Electromagnetic band gap structure based on fractal self-similarity

Abstract

The invention discloses an electromagnetic band gap structure based on fractal self-similarity, and belongs to the technical field of electromagnetic metamaterial and microwave engineering. The electromagnetic band gap structure comprises a plurality of periodically arranged units, each unit is composed of a power supply layer, a dielectric layer and a grounding layer, the power supply layers of the units are connected through Z-shaped bridge lines, and an inductance value in a loop is provided; the power supply layer of each unit comprises an external square ring patch and an internal partial structure, and the external square ring patch and the internal partial structure provide equivalent capacitance of a loop; the inner square structure is connected with the outer square ring patch through a winding line; the power supply layer is tightly attached to the upper surface of the dielectric layer, and the grounding layer is tightly attached to the lower surface of the dielectric layer.

Description

Technical Field

[0001] The present invention relates to the fields of electromagnetic metamaterials and microwave engineering, specifically to a fractal electromagnetic bandgap (EBG) structure with a wide stopband, high suppression depth, and miniaturization for electromagnetic interference suppression in high-density integrated circuits. Specifically, it relates to an EBG structure based on fractal self-similarity. Background Art

[0002] With the continuous development of high-speed and high-density electronic systems, the high integration, miniaturization, high speed and high frequency of digital systems such as multi-layer printed circuit boards and integrated circuits have greatly improved the performance of the systems. However, electromagnetic interference (EMI) has become more prominent and gradually become a very challenging problem.

[0003] An electromagnetic bandgap (EBG) structure, as an artificial electromagnetic metamaterial, typically consists of a periodic arrangement of specific unit structures. It can block the propagation of electromagnetic waves within a specific frequency range and is widely used in antenna design, electromagnetic interference suppression, wireless communications, and radar systems. Common EBG structures include planar and mushroom-shaped. Planar EBGs are more widely used due to their simplicity, ease of fabrication, and wider bandwidth.

[0004] A planar EBG structure typically consists of a power layer, a dielectric layer, and a ground layer. The impedance of the periodic unit is nearly infinite at resonance, preventing electromagnetic waves from propagating near the resonant frequency. This creates a bandgap, which blocks electromagnetic waves within a specific frequency range. A variety of planar EBG structures exist, including the L-bridge EBG and Z-bridge EBG. However, as the noise frequency of high-speed digital systems increases, the limited stopband and suppression depth, as well as the large electrical dimensions, have become bottlenecks in the development of EBG structures. Summary of the Invention

[0005] The purpose of the present invention is to overcome the problems in the prior art and provide an electromagnetic bandgap structure based on fractal self-similarity, which can achieve miniaturization while ensuring a wide stopband and a high suppression depth.

[0006] The present invention provides an electromagnetic bandgap structure based on fractal self-similarity, comprising a plurality of periodically arranged units, each unit comprising a power supply layer, a dielectric layer and a ground layer, the power supply layers of the units being connected by a Z-shaped bridge line to provide an inductance value in a loop; the power supply layer of each unit comprising an external square ring patch and an internal fractal structure, the external square ring patch and the internal fractal structure providing an equivalent capacitance of the loop; the internal fractal structure and the external square ring patch being connected by a meandering line; the upper surface of the dielectric layer being closely attached to the power supply layer, and the lower surface being closely attached to the ground layer.

[0007] Preferably, the internal fractal structure is formed by setting a concave structure on each side of the square structure, the meandering line is located in each concave structure, and one end of the meandering line is connected to the bottom of the concave structure and the other end is connected to the inner wall of the external square ring patch.

[0008] Preferably, the concave structures have the same size and are symmetrically arranged in pairs.

[0009] Preferably, the width of the concave structure is 1 / 3 of the side length of the square structure, and the depth of the concave structure is 1 / 6 of the side length of the square structure.

[0010] Preferably, each outer side of the external square ring patch has an L-shaped hollow structure, so that each outer side of the external square ring patch forms an L-shaped bridge line, and the L-shaped bridge line has a first section and a second section connected to each other. The first sections of the L-shaped bridge lines of two adjacent external square ring patches are parallel and spliced, and the second sections are set in reverse to form a Z-shaped bridge line for connecting the external square ring patches of adjacent units.

