Terahertz electrically controlled diversity switched dual-band reconfigurable intelligent surface

Abstract

The application discloses a terahertz electrically controlled polarization diversity dual-band reconfigurable intelligent surface, which comprises a metal bottom plate, a dielectric substrate and a phase shift structure layer arranged layer by layer from bottom to top; the phase shift structure layer comprises phase shift units arranged in an M*N orthogonal array mode, each column of the phase shift units has an anode lead-out wire and a cathode lead-out wire; each phase shift unit comprises three dipoles, and the dipole is in an I-shaped structure and is formed by two T-shaped branches arranged oppositely at vertices. The application works through electric control, thereby realizing dynamic broadband regulation and control of the phase. Without other relatively complex excitation modes such as optical excitation and temperature excitation, the device has great advantages in miniaturization, practicality and production.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of metamaterials and electromagnetic functional devices, and particularly relates to a terahertz electrically controlled split-switching dual-band reconfigurable intelligent surface. BACKGROUND

[0002] Terahertz (THz) wave is a new type of electromagnetic wave spectrum to be developed, which usually refers to electromagnetic waves with a frequency of 0.1 THz to 10 THz. This frequency range is between millimeter wave and infrared, light, and has many unique electromagnetic properties, so it has extremely important potential value in the fields of physics, chemistry, electronic information, imaging, life science, material science, astronomy, atmospheric and environmental monitoring, national security and anti-terrorism, communication and radar, etc.

[0003] Metasurface is one of the research hotspots in the field of physics and information. However, once the traditional static metasurface is prepared, its function is fixed and cannot be real-time regulated according to different environmental requirements to achieve different functions. From the artificial microstructure metasurface in the 1990s to the concept of coded metasurface in 2010, and then to the information coded metasurface proposed by Academician Cui Tiejun in 2014, the form of metasurface has developed from passive to active, such as intelligent and reconfigurable. Reconfigurable intelligent surface (RIS) is the evolution of Massive MIMO. It only reflects or refracts the incoming signal without the need for radio frequency links, avoiding the problem of hardware complexity and power consumption, and further improving the size of multiple antennas to obtain higher beamforming gain. So far, a large number of electrically controlled reconfigurable metasurfaces based on diodes and varactor tubes have appeared, and the coding form has gradually expanded from single phase coding to amplitude-phase joint coding and polarization coding. The dual-frequency RIS assisted MIMO architecture can be more scalable in terms of the number of transmit antennas, and can reduce signal crosstalk and increase system capacity when used in communication systems. Most of the dual-frequency RISs researched at home and abroad work in the microwave and millimeter wave frequency bands, and are generally designed as high-low frequency structure up-down layering and high-low frequency structure same layer. For the dual-frequency RIS in the terahertz band, it is difficult to realize multi-layer structure due to process limitations, and the bandwidth and efficiency of single-layer structure are limited. Compared with the literature, Zhang, N., et al. "Programmable Coding Metasurface for Dual-Band Independent Real-Time Beam Control." IEEE Journal on Emerging and Selected Topics in Circuits and Systems PP. 99 (2020): 1-1, the implementation method of the dual-frequency structure is to stack two groups of resonant structures with different frequencies and different sizes on a structure to form a double-layer structure. The single-layer dual-frequency structure is to arrange the high-frequency structure and the low-frequency structure left and right or nested. As long as the isolation of the two frequency bands is sufficient to match the impedance, there will be two frequency band resonance states on a single unit structure. The above structures mostly work in the millimeter wave band and are generally based on ferrite material, positive-intrinsic-negative diode, field effect transistor, etc. The ferrite material has large volume, high cost and is not easy to integrate. The problems of large loss of semiconductor switches, large crosstalk between high-frequency and low-frequency structures, and poor linearity hinder the application of dual-frequency RIS in the terahertz band.

