CN115863967A - Radiation enhancement method based on non-uniform plasma - Google Patents
Radiation enhancement method based on non-uniform plasma Download PDFInfo
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Abstract
The invention discloses a radiation enhancement method based on non-uniform plasma, and relates to a plasma enhancement method. The plasma enhanced electric small antenna is realized based on a plasma enhanced electric small antenna, and the plasma enhanced electric small antenna comprises a spherical shell-shaped plasma cover and an electric small antenna positioned in the plasma cover; moreover, plasmas in the plasma hood are non-uniformly distributed along the radius of the plasma hood; the radiation enhancement method comprises the following steps: the plasma density and the size of the plasma shield are adjusted to meet the following condition, so that the radiation of the electrically small antenna is enhanced by the non-uniform plasma.
Description
Technical Field
The present invention relates to a plasma enhancement method.
Background
In recent years, low-temperature gas discharge plasma has attracted more and more attention in the field of regulating electromagnetic waves. This is because plasma can be regarded as a special electromagnetic metamaterial. In one aspect, the dielectric constant (epsilon) of the plasma can be adjusted to be broadband, continuously and dynamically adjustable by adjusting applied parameters, such as discharge power, gas pressure, and discharge gas species. Particularly for weakly colliding plasmas (the collision frequency is much smaller than the electromagnetic wave frequency), the dielectric constant of the plasma can be flexibly switched between the ENG (avalanche-negative), ENZ (avalanche-near-zero) and ELP (avalanche-low-positive) states. On the other hand, under sub-wavelength conditions, the plasma may exhibit electromagnetic characteristics that are distinct from conventional conditions. The characteristics enable the plasma to show huge application potential in the aspect of designing dynamically adjustable, reconfigurable and multifunctional microwave electromagnetic equipment.
On the other hand, the development direction of modern antennas is miniaturization, light weight, ultra wide band, high gain, adjustable beam width angular region (large scan), and full polarization. Wherein ultra-wideband is relatively easy to implement, and the technical core of the rest of the characteristics lies in gain. Miniaturization and high gain are absolutely contradictory. The current method commonly used in the antenna field is to compromise the pair of spears, i.e. to obtain a relatively high gain by increasing the antenna volume. The sub-wavelength plasma enhanced microwave electromagnetic radiation technology developed in recent years provides a new idea for solving the contradiction. In particular, the introduction of the plasma makes the gain improvement of the passive antenna relatively independent, and the modularized method can be used without considering other parameters of the antenna. The significance of this method lies in: does not depend on the antenna structure too much and belongs to an active method. Therefore, as with the active circuit, the plasma enhanced method can achieve effective decoupling of the spear body for miniaturization and high gain.
For the plasma enhancement phenomenon, in 1967, messiaen et al observed that the mercury discharge spherical plasma thin layer had an enhancement effect on the electromagnetic radiation of the spherical antenna working at 300MHz for the first time in the experiment. In 1968, chen and Lin also found that the radiation gain of electrically small antennas can reach more than 20dB in a certain range where the plasma frequency is greater than the frequency of electromagnetic waves. In 2017 to 2018, the design experiments of prosperous and the like realize the enhancement of the receiving and transmitting modulation (gain-10 dB) of the sub-wavelength dense plasma on the electromagnetic wave of-1 GHz. In 2019, laquerbe et al found through experiments that after the plasma loads the electrically small antenna, the electrically small antenna can achieve good impedance matching with a transmission line and obtain radiation gain of about 20dB under a certain working frequency (250 MHz-450 MHz) and discharge power. For the enhanced mechanism, bichuskaya, stuart, ziolkowski, gao, pfeiffer, wang, li, laquerbe, and Laffont et al, give explanations from the perspectives of impedance matching, phase modulation, plasmons, and simple harmonic oscillator models, respectively. But they mostly use a homogeneous plasma approximation model for analysis. In 1973, hizal researches the enhancement effect of plasmas which are distributed from inside to outside in a cosine-decreasing manner on antenna radiation, and finds that the enhancement effect of the nonuniform plasmas containing the sheath layer is superior to that of the uniform plasmas which tightly coat the antenna. In 2018, kong et al studied the enhancement effect of decreasing and increasing plasma density distribution from inside to outside on electrically small antenna radiation, and found that decreasing distribution is more beneficial to improving radiation gain. However, in both the models of Hizal and Kong et al, the minimum values of the plasma density are 0, and in this case, a plasmon resonance may occur in the vicinity of a position where the local plasma frequency is approximately equal to the electromagnetic wave frequency. The presence of plasmon resonances can seriously impair the radiation enhancement effect of the plasmons on electrically small antennas. Furthermore, hizal and Kong et al do not give a general discussion of how to achieve optimal enhancement under non-uniform conditions.
