A broadband paper-based honeycomb microwave absorber with bidirectional impedance gradient

Abstract

The present invention discloses a broadband paper-based honeycomb microwave absorber with bidirectional impedance gradient, relating to the field of electromagnetic radar stealth technology. The absorber comprises a paper-based honeycomb structure comprising N periodically arranged paper-based honeycomb units, each of which has a grounded metal base. Each honeycomb unit comprises six honeycomb walls, which are sequentially designated as first to sixth honeycomb walls. The first to sixth honeycomb walls each have an inner surface printed with an impedance gradient structure; alternatively, the second, fourth, and sixth honeycomb walls each have an inner surface printed with an impedance gradient structure; alternatively, the second, third, fifth, and sixth honeycomb walls each have an inner surface printed with an impedance gradient structure. The impedance gradient structure is constructed using carbon paste and silver paste, achieving a bidirectional impedance gradient from free space to the grounded metal base. The present invention provides a paper-based honeycomb microwave absorber with a lightweight load-bearing capacity, a broadband, low profile, and a small thickness.

Description

Technical Field

[0001] The invention relates to the technical field of electromagnetic protection radar stealth, in particular to a broadband paper-based honeycomb microwave absorber with bidirectional impedance gradient. Background Art

[0002] Traditional paper-based honeycomb absorbers typically utilize an impregnated structure, but these materials are heavy, prone to peeling, and have poor durability, leading to difficult maintenance and performance degradation. These materials also have limited absorption performance and cannot meet high-performance requirements. With technological advancements, printed circuit-based paper-based honeycomb absorbers employ resonant structures to enhance absorption, but these absorbers have limited bandwidth and suffer from impedance matching issues, impacting stability across different frequency bands. Expanding bandwidth typically requires increasing the material thickness, which increases weight and volume, hindering practical application.

[0003] In 2020, the IEEE Asia-Pacific Microwave Conference (APMC2020) published a paper titled "A Paper-based Lightweight Absorber with Ultra-wide Absorption Band." The paper, based on a periodic rectangular honeycomb structure with tapered impedance gradient resistor patterns printed on the honeycomb walls, demonstrated a wide absorption bandwidth between 4.87 GHz and 30 GHz at normal incidence, with a reflection of less than -10 dB, and a thickness of 10 mm (0.16λL).

[0004] In 2023, the journal Applied Physics Letters (APL) published a paper titled "Light-weight Wideband Electromagnetic Wave Absorber Based on Aramid Paper." The paper investigated a lightweight, broadband cellular absorber made from aramid paper containing carbon fibers. A graded silver paste circuit was printed on the aramid paper to improve impedance matching, thereby achieving broadband absorption performance. The absorber exhibited an absorption bandwidth of 133% from 3.6 to 18 GHz, a thickness of 0.19λL at the lowest frequency, a total weight of 18.2 grams, and a density of 28.4 kg / m³.

[0005] In summary, the disclosed paper-based honeycomb absorbing materials have their own limitations depending on their design and structure:

[0006] (1) Traditional impregnated structural materials are heavy, easy to peel off and have poor durability, resulting in performance degradation and unable to meet high performance requirements.

[0007] (2) Honeycomb absorbing materials based on printed circuits can effectively reduce the weight of honeycombs, but they usually adopt a unidirectional impedance gradient structure and have a large thickness. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to overcome the shortcomings of the existing technology and provide a broadband paper-based honeycomb microwave absorber with bidirectional impedance gradient. The present invention aims to solve the technical difficulties of heavy weight and large thickness of traditional honeycomb structures. Based on a three-dimensional paper-based honeycomb structure, a bidirectional impedance gradient structure is printed on the honeycomb wall with carbon paste and silver paste for matching, thereby realizing a paper-based honeycomb microwave absorber with light load, broadband low profile and small thickness.

[0009] The present invention adopts the following technical solutions to solve the above technical problems:

[0010] According to the present invention, a broadband paper-based honeycomb microwave absorber with bidirectional impedance gradient is provided, comprising a paper-based honeycomb structure, wherein the paper-based honeycomb structure comprises N periodically arranged paper-based honeycomb units, where N is a natural number greater than 20, and the bottom plate of the paper-based honeycomb unit is a grounded metal bottom plate; wherein,

[0011] Each paper-based honeycomb unit includes 6 honeycomb walls, which are the first to sixth honeycomb walls, wherein:

[0012] The inner surfaces of the first to sixth honeycomb walls are all printed with impedance gradient structures;

[0013] Alternatively, the inner surfaces of the second, fourth, and sixth honeycomb walls are printed with an impedance gradient structure;

[0014] Alternatively, the inner surfaces of the second, third, fifth, and sixth honeycomb walls are printed with an impedance gradient structure;

[0015] The impedance gradient structure is used to achieve a bidirectional impedance gradient from free space to a grounded metal base plate. The impedance gradient structure is formed by carbon paste and silver paste.