[0004] The present application aims at the defect of single frequency band control of the previous HEMT transistor-super surface phase modulation structure, and proposes a phase modulation of double frequency bands realized by polarization diversity of a composite array of HEMT transistor-super surface microstructure, since the arrangement mode of the HEMT transistor corresponds to terahertz waves of different polarization directions, a composite left-right type structure can be designed according to the arrangement mode, which can exhibit two frequency bands of good isolation in different polarization directions within a single unit, and so far there is no polarization diversity terahertz RIS. Polarization multiplexing is the use of multiple polarizations in a resonant frequency band. Unlike polarization multiplexing, polarization diversity sets the direction of the HEMT on the unit structure to control the phase of the terahertz wave in the X polarization direction at a low frequency band and control the phase of the terahertz wave in the Y polarization direction at a high frequency band, thereby achieving diversity control of the two polarization directions. In the terahertz frequency band, it is difficult to realize punching and multi-layer structure processing due to the limitations of current processing technology. The advantage of this polarization multiplexing structure is to realize feed line multiplexing, with simpler wiring and simpler overall process. From the perspective of simulation results, the high and low frequency isolation is large, and the bandwidth of the double frequency is realized by cross polarization, compared with the previous frequency multiplexing structure of electrically controlled diodes, the use of HEMT transistor to control the frequency band is higher, the number of encoding states is more, and the number of channels is more, compared with the previous static frequency multiplexing structure without external power supply, the control is more flexible. The working mode of the double frequency RIS is quasi-light, and within the 180° frequency band range of phase shift, 1bit column control coding beam scanning and beam shaping can be further realized, and the electronic gas characteristics and resonance mode of the composite super surface microstructure array are controlled by external electrical control means, and the terahertz wave is phase encoded and controlled. The technology is one of the most advanced researches in the world at present, which provides a new way to realize advanced scanning technology. SUMMARY

[0005] The technical problem to be solved by the present application is to provide a phase shift array with adjustable double frequency bands, which is simple in structure, easy to process and low in loss.

[0006] In order to achieve the above technical purpose, the technical scheme adopted by the present application is:

[0007] The terahertz electrically controlled polarization diversity double frequency band reconfigurable intelligent surface comprises a metal bottom plate, a dielectric substrate and a phase shift structure layer arranged layer by layer from bottom to top.

[0008] The phase shift structure layer comprises phase shift units arranged in an M*N orthogonal array mode, and each column of phase shift units has an anode lead-out wire and a cathode lead-out wire.

[0009] Each phase shift unit comprises three dipoles, and the dipole is a I-shaped structure composed of two T-shaped branches arranged opposite at the vertex.

[0010] The T branch is composed of a transverse resonant piece and a longitudinal resonant piece, the transverse resonant pieces of the two T branches in the same dipole are connected by a third resonant piece to form an open resonant ring, and the two vertices are open;

[0011] The T branch is symmetrical along the middle line of the longitudinal resonant piece, and a metal strip is arranged at the vertex of the T branch, and the long side of the metal strip is perpendicular to the symmetry axis of the T branch; the vertices of the two T branches of the same dipole are provided with an ohmic patch, and a doped heterojunction line is arranged on the ohmic patch, and the doped heterojunction line is parallel to and equidistant from the long sides of the two rectangular metal strips;

[0012] Among the three dipoles, the symmetry axes of two dipoles are arranged along the row line direction, which are called A-type dipoles; the symmetry axis of the other dipole is arranged along the column line direction, which is called B-type dipole;

[0013] The A-type dipole is located on one side of the anode lead-out line, the B-type dipole is located on the other side of the anode lead-out line, the doped heterojunction line is connected to the anode connection point of the column through the anode lead-out line, and the open resonant ring is led out to the cathode connection point through the cathode lead-out line.

[0014] Further, the metal of the metal base plate includes one or more of aluminum, silver, and gold.

[0015] Further, the material of the dielectric substrate includes one or more of sapphire, high-resistance silicon, InP, GaAs, and silicon carbide.

[0016] Further, M and N are both integers greater than 2.

[0017] Further, in the same phase shift unit, the opening directions of the two B-type dipoles are opposite, both facing away from each other.

[0018] Further, each column of phase shift units has one anode lead-out line and two cathode lead-out lines, the two cathode lead-out lines are arranged on both sides of the anode lead-out line, and the third resonant piece of the A-type dipole partially overlaps the cathode lead-out line.

[0019] Further, the metal strip is rectangular in shape.

[0020] Further, the material of the ohmic patch includes one or more of Ti, Al, Ni, and Au.

