Programmable terahertz metasurface enabling dual-frequency spot beam steering

Abstract

The present invention discloses a programmable terahertz metasurface capable of dual-frequency beam steering, relating to the technical field of novel artificial electromagnetic materials. The metasurface comprises a plurality of metasurface units, each comprising a quartz substrate, a resonant metal layer, liquid crystal, and a backplane metal layer. The metasurface units are evenly spaced in both the horizontal and vertical directions, forming a rectangular array structure. The metasurface units are interconnected by metal wires in the vertical direction and disconnected from each other in the horizontal direction. The planar structure of the resonant metal layer is a butterfly-shaped simply connected region, comprising an outer boundary and an inner boundary, wherein the outer boundary's geometry is a proportional magnification of the inner boundary's geometry. The present invention can achieve multiple modulation functions at two terahertz frequencies by applying different voltage sequences. Specifically, the metasurface achieves terahertz beam deflection functions at different angles after loading a 1-bit and three-state digital code.

Description

Technical Field

[0001] This invention relates to the field of novel artificial electromagnetic materials technology, and more specifically, to a programmable terahertz metasurface capable of dual-frequency beam modulation. Background Technology

[0002] With the rapid development of modern terahertz beamforming technology, traditional phased array and scanning antennas struggle to address the challenges of high manufacturing precision, low integration, and system complexity. Therefore, there is an urgent need for sophisticated terahertz beamforming technology to achieve high-performance, highly flexible terahertz beamforming systems. This technology holds immense application potential in fields such as wireless communication, biosensing, and imaging.

[0003] The introduction of reconfigurable metasurfaces has brought about a breakthrough in the fine-grained terahertz beam manipulation technology. By introducing tunable materials such as liquid crystals, vanadium dioxide, or semiconductors into the resonant structure, and under the excitation of external electric fields, magnetic fields, heat, and lasers, researchers can precisely control the resonant performance of the device and achieve precise control of the terahertz wavefront. The concept of digitally coded metasurfaces has opened up a new channel for information interaction between metasurfaces and digital devices. External excitations can be applied to the metasurface via a computer through a programmable gate array, further improving the system's integration and operability. The development of this technology not only provides a new solution for terahertz beam manipulation but also lays the foundation for innovative applications in future communication and sensing technologies.

[0004] However, current research on terahertz reconfigurable metasurfaces still has shortcomings: most existing devices only have a single operating frequency, which severely limits the full utilization of the rich terahertz (0.1-10THz) spectrum resources; compared with the microwave band, how to effectively develop and utilize this rich spectrum space has become a key challenge to promote terahertz reconfigurable metasurfaces towards 6G wireless communication applications; therefore, developing terahertz reconfigurable metasurfaces that can achieve precise control of multiple frequency points is not only a key step to solve the bottlenecks of existing technologies, but also an essential path to promote terahertz technology to a higher level of application.

[0005] There are currently no effective solutions to the problems in the relevant technologies. Summary of the Invention

[0006] To address the problems in related technologies, this invention proposes a programmable terahertz metasurface capable of dual-frequency beam modulation. By using this programmable terahertz metasurface, modulation functions such as multi-angle beam deflection can be achieved at both terahertz frequencies by applying different voltage sequences (encoded). This solves the problem that existing active programmable terahertz metasurface devices only have a single operating frequency, which limits the utilization of the terahertz spectrum.

[0007] Therefore, the specific technical solution adopted by the present invention is as follows:

[0008] According to one aspect of the present invention, a programmable terahertz metasurface capable of dual-frequency beam modulation is provided. The programmable terahertz metasurface capable of dual-frequency beam modulation includes a plurality of metasurface units, each metasurface unit including a quartz substrate, a resonant layer metal, a liquid crystal, and a backplate metal; wherein the resonant layer metal is disposed at the bottom end of the quartz substrate, the liquid crystal is disposed at the bottom end of the resonant layer metal, and the backplate metal is disposed at the bottom end of the liquid crystal.

[0009] Furthermore, the metasurface units are arranged at equal intervals in both the horizontal and vertical directions to form a rectangular array structure; the metasurface units are interconnected in the vertical direction by metal wires, while they are disconnected in the horizontal direction, and each column of metasurface units in the rectangular array structure is independently loaded with a different voltage.

[0010] Furthermore, the thickness of the quartz substrate is 300 micrometers; the thickness of both the resonant layer metal and the backplate metal is 220 nanometers, and both the resonant layer metal and the backplate metal are made of gold; the thickness of the liquid crystal is 10 micrometers.