Besides the research on the plasma enhancement effect in the literature, there are also related patents reporting this phenomenon. For example, "a magnetic dipole antenna based on plasmonic medium modulation" disclosed in patent application No. CN201610389875.4 utilizes plasmonic negative permittivity characteristics to improve the radiation capability of the antenna by creating resonance of an electric field inside the magnetic dipole antenna. The device for enhancing electromagnetic radiation of a miniaturized omnidirectional antenna by adopting plasma modulation disclosed in the patent with the application number of CN201610356451 solves the problem that the traditional metal conductor antenna cannot realize high gain and miniaturization at the same time, reduces the volume of the antenna and reduces the radar scattering cross section of the antenna. Patent application No. CN202010093055.7 discloses a tunable, high-resolution, multi-band enhanced plasma generating apparatus, which can simultaneously enhance the intensity of multiple transmitted signals or extract and enhance electromagnetic signals of multiple target frequencies from complex background electromagnetic field. Patent No. CN201910678454.7 discloses a "signal-enhanced plasma stealth antenna window", which can realize selective stealth and enhancement of electromagnetic waves of different target bands in the same system through cooperation of inner and outer layers of plasmas. An enhanced electrically small antenna with stealth function is disclosed in patent application No. CN 202110625957.5. The patent adopts a mode of exciting inner layer plasmas and outer layer plasmas in a staggered mode, and realizes the synergistic effect of stealth and enhancement effect under different communication wave and detection wave combinations in a wider frequency band. However, the above patent does not discuss generally how effective enhancement is achieved by a non-uniform plasma.
In summary, the following problems still exist in the current research on the plasma enhancement technology:
(1) Most of the existing theoretical and numerical simulation researches on sub-wavelength plasma enhanced microwave electromagnetic radiation aim at ideal uniform plasma distribution, and the existing published patents on plasma enhanced phenomena also mainly adopt uniform plasma distribution. While the actual plasma generally has some non-uniformity;
(2) In the existing research on non-uniform plasma, the minimum value of the plasma density is usually 0. In this case, the electromagnetic wave is likely to excite plasmon resonance in the plasma. Since plasmon resonance is usually accompanied by a strong energy absorption process, the occurrence of resonance effects can seriously impair the radiation-enhancing effect of the plasma on electrically small antennas.
In general, there is currently a lack of a general design approach to achieve optimal enhancement with non-uniform plasmas.
Disclosure of Invention
The invention aims to overcome the defects that the physical model of the existing plasma enhancement technology is simple and general discussion for realizing optimal enhancement by utilizing non-uniform plasma is lacked, and provides a radiation enhancement method based on the non-uniform plasma.
