparation method, and its application. Background Technology

[0002] With the rapid development of wireless communication, 5G, the fifth-generation mobile communication technology, has been widely used. However, due to the severe overload of traditional communication frequency bands, they cannot provide the expected transmission rates. 5G and future communication systems will utilize frequency bands closer to millimeter waves and even submillimeter waves. Based on reliable wireless communication systems, fields such as smart electronics, wearable devices, and autonomous driving are also developing rapidly, bringing great convenience to smart living. However, the resulting electromagnetic radiation has a significant negative impact on the reliability of circuits and electronic devices, as well as human health. Traditional rigid absorbing materials, due to their large volume and inflexibility, cannot meet the requirements of lightweight and highly flexible smart wearable devices. Therefore, there is an urgent need to develop lightweight flexible absorbers for microwave absorption and electromagnetic interference resistance.

[0003] Furthermore, in terms of materials, most microwave absorbers currently employ absorbing fillers based on magnetic or dielectric losses. While single-component absorbers possess a certain absorption capacity, their electromagnetic wave attenuation mechanism is singular, and their electromagnetic parameters are poorly controllable, failing to meet the requirements of an ideal microwave absorber. Therefore, there is an urgent need to composite magnetic and dielectric loss materials to fabricate high-performance absorbers. Structurally, traditional planar absorbing materials struggle to maintain good absorption performance at high frequencies. To meet the demands of high-frequency absorbing materials, novel absorbing structures are urgently needed. In summary, there is a need to develop a lightweight, flexible absorber with comprehensive characteristics such as "wide bandwidth, high strength, thinness, lightness, and flexibility" at high frequencies to meet the demands of high-performance flexible absorbers in fields such as smart electronics, smart wearables, and autonomous driving. Summary of the Invention

[0004] The purpose of this invention is to provide a flexible microwave absorbing resin-based composite material, its preparation method, and its application, so as to solve the above-mentioned problems existing in the prior art.

[0005] To achieve the above objectives, the present invention provides the following solution:

[0006] One of the technical solutions of the present invention: a method for preparing a flexible microwave absorbing resin-based composite material, comprising the following steps:

[0007] (1) The flexible photosensitive resin is mixed with multi-walled carbon nanotubes and spherical carbonyl iron, subjected to ultrasonic treatment, and then mechanically stirred to obtain a flexible microwave absorbing resin-based composite slurry.

[0008] (2) The flexible microwave absorbing resin-based composite slurry described in step (1) is subjected to photocuring 3D printing to obtain the flexible microwave absorbing resin-based composite material.

[0009] Further, in step (1), the amount of multi-walled carbon nanotubes added is 0.25 to 0.75 wt. of the sum of the mass of the flexible photosensitive resin and the multi-walled carbon nanotubes, and the amount of spherical carbonyl iron added is 25 to 50 wt. of the sum of the mass of the flexible photosensitive resin and the spherical carbonyl iron.

[0010] Further, the flexible photosensitive resin in step (1) comprises: 87-97 wt.% aliphatic polyurethane acrylic acid, 0-10 wt.% acryloylmorpholine, 0-3 wt.% diphenyl-(2,4,6-trimethylbenzoyl)phosphorus oxychloride, and 0.1-0.3 wt.% UV black pigment; the ultrasonic treatment time is 30 min; the mechanical stirring speed is 60 rpm for 30 min; the photopolymerization 3D printing process parameters in step (2) are: light intensity 10000~20000 μw / cm 2 The first layer exposure time is 5-22s, and the exposure time for the remaining layers is 3-20s. The curing thickness of each layer is 25μm.

[0011] The second technical solution of the present invention: a flexible microwave absorbing resin-based composite material prepared according to the above-mentioned preparation method of flexible microwave absorbing resin-based composite material.

[0012] The third technical solution of the present invention: the application of the above-mentioned flexible absorbing resin-based composite material in electromagnetic shielding.

[0013] Furthermore, the flexible microwave-absorbing resin-based composite material is used to absorb electromagnetic waves.

[0014] The fourth technical solution of the present invention: the application of the above-mentioned flexible absorbing resin-based composite material in the preparation of a multi-level honeycomb structure flexible absorber for high-frequency applications.

[0015] The fifth technical solution of the present invention: a method for fabricating a multi-level honeycomb structure flexible absorber for high-frequency applications, specifically including the following steps:

[0016] S1. The flexible photosensitive resin is mixed with multi-walled carbon nanotubes and spherical carbonyl iron, subjected to ultrasonic treatment and mechanical stirring to obtain a flexible microwave absorbing resin-based composite slurry; the flexible microwave absorbing resin-based composite slurry is subjected to photocuring 3D printing to obtain the flexible microwave absorbing resin-based composite material.

[0017] S2. Test the electromagnetic parameters of the flexible microwave absorbing resin-based composite material prepared in step S1 under electromagnetic waves of 1-40GHz.

[0018] S3. Using the electromagnetic parameters obtained in step S2 and combined with the theoretical model, the electromagnetic parameters of the flexible microwave absorbing resin-based composite material under 75-110GHz electromagnetic waves are obtained by fitting the parameters.

[0019] S4. Import the electromagnetic parameters of the flexible microwave absorbing resin-based composite material obtained in step S3 under 75-110GHz electromagnetic waves into CST Studio Suite 2022 software, and fit to obtain the optimal size of the multi-level honeycomb structure.

