A metamaterial absorption structure that is easy to engineer

Abstract

The application discloses a kind of easily engineering realized metamaterial absorption structure, belong to microwave metamaterial technical field.The metamaterial absorption structure of the application includes: from bottom to top layer stack arrangement metal backplate, intermediate dielectric layer and upper layer resonance layer;Upper layer resonance layer is composed of periodically arranged resonance unit, and the resonance unit is composed of four square slit metal radiation patches connected by lumped capacitance element;Metal backplate is connected with upper layer metal radiation patch by circular metal through-hole, wherein four square slit metal radiation patches are rotationally symmetric and divided into four corners of unit;The slit direction of square slit metal radiation patch is parallel to its side length, and two metal slits in each square slit metal radiation patch are perpendicular to each other, and the right angle formed by two metal slits points to the center of wave-absorbing structure unit.The application obtains multiple perfect absorption frequency points by adjusting the position and length of metal slit, and the wave-absorbing efficiency reaches 99%.

Description

Technical Field

[0001] This invention belongs to the field of microwave metamaterials technology, specifically relating to a material absorption structure that is easy to implement in engineering. Background Technology

[0002] Very High Frequency (VHF) waves refer to electromagnetic waves with a frequency range of 30MHz-300MHz, falling between the high frequency and ultra-high frequency bands. They can be used for television, FM broadcasting, radar, navigation, and mobile communications. In civil aviation, the VHF band is used for ground and air traffic control, clearance, and airport control of civil aircraft. In maritime communications, fishing boats, merchant ships, yachts, cruise ships, lifeboats, and submarines are almost all equipped with VHF communication radios for search and rescue and external communication; therefore, this frequency band is an indispensable communication method for maritime safety. In specific applications, the operating frequency band of the system is relatively narrow. To avoid mutual interference between frequency bands during use, the use of a frequency-selective absorber has become an important means of protecting the operating frequency.

[0003] Metamaterials are artificially designed electromagnetic materials with unique electromagnetic properties. Metamaterials typically have unit dimensions much smaller than the wavelength, allowing for the artificial control of their unit structure, size, and arrangement to achieve specific electromagnetic wave modulation characteristics, such as negative refraction, perfect absorption, and beam manipulation. In current metamaterial design technology, the overall performance of the unit is influenced by the overall structural parameters, making it difficult to control the operating frequency while maintaining other properties by changing a single parameter. Therefore, improving the robustness of structural parameters and ensuring processing accuracy are crucial for successful metamaterial design. Furthermore, as a subwavelength structure, the size of metamaterials is correlated with the operating wavelength. Very high frequency (VHF) waves correspond to wavelengths of 1-10 m. Reducing the thickness of metamaterials in this frequency band and designing unit structures is a primary consideration for engineering applications in this band. Currently, based on metamaterials, the impedance of the incident wave on the unit surface can be altered by using tuning elements (such as variable capacitors and inductors) and tunable materials (such as liquid crystals, graphene, natural cork, and discrete plasma), thereby changing the operating frequency and achieving reconfigurable absorption frequency. The aforementioned methods have given absorbers new vitality at different frequencies and made it possible to reduce the engineering difficulty of absorbers. However, both using tuning elements and tunable materials present significant challenges in engineering implementation. This is because achieving continuous tunability of the operating frequency requires the use of continuous, precise, and controllable tuning elements and materials. Therefore, to reduce the excessive dependence on elements or materials in the engineering implementation of reconfigurable absorbers and to increase the controllability of reconfigurable metamaterial absorbers, it is necessary to explore a frequency-tunable absorption structure that is easy to implement in engineering, thereby promoting the application of absorbers at very high frequencies. Summary of the Invention

[0004] To facilitate the application of metamaterials in the VHF band, this invention proposes an absorption structure that is easy to engineer. This structure reduces the absorption profile while increasing the tunability of the metamaterial structure, thus enabling adjustable beam operating frequencies.

[0005] The technical solution adopted in this invention is as follows:

[0006] This invention provides a metamaterial absorbing structure that is easy to engineer, comprising: a metal backplate, an intermediate dielectric layer, and an upper resonant layer stacked from bottom to top; wherein the upper resonant layer is composed of periodically arranged resonant units, and each resonant unit is composed of four square slit metal radiating patches connected by lumped capacitance elements; wherein the metal backplate and the upper metal radiating patches are connected by circular metal through holes, and the four square slit metal radiating patches are rotate symmetrically located at the four corners of the unit.