The invention discloses a radiation enhancement method based on non-uniform plasma, which is realized based on a plasma enhanced small antenna, wherein the plasma enhanced small antenna comprises a spherical shell-shaped plasma cover and a small electric antenna positioned in the plasma cover; moreover, plasmas in the plasma shield are non-uniformly distributed along the radius of the plasma shield;
the radiation enhancement method comprises the following steps:
the plasma density and the size of the plasma cover are adjusted to meet the following conditions, so that the radiation of the electrically small antenna is enhanced by the non-uniform plasma: dimensions include an inner diameter and an outer diameter;
n c ＝ω 2 ε 0 m e /e 2
n pin /n c ＞1
n pout /n c ＞1
0.05＜r out /λ＜0.1
wherein, ω is p0 Indicating the plasma frequency, n, within the plasma shroud for the optimum enhancement condition of the uniform plasma 0 Indicates the plasma density, n, corresponding to the optimum enhancement condition of the uniform plasma c Represents the critical plasma density, ∈ 0 Represents a dielectric constant in vacuum, m e For electron mass, e represents the amount of elementary charge, n p (r) represents a distribution function of plasma density along a radius direction of the plasma shroud, r represents a distance from a point in the plasma shroud to a center of the plasma shroud, n pin And n pout Respectively representing the plasma density at the inner and outer boundaries of the plasma sheath, r in And r out Respectively, the inner and outer diameters of the plasma sheath, and λ the wavelength of electromagnetic waves radiated by the electrically small antenna in vacuum.
The invention has the beneficial effects that:
the invention provides a general design method capable of realizing non-uniform plasma enhancement, which avoids electromagnetic waves from exciting plasma resonance in the plasma by optimizing the density distribution of the plasma, thereby obtaining a more ideal enhancement effect.
Drawings
FIG. 1 is a schematic cross-sectional view of a plasma enhanced electrically small antenna in the x-z plane;
FIG. 2 is a graph showing the variation of the mode value of the 1 st order electric meter scattering factor with the normalized plasma frequency under the condition of uniform distribution of plasma in the plasma cover;
FIG. 3 is a plasma density distribution curve along the r direction when the plasma density is linearly decreased from the inside to the outside according to the present invention;
FIG. 4 is a graph showing the distribution of plasma density along the r direction when the plasma density is distributed in a decreasing parabolic manner from the inside to the outside in the present invention;
FIG. 5 is a plasma density distribution curve along the r-direction when the plasma density is exponentially distributed from the inside to the outside in the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
It should be noted that the embodiments and features of the embodiments may be combined with each other without conflict.
The invention is further described with reference to the following drawings and specific examples, which are not intended to be limiting.
In a first specific embodiment, the radiation enhancement method based on the non-uniform plasma in this embodiment is implemented based on a plasma enhanced electrically small antenna, which includes a spherical shell-shaped plasma cover and an electrically small antenna located in the plasma cover; moreover, plasmas in the plasma shield are non-uniformly distributed along the radius of the plasma shield;
the radiation enhancement method is as follows:
the plasma density and the size of the plasma cover are adjusted to meet the following conditions, so that the radiation of the electrically small antenna is enhanced by the non-uniform plasma: dimensions include inner and outer diameters;
n c ＝ω 2 ε 0 m e /e 2
n pin /n c ＞1
n pout /n c ＞1
0.05＜r out /λ＜0.1
wherein, ω is p0 Indicating the plasma frequency, n, within the plasma sheath for the optimum plasma boost condition 0 Indicates the plasma density, n, corresponding to the optimum enhancement condition of the uniform plasma c Represents the critical plasma density, ∈ 0 Represents a dielectric constant in vacuum, m e For electron mass, e represents the amount of elementary charge, n p (r) represents a distribution function of plasma density along a radius direction of the plasma shroud, r represents a distance from a point in the plasma shroud to a center of the plasma shroud, n pin And n pout Respectively representing the plasma density at the inner and outer boundaries of the plasma sheath, r in And r out Respectively, the inner and outer diameters of the plasma sheath, and λ the wavelength of electromagnetic waves radiated by the electrically small antenna in vacuum.
Detailed description of the invention
In this embodiment, the plasma density decreases linearly from the inside to the outside along the radius of the plasma cover, and n is a linear decrease p (r) in order to realize the purpose of the method,
other technical solutions of the present embodiment are the same as those of the first embodiment.
