Multi-band radio frequency energy collector

Abstract

The invention belongs to the technical field of radio frequency energy collection, and particularly discloses a multi-band radio frequency energy collector which comprises an antenna structure and an EBG metasurface structure. The antenna structure comprises a metal patch layer, an antenna dielectric layer and an isolation layer, and the isolation layer is connected with the EBG metasurface structure; the metal patch layer comprises a short-arm fan-shaped branch knot, a long-arm fan-shaped branch knot and a double-line micro-strip feeder line, the length of the short-arm fan-shaped branch knot is smaller than that of the long-arm fan-shaped branch knot, and the fan-shaped circle center positions of the short-arm fan-shaped branch knot and the long-arm fan-shaped branch knot are connected with the double-line micro-strip feeder line. By arranging the antenna structure and the EBG metasurface structure, radio frequency energy can be collected in a plurality of common frequency bands, the array design improves the gain of the antenna, enhances the signal receiving capability, expands the effective collection range of the radio frequency energy collector, and is suitable for an application scene farther from a radio frequency signal source. The overall structural design is highly integrated, the structure is compact, and the device is suitable for wearable equipment.

Description

Technical Field

[0001] The present invention relates to the field of radio frequency energy harvesting technology, and in particular to a multi-band radio frequency energy harvester suitable for wearable devices, and more specifically to a multi-band radio frequency energy harvester based on an asymmetric dipole antenna and an electromagnetic band gap (EBG) metasurface. Background Art

[0002] With the development of wearable devices, on the one hand, it is necessary to select suitable materials for wearable devices. Environmentally friendly, flexible and durable materials can maximize the sustainability and comfort of wearable devices. On the other hand, how to provide energy for wearable devices has become a key issue that needs to be solved in wearable systems. Currently, the most common solution for powering wearable devices is still batteries, but the frequent replacement of batteries has increased our demand for energy-independent electronic devices. Energy harvesting technology can help us eliminate batteries from IoT devices or solve the problem of frequent battery replacement to achieve self-powered, which not only reduces the cost of batteries but is also more environmentally friendly.

[0003] In order to solve the energy problem of wearable devices, the current methods of obtaining energy from the external environment mainly include solar energy, wind energy, mechanical vibration, and radio frequency energy (such as WiFi signals, mobile communication signals, etc.). Among them, solar energy is greatly affected by the outdoor and indoor environment, and the collection of wind energy and mechanical energy is not stable enough. On the one hand, radio frequency energy is not restricted by weather, geographical location and time, and is widely present in indoor and outdoor environments. The surrounding mobile terminals, base stations and routers can all be used as radio frequency energy sources. On the other hand, radio frequency energy has higher stability and can be supplied continuously and stably. As long as the wireless communication equipment is in normal working condition, it will continue to transmit radio frequency signals, and the radio frequency energy collection system can continuously and stably collect energy, so the research on the collection of radio frequency energy has received widespread attention.

[0004] In the process of RF energy harvesting, there are two important factors that affect the efficiency of energy harvesting. On the one hand, because the input impedance of the traditional antenna is 50 ohms, and the impedance of the rectifier circuit is relatively high, an impedance matching network is required to match the rectifier circuit. The input impedance of the rectifier circuit will vary with many factors. It is difficult to design an impedance matching network containing nonlinear devices in broadband and multi-band devices, which directly affects the rectification efficiency. However, there are also some new research directions, such as eliminating the impedance matching network. For the higher input impedance of the rectifier, the circuit complexity can be greatly simplified by designing a direct conjugate matching method between the antenna and the rectifier circuit. For example, a non-center-fed dipole antenna can present a high input impedance and can be conjugate matched with the input impedance of the rectifier circuit. At the same time, the asymmetric dipole antenna has a simple structure and is easy to adjust. The antenna design process can be simplified using commercial electromagnetic simulation software. On the other hand, in addition to reducing mismatch losses, the use of antenna arrays and multi-polarized antennas is necessary to expand the receiving area and enhance energy capture. Antenna arrays can generate high gain, improve antenna sensitivity, and enable RF systems to operate at lower input power levels. Existing technologies still have some deficiencies in terms of energy harvesting efficiency, gain, compactness, and safety of RF energy harvesting for wearable devices.

