CN111710985B - Controllable polarization conversion surface based on liquid metal - Google Patents
Controllable polarization conversion surface based on liquid metal Download PDFInfo
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q15/00—Devices for reflection, refraction, diffraction or polarisation of waves radiated from an antenna, e.g. quasi-optical devices
- H01Q15/0006—Devices acting selectively as reflecting surface, as diffracting or as refracting device, e.g. frequency filtering or angular spatial filtering devices
- H01Q15/0013—Devices acting selectively as reflecting surface, as diffracting or as refracting device, e.g. frequency filtering or angular spatial filtering devices said selective devices working as frequency-selective reflecting surfaces, e.g. FSS, dichroic plates, surfaces being partly transmissive and reflective
- H01Q15/002—Devices acting selectively as reflecting surface, as diffracting or as refracting device, e.g. frequency filtering or angular spatial filtering devices said selective devices working as frequency-selective reflecting surfaces, e.g. FSS, dichroic plates, surfaces being partly transmissive and reflective said selective devices being reconfigurable or tunable, e.g. using switches or diodes
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q15/00—Devices for reflection, refraction, diffraction or polarisation of waves radiated from an antenna, e.g. quasi-optical devices
- H01Q15/24—Polarising devices; Polarisation filters
- H01Q15/242—Polarisation converters
- H01Q15/244—Polarisation converters converting a linear polarised wave into a circular polarised wave
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Abstract
The invention belongs to the technical field of antennas, and provides a controllable polarization conversion surface based on liquid metal, which is used for solving the problem that the electromagnetic property of an artificial electromagnetic surface cannot be changed after the artificial electromagnetic surface is processed, so that the reconfigurable property of the electromagnetic property of the artificial electromagnetic surface is realized; the polarization conversion surface comprises M-N controllable polarization conversion units which are periodically arranged, wherein M is more than or equal to 3, N is more than or equal to 3, M and N are positive integers, and the polarization conversion units comprise a metal floor, a medium substrate, a liquid metal micro-flow channel and a liquid metal alloy; the medium substrate is made of PDMS material with liquid metal micro-channels, which are respectively a first medium substrate, a second medium substrate and a coating medium, the first substrate, the second medium substrate and the coating medium are connected by adopting a thermal bond and mode, and the liquid metal micro-channels comprise a fold line type micro-channel and a sawtooth type micro-channel; the working performance of the polarization conversion surface can be regulated and controlled by changing the position state of the liquid metal.
Description
Technical Field
The invention belongs to the technical field of electromagnetic medium characteristic research, and relates to a reconfigurable polarization conversion surface based on liquid metal and a reconfiguration method thereof.
Background
With the continuous development of modern wireless communication technology, people can meet various environments with complex climates in the process of researching and influencing the propagation of electromagnetic waves, because the confidentiality of communication requires that the electromagnetic waves are controllable in real time in the propagation process, polarization is an important characteristic of the electromagnetic waves, and the electromagnetic waves have important roles in increasing communication capacity, improving the confidentiality and the like. There are two main methods for controlling the polarization of electromagnetic waves, namely, directly controlling the polarization of the antenna, and designing a polarization rotating surface and placing the polarization rotating surface on the antenna radiation path or directly using the polarization rotating surface as the radiation surface of the antenna. The former has the advantages of small antenna structure size, wide frequency band, low loss and the like, but the design of a radio frequency bias circuit is complex because the radiation of the antenna is directly regulated and controlled; in contrast, the latter can indirectly control the radiation performance of the antenna by only designing a Reconfigurable Polarization Rotation Surface (RPRS), and the surface-based polarization converter has the characteristics of high efficiency, wide frequency band or multiband, ultrathin thickness and the like, and is known as a very good method for controlling the polarization state of electromagnetic waves.