Detailed description of the invention
This embodiment mode is a further description of the first embodiment mode, and in this embodiment mode, the plasma density is along the plasmaThe radius of the shield decreases from the inside to the outside in a linear parabolic manner, n p (r) is a group of,
other technical solutions of the present embodiment are the same as those of the first embodiment.
Detailed description of the invention
In this embodiment, the plasma density decreases exponentially from the inside along the radius of the plasma cover, and n is a value that is larger than the plasma density of the plasma cover p (r) is a group of,
n p (r)＝4(n pin -n pout )2 -r +2n pout -n pin 。
other technical solutions of the present embodiment are the same as those of the first embodiment.
Detailed description of the invention
This embodiment is a further description of one of the first to fourth embodiments, and in this embodiment, the plasma frequency ω in the plasma cover corresponding to the optimum plasma boost condition is obtained p0 Comprises the following steps:
step one, assuming that plasmas in the plasma cover are uniformly distributed, the 1 st-order electric meter scattering factor of the plasma cover is
Wherein the content of the first and second substances,
x＝kr in
y＝kr out
ψ 1 (z)＝zj 1 (z)
χ 1 (z)＝-zy 1 (z)
ξ 1 (z)＝z[j 1 (z)+iy 1 (z)]
wherein psi' 1 (z)、χ' 1 (z), and ξ' 1 (z) are each psi 1 (z)、χ 1 (z) and xi 1 (z), v denotes a collision frequency of the plasma, ω denotes an angular frequency of the electromagnetic wave radiated from the electrically small antenna, i denotes an imaginary unit, k denotes a wave number of the electromagnetic wave radiated from the electrically small antenna, m p Denotes the refractive index, ω, of the plasma p Denotes the plasma frequency, j 1 (z) and y 1 (z) first order spherical Bessel functions of the first and second types, respectively, z representing an argument of the corresponding function;
step two, solving a 1 Maximum value of the modulus value, the plasma frequency omega under the optimum strengthening condition can be obtained p0 。
Other technical means of the present embodiment are the same as those of one of the first to fourth embodiments.
Detailed description of the invention
In this embodiment mode, the plasma in the spherical plasma cover is weak collision plasma, and the plasma satisfies the requirement of the fifth embodiment mode
v/ω＜0.1。
Other technical means of the present embodiment are the same as those of the fifth embodiment.
Detailed description of the invention
In this embodiment, the sixth embodiment will be further explained, and in this embodiment, the collision frequency v of plasma is 0.1GHz.
Other technical means of the present embodiment are the same as those of the sixth embodiment.
Detailed description of the invention
This embodiment is a further description of one of the first to fourth embodiments, and in this embodiment, a gap is provided between the plasma cover and the small antenna in the plasma-enhanced electric small antenna.
Other technical means of the present embodiment are the same as those of one of the first to fourth embodiments.
Detailed description of the invention
In this embodiment mode, the electrically small antenna is provided eccentrically to the plasma cover.
The other technical means of the present embodiment are the same as those of the seventh embodiment.
Detailed description of the preferred embodiment
In this embodiment, the electrically small antenna is a spherical dipole antenna and is concentrically disposed in the hollow region of the plasma cover;
the working frequency of the electrically small antenna is 1GHz; the electromagnetic wave radiated by the electrically small antenna is polarized in the z-direction and propagates in the x-direction.
The other technical means of the present embodiment are the same as those of the seventh embodiment.
DETAILED DESCRIPTION OF EMBODIMENT (S) OF INVENTION
The invention aims to provide a method for overcoming the resonance attenuation of plasma and realizing high-gain non-uniform plasma size and density distribution aiming at the problem of non-uniform plasma enhanced electrically small antenna radiation efficiency from the viewpoint of practicability.
