CN105305091A - Tunable gradient meta-surface-based reflection electromagnetic wave modulator and design method thereof - Google Patents

Abstract

The invention belongs to the technical field of reflection systems, in particular to a reflective electromagnetic wave modulator based on a broadband adjustable gradient metasurface and a design method thereof. The reflected electromagnetic wave modulator (broadband TGMS) of the present invention is composed of superunits periodically extended in a two-dimensional plane; the superunits are composed of six TGMS units with different structural parameters and phases arranged in order of size and have a broadband phase gradient ; And the TGMS unit is mainly composed of three parts: the upper main resonator and the sub-resonator, the middle dielectric plate and the lower metal ground plate; the present invention realizes the phase dispersion by introducing a varactor diode and a double resonant structure in the gradient metasurface unit Compensation and continuous adjustment of phase; switching from surface wave conversion to beam deflection function, and beam deflection has very high conversion efficiency in a wide frequency band.

Description

Reflective electromagnetic wave modulator based on tunable gradient metasurface and its design method

technical field

The invention belongs to the technical field of reflection systems, and in particular relates to a reflective electromagnetic wave modulator based on an adjustable gradient metasurface and a design method thereof.

Background technique

Metamaterials (MTMs) refer to "specific" artificial composite structures or materials that do not exist in nature, but are designed with sub-wavelength artificial microstructure units and based on electromagnetic theory, with certain electrical or magnetic responses. Although people can arbitrarily manipulate electromagnetic waves through three-dimensional heterotropic media, high loss and fabrication complexity greatly limit its application. Therefore, there are not many real applications at present. As a two-dimensional planar form of anisotropic medium, a metasurface emerges at the historic moment. Due to its unique electromagnetic properties and planar structure, it can conform to high-speed targets such as aircraft, missiles, rockets and satellites without destroying its shape and structure. Aerodynamics and other characteristics have been favored and widely concerned by researchers in recent years. Metasurfaces can be divided into Gradient Metasurfaces (GMS) and Homogenous Metasurfaces (HMS) according to whether the refractive index/phase is gradient. In 2011, the generalized Snell refraction/reflection law discovered based on GMS opened up a new way and field for people to control electromagnetic waves and light, and is promoting a technological innovation in this field. GMS has therefore become a new branch and research hotspot of heterotropic media. Compared with the more mature HMS, GMS is a two-dimensional gradient structure designed based on the idea of phase mutation and polarization control, which can flexibly control the excitation and transmission of electromagnetic waves, and realize singular refraction/reflection, polarization rotation and asymmetry Transmission and other singular functions have more powerful electromagnetic wave control capabilities. At present, related application research is still in its infancy. Nevertheless, GMS has shown great potential application value in stealth surfaces, conformal antennas, digital coding, lithographic printing, etc., and has become a subject commanding height and subject frontier that countries are vying for.

In the past, once the operating frequency of metasurfaces changed, structural parameters had to be redesigned to obtain the same electromagnetic properties, which resulted in low efficiency and poor reusability. With the deepening of metasurface research and the development of electromagnetic manipulation technology, people can realize real-time regulation of unit resonant frequency and surface impedance by adding control devices, and obtain the singular dynamic electromagnetic properties of metasurfaces, which are new functional devices and electromagnetic wave modulation devices. The realization and verification of the system provide new methods and means. However, previous research on tunable metasurfaces was limited to HMS, and there has been no public report on tunable gradient metasurfaces (TunableGMS, TGMS). At the same time, for the adjustable HMS, due to the introduction of the varactor diode, the Q value is very high, the dynamic adjustable range of the phase of the HMS is very small, and the bandwidth is very narrow.

Contents of the invention

In order to overcome the shortcomings of the prior art, the present invention provides a reflective electromagnetic wave modulator based on an adjustable gradient metasurface and a design method thereof.

The present invention firstly provides a Tunable Gradient Metasurface (TGMS) unit, the TGMS unit is mainly composed of three parts: the upper main resonator and the sub-resonator, the middle dielectric plate and the lower metal grounding plate; wherein, the main resonator is I-type metal structure, composed of horizontal metal strips, vertical metal strips, and varactor diodes welded between the openings of the vertical metal strips, the sub-resonator consists of a pair of metal patches of the same size, used for high frequency produce a symmetrical electrical response. In the I-type structure, the horizontal metal strip (with a very narrow line width) is used to provide a high reactance value and play the function of DC bias, preventing high-frequency microwave signals from entering the DC source without affecting the DC bias voltage, thereby improving the circuit. stability.

