A dynamically tunable terahertz spatial power splitter based on metasurface

Abstract

The application discloses a dynamic adjustable terahertz spatial power divider based on a metasurface, which comprises, from bottom to top, a metal reflection layer, a first dielectric substrate, an arrow-shaped metal microstructure array, a second dielectric substrate and a double-layer graphene grating bias structure. By adjusting the length and orientation of the arrow-shaped metal microstructure in the arrow-shaped metal microstructure array, the metasurface power divider has a phase gradient with equal phase intervals, so that the terahertz wave signal is split into a same-polarization wave in a specular reflection direction and a cross-polarization wave in an abnormal reflection direction. By applying different bias voltages to the double-layer graphene grating bias structure, the Fermi level of the graphene layer is adjusted, and the power ratio of the cross-polarization wave and the same-polarization wave is controlled, so that the intensity distribution of the terahertz wave signal in the specular reflection direction and the abnormal reflection direction is realized. Through the power divider, the single-beam incident signal is split into multiple spatial channels, and the intensity in different radiation directions is dynamically distributed.

Description

Technical Field

[0001] This application relates to the field of power divider technology, and in particular to a dynamically adjustable terahertz space power divider. Background Technology

[0002] A power divider is a device that distributes a single input signal into two or more outputs, enabling the distribution and control of the amplitude of multiple signals. In wireless communication systems, the flexible allocation of spatial signal power helps to adjust the strength of signal coverage in multiple radiation directions, thereby improving multi-directional communication efficiency and user experience.

[0003] Traditional power dividers primarily focus on planar multi-port device design, but struggle to achieve power distribution for space carriers in wireless communication links. For example, Chinese patent document CN113161708A discloses a three-way power divider, comprising a signal input terminal, three impedance transformation modules, an isolation module, a phase-shifting circuit module, and three signal output terminals. The signal input is connected to the input terminal of each impedance transformation module, and the output terminal of each impedance transformation module is connected to a corresponding signal output terminal via an isolation module. The isolation module includes a first isolation resistor, a second isolation resistor, and a third isolation resistor. The first isolation resistor is connected in parallel between the first and second signal output terminals, and the second isolation resistor...

[0004] A resistor is connected in parallel between the second signal output terminal and the third signal output terminal, and a third isolation resistor is connected in parallel between the first signal output terminal and the third signal output terminal; the phase shifting circuit module is set between the isolation module and the second signal output terminal; however, this power divider can only distribute the input signal power to multiple output ports to realize the frequency division, distribution or merging of signals, but it is difficult to realize the power distribution of space carriers in wireless communication links. Summary of the Invention

[0005] Based on this, and to address the aforementioned technical problems, a dynamically adjustable terahertz space power divider based on metasurfaces is provided, which can solve the problem that existing power dividers cannot achieve power allocation of space carriers in wireless communication links.

[0006] A dynamically tunable terahertz spatial power divider based on a metasurface includes, from bottom to top, a metal reflective layer, a first dielectric substrate, an arrow-shaped metal microstructure array, a second dielectric substrate, and a double-layer graphene grating bias structure. The double-layer graphene grating bias structure includes a double-layer graphene grating and an insulating layer disposed in the middle of the double-layer graphene grating. By adjusting the length and orientation of the arrow-shaped metal microstructures in the arrow-shaped metal microstructure array, the metasurface power divider is made to have a phase gradient with equal phase intervals, so that the terahertz wave signal is split into a co-polarized wave in the specular reflection direction and a cross-polarized wave in the anomalous reflection direction. By applying different bias voltages to the double-layer graphene grating bias structure, the Fermi level of the graphene layer is adjusted, thereby controlling the power ratio of the cross-polarized wave and the co-polarized wave to achieve intensity distribution of the terahertz wave signal in the specular reflection direction and the anomalous reflection direction.

[0007] Optionally, in the above scheme, adjusting the Fermi level of the graphene layer to regulate the power ratio of the cross-polarized wave and the co-polarized wave, so as to achieve the intensity distribution of the terahertz wave signal in the specular reflection direction and the anomalous reflection direction, includes: when the Fermi level of the graphene layer is adjusted to 0.0 eV, the intensity of the cross-polarized wave of the terahertz wave signal in the anomalous reflection direction reaches its maximum; when the Fermi level of the graphene layer is adjusted to 1.0 eV, the intensity of the co-polarized wave of the terahertz wave signal in the specular reflection direction reaches its maximum.

[0008] Optionally, in the above scheme, the metal reflective layer and the arrow-shaped metal microstructure are made of gold.

[0009] Optionally, in the above scheme, the material of the medium substrate is TOPAS polymer.