[0020] S5. Repeat the preparation steps of step S1, using the multi-level honeycomb structure obtained in step S4 as a 3D printing model, and perform photopolymerization 3D printing to obtain the multi-level honeycomb structure flexible absorber for high-frequency applications.

[0021] Furthermore, "high frequency" in the context of high-frequency applications refers to electromagnetic waves with a frequency of 75-110 GHz.

[0022] Furthermore, the multi-level honeycomb structure includes several hexagonally distributed absorbing units. Each absorbing unit includes an inner hexagonal prism and an outer hexagonal prism arranged correspondingly inside and outside. The edges of the inner and outer hexagonal prisms are arranged correspondingly, and a connecting plate is fixedly connected between the corresponding edges. The wall thickness of any face of the outer hexagonal prism is t, the wall thickness of any face of the inner hexagonal prism is t / 2, the wall thickness of the connecting plate is t / 2, and the distance from the central axis of the inner hexagonal prism to the inner edge of the inner hexagonal prism is a / 2. The outer hexagonal prism... The distance from the central axis of the inner hexagonal prism to the inner corner of the outer hexagonal prism is 'a'. The central axis of the inner hexagonal prism coincides with the central axis of the outer hexagonal prism. The inner side length of the outer hexagonal prism is 'a'. The heights of the inner hexagonal prism, the outer hexagonal prism, and the connecting plate are all 'h'. The multi-level honeycomb structure is composed of repeating unit arrays of the absorbing unit in the longitudinal and transverse directions. That is, six identical absorbing units are arranged circumferentially in one absorbing unit (one identical absorbing unit is connected to each face of the outer hexagonal prism). Two adjacent absorbing units share one outer hexagonal prism face at their junction.

[0023] Furthermore, the dimensions mentioned in step S4 include the inner side length a, wall thickness t, and height h of the outer hexagonal prism.

[0024] Further, in step S2, a vector network analyzer is used to test the electromagnetic parameters of the flexible microwave absorbing resin-based composite material obtained in step S1 under electromagnetic waves of 1-40 GHz. The electromagnetic parameters are specifically the real part of the dielectric constant, the imaginary part of the dielectric constant, the dielectric loss, the real part of the permeability, the imaginary part of the permeability, and the magnetic loss.

[0025] Furthermore, in step S2, the electromagnetic parameters of the flexible microwave absorbing resin-based composite material under 1-40GHz electromagnetic waves were tested in three bands: 1-18GHz, 18-26.5GHz, and 26.5-40GHz. The electromagnetic parameters of the 1-18GHz band were tested using the coaxial method, with the sample shape being a concentric ring, and the dimensions being an inner diameter of 3mm, an outer diameter of 7mm, and a height of 2mm. The electromagnetic parameters of the 18-26.5GHz and 26.5-40GHz bands were tested using the waveguide method, with the sample shape being a cuboid. Specifically, the sample size for the 18-26.5GHz band was 10.67mm × 4.32mm × 2mm, and the sample size for the 26.5-40GHz band was 7.12mm × 3.56mm × 2mm. In step S1, flexible microwave absorbing resin-based composite slurry with the same composition and the same photocuring 3D printing parameters (light intensity, first layer exposure time, exposure time of subsequent layers, and curing thickness of each layer) were used to print flexible microwave absorbing resin-based composite materials with different morphologies using different 3D printing models (concentric rings and cuboids). Then, in step S2, the electromagnetic parameters of the flexible microwave absorbing resin-based composite materials with the corresponding morphologies were tested using the corresponding methods in the corresponding wavebands.

[0026] Furthermore, the theoretical models mentioned in step S3 are the Cole-Cole model and the Lorentzian model, as shown in formula (1) and formula (2) respectively:

[0027]

[0028]

[0029] Where, ε s ε is the static dielectric constant. ∞ μ is the limiting value of the dielectric constant at high frequencies. s f is the static permeability, j is the imaginary part in units, and f is the static permeability. r The resonant frequency is γ, α and k are fitting parameters with values ​​between 0 and 1, and γ is an empirical fitting parameter.

[0030] The real and imaginary parts of the dielectric constant in the electromagnetic parameters are fitted using the Cole-Cole model. The dielectric loss is calculated by the ratio of the real and imaginary parts of the dielectric constant. The real and imaginary parts of the magnetic permeability are fitted using the Lorentzian model. The magnetic loss is calculated by the ratio of the real and imaginary parts of the magnetic permeability.

[0031] Furthermore, the "repeating the preparation step of step S1" mentioned in step S5 refers to using the same flexible microwave absorbing resin-based composite slurry with the same composition as when preparing the flexible microwave absorbing resin-based composite material in step S1, using the same photocuring 3D printing parameters (light intensity, first layer exposure time, exposure time of subsequent layers, and curing thickness of each layer) when photocuring 3D printing the flexible microwave absorbing resin-based composite material obtained in step S1, and printing with a different 3D printing model (multi-level honeycomb structure) than when preparing the flexible microwave absorbing resin-based composite material in step S1.

[0032] The sixth technical solution of the present invention: a multi-level honeycomb structure flexible absorber for high-frequency applications prepared according to the above preparation method.

[0033] The seventh technical solution of the present invention: the application of the above-mentioned multi-level honeycomb structure flexible absorber for high-frequency applications in smart wearable functional devices, smart electronics or intelligent driving.