[0007] The square slit metal radiating patches have slits parallel to their side lengths, and the two metal slits within each square slit metal radiating patch are perpendicular to each other, with the right angle formed by the two metal slits pointing towards the center of the absorbing structure unit. This invention creatively introduces adjustable equivalent capacitance into the resonant structure through the introduction of metal slits, and the inward slits increase the equivalent electrical length of the resonant unit, which is beneficial for miniaturizing the resonant unit size. Furthermore, it effectively ensures the stability of the incident angle of the absorbing structure.

[0008] Furthermore, the lumped capacitance element is located inside the square patch and parallel to the side length of the resonant unit. The lumped capacitance element is circularly connected to four square slotted metal radiating patches. The square slotted metal radiating patches and the lumped capacitance element together constitute an equivalent resonant circuit. In existing frequency-tunable absorption structure designs, absorption spectrum modulation is achieved by changing the electrical parameters of the lumped capacitance element to alter the resonant frequency of the equivalent resonant circuit. This invention, by adjusting the physical position and geometric dimensions of the metal slots, changes the equivalent electrical parameters of the square slotted metal radiating patches, thereby changing the resonant frequency of the equivalent resonant circuit and thus achieving absorption spectrum modulation.

[0009] The lumped capacitor element used in this invention has constant electrical parameters and a fixed capacitance value.

[0010] This invention modulates the resonant frequency of the absorbing structure by adjusting the physical position and geometry of the metal gaps, rather than by changing the electrical parameters of the lumped elements to control the absorption spectrum. Compared to existing technologies, this invention has lower requirements for the electrical parameters of the lumped capacitor elements and is easier to implement in engineering. Furthermore, compared to variable capacitors, the fixed capacitors used in this invention not only have the advantages of stable characteristics, long service life, and less susceptibility to environmental influences, but also have the advantage of low cost.

[0011] Furthermore, the intermediate dielectric layer is provided with four circular metal through holes, which are located at the four corners of the resonant unit, with the top end connected to the upper resonant layer and the bottom end connected to the metal back plate.

[0012] Furthermore, the intermediate dielectric layer is a mature FR-4 dielectric board with low manufacturing cost.

[0013] Furthermore, the side length of the periodic resonant unit is much smaller than the wavelength related to the operating frequency band of the resonant unit, approximately 0.012. ( (Wavelength corresponding to the operating frequency band). The side length of the periodic resonant unit in this invention satisfies the size condition of the metamaterial periodic unit, and since the unit size is much smaller than the operating wavelength, the perfect absorbing structure is robust to a certain extent to the incident angle.

[0014] This invention incorporates a metal backplate at the bottom of the absorbing structure as a total internal reflection mirror to prevent the transmission of input electromagnetic waves. An intermediate dielectric layer serves as the dielectric support structure. The metal backplate, intermediate dielectric layer, and upper resonant unit constitute a classic "sandwich" absorbing structure. The equivalent resonant circuit formed by the lumped capacitance element and the upper resonant unit achieves characteristic impedance consistent with the surrounding environment. A perfect match.

[0015] The working principle of this invention is as follows: When electromagnetic waves are incident on the material absorbing structure, the surface of the upper resonant unit is equivalent to a resonant circuit, inducing a current at the corresponding resonant frequency, while the metal back plate induces a reverse induced current. The induced current generated by the resonant unit and the metal back plate forms an induced loop current within the absorbing structure through the circular metal through-holes at the corners of the unit, thereby generating magnetic resonance. The induced loop current generates dielectric loss through the intermediate dielectric layer and ohmic loss through the resonant unit; thus, it absorbs the incident electromagnetic energy (electromagnetic waves) and converts it into heat energy. The introduction of metal gaps at different positions and with different sizes and lengths results in different equivalent lumped parameters, allowing the absorbing structure to have different resonant frequencies. Therefore, by adjusting the position and size of the metal gaps, the function of perfect absorption under the absorbing structure can be changed, thereby introducing a new dimension of operating frequency control to compensate for the operating frequency deviation caused by material properties, processing and installation errors, and calculation errors in engineering implementation.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] 1. The metamaterial absorbing structure proposed in this invention is easy to implement in engineering. It can achieve multiple perfect absorption frequencies by adjusting the position and length of the metal gaps, with an absorption efficiency of 99% at these frequencies. This metamaterial absorbing structure meets the application requirements for multi-frequency perfect absorption of metamaterial absorbing structures in the field of electromagnetic compatibility in the VHF band and in electromagnetic stealth applications.

[0018] 2. The metamaterial absorbing structure proposed in this invention, which is easy to implement in engineering, can maintain an absorption efficiency of over 90% under TM / TE dual-polarization incident conditions within 50°, demonstrating that this invention can maintain good absorption performance in application scenarios with large incident angles.

