Ultra-thin flexible frequency-coded metasurface and design method thereof

Abstract

The application relates to an ultrathin flexible frequency coding metasurface and a design method thereof, and relates to the field of artificial electromagnetic metamaterials.The frequency coding metasurface designed by the application is composed of optimized reflection type frequency coding supercell structures, the units have different phase-frequency sensitivities, and the coding sequence is designed by utilizing the difference in the phase-frequency sensitivities of the units, so that the continuous regulation of electromagnetic waves is realized.By using a 1-bit coding mode, a two-way beam splitter and a four-way beam splitter can be realized, and by using a 2-bit coding mode, the regulation of a single beam in different directions can be realized.The application has the characteristics of simple structure, easy design, ultrathinness, flexibility, high symmetry, passivity and low cost, and has great application potential and good engineering application prospect in the fields of wireless communication, radar, imaging and signal processing.

Description

Technical Field

[0001] This invention relates to the field of artificial electromagnetic metamaterials. Background Technology

[0002] Electromagnetic metamaterials are artificial composite structures or materials that possess extraordinary electromagnetic properties not found in natural materials, achieved by arranging macroscopic basic units with specific geometric shapes periodically or aperiodically. Domestic scholars translate metamaterials as novel artificial electromagnetic materials or special media. Metamaterials allow for flexible manipulation of electromagnetic waves, and their electromagnetic properties are determined by the unit materials, unit structures, and array arrangement.

[0003] Electromagnetic metasurfaces are two-dimensional metamaterials, typically composed of arrays of periodic or aperiodic two-dimensional subwavelength structural units. Due to the simplicity of their planar structure, metasurfaces have relatively low design costs and manufacturing difficulties, and offer unique advantages in processing and applications. By designing artificial structures at the interface to form phase gradients and artificial wave vectors, metasurfaces can achieve flexible control of electromagnetic waves, significantly reducing device size. They have immense application value in areas such as perfect microwave absorbers, highly directional antennas, ultra-thin electromagnetic cloaks, and next-generation wireless communications. Summary of the Invention

[0004] The purpose of this invention is to meet the current demand for electromagnetic metasurfaces, and therefore proposes an ultrathin flexible frequency-coded metasurface and its design method.

[0005] This invention is achieved through the following technical solution:

[0006] An ultrathin flexible frequency-coded metasurface includes: N reflective tunable meta-unit structures; N is a positive integer; the N reflective tunable meta-unit structures are uniformly arranged in a two-dimensional xy plane and periodically arranged to form a single component, i.e., the ultrathin flexible frequency-coded metasurface; each of the reflective tunable meta-unit structures includes an intermediate dielectric substrate layer, an orthogonal cross-shaped metal pattern patch layer, and a metal reflective layer; the metal pattern patch layer is fixed to the upper surface of the intermediate dielectric substrate layer; the metal reflective layer is fixed to the lower surface of the intermediate dielectric substrate layer;

[0007] The pattern of the metal pattern patch layer is a symmetrical graphic composed of orthogonal cross patterns;

[0008] The pattern of the metal pattern patch layer is used to reflect the amplitude of electromagnetic waves and modulate the phase of the reflective tunable supercell structure in which it is located.

[0009] The ultrathin flexible frequency-coded metasurface has different phase-frequency sensitivities within the operating frequency band, and its phase response curve tends to be linear with frequency variation.

[0010] The design method based on ultrathin flexible frequency-coded metasurfaces is characterized by the following steps:

[0011] Step 1: Determine the modulation function required for the beam control device, and determine the phase required for each reflective tunable supercell structure based on the modulation function;

[0012] Step 2: By adjusting the geometric parameters of the reflective tunable supercell, phase modulation of the corresponding reflective tunable supercell structure is achieved, ensuring that the phase response curve of the reflective tunable supercell has different phase-frequency sensitivities within the operating frequency band. The reflective tunable supercell with low phase-frequency sensitivity is encoded as 0; the reflective tunable supercell with high phase-frequency sensitivity is encoded as 1.