The present invention also provides a reflected electromagnetic wave modulator based on the above TGMS unit, the reflected electromagnetic wave modulator is a broadband tunable gradient metasurface (i.e. broadband TGMS), and the broadband tunable gradient metasurface consists of a superunit in a two-dimensional plane Period extension; the superunit is composed of six TGMS units with different structural parameters and phases arranged in order of size, and has a uniform broadband phase gradient.

The present invention also proposes a parameter design method of the above-mentioned broadband adjustable gradient metasurface, that is, a reflective electromagnetic wave modulator, and the specific steps are as follows:

Step 1: Determine the period p _i of the TGMS unit (that is, the size of the TGMS unit, which is divided into p _x and p _y , where p _x is the size in the x direction, and p _y is the size in the y direction), and the phase difference between adjacent TGMS units φ ₀ (For example, if φ ₀ =60 ^o , then the number of TGMS units is 6, which can be recorded as 1#~6#TGMS units in turn), initial operating frequency f ₀ (generally f ₀ < f _c ), initial capacitance C ₀ ( Generally select the lower limit of the varactor capacitance), and by changing the structural parameters (such as changing h ₂ , h ₃ , w ₃ and C _t , etc.), a group of 1#~6#TGMS unit phases with a linear gradient change structure can be obtained parameters; here, f _c is the critical frequency, h ₂ is the length of the vertical metal line of the I-shaped structure, h ₃ and w ₃ are the height and bandwidth of the patch, and C _t is the total capacitance of the varactor diode;

Step 2: Simulate the reflection phase of the 1#~6#TGMS units obtained above, scan the phase distribution corresponding to different capacitance values C, and obtain the capacitance-phase (C–φ) distribution of each TGMS unit at different frequencies;

Step 3: According to the capacitance C _i required by each TGMS unit at different frequencies of C–φ, set the scanning frequency step size (for example, 0.005GHz) and use a certain TGMS unit (for example, select 1#TGMS unit) at a specific frequency and the reflection phase in the case of C ₀ as the reference point, calculate the required phases of other TGMS units (such as 2#-6#TGMS units) when the uniform phase gradient is strictly satisfied at different frequencies through cubic spline interpolation, and then use the above obtained C-φ distribution and obtain the required capacitance C _i of other TGMS units through cubic spline interpolation. If the C _i obtained by each TGMS unit at this frequency is within the capacitance range achievable by the varactor diode (for example, 0.3pF< C _i <1.2pF), then calculate the next frequency, otherwise change the initial capacitance C ₀ ; repeat Repeat the above steps until a set of parameters C satisfying the capacitance range is obtained. If there are more than one group of capacitance combinations obtained, select the group with the smallest capacitance crossing range; if C ₀ traverses all values in the capacitance range and cannot obtain a set of parameters that meet the requirements, then end the scan, and the frequency reaches the boundary of the adjustable range;

In the fourth step, according to the obtained capacitance value, the voltage value is obtained by inverting the capacitance-voltage (C-V) distribution of the varactor diode. Here, it is necessary to interpolate the C-V curve to obtain the required voltage value at each frequency point;

The fifth step is to arrange the above six TGMS units in order of size to form a super unit; carry out periodic extension on the super unit in the two-dimensional plane, and apply the required voltage, the desired broadband TGMS, that is, the reflected electromagnetic wave modulator, is obtained.

The above steps are all realized by matlab programming.

The present invention combines adjustable technology with GMS, and obtains a TGMS unit with phase compensation and continuous phase adjustment by introducing a varactor diode and a double-resonant structure into the GMS unit; the TGMS unit proposed by the present invention is still in the main resonance A pair of equal large metal patches are ingeniously introduced near the structure. The purpose is to introduce a new resonance. By adjusting the size of the patch and making it cooperate with the main resonance, the smooth transition and cascade of the two resonance frequencies can be realized, thus effectively It reduces the Q value, expands the phase and frequency control range of TGMS, and has a high degree of design freedom; at the same time, TGMS provides broadband dynamic linear gradient and continuous electromagnetic wave control characteristics, which expands the application field of GMS and improves the working efficiency of GMS , reduces the production cost , and has broad application prospects in the fields of electromagnetic wave dynamic modulation, new functional antenna, broadband stealth and large-capacity communication.