[0011] Preferably, the width of the first segment is smaller than the width of the second segment, and the sum of the widths of the two first segments after being spliced together is equal to the width of the second segment.

[0012] Preferably, the width of the first segment is 1 / 2 of the width of the second segment.

[0013] Preferably, the outer annular patch structure, the inner fractal patch structure and the meandering line structure are all copper clad laminates.

[0014] Preferably, the outer annular patch structure, the inner fractal patch structure and the meandering line structure are provided with a gold plating layer.

[0015] Preferably, the power layer and the ground layer are both copper-clad layers with a thickness of 1 ounce, and the dielectric layer adopts a dielectric constant of FR4 as the substrate.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The present invention proposes a fractal self-similar EBG structure, in which each unit of the power plane consists of an internal fractal patch, an external annular patch, and a meandering wire structure connecting the internal and external fractal patches. The internal patch of the present invention utilizes a fractal structure, which, due to its self-similarity, can generate multiple resonance points. The overlapping of these points can widen the stopband range. Adjacent external annular patches of the present invention are connected by Z-shaped bridge wires, which can increase the equivalent inductance of the loop, thereby reducing the resonant frequency. The internal and external fractal patches are connected by meandering wires. The repeated bending design significantly extends the current path of the metal conductor, thereby increasing the equivalent inductance and enabling the EBG structure to achieve a low-frequency stopband. The fractal structure iterates to produce repetitive, similar patterns at multiple scales. Electromagnetic waves undergo multiple reflections, refractions, and scattering within the structure, consuming some of their energy. The self-similarity of the fractal structure generates multiple resonance points, each corresponding to energy loss at a different frequency, forming a superimposed suppression band gap, achieving deep suppression. The meandering wires also extend the propagation distance of electromagnetic waves through their curved paths, causing them to experience a greater phase delay within the structure, thus achieving deep suppression.

[0017] The EBG structure of the present invention can achieve an ultra-wide bandgap of 19.71 GHz with a suppression depth of -40 dB as the standard. The internal patch of the EBG structure of the present invention adopts a fractal structure, which makes the lower cutoff frequency of the EBG structure reach 0.29 GHz. Taking this lower cutoff frequency as the standard, the electrical size of the present invention is 0.029 L , ensuring wide stopband and high suppression depth while achieving miniaturization. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a three-dimensional arrangement schematic diagram of the present invention.

[0019] Figure 2 It is a schematic diagram of the power supply layer structure of the present invention.

[0020] Figure 3 It is a schematic diagram of the power layer unit structure of the present invention.

[0021] Figure 4 It is a schematic structural diagram of the external square ring patch of the power layer unit of the present invention.

[0022] Figure 5 It is a schematic diagram of the fractal patch inside the power layer unit of the present invention.

[0023] Figure 6 It is a schematic diagram of the meandering line structure of the power layer unit of the present invention.

[0024] Figure 7 This is a schematic diagram of the dimensions of the external square ring patch structure of the power layer unit of the present invention.

[0025] Figure 8 Schematic diagram of the structure and dimensions of the embedded unit in the power layer unit of the present invention.

[0026] Figure 9 It is the insertion loss S21 band-stop characteristic curve of the present invention.

[0027] Description of reference numerals: 1. External ring patch, 2. Internal fractal patch, 3. Meandering line. DETAILED DESCRIPTION

[0028] To make the purpose, technical solutions, and advantages of the embodiments of the present disclosure more clear, the technical solutions of the embodiments of the present disclosure will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present disclosure. Obviously, the described embodiments are part of the embodiments of the present disclosure, not all of the embodiments. Based on the described embodiments of the present disclosure, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present disclosure.

[0029] Unless otherwise defined, the technical or scientific terms used herein shall have the ordinary meaning understood by persons of ordinary skill in the field to which the present disclosure pertains. The terms "first", "second" and similar words used in the present disclosure do not indicate any order, quantity or importance, but are merely used to distinguish different components. The terms "include" or "comprise" and similar words mean that the elements or objects appearing before "include" or "comprise" encompass the elements or objects listed after "include" or "comprise" and their equivalents, and do not exclude other elements or objects. The terms "connect" or "connected" and similar words are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. The terms "upper", "lower", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the object being described changes, the relative positional relationship may also change accordingly.

