A polarization-insensitive rectifier surface for harvesting electromagnetic wave energy in the 2.4GHz WiFi band

Abstract

The application discloses a polarization-insensitive rectifying surface for collecting 2.4GHz WiFi band electromagnetic wave energy, and solves the problems of low efficiency of a rectifying surface for collecting low-power environment electromagnetic energy, sensitivity to the polarization direction of incident electromagnetic waves, complexity of a matching and direct current synthesis circuit, and large energy loss. The rectifying surface comprises, from top to bottom, a first metal layer (1), a dielectric substrate (2), a second metal layer (3), an air layer (4) and a metal reflection plate (5); the rectifying surface is composed of m rows and n columns of rectifying surface units (6) which are of the same size and shape, m and n are positive integers greater than or equal to 2, and a low-pass filter (7); the rectifying surface unit (6) is square and is centrally rotationally symmetrical, the first metal layer (1) of the rectifying surface unit (6) comprises one energy receiving unit (61), four matching lines (62), four first bonding pads (63), four second bonding pads (64) and four Schottky diodes (65).

Description

Technical Field

[0001] This invention belongs to the field of microwave radio frequency device technology, and particularly relates to rectifier surfaces in microwave radio frequency devices. Background Technology

[0002] Microwave rectifier surfaces possess the ability to receive and convert electromagnetic wave energy, providing a stable and reliable power supply for various electronic devices. They are widely used in smart homes, mobile devices, medical facilities, and industry, enabling energy harvesting from abundant energy sources. These devices typically emit 2.4 GHz WiFi signals, operating in the range of 2.4 GHz to 2.4835 GHz. To efficiently harvest energy within this frequency band, the operating frequency of the rectifier surface needs to be appropriately matched. However, current research on rectifier surfaces primarily focuses on achieving the highest energy conversion efficiency under high power density input, resulting in lower efficiency in low power density environments. In reality, the WiFi signals received by rectifier surfaces are relatively weak, thus requiring high efficiency operation at low power levels. Compared to traditional microwave rectifier antennas used for energy harvesting, rectifier surfaces consist of numerous elements, possessing a larger receiving aperture area, enabling them to receive and convert more electromagnetic wave energy for use by other devices. Furthermore, the polarization directions of electromagnetic waves generated by various radiation sources are often unknown or inconsistent; therefore, rectifier surfaces need to possess the characteristic of achieving high efficiency for electromagnetic waves with various polarization directions. Therefore, there is an urgent need for an electromagnetic rectifier surface that can collect electromagnetic wave energy in low-power environments within the 2.4GHz WiFi band and is insensitive to polarization direction.

[0003] The 2014 paper "Optimal Matched Rectifying Surface for Space SolarPower Satellite Applications" proposed an I-shaped rectifier surface. This surface unit can simultaneously match free space and the impedance of the rectifier circuit; however, its structural characteristics limit it to receiving electromagnetic wave energy from a single polarization direction and make it inefficient at collecting electromagnetic energy in low-power environments, severely restricting its application range. On the other hand, the 2016 paper "A metasurface for conversion of electromagnetic radiation to DC" proposed a cross-shaped rectifier surface. However, this structure cannot collect electromagnetic energy in the 2.4 GHz WiFi band, and its energy capture efficiency is easily affected by the polarization direction of the space electromagnetic waves, making it difficult to apply in practical scenarios. Therefore, there is an urgent need for a novel rectifier surface technology that can overcome these limitations, efficiently collect electromagnetic energy in low-power environments within the 2.4 GHz WiFi band, and is insensitive to the polarization direction of the incident electromagnetic waves.

[0004] In summary, the main challenges currently facing rectifier surfaces are: how to enable efficient collection of electromagnetic energy in low-power environments, how to extend the operating bandwidth of the rectifier surface to fully cover the 2.4GHz WiFi band, and how to make the rectifier surface insensitive to the polarization direction of incident electromagnetic waves. Summary of the Invention

[0005] The purpose of this invention is to propose a polarization-insensitive electromagnetic rectifier surface technology to achieve efficient collection of ambient electromagnetic energy under low power conditions, expand the operating bandwidth of the rectifier surface, and ensure insensitivity to the polarization direction of the incident electromagnetic wave.

