CN115832710A - Transmission/reflection type conformal multifunctional time modulation super-surface reflector and harmonic generation method thereof - Google Patents
Transmission/reflection type conformal multifunctional time modulation super-surface reflector and harmonic generation method thereof Download PDFInfo
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Abstract
The invention discloses a transmission/reflection type conformal multifunctional time modulation super-surface reflector and a harmonic generation method thereof. The device comprises a reflective flexible multifunctional modulatable super-surface array, a first control interface, a second control interface and a Field Programmable Gate Array (FPGA) time modulation control system; when the conformal multifunctional time modulation super-surface reflector shows a transmission characteristic, the incident electromagnetic wave energy of the conformal multifunctional time modulation super-surface reflector cannot be dissipated by the self resonance of the super-surface reflector, most energy is transmitted to the opposite side, and the backward scattering characteristic shows a low scattering state. When the conformal multifunctional time modulation super-surface reflector is switched to show the reflection characteristic, the backward scattering characteristic shows a high scattering state, and the switching in two opposite states of low scattering and high scattering can be realized through bias voltage control. The invention can modulate incident signals transmitted in different directions, has the advantage of manipulating the incident signals in a wide-angle-range, and can be used for the regulation of the target wide-angle-range single-station RCS.
Description
[ technical field ] A method for producing a semiconductor device
The invention relates to the field of material electromagnetic regulation, in particular to a transmission/reflection type conformal multifunctional time modulation super-surface reflector and a harmonic generation method thereof.
[ background of the invention ]
An electromagnetic meta-surface is a two-dimensional representation of a meta-material, consisting of a series of identical sub-wavelength elements. It has generated unique effects thanks to its unique ability to modulate electromagnetic waves. Therefore, the super-surface is widely applied to various fields such as a spatial filter, a radome, an electromagnetic shield, a beam steering, and the like. Active super-surfaces have attracted extensive research due to their ability to manipulate electromagnetic waves under external excitation. However, active super-surface research has mainly focused on quasi-static situations with only one control function. The influence of time-varying modulation on the interaction mechanism between the active super-surface and the electromagnetic wave is rarely studied.
The harmonic generation phenomenon can be realized by modulating electromagnetic waves by using a time-varying active super-surface, and is widely used in the fields of wireless communication and radar. In recent years, time modulated super surfaces have been proposed, which reveal that time modulation can generate frequency harmonics and achieve harmonic spectral conversion of the scattered signal. The teaching team of southeast university Cui Tiejun designs a time domain digital coding super surface to modulate the frequency spectrum of an incident signal, and a plurality of discrete harmonic peaks can be generated by modulating the phase and the amplitude of the incident signal, and the application of the frequency spectrum in a wireless communication system is also explored and researched. But in the above case, each cell or column occupies one modulation bit, increasing the modulation complexity and the difficulty of application. Moreover, currently in the design of time-modulated super-surfaces, polarization information thereof is often ignored. Most of the time the modulated super-surface can only operate under a specific single polarization, resulting in a significant reduction in its ability to perform complex electromagnetic functions and multi-information operations. In addition, there are many limitations that have not been considered in many practical applications, such as band range, wide-angle domain stability, polarization insensitivity, surface conformality, etc. All these limitations severely reduce the applicability of time modulated super surfaces, hindering their development.
The flexible intelligent skin technology is a hot spot of the current research and has wide application prospect. As an important component, conformal super-surface technology is widely used in different fields. However, the current research on flexible super surfaces is only a static situation, with only one electromagnetic function. They lack flexibility in manipulating electromagnetic waves, and cannot realize real-time dynamic control, which hinders the application of flexible super-surfaces in complex electromagnetic environments. Therefore, in the application of the smart skin technology, the flexible multifunctional time modulation super surface needs to be explored urgently. However, no studies have been reported for conformal flexible multifunctional time-modulated hyper-surfaces. And under the conformal structure, obtaining a flexible multifunctional time modulation super surface with independent polarization control capability is also a greater challenge. Moreover, conformal multifunctional time-modulated super-surfaces have little research on harmonic generation techniques.
[ summary of the invention ]
One objective of the present invention is to provide a Flexible multifunctional time-modulated super surface reflector (FMTMMR) with orthogonal polarization control, which can be used for conformal curved surface to manipulate the harmonic spectrum distribution of the echo. The invention introduces polarization control capability into the time modulation super surface, increases the modulation degree of freedom, and can simultaneously or independently control the orthogonal polarization electromagnetic waves. The flexible multi-functional time modulated super surface reflector (FMTMMR) can be used for curved surface conformality. And, through the on-off state of PIN diode in independent control base plate upper and lower surface, can realize two kinds of different functions, including electromagnetism switching and polarization control. The control network adopts an FPGA external excitation to carry out overall control, so that the complexity of the whole system can be reduced.
Another objective of the present invention is to provide a Transmission/Reflection type Conformal multifunctional time-modulated super surface reflector (T/R-CMTMMR), and a method for generating harmonics of an incident LFM signal in a wide angular range. On the basis of a flexible multifunctional time modulation super surface reflector (FMTMMR) design, the influence of the T/R-CMTMMR on the waveform modulation of an LFM signal is explored, the T/R-CMTMMR can be rapidly and dynamically tuned along with time, and an echo signal can be manipulated in a wide-angle domain. A time modulation model is established from a signal layer, and the effect of reflective multi-harmonic generation is realized. And finally, verifying the effectiveness of the method by using a Linear Frequency Modulation (LFM) signal echo experiment.
