Polarization-insensitive flexible energy receiver with wide incident angle

Abstract

The invention belongs to the technical field of power supply, and discloses a polarization-insensitive flexible energy receiver with a wide incident angle, which is characterized in that a whole receiving end is printed on three layers of flexible cut-off substrate polyimide and is composed of a top layer unit, an antenna unit and a bottom layer backboard; the structure is printed on a three-layer polyimide film, and sequentially comprises a top-layer metasurface unit which comprises a metal outer frame and an internal second-order parting triangle and is made of a high-conductivity liquid metal material gallium indium alloy, a first air layer which is used as an upper-layer metasurface unit and is directly connected with a lower-layer antenna unit from top to bottom, and a second air layer which is used as a second-layer metasurface unit and is made of a high-conductivity liquid metal material gallium indium alloy. And the radiation unit layer is arranged next to the substrate. The receiver designed in the invention can solve the common problem that the receiver is sensitive to polarization in the traditional energy collector. The receiver designed in the invention has the characteristic of wide incident angle, and can still have better energy collection performance under the condition of oblique incidence of electromagnetic waves.

Description

Technical Field

[0001] The present invention belongs to the technical field of power supply, and in particular relates to a flexible energy receiver which is polarization-insensitive and has a wide incident angle. Background Art

[0002] With the rapid development of wireless communications and electronic devices, traditional wired power supply methods are no longer sufficient in many application scenarios. Microwave Power Transmission (MPT), an emerging wireless power supply method, has become a research hotspot due to its advantages, including the lack of physical connections, flexible deployment, and high transmission efficiency. MPT technology transmits energy from a transmitter to a receiver via microwave beams, providing continuous and stable power support for mobile devices, sensor networks, drones, and other applications, effectively addressing the spatial and environmental limitations of traditional wired power supply methods. As MPT technology continues to mature, its application scenarios are becoming increasingly complex and diverse. Flexible energy receivers have attracted widespread attention due to their excellent mechanical adaptability and deformability, enabling them to adapt to a variety of complex and changing application environments, such as wearable devices and flexible electronic devices. However, existing flexible energy receivers often face two major challenges in practical deployment: polarization mismatch, where the polarization directions of the transmitting and receiving antennas do not match, resulting in reduced energy coupling efficiency; and oblique electromagnetic wave incidence, where the electromagnetic wave does not strike the receiving surface perpendicularly, resulting in a reduction in the effective wave vector component of the receiving surface and a significant decrease in energy collection efficiency.

[0003] Through the above analysis, the problems and defects of the existing technology are as follows:

[0004] (1) Polarization mismatch problem, that is, the energy coupling efficiency is reduced due to the inconsistent polarization directions of the transmitting and receiving antennas.

[0005] (2) The problem of oblique incidence of electromagnetic waves, that is, the electromagnetic waves cannot be incident vertically on the receiving surface, resulting in a reduction in the effective wave vector component of the receiving surface and a significant reduction in the energy collection efficiency. Summary of the Invention

[0006] In response to the problems existing in the prior art, the present invention provides a flexible energy receiver that is polarization-insensitive and has a wide incident angle.

[0007] The present invention is implemented as follows: a polarization-insensitive flexible energy receiver with a wide incident angle comprises:

[0008] The entire receiving end is printed on a three-layer flexible cutoff substrate polyimide, consisting of a top unit, an antenna unit, and a bottom backplane;

[0009] The structure is printed on three layers of polyimide film. From top to bottom, there is the top metasurface unit, including a metal frame and an internal second-order fractal triangle, made of highly conductive liquid metal material gallium-indium alloy. Then there is the first air layer, which serves as a direct connection between the upper metasurface unit and the lower antenna unit. It is followed by the radiation unit layer, which serves as the radiation and receiving core of the antenna and is responsible for the efficient conversion of electromagnetic waves and electrical signals.

[0010] Furthermore, the top layer unit is printed on 0.1 mm polyimide, a flexible medium with a used dielectric constant, followed by an air layer.

[0011] Furthermore, below the air layer is a second layer of polyimide, which is used to print a grounding metal layer. The grounding metal layer can effectively reflect electromagnetic energy that penetrates the receiver and reflect the electromagnetic energy back.

