A terahertz waveband metasurface reflection unit based on MEMS switch

Abstract

This invention discloses a metasurface reflective unit based on a MEMS switch in the terahertz band, belonging to the field of radio frequency front-end device technology. It consists of a microstrip antenna unit, a composite beam MEMS switch, a DC bias line, a metal stub, a circular via, metal electrodes, a silicon nitride insulating layer, a silicon substrate, and a back-attached metal ground. The composite beam MEMS switch is composed of a silicon dioxide-supported beam and a metal beam adsorbed below it. The switch's open and closed states are controlled by inputting different DC voltages at the DC port. This intelligent metasurface modulation antenna, utilizing a MEMS switch to control the current path, features high isolation, low insertion loss, and low power consumption. The antenna can achieve a 180° transmit phase difference within a certain bandwidth (295-305 GHz), and even when the MEMS switch operates below 300 GHz, it can guarantee an isolation higher than 15 dB in the open state and an insertion loss lower than 1 dB in the closed state. The microstrip antenna unit and switch have a simple structure and are easy to manufacture, and can be fabricated using silicon-based processes.

Description

Technical Field

[0001] This invention relates to an intelligent metasurface reflective unit based on MEMS switches, which is mainly used in satellite communications in the terahertz band and belongs to the field of radio frequency front-end device technology. Background Technology

[0002] Intelligent metasurfaces (RIS) based on MEMS switches possess the ability to flexibly control the electromagnetic properties of the channel environment. By applying control signals to the tunable components on the electromagnetic unit, the electromagnetic properties of the unit can be dynamically controlled, thereby enabling active and intelligent manipulation of space electromagnetic waves in a programmable manner to form electromagnetic fields with controllable amplitude, phase, polarization, and frequency. Furthermore, as a two-dimensional realization of metamaterials, RIS naturally possesses the characteristics of low cost, low complexity, and easy deployment. It can achieve large beam scanning, low profile area, relatively high radiation gain and gain-before-before ratio, good multi-beamforming capability, low radar cross-section, and good polarization control. Therefore, it has significant research value in long-distance (satellite) communication, high-frequency communication, UAV communication, spectrum sensing and sharing, orbital angular momentum, and airborne and shipborne radar.

[0003] In recent years, following Academician Cui Tiejun's proposal of the programmable metasurface theory, there has been considerable research on intelligent metasurfaces. These mainly include intelligent metasurfaces based on tunable devices such as PIN diodes or varactor diodes loaded in units, intelligent metasurfaces based on spatiotemporal coding, and intelligent metasurfaces with polarization controllable dual programming achieved using a pair of orthogonal polarized waves. These metasurfaces utilize hardware systems such as FPGAs to control the coding state of the digital metasurface in real time, enabling functions such as dynamic control of antenna radiation or scattering states, multi-beam pointing, beam scanning, reduction of radar scattering area, wide-angle dual-beam scanning, and polarization controllability.

[0004] The advantages of PIN diode-controlled metasurfaces are fast reconfiguration switching speed and low switching drive voltage, while the disadvantages are high insertion loss and low switching isolation. Intelligent metasurface reflective units based on tunable materials have the advantages of unique electromagnetic properties, such as polarization conversion, anomalous reflection, and beam focusing; some applicable reconfiguration conditions do not require physical contact. However, their disadvantages include high structural complexity and difficult fabrication. Compared to devices such as PIN diodes or varactor diodes, RF MEMS switches exhibit superior performance at higher operating frequencies, including higher switching isolation and lower insertion loss and power consumption. Among published works, there are very few, if any, applications of MEMS-based intelligent metasurface reflective units with high isolation and low loss in the terahertz high-frequency band. In 2024, Zhu Lihao, Zheng Zhe, and others developed a design for a dual-polarized broadband 1-bit programmable smart metasurface based on PIN diodes for use in 6G smart metasurfaces. However, the operating frequency of the metasurface's reflective unit is low, and the isolation between different reconstruction states is low, which will cause loss and interference in unwanted reconstruction directions. In the same year, Cao Wanwan, Zhang Junwei, and others proposed a dual-polarized 1-bit phase-modulated smart metasurface based on PIN diodes, which achieved a wide 180° phase difference at 6 GHz. However, the antenna of this metasurface has high loss.

[0005] In summary, there are currently very few intelligent metasurface reflective units based on MEMS switches and operating in the terahertz band. Most intelligent metasurface reflective units that are equipped with tunable devices such as PIN diodes or varactor diodes do not have good insertion loss characteristics and cannot meet the requirements of communication equipment applications in the terahertz band. Summary of the Invention

[0006] To address the problems existing in the background technology, this invention designs a terahertz band intelligent metasurface reflective unit based on MEMS switches, which can achieve a 180° phase difference within a certain bandwidth. The designed antenna achieves the characteristics of simple structure, convenient design, high gain, and high integration, and can be used in the terahertz band.

