A broadband reconfigurable frequency selective absorber based on liquid metal

Abstract

An embodiment of the present invention discloses a broadband reconfigurable frequency selective absorber based on liquid metal, which can achieve medium-frequency broadband reconfiguration and high-frequency and low-frequency wave absorption performance. The present invention is composed of at least two periodically arranged multifunctional frequency selective absorber units; in each multifunctional frequency selective absorber unit, it includes: a first lossy layer, a first dielectric layer, an air layer, a second lossy layer, a second dielectric layer, an air layer, a first metal layer, a third dielectric layer, a liquid metal layer, a microchannel layer, a second metal layer, a fourth dielectric layer, and a third metal layer arranged in sequence. In the first lossy layer, a first slotted square ring structure is formed by screen-printed resistive ink; in the second lossy layer, a second slotted square ring structure formed by resistive ink and an embedded circular spiral metal structure; the liquid metal layer is a cross-arranged well-shaped structure; the internal structure of the microchannel layer is a cross-shaped channel formed by lithography, and the liquid metal is filled into the cross-shaped channel.

Description

Technical Field

[0001] The present invention relates to the field of radar stealth technology, and in particular, to a broadband reconfigurable frequency selective absorber based on liquid metal. Background Art

[0002] The radar cross section (RCS) characterizes the scattering ability of a detected target to electromagnetic waves. In free space, the maximum operating distance of a radar is proportional to the fourth root of the target's RCS. That is, the smaller the target's RCS, the smaller the radar operating distance. When the target's RCS is reduced by 12 dB, its maximum operating distance is reduced by half. Therefore, reducing the RCS of a detected target can be regarded as the core of radar stealth technology. The frequency selective surface (FSS), as an artificial electromagnetic periodic structure, has spatial filtering characteristics. For a radar radome based on band-pass FSS, it has good wave-transmitting performance within its own radar passband, does not affect the operation of the internal antenna system, and has total reflection performance outside the passband, and is applied to radar radomes to reduce the backscattering RCS. However, this method is only effective for the single-station RCS. With the development of multi-station radar networking technology, electromagnetic waves scattered in other directions can still be detected, greatly reducing the stealth performance. Therefore, the frequency selective radar absorber (FSR) was proposed. It is a composite structure composed of FSS and a circuit analog absorber (CAA), has frequency selection characteristics, has a band-pass transmission characteristic within the operating frequency band of its own radar, and does not affect the normal operation of the radar antenna; while outside the radar operating passband, the FSR radar radome has the "perfect absorption" characteristic, and uses its high-loss absorbing surface to absorb the detection waves of the enemy radar, effectively reducing the omnidirectional RCS and achieving multi-base station radar detection stealth. However.

[0003] At present, most FSRs have a narrow intermediate-frequency transmission bandwidth and do not have reconfigurable and adjustable performance, and their application prospects are narrow. Therefore, how to realize the reconstruction of the electromagnetic performance of a broadband stealth radome and achieve a part of broadband reconfigurability and absorption performance has become a problem that needs to be studied. Summary of the Invention

[0004] Embodiments of the present invention provide a broadband reconfigurable frequency selective absorber based on liquid metal, which can achieve intermediate-frequency broadband reconfigurability, high-frequency and low-frequency absorption performance, and is applicable to the reconstruction of the electromagnetic performance of a broadband stealth radome.

[0005] To achieve the above object, the embodiments of the present invention adopt the following technical solutions:

[0006] Periodically set multifunctional frequency selective absorber units, and the multifunctional frequency selective absorber units include: a first lossy layer, a first dielectric layer, an air layer, a second lossy layer, a second dielectric layer, an air layer, a first metal layer, a third dielectric layer, a liquid metal layer, a microchannel layer, a second metal layer, a fourth dielectric layer, and a third metal layer arranged in sequence. The first lossy layer includes a slotted square ring structure composed of resistive ink printed by screen printing; the second lossy layer includes a slotted square ring structure composed of resistive ink and a circular spiral metal structure embedded in the four sides of the square ring; the liquid metal layer is a cross-arranged well-shaped structure; the internal structure of the microchannel layer is a cross-shaped channel formed by lithography, and the liquid metal can flow therein.