[0021] Further, the material of the doped heterojunction line includes one or more of AlGaN, GaN, InGaN, GaN, AlGaAs, and GaAs.

[0022] Further, the size of the A-type dipole is larger than that of the B-type dipole.

[0023] Supplementary Note: The A-type dipoles and the B-type dipoles have a length of about 2:1 and a width of 4:3.

[0024] The beneficial effects of the present application are:

[0025] (1) The transistor of the present application has a fast modulation function, so that it can be used as the core dynamic functional material of the present application, and the high-speed phase shift characteristic can be realized.

[0026] (2) In the present application, a two-dimensional planar artificial microstructure is adopted, a large two-small I-shaped dipole structure is used through polarization diversity, and a single-layer array is made to realize phase regulation of two frequency bands of terahertz waves in different polarization directions. Compared with ordinary artificial microstructures, the structure has the characteristics of frequency band control, and the structure is simple and can be realized through microfabrication means, and the process is mature and easy to manufacture.

[0027] (3) The present application works through electrical control, thereby realizing dynamic broadband regulation of phase. Without additional optical excitation, temperature excitation and other more complex excitation modes, the device has great advantages in miniaturization, practicality and production.

[0028] (4) The present application realizes dipole resonance and LC resonance mode through the rapid change of the two-dimensional electron gas concentration of HEMT. When the unit is in the disconnected or connected state, it has two resonances in two frequency bands in different polarization directions. Compared with the traditional phase delay line structure, the array is sensitive to the change of the two-dimensional electron gas concentration of HEMT, and has a low on-off ratio working characteristic. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 It is a structural schematic diagram of a reconfigurable intelligent surface;

[0030] Figure 2 It is a phase shift unit structure schematic diagram, wherein (a) is a side view schematic diagram, and (b) is a top view schematic diagram;

[0031] Figure 3 It is a curve diagram of amplitude and phase shift of the unit structure in two polarization directions;

[0032] Figure 4 It is a current and electric field diagram of the unit structure in the low frequency band in the Y polarization direction under the ideal on-off state;

[0033] Figure 5 It is a current and electric field diagram of the unit structure in the high frequency band in the X polarization direction under the ideal on-off state;

[0034] Figure 6 It is a beam scanning schematic diagram of a reconfigurable intelligent surface. DETAILED DESCRIPTION

[0035] This invention combines artificial microstructures with transistors to form a terahertz electrically controlled polarization diversity dual-band reconfigurable smart surface phase-shift array. A composite array reflector capable of polarization diversity is formed through a two-dimensional planar arrangement. By controlling the on / off state of the transistors to change the resonant mode, phase control of the terahertz wave is achieved in the low-frequency band of the Y-polarization direction and the high-frequency band of the X-polarization direction. Polarization diversity doubles the coding quantity, number of states, and number of channels of this structure compared to ordinary structures. It operates in quasi-optical mode, and further enables 1-bit column-controlled coding beam scanning and beamforming within the 180° phase-shifted frequency band.

[0036] This invention provides an artificial microstructure reflective array that has a frequency response to terahertz electromagnetic waves in two specific frequency bands. Then, the array structure is combined with transistors using microelectronic fabrication technology, and the switching on and off of the transistors is controlled by an external voltage. Finally, the phase of the terahertz wave is controlled by changing the resonant mode of the artificial microstructure through electronic control.

[0037] See Figure 1 , Figure 2 The terahertz electrically controlled diversity switching dual-band reconfigurable smart surface of the present invention includes: a metal substrate, a dielectric substrate on the metal substrate, and a phase-shifting array (phase-shifting structure layer) on the dielectric substrate, wherein the dielectric substrate is a semiconductor material; the phase-shifting structure layer is formed on the upper surface of the substrate by means of a metal coating; a vertical cathode lead (negative electrode feed line) is provided for each column of antenna elements, and all cathode leads in the array are connected to the same external negative electrode; for each phase-shifting unit, the cathode lead extends outward from an I-shaped dipole structure, and the structure is open. At the opening, two rectangular metal strips form two opposing "T"-shaped stubs. The top of each "T"-shaped stub rests on an ohmic patch mounted on a dielectric substrate. Doped heterostructure lines are placed on each ohmic patch, forming a dipole resonant structure. A vertical anode lead (positive feed line) is provided for each column of antenna elements, located on the right side of the element. The anode lead line connects to the doped heterostructure material between the tops of all "T"-shaped stubs in that column. Each column's positive feed line has an external positive electrode, allowing for independent control of each column. The carrier concentration in the doped heterostructure material between the tops of the "T"-shaped stubs is controlled by the voltage difference between the external positive and negative electrodes, achieving on / off adjustment and thus phase modulation of the incident electromagnetic wave.