[0030] Due to their fractal geometry, fractal structures offer high flexibility in structural design and can be combined with other structures to achieve better tuning of equivalent inductance and capacitance characteristics. Fractal patterns formed by varying numbers of iterations are used to construct novel EBG structures. These structures, etched across the entire power plane of a power / ground plane pair, suppress synchronous switching noise in high-speed circuits. The challenge in designing a fractal self-similar EBG structure lies in achieving a wide stopband and high suppression depth while also miniaturizing it.

[0031] This embodiment provides an electromagnetic bandgap (EBG) structure based on fractal self-similarity, comprising several periodically arranged units. Each unit consists of a power layer, a dielectric layer, and a ground layer. The power layers of each unit are connected by Z-shaped bridge wires, providing the inductance of the loop. The power layer of each unit includes an outer square ring patch and an inner fractal structure, which together provide the equivalent capacitance of the loop. The inner fractal structure and the outer square ring patch are connected by a meandering wire 3. The upper surface of the dielectric layer is closely attached to the power layer, and the lower surface is closely attached to the ground layer. Each unit of the EBG structure proposed in this embodiment consists of three parts: the power layer, the dielectric layer, and the ground layer. This embodiment uses fractal bends and meandering wire 3 to extend the current path, significantly increasing the equivalent inductance and shifting the resonant frequency toward lower frequencies, thus breaking through the size limitations of traditional EBGs. In this embodiment, a meandering line structure is embedded in the central area of the Z-shaped bridge, and the internal patch adopts a fractal structure to form a composite resonant unit. Multi-stage resonance superposition achieves ultra-wideband coverage and high suppression depth. By adjusting the geometric parameters, the equivalent inductance is increased, the low-frequency resonant frequency is reduced, and the lower cutoff frequency is made lower.

[0032] In a preferred embodiment, the internal fractal structure is formed by providing a concave structure on each side of the square structure. The meander line 3 is located within each concave structure, with one end of the meander line 3 connected to the bottom of the concave structure and the other end connected to the inner wall of the external square ring patch. In the structure proposed in this embodiment, the internal fractal patch 2 follows fractal principles, ensuring the self-similarity of the structure.

[0033] The concave structure of this embodiment adjusts the equivalent capacitance of the internal patch by modifying the original square structure. This increases the surface area of the internal fractal patch 2, thereby increasing capacitance. This lowers the resonant center frequency, shifts the stopband toward lower frequencies, and reduces the lower cutoff frequency. The self-similarity of the fractal structure of this invention allows it to contain substructures of varying scales within the same structure, each corresponding to a different resonant frequency. Multiple resonant points can extend the EBG stopband range through a superposition effect.

[0034] As a preferred embodiment, the concave structures in this embodiment are of the same size and are symmetrically arranged in pairs. Since the direction of noise propagation is uncertain, the symmetrical concave structures in this embodiment can provide the same high impedance characteristics in multiple directions, achieving all-round noise suppression.

[0035] As a preferred embodiment, the width of the concave structure is 1 / 3 of the side length of the square structure, and the depth of the concave structure is 1 / 6 of the side length of the square structure. The size of the concave structure defined in this embodiment can increase the equivalent capacitance of the internal patch and thus affect the electromagnetic properties of the structure.

[0036] As a preferred embodiment, each outer side of the external square ring patch has an L-shaped hollow structure, so that each outer side of the external square ring patch forms an L-shaped bridge line, and the L-shaped bridge line has a first section and a second section connected to each other. The first sections of the L-shaped bridge lines of two adjacent external square ring patches are parallel and spliced, and the second sections are set in reverse to form a Z-shaped bridge line for connecting the external square ring patches of adjacent units.

[0037] As a preferred embodiment, the width of the first segment is smaller than the width of the second segment, and the sum of the widths of the two first segments after being spliced together is equal to the width of the second segment.

[0038] As a preferred embodiment, the width of the first segment is 1 / 2 of the width of the second segment.

[0039] In this embodiment, the units are connected by bridge lines to increase the equivalent inductance and reduce the resonant frequency. In this embodiment, the equivalent inductance is increased by optimizing the width of the bridge lines.

