A MEMS switchable delay line based terahertz metasurface reflective unit

Abstract

The application discloses a terahertz metasurface reflection unit based on a MEMS switchable delay line, and belongs to the field of radio frequency front-end devices.The unit adopts a sandwich structure of upper and lower glass substrates and a middle bonded metal surface, and a metal radiation patch, a phase delay line and a MEMS switch are integrated on the upper surface.The core is to control the on-off state of the phase delay line through the MEMS switch: when the switch is turned off, the unit is in a reference electrical length;when the switch is turned on, the current path is lengthened, so that the reflection phase lags by about 180 degrees, thereby realizing 1-bit phase coding.The design ingeniously combines the MEMS switch and the delay line, has the advantages of low driving voltage, low reflection loss and high phase control precision in the terahertz frequency band, and provides a feasible hardware solution for the practical application of a reconfigurable intelligent surface in a terahertz communication system.

Description

Technical Field

[0001] This invention relates to a terahertz metasurface reflective unit, which is mainly used in high-speed wireless communication systems and belongs to the field of radio frequency front-end devices. Background Technology

[0002] Reconfigurable Intelligent Surface (RIS) cells based on MEMS switches can flexibly modulate the propagation characteristics of electromagnetic waves in wireless channels. By applying control signals to the tunable elements integrated within the cell, RIS can dynamically adjust its electromagnetic response behavior, thereby precisely controlling parameters such as amplitude, phase, polarization, and frequency of space electromagnetic waves in a programmable manner. As a two-dimensional realization of metamaterials, RIS has advantages such as low cost, low profile, and ease of deployment. It can also achieve wide-angle beam scanning, high gain and front-to-back ratio, multi-beamforming, low radar cross section, and flexible polarization control. Therefore, it shows significant potential in fields such as satellite communication, high-frequency communication, UAV communication, spectrum sensing and sharing, orbital angular momentum transfer, and airborne / shipborne radar.

[0003] Since the theory of programmable metasurfaces was proposed, research on intelligent metasurfaces has made significant progress. This mainly includes designs based on electrically tunable elements such as PIN diodes or varactor diodes, metasurfaces based on spatiotemporal coding, and dual-programmable metasurfaces capable of polarization control. These systems typically rely on hardware such as FPGAs to control the encoded state of the metasurface in real time, enabling functions such as dynamic reconstruction of radiation / scattering characteristics, multi-beam scanning, radar cross-section reduction, and polarization switching. Among these, the PIN diode control scheme has the advantages of fast switching speed and low driving voltage, but generally suffers from high insertion loss and low isolation. While metasurfaces based on tunable materials can achieve unique electromagnetic behaviors such as polarization conversion and anomalous reflection under non-contact conditions, their complex structure and high fabrication difficulty make them challenging. In contrast, RF MEMS switches exhibit superior overall performance at higher frequency bands, including higher isolation, lower insertion loss, and lower power consumption.

[0004] Currently, several programmable metasurface designs based on PIN diodes have been reported, such as a dual-polarized 1-bit unit operating in the 6 GHz band. However, its low operating frequency results in limited isolation between states, making it susceptible to interference and losses from undesirable directions. Other research has achieved a dual-polarized metasurface with 180° phase modulation in the 6 GHz band, but it still faces the challenge of high losses. In summary, existing smart metasurface structures mostly use PIN diodes or varactor diodes as control elements, which struggle to balance low insertion loss and high isolation performance in high-frequency bands such as terahertz, limiting their application in high-frequency communication systems. Therefore, designing a low-loss smart metasurface reflective unit based on MEMS switches and suitable for the terahertz band has significant research value and application prospects. Summary of the Invention

[0005] To address the problems existing in the background technology, this invention designs a terahertz metasurface reflective unit based on a MEMS switchable delay line. This reflective unit has a simple structure, is easy to design, and exhibits low reflection loss, making it a promising 1-bit reflective unit for various applications.

