A curved conformal broadband programmable electromagnetic absorption metasurface

Abstract

The application discloses a curved surface conforming broadband programmable electromagnetic absorption metasurface which is composed of a plurality of periodically arranged reconfigurable electromagnetic units, each reconfigurable electromagnetic unit comprising a top layer dielectric substrate, a low dielectric constant spacing layer and a continuous metal ground layer arranged from top to bottom. The upper surface of the top layer dielectric substrate is provided with a symmetrical metal resonance pattern, a bias feed line and a PIN diode loaded on the metal resonance pattern. By controlling the bias state of the PIN diode, the equivalent impedance and the equivalent current path of the metal resonance pattern are changed, the joint regulation of the unit reflection amplitude and the reflection phase can be realized. The continuous metal ground layer is used for suppressing transmission, so that the reflection regulation of the metasurface is shown as dynamic wave absorption regulation or phase encoding regulation. The reflection modulation depth of the metasurface is not less than 10 dB (maximum 40 dB) under the condition of 5.5-13.5 GHz and 30° curved surface configuration.

Description

Technical Field

[0001] This invention belongs to the fields of electromagnetic functional materials, electromagnetic compatibility, electromagnetic shielding and programmable metasurface technology, specifically relating to a broadband reconfigurable metasurface unit with dynamic absorption control function and a curved conformal broadband programmable electromagnetic absorbing metasurface composed therefrom. Background Technology

[0002] With the development of radar detection, wireless communication, electronic countermeasures, and highly integrated electronic devices, broadband electromagnetic absorption, electromagnetic shielding, and scattering modulation technologies have significant application value in electromagnetic compatibility protection, target stealth, and complex electromagnetic environment control. Traditional absorbing materials typically rely on dielectric loss, magnetic loss, or multilayer impedance matching structures to achieve electromagnetic wave absorption. Their electromagnetic response is essentially fixed after processing, making dynamic adjustment difficult according to actual application requirements. Furthermore, to obtain a wider absorption bandwidth, traditional absorbing structures often require significant thickness or complex multilayer structures, which is not conducive to lightweight, low-profile, and conformal applications. Metasurfaces, composed of periodic or aperiodic arrangements of subwavelength artificial units, can control the amplitude, phase, polarization, and propagation direction of incident electromagnetic waves by adjusting the equivalent electromagnetic parameters of the units. Reflective absorbing metasurfaces based on metallic resonant patterns, dielectric spacers, and metallic grounding layers have advantages such as low profile and easy integration, and have been used in broadband absorption and radar cross-section reduction scenarios. However, existing reconfigurable absorbing metasurfaces still suffer from insufficient broadband dynamic modulation capabilities, complex bias structures, and poor adaptability to curved surfaces. Some structures can only achieve absorption state switching in narrow bands or limited frequency points, making it difficult to obtain a large reflection amplitude modulation depth over a wide frequency range; some structures require complex bias networks or multi-layer metal patterns, which are not conducive to processing and array expansion; when the metasurface is mounted on a curved carrier, bending deformation may also change the unit resonance characteristics and array coupling relationship, leading to a decrease in absorption performance. Therefore, there is an urgent need for a broadband reconfigurable metasurface unit and metasurface array that is simple in structure, easy to bias control, suitable for conformal mounting on curved surfaces, and capable of achieving significant dynamic absorption modulation over a wide frequency range. Summary of the Invention

[0003] The purpose of this invention is to provide a curved, conformal, broadband programmable electromagnetic absorbing metasurface to solve the problems of fixed functional states, insufficient dynamic adjustment capabilities, and insufficient adaptability of curved surface deployment in existing electromagnetic absorbing structures.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: a broadband reconfigurable metasurface unit with dynamic absorption modulation function, the metasurface unit comprising, from top to bottom, a metal resonant layer, a top dielectric substrate, a polymethacrylimide foam spacer layer, and a metal ground layer; the metal resonant layer comprises a symmetrically arranged metal resonant pattern and a PIN diode loaded on the metal resonant pattern; by controlling the bias state of the PIN diode, the equivalent current path and equivalent impedance of the metal resonant pattern are changed, thereby adjusting the reflection amplitude, reflection phase, and absorption characteristics of the metasurface unit.