The technical scheme adopted by the invention for solving the technical problems is as follows:
a Flexible multifunctional time modulation super-surface reflector (FMTMMR) mainly comprises a reflective Flexible multifunctional modulated super-surface array (FMMMA for short), a first control interface, a second control interface and a Field Programmable Gate Array (FPGA) time modulation control system. The reflection-type flexible multifunctional modulable super-surface array overall structure comprises an upper surface metal periodic array, a flexible medium substrate and a lower surface metal periodic array, wherein the upper surface metal periodic array and the lower surface metal periodic array are both composed of a plurality of super-surface metal units (ME for short) which are arranged in a two-dimensional periodic array. The flexible multifunctional time modulation super-surface reflector can be conveniently conformal to the surfaces of different devices through a flexible medium substrate.
The super-surface metal units of the upper surface metal periodic array or the lower surface metal periodic array are integrally printed on the bendable ultrathin flexible medium substrate, and the adjacent super-surface metal units are electrically connected with each other, so that the current can be allowed to pass for integral regulation and control. Wherein: each column of super-surface metal units is connected in series and respectively sums up (+) and (-) electrodes connected to the first control interface; each row of super-surface metal units is also connected in series and summed separately to (+) and (-) electrodes connected to a second control interface. The polarization states of the super-surface metal units controlled by the first control interface and the second control interface are independent and orthogonal to each other. Therefore, they can be independently encoded and driven in real time by the FPGA control circuit.
The Field Programmable Gate Array (FPGA) time modulation control system mainly comprises an upper computer and an FPGA controller. The upper computer is in physical and signal connection with the FPGA controller through the Ethernet and is used for transmitting the binary coding instruction. The output end of the FPGA controller comprises two pairs of control interfaces, wherein one pair of control interfaces loads bias voltage to positive (+) and negative (-) electrodes of the first control interface through electric wires and is used for controlling the electromagnetic switching characteristic of the flexible multifunctional time modulation super-surface reflector under y polarization so as to control the incident electromagnetic wave of the y polarization in real time. And the other pair of control interfaces of the FPGA controller loads bias voltage to the positive (+) electrode and the negative (-) electrode of the second control interface through wires, and the bias voltage is used for controlling the electromagnetic switching characteristic of the flexible multifunctional time modulation super-surface reflector under x polarization so as to control the electromagnetic wave incident by the x polarization in real time. The first control interface and the second control interface of the flexible multifunctional time modulation super-surface reflector can be simultaneously and independently coded and controlled by the FPGA controller, and further multiple functions of full-polarization electromagnetic switching coding and orthogonal polarization control coding can be realized.
The reflective flexible multifunctional modulable super-surface array (FMMMA) structure comprises a plurality of unit structures which are periodically and tightly arranged, and each periodic unit structure mainly comprises two metal layers, a dielectric layer, metalized through holes for connecting the two metal layers and two PIN diodes. The metal pattern is a four-arm spiral structure, consists of four spiral bent metal strips and is connected by four metallized through holes with the diameter of 0.2 mm. Two PIN diodes are respectively welded at the centers of the upper and lower surfaces of the super-surface unit for respectively connecting the spiral metal strips in the vertical and horizontal directions. The helix structure increases the equivalent resonance length of the metal strip, so that the unit structure is more compact, the unit miniaturization can be realized, and the angle stability is improved. Each spiral line can be obtained by rotating one of the bent lines by 90 degrees, 180 degrees and 270 degrees around the center of the unit, so that the whole unit structure has excellent rotational symmetry and can realize good polarization insensitivity.
The metal pattern is designed on a thin flexible dielectric substrate with a relative dielectric constant of 2.2 and a thickness of 0.25mm. The thin dielectric substrate has good flexibility and curvature, and can be used for realizing the conformal curved surfaces of different shapes at will.
The two PIN diodes integrated on the metal layers on the upper surface and the lower surface are respectively connected with two pairs of metal strips which are vertical to each other. By separately controlling the bias voltage of the PIN diode on each layer, two orthogonally polarized electromagnetic waves can be independently manipulated. Thus, by simultaneously or independently switching the on/off state of the PIN diode in the horizontal and vertical directions, two different electromagnetic wave manipulation functions, including full-polarization electromagnetic switching and orthogonal polarization control, can be obtained. In addition, only two PIN diodes are used in each unit structure to control polarization, so that the number of lumped elements is greatly reduced, the manufacturing difficulty is reduced, and the cost is saved.
In the flexible multifunctional time modulation super-surface reflector, two pairs of first control interfaces and second control interfaces are respectively designed on the edges of the upper surface and the lower surface of the reflective flexible multifunctional modulation super-surface array so as to be connected with all feeder units for integral regulation and control. Each column of super-surface metal units is connected in series and respectively sums up (+) and (-) electrodes connected to the first control interface; each row of super-surface metal units is also connected in series and summed separately to (+) and (-) electrodes connected to a second control interface.
The two pairs of interfaces are respectively connected with PIN diodes which are arranged along the vertical direction and the horizontal direction, are isolated from each other and can be simultaneously or independently controlled by external excitation, and then two orthogonally polarized incident electromagnetic waves can be independently regulated and controlled. And the unit structure is used as a bias feeder of the PIN diode, so that an additional feed network is reduced, the negative influence of the additional feed network on the overall performance of the super-surface is avoided, the complexity of system adjustment is simplified, and the conformal application is facilitated.
For the control method of the flexible multifunctional time modulation super-surface reflector, each super-surface unit respectively comprises '0' and '1' digital states in the vertical and horizontal polarization directions, and the digital states are independently adjustable and have a double-bit coding function. The polarization encoding states "ij" (i =0,1 j =0, 1) respectively represent the operating states of the two PIN diodes in two orthogonal polarization directions. Bit 0 represents the off state of the PIN diode with no bias and bit 1 represents the on state of the PIN diode with forward bias. The FPGA control circuit is used for dynamically switching the coding states of the super-surface metal units simultaneously or independently, so that the simultaneous or independent coding regulation and control of the vertically and horizontally polarized electromagnetic waves can be realized.
