Multi-band tunable flexible terahertz lens based on sandwich metamaterial unit

Abstract

The invention relates to a multi-band tunable flexible terahertz lens based on a sandwich metamaterial unit. The multi-band tunable flexible terahertz lens comprises a low-frequency resonance layer, an intermediate-frequency resonance layer, a high-frequency resonance layer and a stress buffer layer, the low-frequency resonance layer comprises a first flexible dielectric plate and a plurality of metal units, each metal unit is a metal sheet of a square structure, and the metal units are periodically arranged on the first flexible dielectric plate; the intermediate-frequency resonance layer comprises a second flexible dielectric plate and a resonance ring structure, the resonance ring structure is arranged on the second flexible dielectric plate, and the resonance ring structure is of an annular structure; the high-frequency resonance layer comprises a third flexible dielectric plate and a plurality of geometric phase shift units, the geometric phase shift units are swastika-shaped metal sheets, and the plurality of geometric phase shift units are arranged on the third flexible dielectric plate in a rotationally symmetrical breaking manner; the low-frequency resonance layers and the intermediate-frequency resonance layers are connected through stress buffer layers, the intermediate-frequency resonance layers and the high-frequency resonance layers are connected through stress buffer layers, and the elasticity modulus of the stress buffer layers is in gradient change from the center to the periphery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of terahertz lenses, in particular to a multi-band tunable flexible terahertz lens based on sandwich supercell units. BACKGROUND

[0002] The existing terahertz lens is mostly a resonant layer designed with a static super surface, the resonant layer includes a dielectric plate and a resonant structure arranged on the dielectric plate, and the resonant structure adopts a metal open loop array or a cross-shaped structure to realize phase modulation of a single frequency band.

[0003] In order to realize that the terahertz lens can support a wider working frequency band, such as the Chinese invention patent application with the publication number CN112909569A and the name of "a three-layer circular inner and outer double-resonance cavity wideband terahertz wave super surface absorber", the patent scheme adopts a three-layer metal dielectric layer stack, the three-layer metal dielectric adopts the same resonant structure, and the resonant structure of the three-layer metal dielectric is sequentially scaled by a multiple from top to bottom, so as to realize that the terahertz lens has a wider working frequency band; but the tuning mode of the terahertz lens of the patent scheme is single, the electromagnetic coupling mechanism is fixed, it is difficult to meet the use demand of independent tuning of multiple frequency bands, and it is not suitable for use in a demand deformation scene.

[0004] In order to realize that the terahertz lens has a deformation ability, such as the Chinese invention patent with the publication number CN112305645B and the name of "a super surface lens", the patent scheme includes a flexible substrate and a light antenna array, the light antenna array is arranged on the flexible substrate, the patent scheme makes the terahertz lens have a deformation ability through the flexible substrate; but the patent scheme is only applicable to the design of a single resonant layer, and the working frequency band range is narrow; if a multi-layer structure design of a multi-layer resonant layer is directly adopted, when bending or stretching, stress concentration will be caused between the resonant layers due to the difference in Young's modulus, causing geometric distortion of the resonant structure, interlayer coupling mismatch and phase response deviation, resulting in instability of multi-band response and phase modulation failure.

[0005] Therefore, the existing terahertz lens cannot simultaneously meet the use demand of having a wider working frequency band, independent tuning of multiple frequency bands, and deformation adaptive ability of wavefront parameter regulation, which seriously limits the application of the terahertz lens in the fields of terahertz adaptive imaging systems, curved conformal communication antennas, biological tissue nondestructive testing equipment, dynamic wearable devices, non-planar imaging systems and the like. SUMMARY

[0006] The purpose of the present application is to provide a multi-band tunable flexible terahertz lens based on sandwich supercell units, which has a wider working frequency band, can independently tune the terahertz waves of multiple frequency bands, and has deformation adaptive ability of wavefront parameter regulation.