[0006] This invention is achieved through the following technical solution:

[0007] A terahertz metasurface reflective unit based on a MEMS switchable delay line includes an upper glass substrate and a lower glass substrate; a bonding metal surface is provided between the upper glass substrate and the lower glass substrate; a metal radiating patch, a MEMS switch and a phase delay line are provided on the upper surface of the upper glass substrate.

[0008] A rectangular defect is provided on one side of the metal radiating patch, and the phase delay line is in the form of a straight line with its inner end connected to the long side of the rectangular defect; a break is provided in the middle of the phase delay line, and a MEMS switch is located at the break to realize the connection and disconnection of the phase delay line.

[0009] Furthermore: the MEMS switch includes an H-shaped metal electrode and a metal beam; the metal beam includes a left support portion, a left connecting portion, an actuating portion, a right connecting portion, and a right support portion connected in sequence;

[0010] The H-shaped metal electrode is located in the fracture surface. The left and right support parts are located on both sides of the H-shaped metal electrode. The actuating part is suspended directly above the H-shaped metal electrode and connected to the corresponding support parts through the connecting parts on both sides. The actuating part is provided with two contacts, which correspond to the edges of the phase delay lines on both sides of the fracture surface.

[0011] Furthermore, the actuating part is etched with periodic circular holes.

[0012] Furthermore: both the left and right connecting parts are trapezoidal, with the upper base of the trapezoid connecting to the moving part and the lower base connecting to the corresponding supporting part; the trapezoidal part has a trapezoidal groove inside.

[0013] Furthermore: the left support of the metal beam is connected to a DC bias metal post, and the H-shaped metal electrode is connected to a ground metal post; the DC bias metal post extends through the opening on the bonding metal surface to the lower surface of the lower glass substrate, and the ground metal post is connected to the bonding metal surface.

[0014] Furthermore: the middle stub of the H-type metal electrode is perpendicular to the phase delay line.

[0015] Compared with the prior art, the present invention has the following advantages: simple structure and convenient manufacturing; it operates in the terahertz frequency band; it has low reflection loss in the terahertz frequency band; and the terahertz MEMS switch has a low driving voltage. Attached Figure Description

[0016] Figure 1 This is a diagram of the overall structure of the metasurface reflective unit.

[0017] Figure 2 This is a top view of a metasurface reflective unit.

[0018] Figure 3 This is a schematic diagram of the surface metal structure of a metasurface reflective unit.

[0019] Figure 4 This is a side view of a MEMS switch structure.

[0020] Figure 5 This is a top view of the upper surface of the upper glass substrate.

[0021] Figure 6 This is a diagram showing the positional relationship between the H-type metal electrode and the phase delay line.

[0022] Figure 7 This is a schematic diagram of the MEMS switch driving voltage.

[0023] Figure 8 It is the reflection loss curve of the metasurface reflection unit.

[0024] Figure 9 It is the reflection phase curve of the metasurface reflection unit.

[0025] In the figure: 1. Metal radiating patch, 2. MEMS switch, 3. Phase delay line, 4. Upper glass substrate, 5. Bonding metal surface, 6. Lower glass substrate, 7. DC bias metal pillar, 8. Metal beam, 8-1. Left connecting part, 8-2. Actuating part, 8-3. Right supporting part, 1-1. Rectangular defect, 9. Grounding metal pillar, 33. H-type metal electrode, 32. Silicon nitride insulating layer, 31. Contact. Detailed Implementation

[0026] The following is in conjunction with the appendix Figure 1-9 The embodiments and examples will further illustrate specific implementations of the present invention in detail.

[0027] like Figure 1 As shown, this embodiment provides a terahertz metasurface reflective unit based on a MEMS switchable delay line, including an upper glass substrate 4 and a lower glass substrate 6, which are connected by a bonding metal surface 5. The upper surface of the upper glass substrate 4 is provided with a metal radiating patch 1, a MEMS switch 2, and a phase delay line 3.

