阅读说明：本技术 一种射频感性耦合等离子体叠加相位梯度超表面吸波结构 (Radio frequency inductive coupling plasma superposition phase gradient super-surface wave-absorbing structure ) 是由 徐浩军 魏小龙 韩欣珉 武欣 常怡鹏 于 2020-07-17 设计创作，主要内容包括：本发明公开了一种射频感性耦合等离子体叠加相位梯度超表面吸波结构,包括等离子体耦合相位梯度超表面结构,等离子体耦合相位梯度超表面结构包括射频感性耦合等离子体源、相位梯度超表面和闭式透波介质腔,其中,射频感性耦合等离子体源置于闭式透波介质腔中,相位梯度超表面固定于闭式透波介质腔外侧底部。相位梯度超表面为由金属铜板、介质基板、金属单元阵列从下到上依次组成的三层结构,金属单元阵列是由6个宽度相等、高度逐渐增加的H型金属贴片从左向右依次设置形成的金属单元在介质基板上从上到下重复排列而成。解决了现有等离子体吸波结构厚度较大、结构适用性较差而难以满足使用需求的问题,以及电磁波衰减幅度小的问题。(The invention discloses a radio frequency inductive coupling plasma superposition phase gradient super-surface wave absorbing structure which comprises a plasma coupling phase gradient super-surface structure, wherein the plasma coupling phase gradient super-surface structure comprises a radio frequency inductive coupling plasma source, a phase gradient super-surface and a closed wave-transmitting medium cavity, wherein the radio frequency inductive coupling plasma source is arranged in the closed wave-transmitting medium cavity, and the phase gradient super-surface is fixed at the bottom of the outer side of the closed wave-transmitting medium cavity. The phase gradient super-surface is a three-layer structure which is formed by sequentially arranging metal copper plates, a dielectric substrate and a metal unit array from bottom to top, wherein the metal unit array is formed by repeatedly arranging metal units which are formed by sequentially arranging 6H-shaped metal patches with equal width and gradually increased height from left to right on the dielectric substrate. The plasma wave-absorbing structure solves the problems that the existing plasma wave-absorbing structure is large in thickness and poor in structure applicability and is difficult to meet the use requirement, and the electromagnetic wave attenuation amplitude is small.)

1. The radio frequency inductive coupling plasma superposition phase gradient super-surface wave-absorbing structure is characterized by comprising a plasma coupling phase gradient super-surface structure (1), wherein the plasma coupling phase gradient super-surface structure (1) comprises a radio frequency inductive coupling plasma source (2), a phase gradient super-surface (3) and a closed wave-transmitting medium cavity (4), the radio frequency inductive coupling plasma source (2) is arranged in the closed wave-transmitting medium cavity (4), and the phase gradient super-surface (3) is fixed at the bottom of the outer side of the closed wave-transmitting medium cavity (4).

2. The structure of claim 1, wherein the phase gradient subsurface (3) is a three-layer structure comprising a copper metal plate, a dielectric substrate, and a metal element array from bottom to top, and the metal element array is formed by arranging 6H-shaped metal patches with equal width and gradually increasing height from left to right in sequence, and the metal elements are arranged on the dielectric substrate from top to bottom in a repeating manner.

3. The structure of claim 2, wherein each H-shaped metal patch has a width of 4.6mm, a vertical metal patch has a width of 0.8mm, two vertical metal patches have a spacing width of 3.0mm, and a horizontal metal patch has a width of 0.8 mm; the height of the 6H-shaped metal patches of each metal unit is 1.5mm, 3.38mm, 3.79mm, 4.06mm, 4.42mm and 5.5mm from left to right in sequence.

4. The radio frequency inductively coupled plasma superimposed phase gradient super-surface wave-absorbing structure as claimed in claim 2 or 3, wherein the horizontal metal patches of 6H-shaped metal patches of each metal unit are located on the same straight line, and the intervals of two H-shaped metal patches adjacent to each other on the left and right in each metal unit are equal; the width of each metal unit is the sum of the width of the H-shaped metal patch and the interval between two adjacent H-shaped metal patches on the right.

5. The structure of claim 4, wherein the interval between two H-shaped metal patches adjacent to each other on the left and right sides of the metal unit is 3.4mm, and the width of each metal unit is 8 mm.

6. The structure of claim 2, 3 or 5, wherein the dielectric substrate is an FR4 dielectric slab with a dielectric constant of 4.5, a dielectric loss tangent of 0.025 and a thickness of 1.85 mm.