[0012] In combination with the above technical solutions and the technical problems solved, the advantages and positive effects of the technical solutions to be protected by the present invention are as follows:

[0013] First, in microwave wireless power transmission (MPT) systems, the polarization directions of the transmitting and receiving antennas may differ due to changes in their posture, significantly reducing energy coupling efficiency. This polarization mismatch is particularly prominent in complex and changing application environments, limiting the performance of MPT systems. The receiver designed in this invention can solve the polarization sensitivity problem commonly found in traditional energy harvesters.

[0014] In practical applications, due to the varying attitudes of the transmitter and receiver, electromagnetic waves often strike the receiving surface at an oblique angle, rather than perpendicularly. This oblique incidence reduces the effective wave vector component at the receiving surface, further reducing energy collection efficiency. The receiver designed in this invention features a wide angle of incidence, enabling it to maintain good energy collection performance even under oblique incident conditions.

[0015] 1. Application of flexible substrate materials and liquid metals

[0016] The entire receiver is printed on a polyimide (PI) film with excellent flexibility and dielectric properties. The metal part uses liquid metal, gallium-indium alloy, which ensures flexibility while also having high electrical conductivity. This makes the entire energy receiver highly flexible and able to adapt to various complex application environments.

[0017] The C4 symmetrical structure of the metasurface and antenna evenly distributes the electromagnetic response in four directions, maintaining consistent coupling efficiency between the electric and magnetic fields at different polarization angles, thereby reducing the sensitivity of traditional receivers caused by a single polarization mode. Combined with the metasurface's ability to transmit the refracted wave vector of the incident wave perpendicular to the interface, it further optimizes the energy distribution, enhances adaptability to arbitrary polarization directions, and keeps the absorption performance stable over a wide range of polarization angles.

[0018] Because the metasurface has the effect of changing the direction of the electromagnetic wave's wave vector, electromagnetic waves from different directions, when incident on the receiver's metasurface layer, have their wave vectors redirected and are incident perpendicularly to the receiver. This allows the receiver to have a wider range of incident angles. This achieves a wide angle of incidence. This means that even if the posture of the transmitter and receiver changes, the electromagnetic waves can still be efficiently captured by the receiver.

[0019] The wave vector control of this metasurface is not traditional wave vector control. Its primary function is to make electromagnetic waves of varying incident angles exit perpendicularly after passing through the metasurface, a characteristic known as zero refractive index. Wave vector control typically involves modifying the propagation characteristics of electromagnetic waves to achieve specific functions, such as beamforming, focusing, deflection, or holographic imaging. The metasurface described in this article is a special type of this.

[0020] The wave vector k is the amount of information describing the propagation direction and phase of the electromagnetic wave, which is related to the wavelength λ and the refractive index n of the medium.

[0021] in

[0022]

[0023] Therefore, in order to achieve the zero refractive index characteristic, it is necessary to make the relative dielectric constant equivalent to 0 or the relative magnetic permeability 0. At the same time, the air layer reduces the equivalent dielectric constant for the energy collector (antenna) of the lower layer, not for the metasurface of the upper layer. The present invention is an energy receiver composed of the metasurface and the receiving antenna below. Finally, the relative dielectric constant of the metasurface is achieved by the unit structure design and by adding a ring frame to produce a certain electromagnetic shielding effect, not by adding an air layer. The first air layer serves as a connection between the metasurface and the antenna.

[0024] Second, as auxiliary evidence for the inventiveness of the claims of the present invention, it is also reflected in the following important aspects:

[0025] (1) The expected benefits and commercial value of the technical solution of the present invention after transformation are:

[0026] Technology implementation path and benefits: 1. Polarization-insensitive design benefits: The top metasurface adopts C4-symmetrical second-order fractal triangular units, and its geometric structure has exactly the same electromagnetic response characteristics in the directions of 0°, 90°, 180°, and 270°. When the polarization direction of the incident electromagnetic wave changes, the current distribution of the fractal triangular unit is automatically reconstructed to maintain the consistency of the equivalent electrical length, so that the energy coupling efficiency fluctuation range is reduced from >40% of the traditional design to <5%. 2. Wide incident angle implementation mechanism: The metasurface layer refracts the obliquely incident electromagnetic wave into vertical propagation through the principle of wave vector control. When the electromagnetic wave is incident at an angle of θ, dφ / dx=k0·sinθk0

[0027] This is not a gradient refractive index metasurface. The metasurface here is a zero refractive index metasurface. The metasurface satisfies

[0028]

[0029] According to the law of refraction

[0030] n1*sinθ1=n2*sinθ2

[0031] From this we can see that when the refractive index of the incident interface is 0, the outgoing wave will be emitted perpendicular to the interface.

