A tunable artificial surface plasmonic transmission line with interdigital structure

Abstract

The application discloses a kind of freely tunable artificial surface plasmon transmission line structure and application.The designed transmission line adopts interdigital H-shaped artificial surface plasmon structure, mainly including three parts of coplanar waveguide structure part, transition structure part and SSPP part, wherein coplanar waveguide section is used to connect with plane microwave structure, transition structure and SSPP section are respectively composed of SSPP unit with different parameters, mode conversion and signal transmission are realized.SSPP unit is provided with interdigital structure in recess, not only can further reduce structure size, but also can control dispersion cut-off frequency.Each unit in SSPP section is coupled in series connection through interdigital structure, the size of interdigital structure can control low-frequency cut-off frequency.Therefore, the interdigital structure at different positions can realize the free tuning of high frequency and low frequency of transmission line.The structure of the application has the characteristics of miniaturization, flexible ultra-thin and high flexibility, and has potential application prospect in ultra-small high-speed communication system.

Description

Technical Field

[0001] This invention belongs to the field of microwave transmission lines, specifically a tunable artificial surface plasmon transmission line with an interdigitated structure, used for high-frequency signal transmission between a chip and a motherboard on-board transmission line structure. Background Technology

[0002] With the full commercialization of 5G communication, communication speeds have increased to centimeter-wave and even millimeter-wave bands. Therefore, transmission lines connecting chips and motherboards need to meet application requirements such as small size, ultra-thin design, high frequency, low loss, and high isolation. Furthermore, with the trend towards high power, miniaturization, and high integration in electronic devices, electromagnetic interference problems caused by high component density or high operating frequencies are becoming increasingly serious. Traditional structures such as microstrip lines and coplanar waveguides cannot be directly applied to high-frequency circuits due to severe transmission loss and crosstalk. Therefore, there is an urgent need to design a novel transmission line structure that can operate at high frequencies.

[0003] Surface plasmon polaritons (SPPs) are electromagnetic waves that propagate along the interface between metals and dielectrics. Their electric field decays exponentially in the direction perpendicular to the conductor surface, leading to their widespread application in miniaturized photonics, high-sensitivity biomedical sensors, and chemical sensing. Artificial surface plasmon polaritons (SSPPs) are artificial periodic array structures that can simulate the physical characteristics of natural SPPs in the optical or infrared bands at microwave, millimeter-wave, and terahertz frequencies. They offer advantages such as controllable dispersion characteristics, tunable cutoff frequency, strong surface wave confinement, and long-distance propagation in ultrathin and flexible materials. However, SSPPs exist as TM modes, requiring mode conversion for integration with existing microwave circuits. Existing transition structures are complex and difficult to fabricate. Furthermore, the dispersion characteristics of SSPP structures are closely related to their size; the unit structure parameters can only be adjusted by regulating the high cutoff frequency of the transmission line through the dispersion frequency, limiting the flexibility of independently controlling the upper and lower cutoff frequencies and thus restricting their application prospects in the microwave and millimeter-wave fields. Summary of the Invention

[0004] To address the shortcomings of the aforementioned background technology and existing methods, this invention designs a tunable artificial surface plasmon transmission line with an interdigitated structure and analyzes the dispersion and transmission characteristics of this structure. The structure has controllable dispersion characteristics and the ability to flexibly adjust the upper and lower cutoff frequencies, thus solving the signal integrity problem of high-frequency on-board transmission lines.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] The tunable SSPP transmission line with an interdigitated structure of the present invention includes a lower flexible dielectric substrate layer and an upper metal conductor layer; the upper metal conductor layer includes a coplanar waveguide structure portion, a transition structure portion, an SSPP structure portion, a transition portion, and a coplanar waveguide structure portion arranged along the x-direction;

[0007] The transition structure consists of five first-class SSPP units, namely the first unit, the second unit, the third unit, the fourth unit, and the fifth unit;

[0008] The first type of SSPP unit includes a first ground line on both sides and a first center signal line, and two first rectangular grooves are etched on the upper and lower sides of the first center signal line.

[0009] The SSPP structure includes five second-type SSPP units, and each pair of second-type SSPP units is coupled and connected by a five-level interdigitated structure.

[0010] The second type of SSPP unit includes a second ground line on both sides and a second center signal line. Two second rectangular grooves are etched on the upper and lower sides of the second center signal line, and a four-level interdigitated structure is provided in the second rectangular groove.

[0011] Furthermore, the coplanar waveguide structure is symmetrical along the x-axis with a length of L1 = 0.5 mm. The widths of the first and second center signal lines are both H = 0.92 mm. The widths of the first and second ground lines are both w = 1 mm. The gaps between the first ground line and the first center signal line, and between the second ground line and the second center signal line, are both g = 0.085 mm.