[0034] The present invention discloses the following technical effects:

[0035] (1) The present invention provides a method for preparing a flexible microwave absorbing resin-based composite material. The microwave absorbing agent system is a composite of spherical carbonyl ferromagnetic loss material and multi-walled carbon nanotube dielectric loss material. This microwave absorbing agent system can enhance the magnetic-dielectric synergistic effect, further increase the multiple reflection loss of electromagnetic waves, and improve the microwave absorption performance of the composite material.

[0036] (2) This invention provides a method for preparing a multi-level honeycomb structure flexible absorber for high-frequency applications based on a flexible absorbing resin-based composite material. The method involves measuring the electromagnetic parameters of the flexible absorbing resin-based composite material under low-frequency (1-40 GHz) electromagnetic waves, and then using a theoretical model to fit its electromagnetic parameters under high-frequency (75-110 GHz) electromagnetic waves. Based on these high-frequency (75-110 GHz) electromagnetic parameters, the optimal multi-level honeycomb structure parameters are designed. This multi-level honeycomb structure is then used as a 3D printing model for photopolymerization 3D printing to obtain the multi-level honeycomb structure flexible absorber for high-frequency applications. This method solves the problem of obtaining high-frequency electromagnetic parameters through measurement. The high reliability of this method is confirmed by comparing measured and fitted values, providing new ideas and important references for the design and preparation of high-frequency absorbing materials and electromagnetic shielding materials.

[0037] (3) The flexible absorbing resin-based composite material and the multi-level honeycomb flexible absorber for high-frequency applications prepared by this invention both have the advantages of high flexibility, self-recovery, and no crease damage during repeated bending. Among them, the multi-level honeycomb flexible absorber still maintains excellent absorption performance at high bending angles (150°).

[0038] (4) The preparation process of the flexible microwave absorbing resin-based composite material provided by this invention differs from traditional preparation processes. It adopts photopolymerization 3D printing, which has the advantages of fast molding speed, high dimensional accuracy, and the ability to prepare complex structures. It provides a new approach for the rapid prototyping and mass production of high-performance flexible microwave absorbers with complex structures. Attached Figure Description

[0039] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0040] Figure 1 The electromagnetic parameters of the flexible microwave absorbing resin-based composite materials prepared in Examples 1-6 of this invention under low-frequency (1-40GHz) electromagnetic waves are shown.

[0041] Figure 2 The electromagnetic parameters of the flexible microwave absorbing resin-based composite materials prepared in Examples 1 to 6 of this invention under high-frequency (75-110GHz) electromagnetic waves are shown.

[0042] Figure 3 This is a comparison chart of the measured and calculated reflection loss of the flexible absorbing resin-based composite material prepared in Example 3 of the present invention.

[0043] Figure 4 The simulation design structure and parameter diagram of the multi-level honeycomb structure obtained in Embodiment 11 of the present invention are shown below.

[0044] Figure 5 This is a diagram illustrating the multi-level honeycomb structure flexible absorber for high-frequency applications, prepared according to Embodiment 12 of the present invention, and its flexibility.

[0045] Figure 6 The reflection loss of the multi-level honeycomb structure flexible absorber for high-frequency applications prepared in Embodiment 12 of the present invention under multiple bending angles. Detailed Implementation

[0046] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0047] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0048] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0049] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be obvious to those skilled in the art. This application specification and embodiments are merely exemplary.

[0050] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0051] The flexible photosensitive resin used in the following examples and comparative examples is the commercially available flexible photosensitive resin LITLIQ FX60 (composed of: 92 wt.% aliphatic polyurethane acrylic acid, 5 wt.% acryloylmorpholine, 2.7 wt.% diphenyl-(2,4,6-trimethylbenzoyl)phosphorus oxychloride, and 0.3 wt.% UV black pigment), provided by Dongguan Shenshuo Technology Co., Ltd.

[0052] The multi-walled carbon nanotubes (99% purity, inner diameter 5-8 nm, outer diameter 10-18 nm, length 8-14 μm) used in the following examples and comparative examples were provided by Shenzhen Suiheng Technology Co., Ltd.

[0053] The spherical carbonyl iron (1-5 μm in diameter) used in the following examples and comparative examples were provided by Yishun Metal Materials Co., Ltd.

[0054] Example 1

[0055] Preparation of flexible microwave absorbing resin-based composite materials

[0056] (1) Mix 60g of flexible photosensitive resin with 0.1504g of multi-walled carbon nanotubes and 20g of spherical carbonyl iron, and sonicate for 30min (ultrasonic power 80W, heating power 100W). Then, mechanically stir at 60rpm for 30min to obtain a flexible microwave absorbing resin-based composite slurry with uniform dispersion of each component.

[0057] (2) The flexible microwave absorbing resin-based composite slurry obtained in step (1) is subjected to photopolymerization 3D printing. The process parameters for photopolymerization 3D printing are a light intensity of 10000 μw / cm. 2 The first layer was exposed for 5 seconds, and the remaining layers were exposed for 3 seconds. Each layer was cured to a thickness of 25 μm. Concentric rings and cuboids of different sizes were used as 3D printing models to obtain three flexible microwave absorbing resin-based composite materials CIP / CNT-1 with the same material composition but different morphological structures: a concentric ring with an inner diameter of 3 mm, an outer diameter of 7 mm, and a height of 2 mm; a cuboid with dimensions of 10.67 mm × 4.32 mm × 2 mm; and a cuboid with dimensions of 7.12 mm × 3.56 mm × 2 mm.