[0005] It should be noted that the information disclosed in the above background technology section is only used to enhance the understanding of the background of the present invention, and therefore may include information that does not constitute the prior art known to ordinary technicians in the field. Summary of the invention

[0006] The purpose of the present invention is to solve the technical problems existing in the background technology. To this end, a multi-band RF energy collector suitable for wearable devices is provided, wherein the final working frequency band includes multiple commonly used WiFi or ISM bands, and can collect RF energy of electromagnetic waves in different polarization directions. The array antenna composed has the characteristics of high gain, which helps to improve the efficiency of wearable devices in RF energy collection. At the same time, the design has a higher RF resource utilization rate per unit area, which can well meet the needs of human wireless sensor networks for RF self-powering.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] A multi-band radio frequency energy harvester, comprising an antenna structure and an EBG metasurface structure;

[0009] The antenna structure comprises a metal patch layer, an antenna dielectric layer and an isolation layer connected in sequence from top to bottom, and the isolation layer is connected to the EBG metasurface structure;

[0010] The metal patch layer includes a short-arm fan-shaped branch, a long-arm fan-shaped branch and a two-line microstrip feeder. The length of the short-arm fan-shaped branch is shorter than that of the long-arm fan-shaped branch. The center position of the fan-shaped circle of the short-arm fan-shaped branch is connected to the two-line microstrip feeder, and the center position of the fan-shaped circle of the long-arm fan-shaped branch is connected to the two-line microstrip feeder.

[0011] The following is a technical solution further defined by the present invention, wherein there are two double-wire microstrip feeders, each of which is connected to a short-arm fan-shaped branch and a long-arm fan-shaped branch, and the short-arm fan-shaped branch (101a) and the long-arm fan-shaped branch (101b) connected to the same double-wire microstrip feeder (101c) are orthogonal to each other.

[0012] The following is a technical solution further defined by the present invention, in which the curvature of the short-arm fan-shaped branch and the long-arm fan-shaped branch are both 30°.

[0013] The following is a technical solution further defined in the present invention: the EBG supersurface structure is composed of a plurality of EBG units, and the plurality of EBG units are distributed in an array and connected to each other.

[0014] The following is a technical solution further defined in the present invention, wherein the EBG unit comprises an EBG dielectric layer and a double-ring EBG, and the double-ring EBG is arranged at the center of the EBG dielectric layer.

[0015] The following is a technical solution further defined by the present invention: a plurality of antenna structures are connected to the EBG super-surface structure, and a spacing is provided between the antenna structures.

[0016] The following is a technical solution further defined by the present invention, wherein a plurality of antenna structure arrays are distributed on the EBG metasurface structure.

[0017] The following is a technical solution further defined in the present invention, wherein each of the antenna structures is located at the center of a structure composed of 9 EBG units in a 3×3 array.

[0018] The following is a technical solution further defined by the present invention, which also includes a rectifier circuit structure, and the rectifier circuit structure is electrically connected to the two-wire microstrip feeder.

[0019] The following is a technical solution further defined in the present invention: the metal patch layer (101) is made of a flexible conductive cloth with a conductivity of 8×105 S / m, the antenna dielectric layer (102) and the EBG dielectric layer (201a) are both made of a felt material with a dielectric constant of 1.2 and a dielectric loss of 0.005, and the isolation layer (103) is made of a foam material with a dielectric constant equal to that of air.

[0020] Compared with the prior art, the present invention has the following technical effects:

[0021] The present invention can collect radio frequency energy in multiple commonly used frequency bands (2.4GHz, 5.2GHz, 5.8GHz) by setting up an antenna structure and an EBG metasurface structure. The array design improves the gain of the antenna, enhances the signal receiving capability, and expands the effective collection range of the radio frequency energy collector, which is suitable for application scenarios farther away from the radio frequency signal source. At the same time, the overall structural design of the present invention is highly integrated and compact. The selected conductive cloth and felt materials have the characteristics of good flexibility, light material, low production cost, and low manufacturing complexity. Both the material and design are suitable for the application of wearable devices and have practical application value.

