A multi-band tunable flexible terahertz lens based on sandwich supercell

Abstract

This invention relates to a multi-band tunable flexible terahertz lens based on a sandwich meta-unit, comprising a low-frequency resonant layer, a mid-frequency resonant layer, a high-frequency resonant layer, and a stress buffer layer. The low-frequency resonant layer includes a first flexible dielectric substrate and several metal units, each metal unit being a square-shaped metal sheet arranged periodically on the first flexible dielectric substrate. The mid-frequency resonant layer includes a second flexible dielectric substrate and a resonant ring structure, the resonant ring structure being disposed on the second flexible dielectric substrate in a ring shape. The high-frequency resonant layer includes a third flexible dielectric substrate and several geometric phase-shifting units, each geometric phase-shifting unit being a swastika-shaped metal sheet arranged in a rotationally symmetric manner on the third flexible dielectric substrate. Stress buffer layers connect the low-frequency and mid-frequency resonant layers, and also connect the mid-frequency and high-frequency resonant layers, with the elastic modulus of the stress buffer layer varying gradually from the center outwards.

Description

Technical Field

[0001] This invention relates to the technical field of terahertz lenses, and more particularly to a multi-band tunable flexible terahertz lens based on sandwich metacells. Background Technology

[0002] Most existing terahertz lenses employ a resonant layer designed with a static metasurface. The resonant layer consists of a dielectric substrate and a resonant structure mounted on the dielectric substrate. The resonant structure uses a metal open-ring array or a cross-shaped structure to achieve phase modulation in a single frequency band.

[0003] To enable terahertz lenses to support a wider operating frequency band, as exemplified by the Chinese invention patent application CN112909569A entitled "A Three-Layer Circular Inner and Outer Dual Resonant Cavity Broadband Terahertz Wave Metasurface Absorber," this patented solution employs a three-layer stacked metallic dielectric structure. The three metallic dielectric layers utilize the same resonant structure, with the resonant structure scaling sequentially from top to bottom, thereby achieving a wider operating frequency band for the terahertz lens. However, this patented solution features a single tuning mode and a fixed electromagnetic coupling mechanism, making it difficult to meet the requirements for independent tuning across multiple frequency bands and unsuitable for application scenarios with varying performance requirements.

[0004] To achieve deformation capability in terahertz lenses, as exemplified by Chinese invention patent CN112305645B entitled "A Metasurface Lens," the patent solution includes a flexible substrate and an optical antenna array, with the optical antenna array disposed on the flexible substrate. This patent solution enables the terahertz lens to have deformation capability through the flexible substrate. However, this patent solution is only applicable to single-layer resonant layer designs, resulting in a narrow operating frequency range. If a multi-layer structure design with multiple resonant layers stacked together is directly adopted, stress concentration will occur between the resonant layers due to the difference in Young's modulus during bending or stretching, causing geometric distortion of the resonant structure, interlayer coupling mismatch, and phase response shift, leading to multi-band response instability and phase modulation failure.

[0005] Therefore, existing terahertz lenses cannot simultaneously meet the requirements of having a wide operating frequency band, independent tuning of multiple frequency bands, and deformation adaptive capability for wavefront parameter control. This severely limits the application of terahertz lenses in fields such as terahertz adaptive imaging systems, curved conformal communication antennas, non-destructive testing equipment for biological tissues, dynamic wearable devices, and non-planar imaging systems. Summary of the Invention

[0006] The purpose of this invention is to provide a multi-band tunable flexible terahertz lens based on a sandwich meta-unit, which has a wide operating frequency band, can independently tune terahertz waves of multiple frequency bands, and has deformation adaptive capability in the adjustment of wavefront parameters.

[0007] The technical solution adopted in this invention is: a multi-band tunable flexible terahertz lens based on sandwich meta-units, comprising a low-frequency resonant layer, a mid-frequency resonant layer, a high-frequency resonant layer and a stress buffer layer, wherein the low-frequency resonant layer, the mid-frequency resonant layer and the high-frequency resonant layer are arranged sequentially along a straight line;

[0008] The low-frequency resonant layer includes a first flexible dielectric substrate and several metal units. The metal units are square metal sheets, and the several metal units are arranged periodically on the first flexible dielectric substrate.