[0058] Example 2

[0059] Preparation of flexible microwave absorbing resin-based composite materials

[0060] (1) Mix 60g of flexible photosensitive resin with 0.3016g of multi-walled carbon nanotubes and 20g of spherical carbonyl iron, and sonicate for 30min (ultrasonic power 80W, heating power 100W). Then, mechanically stir at 60rpm for 30min to obtain a flexible microwave absorbing resin-based composite slurry with uniform dispersion of each component.

[0061] (2) The flexible microwave absorbing resin-based composite slurry obtained in step (1) is subjected to photopolymerization 3D printing. The process parameters for photopolymerization 3D printing are a light intensity of 14000 μw / cm. 2 The first layer exposure time was 8s, and the exposure time for the remaining layers was 6s. The curing thickness of each layer was 25μm. Concentric rings and cuboids of different sizes were used as 3D printing models to obtain three flexible microwave absorbing resin-based composite materials CIP / CNT-2 with the same material composition but different morphological structures: a concentric ring with an inner diameter of 3mm, an outer diameter of 7mm, and a height of 2mm; a cuboid with dimensions of 10.67mm×4.32mm×2mm; and a cuboid with dimensions of 7.12mm×3.56mm×2mm.

[0062] Example 3

[0063] Preparation of flexible microwave absorbing resin-based composite materials

[0064] (1) Mix 60g of flexible photosensitive resin with 0.4534g of multi-walled carbon nanotubes and 20g of spherical carbonyl iron, and sonicate for 30min (ultrasonic power 80W, heating power 100W). Then, mechanically stir at 60rpm for 30min to obtain a flexible microwave absorbing resin-based composite slurry with uniform dispersion of each component.

[0065] (2) The flexible microwave absorbing resin-based composite slurry obtained in step (1) is subjected to photopolymerization 3D printing. The process parameters for photopolymerization 3D printing are a light intensity of 14000 μw / cm. 2 The first layer exposure time was 8 seconds, and the exposure time for the remaining layers was 6 seconds. The curing thickness of each layer was 25 μm. Concentric rings and cuboids of different sizes were used as 3D printing models to 3D print four flexible microwave absorbing resin-based composite materials CIP / CNT-3 with the same material composition but different morphological structures. They were: a concentric ring with an inner diameter of 3 mm, an outer diameter of 7 mm, and a height of 2 mm; a cuboid with dimensions of 10.67 mm × 4.32 mm × 2 mm; a cuboid with dimensions of 7.12 mm × 3.56 mm × 2 mm; and a cuboid with dimensions of 50 × 50 × 0.3 mm.

[0066] Example 4

[0067] Preparation of flexible microwave absorbing resin-based composite materials

[0068] (1) Mix 60g of flexible photosensitive resin with 0.1504g of multi-walled carbon nanotubes and 60g of spherical carbonyl iron, and sonicate for 30min (ultrasonic power 80W, heating power 100W). Then, mechanically stir at 60rpm for 30min to obtain a flexible microwave absorbing resin-based composite slurry with uniform dispersion of each component.

[0069] (2) The flexible microwave absorbing resin-based composite slurry obtained in step (1) is subjected to photopolymerization 3D printing. The process parameters for photopolymerization 3D printing are a light intensity of 17000 μw / cm. 2 The first layer exposure time was 11s, and the exposure time for the remaining layers was 9s. The curing thickness of each layer was 25μm. Concentric rings and cuboids of different sizes were used as 3D printing models to obtain three flexible microwave absorbing resin-based composite materials CIP / CNT-4 with the same material composition but different morphological structures: a concentric ring with an inner diameter of 3mm, an outer diameter of 7mm, and a height of 2mm; a cuboid with dimensions of 10.67mm×4.32mm×2mm; and a cuboid with dimensions of 7.12mm×3.56mm×2mm.

[0070] Example 5

[0071] Preparation of flexible microwave absorbing resin-based composite materials

[0072] (1) Mix 60g of flexible photosensitive resin with 0.3016g of multi-walled carbon nanotubes and 60g of spherical carbonyl iron, and sonicate for 30min (ultrasonic power 80W, heating power 100W). Then, mechanically stir at 60rpm for 30min to obtain a flexible microwave absorbing resin-based composite slurry with uniform dispersion of each component.

[0073] (2) The flexible microwave absorbing resin-based composite slurry obtained in step (1) is subjected to photopolymerization 3D printing. The process parameters for photopolymerization 3D printing are a light intensity of 20000 μw / cm. 2 The first layer exposure time was 22s, and the exposure time for the remaining layers was 20s. The curing thickness of each layer was 25μm. Concentric rings and cuboids of different sizes were used as 3D printing models to obtain three flexible microwave absorbing resin-based composite materials CIP / CNT-5 with the same material composition but different morphological structures: a concentric ring with an inner diameter of 3mm, an outer diameter of 7mm, and a height of 2mm; a cuboid with dimensions of 10.67mm×4.32mm×2mm; and a cuboid with dimensions of 7.12mm×3.56mm×2mm.