[0028] like Figures 1 to 6 As shown, a rectangular defect 1-1 is provided on one side of the metal radiating patch 1, and the phase delay line 3 is a straight line with its inner end connected to the long side of the rectangular defect 1-1. A break is provided in the middle of the phase delay line 3, and the MEMS switch 2 is located at the break to control the connection and disconnection of the phase delay line 3.

[0029] The MEMS switch 2 includes an H-shaped metal electrode 33 and a metal beam 8. The metal beam 8 is composed of a left support, a left connecting part 8-1, an actuating part 8-2, a right connecting part, and a right support 8-3 connected in sequence. The H-shaped metal electrode 33 is located in the break of the phase delay line 3, and the actuating part 8-2 is suspended directly above the H-shaped metal electrode 33 and connected to the support part through the connecting parts on both sides. The lower surface of the actuating part 8-2 is provided with two contacts 31, corresponding to the edges of the phase delay line 3 on both sides of the break. The upper surface of the H-shaped metal electrode 33 is covered with a silicon nitride insulating layer 32.

[0030] Preferably, the actuating part 8-2 is etched with periodic circular holes to reduce its rigidity and facilitate actuation. The left connecting part 8-1 and the right connecting part are both trapezoidal structures. The upper base of the trapezoidal structure is connected to the actuating part 8-2, and the lower base is connected to the corresponding support part. The trapezoidal structure has a trapezoidal groove inside to further optimize the flexibility of the structure and the actuation efficiency.

[0031] The left support of the metal beam 8 is connected to the DC bias metal post 7, and the H-shaped metal electrode 33 is connected to the ground metal post 9. The DC bias metal post 7 passes through the opening on the bonding metal surface 5 and extends to the lower surface of the lower glass substrate 6, and the ground metal post 9 is connected to the bonding metal surface 5.

[0032] The middle branch of the H-shaped metal electrode 33 is arranged perpendicular to the phase delay line 3 to optimize the electric field distribution and driving efficiency.

[0033] In this embodiment, both the upper glass substrate 4 and the lower glass substrate 6 are made of quartz glass with a relative permittivity of 3.78 and a loss tangent of 0.0008. The upper glass substrate 4 has a thickness of 100 μm, and the lower glass substrate 6 has a thickness of 300 μm. All metal structures (including the metal radiating patch 1, the phase delay line 3, the metal beam 8, the H-type metal electrode 33, the DC bias metal pillar 7, and the ground metal pillar 9) are made of gold.

[0034] The metasurface reflective element is excited by an external feed source, and the phase delay line 3 is connected or disconnected by controlling the working state of MEMS switch 2, thereby changing the phase of the reflected wave and achieving 1-bit phase modulation. In the metasurface reflective array, beamforming and other functions can be achieved by combining the states of the elements.

[0035] Figure 7 The relationship between the switching displacement and DC bias voltage of the MEMS switch is demonstrated. When a DC voltage of approximately 8.8V is applied between the DC bias metal pillar 7 and the bonding metal surface 5, the metal beam 8 collapses under the action of electrostatic force, thereby closing the switch.

[0036] Figure 8 The reflection loss curves of the metasurface reflective element are shown in two states. Within the operating frequency band, the reflection loss in both states is less than 2 dB, indicating that the structure has low loss characteristics.

[0037] Figure 9 The reflection phase curves of the metasurface reflective unit in two states are shown. Near the operating frequency, the reflection phase difference between state 1 and state 2 is approximately in the range of 170°-190°, which meets the requirement of 1-bit phase modulation.

[0038] With attachment Figure 1 Taking the metasurface reflective unit structure as an example,

[0039] The structural dimensions of the metal radiating patch 1 and the adjustable phase delay line 3 primarily affect the performance of the metasurface reflective unit, specifically as follows:

[0040] a) The length of the metal radiating patch 1 affects the operating frequency of the metasurface unit; the longer the length, the lower the operating frequency. The width affects reflection loss; setting it within a reasonable range will reduce reflection loss.