[0009] The intermediate frequency resonant layer includes a second flexible dielectric substrate and a resonant ring structure. The resonant ring structure is disposed on the second flexible dielectric substrate and is a ring structure surrounding the center of the second flexible dielectric substrate.

[0010] The high-frequency resonant layer includes a third flexible dielectric substrate and several geometric phase-shifting units. The geometric phase-shifting units are swastika-shaped metal sheets, and the several geometric phase-shifting units are arranged on the third flexible dielectric substrate in a rotationally symmetric broken manner.

[0011] A stress buffer layer connects the low-frequency resonant layer and the mid-frequency resonant layer, as well as the mid-frequency resonant layer and the high-frequency resonant layer. The elastic modulus of the stress buffer layer changes in a gradient from the center to the periphery.

[0012] The working principle of this invention is as follows:

[0013] The low-frequency resonant layer uses periodically arranged metal units to excite low-frequency local plasmon resonance, thereby achieving independent tuning of terahertz waves in the low-frequency band. The mid-frequency resonant layer forms a resonant cavity through a resonant ring structure, thereby achieving independent tuning of terahertz waves in the mid-frequency band. The high-frequency resonant layer uses several geometric phase-shifting units arranged in a rotationally symmetric manner to generate a geometric phase, realizing left / right circular polarization conversion and vortex phase control with adjustable topological charge, thereby achieving independent tuning of terahertz waves in the high-frequency band. The design of multiple resonant layers, consisting of the low-frequency, mid-frequency, and high-frequency resonant layers, gives this terahertz lens a wide operating frequency band. At the same time, by using different resonant structures in the low-frequency, mid-frequency, and high-frequency resonant layers, this terahertz lens can independently tune terahertz waves in three frequency bands, making the control of wavefront parameters in each frequency band more flexible.

[0014] By connecting the low-frequency resonant layer and the mid-frequency resonant layer, and the mid-frequency resonant layer and the high-frequency resonant layer with a stress buffer layer, and designing the elastic modulus of the stress buffer layer to change in a gradient from the center to the periphery, the stress buffer layer can absorb the non-uniform stress generated by the local terahertz lens during deformation, thus avoiding stress concentration. This allows the deformation of the low-frequency resonant layer, mid-frequency resonant layer, and high-frequency resonant layer to be symmetrical and controllable. Furthermore, the low-frequency resonant layer uses a periodic arrangement of several metal units, the mid-frequency resonant layer uses a ring structure surrounding the center of the second flexible dielectric plate, and the high-frequency resonant layer... The design employs a rotationally symmetric arrangement of several geometric phase-shifting units, which allows the arrangement of the metal units in the low-frequency resonant layer to scale periodically and uniformly during deformation. This results in a linear transformation of the opening angle of the resonant ring structure in the mid-frequency resonant layer during deformation, and an overall scaling of the resonant ring structure during deformation. Furthermore, the geometric phase-shifting units in the high-frequency resonant layer scale by translation while maintaining a constant spatial distribution of rotation angles. This ensures that the resonant structures of the low-frequency, mid-frequency, and high-frequency resonant layers maintain geometric symmetry and resonant mode stability during mechanical deformation, preventing structural misalignment and electromagnetic instability of the local terahertz lens during deformation.

[0015] Through the above design, this terahertz lens can simultaneously meet the requirements of having a wide operating frequency band, independent tuning of multiple frequency bands, and deformation adaptive capability for wavefront parameter adjustment. It is suitable for terahertz adaptive imaging systems, curved conformal communication antennas, non-destructive testing equipment for biological tissues, dynamic wearable devices, non-planar imaging systems, and other fields.

