A multi-stage coupling low-frequency magnetic field focusing metasurface based on fano interference

Abstract

The application relates to a multi-stage coupling low-frequency magnetic field focusing metasurface design method based on Fano interference, and belongs to the technical field of low-frequency electromagnetic metamaterials. The core lies in that a double-layer multi-coupling structure is used, magnetic field resonance amplification and Fano interference focusing are cooperatively worked, and efficient capture and spatial local enhancement of a far-field weak magnetic signal are realized. A large-size resonance coil in an upper layer serves as a coupling amplification core, and a weak magnetic field is greatly enhanced through LC resonance; an asymmetric Fano interference is generated through frequency detuning and phase matching of a Fano interference array in a lower layer, and the amplified magnetic field is accurately focused to a small central area; the two layers are stacked at a fixed interval and rigidly fixed. The application solves technical problems such as a small magnetic aperture, strong directivity, low sensitivity of far-field weak signal detection, insufficient angle coverage and signal strength in cross-medium communication and the like of a traditional low-frequency receiving antenna, and realizes synchronous amplification and spatial high-precision focusing of a low-frequency magnetic field.

Description

Technical Field

[0001] This invention relates to the fields of low-frequency electromagnetic wave detection, electromagnetic metamaterials and cross-medium wireless communication, specifically to a multi-level coupled low-frequency metasurface based on Fano interferometry, used for magnetic field focusing, magnetic flux confinement and received signal enhancement. Background Technology

[0002] Low-frequency electromagnetic waves possess advantages such as strong penetration, low propagation loss, and resistance to multipath interference in conductive media like seawater, soil, and building walls, making them valuable for applications in cross-medium communication, emergency search and rescue, underground detection, and underwater early warning. However, traditional low-frequency receiving devices are difficult to miniaturize due to inherent constraints on antenna physical size and radiation efficiency. Existing magnetic receiving antennas rely on high-permeability magnetic cores for miniaturization, but they generally suffer from problems such as small effective magnetic collection aperture, low magnetic field collection efficiency, and strong direction dependence, resulting in insufficient sensitivity for detecting weak magnetic signals in the far field.

[0003] Electromagnetic metasurfaces, as an artificially structured electromagnetic functional interface, can flexibly control the amplitude, phase, propagation direction, and spatial distribution of electromagnetic fields through unit resonance, phase matching, and coherent interference effects. They have outstanding advantages such as compact structure, strong control capability, and easy integration, providing a new technical approach for the efficient collection and precise control of low-frequency magnetic fields.

[0004] In recent years, the Fano interferometry effect, with its asymmetric resonant response and strong local field enhancement characteristics, has shown great application potential in the field of fine electromagnetic field control, providing a new way to achieve high-performance magnetic field focusing. The core feature of Fano interferometry lies in the formation of a sharp asymmetric resonant curve through coherent coupling between discrete and continuous states, which can achieve significant field strength enhancement and energy focusing in the target region. Combining the Fano interferometry mechanism with multi-level coupling synergistic control can simultaneously achieve large-scale magnetic flux collection and high-precision spatial focusing in the low-frequency band. This fundamentally overcomes the technical bottlenecks of low magnetic collection efficiency and insufficient signal sensitivity in traditional miniaturized receiving devices, providing key technical support for building a high-sensitivity, wide-angle coverage low-frequency cross-medium communication system. Summary of the Invention

[0005] This invention aims to solve the technical challenges of traditional low-frequency magnetic field receiving devices, such as small magnetic aperture, low signal acquisition efficiency, strong direction dependence, and insufficient sensitivity for detecting weak signals at long distances. To address these challenges, a multi-stage coupled low-frequency magnetic field focusing metasurface based on Fano interferometry is designed. This invention achieves globally efficient amplification and spatially precise focusing of the low-frequency magnetic field by constructing a "coupled amplification-Fano focusing" synergistic control structure. This significantly improves the signal strength and detectable range of miniaturized receiving antennas, ultimately providing a compact and high-performance low-frequency magnetic field receiving solution for scenarios such as cross-medium emergency communication and underground detection.

