阅读说明：本技术 一种用于菲涅耳区域高效无线能量传输的超材料天线阵列 (Metamaterial antenna array for efficient wireless energy transmission in Fresnel region ) 是由 殷丹 杨钊 赵发定 文光俊 于 2020-11-27 设计创作，主要内容包括：本发明公开一种用于菲涅耳区域高效无线能量传输(WPT)的超材料天线阵列,应用于无线电力传输,针对现有小尺寸的天线阵列无线电力传输效率不高的问题,本发明的超材料天线阵列19,包括通过金属通孔连接到馈电网络的多个紧密间隔的亚波长尺寸电LC(ELC)单元；使用Ansys HFSS的遗传算法优化工具和ELC等效设计模型(包括Floquet端口和主/从边界条件)优化电LC(ELC)单元晶胞参数,以在工作频率上实现最大吸收(或辐射)效率和阻抗匹配,采用本发明天线阵列作为WPT系统的发射天线1与一个接收天线或天线阵列2,无线电力传输效率能够非常接近连续孔径极限值。(The invention discloses a metamaterial antenna array for Fresnel zone efficient wireless energy transmission (WPT), which is applied to wireless power transmission and aims at the problem that the wireless power transmission efficiency of the existing small-sized antenna array is not high; the genetic algorithm optimization tool of Ansys HFSS and ELC equivalent design model (including Floquet port and master/slave boundary conditions) are used to optimize the unit cell parameters of the lc (ELC) unit to achieve maximum absorption (or radiation) efficiency and impedance matching at the operating frequency, and the wireless power transmission efficiency can be very close to the continuous aperture limit value by using the antenna array of the present invention as the transmitting antenna 1 and one receiving antenna or antenna array 2 of the WPT system.)

1. A metamaterial antenna array for efficient wireless energy transfer in a Fresnel zone, comprising a plurality of closely spaced sub-wavelength sized metamaterial units connected to a feed network by metal vias.

2. A metamaterial antenna array for fresnel zone efficient wireless energy transfer as in claim 1, wherein the metamaterial unit comprises: the circuit comprises a copper patch, a dielectric substrate (12), a copper grounding layer (13) which are arranged from top to bottom, and further comprises a metal through hole (14) penetrating through the dielectric substrate (12) and a lumped port (15) arranged on the copper grounding layer (13); the middle of the copper patch comprises an I-shaped opening, the annular copper patch part at the periphery of the I-shaped opening is marked as a square copper ring (10), and the two strip-shaped copper patch parts matched with the I-shaped opening are marked as copper strips (11).

3. A metamaterial antenna array for fresnel zone high efficiency wireless energy transfer as claimed in claim 2, wherein genetic algorithm optimization tools and equivalent models of Ansys HFSS are used to optimize unit cell parameters of metamaterial units, the unit cell parameters comprising: the length s of a gap between adjacent metamaterial units, the width w1 of a square ring of a square copper ring (10), the width w2 of copper bars (11), the distance g between two copper bars (11) and the distance r of a metal through hole (14) from the edge of a metamaterial unit.

4. A metamaterial antenna array for fresnel zone efficient wireless energy transfer as in claim 3, wherein the equivalent model comprises: a master boundary condition (16), a slave boundary condition (17), a Floquet port (18), and a single metamaterial unit defined within the master boundary condition (16) and the slave boundary condition (17).

5. The metamaterial antenna array for fresnel zone efficient wireless energy transfer of claim 4, wherein the optimization objectives of optimizing unit cell parameters of metamaterial units using genetic algorithm optimization tools and equivalent models of Ansys HFSS are: so that the metamaterial unit structure realizes maximum absorption efficiency and impedance matching at a certain specific working frequency.

6. A metamaterial antenna array for efficient wireless energy transfer in the Fresnel zone as claimed in claim 5, wherein the absorption efficiency of a single unit is defined as

η_ms＝(1-|ρ_refl|²)·|τ|²

Where ρ is_reflDenotes the reflectivity of the metamaterial unit cell to the incident plane wave, τ is the transmission coefficient from the surface of the metamaterial unit cell structure to the lumped port (15).

7. Metamaterial antenna array for fresnel zone efficient wireless energy transfer according to claim 6, characterized in that the two copper bars (11) are oriented according to TE or TM polarization direction.