[0006] The technical solution of this invention is as follows: the rectifying surface, from top to bottom, consists of a first metal layer 1, a dielectric substrate 2, a second metal layer 3, an air layer 4, and a metal reflector 5; the rectifying surface is composed of rectifying surface units 6 of the same size and shape, arranged in m rows and n columns, where m and n are positive integers greater than or equal to 2, and a low-pass filter 7; the rectifying surface unit 6 is square, and the patterns of the first metal layer 1 and the second metal layer 3 on it are centrally rotate symmetrically distributed; the rectifying surface unit 6 in the first metal layer 1 includes one energy receiving unit 61, four matching lines 62, four first pads 63, four second pads 64, and four Schottky diodes 65; the rectifying surface unit 6 in the second metal layer 3 includes four second... The DC feeder 66 has four third pads 67. The energy receiving unit 61 is a square ring shape, with adjacent units separated by gaps 9. Interdigitated structures 11 are distributed at one-eighth, two-eighths, three-eighths, five-eighths, six-eighths, and seven-eighths of each side of the energy receiving unit 61. The interdigitated structures 11 at the one-eighth, three-eighths, and six-eighths positions in a clockwise direction are protruding structures, while those at the two-eighths, five-eighths, and seven-eighths positions in a clockwise direction are recessed structures. The protruding structures of adjacent energy receiving units 61 are embedded in the recessed structures, separated by gaps 9. A first straight pad is distributed at the center of each side of the energy receiving unit 61. The first DC feed line 8 connects to the adjacent energy receiving unit 61, providing a path for the output DC. Four matching lines 62, of equal length and width, are located on the two center lines of the rectifier surface unit 6, with one end connected to the midpoint of the inner edge of the energy receiving unit 61 and the other end connected to the corresponding first pad 63. Four metallized vias 10 are located at the center of the second pad 64, passing through the dielectric substrate 2 and connecting to the lower third pad 67. Four Schottky diodes 65 are symmetrically distributed on the center lines of each side of the rectifier surface unit 6, with the anode soldered to the second pad 64 and the cathode soldered to the first pad 63. The output filter circuit 7 consists of one series-connected surface mount inductor 71 and two parallel-connected surface mount inductors 72. The output filter circuit 7 is composed of capacitor 72 and metal ground 73. The input terminal of the output filter circuit 7 is connected to the cross-line at two-eighths of the side of the rectifier surface unit 6 in the nth row and 1st column of the first metal layer 1, and is also connected to one end of the surface mount inductor 71. The output terminal is the output port 12 of the rectifier surface unit, and is also connected to the other end of the surface mount inductor 71. The metal ground 73 of the output filter circuit 7 is connected to the second DC feed line 66 of the rectifier surface unit 6 in the nth row and 1st column of the second metal layer 3. The metal ground 73 on the first metal layer 1 and the metal ground 73 on the second metal layer 3 are connected through metallized via 10. The output port 12 is one of the DC voltage output ports, and the metal ground 73 provides the other DC voltage output port.

[0007] The principle of the technical solution of this invention is as follows: The rectifier surface unit 61 receives electromagnetic wave energy with a working frequency of 2.35GHz-2.6GHz in free space. The collected electromagnetic wave energy enters the Schottky diode 65 through the matching line 62 and is converted into DC energy. The rectifier surface is composed of multiple rectifier surface units 6, forming an m×n array, increasing the area for receiving electromagnetic waves and thus increasing the received energy. Because the rectifier surface unit 6 itself has a rotationally symmetric structure, this rectifier surface can collect electromagnetic energy with different polarization angles in the environment and is insensitive to the polarization direction of the incident energy, maintaining high energy capture efficiency even when the polarization direction of the incident wave changes. Adjusting the length and width of the matching line 62 can achieve impedance matching between the Schottky diode 65 and the energy collection surface 61. The interdigitated structure 11 and the gap 9 on the rectifier surface can change the coupling between adjacent rectifier surface units 6. By changing them, the bandwidth can be controlled within 2.35-2.6GHz, achieving complete coverage of the 2.4GHz WiFi band. In addition, the height of the air layer 4 can also be used to extend the working bandwidth of the rectifier surface. The first DC feeder 8 connects adjacent rectifier surface units 6 together to provide a DC loop, enabling parallel connection of the output DC voltage generated by the Schottky diode 65. The output DC voltage generated by the Schottky diode 65 is introduced into the second DC feeder 66 from the first metal layer 1 through the metallized via 10. The second DC feeders 66 of adjacent rectifier surface units 6 are interconnected to achieve parallel connection of the output DC voltage. The output filter circuit 7 is a low-pass filter that filters out the high-frequency components generated by the rectifier surface, retaining only the DC component. The total DC voltage is output through the output port 12 and the metal ground 73.