[0007] To achieve the above effects, the technical solution adopted by the present invention is as follows:

[0008] A terahertz band metasurface reflective unit based on MEMS switch includes a microstrip antenna unit (1), a composite beam MEMS switch (9), a quartz glass substrate (17), and a back-attached metal ground (18).

[0009] The microstrip antenna unit (1) and the composite beam MEMS switch (9) are both located on the upper surface of the quartz glass substrate; the back-attached metal ground (18) is located on the lower surface of the quartz glass substrate.

[0010] The rectangular patch and the circular through hole (4) at the tail of the microstrip antenna unit are connected by a metal stub (19), and a notch is provided on the metal stub as a circuit breaker; the conduction structure (12) of the composite beam MEMS switch (9) is located directly above the notch;

[0011] Four metal through holes are provided through the quartz glass substrate. The four metal through holes are arranged in a linear array and are all located below the composite beam MEMS switch (9). The metal through holes at both ends form a group and are respectively connected to the corresponding bridge piers of the composite beam MEMS switch (9). The two metal through holes in the middle form another group and are respectively connected to the corresponding metal electrodes.

[0012] One of the two sets of metal vias is not in contact with the back metal ground and is connected to the drive voltage port via a DC bias line.

[0013] Furthermore: the microstrip antenna unit includes a rectangular patch, a rectangular stub, and a tail circular through hole (4); the rectangular stub is connected to one side of the rectangular patch, both of which are located on the upper surface of the quartz glass substrate (17); the tail circular through hole penetrates the substrate and is connected to the back metal ground.

[0014] Furthermore: the composite beam MEMS switch (9) includes an upper beam (10) and a lower metal beam (11) stacked together; the upper beam has a conductive structure (12) on its lower surface at the middle position; two metal electrodes (13 and 14) are located below the left and right actuating arms of the lower metal beam, respectively; the left and right actuating arms of the lower metal beam (11) and the two metal electrodes (13 and 14) are directly connected to the external excitation through DC bias lines (2 and 3).

[0015] Furthermore: the upper beam is made of silicon dioxide, and the lower metal beam is made of gold.

[0016] Furthermore: The upper beam of the composite beam MEMS switch is a symmetrical structure, which is connected from left to right to the left pier (40), left folding arm (42), left action arm (44), left middle arm (45), rectangular structure (46), right middle arm, right action arm, right folding arm and right pier; among them, the left action arm (44), left middle arm (45), right action arm and right middle arm are all corroded with periodic round holes; the conduction structure (12) is a rectangular metal sheet, and two circular contact points are distributed below the metal sheet;

[0017] The metal lower beam (11) of the composite beam is a symmetrical structure, including symmetrical piers, folding arms, and moving arms. The moving arms are corroded with periodic cylindrical holes.

[0018] Furthermore, the upper surfaces of the metal electrodes (13 and 14) on the composite beam MEMS switch are each provided with a corresponding silicon nitride insulating layer (15 and 16).

[0019] Furthermore, the two metal through holes in the middle are connected to the drive voltage port via DC bias lines.

[0020] Compared with existing technologies, this patent has the following beneficial effects:

[0021] A) Compared to traditional PIN diode or varactor diode-based smart metasurface reflector units, the smart metasurface reflector unit based on MEMS switches designed in this invention can achieve good performance in the terahertz frequency band. The antenna unit and switch structure are simple and easy to manufacture, and can be applied to RF circuits such as phased array and metasurface reflector array antennas.

[0022] B) The switch has high isolation when disconnected and low insertion loss when connected.

[0023] C) The switch adopts a folding structure, can work with a driving voltage of 50V, has a short response time, high reliability, and is not easy to break during operation. Attached Figure Description

[0024] Figure 1 This is a top view of the overall structure of the present invention;

[0025] Figure 2 This is a schematic diagram of the structure of the upper surface of the quartz glass substrate of the present invention;

[0026] Figure 3 This is a top view of a microstrip antenna element;

[0027] Figure 4 This is a top view of the DC bias line of the present invention;

[0028] Figure 5 This is a side view of the composite beam MEMS switch of the present invention;

[0029] Figure 6 This is a schematic diagram of the upper beam of the composite beam MEMS switch in this invention;

[0030] Figure 7 This is a schematic diagram of the lower beam of the composite beam MEMS switch in this invention;

[0031] Figure 8 This is a schematic diagram of the intermediate conduction structure of the composite beam MEMS switch in this invention;

[0032] Figure 9 This is a schematic diagram of the metal stub structure of the present invention;

[0033] Figure 10 This is a schematic diagram of the structure of the metal through hole of the present invention;

[0034] Figure 11 This is a three-dimensional perspective view of the overall structure of the present invention;

[0035] Figure 12 This is a comparison chart of the return loss S11 and isolation S21 curves of the MEMS switch in the off state of the present invention.