[0022] The present invention is further described below in conjunction with the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0024] Figure 1 It is a three-dimensional structural schematic diagram of the present invention;

[0025] Figure 2 It is a schematic diagram of the top view of the structure of the present invention;

[0026] Figure 3 is a schematic diagram of the structure of the antenna structure in the present invention, wherein: Figure 3 (a) is a schematic diagram of the three-dimensional structure of the antenna. Figure 3 (b) is a schematic diagram of the top view of the antenna structure;

[0027] Figure 4 : is a schematic diagram of the structure of an EBG unit of the EBG super surface structure in the present invention, wherein: Figure 4 (a) is a schematic diagram of the three-dimensional structure of the EBG unit. Figure 4 (b) is a schematic diagram of the top view of the EBG unit;

[0028] Figure 5 It is a connection relationship diagram of the rectifier circuit structure in the present invention;

[0029] Figure 6 is a comparison diagram of the input impedance and S11 parameter results of the antenna structure in the present invention;

[0030] Figure 7 It is a comparison chart of actual gain results of the antenna structure array in the present invention distributed on different reflection surfaces.

[0031] Figure numerals: 1, antenna structure; 101, metal patch layer; 101a, short arm fan-shaped branch; 101b, long arm fan-shaped branch; 101c, two-wire microstrip feeder; 102, antenna dielectric layer; 103, isolation layer; 2, EBG supersurface structure; 201, EBG unit; 201a, EBG dielectric layer; 201b, double-ring EBG. DETAILED DESCRIPTION

[0032] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention, so the present invention is not limited by the specific embodiments disclosed below.

[0033] In the description of the present invention, it is necessary to understand that the terms "up", "down", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0034] In the description of the present invention, “plurality” means at least two, for example, two, three, etc., unless otherwise clearly and specifically defined.

[0035] In the embodiments of the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the embodiments of the present invention can be understood according to specific circumstances.

[0036] like Figure 1-5 As shown, this embodiment provides a multi-band RF energy harvester based on an asymmetric dipole antenna and an electromagnetic band gap (EBG) metasurface, which mainly includes an antenna structure 1 composed of four asymmetric dipoles, an EBG metasurface structure 2 that acts as a reflector and is composed of a 5×5 EBG unit array, and a rectifier circuit structure.

[0037] like Figure 3As shown, the antenna structure 1 includes an upper metal patch layer 101, a middle antenna dielectric layer 102 and a bottom isolation layer 103. The metal patch layer 101, the antenna dielectric layer 102 and the isolation layer 103 are fixedly connected in turn.

[0038] The metal patch layer 101 is made of a flexible conductive cloth with a conductivity of 8×105S / m; the antenna dielectric layer 102 and the EBG dielectric layer 201a are both made of a felt material with a dielectric constant of 1.2 and a dielectric loss of 0.005, which has low dielectric loss and helps reduce the loss of electromagnetic energy during propagation; the isolation layer 103 fixedly connected to the EBG metasurface structure 2 is made of a foam material with the same dielectric constant as air, which can act as an air layer. The selected conductive cloth and felt materials have the advantages of good flexibility, light material, easy processing and low cost.

