Broadband and quad-band switchable dual-functional terahertz absorber

Abstract

The present application relates to the technical field of terahertz wave absorber, in particular to a dual-functional terahertz wave absorber with wideband and four-frequency band switchable, which is formed by stacking phase change patch layer, wideband absorbing medium layer, phase change bottom layer, metal patch layer, multi-frequency absorbing medium layer and metal bottom layer from top to bottom to form a terahertz wave absorption unit, and then arranging multiple terahertz wave absorption units periodically to form a terahertz wave absorber; in the use process, only by changing the conductivity of the phase change material vanadium dioxide, the switch of absorption characteristics and the flexible change of absorption rate can be realized, and the technical problem that the absorption characteristics of the traditional terahertz wave absorber are fixed once it is made is solved.

Description

Technical Field

[0001] This invention relates to the field of terahertz absorber technology, and more specifically to a broadband and four-band switchable dual-function terahertz absorber. Background Technology

[0002] Terahertz (THz) waves are electromagnetic waves with frequencies between 0.1 THz and 10 THz. This wave is located in the transition band between low-energy electronics and high-energy photonics, and is currently recognized as an electromagnetic wave band with excellent characteristics.

[0003] Terahertz absorbers are important terahertz functional devices, and can be broadly classified into narrowband absorbers, multiband absorbers, and broadband absorbers based on their absorption characteristics. Terahertz absorbers have broad application prospects in electromagnetic stealth, thermal radiation, thermal imaging, and other related fields.

[0004] Early terahertz absorbers were mostly narrowband absorbers and could only operate at fixed frequencies with fixed absorptivity. Changing the absorption characteristics and absorptivity of the absorber required modifications to its geometry and dimensional parameters, necessitating the redesign and remanufacturing of existing devices. Once a traditional terahertz absorber was manufactured, its absorption characteristics were fixed, which to some extent limited the development of terahertz absorbers. Summary of the Invention

[0005] The purpose of this invention is to provide a broadband and four-band switchable dual-function terahertz absorber that changes its absorption characteristics and absorptivity by varying the temperature, aiming to solve the technical problem that the absorption characteristics of traditional terahertz absorbers are fixed once they are manufactured.

[0006] To achieve the above objectives, the present invention provides a broadband and four-band switchable dual-function terahertz absorber, comprising multiple terahertz absorbing units distributed in an N×N pattern, where N is a natural number.

[0007] The terahertz absorbing unit is composed of a phase change patch layer, a broadband absorbing medium layer, a phase change bottom layer, a metal patch layer, a multi-frequency absorbing medium layer, and a metal bottom layer stacked from top to bottom.

[0008] The terahertz absorbing unit has a periodic side length p = 12 μm.

[0009] The phase change patch layer is made of vanadium dioxide with a thickness of t1 = 0.17 μm. The pattern of the phase change patch layer consists of a circle with a radius of r1 = 2 μm, a cracked ring with an inner radius of r2 = 2.2 μm, a ring width of 1 μm, and an opening of 1 μm, an inner square with an inner side length of g1 = 6.5 μm and a width of d1 = 0.5 μm, and an outer square with an inner side length of g2 = 8.5 μm and a width of d2 = 0.75 μm, arranged sequentially from the inside out.

[0010] The broadband absorption dielectric layer is made of polyimide with a dielectric constant of 3.5 and a thickness of h1 = 6.4 μm.

[0011] The phase change substrate is made of vanadium dioxide with a thickness t2 = 0.2 μm.

[0012] The metal patch layer is made of silver with a conductivity of 6.301e7 S / m. The pattern of the metal patch layer is formed by an open ring with an inner radius r3 = 1.7 μm, a ring width of 0.3 μm, and an opening of 0.1 μm; an open ring with an inner radius r4 = 2.7 μm, a ring width of 0.3 μm, and an opening of 1.7 μm; and an open ring with an inner radius r5 = 3.6 μm, a ring width of 0.4 μm, and an opening of 1 μm, arranged sequentially from the inside out. The thickness of the metal patch layer is t3 = 0.1 μm.

[0013] The multi-frequency absorption dielectric layer is made of polyimide with a dielectric constant of 3.5 and a thickness of h2 = 6.8 μm.

[0014] The underlying metal is made of silver, with an electrical conductivity of 6.301e7S / m and a thickness of t4 = 0.2μm.