[0074] Example 6

[0075] Preparation of flexible microwave absorbing resin-based composite materials

[0076] (1) Mix 60g of flexible photosensitive resin with 0.4534g of multi-walled carbon nanotubes and 60g of spherical carbonyl iron, and sonicate for 30min (ultrasonic power 80W, heating power 100W). Then, mechanically stir at 60rpm for 30min to obtain a flexible microwave absorbing resin-based composite slurry with uniform dispersion of each component.

[0077] (2) The flexible microwave absorbing resin-based composite slurry obtained in step (1) is subjected to photopolymerization 3D printing. The process parameters for photopolymerization 3D printing are a light intensity of 20000 μw / cm. 2 The first layer exposure time was 22s, and the exposure time for the remaining layers was 20s. The curing thickness of each layer was 25μm. Concentric rings and cuboids of different sizes were used as 3D printing models to obtain three flexible microwave absorbing resin-based composite materials CIP / CNT-6 with the same material composition but different morphological structures: a concentric ring with an inner diameter of 3mm, an outer diameter of 7mm, and a height of 2mm; a cuboid with dimensions of 10.67mm×4.32mm×2mm; and a cuboid with dimensions of 7.12mm×3.56mm×2mm.

[0078] Example 7

[0079] Electromagnetic parameter testing under low-frequency (1-40GHz) electromagnetic waves

[0080] The electromagnetic parameters of the flexible microwave absorbing resin-based composite materials prepared in Examples 1-6 under low-frequency (1-40GHz) electromagnetic waves were tested (using a vector network analyzer). The electromagnetic parameters of the flexible microwave absorbing resin-based composite materials under 1-40GHz electromagnetic waves were tested in three bands: 1-18GHz, 18-26.5GHz, and 26.5-40GHz. The electromagnetic parameters in the 1-18GHz band were tested using the coaxial method, with the sample shape being a concentric ring, and the dimensions being an inner diameter of 3mm, an outer diameter of 7mm, and a height of 2mm. The electromagnetic parameters in the 18-26.5GHz and 26.5-40GHz bands were tested using the waveguide method, with the sample shape being a cuboid. The sample dimensions for the 18-26.5GHz band were 10.67mm × 4.32mm × 2mm, and the sample dimensions for the 26.5-40GHz band were 7.12mm × 3.56mm × 2mm. The results are as follows: Figure 1 As shown, (a) is the real part of the dielectric constant; (b) is the imaginary part of the dielectric constant; (c) is the dielectric loss; (d) is the real part of the permeability; (e) is the imaginary part of the permeability; and (f) is the magnetic loss.

[0081] from Figure 1 It can be seen that the real part of the complex permittivity of the samples prepared in Examples 1-6 gradually decreases with increasing frequency, exhibiting excellent dispersion characteristics. Furthermore, with the increase of multi-walled carbon nanotube content, the dielectric loss of the material gradually increases; with the increase of spherical carbonyl iron content, the magnetic loss of the material gradually increases. This indicates that the attenuation capability of the flexible microwave absorbing resin-based composite material for electromagnetic waves gradually increases, thus contributing to the improvement of microwave absorption performance.

[0082] Example 8

[0083] Electromagnetic parameter fitting under high frequency (75-110GHz) electromagnetic waves

[0084] Based on the electromagnetic parameters obtained in Example 7 under low-frequency (1-40GHz) electromagnetic waves, the electromagnetic parameters of the flexible microwave absorbing resin-based composite materials prepared in Examples 1-6 under high-frequency (75-110GHz) electromagnetic waves were obtained by fitting with a theoretical model (the electromagnetic parameters of the flexible microwave absorbing resin-based composite materials under 1-75GHz electromagnetic waves were also fitted). The Cole-Cole model was used to fit the real and imaginary parts of the dielectric constant, and the dielectric loss was calculated by the ratio of the real and imaginary parts of the dielectric constant. The Lorentzian model was used to fit the real and imaginary parts of the permeability and the magnetic loss. The magnetic loss was calculated by the ratio of the real and imaginary parts of the permeability. The Cole-Cole model and the Lorentzian model are Equations (1) and (2), respectively:

[0085]

[0086]

[0087] Where, ε s ε is the static dielectric constant. ∞ μ is the limiting value of the dielectric constant at high frequencies. s f is the static permeability, j is the imaginary part in units, and f is the static permeability. r The resonant frequency is γ, α and k are fitting parameters with values ​​between 0 and 1, and γ is an empirical fitting parameter.

[0088] The electromagnetic parameter fitting results are as follows Figure 2 As shown, where: (a) is the real part of the dielectric constant; (b) is the imaginary part of the dielectric constant; (c) is the dielectric loss; (d) is the real part of the permeability; (e) is the imaginary part of the permeability; and (f) is the magnetic loss. Figure 2 As can be seen from the results, the measured electromagnetic parameters and fitted electromagnetic parameters of the flexible microwave absorbing resin-based composite materials prepared in Examples 1-6 are in good agreement under low-frequency (1-40GHz) electromagnetic waves. Based on this, reliable electromagnetic parameters under high-frequency (75-110GHz) electromagnetic waves can be obtained.

[0089] Note: The electromagnetic parameters obtained in this embodiment are intrinsic parameters of the material, which are not related to the material thickness, but only to the material's composition and morphology.