[0039] The metal patch layer 101 is used to receive electromagnetic waves and is composed of 4 asymmetric dipoles, mainly including 2 short-arm fan-shaped branches 101a, 2 long-arm fan-shaped branches 101b and 2 double-line microstrip feed lines 101c. Among them, the arc of the short-arm fan-shaped branches 101a and the long-arm fan-shaped branches 101b are both 30°; the length R1 of the short-arm fan-shaped branches 101a is 10mm; the length R2 of the long-arm fan-shaped branches 101b is 30mm, and the specific size is obtained by adjusting the asymmetry of the dipoles working at 2.4GHz and with a total length of 40mm. The double-line microstrip feed line 101c is a coplanar strip transmission line with a length L1=12mm, a width L2=2mm, and a double-line spacing of 1mm. The strip structure design of the double-line microstrip feed line 101c and the spacing design are convenient for welding circuit components, and the length L1 of the double-line microstrip feed line 101c can adjust the high-frequency impedance. The center of the fan-shaped circle of the short arm fan-shaped branch 101a is fixedly connected to the two-wire microstrip feeder 101c, and the center of the fan-shaped circle of the long arm fan-shaped branch 101b is fixedly connected to the two-wire microstrip feeder 101c. Furthermore, the two pairs of dipole arms are orthogonal to each other (that is, the short arm fan-shaped branch 101a and the long arm fan-shaped branch 101b connected to the same two-wire microstrip feeder 101c are orthogonal to each other), and the cross-polarized dipole structure can better collect the energy of electromagnetic waves with different polarization directions. Figure 6 , which are the input impedance and S11 parameter images of the antenna structure. The results show that within a wide frequency band of the target frequency band, the impedance of the antenna is close to 250 ohms required by the rectifier circuit, thereby achieving conjugate matching with the rectifier circuit.

[0040] The antenna dielectric layer 102 in the middle is the supporting structure of the antenna structure 1. It is 60 mm × 50 mm in size and serves to provide a medium for electromagnetic wave transmission. The thickness of the antenna dielectric layer 102 is h1 = 2 mm. The isolation layer 103 at the bottom uses a foam board, which is the same size as the antenna dielectric layer 102 above it. The thickness of the isolation layer 103 is h2 = 10 mm. The antenna structure 1 and the EBG metasurface structure 2 are fixedly connected by the foam board (isolation layer 103) to reduce the influence of metal coupling on the input impedance of the dipole antenna.

[0041] like Figure 4 As shown, the EBG metasurface structure 2 is composed of 25 EBG units 201 in a 5×5 array and the EBG units 201 are fixedly connected. The size of a single EBG unit 201 is 40mm×40mm. The EBG unit 201 includes an EBG dielectric layer 201a and a double-ring EBG 201b. The double-ring EBG 201b is arranged at the center of the EBG dielectric layer 201a. The inner radius r1 of the double-ring EBG 201b is 8mm, and the outer radius r2 is 15mm. The incident waves in the frequency band of 2.4GHz and 5.2GHz-5.8GHz of the antenna can be well reflected, thereby improving the gain of the antenna. The thickness h3 of the EBG dielectric layer 201a is 3mm.

[0042] like Figure 1 and 2 As shown, 4 antenna structures 1 are fixedly connected to the EBG metasurface structure 2 composed of 25 EBG units 201 in a 5×5 array, and each antenna structure 1 is located at the center of the structure composed of 9 EBG units 201 in a 3×3 array. The antenna structures 1 are provided with a spacing g1 of about 10-20 mm.

[0043] like Figure 7 As shown, the actual gain results of the antenna structure 1 array distributed under different reflection surfaces are: compared with the metal surface, the array composed of EBG units 201 can obtain higher gain in the target frequency band, and each antenna structure 1 is located at the center of the structure composed of 9 EBG units 201 in a 3×3 array. There is a spacing g1 of about 10-20mm between the antenna structures 1. According to research, this can maximize the gain of the antenna array while keeping the structure compact. At the same time, the simulation of the antenna array near the human body using CST shows that the flexible antenna array is also applicable to the human body. The EBG metasurface structure 2 reflects or attenuates the electromagnetic field within the electromagnetic band gap frequency range through its own periodic structure, which not only improves the gain of the antenna array, but also plays a good isolation role, avoiding the influence of complex human body media on the antenna impedance and resonant frequency. Finally, as shown in Figure 7As shown, in the three frequency bands of 2.45 GHz, 5.2 GHz and 5.8 GHz, the array antenna can achieve maximum gains of 13.7 dBi, 14.5 dBi and 13 dBi on the human body respectively.