The invention further designs a Transmission/reflection type conformal multifunctional time-modulated super-surface reflector (T/R-CMTMMR), and particularly relates to a flexible multifunctional time-modulated super-surface reflector (FMTMMR) which is conformal on a cylindrical surface and shows the characteristic of vertical incidence to electromagnetic waves in different incidence directions in space, so that the scattering characteristic regulation and control in a wide angle domain range can be realized. Due to the mirror image principle, it is advantageous compared to conventional planar super-surface reflectors, which are only effective in normal incidence.
Specifically, the transmission/reflection type conformal multifunctional time modulation super surface reflector (T/R-CMTMR) is a transmission/reflection type, when the transmission characteristic is presented by the conformal multifunctional time modulation super surface reflector, the incident electromagnetic wave energy is not dissipated by the self resonance of the super surface reflector, but most energy is transmitted to the opposite side, so the backward scattering characteristic presents a low scattering state. When the conformal multifunctional time modulation super-surface reflector is switched to show the reflection characteristic, the backward scattering characteristic shows a high scattering state, so that the switching can be realized in two opposite states of low scattering and high scattering through bias voltage control;
the conventional time modulation super-surface reflector is wave-absorbing/reflecting, and when the super-surface reflector shows wave-absorbing characteristics, the incident electromagnetic wave energy is dissipated by the resonance of the super-surface reflector, so that the back scattering characteristics of the super-surface reflector also show a low scattering state. However, the wave-absorbing/reflecting type super-surface reflector structure comprises an active impedance layer, a dielectric layer and a metal conductor backboard, and has the advantages of large overall structure thickness, high strength, poor flexibility and difficulty in realizing curved surface conformality;
the transmission/reflection type conformal multifunctional time modulation super surface reflector (T/R-CMTMMR) only has one layer of structure, the thickness of the transmission/reflection type conformal multifunctional time modulation super surface reflector is controllable, the transmission/reflection type conformal multifunctional time modulation super surface reflector can be designed on an extremely thin flexible medium substrate, excellent flexibility and bending degree can be realized, and curved surface conformal is easy to realize.
In order to realize the harmonic generation method in the wide-angle-domain range, the invention utilizes the FPGA control system to generate time modulation waveforms to control the conformal super surface to modulate LFM signals incident in different directions so as to realize wide-angle-domain harmonic regulation.
Specifically, the harmonic generation method based on transmission/reflection type conformal multifunctional time modulation super surface reflector (T/R-CMTMMR) comprises the following steps:
the method comprises the following steps: transmission/reflection type conformal multifunctional time modulation super-surface reflector design
A flexible multifunctional time modulation super surface reflector (FMTMMR) is conformed on the surface of the cylinder, and two pairs of control interfaces of the FPGA time modulation control system are respectively connected with (+) and (-) electrodes of the first control interface and (+) and (-) electrodes of the second control interface. The FPGA time modulation control system can realize electromagnetic regulation and control by outputting different bias voltages.
Step two: time modulation model establishment of conformal multifunctional time modulation super-surface reflector based on transmission/reflection type
The transmission/reflection type conformal multifunctional time modulation super surface reflector (T/R-CMTMR) has broadband switchable electromagnetic characteristics. By varying the bias voltage applied across its array, it is possible to operate in two opposite scattering states. Therefore, according to the electromagnetic reflection characteristics of the transmission/reflection type conformal multifunctional time modulation super-surface reflector in different coding states, a time modulation model can be established.
Wherein, in the on/off state, the frequency range with the reflection coefficient difference larger than 10dB is regarded as the measurement standard of the working bandwidth. Based on the switchable reflection characteristics of the transmission/reflection type conformal multi-function time-modulated super-surface reflector, a "1-x" amplitude modulation model corresponding to the reflection coefficient is established. When the transmission/reflection type conformal multifunctional time-modulated super-surface reflector is switched to a reflective state with high scattering, the amplitude coefficient is normalized to "1". When the transmission/reflection type conformal multifunctional time-modulated super-surface reflector is switched to a reflective state with low scattering, the amplitude coefficient is normalized to "x". The relationship Δ R between the amplitude coefficient "x" and the reflection coefficient difference can be calculated by the following equation:
x＝10 ΔR/20
here, the reflection coefficient difference Δ R = R1-R2. Wherein R1 represents the reflection coefficient of the transmission/reflection type conformal multifunctional time modulation super-surface reflector in the low scattering state, and R2 represents the reflection coefficient of the transmission/reflection type conformal multifunctional time modulation super-surface reflector in the high scattering state.
The transmission/reflection type conformal multifunctional time modulation super-surface reflector modulates the reflection coefficient by using a time-varying coding sequence and finally acts on an incident signal.
Step three: multi-harmonic generation of transmission/reflection based conformal multifunctional time modulated super surface reflectors
For multi-harmonic generation, a periodically coded modulation waveform is applied to a transmission/reflection type conformal multifunctional time-modulated super-surface reflector, the modulation signal spectrum of which contains a series of discrete harmonic frequency components, and the amplitude envelope of which follows a sinc function distribution. When the carrier frequency is f 0 Incident signal of (2) is incident on a time-modulated transmission/reflection conformalAfter the multifunctional time-modulated super-surface reflector is arranged, an incident signal is transmitted/reflected by the conformal multifunctional time-modulated super-surface reflector at a switching speed f s And (4) periodic modulation. After modulation of the transmission/reflection type conformal multifunctional time modulation super surface reflector, the frequency spectrum of the modulated echo signal is no longer the central frequency f 0 A single pulse but containing a plurality of frequency components f 0 A series of discrete harmonics of + nfs, the amplitude envelope obeying a sinc function distribution. The amplitude of the harmonic component is affected by the amplitude coefficient and the modulation duty ratio, the position of the harmonic component is affected by the modulation parameter frequency, and the modulation frequency f s The larger the spacing between adjacent harmonic components. Harmonic distribution can be flexibly regulated and controlled by changing the frequency and the duty ratio of the modulation waveform.