[0005] Furthermore, the metal resonant pattern includes an integrally connected mask-shaped metal main body structure and a bias feed line electrically connected to the mask-shaped metal main body structure; the mask-shaped metal main body structure is symmetrically distributed, including a left pattern part and a right pattern part, with a strip-shaped gap in the middle; opening regions are respectively provided in the pattern parts on both sides to increase the equivalent current path in the mask-shaped metal main body structure and form multiple coupled resonant modes, thereby expanding the working bandwidth of the metasurface unit.

[0006] Furthermore, the PIN diode is disposed at the strip gap of the metal resonant pattern. A DC bias voltage is applied to the PIN diode through a bias feed line to change the equivalent impedance of the PIN diode, thereby changing the local current distribution, equivalent current path, and equivalent surface impedance of the mask-shaped metal main body structure. The linewidth of the bias feed line is much smaller than the linewidth of the main structure in the metal resonant pattern to reduce the influence of the bias feed structure on the radio frequency electromagnetic response.

[0007] Furthermore, the top dielectric substrate serves to support the metal resonant layer and provide mechanical support for the metal resonant layer, PIN diode, and bias feed line. The top dielectric substrate is a low-loss microwave dielectric substrate with a relative permittivity of 2.65. The top dielectric substrate and the metal resonant layer together influence the surface current distribution and equivalent resonance characteristics of the metasurface unit.

[0008] Furthermore, the foam spacer layer is disposed between the top dielectric substrate and the metal ground layer to adjust the electromagnetic coupling strength between the metal resonant layer and the metal ground layer, and to increase the equivalent electromagnetic thickness of the metasurface unit. The foam spacer layer is a polymethacrylimide foam spacer layer with a relative permittivity of 1.05. The foam spacer layer has low dielectric constant, low density, and easy molding properties, which is beneficial for reducing structural weight, reducing dielectric loss, and improving the structural stability of the metasurface unit under curved conformal configurations.

[0009] Furthermore, the top dielectric substrate, foam spacer layer, and metal ground layer constitute a flexible stacked structure, enabling the metasurface unit to adapt to planar, cylindrical, or curved carriers. Multiple broadband reconfigurable metasurface units can be arranged in a two-dimensional periodic array and conformally disposed on the curved carrier, forming a curved configuration with a central angle of 30°, thereby forming a broadband reconfigurable metasurface. The PIN diodes in the broadband reconfigurable metasurface units can be connected to a bias control circuit, which is used to independently control, group control, or control the bias state of the multiple broadband reconfigurable metasurface units as a whole, thereby forming different spatial coding distributions and realizing dynamic absorption modulation, beam modulation, or reflection phase coding modulation.

[0010] Beneficial effects:

[0011] This invention achieves a reflection amplitude modulation depth of at least 10 dB and a maximum modulation depth of 40 dB within a wide frequency range of 5.5 GHz to 13.5 GHz, while maintaining a broadband reconfigurable electromagnetic response in a curved surface configuration with a center angle of 30°. By setting an open region, the equivalent current path in the mask-shaped metal body structure can be increased, forming multiple coupled resonant modes, thereby expanding the operating bandwidth of the metasurface unit. The linewidth of the bias feed line is much smaller than that of the metal body structure, which can reduce the influence of the bias feed structure on the RF electromagnetic response. The polymethacrylamide foam spacer layer has low dielectric constant, low density, and easy molding characteristics, which is beneficial for reducing structural weight, reducing dielectric loss, and improving the structural stability of the metasurface unit in a curved conformal configuration. The continuous metal grounding layer can suppress transmission, so that the absorption rate of the electromagnetic absorption unit is mainly determined by the reflection coefficient. The absorption intensity can be dynamically controlled by adjusting the reflection coefficient by adjusting the bias state. In summary, this invention solves the problems of insufficient broadband dynamic modulation capability, complex bias structure, and poor adaptability to curved carriers in existing reconfigurable absorbing metasurfaces. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of the stacked structure of the electromagnetic absorption unit.