[0016] As a further optimization scheme of the broadband paper-based honeycomb microwave absorber with bidirectional impedance gradient described in the present invention, the impedance gradient structure includes a first impedance gradient structure and a second impedance gradient structure, and the pattern of the impedance gradient structure is a gradient shape, wherein the end of the impedance gradient structure close to the air is the first impedance gradient structure composed of carbon paste, and the end of the impedance gradient structure close to the metal base plate is the second impedance gradient structure composed of silver paste; along with the incident direction of the electromagnetic wave, the area of ​​the first impedance gradient structure gradually increases and then decreases, and the area of ​​the second impedance gradient structure gradually increases.

[0017] As a further optimization scheme of the broadband paper-based honeycomb microwave absorber with bidirectional impedance gradient described in the present invention, the pattern of the impedance gradient structure is a gradient shape, and the gradient shape is a linear change, a step change or a gradient function change.

[0018] As a further optimization solution of the broadband paper-based honeycomb microwave absorber with bidirectional impedance gradient described in the present invention, the impedance gradient structure is a stepped or conical type.

[0019] As a further optimization scheme of the broadband paper-based honeycomb microwave absorber with bidirectional impedance gradient described in the present invention, the impedance gradient structures printed on the honeycomb walls have the same size, and the paper-based honeycomb structure is made of aramid paper or aramid paper doped with carbon fiber.

[0020] As a further optimization scheme of the broadband paper-based honeycomb microwave absorber with bidirectional impedance gradient described in the present invention, the outer aperture size of the paper-based honeycomb unit is 4 mm and the height is 20 mm; the first impedance gradient structure is a stepped type, and the widths of the six steps from top to bottom are 2.5 mm, 3.4 mm, 3.5 mm, 4 mm, 3.7 mm, and 3.4 mm, respectively, and the heights are 3 mm, 3 mm, 3 mm, 4 mm, 3 mm, and 3 mm, respectively.

[0021] As a further optimization scheme of the broadband paper-based honeycomb microwave absorber with bidirectional impedance gradient described in the present invention, the first impedance gradient structure is printed using carbon paste with a sheet resistance of 187Ω / sq, and the second impedance gradient structure is printed using silver paste with a sheet resistance of 5Ω / sq.

[0022] As a further optimization scheme of the broadband paper-based honeycomb microwave absorber with bidirectional impedance gradient described in the present invention, the relative dielectric constant of the paper-based honeycomb unit is 1.6, the relative loss angle is about 0.001, and the thickness of the honeycomb wall of the paper-based honeycomb unit is 0.07 mm.

[0023] As a further optimization solution of the broadband paper-based honeycomb microwave absorber with bidirectional impedance gradient described in the present invention, the metal base plate is copper, and the incident direction of the electromagnetic wave refers to the direction from the air to the metal base plate.

[0024] As a further optimization scheme of the broadband paper-based honeycomb microwave absorber with bidirectional impedance gradient according to the present invention, the impedance gradient structure includes a first impedance gradient structure and a second impedance gradient structure, wherein:

[0025] The first impedance gradient structure is formed on the inner surface of the honeycomb wall by cutting an exponential function curve to form a gradient shape, the upper edge of the gradient shape is cut by the first exponential function curve, and the lower edge of the gradient shape is cut by the second exponential function curve, and the first impedance gradient structure is printed with carbon paste;

[0026] The second impedance gradient structure: the vacancies at the lower left corner and the lower right corner of the inner surface of the honeycomb wall of the paper-based honeycomb unit are printed with silver paste.

[0027] Compared with the prior art, the present invention adopts the above technical solution and has the following technical effects:

[0028] (1) The microwave absorber uses a paper-based honeycomb as a substrate and introduces a printed circuit structure (impedance gradient structure) on the inner wall of the honeycomb to reduce weight and achieve lightweight load-bearing.