[0012] Furthermore, the transition structure is composed of five first-class SSPP units connected in series. The depths of the first rectangular grooves of the first unit, the second unit, the third unit, the fourth unit, and the fifth unit are h1 = 0.08 mm, h2 = 0.16 mm, h3 = 0.24 mm, h4 = 0.32 mm, and h5 = 0.40 mm, respectively.

[0013] Furthermore, the length of the first type of SSPP unit in the transition structure portion is a = 3 mm, the widths of the first center signal line and the first ground line are H = 0.92 mm and w = 1 mm, respectively, the depth and width of the first rectangular groove are h = 2 mm and w2 = 2 mm, respectively, and the first rectangular groove is symmetrical along the x-axis.

[0014] Furthermore, the SSPP structure includes five cascaded second-type SSPP units, which are coupled together by a five-level cross structure. The five-level cross structure has a length of lis1 and a width of w. is1=1.532mm, gap is g is1 =0.035mm, and the range of lis1 is 1.5mm to 2.9mm.

[0015] Furthermore, the second type of SSPP unit has a length of a = 3 mm, a height of the second center signal line of H = 0.92 mm, and a second rectangular groove etched symmetrically along the x-axis on the second center signal line. The depth of the second rectangular groove is sh = 0.4 mm, and a four-level cross structure is provided within the second rectangular groove. The length of the four-level cross structure is lis2, and the width is w. is2 =0.05mm, gap is g is2 =0.05mm, and the range of lis2 is 0 to 1.95mm.

[0016] Furthermore, the lower flexible dielectric substrate layer is made of polyimide with a dielectric constant of 3.5, and the upper metal conductor layer is made of copper.

[0017] The beneficial effects of this invention are:

[0018] The transmission line structure adopts a coplanar double conductor structure, which can be directly connected to a planar microwave circuit. Furthermore, while maintaining the original dispersion characteristics, the double conductor structure enhances the ability to confine the surface electromagnetic field, effectively simplifying the design of the transition structure for exciting the SSPP.

[0019] The transmission line structure can adjust its dispersion characteristics by changing the SSPP unit structure parameters, such as unit length a, rectangular groove depth h, and groove width w2. The interdigitated structure in the groove can further adjust the dispersion characteristics without increasing the linewidth, thereby achieving flexible control of the high cutoff frequency of the transmission line and miniaturization of the transmission line structure.

[0020] In the described transmission line structure, each pair of adjacent SSPP units is coupled together via an interdigital structure. The length, number of stages, and spacing of the interdigital structure can adjust the low cutoff frequency of the transmission line. Therefore, the upper and lower cutoff frequencies of the transmission line can be independently adjusted by the interdigital structures at different locations, allowing the transmission line to be flexibly applied in microwave and millimeter-wave equipment.

[0021] The transmission line uses copper and polyimide materials, which have advantages such as small size, simple structure, low manufacturing cost and high mechanical reliability. It can be used for the transmission of high frequency signals in terminal equipment and has good signal integrity. Attached Figure Description

[0022] Figure 1 This is a three-dimensional structural schematic diagram of the artificial surface plasmon transmission line used in this invention.

[0023] Figure 2This is a top view schematic diagram of the artificial surface plasmon transmission line used in this invention.

[0024] Figure 3 This is a dispersion curve diagram of the artificial surface plasmon transmission line used in this invention.

[0025] Figure 4 The S values ​​of the artificial surface plasmon transmission line used in this invention under different LIS2 values ​​are... 11 Line graph.

[0026] Figure 5 The S values ​​of the artificial surface plasmon transmission line used in this invention under different LIS2 values ​​are... 21 Line graph.

[0027] Figure 6 The S of the artificial surface plasmon transmission line used in this invention under different lis1 values. 11 Line graph.

[0028] Figure 7 The S of the artificial surface plasmon transmission line used in this invention under different lis1 values. 21 Line graph.

[0029] Explanation of main component symbols

[0030] Lower flexible dielectric substrate 1

[0031] Upper metal conductor layer 2

[0032] Coplanar waveguide structure part 3

[0033] Transition structure part 4

[0034] SSPP structural part 5

[0035] Type 1 artificial surface plasmon units 6

[0036] First ground line 7

[0037] First center signal line 8

[0038] First rectangular groove 9

[0039] Type II artificial surface plasmon units 10

[0040] Five-level interdigital structure 11

[0041] Second ground wire 12

[0042] Second center signal line 13

[0043] Second rectangular groove 14

[0044] Four-level interdigital structure 15 Detailed Implementation

[0045] The invention will now be further described with reference to the accompanying drawings.