Finally, the reflection control function of the TGMS of the present invention can be directly extended to the TGMS transmission control.

Description of drawings

Fig. 1 is a flow chart of the broadband TGMS design method of the present invention.

Fig. 2 is the topological structure of the TGMS unit based on the varactor diode of the present invention; wherein, w ₁ and h ₂ are the broadband and length of the vertical metal wires of the I-shaped structure, h ₃ and w ₃ are the height and width of the patch, C _t is the total capacitance of the varactor diode, p _x , p _y are the period of the unit in the x and y directions, w ₂ is the width of the horizontal bias line, d ₁ , d ₂ are the distance between the I-type structure and the patch in y and the spacing in the x direction, h ₁ is the spacing reserved for welding varactor diodes, and h is the thickness of the dielectric plate.

Fig. 3 is the equivalent circuit of the TGMS unit of the present invention;

The circuit parameters extracted in Figure 3 are: L ₁ =18.76nH, C ₁ =0.111pF, L ₂ =0.059nH, C ₂ =0.196pF, R ₁ =8.37Ω, R ₂ =0.114Ω, Z _c =204.9Ω and h _o =58.9 ^o .

Fig. 4 is the equivalent circuit model of the varactor diode in the TGMS unit of the present invention, wherein the left side is the spice circuit model, and the right side is the detection circuit model.

Figure 5 is the C-V curve of the varactor diode SMV1430-079LF.

Fig. 6 is the reflection amplitude curve of the TGMS unit of the present invention under different conditions.

Fig. 7 is the reflection phase curve of the TGMS unit of the present invention under different situations;

In Figure 6 and Figure 7: the unit structure parameters are p _x = p _y =12mm, w ₁ =0.8mm, w ₂ =0.5mm, w ₃ =5.1mm, d ₁ =0.25mm, d ₂ =0.5mm, h ₁ =1.5 mm, h ₂ =4.5 mm and h ₃ =10 mm.

Fig. 8 is the impact curve of the patch width on the reflection characteristics of the TGMS unit of the present invention;

In Figure 8: the unit structure parameters are p _x = p _y =12mm, C _j =0.31pF, w ₁ =0.8mm, w ₂ =0.5mm, w ₃ =5.1mm, d ₁ =0.25mm, d ₂ =1mm , h ₁ =1.5mm, h ₂ =4.5mm and h ₃ =10mm.

Fig. 9 is the topology structure of the TGMS of the present invention.

Fig. 10 is the broadband reflection amplitude curve of units 1#~6# of the present invention at 4.1GHz.

Fig. 11 is the broadband reflection phase curve of units 1#~6# of the present invention at 4.1GHz.

Figure 12 shows the capacitance values of units 1#~6# in TGMS at different frequencies under the comparison scheme.

Figure 13 is the capacitance value of 1#~6# units in TGMS at different frequencies;

In Figure 12 and Figure 13: the unit structure parameters are p _x = p _y =12mm, w ₁ =0.8mm, w ₂ =0.5mm, w ₃ =5.1mm, d ₁ =0.25mm, d ₂ =0.5mm, h ₁ =1.5 mm and h ₃ =2 h ₂ + h ₁ −2 d ₁ .

Figure 14 is the voltage value of 1#~6# units in TGMS at different frequencies.

Figure 15 is the reflection amplitude curve of units 1#~6# under the condition of 6 sets of capacitance and voltage.

Figure 16 is the reflection phase curve of units 1#~6# under the condition of 6 sets of capacitance and voltage.

Fig. 17 is the broadband scattering field amplitude of TGMS under different voltage combinations.

Figure 18 shows the single-frequency scattered field amplitude of TGMS under different voltage combinations.

Fig. 19 is the surface wave-transmission wave conversion device and the simulation field on the surface waveguide wave structure under the first group (1#) voltage.

detailed description

The present invention will be described in detail below in conjunction with the accompanying drawings.