[0008] Advantages and beneficial effects of the present invention: The rectifier surface proposed in this invention can efficiently receive and convert low-power electromagnetic energy in the environment, and its operating frequency fully covers the 2.4GHz WiFi band for electromagnetic energy harvesting in this frequency band environment. Each rectifier surface unit has a centrally rotationally symmetric geometry, which enables the rectifier surface to have high energy conversion efficiency for electromagnetic energy with different polarization angles in the environment, making the rectifier surface polarization insensitive. The matching line not only guides the harvested RF energy to the Schottky diode, but also achieves impedance matching between the Schottky diode and the energy harvesting surface, simplifying the matching circuit and improving the energy conversion efficiency of the rectifier surface. Attached Figure Description

[0009] Figure 1 This is a distribution diagram of each layer of the rectifying surface of the present invention. Figure 2 This is the first layer pattern of the rectifying surface of the present invention. Figure 3 This is the second layer pattern of the rectifying surface of the present invention. Figure 4 This is the first layer pattern of the rectifier surface unit of the present invention. Figure 5 This is the second layer pattern of the rectifier surface unit of the present invention. Figure 6 This is a graph showing the energy capture efficiency of the rectifier surface unit as a function of frequency. Figure 7 It is a graph showing the energy conversion efficiency and output voltage as a function of input power. Implementation

[0010] The present invention will be further described below with reference to the accompanying drawings and specific embodiments: Figure 1 As shown, the rectifying surface, from top to bottom, consists of a first metal layer 1, a dielectric substrate 2, a second metal layer 3, an air layer 4, and a metal reflector 5; Figure 2 As shown, the rectifier surface consists of m rows and n columns of rectifier surface units 6, all of the same size and shape, where m and n are positive integers greater than or equal to 2, and a low-pass filter 7; as Figure 4 As shown, the rectifier surface unit 6 is square, and the patterns of the first metal layer 1 and the second metal layer 3 on it are distributed in a central rotational symmetry. The rectifier surface unit 6 includes one energy receiving unit 61, four matching lines 62, four first pads 63, four second pads 64, and four Schottky diodes 65 in the first metal layer 1. Figure 5 As shown, the rectifier surface unit 6 includes four second DC feed lines 66 and four third pads 67 in the second metal layer 3; as Figure 4 As shown, the energy receiving unit 61 is a square ring shape, with adjacent units separated by gaps 9. Interdigitated structures 11 are distributed at one-eighth, two-eighths, three-eighths, five-eighths, six-eighths, and seven-eighths of each side of the energy receiving unit 61. The interdigitated structures 11 at the one-eighth, three-eighths, and six-eighths positions in a clockwise direction are protruding structures, while those at the two-eighths, five-eighths, and seven-eighths positions in a clockwise direction are recessed structures. The protruding structures of adjacent energy receiving units 61 are embedded in the recessed structures, separated by gaps 9. The center of each side of the energy receiving unit 61 is located at... A first DC feed line 8 is positioned, connecting to an adjacent energy receiving unit 61 to provide a path for the output DC; four matching lines 62 of equal length and width are located on the two center lines of the rectifier surface unit 6, one end connected to the midpoint of the inner edge of the energy receiving unit 61, and the other end connected to the corresponding first pad 63; four metallized vias 10 are located at the center of the second pad 64, passing through the dielectric substrate 2 and connecting to the lower third pad 67; four Schottky diodes 65 are symmetrically distributed on the center lines of each side of the rectifier surface unit 6, with the anode soldered to the second pad 64 and the cathode soldered to the first pad 63; as shown Figure 2As shown, the output filter circuit 7 consists of a series-connected surface mount inductor 71, two parallel-connected surface mount capacitors 72, and a metal ground 73. The input terminal of the output filter circuit 7 is connected to the cross-finger line at two-eighths of the side of the rectifier surface unit 6 in the nth row and 1st column on the first metal layer 1, and is also connected to one end of the surface mount inductor 71. The output terminal is the output port 12 of the rectifier surface unit, and is also connected to the other end of the surface mount inductor 71. The metal ground 73 of the output filter circuit 7 is connected to the second DC feed line 66 of the rectifier surface unit 6 in the nth row and 1st column on the second metal layer 3. The metal ground 73 on the first metal layer 1 and the metal ground 73 on the second metal layer 3 are connected through a metallized via 10. The output port 12 is one of the DC voltage output ports, and the metal ground 73 provides the other DC voltage output port.