[0044] like Figure 5 As shown, the rectifier circuit structure includes a diode D, an inductor L, and a capacitor C. The two ends of the diode D are respectively connected to the tails of the two two-wire microstrip feeders 101c (the short arm fan-shaped branch 101a is connected to the head of the two-wire microstrip feeder 101c), and the RF signal is converted into a single pulse voltage through the Schottky diode D. This pulsating DC signal still contains a large ripple component. The inductor L and the capacitor C are connected in series to form an LC filter circuit and are connected to the two ends of the diode D. The capacitor C uses its charging and discharging characteristics to smooth the pulsating DC. The inductor L can prevent the AC ripple current, that is, the high-frequency harmonics from passing through, so that only the DC current can pass through the circuit smoothly to reach the load, further improving the filtering effect; finally, the two ends of the resistor R (i.e., the load) are connected to the two ends of the capacitor C. Among them, the SMS7630079LF diode D has good high-frequency characteristics and has a low conduction voltage drop, which is suitable for the RF energy collection application of the present invention. Other diode D models such as HSMS2850 and HSMS2860 can also harvest better RF energy through appropriate selection. The rectifier circuit structure is integrated at the tail of the transmission line of the antenna structure 1 .

[0045] In order to eliminate the impedance matching circuit and generate a high input impedance that can be conjugate matched with the rectifier (i.e., the rectifier circuit structure), the antenna structure 1 adopts a fan-shaped structured dipole. The fan-shaped structured dipole has a wider frequency band and better directivity than an ordinary dipole and has a compact structure. When the total length remains unchanged, the input impedance of the antenna at a certain frequency point can be changed by changing the asymmetry of the dipole antenna (i.e., the short arm fan-shaped branch 101a and the long arm fan-shaped branch 101b). The short arm fan-shaped branch 101a of the dipole antenna is located at the top, and the long arm fan-shaped branch 101b is used in the part close to the transmission line (i.e., the two-wire microstrip feeder 101c), which helps to solve the problem of excessively high impedance at the relevant resonant frequency point. At the same time, the length of the transmission line is changed to an appropriate position to fine-tune the high-frequency impedance. In the simulation optimization, by adjusting the short arm fan-shaped branch 101a, the impedance of the high frequency point can be adjusted. 1a and the arm length of the long-arm fan-shaped branch 101b, the length of the transmission line, etc., adjust the input impedance of the antenna to a high impedance value within the desired frequency band, so as to conjugate match it with the input impedance of the rectifier circuit. The cross-orthogonal arrangement of the two pairs of dipole arms also improves the antenna's efficiency in collecting electromagnetic energy of different polarizations. Finally, the rectifier circuit is designed directly at the tail of the transmission line, eliminating the traditional impedance matching network, realizing direct conjugate matching of the antenna and the rectifier, and converting the RF signal into a DC signal, thereby forming a complete wearable RF energy harvester and improving energy transmission efficiency.

[0046] The structural design of the EBG metasurface structure 2 is to solve the omnidirectional problem of the dipole antenna. The EBG can reflect part of the energy originally radiated in other directions (such as backward radiation) back to the forward direction. At the same time, it can also reduce the sidelobe radiation, gather more energy in the main lobe direction, and improve the gain of the antenna. After exploration, it was found that the dual-ring structure EBG can be well combined with the multi-band dipole antenna to increase the directivity of the antenna. By adjusting the radius of the dual ring and the size of the EBG dielectric layer 201a, the gain of a single antenna in the working frequency band can be significantly improved by 4-5dBi. And looking for the appropriate arrangement of the combination into an array, it was found that the 2×2 antenna array on the 5×5 EBG metasurface can achieve high gain while maintaining a compact structure, greatly improving the efficiency of RF energy collection and improving the receiving capability of the RF system.