[0013] Step 3: Given 1-bit and 2-bit encoded sequences, solve for the radiation field;

[0014] Step 4: By changing the frequency of the incident electromagnetic wave, an ultrathin flexible frequency-coded metasurface is obtained, completing a design based on the ultrathin flexible frequency-coded metasurface.

[0015] In step three, the radiation field is solved using the formula:

[0016]

[0017] Implementation;

[0018] In the formula: θ is the elevation angle of the radiation field. It is the azimuth angle of the radiation field. These are the radiation pattern coefficients of each reflective tunable supercell structure; Md represents the scattering phase of each reflective tunable supercell structure; d represents the period of a supercell, k = λ0 / 2π, and λ0 is the wavelength of the incident electromagnetic wave.

[0019] Beneficial effects:

[0020] 1. In this invention, the electromagnetic metasurface is composed of an optimized reflective frequency-coded supercell structure, which can realize the function of diverse beam control and has good engineering application prospects.

[0021] 2. This invention has the characteristics of simple structure, easy design, ultra-thin, high symmetry, passive and low cost, and has great application potential, which promotes the development of electromagnetic metasurfaces. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the basic unit structure of a frequency-coded metasurface according to an embodiment of the present invention;

[0023] Figure 2 This is a schematic diagram of four frequency-coded metasurface sub-unit structures according to one embodiment of the present invention;

[0024] Figure 3 This invention relates to four frequency-coded metasurface units with different structural sizes and their corresponding amplitude and phase responses, as described in one embodiment of the invention. Figure 3 (a) shows the simulation results of the reflection amplitude of four frequency-coded metasurface sub-units in the 17 to 20 GHz frequency band. Figure 3 (b) Simulation results of the reflection phase of four frequency-coded metasurface units in the 17 to 20 GHz frequency band;

[0025] Figure 4 (a) is a schematic diagram of a 1-bit frequency-coded metasurface, with the corresponding coding arrangement being: '0', '1', '0', '1'… Figure 4 (b) is a simulation model diagram of the frequency-coded metasurface;

[0026] Figure 5 This is a 1-bit frequency-coded metasurface and its corresponding far-field pattern according to an embodiment of the present invention. Figure 5 (ad) represents the far-field radiation patterns generated by a 1-bit frequency-coded metasurface with a coding arrangement of '0', '1', '0', '1'... at 17, 18, 19, and 20 GHz;

[0027] Figure 6 (a) is a schematic diagram of a 1-bit frequency-coded metasurface, with the corresponding coding arrangement as: '0', '1', '0', '1'… / '1', '0', '1', '0'… Figure 6 (b) is a simulation model diagram of the frequency-coded metasurface;

[0028] Figure 7 This is a 1-bit frequency-coded metasurface and its far-field pattern according to an embodiment of the present invention. Figure 7 (ad) Far-field radiation patterns generated by a 1-bit frequency-coded metasurface with the coded arrangement '0', '1', '0', '1'… / '1', '0', '1', '0'… at 17, 18, 19 and 20 GHz;

[0029] Figure 8 (a) is a 2-bit frequency-coded metasurface, with the corresponding coded arrangement as: '00', '01', '10', '11', '00', '01', '10', '11'… Figure 8 (b) is a simulation model diagram of a 2-bit frequency-coded metasurface;

[0030] Figure 9 A 2-bit frequency-coded metasurface and its far-field pattern. Figure 9 (ad) represents the far-field radiation patterns generated at 6, 7.5, 9, and 10.5 GHz for a 2-bit frequency-coded metasurface with the coded arrangement '00-00', '00-01', '00-10', '00-11', '00-00', '00-01', '00-10', '00-11'... Detailed Implementation

[0031] Detailed Description of Embodiments I: The embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein 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 with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0032] The beam control device based on an ultrathin flexible frequency-coded metasurface, according to an embodiment of the present invention, is described below with reference to the accompanying drawings.