[0010] Optionally, in the above scheme, the insulating layer is made of polyvinylidene fluoride terpolymer.

[0011] This application has at least the following beneficial effects:

[0012] This application provides a dynamically tunable terahertz spatial power divider based on metasurfaces. It comprises, from bottom to top, a metal reflective layer, a dielectric substrate, an arrow-shaped metal microstructure array, another dielectric substrate, and a double-layer graphene grating bias structure. The arrow-shaped metal microstructure array exhibits an asymmetrical distribution of metal microstructures to split a single-beam incident terahertz wave signal, propagating it along both specular and anomalous reflection directions. This converts the incident wave signal into reflected signals with different polarization properties, pointing in different radiation directions. By applying different bias voltages to the double-layer graphene grating bias structure, the Fermi level of the graphene layer is adjusted, thereby regulating the intensity distribution of the terahertz wave signal along the specular and anomalous reflection directions. This enables the splitting of a single-beam incident signal into multiple spatial channels and the dynamic intensity distribution along different radiation directions, facilitating flexible signal power configuration during multi-channel synchronous communication. Attached Figure Description

[0013] Figure 1 An overall structural diagram of a dynamically tunable terahertz space power divider based on a metasurface is provided as an embodiment of this application;

[0014] Figure 2 A schematic diagram of the separation of a dynamically tunable terahertz space power divider based on a metasurface provided in one embodiment of this application;

[0015] Figure 3 This is a graph showing the variation of reflection assignments for cross-polarized waves and co-polarized waves in one embodiment of this application;

[0016] Figure 4 This is a diagram showing the cross-polarization reflection phase change of rotating metal microstructures with different orientations in one embodiment of this application.

[0017] Figure 5 This is a graph showing the metasurface work division results corresponding to different Fermi levels in one embodiment of this application;

[0018] Figure 6 This is a diagram showing the phase changes of cross-polarized wave reflection and radiation in one embodiment of this application;

[0019] Figure 7 This is a diagram showing the phase change of reflected and radiated waves in one embodiment of this application;

[0020] Figure 8 This is a diagram showing the switching of the main beam direction of reflection at different Fermi levels in one embodiment of this application;

[0021] Figure 9 This is an example diagram of dual-channel signal modulation in one embodiment of this application. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0023] In recent years, due to their superior control over electromagnetic waves, electromagnetic metasurfaces have attracted significant attention in the research and development of space electromagnetic wave manipulation technology. Consequently, space-division multiple access (SDMA) space carrier modulation devices based on the beamforming properties of metasurfaces have also experienced rapid development. It can be said that metasurfaces offer great convenience for the effective manipulation of space electromagnetic waves and hold great promise as an effective platform for the design and application of space signal power dividers.

[0024] Therefore, this application, based on metasurface beamforming control, incorporates the function of regulating the spatial power division characteristics of electromagnetic waves, which may provide potential solutions for multi-region signal equalization and adjustment, improved communication quality, and efficient signal modulation in wireless communication. This paper designs a multifunctional power divider device that integrates terahertz multi-beamforming and spatial power division characteristics based on a tunable polarization conversion metasurface. This device is used for power distribution regulation of different terahertz beam directions, aiming to achieve dynamic signal adjustment of different spatial channels. Furthermore, this metasurface can also function as a high-efficiency signal modulator for dual spatial channels. Full-wave simulation results confirm all expected functions.

[0025] In one embodiment, such as Figure 2 As shown, a dynamically tunable terahertz spatial power divider based on a metasurface is provided, comprising, from bottom to top, a metal reflective layer 1, a first dielectric substrate 2, an arrow-shaped metal microstructure array 3, a second dielectric substrate 4, and a double-layer graphene grating bias structure 5. The double-layer graphene grating bias structure 5 includes a double-layer graphene grating and an insulating layer disposed in the middle of the double-layer graphene grating. By adjusting the length and orientation of the arrow-shaped metal microstructures in the arrow-shaped metal microstructure array 3, the metasurface power divider is made to have a phase gradient with equal phase intervals, so that the terahertz wave signal is split into a co-polarized wave in the specular reflection direction and a cross-polarized wave in the anomalous reflection direction. By applying different bias voltages to the double-layer graphene grating bias structure 5, the Fermi level of the graphene layer is adjusted, thereby controlling the power ratio of the cross-polarized wave and the co-polarized wave to achieve intensity distribution of the terahertz wave signal in the specular reflection direction and the anomalous reflection direction.

