A composite structure based on multilayer metal thin films and its application

Abstract

This invention discloses a composite structure based on multilayer metal thin films and its applications. The composite structure comprises N+1 alternately stacked dielectric layers and N metal thin film layers, where N is an integer greater than or equal to 2. By adjusting the fundamental parameters of the composite structure, the microwave absorptivity of the composite structure is made greater than 90%. These fundamental parameters include the dielectric layer thickness, dielectric constant, sheet resistance of the metal thin film, and the number of stacked layers. This invention can utilize multilayer metal thin films to attenuate transmitted waves step by step, and achieve impedance matching through the rational selection of multilayer structure parameters, thereby realizing dual suppression of reflection and transmission, ultimately making the absorptivity close to 100%.

Description

Technical Field

[0001] This invention relates to the field of microwave absorption technology, and in particular to a composite structure based on multilayer metal thin films and its applications. Background Technology

[0002] With the rapid development of flexible electronics, wearable devices, radio frequency identification, and microwave communication technologies, ultrathin metal films are increasingly widely used in transparent conductive electrodes, electromagnetic shielding, and microwave absorption. These films typically have thicknesses on the nanometer scale, far smaller than the skin depth of microwave frequencies, causing their electromagnetic behavior to shift from typical reflection-dominated to absorption-dominated. However, single-layer metal films have inherent theoretical limits in microwave absorption. According to electromagnetic theory, while the absorption rate can reach its maximum when the film's resistance matches the free-space impedance, this maximum absorption rate is limited to only 50% due to the energy distribution relationship between reflection, transmission, and absorption, making it difficult for single-layer metal films to achieve efficient microwave absorption.

[0003] Furthermore, the conductivity of ultrathin metal films with single-layer structures is highly sensitive to thickness, continuity, and deposition process, resulting in deviations between actual absorption performance and theoretical values. This makes it difficult to meet the comprehensive requirements of high-efficiency, wide-bandwidth, and lightweight absorbers in fields such as radar stealth, electromagnetic compatibility, and high-power microwave protection. Summary of the Invention

[0004] To address the above problems, the present invention aims to provide a composite structure based on multilayer metal thin films and its applications.

[0005] The technical solution of the present invention is as follows: On the one hand, a composite structure based on multilayer metal thin films is provided, comprising N+1 alternately stacked dielectric layers and N metal thin film layers, where N is an integer greater than or equal to 2; by adjusting the basic parameters of the composite structure, the microwave absorption rate of the composite structure is made to be greater than 90%, wherein the basic parameters include dielectric layer thickness, dielectric constant, sheet resistance of metal thin film, and number of stacked layers.

[0006] Preferably, the basic parameters are obtained through the following steps: S1: Establish an equivalent circuit model based on transmission line theory, regard the composite structure as cascaded transmission line segments, represent each dielectric layer with its characteristic impedance and propagation constant, and represent each metal thin film with its sheet resistance as the admittance connected in parallel between adjacent dielectric layers. S2: Based on the equivalent circuit model, determine the overall transfer matrix of the composite structure when it is placed in air, and then calculate the absorption rate of the composite structure. S3: Establish constraints, and under these constraints, combine the equivalent circuit model and the absorption rate, and use a genetic algorithm to perform global optimization to obtain the optimal combination of basic parameters that satisfies the constraints.

[0007] Preferably, in step S1, the transfer matrix of each dielectric layer in the equivalent circuit model is: (1) Where: M medium,i γ is the transmission matrix of the i-th dielectric layer; i d is the propagation constant of the i-th dielectric layer; i Z is the thickness of the i-th dielectric layer; c,i The characteristic impedance of the i-th dielectric layer; The transfer matrix of each metal thin film layer is: (2) Where: M film,i R is the transfer matrix of the i-th metal thin film layer; s,i Let be the sheet resistance of the i-th metal thin film layer; The overall transmission matrix of the composite structure is: (3) Where: M total M represents the overall transfer matrix of the entire composite structure. medium,N+1 M is the transmission matrix for the last media layer; 11 M 12 M 21 M 22 These are the four elements of the overall transmission matrix.

[0008] Preferably, in step S2, the overall transfer matrix of the composite structure when placed in air is: (4) Where: E0 is the electric field strength at the incident end; H0 is the magnetic field strength at the incident end; E out H represents the electric field strength at the emission end. out η0 is the magnetic field strength at the output end; η0 is the free-space wave impedance. The absorption rate is calculated using the following formula: (5) In the formula: A is the absorption rate.