[0029] (2) By printing a bidirectional impedance gradient structure, the absorber can be ensured to work effectively at a lower frequency band, the thickness can be reduced, broadband absorption can be achieved, and the absorbing performance in practical applications can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 3D structural diagram of a unit of a broadband paper-based honeycomb microwave absorber with bidirectional impedance gradient provided by the first embodiment of the present invention; wherein (a) is a front view and (b) is a top view;

[0031] Figure 2 is a simulation curve diagram of the relationship between reflection coefficient and frequency of the first embodiment of the present invention;

[0032] Figure 3 3D structural diagram of a unit of a broadband paper-based honeycomb microwave absorber with bidirectional impedance gradient provided by a second embodiment of the present invention; (a) is a front view, and (b) is a top view;

[0033] Figure 4 4 is a simulation curve diagram of the relationship between the reflection coefficient and frequency according to the second embodiment of the present invention.

[0034] The reference numerals are explained as follows: 1 is a paper-based honeycomb unit, 2 is a metal base plate, 3 is a first impedance gradient structure, 4 is a second impedance gradient structure, 5 is an impedance gradient structure, 6 is a third impedance gradient structure, 7 is the lower left corner of the inner surface of the honeycomb wall, and 8 is the lower right corner of the inner surface of the honeycomb wall. DETAILED DESCRIPTION

[0035] The technical solution of the present invention is further described in detail below with reference to the accompanying drawings:

[0036] like Figure 1 As shown, Figure 1 3D structural diagram of a unit of a broadband paper-based honeycomb microwave absorber with bidirectional impedance gradient provided by the first embodiment of the present invention. Figure 1 (a) is the front view. Figure 1 (b) is a top view. The first embodiment is as follows:

[0037] A broadband paper-based honeycomb microwave absorber with bidirectional impedance gradient comprises a paper-based honeycomb structure, wherein the paper-based honeycomb structure comprises N periodically arranged paper-based honeycomb units 1, where N is a natural number greater than 20, and a metal base plate 2 with the bottom of the paper-based honeycomb unit grounded; wherein,

[0038] Each paper-based honeycomb unit includes 6 honeycomb walls, which are the first to sixth honeycomb walls, wherein:

[0039] The inner surfaces of the first to sixth honeycomb walls are all printed with impedance gradient structures;

[0040] Alternatively, the inner surfaces of the second, fourth, and sixth honeycomb walls are printed with an impedance gradient structure;

[0041] Alternatively, the inner surfaces of the second, third, fifth, and sixth honeycomb walls are printed with an impedance gradient structure;

[0042] The impedance gradient structure is used to achieve a bidirectional impedance gradient from free space to a grounded metal base plate. The impedance gradient structure is formed by carbon paste and silver paste.

[0043] The paper-based honeycomb microwave absorber has a three-dimensional structure. The relative dielectric constant of the paper-based honeycomb unit 1 is about 1.6, the relative loss angle is about 0.001, and the thickness of the honeycomb wall of the paper-based honeycomb unit 1 is 0.07 mm.

[0044] The impedance gradient structure 5 includes a first impedance gradient structure 3 and a second impedance gradient structure 4. The pattern of the impedance gradient structure is a gradient shape, wherein the end of the impedance gradient structure close to the air is a first impedance gradient structure composed of carbon paste, and the end of the impedance gradient structure close to the metal base plate is a second impedance gradient structure composed of silver paste; along with the incident direction of the electromagnetic wave, the area of ​​the first impedance gradient structure gradually increases and then decreases, and the area of ​​the second impedance gradient structure gradually increases.

[0045] The impedance gradient structure may be a step-shaped or conical shape, etc. The pattern of the impedance gradient structure may be a gradient shape that changes according to a specific rule (such as linear change, step change, or other gradient functions).

[0046] The impedance gradient structures printed on the honeycomb walls have the same size, and the paper-based honeycomb structure is made of aramid paper or aramid paper doped with carbon fiber.

[0047] The first impedance gradient structure is printed using carbon paste with a square resistance of 187Ω / sq, and the second impedance gradient structure is printed using silver paste with a square resistance of 5Ω / sq, achieving bidirectional impedance gradient matching.

[0048] The relative dielectric constant of the paper-based honeycomb unit is 1.6, the relative loss angle is about 0.001, and the thickness of the honeycomb wall of the paper-based honeycomb unit is 0.07 mm.

[0049] The metal base plate is copper, and the incident direction of the electromagnetic wave refers to the direction from the air to the metal base plate.

