Programmable terahertz metasurface capable of realizing dual-frequency-point beam regulation and application thereof

Abstract

The invention discloses a programmable terahertz metasurface capable of achieving dual-frequency-point beam regulation and application thereof, and relates to the technical field of novel artificial electromagnetic materials, the metasurface comprises a plurality of metasurface units, and each metasurface unit comprises a quartz substrate, resonance layer metal, liquid crystal and backboard layer metal; the metasurface units are arranged and distributed at equal intervals in the transverse direction and the longitudinal direction to form a rectangular array structure, the metasurface units are mutually connected through metal wires in the longitudinal direction, and the metasurface units are mutually disconnected in the transverse direction; the plane structure of the resonance layer metal is a butterfly-shaped single-connection area, the butterfly-shaped single-connection area comprises an outer boundary and an inner boundary, and the geometrical shape of the outer boundary is equal-proportion amplification of the geometrical shape of the inner boundary. According to the invention, various modulation functions can be realized at two terahertz frequency points by adding different voltage sequences, and the specific demonstration is that the metasurface realizes terahertz wave beam deflection functions at different angles after loading 1-bit and three-state digital codes.

Description

Technical Field

[0001] The present invention relates to the technical field of novel artificial electromagnetic materials, and in particular to a programmable terahertz metasurface capable of realizing dual-frequency beam control. Background Art

[0002] With the rapid development of modern terahertz beam steering technology, traditional phased array and scanning antennas are difficult to solve the problems of high manufacturing precision, low integration and complex systems. Fine terahertz beam steering technology is urgently needed to realize high-performance and high-flexibility terahertz beam steering systems. Fine terahertz beam steering technology has great application potential in wireless communications, biosensing and imaging.

[0003] The introduction of reconfigurable metasurfaces has brought breakthrough progress in fine terahertz beam control technology. By introducing tunable materials such as liquid crystal, vanadium dioxide or semiconductors into the resonant structure, and under the stimulation 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 excitation can be loaded on the metasurface through a programmable gate array via a computer, further improving the system's integration and operability. The development of this technology not only provides new solutions for terahertz beam control, but also lays the foundation for innovative applications of future communication and sensing technologies.

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

[0005] Currently, no effective solution has been proposed for the problems in the related technologies. Summary of the invention

[0006] In response to the problems in the related art, the present invention proposes a programmable terahertz metasurface that can realize dual-frequency beam control and its application. Through the programmable terahertz metasurface that can realize dual-frequency beam control, modulation functions such as multi-angle beam deflection can be realized at two terahertz frequencies by applying different voltage sequences (encodings), thereby solving the problem in the prior art that active programmable terahertz metasurface devices only have a single operating frequency and limit the utilization of the terahertz spectrum.

[0007] To this end, 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 realizing dual-frequency beam steering is provided. The programmable terahertz metasurface capable of realizing dual-frequency beam steering includes a plurality of metasurface units, and the metasurface units include a quartz substrate, a resonance layer metal, a liquid crystal, and a backplane layer metal; wherein a resonance layer metal is disposed at the bottom end of the quartz substrate, a liquid crystal is disposed at the bottom end of the resonance layer metal, and a backplane layer metal is disposed at the bottom end of the liquid crystal.

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

[0010] Furthermore, the thickness of the quartz substrate is 300 microns; the thickness of the resonance layer metal and the back plate layer metal are both 220 nanometers, and the materials of the resonance layer metal and the back plate layer metal are both gold; the thickness of the liquid crystal is 10 microns.

[0011] Furthermore, the planar structure of the resonant layer metal is a butterfly-shaped simply connected region, which includes an outer boundary and an inner boundary; the geometric shapes of the outer boundary and the inner boundary are both butterfly-shaped, and the geometric shape of the outer boundary is a proportional enlargement of the geometric shape of the inner boundary.