[0019] 3. The metamaterial absorbing structure proposed in this invention, which is easy to engineer, allows for adjustment of the operating frequency by adjusting the metal gaps after fabrication, compared to existing frequency-tunable absorbing structures. This makes it easier to process and does not rely on the electrical parameters of lumped elements, thus reducing the precision requirements for critical structural dimensions. The dielectric layer material and metal material used in this invention are common FR-4 dielectric substrate and oxygen-free copper, avoiding high material and processing costs.

[0020] 4. The frequency-tunable VHF metamaterial perfect absorber structure proposed in this invention has the advantage of low profile, with a structure thickness of 4.075 mm, approximately 0.0015 mm. ( (The operating wavelength is specified). This invention provides a flexible assembly solution for engineering applications, while reducing system complexity and facilitating compact system design. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the structural units of an embodiment of the present invention.

[0022] Figure 2 This is a schematic diagram of a multi-period array according to an embodiment of the present invention.

[0023] Figure 3 This is a side view of a structural unit according to an embodiment of the present invention.

[0024] Figure 4 The graph shows the absorption efficiency results for TE / TM.

[0025] Figure 5 This is a schematic diagram illustrating the effect of the incident angle on TE / TM.

[0026] Figure 6 Schematic diagrams of different metal slotted absorption structure units.

[0027] Figure 7 The results of adjusting the TE / TM absorption frequency for different metal slots are shown in the figure.

[0028] Explanation of reference numerals in the attached diagram: 1 is the metal backplate, 2 is the intermediate dielectric layer, 3 is the upper resonant layer, 4 is the square slotted metal radiating patch, 5 is the metal gap, 6 is the metal through-hole, and 7 is the lumped capacitor element. Detailed Implementation

[0029] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0030] As attached Figure 1 As shown, the metamaterial absorbing structure proposed in this embodiment, which is easy to implement in engineering, adopts a metal-dielectric-metal structure, comprising, from bottom to top, a bottom metal backplate 1, an intermediate dielectric layer 2, and an upper resonant layer 3, all stacked together. The upper resonant layer 3 consists of periodically arranged resonant units, each composed of four square slotted metal radiating patches 4 connected by lumped capacitor elements 7. The slots of the square slotted metal radiating patches 4 are parallel to their side lengths, and the two metal slots 5 within each square slotted metal radiating patch 4 are perpendicular to each other. The right angle formed by the two metal slots 5 points towards the center of the absorbing structure unit. The upper resonant layer and the metal backplate are connected vertically at the four corners of the absorbing structure unit through metal through-holes 6 located in the intermediate dielectric layer 2 (the angle connecting the square radiating patch and the metal through-hole is defined as the outer corner of the patch; defining the outer corner facilitates subsequent positioning of the metal slots).

[0031] The upper resonant layer 3 is fabricated by chemical etching, specifically by chemically etching one side of the copper layer on the selected FR-4 double-layer copper-clad dielectric substrate. After etching, the lumped capacitor element 7 is soldered to the metal resonant unit to form an equivalent resonant circuit at a specific frequency.

[0032] The intermediate dielectric layer 2 is an FR-4 double-layer copper-clad dielectric substrate with a relative permittivity of 4.3, a relative permeability of 1, and a copper layer thickness of 0.035 mm. By controlling the physical location and geometric dimensions of the metal slots, the absorption spectrum of the absorbing structure can be modulated.

[0033] The metal backplate 1 and the intermediate dielectric layer 2 are composed of FR-4 double-layer copper-clad dielectric boards with a size of 34mm×34mm and a thickness of 4mm.

[0034] The upper resonant layer 3 is formed by chemical etching of one side of the copper layer of a selected double-sided copper-clad FR-4 dielectric substrate into a periodic pattern with a specific unit shape as described in this invention. In this embodiment, the square slotted metal radiating patch 4 in the upper resonant layer 3 is a rectangle with an aspect ratio of 1, and the physical location and geometric length of the resonant slots correspond to the corresponding absorption resonant frequencies. Figure 1 This is a schematic diagram of the structure of an embodiment of the present invention.

[0035] The square slotted metal radiating patch 4 is a rectangular metal patch with a length-to-width ratio of 1, measuring 14mm×14mm×0.035mm. The metal slot 5 is a rectangular slit of 8.2mm×0.5mm. Furthermore, the metal slot 5 is located 9mm away from the outer corner of the square metal radiating patch.

[0036] Metal through-hole 6 is a metal post with a radius of 1.25mm, located 2.25mm from the four corners of the metal back plate.

[0037] The lumped capacitor element 7 is a metal film chip capacitor, model ECHU1H121GX5120pF. The lumped capacitor element 7 is soldered to the inner center of two square-slit metal radial patches 4. The lumped capacitor element 7 is used to connect the upper metal resonant layer 3 into an LC resonant circuit.