[0050] A grounded metal base plate is provided at the bottom of the paper-based honeycomb unit 1 to enhance the electromagnetic wave absorption effect, and cooperates with the impedance gradient structure printed on the inner wall to form a multi-layer absorption system to achieve wide-band microwave absorption. The outer aperture size of the paper-based honeycomb unit 1 is 4 mm, and the height of the paper-based honeycomb unit 1 is 20 mm; in the impedance gradient structure, the first impedance gradient structure 3 is a stepped type printed with carbon paste, and the widths of the six steps from top to bottom are 2.5 mm, 3.4 mm, 3.5 mm, 4 mm, 3.7 mm, and 3.4 mm, respectively, and the heights are 3 mm, 3 mm, 3 mm, 4 mm, 3 mm, and 3 mm, respectively.

[0051] Figure 2 : is a simulation curve diagram of the relationship between the reflection coefficient and frequency of the first embodiment of the present invention, as shown in FIG. Figure 2 As shown, the reflection coefficient of the microwave absorber provided by the first embodiment in the frequency band of 1.79 GHz to 18 GHz is less than -10 dB.

[0052] The absorptivity A(ω) of a microwave absorber can be calculated using the formula A(ω)=1-R(ω)-T(ω), where R(ω) is the reflectivity and T(ω) is the transmittance. The reflectivity and transmittance are directly related to their coefficients: R(ω) = │S11│ 2 , T(ω) = │S21│ 2 , S11 is the reflection coefficient, and S21 is the transmission coefficient. In this microwave absorber, the metal base plate at its bottom completely reflects electromagnetic waves, meaning its transmittance is zero. Therefore, when S11 is less than -10dB, the microwave absorber's absorption rate can reach over 90%. Compared to the prior art, the bidirectional impedance gradient paper-based honeycomb microwave absorber provided in the first embodiment combines the advantages of lightweight, broadband absorption, and reduced thickness. Of particular note, its thickness at the lowest operating frequency is only 0.12 λ. L By printing stepped carbon paste and silver paste, bidirectional impedance gradient matching is achieved, thereby maintaining efficient absorption characteristics within a broadband range.

[0053] Figure 3 3D structural diagram of a unit of a broadband paper-based honeycomb microwave absorber with bidirectional impedance gradient provided by the second embodiment of the present invention; wherein, Figure 3 (a) is the front view. Figure 3 (b) is a top view. The second embodiment is as follows:

[0054] A broadband paper-based honeycomb microwave absorber with bidirectional impedance gradient comprises a paper-based honeycomb structure, wherein the paper-based honeycomb structure comprises N periodically arranged paper-based honeycomb units 1, where N is a natural number greater than 20, and the bottom plate of the paper-based honeycomb unit is a grounded metal bottom plate; wherein,

[0055] Each paper-based honeycomb unit includes 6 honeycomb walls, which are the first to sixth honeycomb walls, wherein:

[0056] The inner surfaces of the first to sixth honeycomb walls are all printed with impedance gradient structures;

[0057] Alternatively, the inner surfaces of the second, fourth, and sixth honeycomb walls are printed with an impedance gradient structure;

[0058] Alternatively, the inner surfaces of the second, third, fifth, and sixth honeycomb walls are printed with an impedance gradient structure;

[0059] The impedance gradient structure is used to achieve a bidirectional impedance gradient from free space to a grounded metal base plate. The impedance gradient structure is formed by carbon paste and silver paste.

[0060] The paper-based honeycomb unit 1 has a relative dielectric constant of 1.6, a relative loss factor of approximately 0.001, and a honeycomb wall thickness of 0.07 mm. A grounded metal baseplate is located at the bottom of the unit. The outer aperture of the unit is 4 mm, and the height is 20 mm.

[0061] The impedance gradient structure in the second embodiment includes a third impedance gradient structure 6 and a fourth impedance gradient structure. The impedance gradient structure printed on the inner surface of the honeycomb wall of the paper-based honeycomb unit is bilaterally symmetrical. The third impedance gradient structure 6 is formed into a gradient shape by cutting the exponential function curve on the rectangular base on the inner surface of the honeycomb wall. The upper edge adopts the first exponential function. Type curve cutting, the lower edge uses the second exponential function Type curve cutting, where are the first to sixth constants, is the dependent variable, is the independent variable, e is the natural base, and carbon paste printing with a sheet resistance of 160Ω / sq is used.

[0062] Fourth impedance gradient structure: The vacancies at the lower left corner 7 of the inner surface of the honeycomb wall in the fourth impedance gradient structure and the lower right corner 8 of the inner surface of the honeycomb wall in the fourth impedance gradient structure are printed using silver paste with a square resistance of 5Ω / sq.