[0007] Specifically, the first metal layer and the third metal layer have the same structure, which are four metal square patches of equal size. The second metal layer is four quasi-spiral slot structures of equal size. The number of horizontal and vertical channels of the liquid metal layer in each periodic unit is 7.

[0008] The broadband reconfigurable frequency selective absorber based on liquid metal provided in this embodiment realizes a multifunctional frequency selective absorber with medium-frequency broadband reconfigurability and high-frequency and low-frequency absorption performance by using the fluidity of liquid metal and corresponding structural design. By combining multiple frequency selective surfaces with a lossy layer composed of resistive ink printed by screen printing into a composite structure, a reconfigurable absorption / transmission integrated system is constructed by using the excellent conductivity and fluidity of liquid metal, realizing performance indicators of good impedance matching, wide passband bandwidth, and low insertion loss in the passband; at the same time, the present invention combines microfluidic technology to inject and extract liquid metal in the microchannel layer, enabling the switching between two working modes, that is, the reconfigurability between a band-pass type frequency selective absorber and a band-stop type frequency selective absorber. Description of the Drawings

[0009] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required to be used in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0010] Figure 1 It is a three-dimensional schematic diagram of the unit structure provided by the embodiment of the present invention;

[0011] Figure 2 It is a schematic diagram of the split unit structure provided by the embodiment of the present invention;

[0012] Figure 3 It is a schematic diagram of the structure of the first lossy layer (1) provided by the embodiment of the present invention;

[0013] Figure 4It is a schematic structural diagram of the second lossy layer (4) provided by an embodiment of the present invention;

[0014] Figure 5 It is a side view of the microchannel layer (10) provided by an embodiment of the present invention;

[0015] Figure 6 It is a schematic structural diagram of the liquid metal layer (9) provided by an embodiment of the present invention;

[0016] Figure 7 It is a side view of the liquid metal layer (9) provided by an embodiment of the present invention;

[0017] Figure 8 It is a schematic structural diagram of the first metal layer (7) provided by an embodiment of the present invention;

[0018] Figure 9 It is a schematic structural diagram of the second metal layer (11) provided by an embodiment of the present invention;

[0019] Figure 10 It is a schematic diagram of the result curves of the transmission coefficient and the reflection coefficient in the working mode of the band-pass type frequency selective absorber when the microchannel is filled with liquid metal;

[0020] Figure 11 It is a schematic diagram of the result curve of the reflection coefficient in the working mode of the band-stop type frequency selective absorber when the microchannel is not filled with liquid metal. Detailed implementation manners

[0021] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. The embodiments of the present invention will be described in detail below. Examples of the embodiments are shown in the accompanying drawings, in which the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the accompanying drawings are exemplary and are only used to explain the present invention and should not be construed as limiting the present invention. Those skilled in the art of the present technology can understand that unless specifically stated, the singular forms "a", "an", "the" and "said" used herein may also include the plural forms. It should be further understood that the term "comprising" used in the specification of the present invention means the presence of the described features, integers, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or their groups. It should be understood that when we say that an element is "connected" or "coupled" to another element, it can be directly connected or coupled to other elements, or there may also be intermediate elements. In addition, the "connection" or "coupling" used herein may include wireless connection or coupling. The term "and / or" used herein includes any unit and all combinations of one or more of the associated listed items. Those skilled in the art of the present technology can understand that unless otherwise defined, all terms (including technical terms and scientific terms) used herein have the same meaning as the general understanding of those of ordinary skill in the field to which the present invention belongs. It should also be understood that terms such as those defined in a general dictionary should be understood to have a meaning consistent with the meaning in the context of the prior art and will not be interpreted in an idealized or overly formal sense unless defined as herein.