[0046] One embodiment of the present invention provides a tunable artificial surface plasmon transmission line with an interdigitated structure, which can be applied to the transmission of onboard high-frequency signals. Please refer to [link to relevant documentation]. Figure 1 The tunable artificial surface plasmon transmission line (SSPP transmission line) with interdigitated structure includes a lower flexible dielectric substrate layer 1 and an upper metallic conductor layer 2.

[0047] Please see Figure 2 The upper metal conductor layer 2 includes a coplanar waveguide structure portion 3, a transition structure portion 4, an SSPP structure portion 5, and the coplanar waveguide structure portion 3 arranged along the x-direction. The coplanar waveguide structure portion 3 is used for direct connection with a planar microwave circuit.

[0048] The transition structure portion 4 consists of five Type I artificial surface plasmon resonance (ASPR) units 6, namely, unit 1, unit 2, unit 3, unit 4, and unit 5. Each of these five ASPR units 6 includes a first ground line 7 and a first center signal line 8 located on both sides. Two first rectangular grooves 9 are etched on the upper and lower sides of the first center signal line 8, respectively. The first rectangular grooves 9 are symmetrical along the x-axis. The depths of the first rectangular grooves 9 in the first to fifth units are h1 = 0.08 mm, h2 = 0.16 mm, h3 = 0.24 mm, h4 = 0.32 mm, and h5 = 0.40 mm, respectively. Except for the depth of the first rectangular grooves 9, all other parameters are consistent between the first to fifth units. The transition structure portion 4 is for completing mode switching and momentum matching.

[0049] The second type of artificial surface plasmon unit 10 includes a second ground line 12 and a second central signal line 13 located on both sides. Two second rectangular grooves 14 are etched on the upper and lower sides of the second central signal line 13. The depth of the second rectangular groove 14 is sh = 0.4 mm, the width is w2 = 2 mm, and they are symmetrically distributed along the x-axis. A four-level interdigitated structure 15 is disposed within the second rectangular groove 14. The length of the four-level interdigitated structure 15 is lis2, and the width is w. is2 =0.05mm, gap is g is2 =0.05mm.

[0050] The length lis2 of the four-level interdigitated structure 15 ranges from 0 to 1.95 mm. For example... Figure 3As shown, by changing the length (finger length) lis2 of the four-stage interdigitated structure 15, ranging from 0 to 1.95 mm, the cutoff frequency of the SSPP dispersion curve is reduced from 24.8 GHz to 8.1 GHz, thus enhancing the electric field confinement capability.

[0051] like Figure 4 and Figure 5 As shown, when the length lis2 of the four-stage interdigitated structure 15 gradually decreases from 1.95 mm to 1 mm, the transmission line S 11 The high cutoff frequency of <-10dB has been increased from 7.69GHz to 10GHz, S 21 The high cutoff frequency (>-3dB) is increased from 7.01GHz to 9.81GHz, while the low cutoff frequency remains essentially unchanged. Therefore, the length lis2 of the four-stage interdigitated structure 15 can be independently adjusted to adjust the high cutoff frequency.

[0052] The artificial surface plasmon structure 5 comprises five identical second-type artificial surface plasmon units 10, with each pair of second-type artificial surface plasmon units 10 coupled together by a five-level interdigitated structure 11. The five-level interdigitated structure 11 has a length of lis1, ranging from 1.5mm to 2.9mm, and a spacing of g. is1 =0.035mm, width is w is1 =0.152mm.

[0053] The length lis1 of the five-level interdigital structure 11 ranges from 1.5mm to 2.9mm. For example... Figure 6 and Figure 7 As shown, by changing the length (finger length) lis1 of the five-stage interdigitated structure 11 from 1.5mm to 2.9mm, the transmission line S 11 The low cutoff frequency was reduced from 5.9 GHz to approximately 4.8 GHz, S 21 The low cutoff frequency decreases by >3dB from 5.8GHz to 4.7GHz, while the high cutoff frequency changes only slightly. Therefore, the length lis1 of the five-stage interdigitated structure 11 can be independently adjusted to adjust the low cutoff frequency. Figures 4 to 7 This demonstrates that the upper and lower cutoff frequencies of the tunable artificial surface plasmon transmission line with an interdigitated structure can be independently adjusted, providing great flexibility and making it applicable to miniaturized microwave equipment.

[0054] The material of the lower flexible dielectric substrate layer 1 may include at least one of polyimide, liquid crystal polymer, polytetrafluoroethylene, and polyphenylene sulfide. The material of the upper metal conductor layer 2 may include at least one of copper, silver, and aluminum. In this embodiment, the lower flexible dielectric substrate layer 1 is made of polyimide with a dielectric constant of 3.5 and a thickness of 0.05 mm, and the upper metal conductor layer 2 is made of copper with a thickness of 0.018 mm, thus the transmission line has the characteristics of flexibility and ultrathinness.