[0090] Example 9

[0091] Calculation of reflection loss of flat plate

[0092] Based on the electromagnetic parameters of the flexible microwave absorbing resin-based composite materials prepared in Examples 1-6 obtained in Example 8 under high-frequency (75-110GHz) electromagnetic waves, the microwave absorption performance of the corresponding frequency band was calculated using transmission line theory. The absorption capability of the material can be measured by the reflection loss RL (dB), which can be calculated from the material's electromagnetic parameters. It is generally a negative value, and the larger the negative value, the better the absorption performance. According to transmission line theory, the RL of a single-layer flat plate material can be calculated using formulas (3) and (4):

[0093] Z in =(μ r / ε r ) 1 / 2 tanh[j(2πfd / c)(μ r ε r ) 1 / 2 (3)

[0094] RL(dB) = 20log|(Z) in -1) / (Z in +1)| (4)

[0095] The complex permittivity and complex permeability are expressed as follows:

[0096] ε r =ε′-jε″ (5)

[0097] μ r =μ′-jμ″ (6)

[0098] In the above formula, ε r It is the complex permittivity, μ r ε′ is the complex permeability, ε″ is the real part of the permittivity, ε″ is the imaginary part of the permittivity, μ′ is the real part of the permeability, μ″ is the imaginary part of the permeability, f is the incident wave frequency, d is the thickness of the absorbing material, c is the speed of light, and Z is the absorbing material thickness. in It is the normalized input impedance of the absorbing material.

[0099] RL can intuitively reflect the microwave absorption capability of materials with different thicknesses. An RL value of -10dB indicates that 90% of microwaves are absorbed. The frequency range covered by RL≤-10dB is the effective microwave absorption bandwidth. The calculation results are shown in Table 1.

[0100] Note: In this embodiment, the electromagnetic parameters of the flexible absorbing resin-based composite material obtained from Example 8 under high-frequency (75-110GHz) electromagnetic waves are substituted into the formula for calculation. The thickness d of the absorbing material is equivalent to an independent variable and can be arbitrarily selected. In this embodiment, the thickness is selected in the range of 0-10mm, and the value is taken every 0.1mm to calculate the result. The maximum effective absorbing bandwidth and the minimum RL value, as well as the corresponding thickness, are extracted from the calculation results.

[0101] Table 1

[0102]

[0103] As can be seen from Table 1, the flexible microwave absorbing composite material of composite doped multi-walled carbon nanotubes and spherical carbonyl iron has excellent microwave absorption performance under high frequency (75-110GHz) electromagnetic waves. The flexible microwave absorbing resin-based composite materials prepared in Examples 1 to 6 can achieve the maximum effective microwave absorption bandwidth and minimum RL value with a thin thickness.

[0104] Example 10

[0105] Comparison of measured and calculated reflection loss

[0106] Four 50×50×0.3mm cuboid flexible microwave absorbing resin-based composite materials CIP / CNT-3 prepared in Example 3 were assembled into standard 100mm×100mm square samples. Reflectivity was tested under high-frequency (75-110GHz) electromagnetic waves using the single-end reflection method. The test results are as follows: Figure 3 As shown. From Figure 3 As can be seen, the measured values ​​and the calculated values ​​are in good agreement, which further proves that the electromagnetic parameters obtained by fitting under high frequency (75-110GHz) electromagnetic waves are highly reliable. Moreover, the RL value of the flexible microwave absorbing composite material calculated by transmission line theory can also reflect the microwave absorption capability of the material well.

[0107] Example 11

[0108] Multi-level cellular structure simulation

[0109] The electromagnetic parameters of the flexible microwave absorbing resin-based composite material CIP / CNT-3 obtained in Example 8 under high-frequency (75-110GHz) electromagnetic waves were imported into CST Studio Suite 2022 software, along with the model structure. Boundary conditions and scanning parameter ranges were set to fit the optimal inner side length (a), wall thickness (t), and height (h) of the multi-level honeycomb structure's outer hexagonal prism. Specific structures and parameters are as follows: Figure 4 As shown, where a = 7 mm, t = 1 mm, and h = 2.9 mm.

[0110] Example 12

[0111] Fabrication of Multi-Level Cellular Flexible Absorbers for High-Frequency Applications

[0112] Based on the preparation steps and photopolymerization 3D printing parameters (light intensity, first layer exposure time, subsequent layer exposure times, and curing thickness of each layer) of Example 3, using the multi-level honeycomb structure obtained in Example 11 as the 3D printing model, a multi-level honeycomb structure flexible absorber for high-frequency applications was fabricated. The specific steps are as follows:

[0113] (1) Mix 60g of flexible photosensitive resin with 0.4534g of multi-walled carbon nanotubes and 20g of spherical carbonyl iron, and sonicate for 30min (ultrasonic power 80W, heating power 100W). Then, mechanically stir at 60rpm for 30min to obtain a flexible microwave absorbing resin-based composite slurry with uniform dispersion of each component (the same as the composite slurry in Example 3).

[0114] (2) The flexible microwave absorbing resin-based composite slurry obtained in step (1) was subjected to photopolymerization 3D printing. The multi-level honeycomb structure obtained in Example 11 was used as the printing model. The process parameters for photopolymerization 3D printing were a light intensity of 14000 μw / cm. 2 The first layer was exposed for 8 seconds, and the remaining layers were exposed for 6 seconds. Each layer was cured to a thickness of 25 μm (same as the photopolymerization 3D printing parameters in Example 3), resulting in a total of 116 layers. This yielded a multi-level honeycomb structure flexible absorber for high-frequency applications. Figure 5 As shown. From Figure 5As can be seen, the multi-level honeycomb structure flexible absorber has high flexibility and bendability. Furthermore, it possesses self-healing properties and exhibits no crease damage during repeated bending, which can meet the requirements of smart wearable devices for absorbing materials.