8. Metamaterial antenna array for fresnel zone efficient wireless energy transfer according to claim 7, characterized in that Floquet ports (18) are used in designing metamaterial unit equivalent models for exciting TE or TM polarized electromagnetic plane waves.

Technical Field

The invention belongs to the field of Wireless Power Transmission (WPT), and particularly relates to an antenna array technology based on metamaterials.

Background

Complete Wireless Power Transfer (WPT) system design is a complex design process that has received much attention since the last century. We assume a WPT system based on far-field radiation mechanism, which consists of DC/AC power supply, RF power source, transmitting antenna, receiving antenna and rectifying circuit.

The transmit and receive antenna arrays are an important component of a radiating WPT system and can significantly affect the efficiency of the overall WPT system. In the Fresnel region, the documents "A.F.Kay," Near-field gain of antenna antennas, "IRE Trans.antennas Propag, vol.AP-8, pp.586-593 Nov.1960" and "G.V.Borgiotti," Maximum power transfer between two planar antennas in the Fresnel Zone, "IRE Trans.antennas Propag, vol.AP-14, No.8, pp-158 and 163, Mar.1966" describe the theoretical evaluation of the efficiency of a transmit-receive antenna array for two given continuous apertures and the optimization thereof. However, the proposed method is only valid for the continuous aperture case and does not describe the actual case of a discrete antenna array.

The documents "W.Geyi," Foundations of applied electronics ". New York, NY, USA: Wiley,2010(pp.273-275)," and "L.Shan and W.Geyi," optical design of focused antenna arrays, "IEEE trans.antennas Propag, vol.62, No.11, pp.5565-5571, Nov.2014" provide methods for optimizing aperture illumination when considering discrete antenna arrays. This method can take into account mutual coupling between the antenna elements and is for this reason largely generalized. The "Antenna array" is described in the documents "l.shann and w.geyi," optical design of focused Antenna arrays, "IEEE trans.antennas propag, vol.62, No.11, pp.5565-5571, nov.2014," v.r.gowda, o.yurdureven, g.lipworth, t.zupan, m.s.reynolds, and d.r.smith, "Wireless power transfer in the radial Antenna field," IEEE Antennas Wireless performance.let, vol.15, app.1865-1868,2016., "w.geyi," optical design of Antenna arrays, "IEEE in c.antenna Antenna array" (iw. r. iw. w. r. c.r. w. iw. r. g. g.t. c.w. w. c.5-1868,2016., "Antenna arrays," and "iw. w.r. g. 5. w.r. w.c.r. Antenna arrays," wherein the actual wavelength of the Antenna array is about 0. w.w.r. w.r. Antenna array. In this case, the optimum aperture illumination obtained is very close to the quantized form of the ideal long ellipsoid wave function, except for the minimal deviation due to mutual coupling. Nevertheless, because the area of the antenna array is not large (so the number of antenna elements does not exceed 4x4 or 6x6), the efficiency obtained is far from what can be achieved with a continuous aperture antenna.

Disclosure of Invention

In order to solve the above technical problem, the present invention proposes to apply a metamaterial antenna array for efficient wireless energy transmission in the fresnel region, which is implemented by sub-wavelength sized electric LC cells equipped with metal vias.

The technical scheme adopted by the invention is as follows: a metamaterial antenna array for fresnel zone efficient wireless energy transfer comprising a plurality of closely spaced sub-wavelength sized electric lc (elc) units connected to a feed network by metal vias.

The Electric LC (ELC) unit includes: the integrated circuit comprises copper patches, a dielectric substrate 12, a copper grounding layer 13, metal through holes 14 penetrating through the dielectric substrate 12 and lumped ports 15 arranged on the copper grounding layer 13, wherein the copper patches, the dielectric substrate 12 and the copper grounding layer 13 are arranged from top to bottom; the middle of the copper patch comprises an I-shaped opening, the annular copper patch part on the periphery of the I-shaped opening is marked as a square copper ring 10, and the two strip-shaped copper patch parts matched with the I-shaped opening are marked as copper strips 11.