The existing reconfigurable polarization rotating surface can be roughly divided into two methods of changing a dielectric material and changing an effective metal structure according to an implementation mode. In the former, materials such as graphene, liquid crystal, metal microfluid and the like are generally used for replacing traditional metal and medium materials, and the method has the characteristics of high working frequency band and large design and processing difficulty; in contrast, the latter has the characteristics of easy simulation processing, good electrical controllability, flexible and various structures and the like. At present, the commonly used metal structure of reconfigurable electromagnetic material is designed by radio frequency switch, such as varactor, pin diode and Micro Electro Mechanical System (MEMS) switch for control,
in 2018, yangwanli, gaoxi et al designed a mode of switching the working form of an artificial electromagnetic material by a bias voltage Based on an Active feed artificial electromagnetic surface embedded varactor to realize switching between linear Polarization and circular Polarization Converter in an article A Reconfigurable Polarization Converter Active measurement published by 2018Cross line quick-Regional Radio Science and Wireless Technology Conference (CSQRCC). The device acts as a linear polarization transformer for a bias voltage of 0V, and switches to a linear polarization converting circular polarization converting surface for a bias voltage of-19V. These devices usually require a dc bias circuit for activation, which usually limits the number and range of material states, resulting in complex structure, non-linearity, low processing power, and the like.
In 2017, the Liquid-Metal Polarization-Pattern-Reconfigurable Dipole Antenna published by Meng Wang et al at IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS allowed LMA to enter 5 discrete states in different Polarization and zero directions by electrically driving the Liquid Metal within the capillary, localized surface energy wells built into polyimide clamp wrap fluids that allowed metastable locked LMA, eliminating the need for continuous DC bias voltage to maintain each state. A positive dc bias voltage is applied to the electrolyte solution na (oh) surrounding the liquid metal, creating a surface tension gradient that produces a Marangoni force that pushes the liquid metal in a positive direction. The method uses the surface tension of the liquid metal and the electro-dissolving liquid to drive the LMA to be greatly interfered by the outside, the result can be seriously influenced by the gravitational potential energy of a point, the equipment can normally work when the equipment is required to be completely balanced and has no centrifugal force, and the working condition is completely strictly limited.
In 2020, wangqi et al, in article a Frequency-and Polarization-configurable Slot Antenna Using Liquid Metal published by IEEE Transactions on Antennas and Propagation, indicated that Liquid Metal can be switched before multimode, by injecting Liquid Metal to change the effective Metal structure to affect the radiation performance of the Antenna. The single antenna can radiate three modes of left-hand circularly polarized wave, right-hand circularly polarized wave and linear polarized wave, but the metal structure of the feed antenna cannot be changed and the working bandwidth is narrow. In order to change the problems, the liquid reconfigurable electromagnetic materials can be used for designing a substrate by using soft materials and adopting a physical pressure control driving mode, so that the application scenes and ways of the liquid reconfigurable electromagnetic materials can be increased, and the liquid reconfigurable electromagnetic materials can be changed in shape and can be unfolded during miniaturized storage work due to the liquid flexibility, so that the liquid reconfigurable electromagnetic materials can be more conveniently carried and shipped.
Disclosure of Invention
The invention aims to provide a controllable polarization conversion surface based on liquid metal, which aims to overcome the defects of the prior art, and aims to solve the technical problems that the electromagnetic performance of the conventional polarization conversion surface processing and forming cannot be changed, the reconfigurable state is few and the structure is complex by changing the filling area of the liquid metal to control the working performance of the polarization conversion surface.
In order to achieve the purpose, the invention adopts the technical scheme that:
a controllable polarization conversion surface based on liquid metal comprises M × N controllable polarization conversion units which are periodically arranged, wherein M is more than or equal to 3, N is more than or equal to 3, M and N are positive integers, each polarization conversion unit comprises a metal floor 1, a medium substrate 2, a liquid metal micro-flow channel 3 and a liquid metal alloy 4, and the controllable polarization conversion surface is characterized in that:
the medium substrate 2 consists of a first medium substrate 2.1, a second medium substrate 2.2 and a coating medium 2.3, the first substrate 2.1, the second medium substrate 2.2 and the coating medium 2.3 are connected in a hot key and mode, the liquid metal micro-channel 3 comprises a fold line type micro-channel 3.1 and a sawtooth type micro-channel 3.2, the fold line type micro-channel 3.1 is etched on the upper surface of the first medium substrate 2.1, and two ends of the fold line type micro-channel 3.1 are connected with the edge of the polarization conversion unit to form a double-bow-shaped groove; the sawtooth-shaped micro-channel 3.2 is etched on the upper surface of the second layer of dielectric substrate 2.2, and two ends of the sawtooth-shaped micro-channel 3.2 are connected with the edge of the polarization conversion unit to form a V-shaped groove;
the broken line type micro-flow channel 3.1 and the sawtooth type micro-flow channel 3.2 are symmetrically distributed around the central axis of the u direction, and the position state of the liquid metal alloy 4 in the liquid metal micro-flow channel 3 is controlled through pressurization so as to realize the working performance of the adjustable polarization conversion surface.