[0033] like Figure 1 As shown, the metasurface has a three-layer structure: an intermediate dielectric substrate layer, an orthogonal cross-shaped metal pattern patch layer, and a metal reflective layer. The intermediate dielectric substrate layer is made of polyimide with a dielectric constant of 3.2, a tangent loss of 0.03, and a thickness of 1 mm. The back side uses a complete copper plate, and the front side is covered with aluminum foil and etched with a pattern. The metal thickness on both sides is 0.035 mm. The reflective adjustable metacell structure is square, and its geometric parameters are as follows: square side length p, cross length a, cross slit length b, cross slit width w, substrate thickness d, and arc radius r.

[0034] Furthermore, such as Figure 2 As shown, through simulation optimization, the optimal structural parameters were selected. The parameters for frequency-encoded metasurface encoding unit 1 are: arc radius r1 = 0.8 mm, cross-shaped slot length b1 = 1 mm, and slot width w1 = 0.1 mm; for frequency-encoded metasurface encoding unit 2, arc radius r2 = 2.5 mm, cross-shaped slot length b2 = 3 mm, and slot width w2 = 2.68 mm; for frequency-encoded metasurface encoding unit 3, arc radius r3 = 2.5 mm, cross-shaped slot length b3 = 3 mm, and slot width w3 = 0.92 mm; and for frequency-encoded metasurface encoding unit 4, arc radius r4 = 2.5 mm, cross-shaped slot length b4 = 3 mm, and slot width w4 = 0.28 mm. The remaining parameters are: square side length p = 10 mm and substrate thickness d = 1 mm.

[0035] The dielectric constant is 3.2, the tangent loss is 0.03, and the thickness is 1mm. The back side uses a complete copper plate, and the front side is covered with aluminum foil and etched with patterns. The thickness of the metal layer on both sides is 0.035mm.

[0036] Working Principle: This invention employs the principle of resonant phase modulation to control the phase characteristics of the unit. Based on this principle, different geometric parameters of the unit lead to different resonant characteristics, resulting in different phase dispersions (phase sensitivities). The four coding units in the design have different geometric parameters, thus exhibiting different phase characteristics. These phase characteristics are crucial for realizing the frequency-coded metasurface. To illustrate the underlying physical mechanism, we use a simplified Taylor series to represent the phase response of the digital unit with frequency, as shown below.

[0037]

[0038] Where: f0 represents the initial frequency point of the working frequency band of the designed ultrathin flexible frequency-coded metasurface, and α0 represents the phase response of the frequency-coded metasurface unit at the initial frequency. Here, phase sensitivity refers to the degree of phase change of the unit within the working frequency range. It can be expressed as the ratio of the phase change to the frequency change between the starting and ending frequencies;

[0039] The phase information of a conventional coded metasurface is a frequency-independent constant. Therefore, under this condition, a conventional coded metasurface can only achieve a fixed electromagnetic function within its operating frequency band. For frequency-coded metasurfaces, the difference in higher-order terms in the phase response function of the unit cells can be utilized during design to achieve a change in the phase difference between units with frequency. Here, we only consider metasurface units with different linear phase-frequency sensitivities, i.e., the phase response function of the frequency-coded metasurface units has different first-order response terms. When we use equation (1) to describe the phase information of the metasurface, we find that its phase response changes with frequency. In this case, we must use two parameters to describe the phase response of the coded metasurface. One is the phase at the initial frequency, and the other is the phase sensitivity to frequency. Compared with conventional coded metasurfaces, the phase response at the initial frequency and the phase sensitivity in the operating frequency band both require careful design for the frequency-coded metasurface.

[0040] According to the scattering theory of traditional array antennas, the far-field scattering of the coded metasurface under normal incident radiation can be expressed as:

[0041] θ is the pitch angle. It's the azimuth. These are the radiation pattern coefficients for each coding unit. This refers to the scattering phase. Md represents the period of a supersubunit, d represents the period of a single subunit, k = λ0 / 2π, and M represents the number of units contained in a supersubunit. According to scattering theory, the radiative energy of the encoded metasurface can be described by a directionality function.