[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] The stress buffer layer can absorb the non-uniform stress generated in the deformation process of the terahertz lens and avoid causing stress concentration, so that the deformation of the low-frequency resonance layer, the medium-frequency resonance layer and the high-frequency resonance layer is a symmetrical controllable deformation; and the design of the periodic arrangement of the metal units of the low-frequency resonance layer, the annular structure of the resonance ring structure of the medium-frequency resonance layer arranged around the center of the second flexible dielectric plate, and the rotational symmetrical broken arrangement of the geometric phase shift units of the high-frequency resonance layer makes the arrangement of the metal units of the low-frequency resonance layer in the deformation process be periodically and uniformly scaled, makes the opening angle of the resonance ring structure of the medium-frequency resonance layer in the deformation process be linearly transformed, and makes the resonance ring structure in the deformation process be uniformly scaled, and makes the geometric phase shift units of the high-frequency resonance layer be translationally scaled and the rotational angle spatial distribution be unchanged, so as to realize that the resonance structures of the low-frequency resonance layer, the medium-frequency resonance layer and the high-frequency resonance layer maintain geometric symmetry and stable resonance mode in mechanical deformation, and avoid structural misplacement and electromagnetic instability of the terahertz lens in the deformation process.

[0015] Through the above design, the terahertz lens can simultaneously meet the use requirements of having a relatively wide working frequency band, independent tuning of multiple frequency bands, and deformation adaptive ability of wavefront parameter control, and is suitable for fields such as a terahertz adaptive imaging system, a curved conformal communication antenna, a biological tissue nondestructive testing device, a dynamic wearable device, and a non-planar imaging system.

[0016] Further, the closer to the center of the first flexible dielectric plate, the larger the size of the metal unit, so that the closer to the center of the first flexible dielectric plate, the smaller the distance between the two adjacent metal units.

[0017] Further, the metal unit of the sandwich supercell-based multi-band tunable flexible terahertz lens is made of a nanometer metal wire woven grid.

[0018] Further, the resonance ring structure of the sandwich supercell-based multi-band tunable flexible terahertz lens includes a plurality of resonance units, and the plurality of resonance units are arranged on the second flexible dielectric plate around the center of the second flexible dielectric plate.

[0019] Further, the sandwich supercell-based multi-band tunable flexible terahertz lens has the advantages that the resonant unit comprises an equivalent inductive metal sheet and an equivalent capacitive metal ring, the equivalent inductive metal sheet is a square structure metal sheet, the equivalent inductive metal sheet is arranged on the second flexible dielectric plate, the equivalent capacitive metal ring is a ring structure metal sheet, the equivalent capacitive metal ring is arranged on the equivalent inductive metal sheet, a gap is formed between the equivalent capacitive metal ring and the equivalent inductive metal sheet, and the center of the circular ring of the equivalent capacitive metal ring is on the central axis of the equivalent inductive metal sheet.

[0020] Further, the sandwich supercell-based multi-band tunable flexible terahertz lens has the advantages that the stress buffer layer comprises a plurality of elastic parts, and the plurality of elastic parts are sequentially nested around the center of the stress buffer layer.

[0021] Further, the sandwich supercell-based multi-band tunable flexible terahertz lens has the advantages that the stress buffer layer comprises a plurality of elastic parts, and the plurality of elastic parts are sequentially nested around the center of the stress buffer layer.

[0022] Further, the sandwich supercell-based multi-band tunable flexible terahertz lens has the advantages that the stress buffer layer comprises a plurality of elastic parts, and the plurality of elastic parts are sequentially nested around the center of the stress buffer layer.

[0023] Further, the sandwich supercell-based multi-band tunable flexible terahertz lens has the advantages that the stress buffer layer comprises a plurality of elastic parts, and the plurality of elastic parts are sequentially nested around the center of the stress buffer layer.

[0024] Further, the sandwich supercell-based multi-band tunable flexible terahertz lens has the advantages that the stress buffer layer comprises a plurality of elastic parts, and the plurality of elastic parts are sequentially nested around the center of the stress buffer layer.

[0025] The sandwich supercell-based multi-band tunable flexible terahertz lens has the advantages that the working frequency band is wide, the terahertz waves of multiple frequency bands can be independently tuned, and the wavefront parameter regulation has a deformation self-adaptive capability. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 It is a perspective structural view of an embodiment;

[0027] Figure 2 It is a structural schematic view of a low-frequency resonant layer of an embodiment;

[0028] Figure 3This is a schematic diagram of the structure of the intermediate frequency resonant layer in the 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 is arranged between the low-frequency resonance layer 1 and the medium-frequency resonance layer 2 and between the medium-frequency resonance layer 2 and the high-frequency resonance layer 3 (see FIG. 2). Figure 1 Only the stress buffer layer between the medium-frequency resonance layer and the high-frequency resonance layer is shown, and the stress buffer layer between the low-frequency resonance layer and the medium-frequency resonance 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 resonance layer 1, the medium-frequency resonance layer 2, the high-frequency resonance layer 3, and the stress buffer layer 4 are on the same straight line.