The invention has the beneficial effects that:
(1) The flexible multifunctional time modulation super-surface reflector is designed on a thin flexible medium substrate and has good flexibility and bending degree. And the super-surface has good angular stability and polarization insensitivity. The cell structures are designed to be electrically connected to each other for realizing series feeding of the PIN diodes, and the cells themselves are used as bias feeding lines of the PIN diodes, so that negative effects of an additional feeding network on the active super-surface are avoided. Therefore, the conformal curved surface can be conveniently realized, and the electromagnetic property of the material is not changed.
(2) In conventional time-modulated super-surface designs, polarization information is ignored. Most of the time the modulated super-surface can only operate under a specific single polarization, resulting in a significant reduction in the ability to implement complex electromagnetic functions and multi-information operations. The invention has a plurality of independent control interfaces, thus a plurality of different control functions can be obtained in a single time modulation super surface. When two pairs of control interfaces are driven simultaneously, the flexible conformal multifunctional time-modulated super-surface reflector behaves as a polarization insensitive electromagnetic switch. It can manipulate all polarized incident electromagnetic waves simultaneously. When two pairs of control interfaces are controlled by two separate time-coded sequences, the TE and TM polarized electromagnetic waves can be programmed and controlled independently. The two polarization channels can be independently controlled or time-division coded, which can be used to expand wider and more attractive applications.
(3) The traditional time modulation super surface is in a plane structure form, and due to the mirror image action principle, the time modulation super surface is effective to the modulation of electromagnetic waves only in the vertical incidence direction. The invention provides a conformal time modulation super surface for modulating incident signals transmitted in different directions. It has the unique advantage of steering the incident signal over a wide angular range, and can be used for wide angular range single station RCS conditioning of a target.
[ description of the drawings ]
FIG. 1 is a three-dimensional topology of a reflective flexible multi-functional modulatable super-surface array according to the present invention.
Fig. 2 is a schematic diagram of a flexible multi-functional modulatable super-surface reflector designed according to the present invention.
Fig. 3a-d are reflection coefficients measured by the transmission/reflection type conformal multifunctional modulatable super-surface reflector of the present invention under different incident angles and different polarizations, wherein fig. 3a is "00" state, fig. 3b is "11" state, fig. 3c is "01" state, and fig. 3b is "10" state.
FIG. 4 is a schematic diagram of a transmission/reflection type conformal multifunctional time-modulated super-surface reflector of the present invention with real-time and independent control of orthogonally polarized electromagnetic waves and wide-angle-domain incident signal modulation capability.
FIG. 5 is a transmission/reflection type conformal multifunctional time modulation super-surface reflector period time modulation model established by the present invention.
Fig. 6 is a single frequency incident signal and echo signal spectrum.
FIG. 7 is a schematic diagram of a transmission/reflection type conformal multifunctional time-modulated super-surface reflector measurement scenario.
Fig. 8a and b are time domain results of the measured LFM echo signals, wherein fig. 8a is an unmodulated echo signal and fig. 8b is a modulated echo signal.
Fig. 9a and b show the measured LFM echo signal spectrum distribution results, wherein fig. 9a shows the unmodulated echo signal spectrum distribution, and fig. 9b shows the modulated echo signal spectrum distribution.
[ detailed description ] embodiments
For a better understanding of the method of the present invention, the following description will be given with reference to the accompanying drawings and specific examples.
The invention designs and manufactures a flexible multifunctional time modulation super-surface reflector. In order to be suitable for curved surface conformal application and establish a flexible conformal multifunctional time modulation super-surface reflector with polarization control capability, firstly, a flexible multifunctional switchable super-surface array capable of independently regulating and controlling two orthogonal polarization electromagnetic waves is designed. FIG. 1 depicts the three-dimensional topology of a reflective flexible multi-functional modulable super-surface array as proposed by the present invention.
The reflection type flexible multifunctional modulable super-surface array structure comprises a plurality of super-surface metal unit structures which are periodically and closely arranged, wherein each super-surface metal unit structure mainly comprises a flexible dielectric layer 1, two metal layers 2, a metalized via hole 3 for connecting the two metal layers and two PIN diodes 4.
The metal pattern is a four-arm spiral structure, consists of four spiral bent metal strips and is connected by four metallized through holes with the diameter of 0.2 mm. And the two PIN diodes are respectively welded in the centers of the upper surface and the lower surface of the reflective flexible multifunctional switchable super-surface unit and are used for respectively connecting the spiral metal strips in the vertical direction and the horizontal direction. The helix structure increases the equivalent resonance length of the metal strip, so that the unit structure is more compact, the unit miniaturization can be realized, and the angle stability is improved. The miniaturized unit size can reach 0.12 lambda 0 ×0.12λ 0 ×0.005λ 0 (λ 0 The corresponding wavelength dimension at the center frequency). Each spiral line can be obtained by rotating one of the bent lines by 90 degrees, 180 degrees and 270 degrees around the center of the unit, so that the whole unit structure has excellent rotational symmetry and can realize good polarization insensitivity.
Two PIN diodes are integrated on the metal layers on the upper surface and the lower surface and are used for respectively connecting two pairs of metal strips which are vertical to each other. By separately controlling the bias voltage of the PIN diode on each layer, two orthogonally polarized electromagnetic waves can be independently manipulated. Thus, by simultaneously or independently switching the on/off state of the PIN diode in the horizontal and vertical directions, two different electromagnetic wave manipulation functions, including full-polarization electromagnetic switching and orthogonal polarization control, can be obtained. In addition, only two PIN diodes are used in each unit structure to control polarization, so that the number of lumped elements is greatly reduced, the manufacturing difficulty is reduced, and the cost is saved.