[0042]

[0043] Where θ = arcsin(λ / Γ), λ is the wavelength in free space, and Γ represents the period length of the encoded sequence, according to the generalized Snell's law.

[0044] Far-field function of metasurface scattering, azimuth angle of reflected beam The unit "0" and "1" encode the length of the particle (D) x ) and (D y The following relationship must be satisfied:

[0045]

[0046]

[0047] A 1-bit frequency-coded metasurface is used to illustrate the principle and implementation of multi-beam frequency control. Here, two digital unit coding units, unit 1 and unit 3, are used, and their responses in the 17-20 GHz frequency band are as follows: Figure 2 As shown, they have similar initial phase values ​​and an initial frequency of 17 GHz.

[0048] Encoding units 1 and 3 are encoded as "0" at an initial frequency of 17 GHz. However, their phase changes vary across the entire operating frequency band, with the phase curves approximating linear. In this case, we determine the phase curve using the following formula:

[0049]

[0050] f0 and f1 are the initial frequency and cutoff frequency, respectively. and These are the phase responses at the corresponding frequencies. Therefore, the phase sensitivities of coding unit 1 and coding unit 3 are -31° / GHz and -210° / GHz, respectively, and the phase difference between the two units is approximately 180°.

[0051] like Figure 3As shown in (a)-(b), the amplitude and phase response curves of these four frequency-coded metasurface units were obtained by simulation using the commercial software CST Microwave Studio. Metasurface units with different resonance intensities have different phase-frequency sensitivities near the resonance frequency. That is, the stronger the electromagnetic resonance of the metasurface unit, the more obvious the change trend of its corresponding phase response function near the resonance frequency, and the higher the phase-frequency sensitivity of the metasurface unit. It can be seen that this group of frequency-coded metasurface units has different phase-frequency sensitivities in the range of 17 to 20 GHz, and their phase response curves are approximately linear with the change of frequency.

[0052] Furthermore, such as Figure 4 As shown, Figure 4 (a) is a schematic diagram of a 1-bit frequency-coded metasurface, with the corresponding coding arrangement being: '0', '1', '0', '1'… Figure 4 (b) is a simulation model diagram of the frequency-coded metasurface. In this invention, a super sub-unit arrangement is used, where 4×4 identical frequency-coded metasurface units are grouped into a single super sub-unit. Since the frequency-coded metasurface unit structure F1 has low phase-frequency sensitivity, its corresponding frequency code is '0'; in contrast, the frequency-coded metasurface unit structure F3 has higher phase-frequency sensitivity, and therefore its corresponding frequency code is '1'. These two types of frequency-coded metasurface sub-units have almost identical phase responses at the initial frequency. This invention designs the frequency-coded metasurface by arranging the coding pattern in space, thereby achieving the specified electromagnetic function.

[0053] Figure 5 Showing according to Figure 4 The far-field maps corresponding to the coded metasurface at different frequencies obtained from the simulation of the coded sequence. For example... Figure 5 As shown in (a), at the initial frequency, electromagnetic energy is perpendicularly reflected by the frequency-coded metasurface, corresponding to a single beam emitted along the z-axis in the far field. As the frequency of the incident electromagnetic wave increases, the phase difference between the two frequency-coded metasurface units changes approximately linearly. When the frequency of the incident electromagnetic wave is less than the center frequency, the phase inhomogeneity of the frequency-coded metasurface gradually increases with increasing frequency. At this point, the frequency-coded metasurface will simultaneously generate a perpendicularly emitted single beam and two symmetrically deflected beams. Figure 5 As shown in (b) and (c), when the frequency of the incident electromagnetic wave exceeds the center frequency, the phase inhomogeneity of the frequency-encoded metasurface will gradually decrease, and the vertically emitted beam will gradually transform into two symmetrically deflected beams. Figure 5As shown in (d), when the frequency of the incident electromagnetic wave reaches the cutoff frequency, the single beam emitted perpendicularly along the z-axis almost completely disappears, and the electromagnetic energy is almost entirely converted into two symmetrically deflected beams.