[0011] Furthermore, the planar structure of the resonant layer metal is a butterfly-shaped single-connected region, which includes an outer boundary and an inner boundary; the geometry of both the outer and inner boundaries is butterfly-shaped, and the geometry of the outer boundary is a proportionally enlarged version of the geometry of the inner boundary.

[0012] Furthermore, the external excitation method for loading the metasurface unit is to apply an alternating voltage to the resonant layer metal, and the backplate layer metal is grounded; before and after applying the external electrical excitation, the reflection spectrum of the metasurface unit exhibits two resonant frequency points, a low frequency and a high frequency; before and after applying the external electrical excitation, both resonant frequency points of the reflection spectrum of the metasurface unit undergo a redshift; before and after applying the external electrical excitation, the two resonant frequency points of the reflection spectrum of the metasurface unit will generate a phase difference.

[0013] Furthermore, based on the phase difference generated by the two resonant frequency points of the reflection spectrum of the metasurface unit, the metasurface unit can be digitally encoded, including 1-bit encoding and three-state encoding;

[0014] The 1-bit encoding includes:

[0015] When a first alternating voltage and a second alternating voltage are applied, the metasurface unit exhibits a first phase difference and a second phase difference at two resonant frequency points under electromagnetic wave incident, and the first phase difference and the second phase difference correspond to two states of bit encoding, respectively.

[0016] Furthermore, the tri-state encoding includes:

[0017] When the third, fourth, and fifth alternating voltages are applied, the metasurface unit exhibits a third phase difference, a fourth phase difference, and a fifth phase difference at two resonant frequency points under electromagnetic wave incident conditions, respectively. The third, fourth, and fifth phase differences correspond to the three states of the three-state encoding.

[0018] According to another aspect of the invention, a programmable terahertz metasurface application capable of dual-frequency beam modulation is also provided, which is used to input different digital encoding sequences by computer programming, convert the digital signal sequences into voltage sequences via a digital-to-analog converter and load them into the programmable terahertz metasurface capable of dual-frequency beam modulation, thereby differentially modulating the electromagnetic wave reflection phase through different metasurface units and achieving beam deflection at different angles at the dual frequencies.

[0019] The beneficial effects of the present invention are:

[0020] (1) The present invention can simultaneously achieve beam deflection at two frequency points when a single voltage sequence is loaded on a terahertz metasurface.

[0021] (2) Compared with electromagnetic metasurfaces that only have a single operating frequency, this invention opens up new possibilities for terahertz beam manipulation. By designing different digital sequences by computer and then assigning different voltage sequences to the metasurface after digital-to-analog converter, it can generate dual-frequency beam deflection function under the irradiation of incident electromagnetic waves. Compared with other programmable terahertz metasurfaces that only have one operating frequency, this invention increases the number of operating frequencies of the metasurface. The device realized has the characteristics of multifunctionality, flexible design and programmability. Attached Figure Description

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0023] Figure 1 This is a schematic diagram of the structure of a programmable terahertz metasurface capable of dual-frequency beam control according to an embodiment of the present invention;

[0024] Figure 2 This is a schematic diagram of the metasurface unit in a programmable terahertz metasurface capable of dual-frequency beam control according to an embodiment of the present invention.

[0025] Figure 3 This is a top view of a metasurface unit in a programmable terahertz metasurface capable of dual-frequency beam control according to an embodiment of the present invention.

[0026] Figure 4 This is a front view of a metasurface unit in a programmable terahertz metasurface capable of dual-frequency beam control according to an embodiment of the present invention;

[0027] Figure 5 This is a schematic diagram showing the reflection spectrum of the metasurface under two states in electromagnetic simulation and the phase difference between the two states.

[0028] Figure 6 This is a schematic diagram showing the changes in reflection amplitude and phase difference of the metasurface at two operating frequencies as the external voltage excitation increases;

[0029] Figure 7 This is a display image of the resonant layer metal in a programmable terahertz metasurface capable of dual-frequency beam modulation according to an embodiment of the present invention, under an optical microscope.

[0030] Figure 8 This is a schematic diagram of the overall reflection spectrum of the metasurface and the beam deflection test at two operating frequencies under a 1-bit encoded sequence.

[0031] Figure 9 This is a schematic diagram of the overall reflection spectrum of the metasurface and the beam deflection test at two operating frequencies under the loading of a three-state coding sequence.