Optimizing cell parameters of an electric lc (elc) unit using genetic algorithm optimization tools and equivalent models of Ansys HFSS, the cell parameters comprising: the gap length s between adjacent ELC cells, the square ring width w1 of the square copper ring 10, the width w2 of the two copper bars 11, the distance g between the two copper bars 11, and the distance r of the metal via 14 from the edge of the ELC cell.

The equivalent model comprises: a master boundary condition 16, a slave boundary condition 17, a Floquet port 18, and a single electrical lc (elc) cell defined within the master boundary condition 16 and the slave boundary condition 17.

The optimization objectives of the unit cell parameters of the optimized electric lc (elc) unit using the genetic algorithm optimization tool and equivalent model of Ansys HFSS are: the Electric LC (ELC) unit structure can realize maximum absorption efficiency and impedance matching at a specific working frequency.

The absorption efficiency of a single Electric LC (ELC) cell is defined as

η_ms＝(1-|ρ_refl|²)·|τ|²

Where ρ is_reflRepresenting the reflectivity of the metamaterial unit cell to the incident plane wave, τ is the transmission coefficient from the surface of the electric lc (elc) unit cell structure to the lumped port 15.

The two metal strips 11 are oriented according to the TE or TM polarization direction.

The Floquet port 18 is used to excite TE or TM polarized electromagnetic plane waves.

The invention has the beneficial effects that: the antenna array of the invention consists of sub-wavelength Electric LC (ELC) metamaterial units, and feeds power through metal through holes, and the through holes are connected with a power supply through a properly synthesized feed network; the invention adopts full-wave electromagnetic simulation to calculate the optimal aperture illumination, and provides specific amount of power and specific phase difference for each antenna array unit; compared with the traditional microstrip patch transmission antenna array, the antenna array based on the metamaterial can better integrate the optimal extended ellipsoid wave function and the spherical phase distribution of the continuous aperture, thereby improving the WPT efficiency, and particularly has obvious improvement effect on the small-size antenna aperture.

Drawings

Figure 1 is a transmit antenna array and a receive antenna array in a WPT environment, and the opposite input ports of an equivalent network;

figure 2 is a conventional probe fed microstrip patch antenna, and two WPT systems;

FIG. 3 is a simulated WPT efficiency for the WPT system shown in FIG. 2;

FIG. 4 is a detailed view of an ELC cell array and a single ELC cell employed in the present invention;

FIG. 5 is a diagram of an ELC unit cell and an equivalent full electromagnetic wave simulation model used in its design, as used in the present invention;

FIG. 6 is a WPT system of the present invention;

figure 7 is a simulated WPT efficiency for the WPT system of figures 2 and 6.

Detailed Description

In order to facilitate the understanding of the technical contents of the present invention by those skilled in the art, the present invention will be further explained with reference to the accompanying drawings.

The conventional radiation type WPT system is realized by an antenna array transmitting aperture 1 composed of discrete N antenna units and a receiving aperture 2 composed of M antenna elements 3, the distance between them(D is the aperture size of the transmit antenna array and λ is the wavelength).

As shown in fig. 1. According to the method in the documents "W.Geyi," Foundations of applied electronics ". New York, NY, USA: Wiley,2010(pp.273-275)," and "L.Shan and W.Geyi," optical design of focused antenna arrays, "IEEE Trans.antennas Propag, vol.62, No.11, pp.5565-5571, nov.2014", the whole system can be regarded as a network of N + M ports, and scattering matrices (defining the operating frequency as f) can be used₀) Is described as

Wherein:

representing a scattering matrix; [ b ] a_tx]、[b_rx]Respectively, normalized reflected wave and incident wave vector of transmitting antenna array]For watchesShowing a matrix or vector, [ a ]_tx]、[a_rx]Respectively receiving normalized reflected wave and incident wave vector of antenna array; b_tx,1、b_tx,2、...、b_tx,NRespectively, the normalized reflected waves of the 1 st, 2 nd, … th and Nth antenna elements of the transmit antenna array, b_rx,1、b_rx,2、...、b_rx,MRespectively representing normalized reflected waves of No.1, No. 2, No. … and No. M antenna elements of the receiving antenna array; a is_tx,1、a_tx,2、...、a_tx,NRespectively, the normalized incident waves of the 1 st, 2 nd, … th and Nth antenna elements of the transmitting antenna array, a_rx,1、a_rx,2、...、a_rx,MNormalized incident waves of the 1 st, 2 nd, … th and mth antenna elements of the receiving antenna array are respectively represented. In this case, the Radio Frequency (RF) energy transfer efficiency eta between the transmitting antenna array and the receiving antenna array_airCan be calculated as