7. The structure of any one of claims 1 to 3 or 5, wherein the closed wave-transparent medium cavity (4) is a cylindrical structure manufactured by an all-quartz glass process, the radial diameter of the closed wave-transparent medium cavity is 40cm, and the thickness of the closed wave-transparent medium cavity, namely the height of the cylindrical structure, is 2 cm.

8. The structure of any one of claims 1 to 3 or 5, wherein the RF inductively coupled plasma source (2) is generated by excitation of a power system, a vacuum system and an atmosphere system.

9. The structure of claim 8, wherein the power system comprises a coil antenna (5), a matcher (7), a radio frequency power supply (9), and a water-cooling circulation system;

the radio frequency power supply (9) is connected with the input end of the matcher (7), and the output end of the matcher (7) is connected with the coil antenna (5);

the coil antenna (5) is a spiral coil which is formed by winding a hollow brass tube and has 3 turns, and the water cooling circulation system is communicated with the interior of the coil antenna (5) through an insulating rubber tube;

the vacuum system comprises a vacuum pump (8), a vacuum gauge (11) and a first vacuum valve (12), wherein the vacuum pump (8) is communicated with the interior of the closed wave-transmitting medium cavity (4) through the first vacuum valve (12) and the vacuum gauge (11) in sequence;

the atmosphere system comprises an argon supply device, an oxygen supply device and a mass flow meter (6), wherein the argon supply device and the oxygen supply device are communicated with the input end of the mass flow meter (6), the output end of the mass flow meter (6) is communicated with the inside of the closed wave-transparent medium cavity (4), and a second vacuum valve is arranged between the mass flow meter (6) and the closed wave-transparent medium cavity (4).

10. The structure of any one of claims 1 to 3, 5 or 9, wherein the structure has a wave-absorbing bandwidth of 2 to 18 GHz.

Technical Field

The invention belongs to the technical field of active stealth, and relates to a radio frequency inductive coupling plasma superposition phase gradient super-surface wave-absorbing structure.

Background

The anti-stealth radar technology is rapidly developed, the detection threat faced by future advanced equipment is expanded towards the directions of ultra-wide frequency bands and multi-angular domains, and the reduction of the electromagnetic scattering characteristics of the target becomes the leading edge and the key point of the current target electromagnetic scattering control research. Because the prior appearance and material stealth technology mainly aims at optical wave bands, and the appearance stealth can only reduce radar scattering characteristics in key directions, the wave-absorbing inherent property and thickness requirement of the material stealth cause that the material stealth is difficult to break through broadband stealth, and the radar stealth with wide angle and wide frequency band can not be realized. Compared with the stealth technology of appearance and materials, the plasma electromagnetic scattering control technology is a novel active radar stealth technology based on the effects of resonance absorption, collision attenuation and the like of plasma on electromagnetic waves, and has two remarkable advantages in the aspect of solving the problem of broadband electromagnetic scattering control: first, broadband dynamic wave absorption. The peak electron density of the low-temperature non-magnetized plasma can be 10¹¹To 10¹⁵cm^-3The method comprises the steps of magnitude regulation, wherein a response frequency band can cover a P-Ku radar wave band, and characteristic parameters such as plasma electron density and collision frequency can be changed by regulating the plasma discharge condition, so that the attenuation amplitude and the frequency band of the electromagnetic wave can be regulated; secondly, the plasma has rich action mechanism with electromagnetic waves, and the plasma can generate various physical effects such as refraction, reflection, absorption, focusing/defocusing, frequency conversion, phase shift, modulation and the like on the electromagnetic waves, and the wave absorbing effect on the electromagnetic waves is obviously superior to that of a non-uniform loss dielectric layer under the same thickness.

Plasma stealth technology has been greatly advanced. In the plasma stealth technical research of key radar scattering parts such as an antenna cover, an air inlet channel, a wing leading edge and the like, a radio frequency Inductively Coupled Plasma (ICP) source is adopted, and an attenuation effect is obtained in an L-X frequency band. However, in the conventional plasma stealth technology, the plasma has large thickness and poor structural applicability. The structural characteristics and wave-absorbing requirements of the strong scattering part provide limits for the thickness, wall material and discharge conditions of the inductive plasma source. For an aircraft, the thinner the discharge cavity of the radio frequency plasma is, the more favorable the installation and use of the discharge cavity of the radio frequency plasma at the front edge of the wing, the radar cabin and other strong scattering parts are, but the thin wave transmission cavity structure can affect the discharge characteristic of the plasma, and meanwhile, the reduction of the plasma thickness can reduce the action distance of the radar wave in the plasma, and further the attenuation amplitude of the electromagnetic wave can be reduced.