[0026] Specifically, the overall structure of the designed metasurface spatial power divider is as follows: Figure 1As shown, it is composed of multiple layers of materials and structures, from bottom to top: a metal reflective layer, a first dielectric substrate, an arrow-shaped metal microstructure array, a second dielectric substrate, and a double-layer graphene grating bias structure. The bias structure consists of a double-layer graphene grating and an intermediate insulating layer, which facilitates the modulation of the electromagnetic properties of graphene using electrical bias. After applying a bias voltage, the Fermi level shift of the graphene layer can be freely controlled. Figure 1 The middle arrow is aimed at the power divider. For the incident light, the arrow exits the power divider. It is a homopolarized wave. It is a cross-polarized wave.

[0027] To more clearly demonstrate the internal composition details of the device, Figure 2 This is a schematic diagram of the separation of metasurface unit structures, with the geometric parameters of each layer labeled. ...

[0028] Table 1

[0029]

[0030] Wherein, tp1 is the thickness of the second dielectric substrate 4, tp2 is the thickness of the first dielectric substrate 2, tm is the thickness of the metal reflective layer, ts is the thickness of the insulating layer in the double-layer graphene grating bias structure 5, wg is the width of the graphene microstrip in the double-layer graphene grating bias structure 5, l1 is the length of the axial arm of the arrow in the arrow-shaped metal microstructure 3, w1 is the width of the axial arm in the arrow-shaped metal microstructure 3, w2 is the width of the oblique arm in the arrow-shaped metal microstructure 3, d is the distance from the outer edge of the oblique arm of the arrow to the edge of the dielectric substrate, and p is the geometric period of the periodic unit.

[0031] The designed metasurface device utilizes a bias voltage as an effective way to dynamically control its electromagnetic properties. By changing the applied bias voltage, the Fermi level of graphene can be easily altered, thereby changing the conductivity of the graphene layer. The metasurface structure possesses polarization conversion capabilities; by modulating the Fermi level of the graphene grating, the polarization conversion rate of the device can be effectively controlled, dynamically adjusting the reflection amplitudes of co-polarized and cross-polarized reflected waves. Figure 3 (a) in the middle gives The amplitudes of cross-polarized and co-polarized waves in the device's reflected field vary with the Fermi level of the graphene. Taking a y-polarized plane wave as an example, the amplitudes are... Figure 3 As shown in (a) and (b), within a relatively wide frequency band from 1.75 THz to 2.45 THz, the reflection amplitude of the cross-polarized wave gradually increases with the gradual rise of the graphene Fermi level. The amplitude of reflection of the same polarized wave gradually decreases. The amplitude gradually increases. Therefore, the Fermi level of graphene can be controlled by applying an external bias voltage to achieve dynamic distribution of reflection amplitude between cross-polarized waves and co-polarized waves. If the spatial azimuth angle of the reflection of one type of polarized wave is adjusted by metasurface wavefront control, so that the incident wave signal is converted into a reflected signal with different polarization properties and points to different radiation directions, then dynamic distribution of signal power in different directions can be achieved.

[0032] Taking a mid-frequency of 2.1 THz as an example, this application demonstrates how rotating the orientation of the metal microstructure can induce a 180-degree phase difference in the cross-polarized wave, thus forming a 1-bit metasurface structure. For simplicity, the unit cell shape biased to the left of the metal structure is designated as "0," and the unit cell shape biased to the right is designated as "1," as shown below. Figure 4 As shown, arranging the two unit cell types according to the coding scheme "00110011…" can construct a metasurface device with dual-beam anomalous reflection capability for cross-polarized waves. Due to the symmetry of the metasurface phase distribution, dual beams may be generated at the symmetry angle about the central axis. Figure 5 The image shows the normalized RCS variation of the metasurface at 2.1 THz when graphene is at different Fermi levels. Under certain conditions, the metasurface forms three main reflective beams, with the main beam at 0 degrees azimuth angle primarily formed by co-polarized waves. The main beam at the 0-degree azimuth angle is primarily formed by cross-polarized waves. As can be seen from the figure, with the gradual increase of the Fermi level, the reflection intensity at the 0-degree azimuth angle of the backscattering plane gradually decreases, while... However, the reflection intensity at the azimuth angle gradually increases. Therefore, by adjusting the bias voltage to control the Fermi level of graphene, the beam splitting of a single-beam incident signal into multiple spatial channels and the dynamic distribution of intensity in different radiation directions are realized, which helps to flexibly configure signal power in multi-channel synchronous communication.