The proposed geometry of the reflective flexible multifunctional switchable super-surface array was designed using the CST microwave studio software. Geometric parameters of the proposed cell: a =4.1mm, b =4.1mm, c =2.98mm, d =2.98mm, e =1.6mm, f =0.34mm, g =0.3mm, w =0.22mm, f =2.98mm, k =0.34mm, h =0.25mm.
As shown in fig. 2, the flexible multifunctional time-modulated super-surface reflector manufactured by the invention comprises a reflective flexible multifunctional time-modulated super-surface array 5, a first control interface 6 and a second control interface 7. The total size of the prepared flexible multifunctional time modulation super surface reflector is 263mm multiplied by 263mm and consists of 60 multiplied by 60 units. And welding the PIN diode by using a surface mount technology. The PIN diode is a BAR64-02 model with minimal package TSLP-2-19.
The flexible multi-functional time-modulated super-surface reflector is printed on a thin flexible dielectric substrate. The medium substrate adopts F4BM polytetrafluoroethylene high-frequency microwave board, and the dielectric constant is 2.2, and the loss tangent is 0.0007, and thickness is 0.25mm, has fine pliability and crookedness, can conveniently conform with the cylinder surface. The flexible multifunctional time modulation super-surface reflector can realize a conformal multifunctional modulation super-surface reflector insensitive to the incident electromagnetic wave angle through the conformation with the cylindrical surface.
Each column of reflective flexible multifunctional switchable super surface array units are connected in series and respectively summarize (+) and (-) electrodes connected to a first control interface I; each row of super surface array elements is also connected in series and summed separately to (+) and (-) electrodes connected to the second control interface II. The polarization states of the super-surface array unit controlled by the first control interface I and the second control interface II are independent and orthogonal to each other. They can be coded and controlled independently and in real time by the control circuit.
The two pairs of interfaces are respectively connected with PIN diodes which are arranged along the vertical direction and the horizontal direction, are isolated from each other and can be simultaneously or independently controlled by external excitation, and then two orthogonally polarized incident electromagnetic waves can be independently regulated and controlled. And the unit structure is used as a bias feeder of the PIN diode, so that an additional feed network is reduced, the negative influence of the additional feed network on the overall performance of the super-surface is avoided, the complexity of system adjustment is simplified, and the conformal application is facilitated.
For the control method of the flexible multifunctional time modulation super-surface reflector, each super-surface reflector unit respectively comprises '0' and '1' digital states in the vertical and horizontal polarization directions, and the digital states are independently adjustable and have a double-bit coding function. The polarization encoding states "ij" (i =0,1 j =0, 1) respectively represent the operating states of the two PIN diodes in two orthogonal polarization directions. Bit 0 represents the off state of the PIN diode with no bias and bit 1 represents the on state of the PIN diode with forward bias. The FPGA control circuit is used for dynamically switching the coding states of the super-surface units simultaneously or independently, so that the simultaneous or independent coding regulation and control of the vertically and horizontally polarized electromagnetic waves can be realized. Four different coding states "00", "11", "01", "10" can thus be realized. Four different working states, namely dual polarization reflection, dual polarization transmission, TE polarized wave reflection and TM polarized wave reflection, are correspondingly realized, and then two different regulation and control functions, namely full polarization electromagnetic switching and orthogonal polarization control, can be realized.
Fig. 3a-d are plots of the reflection coefficient versus frequency for two polarizations at different biases and different angles of incidence for the flexible multi-functional time-modulated super-surface reflector proposed in the examples of the present invention. As shown in fig. 3a and b, the flexible multifunctional time-super-surface reflector is designed to have excellent dual-polarization electromagnetic switching function for both TE and TM polarized incident waves, and can be switched between low-scattering and high-scattering states. When the two PIN diodes are operated in the off state, namely the '00' state, the proposed conformal multifunctional super-surface is represented as a broadband reflector and is operated in a high scattering state. In contrast, in the "11" state, all polarizations are in a low scattering state. At normal incidence, the operating bandwidths for TE and TM polarized incident waves with measured differences in reflection coefficients greater than 10dB were both 3GHz (8 GHz-11 GHz). Fig. 3c and d show the reflection coefficients measured in two orthogonal polarizations in the "01" and "10" encoding states. The TE and TM polarized incident electromagnetic waves can be independently manipulated by controlling the bias voltages of two PIN diodes embedded on the upper and lower surfaces, respectively.
In addition, the reflection properties at different oblique angles of incidence were measured and analyzed, as shown in FIGS. 3 a-d. TE and TM polarizations have stable frequency responses even at large angles of incidence up to 45 °. Therefore, the flexible multifunctional time-modulated super-surface reflector can show excellent broadband electromagnetic switching function and polarization control capability in a wide angle range.