[0012] Furthermore, the external excitation method of the metasurface unit is to load an alternating voltage to the resonant layer metal, and the backplane layer metal is grounded; before and after the external electrical excitation is loaded, the reflection spectrum of the metasurface unit shows two resonant frequency points of low frequency and high frequency; before and after the external electrical excitation is loaded, the two resonant frequency points of the reflection spectrum of the metasurface unit are red-shifted; before and after the external electrical excitation is loaded, the two resonant frequency points of the reflection spectrum of the metasurface unit will have 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] Among them, 1 bit encoding includes:

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

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

[0017] When the third alternating voltage, the fourth alternating voltage and the fifth alternating voltage are loaded, the metasurface unit presents a third phase difference, a fourth phase difference and a fifth phase difference at two resonant frequency points under the incidence of electromagnetic waves, and the third phase difference, the fourth phase difference and the fifth phase difference correspond to the three states of the three-state coding respectively.

[0018] According to another aspect of the present invention, a programmable terahertz metasurface application capable of realizing dual-frequency beam steering is provided, which is used to input different digital code sequences through computer programming, convert the digital signal sequences into voltage sequences via digital-to-analog converters and load them into the programmable terahertz metasurface capable of realizing dual-frequency beam steering, differentially modulate the electromagnetic wave reflection phase through different metasurface units, and realize beam deflection of different angles at dual frequencies.

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

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

[0021] (2) Compared with electromagnetic metasurfaces with only a single operating frequency, the present invention opens up new possibilities for terahertz beam control. By designing different digital sequences by computer and assigning different voltage sequences to the metasurface after a digital-to-analog converter, it can generate a dual-frequency beam deflection function under the irradiation of incident electromagnetic waves. Compared with other programmable terahertz metasurfaces with only one operating frequency, the present invention increases the number of operating frequencies of the metasurface, and the device realized is multifunctional, flexible in design, and programmable. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. 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 creative work.

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

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

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

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

[0027] Figure 5 It is a schematic diagram of the reflection spectrum of the metasurface in two states simulated by electromagnetic simulation and the phase difference between the two states;

[0028] Figure 6 It is a schematic diagram of the changes in reflection amplitude and phase difference of the metasurface at two operating frequencies with the increase of external voltage excitation;

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

[0030] Figure 8 It is a schematic diagram of the overall reflection spectrum of the metasurface and the beam deflection test at two operating frequencies when a 1-bit coding sequence is loaded;

[0031] Fig. 9 It is a schematic diagram of the overall reflection spectrum of the metasurface and the beam deflection test at two operating frequencies when a three-state coding sequence is loaded;

[0032] Fig.10 It is a schematic diagram of the overall reflection spectrum of the metasurface when loaded with a 1-bit coding sequence and a three-state coding sequence.

[0033] In the figure:

[0034] 1. Quartz substrate; 2. Resonance layer metal; 3. Liquid crystal; 4. Backplane layer metal. DETAILED DESCRIPTION

[0035] To further illustrate each embodiment, the present invention provides drawings, which are part of the disclosure of the present invention and 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 contents, ordinary technicians in the field should be able to understand other possible implementations and advantages of the present invention. The components in the figures are not drawn to scale, and similar component symbols are generally used to represent similar components.

[0036] According to an embodiment of the present invention, a programmable terahertz metasurface capable of realizing dual-frequency beam steering and applications thereof are provided.

[0037] The present invention is further described with reference to the accompanying drawings and specific embodiments. Figure 1As shown, according to one embodiment of the present invention, a programmable terahertz metasurface capable of realizing dual-frequency beam control is provided, and the programmable terahertz metasurface capable of realizing dual-frequency beam control includes a plurality of metasurface units, and the metasurface units include a quartz substrate 1, a resonance layer metal 2, a liquid crystal 3 and a backplane layer metal 4; wherein, a resonance layer metal 2 is arranged at the bottom end of the quartz substrate 1, a liquid crystal 3 is arranged at the bottom end of the resonance layer metal 2, and a backplane layer metal 4 is arranged at the bottom end of the liquid crystal 3.