[0115] Example 13

[0116] Multi-level honeycomb structure reflection loss test under multiple bending angles

[0117] The multi-level honeycomb flexible absorber for high-frequency applications, prepared in Example 12, was subjected to reflectivity testing under high-frequency (75-110GHz) electromagnetic waves. The bending angle of the multi-level honeycomb flexible absorber was varied, and its absorption performance was tested under six different conditions: 0°, 30°, 60°, 90°, 120°, and 150°. The test results are as follows: Figure 6 As shown. From Figure 6 As can be seen from the example, the multi-level honeycomb structure flexible absorber prepared in Example 12 can achieve effective absorption across the entire frequency band of 75-110GHz in both flat and various bending states, demonstrating excellent absorption performance.

[0118] Comparative Example 1

[0119] Preparation of flexible microwave absorbing resin-based composite materials

[0120] (1) Mix 60g of flexible photosensitive resin with 20g of spherical carbonyl iron, and ultrasonically treat for 30min (ultrasonic power 80W, heating power 100W). Then mechanically stir at 60rpm for 30min to obtain a flexible microwave absorbing resin-based composite slurry with uniform dispersion of each component.

[0121] (2) The flexible microwave absorbing resin-based composite slurry obtained in step (1) is subjected to photopolymerization 3D printing. The process parameters for photopolymerization 3D printing are a light intensity of 10000 μw / cm. 2 The first layer was exposed for 5 seconds, and the remaining layers were exposed for 3 seconds. Each layer was cured to a thickness of 25 μm. Concentric rings and cuboids of different sizes were used as 3D printing models. Three flexible microwave absorbing resin-based composite materials CIP1 with the same material composition but different morphological structures were obtained by 3D printing: a concentric ring with an inner diameter of 3 mm, an outer diameter of 7 mm, and a height of 2 mm; a cuboid with dimensions of 10.67 mm × 4.32 mm × 2 mm; and a cuboid with dimensions of 7.12 mm × 3.56 mm × 2 mm.

[0122] Comparative Example 2

[0123] Preparation of flexible microwave absorbing resin-based composite materials

[0124] (1) Mix 60g of flexible photosensitive resin with 60g of spherical carbonyl iron, and ultrasonically treat for 30min (ultrasonic power 80W, heating power 100W). Then mechanically stir at 60rpm for 30min to obtain a flexible microwave absorbing resin-based composite slurry with uniform dispersion of each component.

[0125] (2) The flexible microwave absorbing resin-based composite slurry obtained in step (1) is subjected to photopolymerization 3D printing. The process parameters for photopolymerization 3D printing are a light intensity of 20000 μw / cm. 2 The first layer exposure time was 11s, and the exposure time for the remaining layers was 9s. The curing thickness of each layer was 25μm. Concentric rings and cuboids of different sizes were used as 3D printing models to obtain three flexible microwave absorbing resin-based composite materials CIP2 with the same material composition but different morphological structures: a concentric ring with an inner diameter of 3mm, an outer diameter of 7mm, and a height of 2mm; a cuboid with dimensions of 10.67mm×4.32mm×2mm; and a cuboid with dimensions of 7.12mm×3.56mm×2mm.

[0126] Comparative Example 3

[0127] Preparation of flexible microwave absorbing resin-based composite materials

[0128] (1) Mix 60g of flexible photosensitive resin with 0.1504g of multi-walled carbon nanotubes, and sonicate for 30min (ultrasonic power 80W, heating power 100W). Then, mechanically stir at 60rpm for 30min to obtain a flexible microwave absorbing resin-based composite slurry with uniform dispersion of each component.

[0129] (2) The flexible microwave absorbing resin-based composite slurry obtained in step (1) is subjected to photopolymerization 3D printing. The process parameters for photopolymerization 3D printing are a light intensity of 7000 μw / cm. 2 The first layer was exposed for 5 seconds, and the remaining layers were exposed for 3 seconds. Each layer was cured to a thickness of 25 μm. Concentric rings and cuboids of different sizes were used as 3D printing models to obtain three flexible microwave absorbing resin-based composite materials CIP3 with the same material composition but different morphological structures: a concentric ring with an inner diameter of 3 mm, an outer diameter of 7 mm, and a height of 2 mm; a cuboid with dimensions of 10.67 mm × 4.32 mm × 2 mm; and a cuboid with dimensions of 7.12 mm × 3.56 mm × 2 mm.

[0130] The reflection loss of the flexible microwave absorbing resin-based composite materials prepared in Comparative Examples 1-3 was calculated according to the calculation method of Example 9 (the electromagnetic parameters required in the calculation process were obtained by the method of Examples 7-8), and the results are shown in Table 2.

[0131] Table 2

[0132]

[0133] As can be seen from Table 2, Comparative Examples 1 to 3 have poor wave absorption capabilities because only a single type of wave absorbing agent was added. Comparative Examples 1 to 3 all require a thickness greater than 4.5 mm to achieve the maximum effective wave absorption bandwidth of the material, which is difficult to meet the requirements of smart wearable devices for thin and light flexible wave absorbing materials.