[0054] Figure 6 (a) is a schematic diagram of a 1-bit frequency-coded metasurface, with the corresponding coding arrangement as: '0', '1', '0', '1'… / '1', '0', '1', '0'… Figure 6 (b) is a simulation model diagram of the frequency-coded metasurface.

[0055] Figure 7 Showing according to Figure 6 The far-field maps corresponding to the coded metasurface at different frequencies obtained from the simulation of the coded sequence. For example... Figure 7 As shown in (a), at the initial frequency, electromagnetic energy is reflected perpendicularly by the frequency-coded metasurface, and its far field corresponds to a single beam emitted along the z-axis. Figure 7 As shown in (b) and (c), as the frequency of the incident electromagnetic wave increases, the main beam pointing towards the z-axis at the initial frequency gradually transforms into four symmetrically emitted anomalously reflected beams, as... Figure 7 As shown in (d), when the frequency of the incident electromagnetic wave continues to increase to the cutoff frequency, the energy of the vertically emitted single beam almost completely disappears, and most of the energy is converted into four beams emitted along the symmetrical azimuth angle.

[0056] Figure 8 (a) is a 2-bit frequency-coded metasurface, with the corresponding coded arrangement as: '00', '01', '10', '11', '00', '01', '10', '11'… Figure 8 (b) is a simulation model diagram of a 2-bit frequency-coded metasurface. Due to the increase in the types of metasurface sub-units, the 2-bit frequency-coded metasurface has a higher degree of design freedom and can achieve more flexible control of electromagnetic waves.

[0057] Figure 9 Showing according to Figure 8 The far-field maps corresponding to the coded metasurface at different frequencies obtained from the simulation of the coded sequence. For example... Figure 9 As shown. Figure 9 As shown in (a), for the first encoding pattern, electromagnetic energy can be seen to be vertically reflected at the initial frequency. Figure 9 As shown in (b) and (c), with the increase of the incident electromagnetic wave frequency, the energy of the originally vertically emitted main beam gradually decreases, while the energy of the beam deflected to the right along the z-axis gradually increases. Figure 9As shown in (d), when the frequency of the incident electromagnetic wave reaches the cutoff frequency, the phase distribution on the surface of the frequency-coded metasurface is uniform and has a certain gradient, which causes the original vertically emitted single beam to almost completely disappear, while the deflected beam to the right of the z-axis evolves into a new main beam pointing at a certain angle. When the frequency of the incident electromagnetic wave increases to the cutoff frequency, the phase difference between the frequency-coded metasurface units becomes a uniform gradient consisting of 0°, 90°, 180°, 270°, 0°, 90°, 180°, 270°… on the corresponding surface phase distribution.

[0058] The frequency-coded metasurface designed in this specific embodiment consists of an optimized reflective frequency-coded metacell structure. The units have different phase-frequency sensitivities, and the coding sequence is designed using these differences to achieve continuous control of electromagnetic waves. A 1-bit coding mode can be used to implement two-beam and four-beam splitters, while a 2-bit coding mode can achieve control of a single beam in different directions.

[0059] This specific implementation features a simple structure, ease of design, ultra-thinness, flexibility, high symmetry, passive operation, and low cost, making it a promising candidate for applications in wireless communication, radar, imaging, and signal processing.

[0060] Specific Implementation Method Two: A design method based on an ultrathin flexible frequency-coded metasurface, characterized by the following steps:

[0061] Step 1: Determine the modulation function required for the beam control device, and determine the phase required for each reflective tunable supercell structure based on the modulation function;

[0062] Step 2: By adjusting the geometric parameters of the reflective tunable supercell, phase modulation of the corresponding reflective tunable supercell structure is achieved, ensuring that the phase response curve of the reflective tunable supercell has different phase-frequency sensitivities within the operating frequency band. The reflective tunable supercell with low phase-frequency sensitivity is encoded as 0; the reflective tunable supercell with high phase-frequency sensitivity is encoded as 1.