[0038] Specifically, Figure 2 , Figure 3 and Figure 4 As shown, they are respectively a schematic diagram, a top view, and a front view of a metasurface unit in a programmable metasurface capable of realizing dual-frequency beam steering of the present invention, wherein the top view is the situation after the quartz substrate 1 is removed. The metasurface unit of the present invention comprises: a quartz substrate 1, a resonance layer metal 2, a liquid crystal 3, and a backplane layer metal 4; wherein the resonance layer metal 2 and the backplane layer metal 4 are respectively on both sides of the liquid crystal 3, and the quartz substrate 1 is closely attached to the other side of the resonance layer metal 2; the metasurface array is arranged in the XY plane, the origin is located at the exact center of the metasurface unit, and the electromagnetic field is vertically incident on the metasurface along the Z direction.

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

[0040] In one embodiment, the thickness of the quartz substrate 1 is 300 microns; the thickness of the resonance layer metal 2 and the back plate layer metal 4 are both 220 nanometers, and the materials of the resonance layer metal 2 and the back plate layer metal 4 are both gold; the thickness of the liquid crystal 3 is 10 microns.

[0041] In one embodiment, the planar structure of the resonant layer metal 2 is a butterfly-shaped simply connected region, which includes an outer boundary and an inner boundary; the geometric shapes of the outer boundary and the inner boundary are both butterfly-shaped, and the geometric shape of the outer boundary is a proportional enlargement of the geometric shape of the inner boundary.

[0042] Specifically, the planar structure of the resonance layer metal 2 is a ring-shaped simply connected area with a hollow center. The outer boundary geometry of the area is an equal-proportion enlargement of the inner boundary geometry, both of which are butterfly-shaped. The geometric structure of the inner boundary of the area is generated by first smoothly connecting multiple discrete geometric points according to the spline interpolation algorithm, and then generating a closed pattern through horizontal and vertical mirroring.

[0043] Specifically, the actual processing process of the terahertz metasurface that can realize dual-frequency beam control is to use ultraviolet lithography technology to generate patterns of the background gold layer and the resonance metal layer on the bottom and top of the double-sided polished quartz substrate respectively, and then use magnetron sputtering technology to deposit a 300-nanometer thick gold film on the two substrates, and formally generate the backplane layer metal 4 and the resonance layer metal 2 through a lift-off process.

[0044] Specifically, Figure 7 As shown, the pattern of the resonant layer is displayed with good edge definition. Subsequently, the reactive ion etching technology is used to inject oxygen to make the device surface hydrophilic, and further spin-coating a light guide agent and ultraviolet exposure are performed to complete the initial orientation of the liquid crystal 3. Next, the device is attached to a circuit board, a 10-micron gap is made using silicon balls, and liquid crystal is poured in. After wire bonding, the metasurface device is completed.

[0045] In one embodiment, the external excitation method for loading the metasurface unit is to load an alternating voltage to the resonance layer metal 2, and the backplane layer metal 4 is grounded; before and after loading the external electrical excitation, the reflection spectrum of the metasurface unit presents two resonance frequency points of low frequency and high frequency; before and after loading the external electrical excitation, the two resonance frequency points of the reflection spectrum of the metasurface unit are both red-shifted; before and after loading the external electrical excitation, the two resonance frequency points of the reflection spectrum of the metasurface unit will have a phase difference.