[0009] Preferably, in step S3, the constraints include the target operating frequency band, the dielectric constant of the dielectric material, the sheet resistance of the metal thin film, the number of alternating stacked layers, and the thickness of the dielectric layer.

[0010] Preferably, the dielectric material has a dielectric constant between 1.5 and 10, and a loss tangent of less than 0.01; the thickness of the metal film is less than the skin depth of the metal.

[0011] Preferably, the thickness of one dielectric layer is , where n is a positive integer; λ is the wavelength of the medium at the operating frequency.

[0012] Preferably, the composite structure is formed by depositing one or more metallic materials on one or more dielectric substrates.

[0013] Preferably, the metal material is NiCr alloy, Au, or Al, and the dielectric substrate is made of ceramic, polytetrafluoroethylene, or polypropylene.

[0014] On the other hand, the application of the composite structure based on multilayer metal thin films described in any one of the above-mentioned claims in a microwave absorber is also provided.

[0015] The beneficial effects of this invention are: This invention can utilize multilayer metal thin films to attenuate transmitted waves step by step, and achieve impedance matching through the rational selection of multilayer structural parameters, thereby realizing dual suppression of reflection and transmission, and ultimately making the absorption rate close to 100%. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art 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.

[0017] Figure 1 This is a schematic diagram of the composite structure based on multilayer metal thin films of the present invention; Figure 2 This is a schematic diagram of the structure of a certain stacked layer; Figure 3 This is a schematic diagram of the equivalent transmission line model of the composite structure based on multilayer metal thin films of the present invention; Figure 4 This is a schematic diagram showing the variation of the absorption rate of the composite structure with the number of layers under different maximum thickness constraints in a specific embodiment. Figure 5 This is a schematic diagram of the impedance distribution of different metal thin film layers in a specific embodiment; Figure 6 This is a schematic diagram of the thickness distribution of different dielectric layers in a specific embodiment; Figure 7This is a schematic diagram showing the microwave absorptivity, reflectivity, and transmittance of the composite structure at a frequency of 2-3 GHz in a specific embodiment. Detailed Implementation

[0018] The present invention will be further described below with reference to the accompanying drawings and embodiments. It should be noted that, unless otherwise specified, the embodiments and technical features described in this application can be combined with each other. It should also be pointed out that, unless otherwise indicated, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. The terms "comprising" or "including" and similar words used in this invention refer to elements or objects preceding the word that encompass the elements or objects listed following the word and their equivalents, without excluding other elements or objects.

[0019] On the one hand, such as Figure 1-2 As shown, the present invention provides a composite structure based on multilayer metal thin films, comprising N+1 alternately stacked dielectric layers and N metal thin film layers, where N is an integer greater than or equal to 2; by adjusting the basic parameters of the composite structure, the microwave absorption rate of the composite structure is made to be greater than 90%, wherein the basic parameters include dielectric layer thickness, dielectric constant, sheet resistance of metal thin film, and number of stacked layers.

[0020] In this invention, multilayer absorption is constructed to reduce transmitted energy, allowing electromagnetic wave energy to be gradually absorbed within the structure. Simultaneously, impedance matching is achieved by adjusting the fundamental parameters of the multilayer structure, reducing reflected energy. When constructing the composite structure described in this invention, the thickness and material parameters of each dielectric and metal film are sequentially set according to the incident direction of the electromagnetic wave. This ensures that the overall structure's input impedance before the 1 / 4 wavelength transmission line matches the load impedance after the 1 / 4 wavelength transmission line, forming impedance matching and thus reducing direct reflection of the electromagnetic wave at the incident interface. When the electromagnetic wave propagates within the multilayer structure, the transmitted portion undergoes multiple absorptions within each metal film, significantly suppressing the transmitted energy. In summary, the overall reflectivity and transmittance of the structure can be suppressed to near-zero levels, achieving highly efficient absorption of electromagnetic waves, with an absorption rate potentially approaching 100%.

[0021] In one specific embodiment, the basic parameters are obtained through the following steps: S1: Establish an equivalent circuit model based on transmission line theory, regard the composite structure as cascaded transmission line segments, represent each dielectric layer with its characteristic impedance and propagation constant, and represent each metal thin film with its sheet resistance as the admittance connected in parallel between adjacent dielectric layers.

[0022] In this invention, the multilayer dielectric-metal alternating structure is regarded as cascaded transmission line segments, such as... Figure 3As shown, each layer can be represented by its characteristic impedance and propagation constant, thus enabling accurate calculation of the input impedance, reflection coefficient, and absorption rate of the entire structure.

