CN112187181A

CN112187181A - Design method of extended interaction oscillator based on Smith Pasel radiation

Info

Publication number: CN112187181A
Application number: CN202011037334.8A
Authority: CN
Inventors: 赵德强; 张平; 曹欣欣
Original assignee: University of Electronic Science and Technology of China
Current assignee: University of Electronic Science and Technology of China
Priority date: 2020-09-28
Filing date: 2020-09-28
Publication date: 2021-01-05
Anticipated expiration: 2040-09-28
Also published as: CN112187181B

Abstract

The invention provides an EIO design method based on Smith-Pasel radiation and working in a high-order mode, and belongs to the technical field of high-frequency terahertz sources. The design method starts by the angle that electrons pass through SHA to generate SPR, and determines the size of the long edge of the hole of the SHA; then, according to the idea that an open quasi-optical cavity consisting of a metal mirror and a grating in Orotron can form a high-order mode, the distance between the metal baffle and the SHA is further determined; a mode of operation is considered to operate effectively when its frequency falls near the peak of the SPR frequency. The invention creatively introduces the related theoretical ideas of SPR and Orotron into the design of EIO, and provides a new angle for researching the working of EIO in a high-order mode.

Description

Design method of extended interaction oscillator based on Smith Pasel radiation

Technical Field

The invention belongs to the technical field of high-frequency terahertz sources, relates to a design method of an Extended Interaction Oscillator (EIO), and particularly relates to an EIO design method based on Smith-Pasel radiation and working in a high-order mode.

Background

The terahertz (THz) science and technology has wide application prospects in the aspects of physics, material science, life science, astronomy, environmental monitoring, information technology, national safety and the like. The terahertz radiation source is an important bottleneck for developing the terahertz scientific technology, and an Extended Interaction Oscillator (EIO) based on vacuum electronics is an important terahertz radiation source. Unfortunately, due to the size-sharing effect, the size of the EIO operating at high frequencies decreases dramatically as the frequency increases, which presents a significant barrier to the development of the device. One possible solution to overcome the frequency limitation is to design the EIO architecture to operate directly in the higher order modes.

However, an EIO operating in a higher order mode may face the problem of mode competition. When an EIO structure is designed, the traditional design idea is that a complete device structure is subjected to cold cavity analysis to obtain a dispersion curve, and corresponding electron lines and the dispersion curve in a dispersion curve graph have a series of intersection points, namely correspond to different modes, so that mode competition occurs; and then continuously optimizing structural parameters, starting oscillation current and starting oscillation voltage in PIC simulation to avoid mode competition. Therefore, the conventional method for designing the vacuum device working in the high-order mode is very tedious and difficult to inhibit mode competition, and a great amount of time is usually needed to complete the whole process of adjusting the device to stably work in a specific high-order mode.

Disclosure of Invention

Aiming at the problems of complicated design thought and low efficiency in the traditional device design method in the background technology, the invention aims to provide an extended interaction oscillator design method based on Smith Persel radiation. The method creatively introduces the related theoretical ideas of Smith Passer Radiation (SPR) and Orotron (Orotron) into the design of a specific EIO device with a trapezoidal slow wave structure, and provides a new angle for researching the working of EIO in a high-order mode. An EIO device designed based on the method can generate stable output and avoid mode competition to a certain extent.

In order to achieve the purpose, the technical scheme of the invention is as follows:

an extended interaction oscillator design method based on Smith Persel radiation comprises the following steps:

step 1, determining the long edge of a hole of a core part Subwavelength Hole Array (SHA) of an extended interaction oscillator, and the specific process is as follows: obtaining Smith Passer Radiation (SPR) spectrograms corresponding to different long edges of the hole by CST simulation, and selecting the length of the side length of the hole according to the required working frequency of the device, wherein the required working frequency is in a main frequency band where the curve peak value in the spectrograms corresponds to the frequency;

step 2. after the hole edge length parameter is determined in the step 1, metal flat plates are symmetrically arranged on the upper part and the lower part of the sub-wavelength long hole array structure, and the distance from the metal flat plates to the sub-wavelength long hole array structure is determined, and the specific process is as follows: based on the Orotron theory, the theoretical formula of the distance H between the metal flat plate and the SHA is H ═ q (lambda/2), wherein q is n/2, and n is a high-order mode TM_n1-2πλ is the wavelength corresponding to the actual working frequency of the device in step 1; substituting the expected working mode and the corresponding wavelength into a formula to obtain a theoretical value of H;