Disclosure of Invention

The invention aims to provide a radio frequency inductive coupling plasma superposition phase gradient super-surface wave-absorbing structure, which aims to solve the problems that the existing plasma wave-absorbing structure is large in thickness and poor in structural applicability and is difficult to meet the use requirement, and the existing thin-layer plasma wave-absorbing structure is small in electromagnetic wave attenuation amplitude.

The technical scheme adopted by the embodiment of the invention is that the radio frequency inductive coupling plasma superposition phase gradient super-surface wave absorbing structure comprises a plasma coupling phase gradient super-surface structure, wherein the plasma coupling phase gradient super-surface structure comprises a radio frequency inductive coupling plasma source, a phase gradient super-surface and a closed wave-transmitting medium cavity, the radio frequency inductive coupling plasma source is arranged in the closed wave-transmitting medium cavity, and the phase gradient super-surface is fixed at the bottom of the outer side of the closed wave-transmitting medium cavity.

Furthermore, the phase gradient super-surface is a three-layer structure which is composed of a metal copper plate, a dielectric substrate and a metal unit array from bottom to top in sequence, wherein the metal unit array is formed by arranging metal units formed by sequentially arranging 6H-shaped metal patches with equal width and gradually increased height from left to right on the dielectric substrate from top to bottom in a repeated manner.

Furthermore, the width of each H-shaped metal patch is 4.6mm, the width of each vertical metal patch is 0.8mm, the interval width between the two vertical metal patches is 3.0mm, and the width of each transverse metal patch is 0.8 mm; the height of the 6H-shaped metal patches of each metal unit is 1.5mm, 3.38mm, 3.79mm, 4.06mm, 4.42mm and 5.5mm from left to right in sequence.

Furthermore, the transverse metal patches of the 6H-shaped metal patches of each metal unit are positioned on the same straight line, and the intervals of the two H-shaped metal patches adjacent to each other on the left and right in each metal unit are equal; the width of each metal unit is the sum of the width of the H-shaped metal patch and the interval between two adjacent H-shaped metal patches on the right.

Further, the interval between two adjacent H-shaped metal patches on the left and right in the metal unit is 3.4mm, and the width of each metal unit is 8 mm.

Furthermore, the dielectric substrate is an FR4 dielectric board with the dielectric constant of 4.5, the dielectric loss tangent value of 0.025 and the thickness of 1.85 mm.

Furthermore, the closed wave-transmitting medium cavity is of a cylindrical structure manufactured by adopting an all-quartz glass process, the radial diameter of the closed wave-transmitting medium cavity is 40cm, and the thickness, namely the height of the cylindrical structure is 2 cm.

Further, the radio frequency inductively coupled plasma source is generated by the cooperation excitation of a power supply system, a vacuum system and an atmosphere system.

Furthermore, the power supply system comprises a coil antenna, a matcher, a radio frequency power supply and a water cooling circulation system;

the radio frequency power supply is connected with the input end of the matcher, and the output end of the matcher is connected with the coil antenna;

the coil antenna is a spiral coil which is wound by a hollow brass tube and has 3 turns, and the water-cooling circulating system is communicated with the interior of the coil antenna through an insulating rubber tube;

the vacuum system comprises a vacuum pump, a vacuum gauge and a first vacuum valve, and the vacuum pump is communicated with the inside of the closed wave-transmitting medium cavity through the first vacuum valve and the vacuum gauge in sequence;

the atmosphere system comprises an argon supply device, an oxygen supply device and a mass flow meter, wherein the argon supply device and the oxygen supply device are communicated with the input end of the mass flow meter, the output end of the mass flow meter is communicated with the inside of the closed wave-transparent medium cavity, and a second vacuum valve is arranged between the mass flow meter and the closed wave-transparent medium cavity.

Further, the wave-absorbing bandwidth of the radio frequency inductive coupling plasma superposition phase gradient super-surface wave-absorbing structure is 2-18 GHz.