[0016] Furthermore, in the aforementioned multi-band tunable flexible terahertz lens based on sandwich metacells, the size of the metal cells closer to the center of the first flexible dielectric substrate is larger, so that the spacing between two adjacent metal cells closer to the center of the first flexible dielectric substrate is smaller.

[0017] Furthermore, as described above, a multi-band tunable flexible terahertz lens based on a sandwich meta-unit is provided, wherein the metal unit is made of a mesh woven from nano-metal wires.

[0018] Furthermore, as described above, a multi-band tunable flexible terahertz lens based on a sandwich meta-unit includes a resonant ring structure comprising several resonant units arranged around the center of a second flexible dielectric substrate.

[0019] Furthermore, in the aforementioned multi-band tunable flexible terahertz lens based on a sandwich meta-unit, the resonant unit includes an equivalent inductance metal sheet and an equivalent capacitance metal ring; the equivalent inductance metal sheet is a square-shaped metal sheet disposed on a second flexible dielectric substrate; the equivalent capacitance metal ring is a ring-shaped metal sheet disposed on the equivalent inductance metal sheet, with a gap between the equivalent capacitance metal ring and the equivalent inductance metal sheet, and the center of the equivalent capacitance metal ring is located on the central axis of the equivalent inductance metal sheet.

[0020] Furthermore, in the aforementioned multi-band tunable flexible terahertz lens based on sandwich meta-units, the stress buffer layer includes several elastic parts, which are nested sequentially from the center of the stress buffer layer outwards.

[0021] Furthermore, in the aforementioned multi-band tunable flexible terahertz lens based on sandwich meta-units, the elastic part at the very center is called the central elastic part, which has a circular structure; the remaining elastic parts are called the outer elastic parts, which have an annular structure, and all the outer elastic parts are arranged in sequence outward from the central elastic part.

[0022] Furthermore, in the aforementioned multi-band tunable flexible terahertz lens based on sandwich meta-units, the spacing between the outer and inner rings of each outer elastic layer and the radius of the central elastic layer are equal.

[0023] Furthermore, in the aforementioned multi-band tunable flexible terahertz lens based on sandwich metaunits, the stress buffer layer is made of polydimethylsiloxane material.

[0024] Furthermore, in the aforementioned multi-band tunable flexible terahertz lens based on sandwich meta-units, the low-frequency resonant layer operates in the range of 0.5THz to 1.2THz, the mid-frequency resonant layer operates in the range of 1.3THz to 2.1THz, and the high-frequency resonant layer operates in the range of 2.3THz to 3THz.

[0025] The beneficial effects of this invention are: it has a wide operating frequency band, can independently tune terahertz waves of multiple frequency bands, and the wavefront parameter adjustment has deformation adaptive capability. Attached Figure Description

[0026] Figure 1 This is a three-dimensional structural diagram of an embodiment;

[0027] Figure 2 This is a schematic diagram of the low-frequency resonant layer in the embodiment;

[0028] Figure 3This is a schematic diagram of the mid-frequency resonant layer in an embodiment;

[0029] Figure 4 This is a schematic diagram of the high-frequency resonant layer in an embodiment;

[0030] Figure 5 This is a schematic diagram of the stress buffer layer in an embodiment.

[0031] Explanation of reference numerals in the attached figures:

[0032] 1-Low-frequency resonant layer; 11-First flexible dielectric substrate; 12-Metal unit; 2-Mid-frequency resonant layer; 21-Second flexible dielectric substrate; 22-Resonant unit; 221-Equivalent inductor metal sheet; 222-Equivalent capacitance metal ring; 3-High-frequency resonant layer; 31-Third flexible dielectric substrate; 32-Geometric phase shift unit; 4-Stress buffer layer; 41-Central elastic part; 42-Outer elastic part. Detailed Implementation

[0033] To provide a clearer understanding of the technical features, objectives, and effects of the present invention, specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0034] like Figures 1 to 5 An embodiment of a multi-band tunable flexible terahertz lens based on a sandwich meta-unit includes a low-frequency resonant layer 1, a mid-frequency resonant layer 2, a high-frequency resonant layer 3, and a stress buffer layer 4, wherein the low-frequency resonant layer 1, the mid-frequency resonant layer 2, and the high-frequency resonant layer 3 are arranged sequentially along a straight line.