[0015] This invention provides a dual-function terahertz absorber that can switch between broadband and four frequency bands. It consists of a terahertz absorbing unit formed by stacking a phase change patch layer, a broadband absorbing medium layer, a phase change bottom layer, a metal patch layer, a multi-frequency absorbing medium layer, and a metal bottom layer from top to bottom. Multiple terahertz absorbing units are then periodically arranged to form a terahertz absorber. During use, the absorption characteristics can be switched and the absorption rate can be flexibly changed simply by changing the conductivity of the phase change material vanadium dioxide through temperature. This solves the technical problem that the absorption characteristics of traditional terahertz absorbers are fixed once they are manufactured. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a three-dimensional structural schematic diagram of a broadband and four-band switchable dual-function terahertz absorber according to the present invention.

[0018] Figure 2 This is a side view of a broadband and four-band switchable dual-function terahertz absorber according to the present invention.

[0019] Figure 3This is a schematic diagram of the phase change patch layer pattern of a broadband and four-band switchable dual-function terahertz absorber according to the present invention.

[0020] Figure 4 This is a schematic diagram of the metal patch layer pattern of a broadband and four-band switchable dual-function terahertz absorber according to the present invention.

[0021] Figure 5 This is a schematic diagram of the absorption spectrum of an embodiment of the present invention as a function of the conductivity of vanadium dioxide.

[0022] Figure 6 When the conductivity of vanadium dioxide is (a) 3×10 5 S / m, (b) 3×10 4 S / m, (c)2×10 4 Schematic diagram of the absorption spectrum of an embodiment of the present invention at S / m and (d)0S / m.

[0023] Figure 7 This is a schematic diagram showing the transmittance of the first three layers of the structure in an embodiment of the present invention at different conductivity values ​​of vanadium dioxide.

[0024] Figure 8 When the conductivity of vanadium dioxide is 3×10 5 S / m, 3×10 4 S / m, 2×10 4 A schematic diagram of the electric field distribution of the (ac) phase change patch layer and the (df) metal patch layer at the frequency point of highest absorption rate in an embodiment of the present invention at S / m.

[0025] Figure 9 When the conductivity of vanadium dioxide is (a) 3×10 5 S / m, (b) 3×10 4 S / m, (c)2×10 4 A schematic diagram of the equivalent impedance of an embodiment of the present invention at S / m.

[0026] Figure 10 This is a schematic diagram showing the relationship between polarization angle and absorptivity when terahertz waves (ac) are incident perpendicularly, and the relationship between incident angle and absorptivity when (df)TE polarized and (gi)TM polarized are incident under different electrical conductivities of vanadium dioxide.

[0027] Figure 11 This is an electric field distribution diagram of the (ad) phase change patch layer and (eh) metal patch layer at the four frequency points with the highest absorption rate in the embodiments of the present invention when the conductivity of vanadium dioxide is 0 S / m.

[0028] Figure 12This is a schematic diagram showing the relationship between polarization angle and absorptivity when vanadium dioxide conductivity is 0 S / m in the embodiments of the present invention, for (a) perpendicular incident terahertz waves, (b) TE polarization and (c) TM polarization incident terahertz waves, and for (c) incident terahertz waves, the relationship between incident angle and absorptivity. Detailed Implementation

[0029] Embodiments of the present invention are described in detail below, examples of which are illustrated 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.

[0030] Please see Figures 1 to 4 This invention provides a broadband and four-band switchable dual-function terahertz absorber, comprising multiple terahertz absorbing units distributed in an N×N pattern, where N is a natural number. Each terahertz absorbing unit is composed of, from top to bottom, a phase change patch layer, a broadband absorbing dielectric layer, a phase change bottom layer, a metal patch layer, a multi-frequency absorbing dielectric layer, and a metal bottom layer stacked together. The periodic side length of the absorbing unit is p = 12 μm.

[0031] The phase change patch is made of vanadium dioxide and consists of a circle with radius r1 = 2 μm, a split ring with inner radius r2 = 2.2 μm, ring width 1 μm, and opening 1 μm, an inner square with inner side length g1 = 6.5 μm and width d1 = 0.5 μm, and an outer square with inner side length g2 = 8.5 μm and width d2 = 0.75 μm. The thickness of the patch is t1 = 0.17 μm.

[0032] The broadband absorption dielectric layer is made of polyimide with a dielectric constant of 3.5 and a thickness of h1 = 6.4 μm.