[0036] Figure 13 This is a comparison chart of the return loss S11 and insertion loss S21 curves of the MEMS switch in the on state of the present invention.

[0037] Figure 14 This is a comparison diagram of the return loss S11 and reflection phase curve of the intelligent metasurface reflection unit based on MEMS switch in the off state of the present invention.

[0038] Figure 15 This is a comparison diagram of the return loss S11 and reflection phase curve of the intelligent metasurface reflection unit based on MEMS switch in the present invention during the switch conduction state.

[0039] Figure 16 This invention presents the return loss S11 and reflection phase difference curves of the intelligent metasurface reflection unit based on MEMS switches in the open and closed states of the switch. Detailed Implementation

[0040] The following is in conjunction with the appendix Figure 1-16 The embodiments and examples will further illustrate specific implementations of the present invention in detail.

[0041] With attachment Figure 1 -Appendix Figure 16 Taking a terahertz smart metasurface reflector unit based on a MEMS switch as an example, this example includes a microstrip antenna unit 1, DC bias lines 2 and 3, metal vias 4, 5, 6, 7, and 8, a composite beam MEMS switch 9 consisting of an upper beam 10 and a lower beam 11, a middle conductive structure 12 in the composite beam, metal electrodes 13 and 14 in the composite beam, silicon nitride insulating layers 15 and 16 on the upper surface of the metal electrodes in the composite beam, a quartz glass substrate 17, a back-attached metal ground 18, a metal stub 19, and ground vias 20 and 21. Since traditional PIN diodes or capacitive diodes have poor switching performance in the terahertz band, the former will result in low isolation, and the latter will result in excessive insertion loss. Therefore, a composite beam MEMS switch is adopted, in which the composite beam is a fixed beam composed of a silicon dioxide upper beam 10, a metal lower beam 11 adsorbed below it, and a middle conductive structure 12. The lower metal beam of the composite beam and the metal electrodes 13 and 14 distributed on both sides below the lower metal beam are connected to the drive voltage port through DC bias lines 2 and 3, respectively.

[0042] The quartz glass substrate 17 has a dielectric constant of 3.78 and a thickness of 50 μm;

[0043] Top view of microstrip antenna element 1 as shown Figure 3 The material is gold, and the thickness is 1µm;

[0044] DC bias lines 2 and 3 top view as shown Figure 4 The material is gold, and the thickness is 1µm;

[0045] Side view of composite beam MEMS switch as shown Figure 5 As shown. During operation, when a driving voltage is applied to the metal electrodes 13 and 14 of the composite beam MEMS switch 9 through DC bias lines 2 and 3, the driving voltage causes electrostatic force between the metal electrodes and the lower metal beam. This causes the lower metal beam 11 to drive the upper silicon dioxide beam 10 to undergo longitudinal deformation, pulling the entire composite beam downwards. Ultimately, this causes the contact below the middle conductive structure 12 of the composite beam to disconnect from the upper contact with the metal stub 19. At this time, the microstrip antenna 1 is connected to the metal via 4 through the metal stub 19, connecting the rectangular patch 1 and the back ground 18, thus forming a current resonant cavity structure. When the middle conductive structure of the composite beam MEMS switch remains stationary, the rectangular patch and the circular via are in an open state. That is, the on / off state of the composite beam MEMS switch is controlled by applying an external driving voltage, thereby forming a current resonant cavity structure to achieve a 180° reflection phase change.

[0046] As attached Figure 6 As shown, the upper beam 10 of the composite beam is a symmetrical structure, composed of structures of different sizes, including left piers 40 and 41, left folding arms 42 and 43, left moving arms 44, left middle arms 45, and rectangular structures 46 and 47. The left moving arms and left middle arms both have periodic circular holes corroded on them.

[0047] As attached Figure 7 As shown, the lower beam 11 of the composite beam MEMS switch has a symmetrical structure, consisting of symmetrical piers 50 and 51, a folding arm 52, and an action arm 53, wherein the action arm is etched with periodic circular holes.