[0022] An embodiment of the present invention provides a broadband reconfigurable frequency selective absorber based on liquid metal. The general design idea is as follows: First, the first lossy layer and the second lossy layer are cascaded into a metamaterial absorbing layer through an air layer; the first metal layer, the third dielectric layer, the microchannel layer, the second metal layer, the fourth dielectric layer, and the third metal layer form a frequency selective surface layer with broadband transmission. Secondly, a circular spiral metal structure is embedded in the lossy layer to achieve LC parallel resonance, so that the transmission frequency band of the metamaterial absorbing layer coincides with the transmission frequency band of the frequency selective surface layer, forming a broadband transmission window with low insertion loss. Finally, by utilizing the excellent fluidity of the liquid metal EGaIn, the extraction and injection of the liquid metal EGaIn in the microchannel are used to realize the switching between two working modes of a band-pass frequency selective absorber and a band-stop frequency selective absorber. Specifically, as Figure 1 、 2 shown, an embodiment of the present invention provides a broadband reconfigurable frequency selective absorber based on liquid metal, which is composed of at least two periodically arranged multifunctional frequency selective absorber units, and can be arranged horizontally and vertically with the unit size as the period;

[0023] In each multifunctional frequency selective absorber unit, it includes: a first lossy layer (1), a first dielectric layer (2), an air layer (3), a second lossy layer (4), a second dielectric layer (5), an air layer (6), a first metal layer (7), a third dielectric layer (8), a liquid metal layer (9), a microchannel layer (10), a second metal layer (11), a fourth dielectric layer (12) and a third metal layer (13) which are arranged in sequence from top to bottom;

[0024] As Figure 3 shown, in the first lossy layer (1), a first slotted square loop structure (14) is formed by screen-printed resistive ink; as Figure 4 shown, in the second lossy layer (4), a second slotted square loop structure (15) is formed by resistive ink, and circular spiral metal structures (16) are embedded in the four sides of the second slotted square loop structure (15);

[0025] The liquid metal layer (9) is a cross-arranged grid-like structure; the internal structure of the microchannel layer (10) is a cross-shaped channel formed by lithography, and liquid metal (17) is filled into the cross-shaped channel and flows therein.

[0026] Specifically, the length l1 of the first lossy layer (1) is 8.8 mm, the width s2 of the first slotted square loop structure (14) therein is 0.5 mm, and the slotted width l2 is 1.9 mm; the length of the second lossy layer (4) is 9.8 mm, the width w1 of the second slotted square loop structure (15) therein is 1.5 mm, and the slotted width l4 is 1.5 mm. The width l5 of the circular spiral metal structure (16) embedded in the second slotted square loop structure (15) is 1.2 mm, the width d2 of the spiral line is 0.1 mm, and the diameter d1 of the metal via is 0.15 mm. The circular spiral metal structure (16) is made of pure copper material.

[0027] The first metal layer (7) is composed of four metal square patches (18) with the same size and shape, and the width of the metal square patch (18) is 4 mm; the first metal layer (7) has the same structural shape as the third metal layer (13); the first metal layer (7) is etched on the third dielectric layer (8).

[0028] In this embodiment, the liquid metal layer (9) is a cross-arranged grid-like structure, the internal structure of the microchannel layer (10) is a cross-shaped channel formed by lithography, and liquid metal can flow therein. In the preferred scheme, both the horizontal and vertical channels of the liquid metal layer (9) in each periodic unit are 7, and the width w2 of each channel is 1 mm; the length and width of each cross-shaped channel in the microchannel layer (10) are both l6 = 1.9 mm, the height h1 is 0.15 mm, and the channel depth h2 is 0.15 mm.

[0029] Four quasi-helical slot structures (19) of equal size are excavated in the second metal layer (11). In the preferred embodiment, tungsten copper is used for the metal, the copper thickness is 0.035 mm, the length and width of the metal square patch are l3 = 4 mm, and the slot width w3 of the quasi-helical slot structure (19) is 0.2 mm.

[0030] In the preferred embodiment of this example, an F4B polytetrafluoroethylene board with a dielectric constant of 2.65 and a loss of 0.002 is used as the dielectric substrate for the first dielectric layer (2), the second dielectric layer (5), and the fourth dielectric layer (12). The third dielectric layer (8) uses a PET polyethylene terephthalate with a dielectric constant of 2.83 and a loss of 0.023 as the dielectric substrate. The liquid metal (17) is a gallium-indium alloy with a conductivity of 3.4×10 6 s. The microchannel layer (10) is made of an acrylic material with a dielectric constant of 2.63 and a loss of 0.012. It should be noted that all dielectric substrates can use Rogers 5880 with lower loss or a dielectric with a low relative dielectric constant, which can further reduce the passband insertion loss, as long as the relative dielectric constant, loss, and thickness of the material meet good impedance matching.