The unit side length of the medium substrate 2 is la, and the value range of la is 8-8.2 mm; the thickness of the first dielectric substrate 2.1 is ld, the range of ld is 2.5-3 mm, the thickness of the second dielectric substrate 2.2 is lc, the range of lc is 1.9-2.2 mm, the thickness of the cladding medium 2.3 is lb, and the range of lb is 0.9-1.2 mm.
The slotting depth of the double-arch-shaped groove is h1, the value range of h1 is 0.3-0.5 mm, the distance between central folding lines of the groove is li, the value range of li is 1.5-1.9 mm, the length of a longitudinal folding line arm is lh, the value range of lh is 5-6.2 mm, the distance between the folding line and the edge of the polarization conversion unit is lk, and the value range of lk is 0.5-1.2 mm; the 3.1 width of the broken line type micro-channel is lg, and the value range of lg is 0.2-0.22 mm.
The groove depth of the V-shaped groove is h2, the value range of h2 is 0.3-0.5 mm, the distance between the corner of the V-shaped groove and the edge of a unit is ls, the value range of ls is 0.5-1 mm, the depth of the V-shaped groove is lf, the value range of lf is 3.4-3.9 mm, and the angle theta is 46-50 degrees; the 3.2 width of the sawtooth-shaped micro-channel is le, and the value range of le is 0.33-0.37 mm.
The liquid metal micro-channel 3 is filled with Liquid Metal Alloy (LMA) which is gallium indium alloy (EGaIn).
The dielectric substrate 2 is made of Polydimethylsiloxane (PDMS), and the PDMS has a dielectric coefficient ∈ of 2.65 and an electric loss tangent of 0.021.
Compared with the prior art, the invention has the following advantages:
1. the Liquid Metal (LMA) used in the invention replaces the traditional solid metal design, and solves the problems that the traditional reconfigurable polarized surface design faces a complex bias network, a slow exchange speed and an expensive manufacturing process. The method of injecting the liquid metal into the microfluidic channel wrapped in the elastic substrate by applying the microfluidic technology enables the design of the reconfigurable artificial electromagnetic structure to be simple and convenient, reduces the whole volume, and is difficult to break when the liquid metal flows along with pressure unlike solid metal, so that the materials can accept certain deformation and have self-healing capability.
2. The liquid metal micro-channel designed by the invention comprises a broken line type micro-channel and a sawtooth type micro-channel, and the polarization conversion surface can freely switch the working mode through the integrated micro-channel design, and simultaneously, the mechanism for controlling the switching of the liquid metal mode is simplified. The liquid metal micro-channel adopts the design of uniform cross section, can avoid the liquid metal injection in-process, because the velocity of flow inequality produces the problem that the bubble influences dielectric constant, conductivity.
3. The controllable polarization conversion surface dielectric substrate consists of three layers of plane structures, and comprises a first layer of dielectric substrate, a second layer of dielectric substrate and a coating medium. The design of the M multiplied by N polarization conversion units is easier to process and splice, the controllable polarization conversion surface reduces the manufacturing difficulty, does not need to use an additional micro-electromechanical control structure, is easy to assemble, and greatly increases the practicability of the controllable polarization conversion surface.
Drawings
FIG. 1 is a schematic diagram of the overall structure of a controllable polarization conversion surface according to the present invention;
FIG. 2 is a schematic diagram of the structure of a controllable polarization conversion surface unit according to the present invention;
FIG. 3 is a schematic diagram of a layered structure of a controllable polarization conversion surface unit according to the present invention;
FIG. 4 is a side view of a controllable polarization conversion surface unit of the present invention;
FIG. 5 is a diagram showing the dimension distribution of "V" -shaped grooves on the upper surface of the second dielectric substrate of the controllable polarization conversion surface unit according to the present invention;
FIG. 6 is a graph showing the dimension distribution of "double-bow" shaped grooves on the upper surface of the first dielectric substrate of the controllable polarization conversion surface unit according to the present invention;
FIG. 7 is a schematic diagram of the direction of u and v polarization and x and y polarization marked by the irradiation of a normal incident wave on a controllable polarization conversion surface according to the present invention;
FIG. 8 is a graph showing the reflection amplitude and reflection phase of u-polarization and v-polarization irradiated by a perpendicular incident wave in state II of the controllable polarization conversion surface of the present invention;
FIG. 9 is a graph showing the results of the co-polarized and cross-polarized reflection amplitudes of a controlled polarization conversion surface of the present invention in state II, illuminated by a normal incident wave;
FIG. 10 is a graph showing the results of u-polarization, v-polarization reflection amplitude and reflection phase for a controlled polarization conversion surface of the present invention in state III, illuminated by a normal incident wave;
FIG. 11 is a graph showing axial ratio results of a controlled polarization conversion surface of the present invention illuminated by a normal incident wave in state III.