The thin-layer plasma coupled phase gradient super-surface wave-absorbing structure with the dynamically adjustable electromagnetic wave attenuation characteristic has the advantages of being thin-layer, dynamically adjustable in wave-absorbing parameters and the like. The plasma is used as a main low-frequency wave-absorbing medium, and the effective wave-absorbing frequency band and attenuation rate of the plasma are regulated and controlled by changing external discharge conditions such as power supply power, working air pressure, gas mixing ratio and the like, so that broadband wave-absorbing effects of different frequency bands are realized; the reflected wave vector of the electromagnetic wave is interfered by the phase gradient super-surface structure to form an abnormal reflection effect, the acting distance of the electromagnetic wave in the thin-layer radio frequency inductive coupling plasma is increased, and the broadband wave absorbing effect is improved. The problems that the existing plasma wave-absorbing structure is large in thickness and poor in structure applicability and is difficult to meet use requirements and the electromagnetic wave attenuation amplitude of the existing thin-layer plasma wave-absorbing structure is small are effectively solved.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.

Fig. 1 is a schematic structural diagram of a radio frequency inductively coupled plasma superimposed phase gradient super-surface wave-absorbing structure according to an embodiment of the present invention.

FIG. 2 is a schematic structural diagram of a phase gradient metasurface according to an embodiment of the invention.

Fig. 3 is a schematic structural diagram of an H-shaped metal patch according to an embodiment of the present invention.

Fig. 4 is a schematic structural diagram of a metal unit composed of 6H-shaped metal patches of different sizes according to an embodiment of the present invention.

Fig. 5 is a phase diagram of a metal unit composed of 6H-shaped metal patches with different sizes selected in the embodiment of the present invention.

FIG. 6 is a schematic structural diagram of a metal unit array of a phase gradient super surface according to an embodiment of the present invention.

FIG. 7 is a schematic view of a wave-absorbing effect testing system of a radio frequency inductively coupled plasma superimposed gradient super-surface wave-absorbing structure according to an embodiment of the invention.

FIG. 8 is a comparison graph of the reflectivity measurement results of the wave-absorbing structure and the plasma wave-absorbing structure in the embodiment of the invention.

In the figure, 1, a plasma coupling phase gradient super-surface structure, 2, a radio frequency inductive coupling plasma source, 3, a phase gradient super-surface, 4, a closed wave-transparent medium cavity, 5, a coil antenna, 6, a mass flowmeter, 7, a matcher, 8, a vacuum pump, 9, a radio frequency power supply, 11, a vacuum gauge and 12, a first vacuum valve.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and the described embodiments are only a part of the embodiments of the present invention, but not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention. The technical solution of the present invention is described in detail below with reference to the accompanying drawings and examples.

The embodiment of the invention provides a radio frequency inductively coupled plasma superposed phase gradient super-surface wave absorbing structure, which comprises a plasma coupled phase gradient super-surface structure 1, wherein the plasma coupled phase gradient super-surface structure 1 comprises a radio frequency inductively coupled plasma source 2, a phase gradient super-surface 3 and a closed wave-transmitting medium cavity 4, the radio frequency inductively coupled plasma source 2 is arranged in the closed wave-transmitting medium cavity 4, the phase gradient super-surface 3 is fixed at the bottom of the outer side of the closed wave-transmitting medium cavity 4, and the radio frequency inductively coupled plasma source 2 is excited and generated by a power supply system, a vacuum system and an atmosphere system. The phase gradient super surface 3 is fixed at the bottom of the outer side of the closed wave-transmitting medium cavity 4, electromagnetic waves firstly enter the radio frequency inductive coupling plasma source 2, then reach the phase gradient super surface 3, and enter the radio frequency inductive coupling plasma source 2 again at a larger emission angle after being abnormally reflected by the phase gradient super surface 3, so that the acting distance of the electromagnetic waves in the radio frequency inductive coupling plasma source 2 is increased.

As shown in fig. 2, the phase gradient super-surface 3 is a three-layer structure composed of a metal copper plate, a dielectric substrate, and a metal element array in sequence from bottom to top, in this embodiment, an FR4 dielectric plate with a dielectric constant r =4.5, a dielectric loss tangent value tan =0.025, and a thickness of 1.85mm is adopted, the metal element array is formed by sequentially arranging 6H-shaped metal patches with periodically changing geometric parameters from left to right, and the metal elements are sequentially and repeatedly arranged from top to bottom, and the 6H-shaped metal patches have equal widths and gradually increased heights. Specifically, the width w4 of each H-shaped metal patch is 4.6mm, the width w1 of each vertical metal patch is 0.8mm, the spacing width w2 between the two vertical metal patches is 3.0mm, the width w3 of each transverse metal patch is 0.8mm, the transverse metal patches of the 6H-shaped metal patches constituting the metal unit are located on the same straight line, and the two H-shaped metal patches adjacent to each other on the left and right are spaced by 3.4 mm. The height m of the 6H-shaped metal patches is 1.5mm, 3.38mm, 3.79mm, 4.06mm, 4.42mm and 5.5mm in sequence. Through the height setting, the phase response of each metal patch is changed, 6H-shaped metal patches form a phase difference of 2 pi, so that the abnormal reflection function of the phase gradient super-surface 3 is realized, as shown in fig. 5, and the arrangement mode of the metal unit array is shown in fig. 6.