[0013] Figure 2 This is a top-down view of the top metal pattern.

[0014] Figure 3 This is a graph showing the reflection coefficient of the electromagnetic absorption unit under different bias conditions.

[0015] Figure 4 This is a graph showing the reflection coefficient of the electromagnetic absorption unit under different bias conditions with an oblique incidence of 30°.

[0016] Figure 5The diagram shows the structure and test results of the conformal broadband reconfigurable metasurface. (a) is the structural schematic of the conformal broadband reconfigurable metasurface, and (b) is the test result.

[0017] Figure 6 The graphs show the measured reflection coefficients of the conformal broadband reconfigurable metasurface under different bias conditions. (a) represents the measured reflection coefficients in the lower frequency band of 4-8 GHz, and (b) represents the measured reflection coefficients in the higher frequency band of 8-14 GHz. Detailed Implementation

[0018] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0019] Reference Figure 1 This embodiment provides an electromagnetic absorption unit with dynamic absorption modulation function. The electromagnetic absorption unit includes a top metal pattern, a dielectric substrate, a foam spacer layer, and a metal ground layer stacked sequentially. The top metal pattern is used to couple with the incident electromagnetic wave and generate a surface current distribution; the top dielectric substrate is used to support the top metal pattern and active devices; the foam spacer layer is disposed between the top dielectric substrate and the metal ground layer to adjust the electromagnetic coupling strength between the top metal pattern and the metal ground layer and increase the equivalent electromagnetic thickness of the electromagnetic absorption unit; the metal ground layer is a continuous metal layer used to suppress the transmission of the incident electromagnetic wave, so that the electromagnetic absorption unit constitutes a reflective electromagnetic absorption structure. The continuous metal ground layer and the top metal resonant pattern together constitute a reflective electromagnetic absorption structure.

[0020] In one specific embodiment, the thickness of the top dielectric substrate is 0.8 mm, the material is polytetrafluoroethylene fiberglass cloth nano-ceramic copper clad laminate F4BTM-1 / 2, and the dielectric constant is 2.65; the thickness of the foam spacer layer is 2.4 mm, the material is polymethacrylimide foam, and the dielectric constant is 1.05; and the metal ground is disposed below the foam spacer layer.

[0021] Reference Figure 2 A metal resonant pattern and PIN diodes are disposed on the top dielectric substrate. The metal pattern includes a mask-shaped metal body structure, PIN diodes loaded on the metal body structure, and bias feed lines electrically connected to the PIN diodes. The mask-shaped metal body structure includes a left-facing patterned portion and a right-facing patterned portion, which serve as the main electromagnetic resonant structure for coupling with incident electromagnetic waves and generating surface currents; the PIN diodes are used to change the local equivalent impedance under different bias states; and the bias feed lines are used to apply a DC bias voltage to the PIN diodes.

[0022] In this example, the period p of the electromagnetic absorption unit is 12.5 mm, and the parameters of the mask-shaped main structure are l1=2.24 mm, l2=1.12 mm, l3=5.6 mm, l4=1.12 mm, l5=4.48 mm, l6=1.12 mm, h1=2.24 mm, h2=5.6 mm, h3=2.24 mm, h4=4.48 mm, l5=6.72 mm, the metal gap is 0.3 mm, and the PIN diode is an SMP1320-040LF type PIN diode. Opening regions are respectively provided in the left and right patterned sections. These opening regions are used to change the surface current path on the mask-shaped metal main structure, causing the surface current to form bypass paths and local coupling paths, thereby facilitating the formation of multiple equivalent current paths and coupled resonant modes to expand the operating bandwidth of the electromagnetic absorption unit.

