TWI530015B - Low frequency surface plasma waveguide structure - Google Patents

Description

Low frequency surface plasma waveguide structure

The present invention relates to a low frequency surface plasma waveguide structure, and more particularly to a novel leaky wave waveguide formed by a special hollow metal square periodic structure surface, which enables the metal surface to transmit electromagnetic waves more efficiently and can provide high supply. A component that directs radiation.

The concept of using surface plasma can manipulate electromagnetic waves to transmit in sub-wavelength lines, which is currently an important topic for effectively increasing the density of devices in photonic loop systems and integrated circuits. Surface Plasmon Polaritors (SPPs) are a mixed excited state of electrons and photons at the interface between metal and medium (usually air). The field amplitude of SPPs has a maximum at the interface and is in the metal and The medium is exponentially decaying. SPPs offer the possibility of directing electromagnetic waves beyond the diffraction limit and thus have attracted wide interest in the field of surface plasma photonics.

Since its electromagnetic field is highly constrained in the vicinity of the interface between metal and medium, the propagation characteristics of the two-dimensional space (ie, surface) inherent in SPPs become the highest priority for the integration of the optical system and the design of sub-wavelength photonic devices. s Choice. In order to transmit signals in relatively low frequency circuits and to extend the concept of surface plasma polarons to lower frequency bands, such as the problem of signal transmission in the terahertz and microwave bands, there is an urgent need.

Generally, the surface plasma frequency of the metal is in the ultraviolet range, so the metal in the terahertz band behaves as a Perfect Electric Conductor (PEC), which makes the SPPs have poor binding to the electromagnetic field on the metal surface, and cannot effectively concentrate the electromagnetic waves. Thereby limiting the general structure of the leaky wave antenna in the terahertz and microwave bands application.

However, the situation due to the surface plasma mode cannot be achieved in the low frequency bands such as microwave and terahertz (THz). Therefore, in order to achieve similar physical phenomena in the low frequency band, high-density periodic metal blocks or periodic slots can be placed on the metal to achieve a high degree of constraint on the electromagnetic field. The waveguide structure used in the prior art is to arrange a plurality of unit cells spaced apart from each other by a predetermined pitch on the upper surface of a flat metal substrate. In the periodic structure in which such solid metal squares are arranged, the electromagnetic field distribution is highly constrained to the middle of the adjacent two unit cell blocks.

In order to solve this problem, if the special structural design can be used to improve the performance of the metal material for the constraints of the electromagnetic field, it should have a high industrial utilization value.

Accordingly, it is an object of the present invention to design a low frequency surface plasma waveguide structure which is provided with a plurality of unit cell blocks at a sub-wavelength period on the upper surface of a metal substrate (each cell block spacing is smaller than the transmission wave) The wavelengths are arranged along a one-dimensional arrangement direction to form a hollow metal square periodic structure. Each cell block includes a groove space. A transmission mode of a low frequency surface plasma polaron is introduced in the forbidden zone of the hollow metal block periodic structure. In the transmission mode of the low frequency surface plasma polaron, the electromagnetic field distribution of each cell block is mostly confined to the groove space in each of the cell blocks.

In a preferred embodiment of the invention, each unit cell includes a base, a through portion and an open slot. The through portion is formed in the unit cell in a through direction perpendicular to the one-dimensional array direction, and a recess space is defined in the unit cell. In the transmission mode of the low-frequency surface plasma polaron, if the structure is used as an antenna, the electromagnetic field distribution of each cell block is mostly confined in the groove space in the cell block, as a waveguide In use, the electromagnetic field is mostly distributed between two adjacent cell blocks, and a small amount is distributed in the groove space of the cell block.

In a preferred embodiment of the present invention, the metal substrate is made of a metal having good conductivity (for example, aluminum, copper, and gold), and the working frequency band of the hollow metal square periodic structure is one of a microwave band or a terahertz band. .