[0032] Figure 10 This is a schematic diagram of the overall reflection spectrum of the metasurface under the loading of a 1-bit encoded sequence and a three-state encoded sequence.

[0033] In the picture:

[0034] 1. Quartz substrate; 2. Resonant layer metal; 3. Liquid crystal; 4. Backplane layer metal. Detailed Implementation

[0035] To further illustrate the various embodiments, the present invention provides accompanying drawings, which are part of the disclosure of the present invention. These drawings are mainly used to illustrate the embodiments and can be used in conjunction with the relevant descriptions in the specification to explain the operating principles of the embodiments. With reference to these drawings, those skilled in the art should be able to understand other possible implementation methods and the advantages of the present invention. The components in the drawings are not drawn to scale, and similar component symbols are generally used to represent similar components.

[0036] According to embodiments of the present invention, a programmable terahertz metasurface capable of dual-frequency beam modulation is provided.

[0037] The present invention will now be further described in conjunction with the accompanying drawings and specific embodiments, such as... Figure 1As shown, according to an embodiment of the present invention, a programmable terahertz metasurface capable of dual-frequency beam modulation is provided. The programmable terahertz metasurface capable of dual-frequency beam modulation includes a plurality of metasurface units, each metasurface unit including a quartz substrate 1, a resonant layer metal 2, a liquid crystal 3, and a backplate layer metal 4; wherein, the resonant layer metal 2 is disposed at the bottom end of the quartz substrate 1, the liquid crystal 3 is disposed at the bottom end of the resonant layer metal 2, and the backplate layer metal 4 is disposed at the bottom end of the liquid crystal 3.

[0038] Specifically, such as Figure 2 , Figure 3 and Figure 4 The figures shown are a schematic diagram, a top view, and a front view of the metasurface unit in the programmable metasurface capable of dual-frequency beam control according to the present invention. The top view shows the situation after removing the quartz substrate 1. The metasurface unit of the present invention includes: a quartz substrate 1, a resonant metal layer 2, a liquid crystal 3, and a backplate metal layer 4; wherein the resonant metal layer 2 and the backplate metal layer 4 are located on opposite sides of the liquid crystal 3, and the quartz substrate 1 is attached to the other side of the resonant metal layer 2; the metasurface array is arranged in the XY plane, with the origin located at the center of the metasurface unit, and the electromagnetic field is incident perpendicularly to the metasurface along the Z direction.

[0039] In one embodiment, the metasurface units are arranged at equal intervals in both the horizontal and vertical directions to form a rectangular array structure; the metasurface units are interconnected in the vertical direction by metal wires, and are disconnected from each other in the horizontal direction; each column of metasurface units in the rectangular array structure is independently loaded with a different voltage.

[0040] In one embodiment, the thickness of the quartz substrate 1 is 300 micrometers; the thickness of the resonant layer metal 2 and the backplate metal 4 is 220 nanometers, and the material of the resonant layer metal 2 and the backplate metal 4 is gold; the thickness of the liquid crystal 3 is 10 micrometers.

[0041] In one embodiment, the planar structure of the resonant layer metal 2 is a butterfly-shaped single-connected region, which includes an outer boundary and an inner boundary; the geometry of both the outer boundary and the inner boundary is butterfly-shaped, and the geometry of the outer boundary is a proportionally enlarged version of the geometry of the inner boundary.

[0042] Specifically, the planar structure of the resonant layer metal 2 is a ring-shaped, single-connected region with a hollowed-out center. The outer boundary geometry of the region is a proportionally enlarged version of the inner boundary geometry, both resembling a butterfly shape. The generation of the boundary geometry within the region is first achieved by smoothly connecting multiple discrete geometric points using a spline interpolation algorithm, and then by generating a closed pattern through horizontal and vertical mirroring.

[0043] Specifically, the actual processing of the terahertz metasurface that enables dual-frequency beam modulation is as follows: using ultraviolet lithography, patterns of a background gold layer and a resonant metal layer are generated on the bottom and top of a double-sided polished quartz substrate, respectively. Then, a 300-nanometer-thick gold film is deposited on the two substrates using magnetron sputtering technology. The backplate metal layer 4 and the resonant metal layer 2 are then formally generated through a lift-off process.

