CN104253294B - A kind of artificial surface plasma field intensity booster - Google Patents

Abstract

The invention provides an artificial surface plasmon field strength enhancer, which includes a traditional coaxial waveguide, a transition waveguide from the coaxial waveguide to an artificial surface plasmon waveguide, and a conical plasma waveguide; wherein, the transition waveguide includes an inner conductor and an outer conductor transition, and the inner conductor The conductor transition is realized by a periodic annular groove array with increasing depth, and the outer conductor transition is realized by a horn antenna with gradually larger opening; the conical plasmonic waveguide is composed of an annular groove array with constant depth and width, decreasing radius, and periodic changes . The invention has a series of advantages such as simple structure, compact size, high-efficiency broadband, high field strength enhancement multiple, and is suitable for matching with traditional microwave or terahertz transmission circuits, and can be used in microwave or terahertz imaging, high-resolution medical Looking glass technology, biological detection, national security, food and agricultural product quality control, global environmental detection, and information and radar communication technology have been widely used.

Description

An Artificial Surface Plasmon Field Enhancer

technical field

The invention relates to a structure of a field strength enhancer, in particular to a structure of an artificial surface plasma field strength enhancer.

Background technique

In recent years, it has been proposed to dig holes or grooves in the metal surface to increase the penetration of electromagnetic fields in the metal, so that SPPs can be engineered at lower frequencies. Such surface plasmons whose plasma frequency is controlled by the surface geometry are called artificial surface plasmons (Spoof Surface Plasmon Polaritons, SSPPs for short). The basic idea is to dig periodically distributed holes on the metal surface. The size and interval of the holes are smaller than the wavelength to enhance the penetration of electromagnetic waves, thereby reducing the plasma frequency of the metal surface by means of an equivalent medium. In 2005, Hibbins et al. confirmed the phenomenon of SSPPs in the microwave range, and since then SSPPs have aroused great interest of researchers.

Generally speaking, metals are approximately ideal conductors in the low frequency band (microwave band), so SPPs cannot propagate on their surface. However, with periodically distributed holes, the surface can not only propagate SPPs, but also achieve sub-wavelength confinement of the field. , and the plasmonic frequency of the periodic subwavelength structure can be flexibly changed by changing the geometric size of the subwavelength structure. Smooth metal wires are currently considered to be one of the best terahertz waveguides. This guided wave has the advantages of low loss and low dispersion, but poor confinement. Therefore, Maier et al. extended the concept of SSPPs to the geometric configuration of metal wires, and theoretically proved that ring-shaped grooves periodically distributed along the length direction on an ideal wire can transmit SSPPs and achieve sub-wavelength confinement of the field. , so as to realize the local enhancement effect of microwave or terahertz wave, for periodic metal wire structure in microwave or terahertz imaging, high-resolution medical endoscopy technology, biological detection, national security, food and agricultural product quality control, global environment Applications in areas such as detection and information and radar communication technology have opened up broad prospects.

The conversion of spatially guided waves into SPPs has been extensively studied, such as via prism coupling or diffraction gratings. However, little research has been done on the conversion of guided waves to SSPPs. In 2013, Southeast University proposed a structure to realize the efficient conversion of guided waves to SSPPs in the microwave frequency band, which consists of traditional coplanar waveguipe (CPW for short) and "tooth-type" plasmonic waveguide (ultra-thin periodic Structural metal strips), and a matching transition zone with a gradual change in groove depth is designed between the two. The matching transition part realizes the wave vector matching and impedance matching of CPW and plasmonic waveguide. This structure realizes high-efficiency and wide-band conversion from guided wave to Spoof SPPs in the microwave segment, and is highly integrated for plasmonic functional devices and circuits in the microwave segment. Created a prospect of application. However, considering the difference between the ultra-thin "tooth-type" plasmonic waveguide and the metal wire-type plasmonic waveguide in the form of electromagnetic field transmission, the above scheme will no longer be applicable.

Contents of the invention

In order to achieve the above object, the technical solution of the present invention is achieved in that:

An artificial surface plasmon field strength enhancer is characterized in that: it comprises a traditional coaxial waveguide and a transition waveguide from the coaxial waveguide to the artificial surface plasmon waveguide, and a conical plasmon waveguide;

Among them, the transition waveguide includes an inner conductor transition and an outer conductor transition. The inner conductor transition is realized by a periodic annular groove array with constant period and width and increasing depth. The outer conductor transition is realized by a horn antenna with a gradually larger opening; the conical plasma The waveguide consists of a periodic ring groove array with constant period, depth and width and decreasing radius.