Detailed Description
The invention is further described with reference to the following figures and specific embodiments:
example 1:
referring to fig. 1, fig. 2, fig. 3, fig. 4, fig. 5, and fig. 6
A controllable polarization conversion surface based on liquid metal comprises M × N controllable polarization conversion units which are periodically arranged, wherein M is more than or equal to 3, N is more than or equal to 3, M and N are positive integers, and each polarization conversion unit comprises a metal floor 1, a medium substrate 2, a liquid metal micro-channel 3 and a liquid metal alloy 4;
the medium substrate 2 consists of a first medium substrate 2.1, a second medium substrate 2.2 and a coating medium 2.3, the first substrate 2.1, the second medium substrate 2.2 and the coating medium 2.3 are connected in a hot key and mode, the liquid metal micro-channel 3 comprises a fold line type micro-channel 3.1 and a sawtooth type micro-channel 3.2, the fold line type micro-channel 3.1 is etched on the upper surface of the first medium substrate 2.1, and two ends of the fold line type micro-channel 3.1 are connected with the edge of the polarization conversion unit to form a double-bow-shaped groove; the sawtooth-shaped micro-channel 3.2 is etched on the upper surface of the second layer of dielectric substrate 2.2, and two ends of the sawtooth-shaped micro-channel 3.2 are connected with the edge of the polarization conversion unit to form a V-shaped groove;
the broken line type micro-flow channel 3.1 and the sawtooth type micro-flow channel 3.2 are symmetrically distributed around the central axis of the u direction, and the position state of the liquid metal alloy 4 in the liquid metal micro-flow channel 3 is controlled through pressurization so as to realize the working performance of the adjustable polarization conversion surface.
The unit side length of the medium substrate 2 is la, the range of the value of la is 8-8.2 mm, and the optimal value is 8 mm; the thickness of the first dielectric substrate 2.1 is ld, the range of ld is 2.5-3 mm, the optimal value is 2.8mm, the thickness of the second dielectric substrate 2.2 is lc, the range of lc is 1.9-2.2 mm, the optimal value is 2mm, the thickness of the cladding medium 2.3 is lb, the range of lb is 0.9-1.2 mm, and the optimal value is 1 mm.
The slotting depth of the double-arch-shaped groove is h1, the value range of h1 is 0.3-0.5 mm, the optimal value of the double-arch-shaped groove is 0.3mm, the distance between central folding lines of the groove is li, the value range of li is 1.5-1.9 mm, the optimal value of li is 1.8mm, the arm length of a longitudinal folding line is lh, the value range of lh is 5-6.2 mm, the optimal value of 6mm, the distance between the folding line and the edge of the polarization conversion unit is lk, the value range of lk is 0.5-1.2 mm, and the optimal value of lk is 0.8 mm; the 3.1 width of the broken line type micro-channel is lg, the value range of lg is 0.2-0.22 mm, and the optimal value is 0.2 mm.
The depth of the groove of the V-shaped groove is h2, the value range of h2 is 0.3-0.5 mm, the optimal value of the groove is 0.3mm, the distance between the corner of the V-shaped groove and the edge of a unit is ls, the value range of ls is 0.5-1 mm, the optimal value of the groove is 0.6mm, the depth of the V-shaped groove is lf, the value range of lf is 3.4-3.9 mm, the optimal value of the groove is 3.5mm, the corner theta is 46-50 degrees, and the optimal value of the groove is 48.8 degrees; the 3.2 width of the sawtooth-shaped micro-channel is le, the value range of le is 0.33-0.37 mm, and the optimal value is 0.35 mm.
The liquid metal micro-channel 3 is filled with Liquid Metal Alloy (LMA) which is gallium indium alloy (EGaIn).