[0006] This invention relates to a multi-level coupled low-frequency magnetic field focusing metasurface based on Fano interferometry, specifically comprising a coupling amplification layer, a magnetic field focusing layer, and an intermediate insulating dielectric layer disposed between the coupling amplification layer and the magnetic field focusing layer, the structural layout of each layer being as follows: Figure 1 As shown.

[0007] The spacing between the coupling amplification layer and the magnetic field converging layer remains fixed. The two are insulated and isolated by the intermediate insulating dielectric layer and are fixed by rigid bonding to ensure stable coupling of the two layers and prevent them from shifting.

[0008] Preferably, the intermediate insulating dielectric layer is made of FR-4 material, which has good insulation performance and structural rigidity; the resonant coils of the coupling amplification layer and the magnetic field converging layer are both made of copper coils, which have excellent conductivity and low loss; the first capacitor, the second capacitor and the third capacitor mentioned later are all film capacitors with an accuracy controlled within ±5%, which can ensure the stability and control accuracy of the resonant frequency.

[0009] Preferably, the coupling amplification layer adopts a multi-turn square coil with a side length of L, and the magnetic field converging layer adopts a multi-turn square coil with a side length of L / 3. The two are designed with corresponding proportions to achieve structural matching. The thickness of the intermediate insulating dielectric layer is set to a preset fixed value to further ensure the coupling stability of the two-layer structure and avoid the effect of spacing deviation on magnetic field control effect.

[0010] Specifically, the coupling amplification layer consists of an LC resonant unit composed of a multi-turn square resonant coil connected in series with a third capacitor. Its core function is to efficiently collect dispersed magnetic flux in space and achieve resonant amplification in the target low-frequency operating band, providing a sufficient energy basis for subsequent magnetic field focusing.

[0011] The magnetic field converging layer adopts a 3×3 planar periodic array structure, consisting of a central resonant unit and eight peripheral resonant units closely fitted and periodically arranged. Both the central and peripheral resonant units employ multi-turn square coil structures, and their geometric dimensions are completely identical, ensuring the symmetry and coupling consistency of the array units. To achieve the Fano interference effect, a first capacitor is connected in series with the central resonant unit, and a second capacitor is connected in series with each peripheral resonant unit. The capacitance values ​​of the first and second capacitors are different, causing frequency detuning between the central and peripheral units.

[0012] Furthermore, the resonant frequency ω0 of the central resonant unit and the resonant frequency ω1 of the surrounding resonant units satisfy a preset ratio ω0:ω1=1:0.9. This ratio design can achieve optimal Fano interference effect and unidirectional magnetic field focusing, ensuring that the magnetic field energy can be directionally converged to the central region.

[0013] Meanwhile, the resonant frequency ω2 of the coupling amplification layer is consistent with the resonant frequency ω0 of the central resonant unit, thereby achieving in-phase coherent resonance of the entire unit, maximizing the synergistic effect of magnetic field amplification and focusing, and avoiding energy loss and control failure caused by frequency deviation.

[0014] This invention achieves highly efficient synergy between the LC resonant amplification effect of the coupling amplification layer and the Fano interference focusing effect of the magnetic field converging layer by synergistically controlling the geometric parameters (number of coil turns, side length), capacitance parameters (capacitance values), and the spacing between the two layers. This ultimately realizes globally efficient amplification and spatially precise focusing of low-frequency magnetic fields, significantly improving the receiving sensitivity of weak magnetic field signals and fundamentally solving the technical pain points of traditional low-frequency receiving devices, such as… Figure 2 As shown.