A method for designing a broadband adjustable gradient metasurface mainly includes four steps, and the method flow is shown in Figure 1, which mainly consists of the following steps:

Step 1: Determine unit period p _i , phase difference φ ₀ between adjacent units (this invention assumes φ ₀ =60 ^o , the number of units is 6), initial operating frequency f ₀ (generally f ₀ < f _c ), initial capacitance C ₀ (generally select the lower limit of the varactor capacitance), and by changing the structural parameters ( h ₂ in the present invention) to obtain a set of structural parameters with a perfect linear gradient in phase;

Step 2: Simulate the reflection phase of the 1#~6# units obtained above, scan the phase distribution corresponding to different capacitance values C, and obtain the capacitance-phase (C–φ) distribution of each unit at different frequencies;

Step 3: Get the required capacitance C _i of each unit at different frequencies according to C-φ, set the scanning frequency step size (0.005GHz in the present invention) and use a certain unit (for example, choose 1# unit) at a specific frequency and C ₀ In this case, the reflection phase is the reference point. Calculate the required phases of other units (2#-6# units) when the uniform phase gradient is strictly satisfied at different frequencies through cubic spline interpolation, and then pass the C-φ distribution obtained above and pass Cubic spline interpolation obtains the required capacitance C _i of other units. If the C _i obtained by each unit at this frequency is within the capacitance range that can be achieved by the varactor diode (0.3pF< C _i <1.2pF in the present invention), then calculate the next frequency, otherwise change the initial capacitance C ₀ and repeat the cycle The above steps are performed until a set of parameters C satisfying the capacitance range is obtained. If there are more than one combination of capacitors, select the group with the smallest capacitor crossing range here, and if C ₀ traverses all the values in the capacitor range and cannot obtain a set of parameters that meet the requirements, then end the scan and the frequency reaches the boundary of the adjustable range.

In the fourth step, the voltage value is obtained by inverting the capacitance-voltage (C-V) distribution of the capacitor tube according to the obtained capacitance value. Here, the C-V curve needs to be interpolated to obtain the required voltage value at each frequency point.

The fifth step is to arrange the above six TGMS units in order of size to form a super unit; carry out periodic extension on the super unit in the two-dimensional plane, and apply the required voltage obtained in the fourth step through the bias line, then the obtained The required broadband TGMS, that is, reflected electromagnetic wave modulator.

The above steps are all realized by matlab programming.

As shown in Figure 2, the TGMS unit designed based on the broadband TGMS design method is mainly composed of three parts: the upper main resonator and the sub-resonator, the middle dielectric plate and the lower metal grounding plate. The main resonator is an I-shaped metal structure, composed of horizontal Composed of metal strips, vertical metal strips, and varactor diodes welded between the openings of the vertical metal strips, the sub-resonator consists of a pair of metal patches of equal size to produce a symmetrical electrical response at high frequencies. Here, the horizontal metal strip with very narrow line width in the I-type structure is used to provide a high reactance value and play the function of DC bias, preventing high-frequency microwave signals from entering the DC source without affecting the DC bias voltage, thereby improving the stability of the circuit. .

When working, the plane electromagnetic wave is vertically incident on the TGMS unit along the -z direction, and the electric field and magnetic field are respectively excited along the y-axis and x-axis directions. The electric field will drive the main resonator and sub-resonator to generate an electrical response at a specific frequency, while the magnetic field will drive the structure to generate a conduction current and a displacement current that flows between the upper metal structure and the metal backplane. As shown in Figure 3, the electrical response of the main resonator is equivalent by the series branches L ₁ , C ₁ and R ₁ , and the electrical response of the sub-resonator is equivalent by the series branches L ₂ , C ₂ and R ₂ , The transmission of electromagnetic waves in the dielectric plate is equivalent to a transmission line with an impedance of Z _c and a length of h , and the metal floor is equivalent to grounding. Here, the inductance L ₁ is composed of the vertical metal wire inductance of the I-type structure and the lead inductance of the varactor diode. The capacitance C ₁ includes the gap capacitance formed by the horizontal metal lines of adjacent units and the junction capacitance of the varactor diode. The electric field drives the microstrip _The response produced by the patch is equivalent to the inductance L2 and the capacitance _C2 , while R1 and R2 _are used to characterize the _loss . According to the transmission line theory, the TGMS unit will generate two electrical resonances, the primary and secondary resonance frequencies are and . Due to the effect of the metal back plate, the present invention belongs to the reflection system, and the electromagnetic wave incident on the TGMS unit has no transmission but reflection. Due to series branch resonance, the TGMS unit is at and There will be two reflection valleys at , and the reflection phase will change abruptly near the resonance frequency. _The size _of f1 and f2 can be manipulated by changing the I-type structure, the physical size of the patch, and tuning the junction capacitance of the varactor diode. Using this property, a TGMS unit with a linear phase gradient can be designed _at the operating frequency f0 .