The dielectric substrate 2 is made of Polydimethylsiloxane (PDMS), and the PDMS has a dielectric coefficient ∈ of 2.65 and an electric loss tangent of 0.021.
The polarization control function based on the liquid metal controllable polarization conversion surface adjusts the reflection characteristics of the polarization conversion surface to the vertical incidence electromagnetic wave by changing the position state of the liquid metal alloy 4 in the liquid metal micro flow channel 3. The designed controllable PCM can distinguish three working states through the filling layout of the LMA in the micro-channel. State I: when the liquid metal micro-channel 3 of the controllable PCM unit is emptied into air, the whole body presents the total reflection characteristic similar to an ideal PEC, and the polarization of the reflected wave is not influenced. And state II: the broken line type micro-channel 3.1 is filled with liquid metal alloy 4; when air is in the sawtooth-shaped micro-channel 3.2, the controllable polarization conversion unit can realize polarization rotation in the second working state. And state III: the sizes of the broken line type micro-channel 3.1 and the zigzag type micro-channel 3.2 are not changed, liquid metal alloy 4 is filled in the broken line type micro-channel and the zigzag type micro-channel, and the controllable polarization conversion unit can realize conversion from linear polarization to circular polarization in a third working state.
In the state I, the liquid metal micro-channel 3 is filled with air, and the structure has no other metal structures except the metal floor 1, and cannot generate polarization deflection influence on the vertical incident electromagnetic wave, so that the incident wave is completely reflected and polarization conversion does not occur at the moment.
In the state II, the invention is in the broken line type micro-channel 3.1Liquid metal alloy 4 is filled, and air is filled in the sawtooth-shaped micro-channel 3.2. At the moment, the metal structure in the controllable polarization conversion surface consists of liquid metal 4 in a broken line type micro-channel 3.1 and a metal floor 1, and under the irradiation of electromagnetic waves with the vertical incident polarization direction being the x direction, the electric field of incident waves can be decomposed into two electric fields with equal amplitude in the u direction and the v direction
According to the electric field mode, the original incident wave can be decomposed into two electromagnetic waves with mutually perpendicular polarization, equal amplitude and same phase
At this time, the broken line type metal structure 3.1 is electromagnetic wave in the u direction to the electric field
Fully transmissive, and electromagnetic waves in the v-direction for the electric field
The light is reflected completely and reflected completely,
after passing through the first layer of the cladding substrate 2.1, the reflection occurs on the metal floor 1 and is reflected back to the upper surface of the first layer of the dielectric substrate 2.1 again, and the PEC reflection does not change the polarization direction and can completely project through the fold-line metal structure 3.1; but due to propagation through the first dielectric substrate 2.1
Lagged behind in phase
180 deg. at this time
The real electric field direction of the first layer of dielectric substrate 2.1 is the-u direction, the electric field on the upper surface of the first layer of dielectric substrate 2.1 consists of equal-amplitude and equal-phase electric fields in the-u and v directions, and the total electric field at the moment can be known through combinationThe direction is the-y direction, as is the polarization direction of the reflected electromagnetic wave, when the controllable polarization switching surface can perform polarization rotation in state II.
In the state III, the broken line type micro-flow channel 3.1 and the sawtooth type micro-flow channel 3.2 are both filled with liquid metal alloy 4. At the moment, the internal metal structure of the controllable polarization conversion surface consists of three layers, namely liquid metal 4 in a sawtooth type micro-channel 3.2 at the uppermost layer, liquid metal 4 in a broken line type micro-channel 3.1 and a metal floor 1; under the condition that electromagnetic waves in the x polarization direction are vertically incident, the electric field of incident waves can be decomposed into two electric fields with equal amplitude in the u and v directions
The original incident wave can be decomposed into two electromagnetic waves with mutually perpendicular polarization, equal amplitude and same phase according to the electric field mode
The incident wave is then guided on the sawtooth-shaped metal structure 3.2 by its structural properties
Electric field of
Pointing in the-u direction in the opposite direction, and then continuously transmitting through the second dielectric substrate 2.2 to meet the meander line layer metal structure 3.1 due to its polarization in the u direction
Is totally transmitted so that
Continuously passes through the first layer of dielectric substrate 2.1 and then encounters the metal floor 1 to be totally reflected into a reflected wave
The phase lag when reaching the zigzag metal structure 3.2 is 270 degrees. While
Electric field
The direction is unchanged, part of the radiation is reflected, the other part of the radiation continuously penetrates through the second layer of dielectric substrate 2.2 and meets the fold line type metal structure 3.1, and the total reflection is carried out on the electromagnetic wave polarized in the v direction, so that the electromagnetic wave polarized in the v direction
Where it becomes totally a reflected wave
When the light is emitted back to the sawtooth-shaped metal structure again, the phase position of the light is the same as the previous projection phase position; the reflected wave now polarized in the u direction
Reflected wave in the v direction with polarization
The polarization is orthogonal, the size is equal, the phase lags by 270 degrees, circular polarization reflected waves are finally formed after combination, and at the moment, the working state of the controllable polarization conversion surface is that incident linear polarization waves are converted into circular polarization waves to be reflected.