The present invention can adjust the structural size of the transitional waveguide and the conical plasmonic waveguide according to the type and size of the coaxial waveguide, so as to realize the conversion of the microwave or terahertz band space guided wave to SSPPs, and then achieve the field strength enhancement in the microwave or terahertz band effect, to achieve a wider application of artificial surface plasmon metamaterials.

The present invention has following beneficial effect:

1. The present invention mainly proposes an artificial surface plasmon field booster structure, including a traditional coaxial waveguide and a transitional waveguide from the coaxial waveguide to the artificial surface plasmon waveguide, and a conical plasmon waveguide structure. On the one hand, this structure draws on the design idea of coaxial waveguide to artificial surface plasmon waveguide transformation structure, and proposes to use the annular groove structure with increasing depth to realize the wavenumber matching between coaxial waveguide and artificial surface plasmon waveguide and the outer conductor adopts horn antenna gradient to achieve impedance matching between coaxial waveguide and artificial surface plasmon waveguide, so as to realize the efficient conversion of space guided wave to SSPPs. Shaped plasmonic waveguides are used to achieve high field focusing capabilities. This three-dimensional structure can realize high-efficiency input of signals and high focus of field strength, and has greater flexibility in the design of microwave devices and integrated circuit structures.

2. Strong innovation and good technical foresight: the invention realizes highly focused and efficient transmission of electromagnetic waves in the microwave or terahertz frequency band, with strong innovation, and no such structure has been seen at home and abroad; it can be well integrated with traditional microwave transmission lines Used together, the application range of the artificial surface plasmon device is expanded, and it has good technical foresight.

3. Large field strength enhancement coefficient: the present invention can finally realize the high focus of the terminal field strength of the artificial surface plasmon field strength enhancer. The field strength at the apex of the conical plasmonic structure can reach nearly 12 times the field strength at the incident port of the signal source, and can reach nearly 5 times the field strength at the end of the transition waveguide.

4. Wide range of applications: the present invention can be widely used in the fields of microwave or terahertz imaging, high-resolution medical endoscopy technology, biological detection, national security, food and agricultural product quality control, global environmental detection, and information and radar communication technology. application.

Description of drawings:

Fig. 1 is the front view of embodiment one;

Fig. 2 (a) is the structural section front view of embodiment two;

Fig. 2 (b) is the left side view of the coaxial waveguide part of embodiment two;

Fig. 2 (c) is the inner and outer conductor figure of the transition part of embodiment two;

Fig. 2 (d) is the artificial surface plasmon waveguide figure of embodiment two;

Fig. 3 is a graph showing the influence of the variation of the groove depth of the transition waveguide annular groove array on its dispersion characteristics in the second embodiment;

Fig. 4 is a graph showing the influence of the change of the radius of the plasmonic waveguide annular groove array on its dispersion characteristics in the second embodiment;

Fig. 5 is a graph showing the variation of field strength with frequency at the observation point in the second embodiment.

Specific implementation plan:

Below in conjunction with accompanying drawing, the implementation of technical scheme is described in further detail:

Embodiment one

As shown in Figure 1 and Figure 2(a), the field booster consists of three parts. Area I is a traditional coaxial waveguide, which is used as the input end of the signal; Area II is a transitional waveguide, including inner conductor transition and outer conductor transition. The inner conductor transition is realized by a periodic annular groove array with constant period and width and increasing depth , the transition of the outer conductor is realized by the horn antenna whose opening gradually expands; area III is a conical plasmonic waveguide, which is composed of a periodic ring groove array with constant period, depth and width, and decreasing radius. The structural size parameters of the transitional waveguide and the conical ion waveguide are adjusted according to the type and size of the coaxial waveguide, matching with the coaxial waveguide parameters (such as waveguide type, waveguide length, waveguide cross-sectional size, etc.).

Embodiment two

Taking the structure shown in Figure 2(b) as an example, area I is a traditional coaxial waveguide, with a single total length L ₁ =200 microns, the outer diameter of the inner conductor of the waveguide 2R ₁ =280 microns, and the inner diameter of the outer conductor 2R ₂ =644 microns, Wall thickness t=10 microns. The coaxial waveguide is used as the input end of the guided wave signal.