[0038] The frequency-tunable VHF metamaterial perfect absorption structure proposed in this invention was analyzed by full-wave electromagnetic simulation using commercial electromagnetic simulation software. The absorption structure unit was set as a periodic boundary around its perimeter, and the upper and lower ports adopted the Floquet port mode to obtain the S-parameter curves of the absorption structure.

[0039] Its absorption efficiency is shown in the attached figure. Figure 4 As shown, changing the polarization of the incident electromagnetic wave, from Figure 4 As shown, the absorbing structure used in this invention can achieve an absorption efficiency of 99.3% at a working frequency of 108.7 MHz under TE / TM incident polarization.

[0040] By setting the incident angle of the incident wave respectively θ The influence of incident angle on the absorption efficiency of the absorbing structure was analyzed for 0°, 10°, 20°, 30°, 40°, 50°, 60°, and 70°. A schematic diagram illustrating the influence of TE / TM polarization incident angle is attached. Figure 5 As shown in the figure, simulation results indicate that under TE / TM polarization, the absorption efficiency of the absorbing structure gradually decreases with increasing incident angle, from 99.38% to 94.08%, while maintaining an absorption rate above 90%. However, when the incident angle increases to 60°, the absorption efficiency drops sharply to 87.4%, and further decreases to 74.15% when the incident angle increases to 70°. These results demonstrate that the absorbing structure used in this invention can maintain good absorption efficiency over a wide range of incident angles under TE / TM polarization.

[0041] As attached Figure 6 As shown, the frequency-tunable function of the absorbing structure is analyzed by changing the physical location and geometry of the metal gaps. TE / TM polarized incident results are attached. Figure 7As shown in the figure. Simulation results show that by adjusting the physical position and geometry of the metal slots, the absorption frequency of the structure can be shifted within the 100-111 MHz frequency range, while maintaining an absorption rate above 80%. As the length of the metal slots gradually increases and the physical position gradually moves inward towards the inner part of the unit, the absorption frequency of the absorbing structure gradually shifts to lower frequencies. The absorption efficiency reaches its peak when the metal slot is 9 mm away from the outer corner of the square metal radiating patch, and gradually decreases as it moves to both sides. The above results demonstrate that, under TE / TM polarization, the absorption frequency of the absorbing structure of this invention can be adjusted by combining different combinations of the physical positions and geometry of the metal slots.

[0042] The simulation results above demonstrate that the VHF metamaterial perfect absorption structure of this invention, which is easy to implement in engineering, possesses perfect absorption, adjustable absorption frequency, low profile, and maintains high absorption performance even at large incident angles. It has broad application prospects and practical value in electromagnetic compatibility within the VHF range. Any changes to the parameters mentioned in this invention, as well as the design shape of the various resonant structures, fall within the scope of protection of this invention.

Claims

1. A metamaterial absorption structure for very high frequencies that is easily engineered, characterized in that, include: The metal backplate (1), the intermediate dielectric layer (2), and the upper resonant layer (3) are stacked from bottom to top. The upper resonant layer (3) is composed of periodically arranged resonant units. Each resonant unit consists of four square slotted metal radiating patches (4) connected by lumped capacitor elements (7). The lumped capacitor elements (7) have constant electrical parameters and fixed capacitance values. The lumped capacitor elements (7) are located inside the square slotted metal radiating patches (4) and are parallel to the side length of the resonant unit. The square slotted metal radiating patches (4) and the lumped capacitor elements (7) together constitute an equivalent resonant circuit. The metal back plate (1) and the upper metal radiation patch (4) are connected by a circular metal through hole (6), wherein four square slotted metal radiation patches (4) are rotate symmetrically located at the four corners of the unit; The slit direction of the square slit metal radiation patch (4) is parallel to its side length, and the two metal slits (5) in each square slit metal radiation patch (4) are perpendicular to each other, and the right angle formed by the two metal slits (5) points to the center of the absorbing structure unit; the absorption spectrum can be controlled by adjusting the physical position and geometric size of the metal slits (5). The side length of the resonant unit is 0.

012. The structural thickness is 0.0015. , This refers to the wavelength corresponding to the operating frequency band.

2. The easily engineerable metamaterial absorption structure for very high frequencies according to claim 1, characterized in that, The intermediate dielectric layer (2) is provided with four circular metal through holes (6), which are located at the four corners of the resonant unit. The top end is connected to the upper resonant layer (3), and the bottom end is connected to the metal back plate (1).

3. The easily engineering-implementable metamaterial absorption structure for very high frequencies according to claim 1, characterized in that, The intermediate dielectric layer (2) is an FR-4 dielectric board.

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