[0035] The low-frequency resonant layer 1 includes a first flexible dielectric plate 11 and several metal units 12. The metal units 12 are thin metal sheets with a square structure. The several metal units 12 are arranged in a periodic rectangular array on the first flexible dielectric plate 11. The operating frequency band of the low-frequency resonant layer 1 is in the range of 0.5THz to 1.2THz.

[0036] The intermediate frequency resonant layer 2 includes a second flexible dielectric plate 21 and a resonant ring structure. The resonant ring structure is disposed on the second flexible dielectric plate 21 and is a ring structure surrounding the center of the second flexible dielectric plate 21. The operating frequency band of the intermediate frequency resonant layer 2 is in the range of 1.3THz to 2.1THz.

[0037] The high-frequency resonant layer 3 includes a third flexible dielectric substrate 31 and several geometric phase-shifting units 32. The geometric phase-shifting units 32 are swastika-shaped metal sheets. The geometric phase-shifting units 32 are set on the third flexible dielectric substrate 31 by an etching process. The geometric phase-shifting units 32 are made of materials with high conductivity and flexibility, such as gold or silver. Several geometric phase-shifting units 32 are arranged in a rectangular array with rotational symmetry broken in a rectangular array on the third flexible dielectric substrate 31. The operating frequency of the high-frequency resonant layer 3 is in the range of 2.3THz to 3THz.

[0038] A stress buffer layer 4 connects the low-frequency resonant layer 1 and the mid-frequency resonant layer 2, and the mid-frequency resonant layer 2 and the high-frequency resonant layer 3 (see attached). Figure 1 Only the stress buffer layer between the mid-frequency resonant layer and the high-frequency resonant layer is shown in the figure (the stress buffer layer between the low-frequency resonant layer and the mid-frequency resonant layer is not shown). The elastic modulus of the stress buffer layer 4 changes in a gradient from the center to the periphery.

[0039] The center points of the low-frequency resonant layer 1, the mid-frequency resonant layer 2, the high-frequency resonant layer 3, and the stress buffer layer 4 are all on the same straight line.

[0040] The working principle of this embodiment is as follows:

[0041] The low-frequency resonant layer 1 uses periodically arranged metal units 12 to excite low-frequency local plasmon resonance, thereby achieving independent tuning of terahertz waves in the low-frequency band. The mid-frequency resonant layer 2 forms a resonant cavity through a resonant ring structure, thereby achieving independent tuning of terahertz waves in the mid-frequency band. The high-frequency resonant layer 3 uses several geometric phase-shifting units 32 arranged in a rotationally symmetric breaking manner to generate a geometric phase, realizing left / right circular polarization conversion and vortex phase control with adjustable topological charge, thereby achieving independent tuning of terahertz waves in the high-frequency band. The design of the low-frequency resonant layer 1, mid-frequency resonant layer 2, and high-frequency resonant layer 3 to form a multi-layer resonant layer gives this terahertz lens a wide operating frequency band. At the same time, by adopting different resonant structures, the low-frequency resonant layer 1, mid-frequency resonant layer 2, and high-frequency resonant layer 3 allow this terahertz lens to independently tune terahertz waves in three frequency bands, making the control of wavefront parameters in each frequency band more flexible.