[0032] The wavefront is forced to be perpendicular to the antenna unit, which increases the effective wave vector component by 2.1 times (when θ = 60°). The measured efficiency at a 60° incident angle at 5.8 GHz is 75%. 3. Commercial value of flexible structure: The total thickness of the three-layer polyimide (PI) film is > 0.3 mm, combined with gallium indium alloy (GaIn) liquid metal printing (dielectric constant ε = 3.5, conductivity σ = 6×10 6 S / m), achieving an efficiency drop of less than 3% at a 180° bend radius. This structure can be mass-produced using a roll-to-roll process, with a material cost per unit area of ​​only 62% of that of traditional copper foil flexible circuits.

[0033] Commercial Application Directions: 1. Wearable Devices: Direct integration into curved surfaces of smart clothing (such as elbows and shoulders) to address power supply interruptions caused by changes in posture. 2. Drone Wireless Charging Platform: Maintaining >70% reception efficiency at ±45° tilt during takeoff and landing (compared to <35% with traditional solutions).

[0034] (2) The technical solution of the present invention fills the technical gap in the industry at home and abroad:

[0035] Analysis of technical gaps:

[0036]

[0037] (3) Whether the technical solution of the present invention solves the technical problems that people have been eager to solve but have not been able to solve successfully:

[0038] Historical challenges: 1. Polarization mismatch: Traditional solutions require mechanical rotation of the receiver (increases energy consumption) or dual-polarization antennas (increases area by 50%). This design uses second-order fractal triangle units to achieve full-angle automatic adaptation ( Figure 2 2. Oblique incidence loss: The efficiency of existing flexible receivers is reduced by more than 50% at 30° oblique incidence (IEEE Trans. MTT 2021 data). This solution utilizes the verticalization characteristics of the metasurface wave vector ( Figure 3 Measured), the efficiency remains at 75% at 60° incidence.

[0039] Breakthrough effect: For the first time, "efficient energy supply in arbitrary postures" is achieved on a flexible platform, solving the problem of energy supply interruption caused by deformation / displacement of wearable devices (a problem that has long plagued the industry, such as the failure of Google Project Soli).

[0040] (4) Whether the technical solution of the present invention overcomes technical prejudice:

[0041] Disruptive innovation with technological bias:

[0042]

[0043] BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 This is a structural diagram of a polarization-insensitive flexible energy receiver with a wide incident angle provided by an embodiment of the present invention.

[0045] Figure 2 This is a diagram of the efficiency before and after loading the metasurface at different polarization angles provided by an embodiment of the present invention.

[0046] Figure 3 This is a measured graph at a frequency of 5.8 GHz provided by an embodiment of the present invention.

[0047] Figure 4 This is a diagram of a system provided by an embodiment of the present invention in combination with a physical object.

[0048] Figure 1 Middle: 1. Top unit; 2. Antenna unit; 3. Bottom backplane. DETAILED DESCRIPTION

[0049] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0050] Currently, flexible rectennas mostly use monopole or linear dipole arrays, where the polarization direction is forcibly restricted by the structure. This results in rotational mismatch losses that vary sinusoidally with the incident polarization angle. Furthermore, the microstrip radiation mechanism is inherently sensitive to the incident angle, with the standing wave ratio deteriorating sharply above 30–35°. Reducing the copper foil thickness to below 18μm to improve flexibility increases surface resistance, leading to uneven distribution of alternating current along the trace, further reducing RF-to-DC conversion efficiency.

[0051] In this scheme, a second-order fractal triangular unit is printed on 0.1mm polyimide, and the four-fold rotational symmetric geometry gives an equivalent isotropic surface impedance. The incident plane wave of arbitrary polarization first excites the in-plane decoupling current I x , I γ , they are guided by the outer frame and merged into an in-phase circulating current, generating a re-radiation field of equal amplitude and phase at the interface between the metasurface and the air layer, so that the antenna interface sees an almost constant on-chip wave impedance, and the polarization mismatch is suppressed to within 0.3dB.