In terms of effects, the solid metal square periodic structure in the prior art is compared with the magnetic field distribution of the hollow metal square periodic structure of the present invention, in the transmission mode of the hollow metal square periodic structure of the present invention, the low frequency surface plasma polaron mode The electromagnetic field distribution is mostly concentrated in the groove space of the cell block and between the two cell blocks, so that the electromagnetic field can be more highly constrained, and has better transmission effect than the solid metal block periodic structure array waveguide.

The design of the invention can realize the height constraint of the electromagnetic field and provide the scanning element for changing the direction of the main beam with the frequency, and select the corresponding structure size in operation to adjust the frequency of use.

This structure has many of the superior features not found in many other low frequency surface plasma waveguides. The geometric parameters of the appropriate selection structure can achieve the function of highly constrained guided waves in the specified frequency range. On the other hand, this structure can provide scanning elements that change the direction of the main beam with frequency.

When applied, the waveguide structure can be reduced to a certain extent and used for guided wave transmission in the terahertz (THz) band, which can provide more effective constraints on the electromagnetic field. In addition to this, adjusting the geometry of the structure allows the waveguide itself to provide directional narrow beam radiation.

The specific techniques used in the present invention will be further illustrated by the following examples and the accompanying drawings.

100‧‧‧ hollow metal square periodic structure

1‧‧‧ unit cell

10‧‧‧ base

11‧‧‧through department

12‧‧‧ left side

13‧‧‧ right side

14‧‧‧ horizontal top

141‧‧‧ left horizontal top

142‧‧‧right horizontal top

2‧‧‧Metal substrate

21‧‧‧ upper surface

3‧‧‧Open slot

4‧‧‧ Groove space

A‧‧‧single cell spacing

A1‧‧‧ groove width

A2‧‧‧Open slot width

C1‧‧‧ hollow structure dispersion curve

C2‧‧‧solid structural dispersion curve

C3‧‧‧Electromagnetic wave free air dispersion curve

D‧‧‧ unit cell array period length

H‧‧‧ unit cell height

H1‧‧‧ groove depth

I1‧‧‧1D alignment

I2‧‧‧ horizontal direction

L‧‧‧ unit cell length

Figure 1 is a perspective view showing the low frequency surface plasma waveguide structure of the present invention.

Fig. 2 is an enlarged perspective view showing the unit cell of the present invention.

Fig. 3 is a cross-sectional view showing the section 3-3 in Fig. 2.

Fig. 4 is a graph showing the dispersion relationship between the operating frequency and the propagation constant of the low-frequency surface plasma waveguide structure and the solid low-frequency surface plasma waveguide structure having the hollow groove space of the present invention.

Referring to Figure 1, there is shown a perspective view of a low frequency surface plasma waveguide structure of the present invention. The low frequency surface plasma waveguide structure of the present invention comprises a plurality of unit cell blocks 1 spaced apart from each other by a predetermined pitch, which are arranged on the upper surface 21 of a flat metal substrate 2. Each unit cell 1 is arranged in a line in a one-dimensional array direction I1 along the one-dimensional array direction I1 on the upper surface 21 of the metal substrate 2 to form a hollow hollow block periodic structure. ).

Referring to Figures 2-3, respectively, are enlarged perspective and cross-sectional views of a unit cell 1 of a specific embodiment of the present invention. A through portion 11 is formed in the base 10 of the unit cell 1. The through portion 11 penetrates the cell block 1 in a horizontal through direction I2 perpendicular to the one-dimensional array direction I1, so that the cell block 1 forms a left side portion 12, A corresponding to the right side portion 13 of the left side portion 12 and a horizontal top portion 14 spanning between the left side portion 12 and the right side portion 13. The through portion 11 defines a recessed space 4 formed by the left side portion 12, the right side portion 13 and the horizontal top portion 14 in the unit cell block 1 to constitute the hollow metal square periodic structure 100 of the present invention.

In addition, an open slot 3 is formed in the horizontal through portion 14 at the horizontal top portion 14, and the horizontal top portion 14 is partitioned to form a left horizontal top portion 141 and a corresponding right horizontal top portion 142.