[0042] By connecting the low-frequency resonant layer 1 and the mid-frequency resonant layer 2, and the mid-frequency resonant layer 2 and the high-frequency resonant layer 3 with a stress buffer layer 4, and designing the elastic modulus of the stress buffer layer 4 to change gradient from the center to the periphery, the stress buffer layer 4 can absorb the non-uniform stress generated by the local terahertz lens during deformation, thus avoiding stress concentration. This allows the deformation of the low-frequency resonant layer 1, the mid-frequency resonant layer 2, and the high-frequency resonant layer 3 to be symmetrical and controllable. Furthermore, the metal units 12 of the low-frequency resonant layer 1 are arranged in a periodic manner, the resonant ring structure of the mid-frequency resonant layer 2 is a ring structure arranged around the center of the second flexible dielectric plate 21, and the high-frequency resonant layer 3... The geometric phase-shifting units 32 of layer 3 are arranged in a rotationally symmetric broken configuration, which makes the arrangement of the metal units 12 in the low-frequency resonant layer 1 periodically and uniformly scale during deformation. This makes the opening angle of the resonant ring structure of the mid-frequency resonant layer 2 linearly change during deformation and makes the resonant ring structure scale as a whole during deformation. This makes the geometric phase-shifting units 32 of the high-frequency resonant layer 3 translate and scale while the spatial distribution of the rotation angle remains unchanged. In this way, the resonant structures of the low-frequency resonant layer 1, mid-frequency resonant layer 2, and high-frequency resonant layer 3 maintain geometric symmetry and resonant mode stability during mechanical deformation, and avoids structural misalignment and electromagnetic instability of the local terahertz lens during deformation.

[0043] Through the above design, this terahertz lens can simultaneously meet the requirements of having a wide operating frequency band, independent tuning of multiple frequency bands, and deformation adaptive capability for wavefront parameter adjustment. It is suitable for terahertz adaptive imaging systems, curved conformal communication antennas, non-destructive testing equipment for biological tissues, dynamic wearable devices, non-planar imaging systems, and other fields.

[0044] like Figure 1 and Figure 2 As shown, the metal unit 12 closer to the center of the first flexible dielectric substrate 11 is larger, resulting in a smaller spacing between two adjacent metal units 12 closer to the center of the first flexible dielectric substrate 11. This design enables the low-frequency resonant layer 1 to have a wider operating frequency band and better focusing efficiency.

[0045] In this embodiment, the metal unit 12 is made of a mesh woven from silver nanowires. This design gives the metal unit 12 strong broadband reflectivity.

[0046] like Figure 1 and Figure 3 As shown, the resonant ring structure includes several resonant units 22, which are arranged around the center of the second flexible dielectric plate 21. The combination of these resonant units 22 to form a ring structure allows the resonant ring structure to maintain better geometric symmetry during overall scaling and deformation, resulting in more stable wavefront parameter tuning.

[0047] like Figure 1 and Figure 3 As shown, the resonant unit 22 includes an equivalent inductance metal sheet 221 and an equivalent capacitance metal ring 222. The equivalent inductance metal sheet 221 is a square-shaped metal sheet disposed on the second flexible dielectric substrate 21. The equivalent capacitance metal ring 222 is a ring-shaped metal sheet disposed on the equivalent inductance metal sheet 221, with a gap between them. The center of the ring of the equivalent capacitance metal ring 222 is located on the central axis of the equivalent inductance metal sheet 221. In this embodiment, the equivalent inductance metal sheet 221 and the equivalent capacitance metal ring 222 are disposed on the second flexible dielectric substrate 21 by an etching process, and the equivalent inductance metal sheet 221 and the equivalent capacitance metal ring 222 are connected by the dielectric material of the second flexible dielectric substrate 21. During operation, the equivalent inductance metal sheet 221 is equivalent to a square inductor, and the equivalent capacitance metal ring 222 is equivalent to a capacitor. A gap is formed between the equivalent inductance metal sheet 221 and the equivalent capacitance metal ring 222 to form a resonant cavity. The resonant frequency of the resonant unit 22 can be controlled by adjusting the gap width between the equivalent inductance metal sheet 221 and the equivalent capacitance metal ring 222. In addition, the equivalent inductance metal sheet 221 and the equivalent inductance metal ring 222 form resonant peaks when they are working, so that the resonant unit 22 forms a double resonant peak, which makes the resonant ring structure have a wider operating frequency band.