[0047] Therefore, the product of the present invention can effectively collect and rectify radio frequency energy in multiple frequency bands (2.4GHz, 5.2GHz, 5.8GHz), covering the commonly used WiFi or ISM bands; on the one hand, the array arm of the cross-polarization design can receive radio frequency energy in more dimensions, and on the other hand, the high-gain array design can also expand the effective collection range of the radio frequency energy collector; the impedance-free matching design is adopted, and rectification is performed directly on the transmission line of the antenna, eliminating the need for additional space for circuit design. The size of the entire radio frequency collection system is 1.6λ (2.4GHz wavelength), which has the advantage of compact structure compared to other array structures used for radio frequency energy collection; the felt and conductive fabric materials used have the advantages of good flexibility and light material. In wearable devices, as the human body moves, the flexibility of the material can ensure that the antenna and EBG structure maintain stable performance and will not be damaged or affect the function due to bending, and are suitable for human wear.

[0048] The above is only a preferred embodiment of the present invention, and does not limit the present invention in any form. Any technician familiar with the art can make many possible changes and modifications to the technical solution of the present invention by using the above disclosed methods and technical contents without departing from the scope of the technical solution of the present invention, or modify it into an equivalent embodiment of equivalent changes. Therefore, all equivalent changes made according to the shape, structure and principle of the present invention without departing from the content of the technical solution of the present invention should be included in the protection scope of the present invention.

Claims

1. A multi-band radio frequency energy harvester, characterized in that: It includes an antenna structure (1) and an EBG metasurface structure (2); The antenna structure (1) comprises a metal patch layer (101), an antenna dielectric layer (102) and an isolation layer (103) which are connected in sequence from top to bottom, and the isolation layer (103) is connected to the EBG super surface structure (2); The metal patch layer (101) comprises a short arm fan-shaped branch (101a), a long arm fan-shaped branch (101b) and a two-line microstrip feeder (101c); the length of the short arm fan-shaped branch (101a) is shorter than the length of the long arm fan-shaped branch (101b); the center position of the fan-shaped circle of the short arm fan-shaped branch (101a) is connected to the two-line microstrip feeder (101c); and the center position of the fan-shaped circle of the long arm fan-shaped branch (101b) is connected to the two-line microstrip feeder (101c).

2. A multi-band radio frequency energy harvester as claimed in claim 1, characterized in that: There are two double-line microstrip feed lines (101c), each of which is connected to a short-arm fan-shaped branch (101a) and a long-arm fan-shaped branch (101b), and the short-arm fan-shaped branch (101a) and the long-arm fan-shaped branch (101b) connected to the same double-line microstrip feed line (101c) are orthogonal to each other.

3. The multi-band radio frequency energy harvester according to claim 1, characterized in that: The curvatures of the short-arm fan-shaped branch nodes (101a) and the long-arm fan-shaped branch nodes (101b) are both 30°.

4. The multi-band radio frequency energy harvester according to claim 1, characterized in that: The EBG supersurface structure (2) is composed of a plurality of EBG units (201), and the plurality of EBG units (201) are distributed in an array and connected to each other.

5. The multi-band radio frequency energy harvester according to claim 4, characterized in that: The EBG unit (201) comprises an EBG dielectric layer (201a) and a double-ring EBG (201b), wherein the double-ring EBG (201b) is arranged at the center of the EBG dielectric layer (201a).

6. The multi-band radio frequency energy harvester according to claim 4, characterized in that: A plurality of antenna structures (1) are connected to the EBG supersurface structure (2), and spacing is provided between the antenna structures (1).

7. The multi-band radio frequency energy harvester according to claim 6, characterized in that: A plurality of antenna structures (1) are distributed in an array on an EBG super-surface structure (2).

8. The multi-band radio frequency energy harvester according to claim 6, characterized in that: Each of the antenna structures (1) is located at the center of a structure composed of 9 EBG units (201) in a 3×3 array.

9. The multi-band radio frequency energy harvester according to claim 1, characterized in that: It also comprises a rectifier circuit structure, which is electrically connected to the two-wire microstrip feeder (101c).

10. The multi-band radio frequency energy harvester according to claim 5, characterized in that: The metal patch layer (101) is made of a flexible conductive cloth with a conductivity of 8×105 S / m, the antenna dielectric layer (102) and the EBG dielectric layer (201a) are both made of a felt material with a dielectric constant of 1.2 and a dielectric loss of 0.005, and the isolation layer (103) is made of a foam material with a dielectric constant equal to that of air.

Images