The transition waveguide is connected with the coaxial waveguide to efficiently convert signals into SSPPs signals. As shown in Fig. 2(c), the transitional waveguide region II includes inner conductor and outer conductor transitions. The gradient depth of the inner conductor transition annular groove array is gradually increased from h ₁ =2.5 microns to h ₂ =30 microns according to the step size Δh=2.5 microns, and the rest of the annular groove array maintains the gradual final depth h ₂ , It is used to realize the wavenumber matching between the coaxial waveguide and the artificial surface plasmon waveguide, and the influence of the change of the depth of the annular groove on its dispersion characteristics is shown in Figure 3. The inner diameter of the horn antenna of the outer conductor gradually increases from 2R ₂ =644 microns according to the cone angle α=10°, and ends at the total length of the transition waveguide, with a thickness of t=10 microns, which is used to realize the connection between the coaxial waveguide and the artificial surface plasmon waveguide Impedance matching between them, the horizontal period interval between two adjacent annular grooves in the transition waveguide is p=100 microns, the width of the grooves is a=50 microns, and the total length of the transition waveguide is L ₂ =1600 microns.

Conical plasmonic waveguides as carriers for enhanced transmission of SSPPs signals. As shown in Figure 2(d), in the conical plasmonic waveguide of region III, the conductor radius decreases from R ₁ =140 microns to R ₃ =40 microns according to a constant step size ΔR=5 microns; The horizontal period distance value is p=100 microns, the width of the groove is a=50 microns, the depth is h ₂ =30 microns, all remain unchanged, the length L ₃ =2100 microns, the change of the radius of the annular groove affects the dispersion characteristics The effect is shown in Figure 4. The total length of the field enhancer in this embodiment is 3900 microns.

According to embodiment two, utilize electromagnetic simulation software to obtain the field strength enhancement performance as shown in Figure 5, the field strength at the vertex (observation point 3) of the conical plasma structure can reach the coaxial line incident port (observation point 1 ) is nearly 12 times the field strength, and can reach about 5 times the field strength at the end of the transition waveguide (observation point 2).

Claims (5)

1. an artificial surface plasma field intensity booster, it is characterised in that: include that traditional coaxial waveguide and coaxial waveguide are to people The transition waceguide of work surface plasma waveguide, and cone plasma waveguide；

Wherein, transition waceguide includes inner conductor transition and outer conductor transition, and inner conductor transition is passed by cycle and constant width, the degree of depth The periodicity ring groove array increased realizes, and the electromagnetic horn that outer conductor transition is become larger by opening realizes；Cone plasma Waveguide is constant by cycle, depth and width, the periodicity ring groove array composition of decreasing radius.

A kind of artificial surface plasma field intensity booster the most according to claim 1, it is characterised in that: in transition waceguide, The ring groove array gradual change of inner conductor transition uses the degree of depth from h₁It is incremented to h according to constant step size △ h₂, its of ring groove array Remaining part divides ultimate depth h keeping gradual change₂；The horizontal cycle distance of adjacent two grooves of ring groove array is p；Outer conductor mistake The electromagnetic horn gradual change crossed uses internal diameter from 2R₂It is incremented by according to cone angle is smooth, arrives and terminate at the total length of transition waceguide, thick Spending and keep constant for t, transition waceguide total length is L₂, parameter h₁、△h、h₂、p、R₂、t、α、L₂Join with coaxial waveguide Number matches.

A kind of artificial surface plasma field intensity booster the most according to claim 1 and 2, it is characterised in that: cone etc. The conductor radius of ion waveguide is from R₁It is decremented to R according to constant step size △ R₃；The horizontal cycle distance of adjacent two ring grooves is P, recess width is a, and the degree of depth is h₂, all keep constant；Total length is L₃, parameter R₁、△R、R₃、p、a、h₂、L₃ With coaxial waveguide match parameters.

A kind of artificial surface plasma field intensity booster the most according to claim 1 and 2, it is characterised in that: coaxial waveguide Input as guided wave signals.

A kind of artificial surface plasma field intensity booster the most according to claim 3, it is characterised in that: coaxial waveguide conduct The input of guided wave signals.