[0033] The aforementioned metasurface distributes the power of the cross-polarized anomalous reflection signal evenly across two symmetrical azimuth angles, thus reducing the signal power in the symmetrical radiation direction. To achieve efficient signal modulation in the dual spatial channels, the main beam of the cross-polarized wave needs to be constrained into a single-beam anomalous reflection to form a two-path signal radiation conversion between the specular reflection channel and the anomalous reflection channel. This can generally be achieved by adding additional phase compensation or reconstructing the phase gradient on a 1-bit metasurface to form directional radiation of a single beam; here, a gradient-type metasurface with phase abrupt change characteristics is used. For the metasurface designed in this application, the arm length of the metal microstructure is changed. Furthermore, the orientation of the rotating microstructure makes it easier to obtain a sufficiently large abrupt change in the cross-polarized reflection phase. When the Fermi level of graphene is at 0.0 eV, the metasurface will primarily exhibit reflection of cross-polarized waves. For example... Figure 6 As shown in (a), with the arm length As the frequency increases, the cross-polarized reflection phase gradually decreases, and with the rotation of the microstructure orientation, the phase change can cover a 360-degree range. This section also uses 2.1 THz as an example. Figure 6 The arm length is shown in (a) and (b) respectively. The value is chosen from 3 of the 2 possible orientations, meaning that from left to right, the first microstructure is oriented to the left, and the arm length... The size is 25µm, the second microstructure faces left, and the arm length is... It is 29.5 μm in size, the third microstructure faces left, and the arm length is... The size is 36.6 μm, the fourth microstructure faces right, and the arm length is... The size is 25 μm, the fifth microstructure faces right, and the arm length is... It is 29.5 μm in size, the third microstructure is oriented to the right, and the arm length is... It is 36.6um. Figure 6 The arm length is shown in (a) and (b) respectively. The changes in the cross-polarization phase spectrum and amplitude spectrum corresponding to the three values ​​for the two orientations are shown. It is easy to see that the phase abrupt change interval of cross-polarization at the operating frequency is about 60 degrees, and each arm length has a high reflection amplitude, thus ensuring the high radiation efficiency of the cross-polarized wave. When the graphene Fermi level is at 1.0 eV, the metasurface will mainly produce reflection of the same polarized wave. Figure 7 The arm lengths are given in (a) and (b) respectively. The co-polarization phase spectrum and amplitude spectrum are observed for different values ​​and orientations. It can be found that at the operating frequency, the co-polarization reflection phase hardly changes with the arm length and also has a large reflection amplitude, ensuring the radiation efficiency of the co-polarized wave in this state.

[0034] The above three arm lengths By arranging the units corresponding to the two orientations in an increasing order (i.e., the left half of the microstructure faces left and the right half faces right, with the left and right halves arranged in an increasing order of arm length), a phase-gradient metasurface with a 60-degree phase shift interval can be constructed. According to the generalized Snell's law, the anomalous reflection angle of a normally incident electromagnetic wave can be obtained by the following formula:

[0035] (1)

[0036] in, Indicates the reflection angle. This represents the wavelength in a vacuum (related to frequency). This represents the phase gradient.

[0037] The theoretical reflection angle of the cross-polarized wave is calculated to be 28.42 degrees using formula (1). Then, by controlling the Fermi level of graphene using a bias voltage, dynamic switching of a single main beam between specular and anomalous reflection directions can be achieved. For example... Figure 8 As shown, at 2.1 THz, when the graphene Fermi level is 0.0 eV, the metasurface mainly produces anomalous reflection at a 28-degree azimuth angle, consistent with the prediction of the generalized Snell's law, and the reflection amplitude reaches 0.87, exhibiting high anomalous reflection efficiency. When the graphene Fermi level switches to 1.0 eV, the metasurface's main beam becomes specular reflection at a 0-degree azimuth angle, with a reflection amplitude reaching 0.86, also exhibiting high reflection efficiency. Therefore, by changing the bias voltage applied to the graphene grating, efficient signal modulation in both 0-degree and 28-degree spatial channels can be achieved simultaneously.

[0038] The graphene Fermi level and the bias voltage have the following approximate relationship:

[0039] (2)

[0040] Where Vg represents the magnitude of the bias voltage and is the independent variable of the formula, and EF represents the Fermi level and is the dependent variable of the formula. and These are the relative permittivity and vacuum permittivity of the insulating layer, respectively. , ts is the thickness of the insulating layer. e represents the electron charge; νf represents the Fermi velocity. ;ℏ is the reduced Planck constant, .