[0023] In this example, a PIN diode is applied at a predetermined position on the mask-shaped metal body structure. This predetermined position is located in the current-concentrated region of the mask-shaped metal body structure. By controlling the bias state of the PIN diode, its equivalent impedance can be changed, thereby altering the local current distribution and equivalent surface impedance of the mask-shaped metal body structure. When the PIN diode is in the conducting state, it can be equivalent to a low-impedance connection state, causing the electromagnetic absorption unit to form a first equivalent surface impedance state. When the PIN diode is in the cutoff state, it can be equivalent to a high-impedance or capacitive connection state, causing the electromagnetic absorption unit to form a second equivalent surface impedance state. Since different equivalent surface impedance states correspond to different reflection coefficients, the electromagnetic absorption unit can dynamically switch between different absorption states. Because the metal grounding layer can suppress electromagnetic wave transmission, the absorption rate of the electromagnetic absorption unit is mainly determined by the reflection coefficient. When transmission is approximately zero, the absorption rate A can be expressed as:

[0024] (1)

[0025] in, This represents the reflection coefficient of the electromagnetic absorption unit. Therefore, the reflection coefficient can be changed by adjusting the bias state of the PIN diode. This allows for dynamic control of absorption intensity.

[0026] Reference Figure 3The electromagnetic absorption unit was simulated using the CST Microwave Studio frequency domain solver. Periodic boundary conditions were used to simulate an infinite periodic array structure, and the electric field polarization direction of the incident electromagnetic wave was matched with the arrangement direction of the PIN diodes. By changing the forward bias current applied to the PIN diodes, the reflection coefficient curves of the electromagnetic absorption unit under different bias states were obtained. In this embodiment, the bias current states included 0 mA, 1 μA, 10 μA, 20 μA, 30 μA, 50 μA, and 1 mA. Simulation results show that as the bias state of the PIN diodes changes, the equivalent impedance of the PIN diodes changes, thereby adjusting the local surface current path and equivalent surface impedance of the mask-shaped metal body structure. This allows the electromagnetic absorption unit to achieve a reflection amplitude modulation depth of no less than 10 dB in a wide frequency range from 5.5 GHz to 13.5 GHz, with a maximum modulation depth of up to 40 dB.

[0027] Reference Figure 4 To verify the operational stability of the electromagnetic absorption unit under oblique incidence conditions, the reflection coefficient of the electromagnetic absorption unit under 30° oblique incidence conditions was simulated and analyzed. Under 30° oblique incidence conditions, the electromagnetic absorption unit still maintains a reflection amplitude modulation depth of not less than 10 dB in most frequency ranges from 5.5 GHz to 13.5 GHz, indicating that the electromagnetic absorption unit has good adaptability to changes in the incident angle within a certain range.

[0028] Reference Figure 5 This embodiment further provides a curved conformal broadband reconfigurable metasurface. The curved conformal broadband reconfigurable metasurface includes 41*13 electromagnetic absorption units, which are arranged in a two-dimensional periodic array and conformally disposed on the surface of the curved carrier. Figure 5 (a) shows a schematic diagram of the structure of a conformal broadband reconfigurable metasurface. Figure 5 Figure (b) shows a test diagram of the aforementioned conformal broadband reconfigurable metasurface. The broadband reconfigurable metasurface is bent into a curved configuration with a central angle of 30° to simulate its application on curved carriers or non-planar electromagnetic protection surfaces. The conformal broadband reconfigurable metasurface is connected to PIN diodes in each electromagnetic absorption unit via a bias control circuit. This bias control circuit is used to independently control, group control, or control the bias states of the multiple electromagnetic absorption units as a whole, thereby forming different spatial coding distributions and realizing dynamic absorption modulation, beam modulation, or reflection phase coding modulation.