[0063] In the second embodiment, along with the incident direction of the electromagnetic wave, the printed area gradually changes along the curve, the area of ​​the third impedance gradient structure gradually increases and then decreases, and the area of ​​the fourth impedance gradient structure gradually increases, realizing bidirectional impedance gradient matching. Figure 4 This is a simulation curve diagram of the relationship between the reflection coefficient and frequency of the second embodiment of the present invention. After optimization, when The reflection coefficient of the microwave absorber provided by the second embodiment in the frequency band of 1.75 GHz to 18 GHz is less than -10 dB, and its thickness at the lowest operating frequency is only 0.117 λ. L , achieving broadband and low-profile effects.

[0064] The above description is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a technician familiar with this technical field within the technical scope disclosed by the present invention should be covered by the scope of protection of the present invention.

Claims

1. A broadband paper-based honeycomb microwave absorber with bidirectional impedance gradient, characterized in that: The invention comprises a paper-based honeycomb structure, wherein the paper-based honeycomb structure comprises N paper-based honeycomb units arranged periodically, where N is a natural number greater than 20, and the bottom plate of the paper-based honeycomb unit is a grounded metal bottom plate; wherein, Each paper-based honeycomb unit includes 6 honeycomb walls, which are the first to sixth honeycomb walls, wherein: The inner surfaces of the first to sixth honeycomb walls are all printed with impedance gradient structures; Alternatively, the inner surfaces of the second, fourth, and sixth honeycomb walls are printed with an impedance gradient structure; Alternatively, the inner surfaces of the second, third, fifth, and sixth honeycomb walls are printed with an impedance gradient structure; The impedance gradient structure is used to achieve a bidirectional impedance gradient from free space to the grounded metal base plate. The impedance gradient structure is made of carbon paste and silver paste. The impedance gradient structure includes a first impedance gradient structure and a second impedance gradient structure. The pattern of the impedance gradient structure is a gradient shape, wherein the end of the impedance gradient structure close to the air is the first impedance gradient structure composed of carbon paste, and the end of the impedance gradient structure close to the metal base plate is the second impedance gradient structure composed of silver paste. With the incident direction of the electromagnetic wave, the area of ​​the first impedance gradient structure gradually increases and then decreases, and the area of ​​the second impedance gradient structure gradually increases. The first impedance gradient structure is formed on the inner surface of the honeycomb wall by cutting an exponential function curve to form a gradient shape, the upper edge of the gradient shape is cut by the first exponential function curve, and the lower edge of the gradient shape is cut by the second exponential function curve, and the first impedance gradient structure is printed with carbon paste; The second impedance gradient structure: the vacancies at the lower left corner and the lower right corner of the inner surface of the honeycomb wall of the paper-based honeycomb unit are printed with silver paste.

2. The broadband paper-based honeycomb microwave absorber with bidirectional impedance gradient according to claim 1, characterized in that: The pattern of the impedance gradient structure is a gradient shape, and the gradient shape is a linear change, a step change or a gradient function change.

3. The broadband paper-based honeycomb microwave absorber with bidirectional impedance gradient according to claim 1, characterized in that: The impedance gradient structure is a step-type or a pointed cone-type.

4. The broadband paper-based honeycomb microwave absorber with bidirectional impedance gradient according to claim 1, characterized in that: The impedance gradient structures printed on the honeycomb walls have the same size, and the paper-based honeycomb structure is made of aramid paper or aramid paper doped with carbon fiber.

5. The broadband paper-based honeycomb microwave absorber with bidirectional impedance gradient according to claim 1, characterized in that: The outer aperture size of the paper-based honeycomb unit is 4mm and the height is 20mm; the first impedance gradient structure is a stepped type, with the widths of the six steps from top to bottom being 2.5mm, 3.4mm, 3.5mm, 4mm, 3.7mm, and 3.4mm, and the heights being 3mm, 3mm, 3mm, 4mm, 3mm, and 3mm, respectively.

6. The broadband paper-based honeycomb microwave absorber with bidirectional impedance gradient according to claim 1, characterized in that: The first impedance gradient structure is printed using a carbon paste with a sheet resistance of 187Ω / sq, and the second impedance gradient structure is printed using a silver paste with a sheet resistance of 5Ω / sq.

7. The broadband paper-based honeycomb microwave absorber with bidirectional impedance gradient according to claim 1, characterized in that: The relative dielectric constant of the paper-based honeycomb unit is 1.6, the relative loss angle is about 0.001, and the thickness of the honeycomb wall of the paper-based honeycomb unit is 0.07 mm.

8. The broadband paper-based honeycomb microwave absorber with bidirectional impedance gradient according to claim 1, characterized in that: The metal base plate is copper, and the incident direction of the electromagnetic wave refers to the direction from the air to the metal base plate.

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