[0040] This embodiment achieves a frequency bandgap in the 0.29-20 GHz range, using a -40 dB suppression depth as the standard. The internal patches of the EBG structure in this embodiment utilize a fractal structure, achieving a lower cutoff frequency of 0.29 GHz. Based on this lower cutoff frequency, the electrical dimensions of this embodiment are 0.029L, ensuring a wide stopband and high suppression depth while achieving miniaturization.

[0041] The present invention is further described in detail below with reference to the accompanying drawings and specific examples.

[0042] The electromagnetic bandgap structure based on fractal self-similarity provided in this embodiment is as follows: Figure 1 As shown, it includes three parts: power layer, dielectric layer and ground layer. The power layer is composed of a specific metal structure, such as Figure 2 As shown, each unit consists of an outer ring patch 1 with a metal structure, an inner fractal patch 2, and a meandering line 3. Both the power and ground layers are metal layers, each clad in 1-ounce copper. 1-ounce copper foil weighs 28.35 grams uniformly over 1 square foot, representing the average thickness of the copper foil using weight per unit area.

[0043] The dielectric layer of this embodiment adopts a dielectric constant FR4 as substrate; Figure 1 It can be seen that the upper surface of the dielectric layer is closely attached to the power layer etched with a specific metal pattern, and the lower surface is closely attached to the ground layer.

[0044] In this embodiment, the three-dimensional coordinates of the electromagnetic band gap structure based on fractal self-similarity are set as follows: Figure 1 As shown, the input port uses a 50-ohm standard coaxial cable to connect to an external antenna horn to generate a far-field excitation plane wave, and both input port 1 and input port 2 are set on the ground layer.

[0045] Example 1 This embodiment designs a 3×3 array EBG structure with a size of 90mm×90mm×0.2mm. The dielectric layer uses FR4 dielectric material, which has a loss tangent of 0.02 and a dielectric constant of 4.4. The metal layer uses copper foil with a thickness of 0.035mm and a conductivity of 5.8E+0.07S / m. The coordinate axis is set as follows Figure 1 As shown, the origin of the coordinate axis is located at the center of the ground layer, input port 1 is set at 30 mm away from the origin along the negative direction of the x and y axes, and input port 2 is set at the origin of the coordinate axis.

[0046] The power layer structure in this example is as follows Figure 2 As shown in the figure, its material is copper and its size is 90mm×90mm×1oz (0.035mm). The structure of each unit of the power layer is as follows Figure 3 As shown, each unit of the power layer includes an outer ring patch 1, an inner fractal patch 2, and a meandering line 3 for connecting the outer ring patch 1 and the inner fractal patch 2. Figure 4 The structure of the outer ring patch 1 is shown. Figure 5 The structure of the internal fractal patch 2 is shown. Figure 6 The structure of the meander line 3 is illustrated.

[0047] In this example, the dielectric layer is square in shape, made of FR4, has a dielectric constant of 4.4, and has a size of 90 mm×90 mm×0.2 mm.

[0048] When designing the EBG structure of this embodiment, the above-mentioned specific parameters such as diameter, width, and side length are finely optimized. In this embodiment, the above-mentioned multiple parameters work together to improve the stopband performance of the EBG structure of this embodiment.

[0049] For the meander line structure, The narrower the line width, the greater the equivalent inductance L of the current path. However, too narrow a line width (e.g., <0.1 mm) will increase conductor loss and reduce the suppression depth. Therefore, this embodiment optimizes the width of the meandering line, the spacing between adjacent horizontal segments, and the gap with the concave structure.

[0050] At the same time, too small a distance between adjacent patches can cause short circuits or parasitic coupling. A larger side length increases the equivalent capacitance C between the patch and ground. However, a side length that is too large takes up more space, hindering miniaturization. Therefore, this embodiment also optimizes the side length of the patch.

[0051] Specifically, the metal structure size of the EBG structure power layer in this embodiment is as follows: Figure 7 and Figure 8 As shown. Among them, =30mm, =14mm, =12mm, 1=0.1mm, 2=0.2mm, 1=0.2mm, 2=0.2mm, 1=14.5mm, 3=0.2mm, 3=0.2mm, 4 = 0.2 mm. Therefore, the size of each unit is 30 mm × 30 mm. The basic composition of each unit is the same, including the power layer, dielectric layer and ground layer. The power layer includes the outer square ring patch 1, the inner fractal patch 2 and four meandering lines 3 for connecting the square ring patch 1 and the inner fractal patch 2. Among them, the side length of the EBG unit structure of the power layer is , the inner diameter of the outer square ring patch 1 is , the width of the bridge line connecting the outer square ring patch 1 and the adjacent unit structure is 1. The width of the Z-type bridge line is 2. The side length of the internal fractal patch is d, and the width of the meander line is 3.