[0015] The beneficial effects of this invention are as follows: By constructing a multi-level coupling structure consisting of a coupling amplification layer, a magnetic field converging layer, and an intermediate insulating dielectric layer, this invention innovatively introduces the synergistic effect of Fano interference mechanism and LC resonant amplification, organically combining global magnetic field amplification with local precise focusing. This effectively solves the technical problems of traditional low-frequency magnetic field receiving devices, such as small magnetic aperture, low signal acquisition efficiency, strong direction dependence, and insufficient sensitivity for detecting weak signals at long distances. This metasurface structure is compact, easy to integrate, and can stably cover the low-frequency operating band. It can meet various practical application needs such as cross-medium emergency communication, underground detection, underwater early warning, and weak magnetic signal detection. It is highly practical and has extremely high engineering and promotion value. Attached Figure Description

[0016] Figure 1 Schematic diagram of a multi-level coupled low-frequency magnetic field focusing metasurface structure based on Fano interferometry

[0017] Figure 2 Schematic diagram of the working principle of multi-level coupled low-frequency magnetic field focusing metasurface based on Fano interferometry

[0018] Figure 3 This is a graph showing the magnetic field intensity distribution in the back region of the metasurface.

[0019] Figure 4 This is a schematic diagram of the deployment of a building indoor cross-medium low-frequency magnetic field communication system.

[0020] Figure 5 This is a comparison spectrum of the received signals before and after the metasurface of this invention is added in a cross-medium communication scenario. Detailed Implementation

[0021] Example 1: Application of High-Precision Focusing Acquisition and Detection of Weak Low-Frequency Magnetic Fields

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] like Figure 1 As shown, a multi-level coupled low-frequency magnetic field focusing metasurface based on Fano interference includes: a coupling amplification layer; a magnetic field converging layer; and an intermediate insulating dielectric layer disposed between the coupling amplification layer and the magnetic field converging layer;

[0024] in,

[0025] The intermediate insulating dielectric layer is made of polytetrafluoroethylene and has a thickness of 2 mm;

[0026] The multi-turn square coil of the coupling amplification layer is a 5-turn copper coil with a side length of 15 cm and a wire diameter of 1 mm. It is connected in series with a 200 nF thin film capacitor with an accuracy of ±5% to form an LC resonant unit.

[0027] The magnetic field converging layer is a 3×3 planar periodic array structure, consisting of a central resonant unit and eight peripheral resonant units arranged in close fit. All coils are 14-turn square copper coils with a side length of 5 cm and a wire diameter of 0.8 mm. The central unit is connected in series with a 160 nF capacitor, the peripheral units are connected in series with a 200 nF capacitor, and a film capacitor with an accuracy of ±5%.

[0028] The center resonant unit has a Q value of 72, the peripheral resonant unit has a Q value of 65, and the coupling amplification layer has a Q value of 69. The quality factors of the three are matched with each other. The metasurface has a working center frequency of 100 kHz and a bandwidth of 1 kHz, and has stable resonance characteristics and efficient magnetic field control performance.

[0029] The resonant frequency ω0 of the central resonant unit and the resonant frequency ω1 of the surrounding resonant units satisfy a preset ratio ω0:ω1=1:0.9 to achieve optimal Fano interference and unidirectional magnetic field focusing.

[0030] The resonant frequency ω2 of the coupling amplification layer is equal to the resonant frequency ω0 of the central resonant unit, thus achieving in-phase coherent resonance of all units.

[0031] In this embodiment, a high-precision function signal generator drives the excitation coil to radiate a weak low-frequency magnetic field of 100 kHz with a field strength of 0.04 μT, which is incident on the overall metasurface structure. The incident magnetic field is first amplified by the LC resonance of the coupling amplification layer, and then the magnetic field is focused behind the central unit by the Fano interference effect between the center and the surrounding units of the magnetic field converging layer. A high-resolution vector magnetometer and a magnetic field acquisition device measure the magnetic field distribution on the metasurface point by point and generate the magnetic flux distribution, recording the difference in magnetic field strength between the central region and the surrounding region.

[0032] The results are as follows: Figure 3 As shown, this metasurface can concentrate more than 60% of the total magnetic flux to the central region, which accounts for only 11% of the total area, with a peak magnetic field strength of 0.4 μT at the center, an increase of about 10 times; the magnetic field strength in the surrounding region is all below 0.2 μT, and the magnetic field focusing directionality is good.