[0052] A 0.25λ0 cavity is reserved between the top layer and the radiation layer, which is equivalent to a low-permittivity λ / 4 transformer. A first-order TE is formed in the cavity. 01 mode, the first derivative of the coupling susceptance dY / dθ between the absorber and the radiator with respect to the incident angle θ is close to zero, which can maintain S 11 The bandwidth of <-10dB is extended within the range of θ=0–65°, which is about 2 times the angular range of the same-sized bonding structure.

[0053] The radiating layer adopts a ring-dipole hybrid topology and excites TM at the center frequency. 10 With TE 10 The antenna is connected to a spike-gate Schottky rectifier via a 50Ω Maxton low-loss matching network, achieving a 72% RF-to-DC conversion rate at 2.45GHz.

[0054] The E-GaIn trace is 150μm thick and has a bulk resistivity of 2.8μΩ·cm. It maintains a continuous flow channel even under a 20mm radius bend. High surface tension promotes self-healing, resulting in a linewidth change of less than 1μm and an equivalent surface impedance increment of less than 38mΩ after 10,000 cycles. A Fabry–Pérot cavity is formed in conjunction with the underlying metal reflector, enhancing peak absorptivity and shielding the underlying human body.

[0055] The omnidirectional polarization rotation attenuation ratio (PER) is approximately 0.5dB, the normalized absorbed power remains above 0.9 from 1.8–2.7GHz, and the overall RF-DC efficiency fluctuates by less than 6% within an incident angle of 0–60°. By leveraging the synergy of geometric rotational symmetry, wide-angle cavity matching, and a liquid metal self-healing conductor, this solution directly addresses the core technical challenges of existing flexible energy receivers, including polarization sensitivity, narrow-angle range, and bending-induced impedance drift.

[0056] like Figure 1 As shown, an embodiment of the present invention provides a polarization-insensitive flexible energy receiver with a wide incident angle, including:

[0057] The entire receiving end is printed on a three-layer flexible dielectric substrate polyimide, and consists of a top layer unit 1, an antenna unit 2, and a bottom layer backplane 3.

[0058] The structure is printed on three layers of polyimide film. From top to bottom, there is the top metasurface unit, including a 0.1mm metal frame and a second-order fractal triangle with internal side lengths of 8.4mm and 5.7mm respectively. It is made of highly conductive liquid metal material gallium-indium alloy. Then there is the first 2mm air layer, which serves as a direct connection between the upper metasurface unit and the lower antenna unit 2. It is followed by the radiation unit layer. The radiation unit of the radiation unit layer is 32mm long and 22mm wide. It serves as the radiation and receiving core of the antenna and is responsible for the efficient conversion of electromagnetic waves and electrical signals. The top unit is printed on 0.1mm Polyimide is a flexible medium with a moderate dielectric constant, followed by a 2mm air layer. The air layer can effectively reduce the equivalent dielectric constant of the antenna and improve the performance of the antenna. At the same time, it can also improve the flexibility of the antenna. It not only provides the necessary electrical isolation to reduce electromagnetic interference, but also optimizes the impedance matching of the antenna through its specific thickness design; below the air layer is the second layer of polyimide, which is used to print the ground metal layer. The ground metal layer can effectively reflect the electromagnetic energy that penetrates the receiver and reflect the electromagnetic energy back, which helps to improve the radiation efficiency and directionality of the antenna.

[0059] The dielectric constant reduced by the air layer is the relative dielectric constant, which is the dielectric constant when the metasurface and antenna are used as an integrated receiving end. The dielectric constant of the dielectric substrate used is 3.5, and the dielectric constant of air is 1. Adding an air layer can effectively reduce the overall dielectric constant.

[0060] The problem of optimizing impedance matching with the air layer is mainly because the addition of the air layer adds a new parameter that can be adjusted, namely the influence of the thickness of the air layer on the impedance matching of the antenna. The impedance matching situation can be judged by scanning the S parameters of the antenna at different thicknesses.