As shown in fig. 1, the plasma enhanced electrically small antenna comprises a spherical shell type plasma cover 1 and an electrically small antenna system 2;
the inner diameter and the outer diameter of the spherical shell-shaped plasma cover 1 are r in And r out ；
The electrically small antenna system 2 is positioned in the spherical shell-shaped plasma cover and is eccentrically or concentrically arranged, so that the requirements of
r a ＜r in , (1)
Wherein r is a Indicating the radius corresponding to the smallest sphere that can accommodate the electrically small antenna system.
A gap exists between the plasma cover and the antenna system;
the plasma in the spherical shell-shaped plasma cover is weak collision plasma, and the requirements are met
v/ω＜0.1, (2)
Where v is the collision frequency of the plasma and ω represents the angular frequency of the electromagnetic wave radiated by the electrically small antenna.
When the plasma cover is opened, the plasma parameters in the plasma cover are obtained through the following two steps:
in the first step, assuming that the plasma in the plasma cover is uniformly distributed, the 1 st order electric meter scattering factor of the plasma spherical shell is
Wherein the content of the first and second substances,
x＝kr in , (6)
y＝kr out , (7)
ψ 1 (z)＝zj 1 (z), (8)
χ 1 (z)＝-zy 1 (z), (9)
wherein k is the wave number of the electromagnetic wave radiated by the electrically small antenna; m is p Represents the refractive index of the plasma; omega p Represents the plasma frequency; j is a unit of a group 1 (z) and y 1 (z) denotes the first class and the first class, respectivelyThe second class of first order Bessel functions, z represents the argument of the corresponding function, and i represents the imaginary unit.
Is the first type of ball Hankel function.
By solving for a 1 Maximum value of modulus value, plasma frequency omega under optimum strengthening condition can be obtained p0 I.e. by
max|a 1 |→ω p0 , (11)
Secondly, on the basis of uniform plasma, the size and density distribution of the non-uniform plasma should meet the requirements
n c ＝ω 2 ε 0 m e /e 2 , (13)
n pin /n c ＞1, (15)
n pout /n c ＞1, (16)
0.05＜r out /λ＜0.1, (18)
Wherein, ω is p0 Indicating the plasma frequency in the plasma cover corresponding to the optimal enhancement condition of the uniform plasma; n is 0 The plasma density corresponding to the optimal enhancement condition of the uniform plasma is represented, namely the plasma density corresponding to the optimal enhancement condition under the uniform distribution of the plasma is represented; n is a radical of an alkyl radical c Indicating plasma frequency and electricityThe corresponding plasma density when the magnetic wave frequencies are equal, namely the critical plasma density; epsilon 0 Represents a dielectric constant in vacuum, m e For electron mass, e represents the amount of elementary charge, n p (r) represents a distribution function of plasma density along a radius direction of the plasma shroud, r represents a distance from a point in the plasma shroud to a center of the plasma shroud, n pin And n pout Respectively representing the plasma density at the inner and outer boundaries of the plasma sheath, r in And r out Respectively, the inner and outer diameters of the plasma sheath, and λ the wavelength of electromagnetic waves radiated by the electrically small antenna in vacuum.
Inner diameter r of the shell-and-ball type plasma cover 1 in =1cm, outer diameter r out ＝2cm；
The electrically small antenna system 2 is a spherical dipole antenna concentrically placed in the hollow region of the plasma sheath, where r a =0.2cm, feed voltage 1V;
and (3) researching the enhancement effect of the non-uniform plasma on the radiation of the electrically small antenna by adopting a numerical simulation method. The collision frequency of the plasma is 0.1GHz, and the working frequency of the electrically small antenna is 1GHz (the electromagnetic wave is polarized along the z direction, and the electromagnetic wave is transmitted along the x direction).
Under the condition that the above conditions are satisfied, the following three plasma density non-uniform distribution cases are taken as examples:
1. when the plasma density is linearly decreased from the inside to the outside, the plasma density distribution in the r direction is as shown in fig. 3.