and 3, enclosing the structure obtained in the step 2 to determine the width of a resonant cavity (Slab-x), wherein the specific process is as follows: obtaining characteristic impedance values corresponding to different resonant cavity widths in the working mode determined in the step 2 through CST simulation, drawing a relation curve, and taking numerical values corresponding to the characteristic impedance values in the range from-50 to the peak value of the relation curve as width values of the resonant cavity;

and 4, arranging a rectangular coupling small hole and a standard output waveguide on the basis of the structure determined in the step 3 to obtain the extended interaction oscillator.

Preferably, the extended interaction oscillator designed by the present invention operates at TM_51-2πMode(s).

Further, n is more than or equal to 1 and less than or equal to 11.

Further, the main frequency band in step 1 is a range of ± 20GHZ of the frequency corresponding to the peak of the curve in the spectrogram.

Furthermore, simulation of CST in step 1 is performed under the action of electron beam clusters.

Further, the Subwavelength Hole Array (SHA) in step 1 is a cuboid structure, a cylindrical electron beam channel is arranged in the center of the subwavelength hole array, and through holes which are periodically arranged are arranged on a surface parallel to the direction of the electron beam channel.

In summary, due to the adoption of the technical scheme, the invention has the beneficial effects that:

1. the design method starts by the angle that electrons pass through SHA to generate SPR, and determines the size of the long edge of the hole of the SHA; then, according to the idea that an open quasi-optical cavity consisting of a metal mirror and a grating in Orotron can form a high-order mode, the distance between the metal baffle and the SHA is further determined; a mode of operation is considered to operate effectively when its frequency falls near the peak of the SPR frequency. The invention creatively introduces the related theoretical ideas of SPR and Orotron into the design of EIO, and provides a new angle for researching the working of EIO in a high-order mode.

2. The design method of the invention determines the parameters from the part of the device, gradually adjusts to form a complete structure, and the design idea is completely different from the traditional design mode; the device obtained by the design method can work in a working mode well, and mode competition is effectively avoided; meanwhile, the EIO working in a high-order mode can be rapidly designed through the design idea of the invention, so that the research and development period can be reduced.

3. Based on the EIO device designed by the invention, when the working voltage is 30kV, the working current is 0.1A and the magnetic field intensity is 0.4T, the device can stably work in the TM with the frequency of 470GHz_51-2πAnd the output power can reach 293W, and the output efficiency is 9.7%.

Drawings

FIG. 1 is a schematic and a spectrogram of SPR radiation generation;

wherein, (a) is a schematic diagram of the electron generation SPR radiation through the SHA electron beam channel; (b) are spectrograms of different hole side lengths. (the gray shaded area is the SPR main band with 350 μm holes)

Fig. 2 is a schematic diagram of the structure of SHA with a mirror.

Fig. 3 is a simulation plot of field distribution versus distance of the metal plate to the SHA for different modes at an operating frequency of 466 GHz.

FIG. 4 is TM_51-2πThe characteristic impedance (R/Q) and frequency of the mode is plotted as a function of the width of the cavity.

Fig. 5 is a cross-sectional view of the complete structure in the Z-0 plane and the X-0 plane.

FIG. 6 is a dispersion map of a fully structured EIO device with output.

FIG. 7 is a graph of the axial electric field distribution in the electron beam path at different distances of the metal shield and SHA;

wherein (a) the distance is 800 μm; (b) the distance was 450 μm.

FIG. 8 is a graph of a performance simulation of an EIO device having a complete structure;

wherein, (a) is output power diagram of port, (b) is frequency spectrum diagram, and (c) is E when 10ns_zThe field profile (d) is the spatial phase diagram of the electrons.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail with reference to the following embodiments and accompanying drawings.