[0033] The phase change substrate is made of vanadium dioxide, and its thickness t2 = 0.2 μm.

[0034] The metal patch layer is made of silver, and its electrical conductivity σsilver is 6.301e7 S / m. The patch layer consists of an open ring with an inner radius r3 = 1.7 μm, a ring width of 0.3 μm, and an opening of 0.1 μm; an open ring with an inner radius r4 = 2.7 μm, a ring width of 0.3 μm, and an opening of 1.7 μm; and an open ring with an inner radius r5 = 3.6 μm, a ring width of 0.4 μm, and an opening of 1 μm. The thickness of the patch layer is t3 = 0.1 μm.

[0035] The multi-frequency absorption dielectric layer is made of polyimide with a dielectric constant of 3.5 and a thickness of h2 = 6.8 μm.

[0036] The metal substrate is made of silver, which has an electrical conductivity of 6.301e7 S / m and a thickness of t4 = 0.2 μm.

[0037] Traditional terahertz absorbers, once manufactured, have fixed absorption characteristics and absorptivity that are difficult to change. The purpose of this invention is to achieve switching of absorption characteristics and flexible alteration of the absorptivity without altering the absorber's structural dimensions. To achieve this, the invention places vanadium dioxide-related structural layers (phase change patch layer and phase change bottom layer) in the upper half of the absorber's absorbing unit and separates them with a dielectric layer. This leverages the characteristic of vanadium dioxide switching between insulating and metallic states at different temperatures, thereby achieving switching of the absorber's absorption characteristics. The designed terahertz absorber should exhibit polarization insensitivity and maintain good absorption characteristics even when electromagnetic waves are incident at large angles. Based on these two objectives, the absorbing unit should be designed to be as symmetrical as possible in the x and y directions. The absorbing unit uses a metal bottom layer with a thickness greater than the skin depth to block the transmission of incident electromagnetic waves. When the designed absorber's transmittance is 0, high absorption can be achieved by simply reducing the absorber's reflection using methods such as impedance matching and multiple reflection interference cancellation. In impedance matching theory, the entire absorbing device can be considered as a whole, with a characteristic impedance of z and a free space impedance of z0. When these two impedances are equal, the absorber achieves impedance matching with the free space. At this point, electromagnetic waves can enter the absorber and be attenuated to the maximum extent, thus achieving better absorption. When the free space impedance is z0, the reflection coefficient S... 11 It can be represented as:

[0038]

[0039] In the formula, Where μ and ε represent the equivalent permeability and equivalent permittivity of the absorber, respectively, and μ0 and ε0 represent the permeability and permittivity of free space, respectively. By designing specific equivalent permeability μ and equivalent permittivity ε to make z = z0, the impedance matching between the absorbing structure and the free space impedance can be achieved.

[0040] Compared to impedance matching theory, multiple reflection interference theory is more intuitive. When an electromagnetic wave acts on an absorber, part of the wave is reflected back at the surface of the absorber structure, while the other part enters the absorber structure and continues to propagate, eventually being reflected at a non-porous metal substrate with a thickness greater than the skin depth. If the reflected wave at the initial incident point is in phase with the outgoing wave reflected back from the metal substrate, constructive interference increases reflection; if the phases are opposite, destructive interference decreases reflection.

[0041] Furthermore, the present invention also proposes specific embodiments for simulation verification (see details). Figures 5 to 12 ):

[0042] Specifically, the broadband and four-band switchable dual-function terahertz absorber was numerically calculated using the finite element method, and its performance was simulated using CST Studio Suite. The x and y directions were set as periodic boundaries, and the z direction as an open boundary. The terahertz wave was incident perpendicular to the surface along the -z direction.

[0043] The dielectric constant of vanadium dioxide in the terahertz band is described using the Drude model:

[0044]

[0045] In the formula, ω represents the incident angular frequency, and ε ∞ =12 is the high-frequency dielectric constant, γ = 5.75 × 10⁻⁶. 13 It is the collision frequency. σ is the electrical conductivity of vanadium dioxide, and ω... p (σ) is the plasma frequency that depends on the conductivity, ω p Both (σ) and σ are proportional to the free carrier density. The relationship between the conductivity of vanadium dioxide and the plasma frequency can be approximated as:

[0046]

[0047] In the formula, σ0 = 3 × 10 5 S / m, ω p (σ)=1.4×10 15 The electrical conductivity of vanadium dioxide (rad / s) can be controlled by changing the temperature.