Different normalized plasma frequencies (ω) can be calculated from equations (3) - (10) pe Omega) condition of uniform plasma spherical shell, and amplitude of first-order electric meter scattering factor | a of uniform plasma spherical shell 1 The variation characteristic of | is shown in fig. 2. It can be seen that when | a 1 When | takes the maximum value, the plasma frequency ω p0 =2.069 × 2 π rad/s, corresponding to a plasma density of n 0 ＝5.3096×10 16 m -3 . Based on equation (14), the plasma density is linearly decreased from the inside to the outside, i.e.
The relationship between the plasma density at the inner and outer boundaries of the plasma sheath can be obtained from the equation (17)
11n pin +17n pout ＝28n 0 (20)
Considering equations (15) and (16), let n pin ＝8×10 16 m -3 Then n is obtained from the formula (20) pout ＝3.5688×10 16 m -3 . Furthermore, the radiation gain of the electrically small antenna is 25.6894dB by substituting the relevant parameters into COMSOL software simulation.
2. When the plasma density is distributed in a parabolic decreasing manner from the inside to the outside, the plasma density distribution in the r direction is as shown in fig. 4.
Different normalized plasma frequencies (ω) can be calculated from equations (3) - (10) pe Omega) condition of uniform plasma spherical shell, and amplitude of first-order electric meter scattering factor | a of uniform plasma spherical shell 1 The variation characteristic of | is shown in fig. 2. It can be seen that when | a 1 When | takes the maximum value, the plasma frequency ω p0 =2.069 × 2 π rad/s, corresponding to a plasma density of n 0 ＝5.3096×10 16 m -3 . Based on equation (14), let the plasma density decrease from the inside to the outside in a parabolic manner, i.e.
The relationship between the plasma density at the inner and outer boundaries of the plasma sheath can be obtained from the equation (17)
39n pin +31n pout ＝70n 0 (22)
Considering equations (15) and (16), let n be pin ＝8×10 16 m -3 Then n is obtained from the formula (22) pout ＝1.9249×10 16 m -3 . Furthermore, the radiation gain of the electrically small antenna is 23.7973dB by substituting the relevant parameters into COMSOL software simulation.
3. When the plasma density is exponentially distributed from the inside to the outside, the plasma density distribution in the r direction is as shown in fig. 5.
Different normalized plasma frequencies (ω) can be calculated from equations (3) - (10) pe Omega) condition of uniform plasma spherical shell, and amplitude of first-order electric meter scattering factor | a of uniform plasma spherical shell 1 The variation characteristic of | is shown in fig. 2. It can be seen that when | a 1 When | takes the maximum value, the plasma frequency ω p0 =2.069 × 2 π rad/s, corresponding to a plasma density of n 0 ＝5.3096×10 16 m -3 . Based on equation (14), the plasma density is exponentially distributed from inside to outside, i.e.
n p (r)＝4(n pin -n pout )2 -r +2n pout -n pin (23)
The relationship between the plasma density at the inner and outer boundaries of the plasma sheath can be obtained from the equation (17)
Considering equations (15) and (16), let n pin ＝8×10 16 m -3 Then n is obtained from the formula (24) pout ＝3.9408×10 16 m -3 . Furthermore, the radiation gain of the electrically small antenna is 24.7247dB by substituting the relevant parameters into COMSOL software simulation.
Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims. It should be understood that features from different dependent claims and herein may be combined in ways other than those described in the original claims. It is also to be understood that features described in connection with individual embodiments may be used in other embodiments.