[0033] Example 2: Application of Low-Frequency Magnetic Field Communication Signal Enhancement in Building Indoors

[0034] This embodiment employs the aforementioned multi-level coupled low-frequency magnetic field focusing metasurface based on Fano interferometry for cross-medium low-frequency magnetic coupling communication in complex indoor building environments with wall obstruction. Figure 4 The diagram shown illustrates the setup of the experimental system and the communication path in this embodiment.

[0035] In this embodiment, the communication environment is a standard office building;

[0036] The receiver is fixed indoors on the fifth floor and uses a small magnetic receiving antenna with a radius of 5 cm. The metasurface is coaxially attached to the receiving antenna. The spectrum analyzer is used to measure the signal strength and signal-to-noise ratio of the receiver. The angle adjustment platform is used to adjust the azimuth angle of the receiver and test the detectable angle range. The oscilloscope is used to record the output voltage signal and compare the signal changes before and after the metasurface is added.

[0037] The transmitter is located on the second basement level of the building and uses a ring-shaped transmitting antenna with a radius of 30 cm.

[0038] In this embodiment, the specific parameters of the metasurface are consistent with those in Embodiment 1;

[0039] The working process of this embodiment is as follows: A low-frequency signal generator excites the transmitting coil to radiate a constant 100 kHz low-frequency magnetic field signal. After penetrating multiple layers of walls and floors, the signal forms a weak attenuated magnetic field, which is incident on the surface of the metasurface structure. The incident magnetic field is amplified as a whole through the LC resonance of the coupling amplification layer. Then, the dispersed magnetic flux is directionally squeezed and focused to the central receiving area by the Fano coherent interference effect between the magnetic field converging layer units. The high-sensitivity magnetic receiving antenna at the back end collects the focused and enhanced magnetic field signal. The spectrum analyzer and lock-in amplifier record the received signal strength, signal-to-noise ratio and output voltage change data, and compare the communication performance differences before and after the metasurface is added.

[0040] After adding this metasurface, the magnetic field amplification and focusing effects are significantly improved, the effective receiving range is extended from 40° to 80°, the signal power is increased by 19 dB, the output voltage signal is enhanced by more than 8 times, and the signal-to-noise ratio is greatly improved, enabling stable long-distance non-line-of-sight cross-medium communication, such as... Figure 5 As shown.

Claims

1. A multi-level coupled low-frequency magnetic field focusing metasurface based on Fano interferometry, characterized in that, It includes a coupling amplification layer, a magnetic field converging layer, and an intermediate dielectric layer; the distance between the coupling amplification layer and the magnetic field converging layer is kept fixed, and the two are insulated and separated by the intermediate dielectric layer.

2. The metasurface according to claim 1, characterized in that, The magnetic field converging layer includes a central resonant unit and peripheral resonant units; the array units are arranged in a planar periodic manner in a tightly fitted form to form a planar array. Both the central resonant unit and the peripheral resonant units adopt a multi-turn square coil structure, and their geometric dimensions remain consistent. The central resonant unit is connected in series with a first capacitor, and the peripheral resonant unit is connected in series with a second capacitor. The capacitance values ​​of the first capacitor and the second capacitor are different from each other. The resonant frequencies of the central resonant unit and the peripheral resonant units satisfy a preset ratio of 1:0.9 to achieve optimal Fano interference and unidirectional magnetic field focusing.

3. The metasurface according to claim 1, characterized in that, The coupling amplification layer includes a resonant coil and a third capacitor; The resonant coil and the third capacitor are connected in series and are disposed together above the dielectric substrate to form an LC resonant unit; The resonant coil is used to collect spatial magnetic flux, and the third capacitor is used to cooperate with the resonant coil to achieve resonance in the target frequency band. The resonant frequency of the coupling amplification layer is consistent with the resonant frequency of the central resonant unit of the magnetic field converging layer, so as to achieve coherent resonance of all units in phase.

4. The metasurface according to claim 1, characterized in that, The quality factors of the central resonant unit, the peripheral resonant unit, and the coupling amplification layer are matched to ensure that the structure has stable resonant characteristics and magnetic field control performance.

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