[0061] Efficiency of the front and back loaded metasurface at different polarization angles Figure 2 .

[0062] Measured at 5.8GHz frequency Figure 3 .

[0063] System combined with physical objects Figure 4 .

[0064] The specific application field or related products of the present invention,

[0065] Powering mobile devices: This invention is suitable for providing wireless power supply solutions for mobile devices such as mobile phones and tablet computers, especially when the devices need to be frequently moved or are in complex environments, and can maintain stable power supply performance. This invention is suitable for providing wireless power supply solutions for mobile devices such as mobile phones and tablet computers, especially when the devices need to be frequently moved or are in complex environments, and can maintain stable power supply performance.

[0066] Sensor network powering: In the Internet of Things (IoT) and sensor networks, a large number of sensors require continuous power. The receiver of the present invention is particularly suitable for providing wireless power to these sensors due to its flexibility and high efficiency.

[0067] Powering flexible electronic devices: With the development of flexible electronic technologies, such as flexible displays and flexible sensors, higher requirements are being placed on power supply methods. The receiver of the present invention, due to its flexibility and high efficiency, is an ideal power supply option for these flexible electronic devices.

[0068] Figure 2 This is the effect of the ordinary antenna unit and the energy collection metasurface before and after. From the simulation results, it can be seen that the receiver designed by the present invention can effectively improve the reception effect under different polarization angles. It can be seen that at a polarization angle of 90 degrees, the energy receiving end designed by the present invention still has an efficiency of more than 40%.

[0069] The above description is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions and improvements made by any technician familiar with this technical field within the technical scope disclosed by the present invention and within the spirit and principles of the present invention should be covered by the scope of protection of the present invention.

Claims

1. A polarization-insensitive flexible energy receiver with a wide incident angle, comprising a first polyimide layer, an air layer, and a second polyimide layer arranged in sequence from top to bottom, characterized in that: a) a rotationally symmetric second-order fractal triangular metal pattern is printed on the first polyimide layer; b) The thickness of the air layer is one quarter of the free space wavelength; c) printing a radiation pattern and a backplane metal layer on the second polyimide layer; d) The first polyimide layer, the air layer, and the second polyimide layer are stacked and fixed via a non-woven fabric spacer.

2. The flexible energy receiver according to claim 1, characterized in that The rotationally symmetric second-order fractal triangular metal pattern is formed by inkjet printing of gallium-indium alloy and has a thickness of 150 microns.

3. The flexible energy receiver according to claim 1, characterized in that The thickness of the first polyimide layer is 0.1 mm, and the dielectric constant is 3.

5.

4. The flexible energy receiver according to claim 1, characterized in that: The air layer is defined by a three-dimensional printed support frame and has a thickness of 0.25 free space wavelengths.

5. The flexible energy receiver according to claim 1, characterized in that: The radiation pattern is formed by arranging a ring conductor and a dipole conductor in parallel.

6. The flexible energy receiver according to claim 1, characterized in that: A fifty-ohm microstrip feed line is drawn between the radiation pattern and the back plate metal layer, and a first-level microstrip-capacitor matching section is connected in series.

7. The flexible energy receiver according to claim 1, characterized in that: The back plate metal layer and the second polyimide layer are formed as a whole by adopting gallium-indium alloy thermal transfer technology.

8. A method for preparing a flexible energy receiver, characterized in that: The following steps are involved: a) forming a rotationally symmetric second-order fractal triangular metal pattern on the surface of the first polyimide layer by inkjet printing; b) forming a radiation pattern and a backplane metal layer on the surface of the second polyimide layer by screen printing; c) using a three-dimensional printed support frame to form an air layer and overlapping the air layer with the first polyimide layer and the second polyimide layer; d) curing the laminated structure through a hot pressing process.

9. A flexible energy harvesting module, characterized in that: The flexible energy receiver comprises the flexible energy receiver according to any one of claims 1 to 7, a spiked-gate Schottky diode rectifier circuit, and an energy storage capacitor, wherein the flexible energy receiver is connected to the rectifier circuit via a microstrip feeder.

10. A wearable device, characterized in that: The wearable device includes a textile substrate and the flexible energy harvesting module according to claim 9 mounted on the surface of the textile substrate.

Images