[0044] Specifically, such as Figure 7 As shown, the pattern of the resonant layer is displayed with excellent edge clarity. Subsequently, reactive ion etching was used to make the device surface hydrophilic by injecting oxygen, followed by spin-coating of a photoguide agent and ultraviolet exposure to complete the initial alignment of liquid crystal 3. Next, the device was mounted on a circuit board, a 10-micron gap was created using silicon spheres, and liquid crystal was filled in. After wire bonding, the metasurface device fabrication was completed.

[0045] In one embodiment, the external excitation method for loading the metasurface unit is to apply an alternating voltage to the resonant layer metal 2, and the backplate layer metal 4 is grounded; before and after the external electrical excitation is applied, the reflection spectrum of the metasurface unit exhibits two resonant frequency points, a low frequency and a high frequency; before and after the external electrical excitation is applied, both resonant frequency points of the reflection spectrum of the metasurface unit undergo a redshift; before and after the external electrical excitation is applied, the two resonant frequency points of the reflection spectrum of the metasurface unit will generate a phase difference.

[0046] Specifically, the external excitation method for the metasurface unit is to apply an alternating voltage to the resonant layer metal 2, while the backplate metal 4 is grounded. After a vertically incident electromagnetic wave, the reflection spectrum of the metasurface unit exhibits both a low-frequency resonance at approximately 400 GHz and a high-frequency resonance at approximately 700 GHz when no external voltage excitation is applied. When the metasurface unit is externally electrically excited, both resonances exhibit a redshift, resulting in frequency shifts of approximately 30 GHz and 50 GHz, respectively. The causes of the two resonances are not consistent: the low-frequency resonance is directly generated by dipole oscillations excited by the incident electromagnetic wave, while the high-frequency resonance is generated by the combined action of multiple higher-order harmonic oscillations excited by the same electromagnetic wave. Before and after applying external electrical excitation, the metasurface unit can generate a phase difference of more than 270 degrees at both frequencies.

[0047] Specifically, such as Figure 5 As shown, the reflection spectrum of the metasurface in the "off" state without voltage and the "on" state after voltage is applied, as well as the phase difference between the two states, are simulated by electromagnetic simulation. The two resonant frequencies of 406.4 GHz and 687.8 GHz in the "off" state are redshifted by 38.5 GHz and 49.0 GHz, respectively, after the metasurface enters the "on" state. This large redshift causes the metasurface to produce phase difference changes of 266.61 degrees and 271.06 degrees at operating frequency 1 (388.4 GHz) and operating frequency 2 (665.4 GHz), respectively.

[0048] Specifically, such as Figure 6 As shown, with the increase of external voltage excitation, the dielectric constant of the liquid crystal directly transitions from 2.465 to 3.5. During the transition, the reflection amplitude and phase difference of the metasurface at operating frequency 1 and operating frequency 2 change. This further proves that the phase change of the metasurface transitions continuously from 0 to close to 270 degrees, ensuring its ability to achieve 1-bit encoding and three-state digital encoding.

[0049] In one embodiment, based on the phase difference generated by two resonant frequency points of the reflection spectrum of the metasurface unit, the metasurface unit can be digitally encoded, including 1-bit encoding and tri-state encoding;

[0050] The 1-bit encoding includes:

[0051] When a first alternating voltage and a second alternating voltage are applied, the metasurface unit exhibits a first phase difference and a second phase difference at two resonant frequency points under electromagnetic wave incident, and the first phase difference and the second phase difference correspond to two states of bit encoding, respectively.

[0052] Tri-state coding includes:

[0053] When the third, fourth, and fifth alternating voltages are applied (in this embodiment, the third alternating voltage is the same as the first alternating voltage, and the fifth alternating voltage is the same as the second alternating voltage), the metasurface unit exhibits a third phase difference, a fourth phase difference, and a fifth phase difference at two resonant frequency points under electromagnetic wave incident, and the third phase difference, the fourth phase difference, and the fifth phase difference correspond to the three states of the three-state encoding.

[0054] Specifically, the fixed relationship between the voltage sequence applied to the metasurface and the computer-controlled digital encoding is as follows: when 0V and 15V are applied before and after the voltage, respectively, the metasurface units can exhibit reflection phase differences of 0 degrees and 180 degrees at two frequency points under electromagnetic wave incidence, corresponding to 1-bit digital encoding 0, 1; when 0V, 11V, and 15V are applied before and after the voltage, respectively, the metasurface units can exhibit reflection phase differences of 0 degrees, 120 degrees, and 240 degrees at two other frequency points under electromagnetic wave incidence, corresponding to tri-state encoding 0, 1, 2. The actual number of metasurface units processed is 112*112, with every 2 columns combined into 1 column for control, resulting in a total of 56 columns under independent control.