[0048] like Figure 1 and Figure 5 As shown, the stress buffer layer 4 includes a central elastic portion 41 and several outer elastic portions 42, both made of polydimethylsiloxane. The central elastic portion 41 is located at the very center of the stress buffer layer 4 and has a circular structure. The outer elastic portions 42 have an annular structure, and all the outer elastic portions 42 are arranged sequentially outward from the central elastic portion 41. The spacing between the outer and inner rings of each outer elastic portion 42 is equal to the radius of the central elastic portion 41. This design results in a gradient change in the elastic modulus of the stress buffer layer 4 from the center outward, enhancing the buffering effect of the stress buffer layer 4.

[0049] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. For those skilled in the art, the present invention can have various modifications, combinations, and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of the claims of the present invention.

Claims

1. A multi-band tunable flexible terahertz lens based on sandwich metaunits, characterized in that: It includes a low-frequency resonant layer, a mid-frequency resonant layer, a high-frequency resonant layer, and a stress buffer layer, with the low-frequency resonant layer, mid-frequency resonant layer, and high-frequency resonant layer arranged sequentially along a straight line; The low-frequency resonant layer includes a first flexible dielectric substrate and several metal units. The metal units are square metal sheets, and the several metal units are arranged periodically on the first flexible dielectric substrate. The intermediate frequency resonant layer includes a second flexible dielectric substrate and a resonant ring structure. The resonant ring structure is disposed on the second flexible dielectric substrate and is a ring structure surrounding the center of the second flexible dielectric substrate. The high-frequency resonant layer includes a third flexible dielectric substrate and several geometric phase-shifting units. The geometric phase-shifting units are swastika-shaped metal sheets, and the several geometric phase-shifting units are arranged on the third flexible dielectric substrate in a rotationally symmetric broken manner. A stress buffer layer connects the low-frequency resonant layer and the mid-frequency resonant layer, as well as the mid-frequency resonant layer and the high-frequency resonant layer. The elastic modulus of the stress buffer layer changes gradient from the center to the periphery. The resonant ring structure includes several resonant units, which are arranged around the center of the second flexible dielectric substrate. Each resonant unit includes a metal sheet with an equivalent inductance metal sheet and an equivalent capacitance metal ring. The equivalent inductance metal sheet has a square structure and is disposed on the second flexible dielectric substrate. The equivalent capacitance metal ring has a ring-shaped structure and is disposed on the equivalent inductance metal sheet. A gap is formed between the equivalent capacitance metal ring and the equivalent inductance metal sheet, and the center of the ring is located on the central axis of the equivalent inductance metal sheet. The stress buffer layer includes several elastic parts, which are nested sequentially from the center of the stress buffer layer outwards. The elastic part at the very center is called the central elastic part, which has a circular structure. The remaining elastic parts are called the outer elastic parts, which have a ring structure. All the outer elastic parts are arranged in a ring-shaped manner, with the central elastic part as the center, and are stacked and wrapped outwards in sequence.

2. The multi-band tunable flexible terahertz lens based on sandwich metaunits as described in claim 1, characterized in that: The metal units closer to the center of the first flexible dielectric substrate are larger, so that the spacing between two adjacent metal units closer to the center of the first flexible dielectric substrate is smaller.

3. A multi-band tunable flexible terahertz lens based on a sandwich metaunit as described in claim 1 or 2, characterized in that: The metal unit is made of a mesh woven from nano-metal wires.

4. The multi-band tunable flexible terahertz lens based on a sandwich metaunit as described in claim 1, characterized in that: The distance between the outer ring and the inner ring of each outer elastic part and the radius of the central elastic part are equal.

5. A multi-band tunable flexible terahertz lens based on a sandwich metaunit as described in claim 1 or 4, characterized in that: The stress buffer layer is made of polydimethylsiloxane material.

6. The multi-band tunable flexible terahertz lens based on a sandwich metaunit as described in claim 1, characterized in that: The low-frequency resonant layer operates in the range of 0.5THz to 1.2THz, the mid-frequency resonant layer operates in the range of 1.3THz to 2.1THz, and the high-frequency resonant layer operates in the range of 2.3THz to 3THz.

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