Claims (10)
1. A radiation enhancement method based on non-uniform plasma is characterized in that the method is realized based on a plasma enhanced electric small antenna, wherein the plasma enhanced electric small antenna comprises a spherical shell-shaped plasma cover and an electric small antenna positioned in the plasma cover; moreover, plasmas in the plasma shield are non-uniformly distributed along the radius of the plasma shield;
the radiation enhancement method is as follows:
the plasma density and the size of the plasma cover are adjusted to meet the following conditions, so that the radiation of the electrically small antenna is enhanced by the non-uniform plasma: the dimensions include an inner diameter and an outer diameter;
n c ＝ω 2 ε 0 m e /e 2
n pin /n c ＞1
n pout /n c ＞1
0.05＜r out /λ＜0.1
wherein, ω is p0 Indicating the plasma frequency, n, within the plasma sheath for the optimum plasma boost condition 0 Indicates the plasma density, n, corresponding to the optimum enhancement condition of the uniform plasma c Represents the critical plasma density, ∈ 0 Represents a dielectric constant in vacuum, m e For electron mass, e represents the amount of elementary charge, n p (r) distribution function of plasma density along radius direction of plasma coverThe number, r, represents the distance from a point in the plasma shroud to the center of the plasma shroud, n pin And n pout Respectively representing the plasma density at the inner and outer boundaries of the plasma sheath, r in And r out Respectively, the inner and outer diameters of the plasma sheath, and λ the wavelength of electromagnetic waves radiated by the electrically small antenna in vacuum.
2. The non-uniform plasma based radiation enhancement method as claimed in claim 1, wherein the plasma density decreases linearly from inside to outside along the radius of the plasma sheath, n p (r) is a group of,
3. the non-uniform plasma-based radiation enhancement method of claim 1, wherein the plasma density decreases in a linear parabolic manner from inside to outside along a radius of the plasma sheath, and n is p (r) is a group of,
4. a non-uniform plasma based radiation enhancement method as claimed in claim 1, wherein the plasma density decreases exponentially from inside to outside along the radius of the plasma sheath, n p (r) in order to realize the purpose of the method,
n p (r)＝4(n pin -n pout )2 -r +2n pout -n pin 。
5. a non-uniform plasma based radiation enhancement method as claimed in one of claims 1 to 4, characterized in that the plasma frequency ω inside the plasma housing corresponding to the optimal enhancement condition of the uniform plasma is obtained p0 The steps are as follows:
step one, assuming that plasmas in the plasma cover are uniformly distributed, the 1 st-order electric meter scattering factor of the plasma cover is
Wherein, the first and the second end of the pipe are connected with each other,
x＝kr in
y＝kr out
ψ 1 (z)＝zj 1 (z)
χ 1 (z)＝-zy 1 (z)
ξ 1 (z)＝z[j 1 (z)+iy 1 (z)]
wherein psi' 1 (z)、χ' 1 (z), and ξ' 1 (z) are each psi 1 (z)、χ 1 (z) and xi 1 (z), v denotes a collision frequency of the plasma, ω denotes an angular frequency of the electromagnetic wave radiated from the electrically small antenna, i denotes an imaginary unit, k denotes a wave number of the electromagnetic wave radiated from the electrically small antenna, m p Denotes the refractive index, ω, of the plasma p Denotes the plasma frequency, j 1 (z) and y 1 (z) first order spherical Bessel functions of the first and second types, respectively, z representing an argument of the corresponding function;
step two, solving a 1 Maximum value of the modulus value, the plasma frequency omega under the optimum strengthening condition can be obtained p0 。
6. The non-uniform plasma based radiation enhancement method as claimed in claim 5, wherein the plasma in the spherical plasma shield is a weak impact plasma satisfying
v/ω＜0.1。
7. A non-uniform plasma based radiation enhancement method according to claim 6, wherein the collision frequency v of the plasma is 0.1GHz.
8. A non-uniform plasma based radiation enhancement method according to one of claims 1-4 wherein there is a gap between the plasma sheath and the electrically small antenna in the plasma enhanced electrically small antenna.
9. A non-uniform plasma based radiation enhancement method as recited in claim 7, wherein the electrically small antenna is positioned off-center with respect to the plasma sheath.
10. The non-uniform plasma based radiation enhancement method of claim 7, wherein the electrically small antenna is a spherical dipole antenna concentrically disposed within the hollow region of the plasma sheath;
the working frequency of the electrically small antenna is 1GHz; the electromagnetic wave radiated by the electrically small antenna is polarized in the z-direction and propagates in the x-direction.
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