[0031] In this embodiment, the multifunctional frequency selective absorber unit includes a first lossy layer, a first dielectric layer, an air layer, a second lossy layer, a second dielectric layer, an air layer, a first metal layer, a third dielectric layer, a liquid metal layer, a microchannel layer, a second metal layer, a fourth dielectric layer, and a third metal layer arranged in sequence. Among them, the first lossy layer is a slotted square ring structure composed of screen-printed resistive ink; the second lossy layer includes a slotted square ring structure composed of resistive ink and circular helical metal structures embedded in the four sides of the square ring; the liquid metal layer is a cross-arranged grid structure; the internal structure of the microchannel layer is a cross-shaped channel formed by lithography, and the liquid metal can flow in it to achieve medium-frequency broadband reconfigurability and high-frequency and low-frequency wave absorption performance. Compared with previous work, this invention patent can achieve a wider wave transmission frequency band, smaller transmission insertion loss, and function switching, and is suitable for the electromagnetic performance reconstruction of broadband stealth radomes.

[0032] This embodiment also provides the electromagnetic parameter curves in two working modes as Figures 10 - 11 shown. When the liquid metal is pumped out of the microchannel, the working mode is a band-pass type frequency selective absorber, as Figure 10As shown, it can achieve medium-frequency broadband transmission, high-frequency and low-frequency wave absorption; the frequency range with a passband insertion loss above -3 dB is 10.1 GHz - 15.6 GHz, the relative bandwidth is 42.8%, the minimum insertion loss within the passband is 0.93 dB, the low-frequency absorption band bandwidth is 46.4%, and the high-frequency absorption band bandwidth is 41.5%; within the frequency range of 4 - 24 GHz, the reflection coefficient is below -10 dB and the relative bandwidth reaches 110.6%. When liquid metal is injected into the microchannel, the working mode is a band-stop frequency selective absorber, such as Figure 11 As shown, it can achieve medium-frequency reflection, high-frequency and low-frequency wave absorption; the frequency range with a reflection coefficient in the reflection band greater than -3 dB is 12.1 GHz - 13.77 GHz, the relative bandwidth is 12.8%, the low-frequency absorption bandwidth is 70.8%, and the high-frequency absorption bandwidth is 25.6%.

[0033] In practical applications, a flexible radome can quickly switch its state according to different scenario requirements to adapt to different performance needs. Therefore, the intelligence of microwave devices has become a future trend, and at the same time, the FSR that better suits the intelligent era has more practical and innovative value. Most traditional tunable FSRs use active devices such as PIN diodes and varactor diodes as tuning elements to achieve function switching. However, this method results in a complex structure and requires a feeding system for control, increasing the processing difficulty. In this embodiment, an eutectic gallium indium alloy (EGaIn) of liquid metal, which has both conductivity and fluidity and is non-toxic and harmless compared to ordinary liquid metal mercury, is used to implement a tunable FSR. By injecting and extracting the liquid metal EGaIn, function switching is achieved. In this embodiment, by utilizing the excellent conductivity and fluidity of the liquid metal EGaIn, a frequency selective absorber based on liquid metal is studied and designed. In addition to being applicable to the stealth of radomes, it can also be applied in the field of antenna communication. Among them, medium-frequency can achieve the communication of broadband antennas, and high-frequency and low-frequency achieve stealth.

[0034] Generally speaking, the advantages of this embodiment are as follows: First, aiming at the defects of the existing FSR, such as narrow passband bandwidth, large insertion loss within the passband, and non-adjustability, by combining frequency selective surfaces and microfluidic technology, a wider transmission frequency band, smaller transmission insertion loss, and reconfigurable function are achieved, with lower cost and insensitivity to polarization; Second, by embedding a circular spiral structure in the resistive ink and then combining it with the frequency selective surface, on the premise of ensuring good impedance matching, by adjusting the structural parameters, the reflection of incident waves is reduced, and an excellent wave absorption / wave transmission integrated structure design is achieved; Third, by controlling the flow of liquid metal, the switching of working modes is realized, which is applied to the electromagnetic performance reconstruction of broadband stealth radomes and better suits the "intelligent" application prospect.