[0046] Specifically, the external excitation method of the metasurface unit is to load an alternating voltage to the resonance layer metal 2, and the backplane layer metal 4 is grounded. After the vertical incident electromagnetic wave, the reflection spectrum of the metasurface unit simultaneously presents a low-frequency resonance of about 400 GHz and a high-frequency resonance of about 700 GHz at the resonance frequency point when no external voltage excitation is loaded; when the metasurface unit is externally electrically excited, both resonances are red-shifted, resulting in resonance frequency shifts of about 30 GHz and about 50 GHz, respectively. The causes of the two resonances are not consistent. The low-frequency resonance is directly generated by the dipole oscillation excited by the incident electromagnetic wave, while the high-frequency resonance is generated by the joint action of multiple high-order resonator oscillations excited by the same electromagnetic wave. Before and after the external electrical excitation is loaded, the metasurface unit can produce a phase difference of more than 270 degrees at both frequency points.

[0047] Specifically, Figure 5 As shown, the reflection spectra of the metasurface in the "off" state without voltage applied and the "on" state after voltage applied are simulated by electromagnetic simulation, as well as the phase difference between the two states; the two resonant frequencies of 406.4 GHz and 687.8 GHz in the "off" state are red-shifted by 38.5 GHz and 49.0 GHz respectively after the metasurface enters the "on" state. This large red-shift causes the metasurface to produce a phase difference change of 266.61 degrees and 271.06 degrees at working frequency 1 (388.4 GHz) and working frequency 2 (665.4 GHz), respectively.

[0048] Specifically, Figure 6 As shown, with the increase of external voltage excitation, the dielectric constant of the liquid crystal directly transitions continuously from 2.465 to 3.5. During the transition process, 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 is a continuous transition from 0 to nearly 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 three-state encoding;

[0050] Among them, 1 bit encoding includes:

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

[0052] Three-state encoding includes:

[0053] When the third alternating voltage, the fourth alternating voltage and the fifth alternating voltage are loaded (in the present embodiment, the third alternating voltage is consistent with the first alternating voltage, and the fifth alternating voltage is consistent with the second alternating voltage), the metasurface unit presents a third phase difference, a fourth phase difference and a fifth phase difference at two resonant frequency points under the incidence of electromagnetic waves, respectively, and the third phase difference, the fourth phase difference and the fifth phase difference correspond to the three states of the three-state coding, respectively.

[0054] Specifically, the fixed connection between the voltage sequence loaded on the metasurface and the digital code controlled by the computer is: when the external voltage of 0V and 15V is loaded on the front and back, the metasurface unit can present a reflection phase difference of 0 and 180 degrees at two frequency points under the incidence of electromagnetic waves, corresponding to the 1-bit digital code 0, 1; when the external voltage of 0V, 11V and 15V is loaded on the front and back, the metasurface unit can present a reflection phase difference of 0, 120 and 240 degrees at the other two frequency points under the incidence of electromagnetic waves, corresponding to the three-state code 0, 1, 2. The total number of metasurface units actually processed is 112*112, and every 2 columns are combined into 1 column for control, so there are 56 columns for independent control.

[0055] Specifically, the geometric parameters of the programmable terahertz metasurface for dual-frequency beam steering 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 represents the discrete geometric control point parameters for generating the resonant layer metal plane structure. Specifically, in the first quadrant of the polar coordinate system, ri (i=1,2,…,15) takes values ​​of 0 and 1, representing the origin and the farthest distance limited by the period of the metasurface unit, respectively. The difference between the angles of adjacent points is 7.5 degrees. These 15 parameters can be smoothly connected by the spline interpolation algorithm, and then the external structure of the resonant layer can be generated by the mirror operation of the X-axis and Y-axis. The internal holes are similar to the external holes, and the parameter s is used as the geometric scaling ratio of the internal and external structures.

[0056] Table 1. Geometric parameters of metasurface units

[0057]

[0058]

[0059] According to another embodiment of the present invention, a programmable terahertz metasurface application that can realize dual-frequency beam control is also provided, which is used to load various voltage sequences using a digital-to-analog converter according to the digital coding form, differentially modulate the electromagnetic wave reflection phase through different metasurface units, and realize beam deflection, focusing and holographic imaging applications at different angles at dual frequencies.