[0041] As shown in equation (2), when the bias voltage is 0V, the Fermi level of graphene is also 0.0eV, while the bias voltage required to tune the Fermi level to 1.0eV is about 17V. If a rectangular alternating voltage (bias voltage) with a period of T is applied to the graphene grating, signal modulation based on amplitude shift keying can be realized simultaneously in the dual spatial channels. Figure 9 The paper presents the bias loading variations and the corresponding signal modulation results. The signal modulation depths at the 28° and 0° reflection directions respectively reach [values ​​missing]. In addition, the signals on the two spatial channels have a half-cycle delay. By performing half-cycle compensation on any one of the signals, it is possible to synchronously achieve high-efficiency modulation of the carriers in the two channels, forming the same digital information transmission, and both digital information have high signal strength.

[0042] In one embodiment, adjusting the Fermi level of the graphene layer to achieve intensity distribution of the terahertz wave signal in the specular reflection direction and the anomalous reflection direction includes: when the Fermi level of the graphene layer is adjusted to 0.0 eV, the intensity of the terahertz wave signal in the anomalous reflection direction is... When the Fermi level of the graphene layer is adjusted to 1.0 eV, the intensity of the terahertz wave signal in the direction of mirror reflection is: .

[0043] In one embodiment, the metal reflective layer and the arrow-shaped metal microstructure are made of gold.

[0044] Specifically, the metal reflective layer and metal microstructure are made of gold, and the metal arrow-shaped structure is located on the diagonal of the basic unit.

[0045] In one embodiment, the substrate material is TOPAS polymer.

[0046] Specifically, the dielectric substrate material is TOPAS polymer, which has low loss and low dispersion characteristics (refractive index of about 1.53) in the terahertz band, and is an ideal substrate material commonly used in broadband terahertz devices.

[0047] In one embodiment, the insulating layer is made of polyvinylidene fluoride terpolymer.

[0048] Specifically, a polyvinylidene fluoride terpolymer is used as an insulating layer between the two graphene gratings. This material has high dielectric strength (dielectric constant of approximately 65), which can fully ensure the safety of the bias structure under applied bias voltage.

[0049] This application designs a metasurface-based spatial power divider and verifies its expected functionality through full-wave simulation. It can dynamically adjust the power distribution across different spatial channels by splitting a single-beam terahertz signal through polarization conversion rate adjustment. It can also function as an amplitude-shift keying carrier modulator, achieving simultaneous and efficient modulation of signals in two spatial channels using only one voltage source. The simulation results demonstrate the expected performance and effectiveness of the device. The proposed metasurface device shows promise for applications in wireless communication, polarization control, and other terahertz technologies.

[0050] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0051] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A dynamically tunable terahertz spatial power divider based on metasurfaces, characterized in that, The device comprises, from bottom to top, a metal reflective layer, a first dielectric substrate, an arrow-shaped metal microstructure array, a second dielectric substrate, and a double-layer graphene grating bias structure. The double-layer graphene grating bias structure includes a double-layer graphene grating and an insulating layer disposed in the middle of the double-layer graphene grating. By adjusting the length of the oblique arms of the arrow-shaped metal microstructures in the arrow-shaped metal microstructure array and the orientation of the arrow-shaped metal microstructures, the metasurface power divider is made to have a phase gradient with equal phase intervals, so that the terahertz wave signal is split into a co-polarized wave in the specular reflection direction and a cross-polarized wave in the anomalous reflection direction. By applying different bias voltages to the double-layer graphene grating bias structure, the Fermi level of the graphene layer is adjusted, thereby controlling the power ratio of the cross-polarized wave and the co-polarized wave to achieve intensity distribution of the terahertz wave signal in the specular reflection direction and the anomalous reflection direction.

2. The dynamically tunable terahertz spatial power divider based on metasurfaces according to claim 1, characterized in that, The adjustment of the Fermi level of the graphene layer, thereby controlling the power ratio of the cross-polarized wave and the co-polarized wave, to achieve the intensity distribution of the terahertz wave signal in the specular reflection direction and the anomalous reflection direction, includes: when the Fermi level of the graphene layer is adjusted to 0.0 eV, the intensity of the cross-polarized wave of the terahertz wave signal in the anomalous reflection direction reaches its maximum; when the Fermi level of the graphene layer is adjusted to 1.0 eV, the intensity of the co-polarized wave of the terahertz wave signal in the specular reflection direction reaches its maximum.

3. The dynamically tunable terahertz spatial power divider based on metasurfaces according to claim 1, characterized in that, The metal reflective layer and the arrow-shaped metal microstructure are made of gold.

4. The dynamically tunable terahertz spatial power divider based on metasurfaces according to claim 1, characterized in that, The first and second dielectric substrates are made of TOPAS polymer.

5. The dynamically tunable terahertz spatial power divider based on metasurfaces according to claim 1, characterized in that, The insulating layer is made of polyvinylidene fluoride terpolymer.

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