[0038] The substrate is made of sapphire, high-resistivity silicon, InP, GaAs, or silicon carbide. The feed line and phase shift unit patches are made of Au, Ag, Cu, or Al. The ohmic patches are made of Ti, Al.Ni, or Au. The doped heteromaterial can be AlGaN / GaN, InGaN / GaN, or AlGaAs / GaAs. The artificial microstructure polarization deflection and reflection array is an array of multiple units, MN, where M>2 and N>2.

[0039] Embodiment:

[0040] This embodiment includes:

[0041] Metal base plate, material is metal aluminum, silver, gold and other good conductors,

[0042] Semiconductor substrate, material is sapphire, high resistance silicon, silicon carbide and other,

[0043] MxN orthogonal array arranged phase shift unit arranged on the semiconductor substrate.

[0044] Referring to Figure 2 , the phase shift unit includes an I-shaped structure 3 and a dipole resonant structure 4, the dipole resonant structure 4 is arranged at the opening between the I-shaped structures, the two end points of the I-shaped structure are respectively connected with a rectangular metal strip, the two connection points are symmetrically arranged, and between the two rectangular metal strips at the opening, the upper surface of the dielectric substrate is provided with an ohmic patch, and a doped heterojunction line is arranged above the ohmic patch, the doped heterojunction line is parallel to and equidistant from the two rectangular metal strips.

[0045] In the phase shift unit array, one cathode lead-out line 1 and one anode lead-out line 2 are respectively arranged on both sides of each column of phase shift units along the column line direction, and each column of phase shift units is located between the corresponding cathode lead-out line and anode lead-out line of the column;

[0046] In each column, the doped heterojunction line of the phase shift unit is connected to the anode lead-out line of the column, and the I-shaped dipole opening is connected to the cathode lead-out line of the column.

[0047] Each cathode lead-out line is connected to the same cathode bus, and the cathode bus has an external cathode connection end; and each anode lead-out line is independent of each other.

[0048] The material of the ohmic patch is Ti, Al, Ni or Au, and the material of the doped heterojunction line is AlGaN / GaN, InGaN / GaN, AlGaAs / GaAs, AlGaAs / InGaAs, AlGaAs / InGaAs / InP and the like.

[0049] As Figure 1 , 2 , the anode lead-out line and the cathode lead-out line are arranged on the left and right sides of each column of units, the anode lead-out line is connected to the doped heterojunction line between the tops of all "T" type branches of the column, and all anode lead-out lines are connected to different external positive electrodes, the carrier concentration of the doped heterojunction material between the tops of the "T" type branches is controlled by the voltage difference between the external positive electrode and the external negative electrode, the on-off switching is realized, and the phase of the electromagnetic wave beam is adjusted.

[0050] The application realizes phase control of terahertz reflected electromagnetic waves by changing the on-off state of the transistor, and the on-off state is controlled by the size of the applied voltage.