In this embodiment, the dielectric plate is made of polytetrafluoroethylene glass cloth plate, the dielectric constant ε _r = 2.65, the thickness h = 6mm, and the electrical tangent loss tanσ = 0.001. The varactor diode adopts SMV1430-079LF, and its spice and detection equivalent circuit model are shown in Figure 4, where R _s , L _s , and C _s represent the parasitic resistance of the varactor diode, package lead inductance and shell capacitance, C _j Represents the junction capacitance of the die, which can generally be ignored due to the small influence of C _s . At this time, the equivalent circuit model of the diode can be equivalent by connecting R _s , L _s and C _j in series, where L _s =0.7nH, R _s ≈1Ω, and the variation curve of the typical value of C _j with voltage is shown in Figure 5 , when a small reverse bias voltage is applied to both ends of the diode, the diode exhibits a large capacitance, and the maximum capacitance C _j =1.24pF is present at 0V. When the reverse voltage gradually increases, C _j keeps changing Small, until the threshold voltage is 30v, the capacitance reaches a minimum of C _j =0.31pF.

In order to illustrate the unique electromagnetic characteristics and advantages of the TGMS unit of the present invention, the electromagnetic characteristics of the unit in six different situations are simulated using CSTMicrowaveStudio, where the boundaries along the x, y and z directions are respectively set as magnetic boundaries, electrical boundaries and wave ports. As shown in Figure 6 and Figure 7, when there is no patch, there is only one resonance point on the dot-dash line curve, and the amplitude and phase of the unit at the resonance change very sharply, and the phase presents an asymptotic behavior when it is far away from the resonance, and the frequency of the phase regulation The range is very narrow and the Q value is high. When the metal patch is introduced, there are obviously two resonance points f ₁ and f ₂ on the amplitude spectrum of the dotted line and the arrow line, and due to the interaction between the main and secondary resonators, f ₁ moves slightly to the low frequency. At the same time, the amplitude resonance intensity and phase change at f ₁ and f ₂ are obviously weakened, the Q value is effectively reduced, the reflection amplitude is large and the amplitude consistency is good, and the frequency control range of the phase is obviously widened. At the same time, it can also be seen that when the thickness of the dielectric plate increases from 1.5mm to 6mm, the amplitude resonance strength and phase change of the TGMS unit are also significantly weakened, and the Q value is reduced, but the phase adjustment range increased by this method is very limited. Finally, in the three cases, it can be seen that when C _j increases from 0.1pF to 1.2pF, the resonance frequency decreases significantly. Changing the value of C _j can effectively control the resonance frequency and phase, and at the same time, the intensity of resonance intensity and phase changes with the The increase of C _j is obviously enhanced, and the Q value increases.

In order to further verify the influence and regulation of the physical size of the patch on the reflection characteristics of the TGMS unit and f2 , Fig. ₈ shows the curves of the reflection coefficient changing with the height and width of the patch. It can be seen that when the height and width of the patch increase, f ₂ gradually decreases while f ₁ remains almost unchanged, and at the same time the phase near f ₂ changes significantly while the phase near f ₁ also remains almost unchanged, again proving the sub-resonance _The size of f2 caused by and tuning the patch can be tuned independently. It should be noted that the increased patch size will slightly reduce the reflection amplitude at f2 , which will worsen the consistency of the reflection amplitude _on the entire frequency spectrum to a certain extent.

The principle of TGMS to realize the function of surface wave conversion and beam deflection is: according to the law of generalized reflection and refractive index , when the electromagnetic wave irradiates the TGMS at the incident angle ?? _i , the reflection angle?? _r satisfies ,here The phase gradient produced for unit length TGMS can be calculated as ,?? is the wavelength of the electromagnetic wave in free space, is the refractive index. When the electromagnetic wave is vertically incident on the TGMS from free space, the reflection angle can be simplified as . by rational design can make the working frequency f ₀ , that is and , according to the size of the superelement The critical frequency f _c can be calculated. when When , TGMS can convert the transmitted electromagnetic waves into surface waves, and the scattered electromagnetic waves are very weak; and when and continuously increasing, at this time and It is constantly decreasing, and through reasonable design, TGMS can realize continuous beam deflection.

Table 1 Size (mm), reflection amplitude and phase of each TGMS unit in the superunit

.