Assuming impedance matching, equation (3) can be rewritten as a form of eigenvalue problem:

([S_rx-tx]^T[S_rx-tx])[a_tx]＝η_air[a_tx] (4)

let [ A]＝([S_rx-tx]^H[S_rx-tx]) Then [ A ] is]The corresponding maximum characteristic value is the energy transmission efficiency eta_airAnd its corresponding eigenvector is the optimal excitation vector a_tx]. The scattering matrix [ S ] is calculated using computer-aided design (CAD) tools such as IE3D or HFSS_rx-tx]Mutual coupling between the antenna element and the environment can be taken into account.

In the literature "L.Shann and W.Geyi," Optimal design of focused anti-enannays, "IEEE Trans. Antennas Propag, vol.62, No.11, pp.5565-5571, Nov.2014," V.R.Gowda, O.Yurdeseven, G.Lipworth, T.Zupan, M.S.Reynolds, and D.R.Smith, "Wireless Power transfer in the radial near field," IEEE AntennasIn the actual case described in Wireless propag.lett., vol.15, pp.1865-1868,2016 "," w.geyi ", optical design of Antenna array," in proc. ieee International work hop on Antenna Technology (IWAT), Sydney, NSW, Australia, mar.2014 ", the discrete Antenna array aperture is designed with a conventional microstrip patch Antenna 4 as shown in fig. 2, with an inter-element distance d of about 0.5 λ -0.6 λ, where λ is the wavelength. In this way, the impedance matching of the antenna elements is not severely affected by mutual coupling. Although the design of such an aperture and its feed network is simple (synthesized by the method in (4)), the efficiency η obtained by solving (4)_airThe ideal efficiency achieved with continuous holes is still far from being achieved, as shown in figure 3.

According to the documents "A.F.Kay", "Near-field gain of aperture antennas", "IRE Trans. antennas Propag, vol.AP-8, pp.586-593 Nov.1960", "G.V.Borgiotti", "Maximum power transfer between plan antennas in the Fresnel Zone", "IRE Trans. antennas Propag, vol.AP-14, No.8, pp-158-163, Mar.1966", it can be determined that two square continuous transmitting and receiving apertures A.A.are used, respectively_txdxD and A_coll＝D_rxxD_rxObtainable efficiency η_airIs composed of

Wherein f is_tx(.) and f_rx(.) are functions of the strength of the transmitted and received electromagnetic fields respectively, is a surface A_collAnd A_txIs the distance between two common points P ═ x, y,0 and P ═ x ', y', 0, k is the wave number, a is the wave number_collDenotes the surface of the receiving antenna 2, A_txThe surface of the emissive array 1 is shown. In particular, leading to a maximum efficiency η_airCan be referred toThe documents "A.F.Kay," Near-field gain of illumination antennas, "IRE Trans. antennas Propag, vol.AP-8, pp.586-593 Nov.1960", "G.V.Borgiotti," Maximum power transfer between plan antennas in the Fresnel Zone, "IRE Trans. antennas Propag, vol.AP-14, No.8, pp-158-163, Mar.1966", the optimum illumination function expression is:

where m (.) and n (.) correspond to angular extensional spherical wave functions.

The result of fig. 3 is two 3x 3(N ═ 9)5 and 4x4(N ═ 16)6 microstrip patch antenna arrays (D ═ 0.6393 λ for N ═ 9 arrays and D ═ 0.4795 λ for N ═ 16 arrays) of D ═ 99.2mm in both cases, which were found by solving (4), and a single patch antenna 4 was used as the transmit array 1, and a single patch antenna 2(M ═ 1), with continuous aperture limitation, as found by calculating equation (5). Microstrip patch antenna design (using commercial software HFSS) on a Rogers RO4003C dielectric substrate with a thickness h of 1.524mm at a frequency f₀Other microstrip patch antenna parameters are as follows: l ═ 13.36 (patch length) and p_pin4.71mm (distance), p_pinIndicating the position of the probe 7 relative to the edge of the patch. The gap between microstrip patch antenna array results and continuous aperture limitations is due to the limited number of antenna elements of such arrays, which results in a poor quantification of the ideal prolate spheroidal wave function and spherical phase distribution.