step 1, determining the long edge of a hole of a core part Subwavelength Hole Array (SHA) of an extended interaction oscillator, and the specific process is as follows: obtaining Smith Passer Radiation (SPR) spectrograms corresponding to different long edges of the hole by CST simulation, and selecting the length of the side length of the hole according to the actually required working frequency of the device, wherein the required working frequency is in a main frequency band where the curve peak value corresponds to the frequency in the spectrograms;

step 2. after the hole edge length parameter is determined in the step 1, metal flat plates are symmetrically arranged on the upper part and the lower part of the sub-wavelength long hole array structure, and the distance from the metal flat plates to the sub-wavelength long hole array structure is determined, and the specific process is as follows: based on the Orotron theory, the theoretical formula of the distance H between the metal flat plate and the SHA is H ═ q (lambda/2), wherein q is n/2(n is a high-order mode TM)_n1-2πThe order of (d), λ is the wavelength corresponding to the actual operating frequency of the device in step 1; substituting the expected working mode and the corresponding wavelength into a formula to obtain a theoretical value of H;

and 3, sealing the periphery of the structure obtained in the step 2, and determining the width of the resonant cavity, wherein the specific process is as follows: obtaining characteristic impedance values corresponding to different resonant cavity widths in the working mode determined in the step 2 through CST simulation, drawing a relation curve, and taking a numerical value corresponding to a high characteristic impedance value as a width value of the resonant cavity;

Example 1

In the embodiment, the core structure of the extended interaction oscillator is a Subwavelength Hole Array (SHA), and three main influence parameters, namely, the long side of the SHA hole, the distance between the metal flat plate and the SHA, and the width of the resonant cavity, are mainly researched in the invention. Other parameters have small influence on the effect in the invention, so the design is reasonable in size. The devices were designed and fabricated based on smith-pasier radiation (SPR), which produces a schematic and a spectrum as shown in figure 1. When the core structure SHA is a cuboid structure, a cylindrical electron beam channel is arranged at the center of the core structure SHA, and the radius of the channel is 60 mu m; the surface parallel to the direction of the electron beam passage was provided with through holes arranged periodically, the hole width was 70 μm, and the hole pitch was 140 μm. When electrons pass through the electron beam channel, four dipoles are excited to oscillate compared with the traditional grating structure; these moving dipoles oscillate and their radiation will radiate through the aperture into the upper half of the space, i.e. smith-pascal radiation (SPR), and the long sides of the aperture must influence the SPR. Using PIC simulations, SPR radiation spectra were generated using electron bunches of 30ekV through the electron beam path. It can be seen from the figure that if the actually required operating frequency of the device is 466GHz, the length of the side length of the aperture is 350 μm, and the required operating frequency is within 430GHz-480GHz of the main frequency band in which the peak of the 350 μm curve in the spectrogram corresponds to 455 GHz.

According to Orotron, the theory of sparse mode can be formed by using a structure in which a metal mirror and a grating form an open quasi-optical cavity. Similarly, we add two metal plates (i.e. mirrors) symmetrically above and below the SHA, where the metal plates and SHA are used to support the formation of higher order modes at the desired frequencies, and the metal plates act as simple mirror surfaces to confine the SPR formed by electrons passing through the SHA to a spatial range, where the higher order modes can be formed. The distance between the metal plate and the SHA determines the order of the mode formed by the field. By adjusting the distance, the order of the higher order mode can be selected.Fig. 2 is a schematic diagram of the structure of SHA with a mirror. The oscillation operation (main band shown in fig. 1 (b)) can be performed as long as the frequency of the operation mode falls within a certain range around the SPR radiation peak. If the designed structure works in TM mode_51-2πIn the mode, the corresponding operating frequency is 466GHz, and the theoretical value of the distance H between the metal plate and the SHA is 804 μm, which can be calculated by combining the formula (H ═ q (λ/2)) in step 2. The simulation result shown in FIG. 3 is the same as that of the TM_51-2πIn mode, the distance between the metal plate and the SHA is substantially uniform at 800 μm.

Further, the structure of fig. 2 was closed on both sides, resulting in a vacuum electronic device of a conventional EIO structure. Obtaining TM by CST simulation_51-2πCharacteristic impedance values corresponding to different resonant cavity widths in the working mode are plotted, and a relation graph of characteristic impedance (R/Q) and frequency variation along with the width (Slab-x) of the resonant cavity is shown in FIG. 4. As can be seen from fig. 4, when the width of the resonant cavity is 800 μm, the corresponding characteristic impedance is 879 Ω.

Fig. 5 is a cross-sectional view of the complete structure in the Z-0 plane and the X-0 plane. A rectangular aperture is adopted as a coupling part, and a standard waveguide BJ2600(WR3) is designed, so far, the structure design is completed.