[0029] Reference Figure 6The reflection coefficient of the conformal broadband reconfigurable metasurface under different bias states was measured. During the test, a metal plate with the same or similar size as the conformal broadband reconfigurable metasurface was used as a reference to normalize the measured reflection results, thereby obtaining the electromagnetic loss or reflection modulation results of the conformal broadband reconfigurable metasurface. The measured results show that under the curved configuration, the broadband reconfigurable metasurface still exhibits significant differences in reflection coefficient under different bias states, indicating that it can still maintain dynamic absorption modulation capability under the conformal configuration. In one specific embodiment, the conformal broadband reconfigurable metasurface maintains a reflection amplitude modulation depth of not less than 10 dB in the target frequency band of 5 GHz to 13.5 GHz, and the maximum reflection amplitude modulation depth can reach 40 dB.

[0030] The above description is only a preferred embodiment of the present invention and does not constitute a limitation on the present invention. For those skilled in the art, various modifications and improvements can be made without departing from the innovative concept of the present invention, but these changes all fall within the protection scope of the present invention.

Claims

1. A conformal broadband programmable electromagnetic absorbing metasurface, characterized in that, It includes multiple periodically arranged electromagnetic absorption units; Each of the electromagnetic absorption units includes a top dielectric substrate, a foam spacer layer, and a continuous metal grounding layer stacked from top to bottom; The top dielectric substrate has a metal resonant pattern and a PIN diode loaded on the metal resonant pattern; The metal resonant pattern includes a mask-shaped symmetrical metal main body structure and a thin bias feed line connected to the PIN diode, wherein the line width of the thin bias feed line is smaller than the feature line width of the mask-shaped symmetrical metal main body structure. The PIN diode is disposed in the current concentration region of the mask-shaped symmetrical metal body structure and is used to change its equivalent impedance under external bias control. The continuous metal grounding layer is a continuous metal layer used to suppress the transmission of electromagnetic waves.

2. The conformal broadband programmable electromagnetic absorbing metasurface according to claim 1, characterized in that, The foam spacer layer is a polymethacrylimide foam spacer layer, and the relative permittivity of the foam spacer layer is lower than that of the top dielectric substrate.

3. The conformal broadband programmable electromagnetic absorbing metasurface according to claim 1, characterized in that, The continuous metal grounding layer is a continuous metal floor, and the continuous metal grounding layer and the metal resonant pattern on the top dielectric substrate together constitute a reflective electromagnetic absorption structure.

4. The conformal broadband programmable electromagnetic absorbing metasurface according to claim 1, characterized in that, The mask-shaped symmetrical metal main body structure includes a left patterned part and a right patterned part, with a strip-shaped gap between the left patterned part and the right patterned part, and the PIN diode is disposed in the strip-shaped gap; the left patterned part and the right patterned part are respectively provided with opening areas.

5. A conformal broadband programmable electromagnetic absorbing metasurface according to any one of claims 1 to 4, characterized in that, It also includes a bias control circuit, which is electrically connected to the PIN diode through the thin bias feed line and is used to apply a DC bias voltage to the PIN diode.

6. The conformal broadband programmable electromagnetic absorbing metasurface according to claim 5, characterized in that, The bias control circuit is configured to independently control the bias state of the PIN diodes in a single electromagnetic absorption unit, or to group and control the bias state of the PIN diodes in multiple electromagnetic absorption units, or to control the bias state of the PIN diodes in all electromagnetic absorption units as a whole.

7. The conformal broadband programmable electromagnetic absorbing metasurface according to claim 1, characterized in that, The top dielectric substrate, foam spacer layer and continuous metal ground layer constitute a flexible and bendable stacked structure, and the metasurface is used to adapt to planar carriers, cylindrical carriers or curved carriers.

8. The conformal broadband programmable electromagnetic absorbing metasurface according to claim 7, characterized in that, Multiple electromagnetic absorption units are arranged in a two-dimensional periodic array and conformally disposed on the curved carrier, and the array is bent to form a curved configuration with a central angle of 30°.

Images