According to the above principles and the unique electromagnetic characteristics of the TGMS unit of the present invention, through reasonable design, the above surface wave conversion function and continuous beam deflection function can be realized by only one TGMS, which has excellent characteristics such as high integration and multi-function. The super unit of the present invention is composed of 6 TGMS units of different sizes, the phases between adjacent units lag by ^60o sequentially, the phase completely covers ^360o , and has a reflection amplitude of nearly 1 and a uniform linear phase gradient. Here, the initial phase gradients of the six TGMS units 1#~6# in the superunit are realized by changing the vertical metal wire length h ₂ of the I-shaped structure and fixing the distance d ₁ between the patch and the I-shaped structure and other structural parameters, According to h ₃ =2 h ₂ + h ₁ -2 d ₁ , it can be seen that the height h ₃ of the patch changes in the same amplitude as h ₂ . Two-dimensional TGMS can be formed by periodically extending superunits in two mutually orthogonal directions. The high reflection amplitude and linear phase gradient achieved with TGMS can be used to manipulate the beam deflection direction and energy of reflected electromagnetic waves. There are two ways to construct the superunit here. One is that the phase gradient formed by the 1#~6# TGMS unit is along the direction of the magnetic field, which is called the TE wave mode, and the other is that the phase gradient is along the direction of the electric field, which is called the TM wave mode. Since the electric field of the surface wave in the TE mode is weak and inconvenient for actual measurement, the TGMSs in this embodiment are designed in an arrangement of the TM wave mode. The final TGMS is shown in Figure 9. Each row is composed of 30 identical units, which can be fed separately by a DC voltage source and a DC bias circuit. Therefore, the TGMS of the present invention requires 6 different voltages for independent control.

The size of the superelement according to the invention The critical frequency that can be calculated is fc = _4.167GHz . For the convenience of tuning and more intuition, the initial linear phase gradient of each TGMS unit in the present invention is designed at 4.1GHz and Cj ₌ 1.2pF, which is close to the upper limit capacitance. At this time, the diode The reverse bias voltage at both ends is close to the lower limit of 0V. Table 1 shows the size of each TGMS unit and the reflection amplitude and phase at 4.1GHz. Figure 10 and Figure 11 show their broadband reflection characteristics. It can be seen that the reflection amplitude of each TGMS unit at 4.1GHz is greater than 0.87, the amplitude consistency is good and the phase strictly meets the uniform linear gradient, while the nonlinearity of the phase dispersion makes GMS no longer have a uniform linear phase gradient when f ₀ deviates from 4.1GHz. At the same time, it can also be seen that as h ₂ and h ₃ continue to decrease, both f ₁ and f ₂ move to high frequency, but because the change of f ₂ is slower than that of f ₁ , the two resonant frequencies are close to each other and finally merged into A wider, deeper resonance valley. Since f ₀ < f _c at 4.1GHz, TGMS can realize the conversion from propagating wave to surface wave. However, when the frequency increases and f ₀ > f _c , due to the non-uniform phase gradient part of the energy will be mirror reflected, the deflection reflection efficiency will decrease and gradually move away from the TGMS phase dispersion and And exacerbated. The invention realizes the independent regulation of six phases by independently regulating the capacitance of six unit diodes, and solves two major problems, one is to realize high-efficiency deflection reflection, and the other is to realize continuously adjustable frequency and maximum bandwidth.

In order to illustrate the superiority of the capacitance combination scheme obtained by the present invention, another comparison scheme is given here, that is, keep the C ₀ of the 1# unit unchanged and only change the capacitance values of the other 5 units. Fig. 12 and Fig. 13 show the variation curves of capacitance with frequency finally obtained under the two schemes. It can be seen that the frequency range that strictly satisfies the linear phase gradient in the comparison scheme is only 4.1-5.82GHz, while the frequency regulation obtained by the scheme of the present invention is The range is 4.1-6.6GHz. Compared with the comparison scheme, the control range has been effectively expanded. This is due to the more degrees of freedom provided by the fully controllable capacitance. The capacitance curves are exactly the same. Finally, the voltage values required by each unit at different frequencies are shown in Figure 14. It can be seen that the voltage and capacitance curves are obviously inversely proportional.