The present invention proposes a metamaterial-based antenna array 8 composed of a large number of sub-wavelength electric lc (elc) cells 9 as shown in fig. 4 to better sample the ideal prolate spheroidal wave function and spherical phase distribution.

The design of a single ELC unit was performed using the equivalent full electromagnetic wave simulation model in fig. 5.

In particular, the ELC unit comprises, in order from top to bottom: a copper patch, a dielectric substrate 12(Rogers RO4003C, thickness 1.524 mm) and a copper ground layer 13; the middle of the copper patch comprises an I-shaped opening, the annular copper patch part on the periphery of the I-shaped opening is marked as a square copper ring 10, and the two strip-shaped copper patch parts matched with the I-shaped opening are marked as copper strips 11. Two of the copper strips 11 are oriented according to the desired polarization direction (TE-transverse electric field, or TM-transverse magnetic field).

The induced current on the ELC unit is guided by metal vias 14 through the dielectric substrate 12 and connected to the lumped port 15 through resistive impedance (representing the equivalent source impedance). The distance between the two copper bars 11 is g. The resistive impedance of the lumped port 15 may be considered a predetermined value or may be optimized for optimal efficiency. The master 16 and slave 17 boundary conditions were used to simulate the case of an infinite size array, and the float mode port 18 was used to excite TE or TM polarized electromagnetic plane waves. The cell parameters L, s, w1, w2, g and r shown in fig. 5 were optimized using the genetic algorithm optimization tool of Ansys HFSS, to give an example of achieving maximum absorption (or radiation) efficiency and impedance matching at an operating frequency of 5.8 GHz. Absorption efficiency is defined as

η_ms＝(1-|ρ_refl|²)·|τ|² (7)

Wherein the unit cell parameter L represents the square side length of the square sub-wavelength Electric LC (ELC) unit 9, s represents the gap length between adjacent ELC units, w1 is the width of the square copper ring 10, w2 is the width of two copper bars, g is the distance between two bars, r is the distance of the metal via from the edge of the ELC unit, ρ_reflRepresenting the reflectivity of the cell to an incident plane wave and τ is the transmission coefficient from the cell surface to the resistive load 15. The optimized cell size is: l12.4 mm, s 2mm, w1 2.91mm, w2 0.27mm, g 2.64mm, r 4.61mm (copper conductivity 58 × 10)⁶S/m²And the thickness is 0.035 mm).

A finite N × N array of ELC units 19 designed as described above with D ═ 99.2mm is shown in fig. 6 (in the specific case, N ═ 8). The array serves as a transmit array 1 and a single microstrip patch antenna 4 serves as a receive antenna 2. For this WPT system, a plurality of scattering matrices [ S ] of distances R were simulated by means of a CAD tool Ansys HFSS_tx-rx]. Then, the characteristic value problem (4) is solved by using a function 'eig' in Matlab, and the optimal excitation vector [ a ] of each distance is calculated_tx]。

The WPT efficiency for the above mentioned WPT system as a function of R is shown in figure 7 and compared to the WPT efficiency reported in figure 3 (for a reasonable comparison the metamaterial based antenna array 19 and the patch antenna arrays 5 and 6 are of the same size). It can be seen that the WPT system using the metamaterial-based antenna array 19 as the transmitting antenna can achieve higher wireless energy transmission efficiency, which is very close to the continuous aperture limit. This is because metamaterial-based antenna arrays can better synthesize an optimal continuous illumination profile, which improves efficiency by placing more antenna elements N on the same surface. Therefore, the metamaterial antenna array for the efficient wireless energy transmission of the Fresnel area is very suitable for a transmitting/receiving array with limited wireless energy transmission aperture size.

It will be appreciated by those of ordinary skill in the art that the embodiments described herein are intended to assist the reader in understanding the principles of the invention and are to be construed as being without limitation to such specifically recited embodiments and examples. Various modifications and alterations to this invention will become apparent to those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the claims of the present invention.