The flexible multifunctional time modulation super-surface reflector designed by the invention is of a transmission/reflection type, when the flexible multifunctional time modulation super-surface reflector shows a transmission characteristic, the energy of incident electromagnetic waves is not dissipated by the self resonance of the super-surface reflector, but most of the energy is transmitted to the opposite side, so that the backward scattering characteristic shows a low scattering state. When the flexible multifunctional time modulation super-surface reflector is switched to show the reflection characteristic, the backward scattering characteristic shows a high scattering state, so that the switching in two opposite states of low scattering and high scattering can be realized through bias voltage control. The conventional time modulation super-surface reflector is wave-absorbing/reflecting, and when the time modulation super-surface reflector shows wave-absorbing characteristics, the incident electromagnetic wave energy is dissipated by the resonance of the super-surface reflector, so that the back scattering characteristics of the time modulation super-surface reflector also show a low scattering state. However, the wave-absorbing/reflecting time modulation super-surface reflector structure comprises an active impedance layer, a dielectric layer and a metal conductor backboard multilayer structure, and is large in overall structure thickness, high in strength, poor in flexibility and difficult to realize curved surface conformality. The transmission/reflection type time modulation super-surface reflector only has one layer of structure, the thickness of the transmission/reflection type time modulation super-surface reflector is controllable, the transmission/reflection type time modulation super-surface reflector can be designed on an extremely thin flexible medium substrate, excellent flexibility and bending degree can be realized, and the curved surface is easy to conform.
The flexible multifunctional time modulation super-surface reflector designed by the invention can be easily conformed on the surface of a cylinder, and the flexible multifunctional time modulation super-surface reflector conformed on the cylinder has the characteristic of vertical incidence on electromagnetic waves in different incidence directions in space, so that the scattering characteristic regulation and control in a wide angular domain range can be realized. Due to the mirror image principle, it is advantageous compared to conventional planar super-surface reflectors, which are only effective in normal incidence.
In order to realize the wide-angle-domain harmonic generation method, the invention firstly provides a conformal multifunctional time modulation super-surface reflector, which utilizes an FPGA time modulation control system to generate time modulation waveforms to control the conformal time modulation super-surface reflector to modulate LFM signals incident in different directions so as to realize wide-angle-domain harmonic regulation.
The invention relates to a transmission/reflection type conformal time modulation super-surface reflector design, time modulation model establishment based on the transmission/reflection type conformal time modulation super-surface reflector and multi-harmonic generation based on the transmission/reflection type conformal time modulation super-surface reflector, which comprises the following concrete steps:
the method comprises the following steps: transmission/reflection type conformal multifunctional time modulation super surface reflector design
For conformal multi-functional modulatable super-surface reflector structures, small cell sizes need to be designed to obtain good electromagnetic properties. Therefore, the invention firstly designs a miniaturized multifunctional modulable super-surface reflector with good angle stability.
As shown in fig. 4, the transmission/reflection type conformal multifunctional time-modulated super surface reflector conforms a flexible multifunctional time-modulated super surface reflector (FMTMMR) on a cylindrical surface. The FPGA time modulation control system comprises two pairs of control interfaces which are respectively connected with (+) and (-) electrodes of a first control interface and (+) and (-) electrodes of a second control interface of the conformal multifunctional time modulation super-surface reflector. The FPGA time modulation control system can realize electromagnetic regulation and control by outputting different bias voltages.
The PIN diodes of the conformal multifunctional modulatable super-surface reflector are controlled to be switched in an off/on state through the bias voltage, so that the conformal multifunctional modulatable super-surface reflector can be switched in two opposite reflection states, namely a low scattering state and a high scattering state.
The FPGA time modulation control system can generate bias voltage which changes along with time, and then the conformal multifunctional switchable super-surface reflector is controlled to show different reflection characteristics at different moments. Therefore, the reflection characteristic of the conformal multifunctional time modulation super-surface reflector is shown as a function of time, and the incident signal can be regulated.
The designed FPGA time modulation control system mainly comprises an upper computer and an FPGA controller. First, the upper computer generates binary coded instructions containing "0" and "1" sequences to produce the required time modulated sequences, which are then sent to the FPGA controller. Upon receiving the instruction, the FPGA controller generates the required time-varying dc bias voltage to drive the PIN diodes. With respect to the binary coded sequence, the code "1" corresponds to the forward bias voltage of the PIN diode, and the code "0" corresponds to a zero bias voltage. Thus, they can operate the PIN diodes in the on and off states. Finally, bias voltages are applied to the positive and negative electrodes of the super-surface reflector for driving the super-surface reflector to switch between the low scattering and high scattering states. Wherein the on state of the PIN diode corresponds to a low scattering state of the conformal multifunctional time-modulated super surface reflector and the off state corresponds to a high scattering state.
Step two: time modulation model establishment of conformal multifunctional time modulation super-surface reflector based on transmission/reflection type
The transmission/reflection type conformal multifunctional time modulation super-surface reflector designed by the invention has broadband switchable electromagnetic characteristics. By varying the bias voltage, it can operate in two opposite scattering states. Thus, a temporal modulation model for amplitude modulation is established in fig. 5. In the on/off state of the PIN diode, the frequency range with a reflection coefficient difference greater than 10dB is considered as a measure of the operating bandwidth. Based on the switchable reflection characteristics of the transmission/reflection type conformal multifunctional time-modulated super-surface reflector, a "1-x" amplitude modulation model corresponding to the reflection coefficient was established, as shown in fig. 5. When the transmission/reflection type conformal multifunctional time-modulated super-surface reflector is switched to a reflective state with high scattering, the amplitude coefficient is normalized to "1". The amplitude coefficient is normalized to "x" when the transmission/reflection type conformal multifunctional time-modulated super-surface reflector is switched to a reflective state with low scattering. The relationship Δ R between the amplitude coefficient "x" and the reflection coefficient difference can be calculated by the following equation:
x＝10 ΔR/20
here, the reflection coefficient difference Δ R = R1-R2. Wherein R1 represents the reflectance of the super-surface in the low scattering state, and R2 represents the reflectance of the super-surface in the high scattering state.
The transmission/reflection type conformal multifunctional time modulation super-surface reflector modulates the reflection coefficient by using a time-varying coding sequence and then acts on an incident signal. The periodic code modulation waveform acts on the transmission/reflection type conformal multifunctional time modulation super-surface reflector, and the time domain response of the periodic code modulation waveform can be expressed as:
wherein T is w Is the code width, T, of the high scattering state s Is the coding period, α = T w /T s Is the duty cycle of the periodically coded modulation signal, n represents the number of periodic codes,
representing a convolution operation.