[0063] Step 3: Given 1-bit and 2-bit encoded sequences, solve for the radiation field;

[0064] Step 4: By changing the frequency of the incident electromagnetic wave, an ultrathin flexible frequency-coded metasurface is obtained, completing a design based on the ultrathin flexible frequency-coded metasurface.

[0065] In step three, the radiation field is solved using the formula:

[0066]

[0067] Achieved; where: the parameters are defined as follows: θ is the pitch angle, It's the azimuth. These are the radiation pattern coefficients for each coding unit. It is the scattering phase. Md represents the period of a super subunit, d represents the period of a single subunit, and k = λ0 / 2π.

[0068] In the description of this specification, those skilled in the art can combine and integrate the different embodiments or examples described herein, as well as the features of the different embodiments or examples.

[0069] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. An ultrathin flexible frequency-coded metasurface, characterized in that: it include: N reflective tunable supercell structures; N is a positive integer; the N reflective tunable supercell structures are uniformly arranged in the xy two-dimensional plane and periodically arranged to form a single component, namely: an ultrathin flexible frequency-coded metasurface; each of the reflective tunable supercell structures includes an intermediate dielectric substrate layer, an orthogonal cross-shaped metal pattern patch layer, and a metal reflective layer; the metal pattern patch layer is fixed to the upper surface of the intermediate dielectric substrate layer; the metal reflective layer is fixed to the lower surface of the intermediate dielectric substrate layer; The pattern of the metal pattern patch layer is a symmetrical graphic composed of orthogonal cross patterns. Each symmetrical graphic is a square with a quarter circle removed, and the four symmetrical graphics form a cross-shaped opening. The pattern of the metal pattern patch layer is used to reflect the amplitude of electromagnetic waves and modulate the phase of the reflective tunable supercell structure in which it is located. The ultrathin flexible frequency-coded metasurface has different phase-frequency sensitivities within the operating frequency band, and its phase response curve tends to be linear with frequency change. The reflective tunable meta-unit with low phase-frequency sensitivity is encoded as 0, and the reflective tunable meta-unit with high phase-frequency sensitivity is encoded as 1.

2. The ultrathin flexible frequency-encoded metasurface according to claim 1, characterized in that, The intermediate dielectric substrate layer is a polyimide layer.

3. The ultrathin flexible frequency-encoded metasurface according to claim 1, characterized in that, The orthogonal cross-shaped metal patch layer is made of aluminum foil with etched patterns.

4. The ultrathin flexible frequency-encoded metasurface according to claim 1, characterized in that, The metallic reflective layer is a copper plate.

5. A design method for an ultrathin flexible frequency-coded metasurface as described in any one of claims 1-4, characterized in that, Includes the following steps: Step 1: Determine the modulation function required for the beam control device, and determine the phase required for each reflective tunable supercell structure based on the modulation function; Step 2: By adjusting the geometric parameters of the reflective tunable supercell, phase modulation of the corresponding reflective tunable supercell structure is achieved, ensuring that the phase response curve of the reflective tunable supercell has different phase-frequency sensitivities within the operating frequency band. The reflective tunable supercell with low phase-frequency sensitivity is encoded as 0; the reflective tunable supercell with high phase-frequency sensitivity is encoded as 1. Step 3: Given 1-bit and 2-bit encoded sequences, solve for the radiation field; Step 4: By changing the frequency of the incident electromagnetic wave, an ultrathin flexible frequency-coded metasurface is obtained, thus completing the design of an ultrathin flexible frequency-coded metasurface.

6. The design method for an ultrathin flexible frequency-coded metasurface according to claim 5, characterized in that, In step three, the radiation field is solved using the formula: Implementation; In the formula: θ is the elevation angle of the radiation field. It is the azimuth angle of the radiation field. These are the radiation pattern coefficients of each reflective tunable supercell structure; It is the scattering phase of each reflective tunable supercell structure; Md represents the period of a super subunit, d represents the period of a single subunit, k = λ0 / 2π, and λ0 is the wavelength of the incident electromagnetic wave.

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