[0052] The outer annular patch 1, the inner fractal patch 2 and the meandering line 3 in this embodiment are all made of copper clad plates, which can be prepared by a printed circuit board process, and a chemical corrosion method or an etching method is used to prepare a copper clad plate on a dielectric layer substrate. Figure 2 The FSR structure shown in the figure. The copper-clad laminate material can be selected based on the application environment. To protect the metal surface, the metal pattern can be gold-plated. Depending on the application environment, the prepared EBG structure can be further protected against environmental hazards. For example, chemical vapor deposition (CVD) can be used to grow a dielectric protective film to protect against water and acid, alkali, and salt spray environments.

[0053] The insertion loss S21 curve of the EBG structure of this embodiment is as follows: Figure 9 Insertion loss S21 refers to the signal size measured from input port 2 when the stimulus is input from input port 1. Figure 9 Taking the suppression depth of -40dB as the standard, the stopband range provided by the EBG structure is 0.29GHz-20GHz, indicating that the structure can effectively suppress electromagnetic interference in high-density integrated system packaging circuits.

[0054] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. An electromagnetic band gap structure based on fractal self-similarity, characterized in that: The invention comprises a plurality of periodically arranged units, each of which is composed of a power supply layer, a dielectric layer and a ground layer. The power supply layers of the units are connected by a Z-shaped bridge line to provide the inductance value in the loop. The power supply layer of each unit includes an external square ring patch and an internal fractal structure, which provide the equivalent capacitance of the loop. The internal fractal structure and the external square ring patch are connected by a meandering line. The upper surface of the dielectric layer is closely attached to the power supply layer, and the lower surface is closely attached to the ground layer.

2. The electromagnetic band gap structure based on fractal self-similarity according to claim 1, wherein: The internal fractal structure is formed by setting a concave structure on each side of the square structure. The meandering line is located in each concave structure, and one end of the meandering line is connected to the bottom of the concave structure and the other end is connected to the inner wall of the external square ring patch.

3. The electromagnetic band gap structure based on fractal self-similarity according to claim 2, wherein: The concave structures have the same size and are symmetrically arranged in pairs.

4. The electromagnetic band gap structure based on fractal self-similarity according to claim 2, wherein: The width of the concave structure is 1 / 3 of the side length of the square structure, and the depth of the concave structure is 1 / 6 of the side length of the square structure.

5. The electromagnetic band gap structure based on fractal self-similarity according to claim 1, wherein: Each outer side of the external square ring patch has an L-shaped hollow structure, so that each outer side of the external square ring patch forms an L-shaped bridge line. The L-shaped bridge line has a first section and a second section connected to each other. The first sections of the L-shaped bridge lines of two adjacent external square ring patches are parallel and spliced, and the second sections are set in reverse to form a Z-shaped bridge line for connecting the external square ring patches of adjacent units.

6. The electromagnetic band gap structure based on fractal self-similarity according to claim 5, characterized in that: The width of the first segment is smaller than the width of the second segment, and the sum of the widths of the two spliced first segments is equal to the width of the second segment.

7. The electromagnetic band gap structure based on fractal self-similarity according to claim 5, wherein: The width of the first segment is 1 / 2 of the width of the second segment.

8. The electromagnetic band gap structure based on fractal self-similarity according to claim 1, wherein: The external annular patch structure, the internal fractal patch structure and the meandering line structure are all copper-clad laminates.

9. The electromagnetic band gap structure based on fractal self-similarity according to claim 1, wherein: The outer ring patch structure, the inner fractal patch structure and the meandering line structure all have a gold plating layer.

10. The electromagnetic band gap structure based on fractal self-similarity according to claim 1, wherein: The power layer and the ground layer are both copper-clad layers with a thickness of 1 ounce. The dielectric layer uses a dielectric constant of FR4 as the substrate.

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