It is fourier transformed, and its spectrum is represented as:
wherein A is 0 ＝(1-x)T w f s +x,A n ＝(1-x)T w f s sinc(nT w f s ),f s ＝1/T s Is the modulation frequency.
The above equation shows that the modulated signal spectrum contains a series of discrete harmonic frequency components f 0 +nf s The position of the frequency component of the discrete harmonic being dependent on the modulation frequency f s The overall harmonic component amplitude envelope follows a sinc function distribution.
Step three: multi-harmonic generation of transmission/reflection based conformal multifunctional time-modulated super-surface reflectors
When an incident signal s (t) is incident on the transmission/reflection type conformal multifunctional time-modulated super-surface reflector, the incident signal is modulated by the transmission/reflection type conformal multifunctional time-modulated super-surface reflector, and a modulated echo signal can be expressed as:
r(t)＝s(t)·p(t)
after Fourier transform, the frequency spectrum is
By performing convolution operation on the periodic modulation waveform spectrum and the incident signal spectrum, the following results can be obtained:
by analyzing the above equation, it can be seen that the spectrum of the modulated echo signal is no longer a single pulse at the center frequency, but rather a set of harmonics containing multiple frequency components.
To verify the correctness of its theory, the center frequency f is used 0 A single frequency signal of =10GHz as an incident signal for simulation. The modulation parameter of the transmission/reflection type conformal multifunctional time modulation super surface reflector is f s =10MHz, α =0.6, and the spectrum of the reflected echo signal is shown in fig. 6. It can be observed that the reflected echo signal produces a series of discrete harmonic frequency components f 0 +nf s Multiple newly generated discrete harmonics are carried along the centerThe frequency part is expanded to two sides and is symmetrically distributed, the interval between adjacent harmonics is fs, and the frequency is modulated along with the frequency f s Increases the distance between adjacent harmonic peaks. The overall amplitude envelope of the harmonic frequency components follows a sinc function distribution.
To verify the harmonic generation effect of the transmission/reflection type conformal multifunctional time modulation super surface reflector, an LFM signal echo response experiment was designed and performed, as shown in fig. 7. The parameter of the Linear Frequency Modulation (LFM) signal in the experiment is the carrier frequency f 0 =10GHz, signal bandwidth B =200MHz, pulse width T p =40 μ s. The constructed LFM signal system comprises a signal generating and signal processing system. The signal generation system consists of an Arbitrary Waveform Generator (AWG), an up-converter (UC) and a transmitting antenna. Carrier frequency f 0 A chirp signal of =10GHz is generated by the AWG and the up-converter and then transmitted through the transmitting antenna. The signal processing system comprises a receiving antenna, a Down Converter (DC) module, an Intermediate Frequency Adjustment (IFA) module and data acquisition equipment. The receiver antenna receives the modulated echo signal. The baseband signal is then obtained after DC and IFA processing. Finally, the signal is saved in a data acquisition device.
To verify the effect of a transmission/reflection type conformal multifunctional time-modulated super-surface reflector on the modulation of a Linear Frequency Modulation (LFM) signal, a modulation frequency f is carried out s Transmission/reflection type conformal multifunctional time modulation super surface reflector modulation experiment with 1MHz and duty cycle α = 0.4.
The measured echo signals modulated by the non-transmit/reflect conformal multifunctional time-modulated super-surface reflector and modulated by the transmit/reflect conformal multifunctional time-modulated super-surface reflector are shown in fig. 8a, b. As shown in fig. 8b, after the transmission/reflection type conformal multifunctional time-modulated super-surface reflector performs periodic modulation, the LFM signal is divided into several parts in a fast time.
And the echo signals are processed by orthogonal demodulation and fast time filtering. The measured spectra of the LFM echo signal without and with modulation by the transmit/reflect type conformal multifunctional time-modulated super-surface reflector are shown in fig. 9. As can be seen from fig. 9b, the spectrum of the modulated echo signal produces a plurality of discrete harmonic components which are distributed within the original frequency band.
From simulation and actual measurement results, it is easily seen that the reflection spectrum based on the transmission/reflection type conformal multifunctional time modulation super-surface reflector has a multi-harmonic effect, which is consistent with theoretical analysis, and the effectiveness of the method provided by the invention is proved.
Claims (5)
1. A flexible multi-functional time-modulated super-surface reflector, characterized by: the system comprises a reflective flexible multifunctional modulatable super-surface array FMMMA, a first control interface, a second control interface and a field programmable gate array FPGA time modulation control system; the reflective flexible multifunctional modulatable super-surface array FMMMA overall structure comprises an upper surface metal periodic array, a flexible medium substrate and a lower surface metal periodic array, wherein the upper surface metal periodic array and the lower surface metal periodic array are both composed of a plurality of super-surface metal units which are arranged in a two-dimensional periodic array; the flexible multifunctional time modulation super-surface reflector is conformal to the surfaces of different devices through a flexible medium substrate;
the super-surface metal units of the upper surface metal periodic array or the lower surface metal periodic array are integrally printed on the bendable ultrathin flexible medium substrate, and the adjacent super-surface metal units are electrically connected with each other to allow current to pass for integral regulation and control; wherein: each column of super-surface metal units is connected in series and respectively sums up (+) and (-) electrodes connected to the first control interface; each row of super-surface metal units is also connected in series and respectively sums up (+) and (-) electrodes connected to the second control interface; the polarization states of the super-surface metal units controlled by the first control interface and the second control interface are mutually independent and orthogonal to each other; therefore, the FPGA control circuit independently encodes and drives in real time;
the field programmable gate array FPGA time modulation control system comprises an upper computer and an FPGA controller; the upper computer is in physical and signal connection with the FPGA controller through the Ethernet and is used for transmitting a binary coding instruction; the output end of the FPGA controller comprises two pairs of control interfaces, wherein one pair of control interfaces loads bias voltage to positive (+) and negative (-) electrodes of the first control interface through wires and is used for controlling the electromagnetic switching characteristic of the flexible multifunctional time modulation super-surface reflector under y polarization so as to control the incident electromagnetic wave of the y polarization in real time; the other pair of control interfaces of the FPGA controller loads bias voltage to positive (+) and negative (-) electrodes of the second control interface through electric wires for controlling the electromagnetic switching characteristic of the flexible multifunctional time modulation super-surface reflector under x polarization so as to control the electromagnetic wave incident by the x polarization in real time; the first control interface and the second control interface of the flexible multifunctional time modulation super-surface reflector are simultaneously and independently coded and controlled by the FPGA controller, and therefore multiple functions of full-polarization electromagnetic switching coding and orthogonal polarization control coding are achieved.