Example 2
This embodiment has the same structure as embodiment 1, and only the following parameters are adjusted:
the unit side length la of the medium substrate 2 is 8 mm; the thickness ld of the first dielectric substrate 2.1 is 2.5mm, the thickness lc of the second dielectric substrate 2.2 is 1.9mm, and the thickness lb of the cladding dielectric 2.3 is 0.9 mm.
The upper surface of the first medium substrate 2.1 is etched with a double-arch groove, the groove depth h1 is 0.3mm, the distance li between the central broken line is 1.5mm, the arm length lh of the longitudinal broken line is 5mm, the distance between the broken line and the edge of the polarization conversion unit is lk is 0.5mm, and the width lg of the broken line type micro-channel 3.1 is 0.2 mm.
The upper surface of the second layer of dielectric substrate 2.2 is etched with a V-shaped groove, the groove depth h2 is 0.3mm, the distance ls between the corner of the V shape and the edge of the cell is 0.5mm, the depth lf of the V shape is 3.4mm, the corner theta is 46 degrees, and the width le of the sawtooth-shaped micro-channel 3.2 is 0.33 mm.
Example 3
This embodiment has the same structure as embodiment 1, and only the following parameters are adjusted:
the unit side length la of the medium substrate 2 is 8.2 mm; the thickness ld of the first dielectric substrate 2.1 is 3mm, the thickness lc of the second dielectric substrate 2.2 is 2.2mm, and the thickness lb of the cladding dielectric 2.3 is 1.2 mm.
The upper surface of the first medium substrate 2.1 is etched with a double-arch groove, the groove depth h1 is 0.5mm, the distance li between the central broken line is 1.9mm, the arm length lh of the longitudinal broken line is 6.2mm, the distance lk between the broken line type micro-channel and the unit edge is 1.2mm, and the width lg of the broken line type micro-channel is 0.22 mm.
The upper surface of the second layer of dielectric substrate 2.2 is etched with a V-shaped groove, the groove depth h2 is 0.5mm, the distance ls between the corner of the V shape and the edge of the cell is 1mm, the depth lf of the V shape is 3.9mm, the corner theta is 50 degrees, and the width le of the sawtooth-shaped micro-channel 3.2 is 0.37 mm.
The technical effects of the present invention are further described in detail in the following in combination with simulation tests:
referring to fig. 7, the controllable polarization conversion surface structure in example 1 was modeled in commercial simulation software HFSS — 18.2.
In the state II, the broken line type micro-channel is filled with LMA, and the sawtooth type micro-channel is filled with air.
Referring to fig. 8, a graph of the results of the variation of the reflection coefficients and the reflection phases of the u-polarized wave and the v-polarized wave with frequency in state ii is shown. The amplitudes of the reflected waves are approximately equal in the 6GHz to 21GHz band and are all greater than-2 dB. And phase difference exists between the reflection coefficients, the phase difference is kept at 180 degrees +/-37 degrees in a frequency band from 6.4GHz to 20.2GHz, and the phase constraint condition for realizing the linear polarization rotation phenomenon is met. The PCM exhibits the same polarization control characteristics for x-polarized and y-polarized waves, and therefore only x-polarized incidence is discussed.