[0055] The artificial surface plasmon structure of the present invention is simple in design and small in size, with controllable dispersion characteristics and adjustable upper and lower frequencies, and has good transmission characteristics in the broadband range.

[0056] The above description is merely a preferred embodiment of the present invention and should not be construed as limiting the present invention. Therefore, any equivalent variations made in accordance with the present invention are still within the scope of the present invention.

Claims

1. A tunable artificial surface plasmon transmission line employing an interdigitated structure, characterized in that: A lower flexible dielectric substrate layer and an upper metallic conductor layer; The upper metal conductor layer includes a coplanar waveguide structure portion, a transition structure portion, an artificial surface plasmon structure portion, a transition structure portion, and a coplanar waveguide structure portion arranged along the x-direction; Both transition structures consist of five type-1 artificial surface plasmon units, namely the first unit, the second unit, the third unit, the fourth unit, and the fifth unit; Each type I artificial surface plasmon unit includes a first ground line and a first center signal line located on both sides, and two first rectangular grooves are etched on the upper and lower sides of the first center signal line. The artificial surface plasmon structure includes five type II artificial surface plasmon units, and each pair of type II artificial surface plasmons is coupled and connected by a five-level interdigitated structure. Each type II artificial surface plasmon unit includes a second ground line and a second central signal line located on both sides. Two second rectangular grooves are etched on the upper and lower sides of the second central signal line, and a four-level interdigitated structure is provided in the second rectangular groove.

2. The tunable artificial surface plasmon transmission line with an interdigitated structure according to claim 1, characterized in that, The coplanar waveguide structure is symmetrical along the x-axis and has a length of L1. The width of the first center signal line and the width of the second center signal line are both H. The width of the first ground line and the width of the second ground line are both w. The gap between the first ground line and the first center signal line and the gap between the second ground line and the second center signal line are both g. Wherein, L1=0.5mm, H=0.92mm, w=1mm, and g=0.085mm.

3. The tunable artificial surface plasmon transmission line with an interdigitated structure according to claim 1, characterized in that, The transition structure is composed of five first-type artificial surface plasmon units connected in series. The depths of the first rectangular grooves located in the first unit, the second unit, the third unit, the fourth unit, and the fifth unit are h1, h2, h3, h4, and h5, respectively, where h1 = 0.08 mm, h2 = 0.16 mm, h3 = 0.24 mm, h4 = 0.32 mm, and h5 = 0.40 mm.

4. The tunable artificial surface plasmon transmission line with an interdigitated structure according to claim 1, characterized in that, The length of each first type of artificial surface plasmon unit is a, the width of the first central signal line and the width of the first ground line are H and w, respectively, the depth and width of the first rectangular groove are h and w2, respectively, and the first rectangular groove is symmetrical along the x-axis, where a=3mm, H=0.92mm, w=1mm, h=2mm, and w2=2mm.

5. The tunable artificial surface plasmon transmission line with an interdigitated structure according to claim 1, characterized in that, The artificial surface plasmon structure comprises five cascaded Type II artificial surface plasmon units. Two cascaded Type II artificial surface plasmon units are coupled together via a five-level cross-connection structure. The length of the five-level cross-connection structure is lis1, and the width is w. is1 The gap is g is1 Among them, lis1 ranges from 1.5mm to 2.9mm, w is1 =1.532mm, g is1 =0.035mm.

6. The tunable artificial surface plasmon transmission line with an interdigitated structure according to claim 1, characterized in that, The length of the second type of artificial surface plasmon unit is *a*, the height of the second central signal line is *H*, the second central signal line is etched with two second rectangular grooves symmetrical along the x-axis, the depth of the second rectangular grooves is *sh*, and the length of the four-level cross structure disposed within the second rectangular grooves is *lis2*, and the width is *w*. is2 The gap is g is2 Where a = 3 mm, H = 0.92 mm, sh = 0.4 mm, lis2 ranges from 0 to 1.95 mm, w is2 =0.05mm, g is2 =0.05mm.

7. The tunable artificial surface plasmon transmission line with an interdigitated structure according to claim 1, characterized in that, The material of the lower flexible dielectric substrate layer includes at least one of polyimide, liquid crystal polymer, polytetrafluoroethylene, and polyphenylene sulfide.

8. The tunable artificial surface plasmon transmission line with an interdigitated structure according to claim 7, characterized in that, The material of the lower flexible dielectric substrate is polyimide with a dielectric constant of 3.

5.

9. The tunable artificial surface plasmon transmission line with an interdigitated structure according to claim 1, characterized in that, The material of the upper metal conductor layer includes at least one of copper, silver, and aluminum.

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