[0023] In a specific embodiment, the transfer matrix of each dielectric layer in the equivalent circuit model is: (1) Where: M medium,i γ is the transmission matrix of the i-th dielectric layer; i Let be the propagation constant of the i-th dielectric layer. Where j is the imaginary unit; ω is the angular frequency; μ0 is the free permeability; ε i d is the dielectric constant of the i-th dielectric layer; i Z is the thickness of the i-th dielectric layer; c,i Let be the characteristic impedance of the i-th dielectric layer. ; The transfer matrix of each metal thin film layer is: (2) Where: M film,i R is the transfer matrix of the i-th metal thin film layer; s,i Let be the sheet resistance of the i-th metal thin film layer; The overall transmission matrix of the composite structure is: (3) Where: M total M represents the overall transfer matrix of the entire composite structure. medium,N+1 M is the transmission matrix for the last media layer; 11 M 12 M 21 M 22 These are the four elements of the overall transmission matrix.

[0024] S2: Based on the equivalent circuit model, determine the overall transfer matrix of the composite structure when it is placed in air, and then calculate the absorption rate of the composite structure.

[0025] In one specific embodiment, the overall transfer matrix of the composite structure when placed in air is: (4) Where: E0 is the electric field strength at the incident end; H0 is the magnetic field strength at the incident end; E out H represents the electric field strength at the emission end. out η0 is the magnetic field strength at the output end; η0 is the free-space wave impedance. The absorption rate is calculated using the following formula: (5) In the formula: A is the absorption rate.

[0026] S3: Establish constraints, and under these constraints, combine the equivalent circuit model and the absorption rate, and use a genetic algorithm to perform global optimization to obtain the optimal combination of basic parameters that satisfies the constraints.

[0027] In one specific embodiment, the constraints include the target operating frequency band, the dielectric constant of the dielectric material, the sheet resistance of the metal thin film, the number of alternating stacked layers, and the thickness of the dielectric layer.

[0028] In one specific embodiment, the dielectric material has a dielectric constant between 1.5 and 10, and a loss tangent of less than 0.01; the thickness of the metal thin film is less than the skin depth of the metal; with a fixed thickness, a higher number of alternating stacked layers generally results in higher absorption, and fewer layers can be selected while still meeting absorption requirements; the main function of the dielectric layer is to provide phase delay and impedance transformation, wherein the thickness of one dielectric layer is... , where n is a positive integer; λ is the wavelength in the medium at the operating frequency, used for impedance transformation. Therefore, a thinner thickness can be selected while meeting the absorption rate target.

[0029] In one specific embodiment, the frequency is set to 2.45 GHz, the dielectric constant of the dielectric is set to 2.2, its length at 1 / 4 wavelength is approximately 20 mm, the number of dielectric layers is constrained to 2-10 layers, the corresponding number of metal thin film layers is 1-9 layers, and the sheet resistance is constrained to 200-10000 Ω / □. Using the above basic parameter design method, the maximum microwave absorption rate of the composite structure under the constraint of a maximum dielectric layer thickness of 10 mm, 15 mm, and 20 mm is analyzed. The results are as follows: Figure 4 As shown.

[0030] from Figure 4 It can be seen that, with a fixed maximum dielectric layer thickness, more layers are more conducive to achieving the goal of high absorption rate; compared with other thicknesses, it is easier to achieve high absorption rate when the maximum constraint thickness meets the condition of being greater than or equal to 1 / 4 wavelength, and with a fixed number of layers, the larger the maximum constraint thickness, the more conducive it is to achieving high absorption rate.

[0031] In another specific embodiment, the center frequency is set to 2.5 GHz, the operating frequency is constrained to 2-3 GHz, the dielectric constant of the dielectric is set to 2.2, the number of dielectric layers is constrained to 5, the number of metal thin film layers is 4, the sheet resistance is constrained to 200-10000 Ω / □, the maximum thickness is constrained to 20 mm, and the absorption rate A is set to greater than 90%. The specific parameters of the dielectric layer thickness and the sheet resistance of the metal thin film are calculated using a genetic algorithm, and the results are as follows. Figure 5 and Figure 6 As shown.

[0032] according to Figure 5 and Figure 6 The calculation results ultimately led to the selection of a composite structure with four metal thin film layers and five dielectric layers. This composite structure exhibited good microwave absorptivity, microwave reflectivity, and microwave transmittance at frequencies of 2-3 GHz, as shown in the following figures. Figure 7 As shown. From Figure 7 It can be seen that the microwave absorption rate of this composite structure is greater than 90% in the operating frequency range, which is a significant improvement compared to the single-layer structure.