[0048] As attached Figure 8 As shown, the middle conductive structure 12 of the composite beam is a rectangular metal sheet, and a cylindrical contact is distributed on both sides of the metal sheet, which is attached to both sides of the silicon dioxide upper beam 10.

[0049] As attached Figure 9 As shown, the metal stub has a notch in the middle and is composed of two symmetrical square structures 57.

[0050] Metal through-holes as shown in the attached image Figure 10 As shown, it consists of an outer circular structure 59 and an inner cylindrical structure 60.

[0051] Appendix Figure 11 and 12 These are the scattering parameter curves of the return loss S11 and S21 under the switch-off and switch-on states, respectively.

[0052] The dimensions of the intermediate conductive structure, the metal stub structure, and the circular via size affect the RF performance parameters of the metasurface reflective unit. The dimensions of the composite beam and metal electrodes affect performance parameters such as the driving voltage. These effects are mainly manifested in the following ways:

[0053] A. The narrower the overall width of the intermediate conductive structure, the better the isolation when the switch is open;

[0054] The switch in this design uses a rectangular conduction structure. By adjusting the size of the conduction structure, the isolation can be optimized.

[0055] B. A longer overall switch length and a longer metal stub length will result in better switch isolation and lower drive voltage, but at the same time it will deteriorate the RF performance of the metasurface reflector unit, generate unnecessary resonant points, and affect the layout and use.

[0056] C. The size of the circular through hole mainly affects the phase difference generated when the switch is turned on or off.

[0057] D. The dimensions of the silica material beam and the metal beam mainly affect the performance of the driving voltage and response time. This design adopts a folding structure, and by continuously optimizing the dimensions of the actuator arm and the rectangular structure, the working voltage of the driving voltage is stabilized between 40-50V, and the response time is on the order of microseconds.

[0058] E. The size and spacing of the periodic cylindrical holes will affect the magnitude of the electrostatic force between the metal electrode and the beam, and thus also affect the magnitude of the operating voltage of the driving voltage.

[0059] Therefore, selecting appropriate composite beam dimensions, metal stub dimensions, composite beam conduction structure dimensions, and circular via dimensions is crucial for improving the RF performance of the entire metasurface reflective unit.

[0060] The following section uses one dimension to illustrate the size of the structure in the attached diagram. The data below is in micrometers.

[0061] Figure 2 The dimensions are: Structure 22 = Structure 23 = 500; Structure 24 = Structure 26 = 70; Structure 25 = 40; Structure 27 = 290; Structure 28 = 30; Structure 29 = Structure 30 = 10;

[0062] Figure 4 The dimensions are: Structure 31 = 2525; Structure 32 = 110; Structure 33 = 100; Structure 34 = 50; Structure 35 = 30; Structure 36 = 10.

[0063] Figure 5The dimensions are as follows: metal electrode 13 width = 35; pier structure 37 = 30; composite beam structure 38 thickness = 1; metal beam structure 39 thickness = 0.5; composite beam intermediate conductive structure 40 thickness = 0.2; stub structure 41 thickness = 1;

[0064] Figure 6 , Figure 7 The dimensions are as follows: Structure 42 = Structure 52 = 35; Structure 43 = Structure 53 = 30; Structure 44 = Structure 54 = 15; Structure 45 = Structure 55 = 10; Structure 46 = 10; Structure 47 = Structure 56 = Structure 49 = 30; Structure 48 = 10; Diameter of periodic circular hole structure 50 = 5; Diameter of structure 51 = 3;

[0065] Figure 8 The dimensions are as follows: intermediate conductive structure 56 = 40; structure 57 = 10; corrosive circular hole structure 58 diameter = 3;

[0066] Figure 9 The dimensions are: Structure 59 = 10; Structure 60 = 30;

[0067] Figure 10 The dimensions are: outer circular structure 61 diameter = 45; inner cylindrical structure 62 diameter = 30;

[0068] The thickness of the quartz glass substrate is 17 = 50; the thickness of the back-attached metal ground and DC bias line is 1; under this structure, the terahertz band intelligent metasurface reflection unit based on MEMS switch operates below 300 GHz, and can achieve a phase difference of 180 ± 20° within a certain bandwidth range (290-305), and the isolation is greater than -18 dB when the switch is open, and the insertion loss is less than -1 dB when the switch is closed;

[0069] Appendix Figure 11 This is a three-dimensional image of the overall structure of the intelligent metasurface reflective unit;

[0070] When the switch is in the open state, the return loss S 11 Isolation S 21 The curve is attached. Figure 12 As shown;

[0071] Figure 12 The display shows the return loss S in the off state of the composite beam MEMS switch. 11 Isolation S 21 The graph shows that the return loss of the switch is significantly higher than -1.1dB in the 220-320GHz range. 21 Significantly less than -16dB.