And (3) performing performance verification on the extended interaction oscillator designed based on the steps, and analyzing mode competition from two angles of characteristic impedance and electric field distribution. FIG. 6 is a dispersion diagram of an EIO device with a complete structure having an output, and from Table 1, it can be seen that the values of the characteristic impedance of the modes in the vicinity of the electron beam, the operating mode TM_51-2πClearly higher than the other modes, which may reflect to some extent that the mode is relatively easy to interact with the electron beam. The characteristic impedance values in the different modes are specifically shown in table 1.

TABLE 1

FIG. 7 is a graph showing the axial electric field distribution in the electron beam path at different distances between the metal plate and the SHA. As can be seen from FIG. 7, the metal plate and SHAAt a distance of 800 μm, TM_51-2πThe electric field strength of a mode is significantly stronger than the other Two Modes (TM)_11-2π、TM_31-2π) When the distance is 458 μm, TM_31-2πThe electric field strength of a mode is significantly stronger than that of the other Two (TM)_11-2π、TM_51-2π). It is demonstrated that when the frequency of the higher-order mode corresponds to the main frequency range of SPR, an electric field distribution significantly stronger than that of other modes can be obtained, thereby avoiding mode competition to a certain extent.

In order to verify that our structure can work effectively, the invention adopts CST simulation to perform thermal cavity verification on the device. The electron beam voltage was set at 30kV, the current at 0.1A, and the magnetic field strength at 0.4T. The simulation results are shown in FIG. 8, where the output power is about 293W and the operating frequency is 470.94 GHz. When the 10ns device works stably, the working mode is TM_51-2πMode(s). From the electron space phase diagram (d), it can be seen that the electron beam well converts the energy into the electromagnetic wave, and the working efficiency of the device is calculated to be 9.7%. In summary, the method for efficiently designing the EIO operating in the high-order mode proposed in the present invention is feasible, and when the EIO operates in the high-frequency high-order mode, better output power and working efficiency are obtained.

While the invention has been described with reference to specific embodiments, any feature disclosed in this specification may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise; all of the disclosed features, or all of the method or process steps, may be combined in any combination, except mutually exclusive features and/or steps.

Claims

1. An extended interaction oscillator design method based on Smith Persel radiation is characterized by comprising the following steps:

step 1, determining the long edge of a hole of a core part subwavelength hole array of an extended interaction oscillator, and the specific process is as follows: obtaining Smith Passer radiation spectrograms corresponding to different long edges of the hole by CST simulation, and selecting the length of the side length of the hole according to the required working frequency of the device, wherein the required working frequency is in a main frequency band where the curve peak value corresponding frequency in the spectrograms is located;

step 2. after the hole edge length parameter is determined in the step 1, metal flat plates are symmetrically arranged on the upper part and the lower part of the sub-wavelength long hole array structure, and the distance from the metal flat plates to the sub-wavelength long hole array structure is determined, and the specific process is as follows: the theoretical formula of the distance H between the metal flat plate and the SHA is H ═ q (lambda/2), and the value H is determined according to the required working high-order mode, wherein q is n/2, and n is a high-order mode TM_n1-2πλ is the wavelength corresponding to the working frequency required by the device in step 1;

and 3, enclosing the structure obtained in the step 2 to form a resonant cavity, and determining the width of the resonant cavity, wherein the specific process is as follows: obtaining characteristic impedance values corresponding to different resonant cavity widths in the working high-order mode determined in the step 2 through CST simulation, drawing a relation curve, and taking numerical values corresponding to the characteristic impedance values in the peak value-50-peak value of the relation curve as width values of the resonant cavity;

2. The extended interaction oscillator design method of claim 1, wherein 1 ≦ n ≦ 11.

3. The extended interaction oscillator design method of claim 2 wherein n is 5, i.e., the desired higher order mode of operation is TM_51-2πMode(s).

4. The method as claimed in claim 1, wherein the main frequency band in step 1 is within ± 20GHZ of the peak corresponding frequency of the curve in the spectrogram.

5. The extended interaction oscillator design method of claim 1 where the CST simulation in step 1 is performed under e-beam cluster.

6. The extended interaction oscillator design method according to claim 1, wherein the subwavelength hole array in step 1 is a rectangular parallelepiped structure, a cylindrical electron beam channel is provided at the center thereof, and through holes are provided in a plane parallel to the direction of the electron beam channel in a periodic arrangement.