[0011] To further illustrate the feasibility of the above technical solution, a specific design example is given below: a polarization-insensitive rectifier surface for collecting electromagnetic wave energy in the 2.4GHz WiFi band. The dielectric substrate is an F4B substrate with a thickness of 1mm and a relative permittivity of 2.6. The Schottky diode 65 is an MA4E2200, and the air layer 4 is 9mm thick. The rectifier surface has 4 rows and 4 columns of rectifier surface units, and the DC output is in parallel. The rectifier surface operates at 2.35GHz-2.6GHz, and the DC output terminal is connected to a 25-ohm load. When uniform planar electromagnetic waves with different polarization directions irradiate the rectifier surface, the energy capture efficiency of the rectifier surface for electromagnetic waves is as follows: Figure 6 As shown in the figure, even with changes in the polarization direction of the incident wave, the rectifier surface maintains a high energy capture efficiency in the 2.35GHz-2.6GHz range, with an energy capture efficiency exceeding 90% across the operating frequency band. The curves showing the rectifier efficiency of a single rectifier diode versus the output DC voltage as a function of input power at an operating frequency of 2.45GHz are shown below. Figure 7 As shown, when the input power is -20dBm, the rectification efficiency reaches 23%, and the output DC voltage is 59.7mV, meaning that a single diode can output 2.3μW of DC power at a 10μW RF input power. Therefore, the entire rectifier surface can generate 147.2μW of DC power. When the input power is -10dBm, the rectification efficiency of a single diode is 43.6%, and the output DC voltage is 264mV, meaning that a single diode can output 43.6μW of DC power at a 100μW RF input power. Therefore, the entire rectifier surface can generate 2.79mW of DC output power.

Claims

1. A polarization-insensitive rectifier surface for collecting electromagnetic wave energy in the 2.4GHz WiFi band, characterized in that: The rectifier surface, from top to bottom, consists of a first metal layer (1), a dielectric substrate (2), a second metal layer (3), an air layer (4), and a metal reflector (5); the rectifier surface is composed of m rows and n columns of rectifier surface units (6) of the same size and shape, where m and n are positive integers greater than or equal to 2, and a low-pass filter (7); the rectifier surface unit (6) is square, and the patterns of the first metal layer (1) and the second metal layer (3) on it are centrally rotate symmetrically distributed; the rectifier surface unit (6) in the first metal layer (1) includes one energy receiving unit (61), four matching lines (62), four first pads (63), four second pads (64), and four Schottky diodes (65); the rectifier surface unit (6) in the second metal layer (3) Includes 4 second DC feed lines (66) and 4 third pads (67); the energy receiving unit (61) is a square ring shape, and adjacent units are separated by gaps (9). Interdigitated structures (11) are distributed at one-eighth, two-eighths, three-eighths, five-eighths, six-eighths, and seven-eighths of each side of the energy receiving unit (61). Among them, the interdigitated structures (11) at one-eighth, three-eighths, and six-eighths in the clockwise direction are protruding structures, and the interdigitated structures (11) at two-eighths, five-eighths, and seven-eighths in the clockwise direction are recessed structures. The protruding structures of the interdigitated structures of adjacent energy receiving units (61) are embedded in the recessed structures and are separated by gaps (9). Each side of the energy receiving unit (61) The first DC feed line (8) is located at the center of the rectifier surface unit (6), and the first DC feed line (8) connects to the adjacent energy receiving unit (61) to provide a path for the output DC; four matching lines (62) are of equal length and width, located on the two center lines of the rectifier surface unit (6), one end of which is connected to the midpoint of the inner side of the energy receiving unit (61), and the other end is connected to the corresponding first pad (63); four metallized vias (10) are located at the center of the second pad (64), pass through the dielectric substrate (2), and connect to the third pad (67) below; four Schottky diodes (65) are symmetrically distributed on the center lines of each side of the rectifier surface unit (6), with the anode soldered to the second pad (64) and the cathode soldered to the first pad (63); a low-pass filter ( 7) The low-pass filter (7) is composed of a series surface mount inductor (71), two parallel surface mount capacitors (72) and a metal ground (73). The input terminal of the low-pass filter (7) is connected to the cross finger line at two-eighths of the side of the rectifier surface unit (6) in the nth row and 1st column on the first metal layer (1), and is also connected to one end of the surface mount inductor (71). The output terminal is the output port (12) of the rectifier surface, and is also connected to the other end of the surface mount inductor (71). The metal ground (73) of the low-pass filter (7) is connected to the second DC feed line (66) of the rectifier surface unit (6) in the nth row and 1st column on the second metal layer (3). The metal ground (73) on the first metal layer (1) and the metal ground (73) on the second metal layer (3) are connected through a metallized via (10).Output port (12) is one of the DC voltage output ports, and metal ground (73) provides the other DC voltage output port.

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