[0048] Absorption rate is an important parameter reflecting the performance of an absorption device. The formula for calculating the absorption rate is:

[0049] A = 1 - |S 11 2 -|S 21 | 2 (4)

[0050] Among them, S 11 and S 21 Let S represent the reflection coefficient and transmission coefficient of the incident wave after it strikes the absorbing device, respectively. Within the simulation frequency range, the thickness of the metal substrate is much greater than its skin depth, and the transmission coefficient S of this absorber is... 21 Since it is almost zero, the formula for absorption rate can be simplified to A = 1 - |S|. 11 | 2 .

[0051] Figure 5The absorption spectrum of vanadium dioxide (vanadium dioxide) as a function of its electrical conductivity is shown. Vanadium dioxide is a metal oxide with phase transition properties. At room temperature, vanadium dioxide has a monoclinic crystal structure with high resistivity and insulating properties. When the temperature is above 68℃, vanadium dioxide transforms into a cubic rutile structure, exhibiting metallic properties. The electrical conductivity of vanadium dioxide increases with increasing temperature. Near 68℃, a phase transition effect occurs from an insulating state to a metallic state, at which point the conductivity of vanadium dioxide can increase by three to four orders of magnitude within a small temperature range. The phase transition of vanadium dioxide is reversible; when the temperature drops below 68℃ again, its conductivity can completely recover to its initial state. Figure 5 It can be seen that vanadium dioxide exhibits a broadband absorption effect when it has high conductivity. When vanadium dioxide is in an insulating state, it achieves high absorption in four frequency bands in the terahertz band.

[0052] Figure 6 This further demonstrates that the electrical conductivity of vanadium dioxide is 3×10⁻⁶. 5 S / m, 3×10 4 S / m, 2×10 4 The absorption spectra of the absorber at S / m and 0 S / m. When the terahertz wave is incident perpendicularly, the conductivity of vanadium dioxide is 3 × 10⁻⁶. 5 At S / m, the absorption rate exceeds 90% in the range of 3.06-7.61 THz, with an absolute bandwidth of 4.55 THz; the conductivity of vanadium dioxide is 3×10⁻⁶. 4 At S / m, the absorption rate exceeds 90% in the range of 3.18-8.91 THz, with an absolute bandwidth of 5.73 THz; the conductivity of vanadium dioxide is 2×10⁻⁶. 4 At a conductivity of 0 S / m, the absorption rate exceeds 90% in the range of 2.78-9.22 THz, with an absolute bandwidth of 6.44 THz. When the conductivity of vanadium dioxide is 0 S / m, high absorption is achieved in four frequency bands, with absorption rates reaching 99% at frequencies of 2.23 THz, 4.06 THz, 5.80 THz, and 9.82 THz.

[0053] Figure 7 The transmission characteristics of the three-layer structure of the absorber (phase change patch layer, broadband absorbing dielectric layer, and phase change bottom layer) under different conductivity values ​​of vanadium dioxide are shown. When the conductivity of vanadium dioxide is 3×10⁻⁶, the transmission characteristics are compared. 5 At a transmittance of S / m, the transmittance is less than 0.1, therefore the broadband absorption effect at this point is mainly achieved by the first three layers of the absorber. As the conductivity of vanadium dioxide gradually decreases, the isolation effect of the phase change substrate composed of vanadium dioxide thin film gradually weakens, and terahertz waves begin to penetrate through the vanadium dioxide thin film and enter the metal patch layer. The absorption effect after the decrease in vanadium dioxide conductivity is achieved by the six layers of the absorber together.