In order to illustrate the effectiveness of the above method without loss of generality, here we randomly select six groups (1#~ 6#) Capacitance and voltage are used as samples for verification. CST is used to carry out electromagnetic simulation on units 1#~6# under 6 kinds of capacitance and voltage conditions. Figure 15 and Figure 16 show the reflection amplitude and phase curves of units 1#~6#. From the amplitude curves, it can be seen that the reflection amplitudes of the six units in all cases have certain changes but are greater than 0.85, and the amplitude consistency of the first three cases (5.5, 6, 6.5 GHz) is obviously better than the latter three Amplitude consistency in the case. From the phase curves, it can be seen that the phase curves of units 1#~6# in all cases are parallel to each other and the phases between the units strictly satisfy the linear phase gradient, which verifies the validity of the superunit design.

In order to verify the multifunctional characteristics of the TGMS of the present invention, the scattered field simulation of the TGMS containing 5 superunits is carried out by using CST. Here, both the phase gradient and the electric field are along the y-axis direction and the two boundaries in this direction are set as open boundaries, the plane electromagnetic wave is vertically incident along the -z direction, there is only one unit in the x-direction and the two boundaries in this direction are set as magnetic boundaries, For simulating infinite metasurfaces. Since only the reflection characteristics of TGMS are concerned here, that is, only the amplitude of the spatial scattering field in the upper half of the yoz plane (-90 ^o <θ <90 ^o ) is concerned, and the energy transmitted by the open boundary is not considered. Figure 17 and Figure 18 respectively show the amplitude distribution of the scattered field of TGMS at different frequencies. It can be seen that when the voltage on the varactor diode is the first set of voltage conditions (4.1GHz), the scattered field of TGMS is lower than 4.1GHz It is very weak, which is the surface wave effect; while in the last five groups of voltage conditions, the energy is mainly concentrated in the +1 order scattering direction near the operating frequency f ₀ of the perfect linear gradient, and the image (0 order) and -1 order scattering fields are very weak , so the relative efficiency of TGMS at f ₀ is greater than 85% in the latter five voltage situations, and the inconsistency of the total reflected energy at different frequencies is caused by the different absorption of TGMS. When the frequency is far away from f ₀ , the field intensity of the 0-order and -1-order scattering increases in different degrees, and when no bias voltage is applied to the TGMS, the 0-order scattering of TGMS becomes very large, and the -1-order scattering is very small. The conversion efficiency drops sharply. Since the TGMS of the present invention has a perfect uniform phase gradient in the range of 4.1-6.6 GHz, the high-efficiency beam deflection has a very wide working bandwidth. At the same time, the function of TGMS surface wave conversion is switched to beam deflection and the deflection angle is gradually tuned from nearly 90 degrees at 4.1GHz to 39.9 degrees at 6.5GHz, realizing multi-functional switching and broadband work with efficient beam deflection.

To further illustrate the surface wave characteristics of TGMS at 4.1GHz, a device for converting surface waves into propagating waves is designed here, its performance is quantitatively described and the wavelength of surface waves is calculated. Since the surface wave coupled to the gradient metasurface is not an eigenstate, it is an excited state driven by the incident electromagnetic wave and cannot be transmitted freely. An eigensurface wave structure must be designed to guide its free transmission. As shown in Figure 19, the simulation device is composed of TGMS, surface waveguide wave structure and absorbing material. The gradient metasurface on the left side of the system irradiated vertically by the incident electromagnetic wave is first transformed into a stimulated surface wave, which will couple the intrinsic surface plasmons on the high impedance surface on the right side of the system, thereby guiding the energy out . In order to prevent the propagating surface wave from being reflected at the end and thus affect the propagation of the surface wave, an additional section of gradually absorbing structure is loaded at the end of the waveguide structure to suppress its reflection. At the same time, in order to achieve efficient conversion of the stimulated surface wave to the intrinsic surface wave, the key to the design of the guided wave structure is that its wave vector must be equal to the gradient of the superelement, that is, , so as to achieve wave vector matching, here is the wave vector at the critical frequency. The intrinsic surface wave structure adopts a patch structure, and its structural parameters can be obtained by scanning the dispersion curve in commercial electromagnetic simulation software, so that its wave vector at 4.1GHz . From the simulation results, it can be seen that the intrinsic surface wave structure can efficiently convert the stimulated surface wave into the transmitted surface wave, and the wavelength of the transmitted wave λ≈70.6mm, which can be converted into , which achieves wave-vector matching.