[0033] In summary, by using the equivalent transmission line model and optimization design method described above, the specific values ​​of each parameter in the composite structure can be quickly determined based on the target frequency and material library, thereby achieving efficient microwave absorption.

[0034] In one specific embodiment, the composite structure is formed by depositing one or more metallic materials on one or more dielectric substrates. Optionally, the metallic material is a NiCr alloy, Au, or Al, and the dielectric substrate is made of ceramic, polytetrafluoroethylene, or polypropylene.

[0035] On the other hand, the present invention also provides an application of the composite structure based on multilayer metal thin films described in any one of the above claims in a microwave absorber.

[0036] The above description is merely a representative embodiment of the present invention and is not intended to limit the present invention in any way. Any embodiment made by those skilled in the art without departing from the scope of the present invention and utilizing the disclosed technical content is an equivalent embodiment of the present invention. Any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A composite structure based on multilayer metal thin films, characterized in that, It includes N+1 alternating dielectric layers and N metal thin film layers, where N is an integer greater than or equal to 2; the microwave absorption rate of the composite structure is made greater than 90% by adjusting the basic parameters of the composite structure, including the dielectric layer thickness, dielectric constant, sheet resistance of the metal thin film, and number of stacked layers.

2. The composite structure based on multilayer metal thin films according to claim 1, characterized in that, The basic parameters are obtained through the following steps: S1: Establish an equivalent circuit model based on transmission line theory, regard the composite structure as cascaded transmission line segments, represent each dielectric layer with its characteristic impedance and propagation constant, and represent each metal thin film with its sheet resistance as the admittance connected in parallel between adjacent dielectric layers. S2: Based on the equivalent circuit model, determine the overall transfer matrix of the composite structure when it is placed in air, and then calculate the absorption rate of the composite structure. S3: Establish constraints, and under these constraints, combine the equivalent circuit model and the absorption rate, and use a genetic algorithm to perform global optimization to obtain the optimal combination of basic parameters that satisfies the constraints.

3. The composite structure based on multilayer metal thin films according to claim 2, characterized in that, In step S1, the transfer matrix of each dielectric layer in the equivalent circuit model is: （1） Where: M medium,i γ is the transmission matrix of the i-th dielectric layer; i d is the propagation constant of the i-th dielectric layer; i Z is the thickness of the i-th dielectric layer; c,i The characteristic impedance of the i-th dielectric layer; The transfer matrix of each metal thin film layer is: （2） Where: M film,i R is the transfer matrix of the i-th metal thin film layer; s,i Let be the sheet resistance of the i-th metal thin film layer; The overall transmission matrix of the composite structure is: （3） Where: M total M represents the overall transfer matrix of the entire composite structure. medium,N+1 M is the transmission matrix for the last media layer; 11 M 12 M 21 M 22 These are the four elements of the overall transmission matrix.

4. The composite structure based on multilayer metal thin films according to claim 3, characterized in that, In step S2, the overall transfer matrix of the composite structure when placed in air is: （4） Where: E0 is the electric field strength at the incident end; H0 is the magnetic field strength at the incident end; E out H represents the electric field strength at the emission end. out The magnetic field strength at the output end; η0 is the free-space wave impedance; The absorption rate is calculated using the following formula: （5） In the formula: A is the absorption rate.

5. The composite structure based on multilayer metal thin films according to claim 2, characterized in that, In step S3, the constraints include the target operating frequency band, the dielectric constant of the dielectric material, the sheet resistance of the metal thin film, the number of alternating stacked layers, and the thickness of the dielectric layer.

6. The composite structure based on multilayer metal thin films according to claim 5, characterized in that, The dielectric constant of the dielectric material is between 1.5 and 10, and the loss tangent of the dielectric material is less than 0.01; the thickness of the metal thin film is less than the skin depth of the metal.

7. The composite structure based on multilayer metal thin films according to claim 5, characterized in that, The thickness of one of the dielectric layers is , where n is a positive integer; λ is the wavelength of the medium at the operating frequency.

8. The composite structure based on multilayer metal thin films according to claim 1, characterized in that, The composite structure is formed by depositing one or more metallic materials on one or more dielectric substrates.

9. The composite structure based on multilayer metal thin films according to claim 8, characterized in that, The metallic material is NiCr alloy, Au, or Al, and the dielectric substrate is made of ceramic, polytetrafluoroethylene, or polypropylene.

10. The application of the composite structure based on multilayer metal thin films as described in any one of claims 1-9 in microwave absorbers.

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