[0060] Specifically, Figure 8 (a) and Figure 8 (b) shows the overall reflection spectrum of the actually processed metasurface in the observed frequency band (250 GHz to 750 GHz) within the emission angle range of 15 to 60 degrees under the loading of a 1-bit digital coding sequence \0011\, as well as the beam deflection test at working frequency 1 and working frequency 2.

[0061] Specifically, in order to demonstrate the function of the programmable terahertz metasurface that can realize dual-frequency beam steering, in the first example, we input a digital code sequence of “…001100110011…” into the computer and load the voltage sequence on the metasurface through a digital-to-analog converter. Figure 8 (a) shows the overall reflection spectrum of the metasurface in the observed frequency band (250 GHz to 750 GHz) within the emission angle range of 15 to 60 degrees; Figure 8 In (b), beam deflection signals are observed at both operating frequency 1 (384 GHz) and operating frequency 2 (648 GHz), with reflection amplitudes of 0.22 and 0.18, respectively, and beam deflection angles of 36 and 25 degrees, respectively. The calculation result is consistent with the result calculated by the generalized Snell's law formula θ = arcsin (λ / Γ), where λ represents the free space wavelength and Γ represents the length of a gradient cycle.

[0062] Specifically, Fig. 9 (a) and Fig. 9(b) shows the overall reflection spectrum of the actually processed metasurface in the observed frequency band (250 GHz to 750 GHz) within the emission angle range of 15 to 60 degrees under the loading of the three-state digital coding sequence \001122\, as well as the beam deflection test at working frequency 1 and working frequency 2.

[0063] Specifically, in the second example, we use a digital code sequence of "…012012012…" input into a computer to load a voltage sequence on the metasurface via a digital-to-analog converter. Fig. 9 (a) shows the overall reflection spectrum of the metasurface; Fig. 9 In (b), beam deflection signals are observed at both operating frequency 1 (386 GHz) and operating frequency 2 (666 GHz), the reflection amplitude of the signal is slightly less than 0.15, and the beam deflection angles are 26 degrees and 20 degrees, respectively. The calculation results still conform to the generalized Snell's law.

[0064] Specifically, Fig.10 (a) and Fig.10 (b) shows the overall reflection spectra of the actually processed metasurface in the observed frequency band (250 GHz to 750 GHz) within the emission angle range of 15 to 80 degrees when loading a 1-bit digital code sequence \01\ and loading a 1-bit digital code sequence \000111\, respectively; Fig.10 (c) and Fig.10 (d) shows the overall reflection spectra of the actually processed metasurface in the observed frequency band (250 GHz to 750 GHz) within the emission angle range of 15 to 80 degrees when loaded with the three-state digital coding sequence \012\ and loaded with the three-state digital coding sequence \001122\, respectively.

[0065] Specifically, in the third example, we continue to expand and demonstrate more of the programmable functions of the actual processed metasurface. Fig.10 (a) and Fig.10 (d) The beam deflection capability of the metasurface under other 1-bit digital coding sequences “…0101010101…” and “…000111000111…” is shown, and beam deflection signals can be observed near 380 GHz and 650 GHz. Fig.10 (c) and Fig.10 (d) shows the beam deflection capability of the metasurface under other sequences of three-state digital coding “…012012012…” and “…000111222000…”, and beam deflection signals around 380 GHz and 650 GHz can still be observed. The above beam deflection results are consistent with the results calculated by the generalized Snell's law formula.

[0066] Through the above embodiments, it can be seen that by designing different digital sequences by computer and giving different voltage sequences to the metasurface after the digital-to-analog converter, it can generate the function of dual-frequency beam deflection under the irradiation of incident electromagnetic waves. Compared with other programmable terahertz metasurfaces with only one working frequency, the present invention increases the number of working frequencies of the metasurface. The realized device has the characteristics of multi-function, flexible design, and programmability.