In the figure, the geometric parameters of the solid metal square periodic structure are respectively expressed as follows: the spacing of the unit cells is a = 5 mm (mm)

Single cell array period length d=10 mm (mm)

Single cell height h=4 mm (mm)

Single cell length L = 5 mm (mm)

For the hollow metal square periodic structure of the embodiment having the hollow groove space of the present invention, the groove space of the following size is additionally introduced in the solid metal block structure: the groove width a1=3.0 mm (mm)

Opening slot width a2=1.0 mm (mm)

Groove depth h1=2.0 mm (mm)

A low frequency spoof surface plasmon polaritons is introduced in the forbidden zone of the hollow metal block periodic structure 100 by the recessed space 4 in each unit cell 1 and the open slot 3 Transmission mode. In the transmission mode of the low-frequency surface plasma polaron, when the invention is used as the structure of the antenna, the electromagnetic field distribution of each cell block is mostly confined in the groove space of the unit cell, if used as a waveguide. When the electromagnetic field is mostly distributed between two adjacent cell blocks, a small amount is distributed in the groove space of the cell block.

In a preferred embodiment of the invention, the metal substrate 2 is made of a highly conductive metal such as one of aluminum, copper, and gold. The working frequency band of the hollow metal block periodic structure 100 is set to a microwave frequency band or a terahertz frequency band (THz).

Referring to Fig. 4, there is shown a graph showing the relationship between the operating period of the hollow metal square of the present invention and the propagation constant of the prior art solid metal square periodic structure and the propagation constant. The ordinate in the figure represents the operating frequency, and the abscissa indicates the propagation constant β . The hollow structure dispersion curve C1 shown in the drawing represents the dispersion curve of the hollow metal square periodic structure of the present invention, and the solid structure dispersion curve C2 represents the dispersion curve of the solid metal square periodic structure in the prior art.

The results of numerical simulations and experiments will mainly focus on the bases in the waveguide structure. Mode, such a mode is easily excited in the X-band of the microwave, and the electromagnetic field is highly constrained in the periodic structure of the metal waveguide. The numerical results show that for the surface plasma waveguide of the solid metal square periodic structure, the cutoff frequency of the fundamental mode is 9.72 GHz, and the progressive frequency is 11.506 GHz, and the width of the operating band is 1.786 GHz. The operating frequency of the solid metal square periodic structure falls within this range. The electromagnetic field is highly constrained to the middle of two adjacent cell blocks.

For the array structure of hollow metal blocks, the cutoff frequency is 9.0 GHz, while the progressive frequency is 11.504 GHz, and the width of the operating band is 2.504 GHz. The hollow metal square periodic structure has an electromagnetic field distribution in this frequency range, and most of the energy enters the slot area of the hollow metal block and a small amount is located outside the hollow area, so that the electromagnetic field can be effectively confined in the wider frequency range at the sub-wavelength. Under the size.

For the hollow metal square periodic structure, since each unit cell is hollowed out, an additional transmission mode is introduced within the forbidden band of the original solid metal square periodic structure. In the structural dispersion curve of the periodic arrangement of hollow metal squares, the electromagnetic field distribution at the bottom of the forbidden band at β = 0.5 (frequency 11.504 GHz) is almost completely confined between adjacent two unit cells. Since the field distribution is very different, there is a new Forbidden band structure. The width of the forbidden zone additionally introduced due to the formation of the hollow metal blocks is 0.451 GHz. The frequency range of the leakage region will range from 12.3279 GHz to 13.068 GHz, and the scanning bandwidth is 0.7401 GHz.

By excavating holes with a subwavelength period on the surface of the metal (the size and depth of the holes are smaller than the wavelength), not only the electromagnetic wave transmission effect can be enhanced, but also the subwavelength of the electromagnetic field can be highly constrained, and the real surface plasma electrode The chemistries are very similar, and in practical applications, spoof SPPs (SSPPs) have greater operational flexibility. The equivalent surface plasmon frequency of the surface layer of the structure is only related to the geometric parameters of the surface structure. Therefore, an effective way is to spread the terahertz wave or lower frequency microwave band on the metal plane. The existence of SSPPs has been experimentally verified in both the microwave and terahertz bands.