[0051] The simulation results show that the applied voltage changes the off and on states of the transistor, and realizes phase control of the terahertz beam. Figure 3 The left and right respectively represent the state characteristics of the Y polarization low frequency band and the X polarization low frequency band, Figure 3 The upper and lower respectively represent the amplitude and phase shift characteristics of the phase shift unit under a specific voltage in two polarization directions. Figure 3 The upper represents the amplitude characteristics of the unit, Ns=1x10 16 m -2 Ns=1x10 17 m -2 Under the two states, the insertion loss of the unit structure is small, and the dynamic adjustable array can realize efficient modulation of the phase. Figure 3 Ns=1x10 16 m -2 The left represents that the transistor under the artificial electromagnetic medium is in the pinch-off state at a specific voltage, Ns=1x10 17 m -2 The right represents that the transistor is in the on state at a specific voltage. It can be seen that the reflection phase of the unit structure changes obviously with the state of the transistor. At 0.22THz, there is a 180-degree phase difference between the units in Ns=1x10 16 m -2 and Ns=1x10 17 m -2 , and the maximum change band is about 15GHz. At 0.36THz, there is a 180-degree phase difference between the units in Ns=1x10 16 m -2 and Ns=1x10 17 m -2 , and the maximum change band is about 36GHz, and the adjustable range of the high and low frequency bands is relatively large. Figure 4 The left and right respectively represent the state characteristics of the Y polarization low frequency band and the X polarization low frequency band, Figure 5 The left and right respectively represent the state characteristics of the Y polarization low frequency band and the X polarization low frequency band, Figure 4 and Figure 5 illustrate the phase shift mechanism of the polarization diversity phase shift structure. Table 1 illustrates the coding sequence of the beam scanning. Figure 6The beam simulation scanning diagrams of the 32x32 RIS array in the high frequency band of the X polarization direction and the low frequency band of the Y polarization direction are 13.7°-80° and 13.1°-81° respectively, indicating that the array composed of the structure can continuously scan beams in two polarization directions.

[0052] Table 1

[0053]

[0054] Note: Nx represents the number of adjacent in-phase unit intervals.

Claims

1. A terahertz electrically controlled polarization diversity dual-band reconfigurable smart surface, characterized in that, It includes a metal base plate, a dielectric substrate, and a phase-shifting structure layer arranged layer by layer from bottom to top; The phase shift structure layer includes phase shift units arranged in an M×N orthogonal array, and each column of phase shift units has an anode lead and a cathode lead; Each phase shift unit includes three dipoles, which are I-shaped structures composed of two T-shaped branches arranged with their vertices facing each other. A T-shaped stub is formed by connecting a transverse resonator and a longitudinal resonator. The transverse resonators of two T-shaped stubs in the same dipole are connected by a third resonator to form an open resonator ring with an opening between the two vertices. The T-shaped stubs are symmetrical along the centerline of the longitudinal resonant plate. A metal strip is placed at the vertex of the T-shaped stub, and the long side of the metal strip is perpendicular to the axis of symmetry of the T-shaped stub. An ohmic patch is placed between the vertices of the two T-shaped stubs of the same dipole. A doped heteroline is placed on the ohmic patch, and the doped heteroline is parallel to and equidistant from the long sides of the two rectangular metal strips. Of the three dipoles, two dipoles have their axes of symmetry along the row lines, which are called type A dipoles; the other dipole has its axis of symmetry along the column lines, which is called type B dipoles. Type A dipoles are located on one side of the anode lead-out line, and Type B dipoles are located on the other side of the anode lead-out line. The doped heteroline is connected to the anode connection point of this column through the anode lead-out line, and the open resonant ring is led out to the cathode connection point through the cathode lead-out line. Both M and N are integers greater than 2; In the same phase-shifting unit, the opening directions of the two type B dipoles are opposite, both facing away from each other; Each phase shift unit has one anode lead and two cathode leads. The two cathode leads are respectively located on both sides of the anode lead. The third resonator of the type A dipole partially overlaps with the cathode lead. The dielectric substrate is made of one or more of the following materials: sapphire, high-resistivity silicon, InP, GaAs, and silicon carbide. The material of the doped heterowire includes one or more of AlGaN, GaN, InGaN, GaN, AlGaAs, and GaAs; The size of the type A dipole is larger than that of the type B dipole.

2. The terahertz electrically controlled polarization diversity dual-band reconfigurable smart surface as described in claim 1, characterized in that, The metal base plate may be one or more of aluminum, silver, and gold.

3. The terahertz electrically controlled polarization diversity dual-band reconfigurable smart surface as described in claim 1, characterized in that, The metal strip is rectangular in shape.

4. The terahertz electrically controlled polarization diversity dual-band reconfigurable smart surface as described in claim 1, characterized in that, The material of the ohmic patch includes one or more of Ti, Al, Ni, and Au.

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