Referring to fig. 9, a graph showing the reflection amplitude of the co-polarized wave and the cross-polarized wave as a function of frequency when irradiated with the electromagnetic wave in the vertical incident x-polarization direction in state ii is shown. It can be seen from the figure that the cross-polarized reflection coefficient is greater than-3 dB in the full frequency band, the co-polarized reflection coefficient is lower than-10 dB in the range from 6.4GHz to 20.2GHz, and there are three resonance points: 7.2GHz, 9GHz and 17.7GHz, corresponding to the frequency points in fig. 8 where the reflection phase difference is close to 180 °. The simulation results prove that when the broken-line micro-channel is filled with LMA and air exists in the sawtooth micro-channel, the controllable PCM in the working state can present linear polarization rotation characteristics for x-polarization or y-polarization vertical incident waves from 6.4GHz to 20.2 GHz.
In the state III, LMA is filled in both the broken line type micro-channel and the V-type layer micro-channel.
Referring to fig. 10, a graph showing the results of the variation of the reflection amplitude and the reflection phase with frequency of the u-polarized reflected wave and the v-polarized reflected wave irradiated by the normal incident wave in the iii state is shown. As can be seen from the figure, under the irradiation of the electromagnetic waves with two polarizations, the amplitude of the reflection coefficient from 7GHz to 16GHz is still kept above-2 dB, but the phase difference between the reflection coefficients is increased, and the phase difference from 7.2GHz to 15.8GHz is kept in the range of 270 degrees +/-19.4 degrees, so that the phase constraint condition for converting the linear polarization incident wave into the circular polarization reflected wave is met.
Referring to fig. 11, a graph showing the results of the axial ratio of the far field of the reflected wave irradiated by the normal incident wave in the iii state as a function of frequency is shown. As shown, the reflected wave AR is less than 3dB at 7.6GHz to 15.5 GHz. The frequency bandwidth (relative bandwidth 68.4%) for realizing the conversion from linear polarization to circular polarization is narrower than the frequency bandwidth (relative bandwidth 74.8%) for which the reflection phase difference satisfies the phase constraint range, because the phase constraint range is derived on the premise of perfect total reflection (reflection amplitude equal to 0dB), but in practice, there is a partial energy loss, which narrows the bandwidth for realizing the conversion from linear polarization to circular polarization. The results prove that when the multifunctional micro-channels are filled with LMA, the controllable PCM can realize the conversion from linear polarization to circular polarization in the range of 7.6GHz to 15.5GHz for x-polarization or y-polarization vertical incidence waves in the working state.
TABLE 1 correspondence of controllable PCM structural features and implementation functions based on LMA
Referring to table 1, it is realized that the switching of the reflected wave polarization state can be realized by the control in the form of the layout of the LMA in the controllable PCM. Table 1 summarizes the functional implementation of the controllable PCM, state I: when the liquid metal micro-channel 3 is not filled with the liquid metal alloy 4, the controllable PCM has no polarization control function in the full frequency band; in the state II, after the broken line type micro-channel 3.1 is filled with the liquid metal alloy 4, the controllable PCM realizes the linear polarization rotation phenomenon between 6.4GHz and 20.2 GHz; and in the state III, after the liquid metal alloy 4 is injected into the sawtooth-shaped micro-channel 3.2, the controllable PCM can realize the conversion phenomenon from linear polarization to circular polarization at 7.6GHz to 15.5 GHz. Further analysis shows that the working frequency bands of the state II and the state III are overlapped, namely the controllable PCM can realize the switching of the linear polarization rotation phenomenon and the linear polarization to circular polarization conversion phenomenon at 7.6GHz to 15.5GHz by the control of the LMA.
The simulation result shows that the invention changes the metal structure layout form in the PCM through the injection of the LMA, and further changes the reflection response to the vertical incidence linear polarization wave, so that the controllable PCM realizes the switching of the linear polarization rotation phenomenon and the linear polarization to circular polarization conversion phenomenon within the frequency range of 7.6GHz to 15.5 GHz.
The above description and examples are only preferred embodiments of the present invention and should not be construed as limiting the present invention, it will be obvious to those skilled in the art that various modifications and changes in form and detail may be made based on the principle and construction of the present invention after understanding the content and design principle of the present invention, but such modifications and changes based on the inventive concept are still within the scope of the appended claims.