Further research has shown that one-dimensional periodic distribution of grooves on metal surfaces and metal lines can support the propagation of SSPPs in the terahertz band. And the dispersion of SSPPs The system can be arbitrarily adjusted by changing the periodic structure of the groove on the metal surface, and its field constraint, loss and other properties are only dependent on the geometric parameters of the periodic surface structure. Since the guided wave characteristics of the low-frequency surface plasma polariton waveguide are determined by the geometry of the waveguide itself, there are more advantages in designing the waveguide component. Therefore, many waveguide schemes based on the low-frequency surface plasma polaron transport mechanism have been proposed by researchers, especially the periodic array of metal blocks is most easily realized in the low frequency band. There is a groove in each cell block of one of the structures, and these metal periodic structures can support surface waves.

In the present invention, a recess is introduced into each of the unit cell structures of the periodic arrangement to introduce an additional transmission mode into the band gap of the originally recessed metal square periodic structure. Most of the electromagnetic fields in this new transmission mode will be concentrated inside the grooves of the unit cell. In addition, since the dispersion curve corresponding to this mode will intersect the electromagnetic wave free air dispersion curve C3 (Light line) and enter the radiation region of the periodic structure. It was verified by experimental measurements that the metal periodic structure can provide a pencil beam scanned with frequency in this frequency band, and the scanning angle exceeds 30 degrees.

This structure has many of the superior features not found in many other low frequency surface plasma waveguides. The geometric parameters of the appropriate selection structure can achieve the function of highly constrained guided waves in the specified frequency range. On the other hand, this structure can also provide scanning elements that change the direction of the main beam with frequency.

The leakage wave radiation presented by the structure of the present invention has a high degree of directivity, and the main beam always has a certain elevation angle with respect to the z-axis. According to the theoretical analysis, the beam with obvious directionality can range from 304 ⁰ at 12.5 GHz to 336 ⁰ at 12.9 GHz, with a total elevation range of 32 ⁰ .

The solid metal square periodic structure is compared with the magnetic field distribution of the hollow metal square periodic structure of the present invention. In the transmission mode of the hollow metal square periodic structure of the present invention, the electromagnetic field distribution of the low frequency surface plasma polaron mode is mostly concentrated on the unit cell. Within the groove space of the square, thus the height of the electromagnetic field can be achieved, compared to the solid metal square The structure of the arrayed waveguide has a better transmission effect.

It can be seen from the above embodiments that the present invention has industrial utilization value, and thus the present invention has been in conformity with the requirements of the patent. The above embodiments are merely illustrative of the preferred embodiments of the present invention, and those skilled in the art can make various other modifications and changes in accordance with the embodiments of the present invention. However, various modifications and changes made in accordance with the embodiments of the present invention are still within the scope of the invention and the scope of the invention as defined below.

1‧‧‧ unit cell

10‧‧‧ base

11‧‧‧through department

12‧‧‧ left side

13‧‧‧ right side

142‧‧‧right horizontal top

2‧‧‧Metal substrate

21‧‧‧ upper surface

3‧‧‧Open slot

4‧‧‧ Groove space

I1‧‧‧1D alignment

I2‧‧‧ horizontal direction

Claims (14)