[0067] It should be noted that the above is only a preferred embodiment of the present invention in the terahertz band. The resonant unit structure of the present design is not limited to the annular single-connected area. Other metasurfaces that can realize dual-frequency beam control functions should also be considered as the protection scope of the present invention. In addition, the same structure can be directly extended to microwave, infrared and visible light bands through size scaling.

[0068] 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 principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A programmable terahertz metasurface capable of dual-frequency beam control, characterized in that: The programmable terahertz metasurface capable of realizing dual-frequency beam control includes a plurality of metasurface units, wherein the metasurface units include a quartz substrate, a resonance layer metal, a liquid crystal, and a backplane layer metal; Wherein, a resonance layer metal is arranged at the bottom of the quartz substrate, a liquid crystal is arranged at the bottom of the resonance layer metal, and a backplane layer metal is arranged at the bottom of the liquid crystal.

2. The programmable terahertz metasurface capable of realizing dual-frequency beam control according to claim 1, characterized in that: The metasurface units are arranged and distributed at equal intervals in the horizontal and vertical directions to form a rectangular array structure; The metasurface units are connected to each other in the longitudinal direction through metal wires, and are disconnected from each other in the transverse direction. Each column of metasurface units in the rectangular array structure is independently loaded with different voltages.

3. The programmable terahertz metasurface capable of realizing dual-frequency beam control according to claim 1, characterized in that: The thickness of the quartz substrate is 300 microns; The thickness of the resonance layer metal and the back plate layer metal are both 220 nanometers, and the materials of the resonance layer metal and the back plate layer metal are both gold; The thickness of the liquid crystal is 10 micrometers.

4. The programmable terahertz metasurface capable of realizing dual-frequency beam control according to claim 1, characterized in that: The plane structure of the resonant layer metal is a butterfly-shaped simply connected region, and the butterfly-shaped simply connected region includes an outer boundary and an inner boundary; The geometric shapes of the outer boundary and the inner boundary are both butterfly shapes, and the geometric shape of the outer boundary is an equal-proportion enlargement of the geometric shape of the inner boundary.

5. The programmable terahertz metasurface capable of realizing dual-frequency beam control according to claim 1, characterized in that: The external excitation method of the metasurface unit is to load an alternating voltage to the resonance layer metal, and the back plate layer metal is grounded; Before and after external electrical excitation, the reflection spectrum of the metasurface unit exhibits two resonant frequency points, low frequency and high frequency; Before and after external electrical excitation is applied, both resonance frequency points of the reflection spectrum of the metasurface unit are red-shifted; Before and after external electrical excitation is applied, a phase difference will occur between the two resonant frequency points of the reflection spectrum of the metasurface unit.

6. The programmable terahertz metasurface capable of realizing dual-frequency beam control according to claim 5, characterized in that: 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 three-state encoding; The 1-bit code includes: When the first alternating voltage and the second alternating voltage are loaded, the metasurface unit presents a first phase difference and a second phase difference at two resonant frequency points under the incidence of electromagnetic waves, and the first phase difference and the second phase difference correspond to two states of bit encoding respectively.

7. The programmable terahertz metasurface capable of realizing dual-frequency beam control according to claim 6, characterized in that: The three-state encoding includes: When the third alternating voltage, the fourth alternating voltage and the fifth alternating voltage are loaded, the metasurface unit presents a third phase difference, a fourth phase difference and a fifth phase difference at two resonant frequency points under the incidence of electromagnetic waves, and the third phase difference, the fourth phase difference and the fifth phase difference correspond to the three states of the three-state coding respectively.

8. Application of a programmable terahertz metasurface capable of dual-frequency beam steering. The terahertz metasurface capable of dual-frequency beam steering according to any one of claims 1 to 7 is used to input different digital code sequences using 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 steering, differentially modulate the electromagnetic wave reflection phase through different metasurface units, and realize beam deflection of different angles at dual frequencies.

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