The phase gradient super surface 3 of the embodiment is made of a microwave substrate, metal units formed by 6H-shaped metal patches with equal width and gradually increased height are periodically etched on one surface of the microwave substrate with metal plated on the two surfaces, no electric connection exists among the metal units, and the metal units can be freely divided and assembled, so that the electromagnetic response among the metal units is mutually independent. The phase gradient super surface 3 can realize the phase gradient of 2 pi, thereby changing the propagation direction of the electromagnetic wave and increasing the acting distance of the electromagnetic wave in the radio frequency inductive coupling plasma source 2.

The closed wave-transparent dielectric cavity 4 is of a cylindrical structure, is manufactured by adopting an all-quartz glass process to realize the lossless transmission of electromagnetic waves, has the radial diameter of 40cm and the thickness of 2cm, and is too large, so that the structural adaptability is influenced, the weight is increased, and the application is inconvenient; the thickness is too small, and the wave absorbing effect is not good.

The power supply system comprises a coil antenna 5, a matcher 7, a radio frequency power supply 9 and a water-cooling circulation system, wherein the coil antenna 5 adopts a spiral coil antenna, and the number of turns of the spiral coil antenna is three. The coil antenna 5 is sleeved on the outer side wall of the closed wave-transmitting medium cavity 4 and used for exciting plasma. The output end of the radio frequency power supply 9 is connected with the input end of the matcher 7, and the output end of the matcher 7 is connected with the coil antenna 5 through a copper plate transmission line.

Vacuum system includes vacuum pump 8, vacuometer 11 and first vacuum valve 12, and vacuometer 11 of this embodiment adopts film vacuum gauge or resistance vacuum gauge, and vacuum pump 8 is in proper order through first vacuum valve 12 and vacuometer 11 and the inside intercommunication in the wave-transparent medium chamber of closed 4, and the wave-transparent medium chamber of closed 4 carries out the evacuation, and first vacuum valve 12 is used for controlling vacuum system's switch, can adopt the vacuum ball valve, and vacuometer 11 is arranged in showing the vacuum degree in the wave-transparent medium chamber of closed 4.

The atmosphere system comprises an argon supply device, an oxygen supply device and a mass flow meter 6, wherein the argon supply device and the oxygen supply device are communicated with the input end of the mass flow meter 6, and the output end of the mass flow meter 6 is communicated with the inside of the closed wave-transparent medium cavity 4 and used for providing mixed gas of oxygen and argon for the closed wave-transparent medium cavity 4. And a second vacuum valve is arranged between the mass flow meter 6 and the closed wave-transparent medium cavity 4 and is used for connecting or disconnecting the mass flow meter 6 and the closed wave-transparent medium cavity 4.

The oxygen is electropositive gas, the argon is electronegative gas, the two gases can be excited to generate plasma, and the parameter distribution of the plasma can be adjusted through different mixing ratios, so that the wave-absorbing frequency band and the wave-absorbing amplitude can be adjusted and controlled.

In the power supply system, the output rated power of the radio frequency power supply 9 is 1000W (50 Ω), the working frequency is 13.56MHz +/-0.005%, the second harmonic output is < -40dB, the parasitic modulation is less than 1%, and a matcher 7 is adopted between the power source, namely the radio frequency power supply 9, and the load, namely the coil antenna 5, so as to adjust the forward power and the reflected power of the radio frequency power supply 9 and prevent the radio frequency power supply 9 from being burnt out due to overlarge reflected power. The coil antenna 5 is a spiral coil and is formed by winding a hollow brass tube with the diameter of 8mm, the number of turns is 3, the diameter of the coil antenna 5 is 20cm, the inside of the coil is connected with the water cooling circulation system through an insulating rubber tube to reduce the temperature of the coil antenna 5, and the insulating rubber tube of the water cooling circulation system is inserted into an interface of the coil antenna 5.