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

[0041] The low-frequency resonance layer 1 excites low-frequency localized plasmon resonance through a plurality of metal units 12 arranged periodically, thereby realizing independent tuning of terahertz waves in the low-frequency band. The medium-frequency resonance layer 2 forms a resonance cavity through a resonant ring structure, thereby realizing independent tuning of terahertz waves in the medium-frequency band. The high-frequency resonance layer 3 arranges a plurality of geometric phase shift units 32 in a rotationally symmetric broken manner to generate geometric phase, realize left / right circularly polarized light conversion, and adjust the topological charge number of the vortex phase, thereby realizing independent tuning of terahertz waves in the high-frequency band. The design of the multi-layer resonance layer composed of the low-frequency resonance layer 1, the medium-frequency resonance layer 2, and the high-frequency resonance layer 3 makes the terahertz lens have a wider working frequency band. At the same time, the low-frequency resonance layer 1, the medium-frequency resonance layer 2, and the high-frequency resonance layer 3 use different resonance structures, so that the terahertz lens can independently tune terahertz waves in three frequency bands, and the adjustment of the wavefront parameters of each frequency band is more flexible.

[0042] The stress buffer layer 4 is connected between the low-frequency resonant layer 1 and the medium-frequency resonant layer 2 and between the medium-frequency resonant layer 2 and the high-frequency resonant layer 3, and the elastic modulus of the stress buffer layer 4 changes in a gradient from the center to the periphery, so that the stress buffer layer 4 can absorb the non-uniform stress generated in the deformation process of the terahertz lens and avoid causing stress concentration, and the deformation of the low-frequency resonant layer 1, the medium-frequency resonant layer 2 and the high-frequency resonant layer 3 is symmetrical and controllable. In addition, the low-frequency resonant layer 1 is arranged in a periodic arrangement mode, the resonant ring structure of the medium-frequency resonant layer 2 is arranged in a ring structure around the center of the second flexible dielectric plate 21, and the geometric phase shift units 32 of the high-frequency resonant layer 3 are arranged in a rotationally symmetrical broken arrangement mode, so that the arrangement of the metal units 12 of the low-frequency resonant layer 1 is periodically and uniformly scaled in the deformation, the opening angle of the resonant ring structure of the medium-frequency resonant layer 2 is linearly transformed in the deformation, and the resonant ring structure is uniformly scaled in the deformation, and the geometric phase shift units 32 of the high-frequency resonant layer 3 are translationally scaled and the rotation angle spatial distribution is unchanged, so that the resonant structures of the low-frequency resonant layer 1, the medium-frequency resonant layer 2 and the high-frequency resonant layer 3 maintain geometric symmetry and stable resonant mode in mechanical deformation, and structural misplacement and electromagnetic instability of the terahertz lens in deformation are avoided.

[0043] Through the above design, the terahertz lens can meet the use requirements of having a wide working frequency band, independent tuning of multiple frequency bands and deformation self-adaptive ability of wavefront parameter adjustment, and is suitable for fields such as terahertz adaptive imaging systems, curved conformal communication antennas, biological tissue nondestructive testing equipment, dynamic wearable devices and non-planar imaging systems.

[0044] As shown in Figure 1 and Figure 2 , the size of the metal unit 12 closer to the center of the first flexible dielectric plate 11 is larger, and the spacing between two adjacent metal units 12 closer to the center of the first flexible dielectric plate 11 is smaller. Through such a design, the low-frequency resonant layer 1 has a wider working frequency band and better focusing efficiency.

[0045] In this embodiment, the metal unit 12 is made of a nanosilver wire woven grid. Through such a design, the metal unit 12 has strong broadband reflection capability.