[0054] Figure 8This is the electric field diagram at the frequency point of highest absorption rate when the microwave absorber produces a broadband absorption effect under different electrical conductivities of vanadium dioxide in its metallic state. When the conductivity of vanadium dioxide is 3 × 10⁻⁶... 5 When S / m, by Figure 8 (a) It can be seen that the energy is mainly concentrated between the circular ring and the cracked ring, at the opening of the cracked ring, between the cracked ring and the inner square in the y-direction, and between the inner square and the outer square. The interaction between different vanadium dioxide surface patch structures produces a broadband absorption effect. Figure 8 (d) It can be seen that there is almost no energy distribution on the metal patch layer at this conductivity. Figure 7 This is because the vanadium dioxide thin film, forming the phase transition underlayer, prevents most terahertz waves from entering the metal patch layer. Figure 8 (df) shows that the energy of the metal patch layer gradually increases as the conductivity decreases. The energy of the metal patch layer is mainly concentrated at the openings of the inner and outer rings, between the opening rings in the y-direction, and on the outer layer of the outer ring. The decrease in conductivity allows terahertz waves to enter the metal patch layer. The electric dipole resonance of the phase change patch layer and the metal patch layer, as well as the loss of terahertz waves by the dielectric layer, cause the conductivity of vanadium dioxide to decrease to 3 × 10⁻⁶. 4 S / m and 2×10 4 The same broadband absorption effect was achieved at S / m.

[0055] To further elucidate the absorption mechanism during broadband absorption by the absorber, the absorption of vanadium dioxide at a conductivity of 3×10⁻⁶ was analyzed. 5 S / m, 3×10 4 S / m, 2×10 4 The equivalent impedance of the absorber at S / m. Figure 9 It can be seen that within the high absorption range, the real part Re(z) of the absorber's relative impedance approaches 1, and the imaginary part Im(z) approaches 0. At this point, the characteristic impedance of the absorber is approximately matched with the free-space impedance. Impedance matching can significantly reduce the reflection of incident terahertz waves by the absorber, thereby achieving a high absorption rate.

[0056] Figure 10 (ac) represents the conductivity of vanadium dioxide, which is 3 × 10⁻⁶. 5 S / m, 3×10 4 S / m, 2×10 4 At S / m, the absorption rate changes as the polarization angle changes from 0° to 90° when the terahertz incident wave is perpendicularly incident. Figure 10 (ac) clearly demonstrates that when terahertz waves are incident perpendicularly, the absorption rate of the absorber when producing a broadband absorption effect is not affected by the polarization angle, exhibiting excellent polarization insensitivity characteristics. Figure 10 (df) and Figure 10(gi) represent the effect of the incident wave angle on the absorbance when the terahertz wave is incident in TE and TM polarization, respectively. Figure 10 (df) shows that when terahertz waves are TE-polarized, the incident angle remains high within the corresponding frequency range of 0°-60°, maintaining a high absorption rate. Figure 10 (gi) It can be seen that when the terahertz wave is incident with TM polarization, it maintains a high absorption rate within the corresponding frequency range of 0°-75°. In summary, when generating a broadband absorption effect, the absorption rate of the terahertz wave under perpendicular incidence is not affected by the polarization angle. Even with oblique incidence between 0° and 60°, it can still function normally and maintain a high absorption rate to achieve wide-angle absorption.

[0057] Figure 11 This shows the electric field distribution of the phase change patch and the metal patch at four frequency points where the absorption rate is highest when the insulating conductivity of vanadium dioxide is 0 S / m. Figure 11 (ad) It can be seen that vanadium dioxide, when in an insulating state, exhibits almost no energy distribution on the phase change patch layer. From Figure 7 It can be seen that at this conductivity, most terahertz waves can pass through the phase transition substrate composed of vanadium dioxide thin film and enter the metal patch layer. Observing the electric field distribution of the metal patch layer, it can be seen that the electric field energy at the frequency of 2.23 THz is mainly concentrated at the openings of the outer ring, middle ring, and inner ring; at the frequency of 4.06 THz, the electric field energy is mainly concentrated at the openings of the inner ring, middle ring, and outer ring; at the frequency of 5.80 THz, the electric field energy is mainly concentrated at the openings of the three rings; and at the frequency of 9.82 THz, the electric field energy is mainly concentrated at the openings of the three rings and the outer ring. The combined effect of different opening rings at different frequency points forms a high absorption effect in four frequency bands.

[0058] Figure 12 (a) shows the relationship between the polarization angle and the absorptivity when a terahertz wave is incident perpendicularly in the vanadium dioxide insulating state. The absorptivity changes with the polarization angle, which is due to the polarization sensitivity caused by the non-symmetrical shape of the metal patch layer that produces the main absorption effect in the vanadium dioxide insulating state in both the x and y directions. Although the absorber is polarization sensitive in the vanadium dioxide insulating state, as... Figure 12 As shown in (b), when terahertz waves are incident with TE polarization, the absorber can still maintain a high absorption rate in the first three frequency bands when the incident angle is less than 75°. Figure 12 As shown in (c), when the terahertz wave is TM polarized and incident perpendicularly, it produces a high absorption rate at frequencies of 6.45 THz and 9.46 THz. The dual-band absorption effect produced by TM polarization can also maintain a high absorption rate when the incident angle is less than 75°.