There are many ways for the TGMS unit of the present invention to realize the phase gradient. For example, the height of the I-type structure, the voltage on the varactor diode and the size of the patch can be tuned, which has a high degree of freedom in design. At the same time, the TGMS provides a wide-band dynamic perfect linearity Gradient and continuous electromagnetic wave control characteristics expand the application field of GMS, improve the working efficiency of GMS, reduce the production cost , and have broad application prospects in the fields of electromagnetic wave dynamic modulation, new function antenna, broadband stealth and large-capacity communication. At the same time, the present invention The reflection control function of TGMS can be directly extended to TGMS transmission control.

Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than to limit the scope of protection of the present invention. Simple modifications or equivalent replacements to the technical solution of the present invention by those skilled in the art will not depart from the present invention. The essence and scope of the technical solution of the invention.

Claims (6)

1. A TGMS unit is characterized in that the unit mainly comprises an upper layer main resonator, an auxiliary resonator, a middle dielectric plate and a lower layer metal grounding plate; the primary resonator is of an I-shaped metal structure and comprises a horizontal metal strip, a vertical metal strip and a variable capacitance diode welded between openings of the vertical metal strip, and the secondary resonator is composed of a pair of metal patches with the same size and used for generating symmetrical electric response at a high frequency.

2. A modulator of reflected electromagnetic waves based on the TGMS unit of claim 1, characterized by a broadband tunable gradient super surface consisting of a periodic continuation of the super unit in a two-dimensional plane; the superunit is composed of 6 TGMS units with different structural parameters and phases which are arranged in sequence according to size and size, and has uniform broadband phase gradient.

3. A method of designing a modulator for reflected electromagnetic waves according to claim 2, characterized by the specific steps of:

the first step is as follows: determining a period of a TGMS unitp _iAdjacent TGMS units have a phase difference phi₀=60^oInitial operating frequencyf ₀Initial capacitanceC ₀Obtaining a group of structural parameters with 1# -6# TGMS unit phases changing in a linear gradient manner by changing the structural parameters;

the second step is that: simulating the obtained reflection phases of the 1# -6# TGMS units, scanning phase distribution corresponding to different capacitance values C, and obtaining capacitance-phase C-phi distribution of each TGMS unit under different frequencies;

the third step: capacitance required by each TGMS unit at different frequencies according to capacitance-phase C-phiC _iSetting scanning frequency step size and using a certain TGMS unit at specific frequency sumC ₀The reflection phase under the condition is a datum point, the phases required by other TGMS units when the phases strictly meet the uniform phase gradient at different frequencies are calculated through cubic spline interpolation, and then the capacitance-phase C-phi distribution obtained through the method is used for obtaining the capacitance required by other TGMS units through cubic spline interpolationC _i(ii) a If obtained per TGMS unit at that frequencyC _iAll within the range of the capacitance that can be reached by the varactor, the next frequency is calculated, otherwise the initial capacitance is changedC ₀(ii) a Repeating the above steps until a set of parameters satisfying the capacitance range is obtainedC(ii) a If the obtained capacitance combination is more than one group, selecting the group with the smallest capacitance spanning range; if it isC ₀Traversing all values in the capacitance range to obtain a set of parameters which meet the requirements, and endingScanning, wherein the frequency reaches the boundary of an adjustable range;

fourthly, according to the obtained capacitance value, obtaining a voltage value through capacitance-voltage C-V distribution reverse-deducing of the variable capacitance diode, and carrying out interpolation calculation on a capacitance-voltage C-V curve to obtain a voltage value required by each frequency point;

fifthly, arranging the 6 TGMS units according to the size sequence to form a superunit; and carrying out periodic continuation on the superunit in a two-dimensional plane, and applying the required voltage obtained in the fourth step through a bias line to obtain the required broadband TGMS, namely the reflected electromagnetic wave modulator.

4. The design method according to claim 2, wherein: the phase deviation caused by phase dispersion is compensated through phase regulation and control of the variable capacitance diode, and the uniform phase gradient of the broadband is realized.

5. The design method according to claim 2, wherein: the construction of the superunit has two modes, namely, a phase gradient formed by the 1# -6# TGMS units is along the direction of a magnetic field and is called as a TE wave mode; the other is that the phase gradient formed by the 1# -6# TGMS units is along the direction of the electric field, which is called TM wave mode.

6. The design method according to claim 2, wherein: the pair of superunits carries out periodic continuation in a two-dimensional plane, namely the superunits are periodically prolonged in two mutually orthogonal directions.