2. A transmission/reflection type conformal multifunctional time-modulated super-surface reflector, characterized by: specifically, the flexible multifunctional time modulation super-surface reflector as claimed in claim 1 is conformal on a cylindrical surface, and the cylindrical conformal multifunctional time modulation super-surface reflector shows a characteristic of vertical incidence in space for electromagnetic waves in different incidence directions, so that scattering characteristic regulation in a wide angular domain range is realized.
3. The transmissive/reflective conformal multifunctional time-modulated super surface reflector of claim 2, wherein: when the conformal multifunctional time modulation super-surface reflector shows a transmission characteristic, the incident electromagnetic wave energy of the conformal multifunctional time modulation super-surface reflector cannot be dissipated by the self resonance of the super-surface reflector, most energy is transmitted to the opposite side, and the backward scattering characteristic shows a low scattering state; when the conformal multifunctional time modulation super-surface reflector is switched to express reflection characteristics, backward scattering characteristics are expressed as a high scattering state, and switching is realized in two opposite states of low scattering and high scattering through bias voltage control.
4. The transmissive/reflective conformal multifunctional time-modulated super surface reflector of claim 2, wherein: in order to realize the harmonic generation method in the wide-angle-domain range, the time modulation waveform is generated by using the FPGA control system, and the conformal super surface is controlled to modulate LFM signals incident in different directions so as to realize wide-angle-domain harmonic regulation.
5. A harmonic generation method based on the transmission/reflection type conformal multifunctional time-modulated super-surface reflector of claim 2, comprising the steps of:
the method comprises the following steps: conformal multifunctional time-modulated super-surface reflector design of transmission/reflection type:
the flexible multifunctional time modulation super-surface reflector is conformally arranged on the surface of the cylinder, and two pairs of control interfaces of the FPGA time modulation control system are respectively connected with (+) and (-) electrodes of a first control interface and (+) and (-) electrodes of a second control interface; the FPGA time modulation control system realizes electromagnetic regulation and control by outputting different bias voltages;
step two: time modulation modeling of a transmission/reflection-based conformal multifunctional time-modulated super-surface reflector:
in the on/off state, the frequency range with the reflection coefficient difference larger than 10dB is regarded as the measurement standard of the working bandwidth; establishing a '1-x' amplitude modulation model corresponding to a reflection coefficient according to switchable reflection characteristics of the transmission/reflection type conformal multifunctional time modulation super-surface reflector; when the transmission/reflection type conformal multifunctional time-modulated super-surface reflector is switched to a reflection state with high scattering, the amplitude coefficient is normalized to "1"; when the transmissive/reflective conformal multifunctional time-modulated super-surface reflector is switched to a reflective state with low scattering, the amplitude coefficient is normalized to "x"; the relationship Δ R between the amplitude coefficient "x" and the reflection coefficient difference is calculated by the following equation:
x＝10 ΔR/20
here, the difference in reflectance Δ R = R1-R2; wherein R1 represents the reflection coefficient of the transmission/reflection type conformal multifunctional time modulation super-surface reflector in a low scattering state, and R2 represents the reflection coefficient of the transmission/reflection type conformal multifunctional time modulation super-surface reflector in a high scattering state;
the transmission/reflection type conformal multifunctional time modulation super-surface reflector modulates the reflection coefficient by using a time-varying coding sequence and finally acts on an incident signal;
step three: multi-harmonic generation of transmission/reflection based conformal multi-functional time modulated super-surface reflectors:
for multi-harmonic generation, a periodically coded modulation waveform is applied to a transmission/reflection type conformal multifunctional time-modulated super-surface reflector, the spectrum of a modulation signal of which contains a series of discrete harmonic frequency components, and the amplitude envelope follows a sinc function distribution; when the carrier frequency is f 0 After the incident signal is incident on the time-modulated transmission/reflection type conformal multifunctional time-modulated super-surface reflector, the incident signal is transmitted by the transmission/reflection type conformal multifunctional time-modulated super-surface reflector at a switching rate f s Periodic modulation; after modulation of the transmission/reflection type conformal multifunctional time modulation super surface reflector, the frequency spectrum of the modulation echo signal is no longer the central frequency f 0 A single pulse of (a) but contains a plurality of frequency components f 0 A series of discrete harmonic distributions of + nfs, the amplitude envelope obeying a sinc function distribution; the amplitude of the harmonic component is affected by the amplitude coefficient and the modulation duty ratio, the position of the harmonic component is affected by the modulation parameter frequency, and the modulation frequency f s The larger the spacing between adjacent harmonic components; the harmonic distribution is regulated by changing the frequency and the duty of the modulation waveform.
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