[0055] Specifically, the geometric parameters of the dual-frequency beam-controlled programmable terahertz metasurface are shown in Table 1, where p represents the metasurface unit period, h represents the thickness of the liquid crystal layer, and r1 to r 15 This represents the discrete geometric control point parameters for generating the metallic planar structure of the resonant layer. Specifically, in the first quadrant of the polar coordinate system, ri (i=1,2,…,15) takes values ​​of 0 and 1 to represent the origin position and the farthest distance limited by the metasurface unit period, respectively, with the argument between adjacent points differing by 7.5 degrees. These 15 parameters can be smoothly connected using a spline interpolation algorithm, and then the external structure of the resonant layer can be generated through mirroring operations on the X and Y axes. The internal holes are similar to the external holes, with parameter s serving as the geometric scaling ratio of the internal and external structures.

[0056] Table 1 Geometric Parameters of Metasurface Units

[0057]

[0058] According to another embodiment of the present invention, a programmable terahertz metasurface application capable of dual-frequency beam modulation is also provided, which is used to load various voltage sequences using a digital-to-analog converter according to a digital encoding form, to differentially modulate the electromagnetic wave reflection phase through different metasurface units, and to realize beam deflection, focusing and holographic imaging applications at different angles at dual frequencies.

[0059] Specifically, such as Figure 8 (a) and Figure 8 (b) shows the overall reflection spectrum of the actual fabricated metasurface in the frequency band (250GHz to 750GHz) observed in the emission angle range of 15° to 60° under the loading of the 1-bit digital encoding sequence \0011\, as well as the beam deflection test at operating frequency 1 and operating frequency 2.

[0060] Specifically, to demonstrate the functionality of a programmable terahertz metasurface capable of dual-frequency beam control in actual fabrication, in the first example, we used a digital-to-analog converter to load a voltage sequence onto the metasurface by inputting a digitally encoded sequence of "...001100110011..." into a computer. Figure 8 (a) Shows the overall reflection spectrum of the metasurface observed in the frequency band (250 GHz to 750 GHz) within the emission angle range of 15 degrees to 60 degrees; while Figure 8 In (b), beam deflection signals were observed at both operating frequency 1 (384 GHz) and operating frequency 2 (648 GHz), with reflection amplitudes of 0.22 and 0.18, and beam deflection angles of 36 degrees and 25 degrees, respectively. This calculation result is consistent with the generalized Snell's law formula. θ =arcsin(λ / Γ) yields the same result, where λ represents the free space wavelength and Γ represents the length of a gradient period.

[0061] Specifically, such as Figure 9 (a) and Figure 9(b) shows the overall reflection spectrum of the metasurface actually processed under the loading of the three-state digital coding sequence \001122\ in the frequency band (250GHz to 750GHz) observed in the emission angle range of 15 degrees to 60 degrees, and the beam deflection test for operating frequency 1 and operating frequency 2.

[0062] Specifically, in the second example, we use a digital-to-analog converter to apply a voltage sequence to the metasurface by inputting the digital encoded sequence "...012012012..." into the computer. Figure 9 (a) shows the overall reflection spectrum of the metasurface; while Figure 9 In (b), beam deflection signals were observed at both operating frequency 1 (386 GHz) and operating frequency 2 (666 GHz), with reflection amplitudes slightly less than 0.15 and beam deflection angles of 26 degrees and 20 degrees, respectively. The results of this calculation still conform to the generalized Snell's law.

[0063] Specifically, such as Figure 10 (a) and Figure 10 (b) shows the overall reflection spectrum of the metasurface actually fabricated under the loading of the 1-bit digital encoding sequence \01\ and the loading of the 1-bit digital encoding sequence \000111\, respectively, in the frequency band (250GHz to 750GHz) observed within the emission angle range of 15 degrees to 80 degrees; Figure 10 (c) and Figure 10 As shown in (d), the overall reflection spectrum of the metasurface actually processed under the loading of the three-state digital coding sequence \012\ and the loading of the three-state digital coding sequence \001122\ is observed in the frequency band (250GHz to 750GHz) within the emission angle range of 15 degrees to 80 degrees.