A low frequency surface plasma waveguide structure comprising: a metal substrate having an upper surface; a hollow metal square periodic structure, the hollow metal square periodic structure operating in a predetermined operating frequency band and defining a forbidden band; the hollow metal The block periodic structure includes a plurality of unit cells spaced apart from each other by a predetermined interval, and each unit cell is arranged on the upper surface of the metal substrate in a one-dimensional arrangement direction with a sub-wavelength period, and each unit cell is Forming an electromagnetic field distribution in the working frequency band; introducing a transmission mode of a low frequency surface plasma polaron in the forbidden band region of the hollow metal square periodic structure; each of the unit cell blocks includes a groove space; In the transmission mode of the low-frequency surface plasma polaron, the hollow metal square periodic structure is an antenna structure, and the electromagnetic field distribution of each of the unit cells is mostly confined to the concave in the unit cell. In the slot space. The low frequency surface plasma waveguide structure of claim 1, wherein each of the unit cell blocks comprises: a base body; a through portion penetrating the base body in a horizontal through direction, wherein the concave body is defined in the base body a groove space, the groove space being constituted by a left side portion, a right side portion corresponding to the left side portion, and a horizontal top portion spanning between the left side portion and the right side portion; an open slot at the level a through direction formed at the top of the horizontal portion, the horizontal top portion being spaced apart to form a left horizontal top portion and a right horizontal top portion; wherein the recessed space in the unit cell block and the open slot are in the hollow a transfer mode of introducing the low frequency surface plasma polaron in the forbidden band region of the metal square periodic structure formula. The low frequency surface plasma waveguide structure of claim 1, wherein the metal substrate is made of a conductive metal such as aluminum, copper or gold. The low frequency surface plasma waveguide structure of claim 1, wherein the working frequency band of the hollow metal square periodic structure is a microwave frequency band. The low frequency surface plasma waveguide structure of claim 1, wherein the working frequency band of the hollow metal square periodic structure is a terahertz frequency band. For example, in the low-frequency surface plasma waveguide structure of claim 1, wherein the geometric parameter of each unit cell is: the spacing of the unit cells a=5 mm unit cell arrangement period length d=10 mm unit cell Block height h = 4 mm unit cell length L = 5 mm groove width a1 = 3.0 mm opening slot width a2 = 1.0 mm groove depth h1 = 2.0 mm. The low frequency surface plasma waveguide structure of claim 1, wherein the forbidden zone has a width of 0.451 GHz. A low frequency surface plasma waveguide structure comprising: a metal substrate having an upper surface; a hollow metal square periodic structure, the hollow metal square periodic structure operating in a predetermined operating frequency band and defining a forbidden band; the hollow metal The block periodic structure includes a plurality of unit cells spaced apart from each other by a predetermined interval, and each unit cell is arranged on the upper surface of the metal substrate in a one-dimensional arrangement direction with a sub-wavelength period, and each unit cell is Forming an electromagnetic field distribution in the working frequency band; introducing a transmission mode of a low frequency surface plasma polaron in the forbidden band region of the hollow metal square periodic structure; each of the unit cell blocks includes a groove space; In the transmission mode of the low-frequency surface plasma polaron, the hollow metal square periodic structure is used as a waveguide structure, and the electromagnetic field distribution is mostly distributed between adjacent two unit cell blocks, and a small amount is distributed in the Within the groove space of the cell block. The low frequency surface plasma waveguide structure of claim 8 , wherein each of the unit cell blocks comprises: a base body; a through portion penetrating the base body in a horizontal through direction, wherein the concave body is defined in the base body a groove space, the groove space being constituted by a left side portion, a right side portion corresponding to the left side portion, and a horizontal top portion spanning between the left side portion and the right side portion; an open slot at the level a through direction formed at the top of the horizontal portion, the horizontal top portion being spaced apart to form a left horizontal top portion and a right horizontal top portion; wherein the recessed space in the unit cell block and the open slot are in the hollow The transmission mode of the low frequency surface plasma polaron is introduced into the forbidden zone of the metal square periodic structure. The low frequency surface plasma waveguide structure of claim 8, wherein the metal substrate is made of a metal having good conductivity (for example, one of aluminum, copper, and gold). The low frequency surface plasma waveguide structure of claim 8, wherein the working frequency band of the hollow metal square periodic structure is a microwave frequency band. The low frequency surface plasma waveguide structure of claim 8, wherein the working frequency band of the hollow metal square periodic structure is a terahertz frequency band. For example, the low-frequency surface plasma waveguide structure of claim 8 wherein the geometric parameter of each unit cell is: the spacing of the unit cells a=5 mm Unit cell arrangement period length d=10 mm unit cell height h=4 mm unit cell length L=5 mm groove width a1=3.0 mm opening slot width a2=1.0 mm groove depth h1 = 2.0 mm. For example, the low frequency surface plasma waveguide structure of claim 8 wherein the forbidden zone has a width of 0.451 GHz.