[0059] Simulation results show that when vanadium dioxide in the absorber is in a metallic state, the absorber can achieve broadband absorption effects with varying conductivity. When terahertz waves are incident perpendicularly, the conductivity of vanadium dioxide is 3 × 10⁻⁶. 5 At S / m, the absorption rate exceeds 90% in the frequency range of 3.06-7.61 THz, with an absolute bandwidth of 4.55 THz; the conductivity of vanadium dioxide is 3×10⁻⁶. 4 At S / m, the absorption rate exceeds 90% in the frequency range of 3.18-8.91 THz, with an absolute bandwidth of 5.73 THz; the conductivity of vanadium dioxide is 2×10⁻⁶. 4 At a frequency of S / m, the absorption rate exceeds 90% in the frequency range of 2.78-9.22THz, with an absolute bandwidth of 6.44THz. This absorber exhibits the advantages of polarization insensitivity and wide-angle absorption when achieving broadband absorption effects with different bandwidths.

[0060] When the vanadium dioxide in the absorber is in an insulating state with a conductivity of 0 S / m, the absorber achieves multi-band absorption. It can generate high absorption in four frequency bands within the terahertz band, achieving 99% absorption rates at 2.23 THz, 4.06 THz, 5.80 THz, and 9.82 THz. When achieving high absorption in four frequency bands, the absorber also exhibits the advantage of wide-angle absorption with TE-polarized incident light.

[0061] The terahertz absorber designed in this invention can switch absorption characteristics and flexibly change the absorption rate simply by changing the conductivity of its phase change material vanadium dioxide through temperature. It has great development prospects in the fields of stealth, selective thermal emitters and solar photovoltaics.

[0062] The above description discloses only one preferred embodiment of the present invention, and should not be construed as limiting the scope of the present invention. Those skilled in the art will understand that all or part of the processes of the above embodiments can be implemented, and equivalent changes made in accordance with the claims of the present invention are still within the scope of the invention.

Claims

1. A broadband and four-band switchable dual-function terahertz absorber, comprising multiple terahertz absorbing units, characterized in that, The terahertz absorbing units are distributed in an N×N pattern, where N is a natural number; The terahertz absorbing unit is composed of a phase change patch layer, a broadband absorbing medium layer, a phase change bottom layer, a metal patch layer, a multi-frequency absorbing medium layer, and a metal bottom layer stacked from top to bottom. The phase change patch layer material is vanadium dioxide, and its thickness is... The pattern of the phase change patch layer is determined by the radius. circle, inner radius Ring width Opening Crack ring, inner side length width The inner frame and its inner side length width The outer frame is arranged sequentially from the inside out.

2. The broadband and four-band switchable dual-function terahertz absorber as described in claim 1, characterized in that, The terahertz absorbing unit has a periodic side length .

3. The broadband and four-band switchable dual-function terahertz absorber as described in claim 1, characterized in that, The broadband absorption dielectric layer is made of polyimide with a dielectric constant of 3.5 and a thickness of [missing information]. .

4. The broadband and four-band switchable dual-function terahertz absorber as described in claim 1, characterized in that, The phase change substrate is made of vanadium dioxide, and its thickness is... .

5. The broadband and four-band switchable dual-function terahertz absorber as described in claim 1, characterized in that, The metal patch layer is made of silver with an electrical conductivity of 6.301e7 S / m. The pattern of the metal patch layer consists of an inner radius... Ring width Opening Opening ring, inner radius Ring width Opening The open ring and inner radius Ring width An opening ring with a 1 μm opening is arranged sequentially from the inside out, and the thickness of the metal patch layer is... .

6. The broadband and four-band switchable dual-function terahertz absorber as described in claim 1, characterized in that, The multi-frequency absorption dielectric layer is made of polyimide with a dielectric constant of 3.5 and a thickness of [missing information]. .

7. The broadband and four-band switchable dual-function terahertz absorber as described in claim 1, characterized in that, The metal substrate is made of silver, with an electrical conductivity of 6.301e7 S / m and a thickness of [missing information]. .

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