Claims (6)
1. A controllable polarization conversion surface based on liquid metal comprises M × N controllable polarization conversion units which are periodically arranged, wherein M is larger than or equal to 3, N is larger than or equal to 3, M and N are positive integers, each polarization conversion unit comprises a metal floor (1), a medium substrate (2), a liquid metal micro-channel (3) and a liquid metal alloy (4), and the controllable polarization conversion surface is characterized in that:
the medium substrate (2) is composed of a first medium substrate (2.1), a second medium substrate (2.2) and a coating medium (2.3), the first medium substrate (2.1), the second medium substrate (2.2) and the coating medium (2.3) are connected in a hot key and mode, the liquid metal micro-channel (3) comprises a fold line type micro-channel (3.1) and a sawtooth type micro-channel (3.2), the fold line type micro-channel (3.1) is etched on the upper surface of the first medium substrate (2.1), and the fold line type micro-channel (3.1) is connected with the edge of the polarization conversion unit to form a double-bow-shaped groove; the sawtooth-shaped micro-channel (3.2) is etched on the upper surface of the second layer of the medium substrate (2.2), and the sawtooth-shaped micro-channel (3.2) is connected with the edge of the polarization conversion unit to form a V-shaped groove;
the periodic extension directions of the broken line type micro-channel (3.1) and the sawtooth type micro-channel (3.2) are consistent, in the polarization conversion unit, the broken line type micro-channel (3.1) and the sawtooth type micro-channel (3.2) are symmetrically distributed around a central axis which is vertical to the extension direction, and the position state of the liquid metal alloy (4) in the liquid metal micro-channel (3) is controlled by pressurization so as to realize the working performance of the adjustable polarization conversion surface; the position states of the liquid metal alloy (4) in the liquid metal micro-channel (3) are divided into three states, namely a state I: the liquid metal micro-channel (3) of the adjustable polarization conversion surface unit is completely emptied into air, and the polarization of reflected waves is not affected; and state II: the broken line type micro-channel (3.1) is filled with liquid metal alloy (4), and the sawtooth type micro-channel (3.2) is filled with air, at the moment, the controllable polarization conversion unit can realize polarization rotation; and state III: the sizes of the broken line type micro-channel (3.1) and the zigzag type micro-channel (3.2) are not changed, liquid metal alloy (4) is filled in the broken line type micro-channel and the zigzag type micro-channel, and at the moment, the controllable polarization conversion unit can realize conversion from linear polarization to circular polarization.
2. A liquid metal based controllable polarization conversion surface according to claim 1, wherein: the unit side length of the medium substrate (2) is la, and the value range of la is 8-8.2 mm; the thickness of the first dielectric substrate (2.1) is ld, the range of ld is 2.5-3 mm, the thickness of the second dielectric substrate (2.2) is lc, the range of lc is 1.9-2.2 mm, the thickness of the cladding dielectric (2.3) is lb, and the range of lb is 0.9-1.2 mm.
3. A liquid metal based controllable polarization conversion surface according to claim 1, wherein: the slotting depth of the double-arch-shaped groove is h1, the value range of h1 is 0.3-0.5 mm, the distance between central folding lines of the groove is li, the value range of li is 1.5-1.9 mm, the length of a longitudinal folding line arm is lh, the value range of lh is 5-6.2 mm, the distance between the folding line and the edge of the polarization conversion unit is lk, and the value range of lk is 0.5-1.2 mm; the width of the broken line type micro-channel (3.1) is lg, and the value range of the lg is 0.2-0.22 mm.
4. A liquid metal based controllable polarization conversion surface according to claim 1, wherein: the groove depth of the V-shaped groove is h2, the value range of h2 is 0.3-0.5 mm, the distance between the corner of the V-shaped groove and the edge of a unit is ls, the value range of ls is 0.5-1 mm, the depth of the V-shaped groove is lf, the value range of lf is 3.4-3.9 mm, and the angle theta is 46-50 degrees; the width of the sawtooth-shaped micro-channel (3.2) is le, and the value range of le is 0.33-0.37 mm.
5. A liquid metal based controllable polarization conversion surface according to claim 1, wherein: the liquid metal micro-channel (3) is filled with Liquid Metal Alloy (LMA) which is gallium-indium alloy (EGaIn).
6. A liquid metal based controllable polarization conversion surface according to claim 1, wherein: the dielectric substrate (2) is made of Polydimethylsiloxane (PDMS), and the dielectric coefficient epsilon of the PDMS is 2.65，Electrical loss tangent of 0.021。
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| CN116014451B (en) * | 2022-12-01 | 2024-05-14 | 黑龙江大学 | Broadband double-back-cavity polarized reconfigurable antenna based on liquid metal switch |
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