[0072] When the switch is closed, the return loss S 11Insertion loss S 21 The curve is attached. Figure 13 As shown;

[0073] Figure 13 The display shows the return loss S in the closed state of the composite beam MEMS switch. 11 Insertion loss S 21 The graph shows that the return loss of the switch is significantly lower than -12.5dB in the 220-320GHz range. 21 Significantly higher than -0.8dB.

[0074] Figure 14 and Figure 15 The figures show the return loss and reflection phase of the metasurface reflective element in the on and off states, respectively; it can be seen that the return loss S of the metasurface reflective element in the on and off states is... 11 It is above -1.2dB in the 220-320GHz range;

[0075] Figure 16 The display shows the reflection phase difference of the metasurface reflective unit in the open and closed states; it can be seen that the metasurface reflective unit has a phase difference of 180°±20° in the range of 285-305GHz;

[0076] In summary, the MEMS-based terahertz band intelligent metasurface reflection unit designed in this invention can be used as a switching unit on phased arrays and RIS transmit / reflect arrays, and the switch has good isolation and loss characteristics in the terahertz band.

[0077] The above is just one example. To obtain intelligent metasurface reflective units that operate at different frequencies, different microstrip antenna unit sizes and switch sizes can be designed for application in different scenarios.

Claims

1. A metasurface reflective unit based on a MEMS switch in the terahertz band, comprising a microstrip antenna unit (1), a composite beam MEMS switch (9), a quartz glass substrate (17), and a back-attached metal ground (18); characterized in that, The microstrip antenna unit (1) and the composite beam MEMS switch (9) are both located on the upper surface of the quartz glass substrate; the back-attached metal ground (18) is located on the lower surface of the quartz glass substrate. The rectangular patch and the circular through-hole (4) at the tail of the microstrip antenna unit are connected by a metal stub (19). The circular through-hole at the tail penetrates the substrate and is connected to the back metal ground. A notch is provided on the metal stub as a circuit breaker. The conductive structure (12) of the composite beam MEMS switch (9) is located directly above the notch. The conductive structure (12) is a rectangular metal sheet with two circular contact points distributed below it. Four metal through holes are provided through the quartz glass substrate. The four metal through holes are arranged in a linear array and are all located below the composite beam MEMS switch (9). The metal through holes at both ends form a group and are respectively connected to the corresponding bridge piers of the composite beam MEMS switch (9). The two metal through holes in the middle form another group and are respectively connected to the corresponding metal electrodes. One of the two sets of metal vias is not in contact with the back metal ground and is connected to the drive voltage port through a DC bias line; The composite beam MEMS switch (9) includes an upper beam (10) and a lower metal beam (11) stacked together; the upper beam has a conductive structure (12) on its lower surface at the middle position; two metal electrodes (13 and 14) are located below the left and right actuating arms of the lower metal beam, respectively; the left and right actuating arms of the lower metal beam (11) and the two metal electrodes (13 and 14) are directly connected to the external excitation through DC bias lines (2 and 3).

2. The terahertz band metasurface reflective unit based on a MEMS switch according to claim 1, characterized in that: The microstrip antenna unit includes a rectangular patch, a rectangular stub, and a circular through-hole at the tail (4); the rectangular stub is connected to one side of the rectangular patch, and both are located on the upper surface of the quartz glass substrate (17).

3. The terahertz band metasurface reflective unit based on a MEMS switch according to claim 1, characterized in that: The upper beam is made of silicon dioxide, and the lower metal beam is made of gold.

4. The terahertz band metasurface reflective unit based on a MEMS switch according to claim 1, characterized in that: The upper beam of the composite beam MEMS switch has a symmetrical structure, which is connected from left to right to the left pier (40), left folding arm (42), left action arm (44), left middle arm (45), rectangular structure (46), right middle arm, right action arm, right folding arm and right pier; among them, the left action arm (44), left middle arm (45), right action arm and right middle arm are all corroded with periodic round holes; The metal lower beam (11) of the composite beam is a symmetrical structure, including symmetrical piers, folding arms, and moving arms. The moving arms are corroded with periodic cylindrical holes.

5. A metasurface reflection unit based on a MEMS switch in the terahertz band according to claim 1, characterized in that: The upper surfaces of the metal electrodes (13 and 14) on the composite beam MEMS switch are provided with corresponding silicon nitride insulating layers (15 and 16).

6. A metasurface reflective unit based on a MEMS switch in the terahertz band according to claim 1, characterized in that: The two metal through holes in the middle are connected to the drive voltage port through a DC bias line.

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