[0064] Specifically, in the third example, we further expand and demonstrate the programmable capabilities of actual fabricated metasurfaces. Figure 10 (a) and Figure 10 (d) The beam deflection capability of the metasurface under other sequences of 1-bit digital encoding, “…0101010101…” and “…000111000111…”, can be observed to have beam deflection signals near 380 GHz and 650 GHz. Figure 10 (c) and Figure 10 (d) The beam deflection capability of the metasurface under other sequences of the three-state digital encoding, “…012012012…” and “…000111222000…”, can still be observed to have beam deflection signals near 380 GHz and 650 GHz. The above beam deflection results are consistent with the results calculated by the generalized Snell's law formula.

[0065] As demonstrated by the above embodiments, by designing different digital sequences using a computer and then applying different voltage sequences to the metasurface after a digital-to-analog converter, it can generate a dual-frequency beam deflection function under the illumination of incident electromagnetic waves. Compared to other programmable terahertz metasurfaces with only one operating frequency, this invention increases the number of operating frequencies of the metasurface. The resulting device features multifunctionality, flexible design, and programmability.

[0066] It should be noted that the above description is only a preferred embodiment of the present invention in the terahertz band. The resonant unit structure of this design is not limited to a ring-shaped single-connected region, and other metasurfaces that can realize dual-frequency beam modulation should also be considered within the scope of protection of this invention. In addition, the same structure can be directly extended to the microwave, infrared, and visible light bands by scaling up the size.

[0067] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A programmable terahertz metasurface capable of dual-frequency beam modulation, characterized in that, The programmable terahertz metasurface capable of dual-frequency beam modulation comprises several metasurface units, each of which includes a quartz substrate, a resonant layer metal, a liquid crystal, and a backplate layer metal. The bottom end of the quartz substrate is provided with a resonant metal layer, the bottom end of the resonant metal layer is provided with liquid crystal, and the bottom end of the liquid crystal is provided with a backplate metal layer. The planar structure of the resonant layer metal is a butterfly-shaped single-connected region, which includes an outer boundary and an inner boundary. Both the outer and inner boundaries have butterfly-shaped geometry, and the geometry of the outer boundary is a proportionally enlarged version of the geometry of the inner boundary. The external excitation method for loading the metasurface unit is to apply an alternating voltage to the resonant layer metal, and the backplate layer metal is grounded.

2. The programmable terahertz metasurface capable of dual-frequency beam modulation according to claim 1, characterized in that, The metasurface units are arranged at equal intervals in both the horizontal and vertical directions, forming a rectangular array structure; The metasurface units are interconnected in the longitudinal direction by metal wires, and are disconnected in the transverse direction. Each column of metasurface units in the rectangular array structure is independently loaded with a different voltage.

3. The programmable terahertz metasurface capable of dual-frequency beam modulation according to claim 1, characterized in that, The thickness of the quartz substrate is 300 micrometers; The thickness of both the resonant layer metal and the backplate metal is 220 nanometers, and the material of both the resonant layer metal and the backplate metal is gold. The thickness of the liquid crystal is 10 micrometers.

4. The programmable terahertz metasurface capable of dual-frequency beam modulation according to claim 1, characterized in that, Before and after applying external electrical excitation, the reflection spectrum of the metasurface unit exhibits two resonant frequency points: a low frequency and a high frequency. Before and after applying external electrical excitation, both resonant frequency points of the reflection spectrum of the metasurface unit undergo redshift. Before and after applying external electrical excitation, the two resonant frequency points of the reflection spectrum of the metasurface unit will generate a phase difference.

5. The programmable terahertz metasurface capable of dual-frequency beam modulation according to claim 4, characterized in that, Based on the phase difference generated by the two resonant frequency points of the reflection spectrum of the metasurface unit, the metasurface unit can be digitally encoded, including 1-bit encoding and three-state encoding; The 1-bit encoding includes: When a first alternating voltage and a second alternating voltage are applied, the metasurface unit exhibits a first phase difference and a second phase difference at two resonant frequency points under electromagnetic wave incident, and the first phase difference and the second phase difference correspond to two states of bit encoding, respectively.

6. The programmable terahertz metasurface capable of dual-frequency beam modulation according to claim 5, characterized in that, The tri-state encoding includes: When the third, fourth, and fifth alternating voltages are applied, the metasurface unit exhibits a third phase difference, a fourth phase difference, and a fifth phase difference at two resonant frequency points under electromagnetic wave incident conditions, respectively, and the third, fourth, and fifth phase differences correspond to the three states of the three-state encoding.

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