In an atmosphere system, working medium gas is argon and oxygen, the mixing proportion of the oxygen in the argon is controlled by a mass flow meter 6, and the air pressure of a discharge cavity, namely a closed wave-transparent medium cavity 4, is regulated and controlled to be 50mTorr to atmospheric pressure by a vacuum meter 11, a vacuum pump 8 and a first vacuum valve 12.

Based on the radio frequency inductive coupling plasma superposition phase gradient super-surface wave-absorbing structure provided by the embodiment of the invention, the power supply power is changed through the radio frequency power supply 9, the working air pressure is adjusted through the vacuum pump 8, the plasma density and the collision frequency excited by the radio frequency inductive coupling plasma source 2 can be changed by controlling the gas mixing proportion through the mass flowmeter 6, so that the regulation and control of the radio frequency inductive coupling plasma source 2 on the wave-absorbing bandwidth and the attenuation rate of electromagnetic waves are realized, the wave-absorbing amplitude and the wave-absorbing bandwidth of the electromagnetic waves can be increased, and the broadband wave absorption within 2-18GHz is realized.

The wave absorbing effect of the embodiment of the invention can be explained by combining the following experimental measurement results, the experimental schematic diagram is shown in fig. 7, the microwave absorbing effect comprises a small-sized microwave darkroom, a vector network analyzer and two horn antennas, the radio frequency inductive coupling plasma source 2 is fixed at the central position of a measurement table, a pair of horn antennas for transmitting and receiving electromagnetic waves are arranged in front of the measurement table, the centers of the two horns and the center of the radio frequency inductive coupling plasma source 2 are kept at the same height and are respectively connected to two ports of the vector network analyzer, and the microwave absorbing effect concretely comprises the following steps:

step S1: and filling mixed gas of argon and oxygen into the closed wave-transmitting medium cavity 4 through an atmosphere system, wherein the air pressure is 10Pa, connecting the electrodes to the coil antenna 5 on the outer side of the closed wave-transmitting medium cavity 4 respectively, and supplying 13.56MHz radio frequency power to the coil antenna 5, wherein the power of the radio frequency power is 500W, and exciting the closed wave-transmitting cavity 4 of the thin layer to generate plasma.

Step S2: outputting an electromagnetic wave signal with the frequency band of 2-18Ghz by a vector network analyzer port, firstly amplifying the electromagnetic wave signal by a power amplifier, and then transmitting the electromagnetic wave signal to a plasma source through a horn antenna;

step S3: the echo signal is returned to the horn antenna on the other side of the central axis symmetry line by the metal reflecting plate on the back of the radio frequency inductive coupling plasma source 2 for receiving, and is sent to the receiving end of the vector network analyzer, and the attenuation rate of the plasma source to the electromagnetic wave is obtained.

Step S4: replacing the metal reflecting plate with the phase gradient super surface 3, repeating the steps S1 and S2, returning the echo signal to the antenna on the other side of the axial symmetry line from the phase gradient super surface 3 for receiving, and sending to the receiving end of the vector network analyzer to obtain the attenuation rate of the plasma source coupling phase gradient super surface to the electromagnetic wave.

Step S5: comparing the results obtained in the steps S3 and S4, as shown in fig. 8, after the phase gradient super-surface 3 is added, the wave-absorbing amplitude and the absorbing bandwidth are both significantly increased, the maximum attenuation rate exceeds-40 dB, and the frequency bands with the attenuation rate lower than-5 dB include 0.53GHz to 1.07GHz, 1.66GHz to 3.74GHz, 6.6GHz to 11.38GHz and 11.53GHz to 12.08GHz, which proves that the phase gradient super-surface 3 can effectively improve the attenuation effect of the plasma on the electromagnetic wave. Especially for thin-layer plasmas with non-uniform electron density distribution, the phase gradient super-surface 3 can effectively increase the propagation distance of electromagnetic waves in the plasmas, so that the attenuation effect of the plasmas on the electromagnetic waves is enhanced. However, due to the limitation of the working bandwidth of the phase gradient super surface 3, the attenuation rate reduction effect in a low frequency band is not obvious, and the average attenuation rate is reduced from-5 dB to-15 dB in the range of 6-12 GHz for effective work. The result indirectly proves that the plasma is used as a main medium for attenuating the electromagnetic wave and has obvious advantages on the wave-absorbing bandwidth.

The above description is only for the preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention shall fall within the protection scope of the present invention.