[0041] b) The overall length of the phase delay line 3 affects the reflection phase difference between the two states of the reflective unit, and the length of the intermediate partition affects the reflection loss of the reflective unit.

[0042] Therefore, selecting appropriate structural dimensions is of great significance for improving the reflective performance of metasurface units. Here, we will illustrate this with an example of a combination of dimensions (the data below are in micrometers).

[0043] Figure 2 The dimensions of the structure are:

[0044] The length of a is 300; the length of b is 180; the length of c is 50; the length of d is 30; the length of e is 200; the length of f is 100; the length of g is 230; the length of h is 70; and the length of i is 20.

[0045] Figure 3 The dimensions of the structure are:

[0046] The length of j is 55; the length of k is 50; the length of l is 75; the length of m is 90; the length of n is 90; and the length of o is 50.

[0047] Within this structural size, the antenna operates in the terahertz band with a center frequency of 300 GHz.

[0048] The above is just one example. To obtain metasurface reflective units that operate at different frequencies, different structural sizes can be used, thus enabling their application in different scenarios.

Claims

1. A MEMS-based switchable delay line based terahertz metasurface reflective unit, characterized by: The application relates to a glass substrate for a radar antenna, which comprises an upper glass substrate (4) and a lower glass substrate (6); a bonding metal surface (5) is arranged between the upper glass substrate (4) and the lower glass substrate (6); a metal radiation patch (1), a MEMS switch (2) and a phase delay line (3) are arranged on the upper surface of the upper glass substrate (4); one side of the metal radiation patch (1) is provided with a rectangular defect (1-1), the phase delay line (3) is in a straight line form, and the inner end of the phase delay line (3) is connected to the long side of the rectangular defect (1-1); a fracture is arranged at the middle position of the phase delay line (3), and the MEMS switch (2) is arranged at the fracture and used for realizing the connection and disconnection of the phase delay line (3). The MEMS switch (2) comprises an H-shaped metal electrode (33) and a metal beam (8); the metal beam (8) comprises a left side supporting portion, a left side connecting portion (8-1), a moving portion (8-2), a right side connecting portion and a right side supporting portion (8-3) which are sequentially connected. The H-shaped metal electrode (33) is arranged in the fracture, the left side supporting portion and the right side supporting portion (8-3) are respectively arranged on the two sides of the H-shaped metal electrode (33), the moving portion (8-2) is suspended above the H-shaped metal electrode (33) and is connected with the corresponding supporting portion through the connecting portions on the two sides; two contact points (31) are arranged on the moving portion (8-2) and correspond to the edges of the phase delay line (3) on the two sides of the fracture respectively. The left side supporting portion of the metal beam (8) is connected with a direct current bias metal column (7), and the H-shaped metal electrode (33) is connected with a grounding metal column (9); the direct current bias metal column (7) extends to the lower surface of the lower glass substrate (6) through an opening in the bonding metal surface (5), and the grounding metal column (9) is connected with the bonding metal surface (5).

2. The MEMS switchable delay line based terahertz metasurface reflective unit of claim 1, wherein: Periodic circular holes are etched on the moving portion (8-2).

3. The MEMS switchable delay line based terahertz metasurface reflective unit of claim 1, wherein: The left side connecting portion (8-1) and the right side connecting portion are both in trapezoidal shapes, the upper bottom of the trapezoidal shape is connected with the moving portion (8-2), and the lower bottom of the trapezoidal shape is connected with the corresponding supporting portion; a trapezoidal groove is arranged in the trapezoidal shape.

4. The MEMS switchable delay line based terahertz metasurface reflective unit of claim 1, wherein: The middle branch of the H-shaped metal electrode (33) is perpendicular to the phase delay line (3).

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