[0046] As shown in Figure 1 and Figure 3 , the resonant ring structure includes a plurality of resonant units 22, and the plurality of resonant units 22 are arranged on the second flexible dielectric plate 21 around the center of the second flexible dielectric plate 21. The ring structure is composed of a plurality of resonant units 22, so that the resonant ring structure can maintain better geometric symmetry when uniformly scaled in the deformation, and the wavefront parameter tuning is more stable.

[0047] As shown in Figure 1 and Figure 3 , the resonant unit 22 comprises an equivalent inductive metal sheet 221 and an equivalent capacitive metal ring 222; the equivalent inductive metal sheet 221 is a square structure metal sheet, and the equivalent inductive metal sheet 221 is arranged on the second flexible dielectric plate 21; the equivalent capacitive metal ring 222 is a ring structure metal sheet, and the equivalent capacitive metal ring 222 is arranged on the equivalent inductive metal sheet 221, and a gap is formed between the equivalent capacitive metal ring 222 and the equivalent inductive metal sheet 221, and the center of the circular ring of the equivalent capacitive metal ring 222 is on the central axis of the equivalent inductive metal sheet 221. In the embodiment, the equivalent inductive metal sheet 221 and the equivalent capacitive metal ring 222 are arranged on the second flexible dielectric plate 21 through an etching process, and the equivalent inductive metal sheet 221 and the equivalent capacitive metal ring 222 are connected through the dielectric material of the second flexible dielectric plate 21. In operation, the equivalent inductive metal sheet 221 is equivalent to a square inductor, and the equivalent capacitive metal ring 222 is equivalent to a capacitor, and a gap is formed between the equivalent inductive metal sheet 221 and the equivalent capacitive metal ring 222 to form a resonant cavity, and the resonant frequency of the resonant unit 22 is controlled by adjusting the gap width between the equivalent inductive metal sheet 221 and the equivalent capacitive metal ring 222; in addition, the equivalent inductive metal sheet 221 and the equivalent inductive metal sheet 221 form a resonant edge in operation, respectively, so that the resonant unit 22 forms a double resonant edge, so that the resonant ring structure has a wider working frequency band.

[0048] As shown in Figure 1 and Figure 5 , the stress buffer layer 4 comprises a central elastic part 41 and a plurality of outer elastic parts 42, and the central elastic part 41 and the outer elastic part 42 are both made of polydimethylsiloxane material; the central elastic part 41 is located at the centermost position of the stress buffer layer 4, and the central elastic part 41 is a circular structure; the outer elastic part 42 is a ring structure, and all the outer elastic parts 42 are sequentially wrapped and laid out outward from the central elastic part 41 as the center; the distance between the outer ring and the inner ring of each outer elastic part 42 is equal to the radius of the central elastic part 41. By such design, the elastic modulus of the stress buffer layer 4 changes from the center to the periphery in a gradient manner, thereby enhancing the buffering effect of the stress buffer layer 4.

[0049] The above only describes the preferred embodiments of the present application and is not used to limit the present application. For those skilled in the art, the present application can have various modifications, combinations and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the scope of the claims of the present application.

Claims

1. A multi-band tunable flexible terahertz lens based on a sandwich metaunit, 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 in a gradient from the center to the periphery.

2. The multi-band tunable flexible terahertz lens based on a sandwich metaunit 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 resonant ring structure includes several resonant units, which are arranged around the center of the second flexible dielectric plate.

5. A multi-band tunable flexible terahertz lens based on a sandwich metaunit as described in claim 4, characterized in that: The resonant unit includes a thin metal sheet comprising 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 is a thin metal sheet with a ring structure and is 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.

6. The multi-band tunable flexible terahertz lens based on a sandwich metaunit as described in claim 1, characterized in that: The stress buffer layer includes several elastic parts, which are nested sequentially from the center of the stress buffer layer outwards.

7. A multi-band tunable flexible terahertz lens based on a sandwich metaunit as described in claim 6, characterized in that: 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-shaped structure. All the outer elastic parts are arranged in a sequential manner, layered outward from the central elastic part.

8. A multi-band tunable flexible terahertz lens based on a sandwich metaunit as described in claim 7, 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.

9. A multi-band tunable flexible terahertz lens based on a sandwich metaunit as described in claim 1, 6, 7, or 8, characterized in that: The stress buffer layer is made of polydimethylsiloxane material.

10. A 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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