[0134] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for fabricating a multi-level honeycomb structure flexible absorber for high-frequency applications, characterized in that, Specifically, the following steps are included: S1. Flexible photosensitive resin is mixed with multi-walled carbon nanotubes and spherical carbonyl iron, subjected to ultrasonic treatment and mechanical stirring to obtain a flexible microwave absorbing resin-based composite slurry; the flexible microwave absorbing resin-based composite slurry is subjected to photocuring 3D printing to obtain a flexible microwave absorbing resin-based composite material. S2. Test the electromagnetic parameters of the flexible microwave absorbing resin-based composite material prepared in step S1 under electromagnetic waves of 1-40GHz. S3. Using the electromagnetic parameters obtained in step S2 and combined with the theoretical model, the electromagnetic parameters of the flexible microwave absorbing resin-based composite material under 75-110GHz electromagnetic waves are obtained by fitting the parameters. S4. Import the electromagnetic parameters of the flexible microwave absorbing resin matrix composite material obtained in step S3 under 75-110GHz electromagnetic waves into CSTStudioSuite2022 software, and fit to obtain the optimal size of the multi-level honeycomb structure. S5. Repeat the preparation steps of step S1, using the multi-level honeycomb structure obtained in step S4 as a 3D printing model, perform photopolymerization 3D printing to obtain the multi-level honeycomb structure flexible absorber for high-frequency applications. In the context of high-frequency applications, "high frequency" refers to electromagnetic waves with a frequency of 75-110 GHz. In step S2, the electromagnetic parameters of the flexible microwave absorbing resin-based composite material under 1-40GHz electromagnetic waves were tested in three bands: 1-18GHz, 18-26.5GHz, and 26.5-40GHz. The electromagnetic parameters in the 1-18GHz band were tested using the coaxial method, with the sample shape being a concentric ring, measuring 3mm inner diameter, 7mm outer diameter, and 2mm height. The electromagnetic parameters in the 18-26.5GHz and 26.5-40GHz bands were tested using the waveguide method, with the sample shape being a cuboid. Specifically, the sample dimensions for the 18-26.5GHz band were 10.67mm × 4.32mm × 2mm, and for the 26.5-40GHz band, they were 7.12mm × 3.56mm × 2mm. The electromagnetic parameters specifically included the real part of the dielectric constant, the imaginary part of the dielectric constant, the dielectric loss, the real part of the permeability, the imaginary part of the permeability, and the magnetic loss. The theoretical models mentioned in step S3 are the Cole-Cole model and the Lorentzian model, respectively, as shown in formula (1) and formula (2): Where, ε s ε is the static dielectric constant. ∞ μ is the limiting value of the dielectric constant at high frequencies. s f is the static permeability, j is the imaginary part in units, and f is the static permeability. r The resonant frequency is given by α and k, which are fitting parameters ranging from 0 to 1, and γ is an empirical fitting parameter. The real and imaginary parts of the dielectric constant in the electromagnetic parameters are fitted using the Cole-Cole model, and the dielectric loss is calculated by the ratio of the real and imaginary parts of the dielectric constant. The real and imaginary parts of the magnetic permeability are fitted using the Lorentzian model, and the magnetic loss is calculated by the ratio of the real and imaginary parts of the magnetic permeability. The multi-level honeycomb structure in step S4 includes several hexagonally distributed absorbing units. Each absorbing unit includes an inner hexagonal prism and an outer hexagonal prism arranged correspondingly inside and outside. The edges of the inner and outer hexagonal prisms are arranged correspondingly, and a connecting plate is fixedly connected between the corresponding edges. The wall thickness of any face of the outer hexagonal prism is t, the wall thickness of any face of the inner hexagonal prism is t / 2, the wall thickness of the connecting plate is t / 2, the distance from the central axis of the inner hexagonal prism to the inner corner of the inner hexagonal prism is a / 2, the distance from the central axis of the outer hexagonal prism to the inner corner of the outer hexagonal prism is a, the central axis of the inner hexagonal prism coincides with the central axis of the outer hexagonal prism, the inner side length of the outer hexagonal prism is a, and the height of the inner hexagonal prism, the outer hexagonal prism, and the connecting plate are all h. The multi-level honeycomb structure is composed of repeating unit arrays of the absorbing units in the longitudinal and transverse directions. The dimensions mentioned in step S4 include the inner side length a, wall thickness t, and height h of the outer hexagonal prism.

2. The preparation method according to claim 1, characterized in that, The flexible photosensitive resin in step S1 comprises: 87-97 wt.% aliphatic polyurethane acrylic acid, 0-10 wt.% acryloylmorpholine, 0-3 wt.% diphenyl-(2,4,6-trimethylbenzoyl)phosphorus oxide, and 0.1-0.3 wt.% UV black pigment; the ultrasonic treatment time is 30 min; the mechanical stirring speed is 60 rpm for 30 min; and the photopolymerization 3D printing process parameters are: light intensity 10000-20000 μw / cm². 2 The first layer exposure time is 5-22s, and the exposure time for the remaining layers is 3-20s. The curing thickness of each layer is 25μm.

3. A multi-level honeycomb structure flexible absorber for high-frequency applications, prepared by the preparation method according to any one of claims 1-2.

4. The application of a multi-level cellular structure flexible absorber for high-frequency applications as described in claim 3 in smart wearable functional devices, smart electronics, or smart driving.

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