[0035] Each embodiment in this specification is described in a progressive manner. For the same or similar parts among the embodiments, reference can be made to each other. Each embodiment focuses on the differences from other embodiments. In particular, for the device embodiments, since they are basically similar to the method embodiments, the description is relatively simple. For the relevant parts, reference can be made to the corresponding descriptions in the method embodiments. As described above, the above are only specific implementation manners of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A broadband reconfigurable frequency selective absorber based on liquid metal, characterized in that It is composed of at least two multifunctional frequency selective absorber units; In each multifunctional frequency selective absorber unit, it includes: a first lossy layer (1), a first dielectric layer (2), an air layer (3), a second lossy layer (4), a second dielectric layer (5), an air layer (6), a first metal layer (7), a third dielectric layer (8), a liquid metal layer (9), a microchannel layer (10), a second metal layer (11), a fourth dielectric layer (12) and a third metal layer (13) arranged in sequence from top to bottom; In the first lossy layer (1), a first slotted square ring structure (14) is formed by screen-printing resistive ink; In the second lossy layer (4), a second slotted square ring structure (15) is formed by resistive ink, and a circular spiral metal structure (16) is embedded in the four sides of the second slotted square ring structure (15); The liquid metal layer (9) is a cross-arranged grid structure; The internal structure of the microchannel layer (10) is a cross-shaped channel formed by lithography, and liquid metal (17) is filled into the cross-shaped channel.

2. The broadband reconfigurable frequency selective absorber based on liquid metal according to claim 1, wherein An F4B polytetrafluoroethylene plate with a dielectric constant of 2.65 and a loss of 0.002 is used as the dielectric substrate for the first dielectric layer (2), the second dielectric layer (5) and the fourth dielectric layer (12).

3. The broadband reconfigurable frequency selective absorber based on liquid metal according to claim 1, wherein The length l1 of the first lossy layer (1) is 8.8 mm, the width s2 of the first slotted square ring structure (14) therein is 0.5 mm, and the slotted width l2 is 1.9 mm; The length l3 of the second lossy layer (4) is 9.8 mm, the width w1 of the second slotted square ring structure (15) therein is 1.5 mm, and the slotted width l4 is 1.5 mm.

4. The broadband reconfigurable frequency selective absorber based on liquid metal according to claim 3, wherein The width l5 of the circular spiral metal structure (16) embedded in the second slotted square ring structure (15) is 1.2 mm, the width d2 of the spiral line is 0.1 mm, and the diameter d1 of the metal via is 0.15 mm.

5. The broadband reconfigurable frequency selective absorber based on liquid metal according to claim 4, characterized in that, The circular spiral metal structure (16) is made of pure copper material.

6. The broadband reconfigurable frequency selective absorber based on liquid metal according to claim 1, wherein The first metal layer (7) is composed of four metal square patches (18) with the same size and shape, and the width of the metal square patch (18) is 4 mm; The first metal layer (7) has the same structural shape as the third metal layer (13); The first metal layer (7) is etched on the third dielectric layer (8).

7. The broadband reconfigurable frequency selective absorber based on liquid metal according to claim 6, characterized in that, The third dielectric layer (8) uses PET polyethylene terephthalate with a dielectric constant of 2.83 and a loss of 0.023 as the dielectric substrate.

8. The broadband reconfigurable frequency selective absorber based on liquid metal according to claim 1, characterized in that, Four equal-sized quasi-spiral slit structures (19) are excavated in the second metal layer (11), and the slit width w3 of the quasi-spiral slit structure (19) is 0.2 mm.

9. The broadband reconfigurable frequency selective absorber based on liquid metal according to claim 1, characterized in that, The liquid metal (17) is a gallium-indium alloy with a conductivity of 3.4×10 6 s.

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