Miniaturized low frequency loop antenna

Abstract

This application relates to the technical field of antennas, and in particular to a miniaturized low-frequency loop antenna, comprising a loop frame made of a non-magnetic insulating material, a loop winding cavity formed on the loop frame, and a plurality of partition plates spaced axially on the loop frame, the partition plates being coaxially disposed within the loop winding cavity, dividing the loop winding cavity into a plurality of winding slots arranged axially, with wire passages provided on the partition plates, and adjacent winding slots connected by the wire passages; a magnetic layer equal in number to the number of winding slots and correspondingly disposed, and the magnetic layers forming a surrounding magnetic circuit with an air gap around the winding slots; an excitation coil including winding segments, the number of winding segments equal to the number of winding slots, one winding segment wound in a corresponding winding slot and located within the surrounding magnetic circuit, and adjacent winding segments electrically connected in series by connecting wires passing through the wire passages. This application can meet the requirements of antenna miniaturization and reliability in practical applications.

Description

Technical Field

[0001] This application relates to the field of antenna technology, and in particular to a miniaturized low-frequency loop antenna. Background Technology

[0002] Currently, low-frequency electromagnetic waves (3-300kHz) possess the physical characteristics of long wavelength and strong penetrating power, effectively penetrating media such as water, soil, and buildings. Therefore, they have wide applications in underwater communication, underground communication, long-wave time synchronization, geological exploration, and wireless power transmission. In these applications, low-frequency electromagnetic coupling devices are the core components for realizing electromagnetic energy conversion and transmission, and their performance directly determines the efficiency and reliability of the entire system.

[0003] To ensure radiation efficiency, the size of low-frequency antennas must match the operating wavelength. However, the wavelengths of low-frequency electromagnetic waves are typically on the order of kilometers, making traditional low-frequency antennas quite bulky. To achieve miniaturization of low-frequency antennas, ferrite core antennas are commonly used. This involves introducing a ferrite core into the antenna frame to enhance the magnetic field, thereby achieving the required inductance and radiation performance within a smaller physical size. While ferrite core antennas effectively improve electromagnetic performance, ferrite materials are inherently brittle and fragile, exhibiting extremely poor resistance to shock and vibration. In harsh environments requiring vibration and shock, such as industrial, automotive, or outdoor applications, the ferrite core is highly susceptible to breakage, leading to antenna failure and severely limiting the reliable application of low-frequency antennas in these scenarios.

[0004] Therefore, antennas in related technologies cannot simultaneously meet the requirements of miniaturization and reliability in practical applications. Summary of the Invention

[0005] To meet the requirements of miniaturization and reliability in practical applications, this application provides a miniaturized low-frequency loop antenna.

[0006] This application provides a miniaturized low-frequency loop antenna, which adopts the following technical solution:

[0007] A miniaturized low-frequency loop antenna, comprising:

[0008] An annular frame is made of non-magnetic insulating material. An annular winding cavity is formed on the annular frame. Several partition plates are spaced apart along the axial direction on the annular frame. The partition plates are coaxially arranged in the annular winding cavity. The partition plates divide the annular winding cavity into multiple winding slots arranged along the axial direction. A wire passage is opened on the partition plate, and adjacent winding slots are connected through the wire passage.

[0009] The number of magnetic layers (3) is equal to that of the winding grooves (13). One magnetic layer (3) is disposed on the inner wall of one winding groove (13). The magnetic layer forms a surrounding magnetic circuit with an air gap (33) along the cross-sectional direction of the winding groove (13).

[0010] An excitation coil includes winding segments, the number of which is equal to the number of winding slots. Each winding segment is wound in a corresponding winding slot and located within the surrounding magnetic circuit. Adjacent winding segments are electrically connected in series via connecting wires passing through the winding channel.

[0011] By adopting the above technical solution, the annular frame is made of non-magnetic insulating material and forms an annular winding cavity, providing rigid support and electrical insulation for the antenna. A magnetic layer is disposed on the inner wall of the winding slot and forms a surrounding magnetic circuit, allowing magnetic flux to surround the winding segments of the excitation coil from multiple directions, reducing the demagnetization factor, increasing the effective permeability, enhancing the equivalent magnetic dipole moment, and achieving antenna miniaturization. An air gap is provided in the surrounding magnetic circuit, where magnetic flux is forced to leave the magnetic layer and enter free space, forming a leakage magnetic field and achieving electromagnetic radiation. A partition plate divides the annular winding cavity into multiple winding slots, and the excitation coil is divided into multiple winding segments wound in each slot, reducing the potential difference between adjacent turns, improving insulation reliability, and making the magnetic flux distribution more uniform. Each winding segment is connected in series through connecting wires in the wire passage, ensuring the overall electrical continuity of the excitation coil.

[0012] Optionally, the magnetic layer includes a horizontal section and a vertical section. The horizontal section is disposed on the inner wall of the winding groove on both sides of the annular skeleton along the axial direction. The vertical section is disposed on the inner wall of the winding groove on both sides of the radial direction. The horizontal section and the vertical section are connected end to end to form the circumferential magnetic circuit. The air gap is disposed on the vertical section.

[0013] By adopting the above technical solution, the horizontal and vertical sections are respectively set on the inner walls of the axial and radial sides of the winding slot, connecting end to end to form a rectangular magnetic circuit that surrounds the winding section from four directions: top, bottom, inside, and outside, thus improving the magnetic flux confinement effect. The air gap is set on the vertical section, which is located on the radial sides of the winding slot. The outermost vertical section faces the external space of the antenna, which is beneficial for magnetic flux leakage into the external space and the formation of effective far-field radiation.

[0014] Optionally, the magnetic layer is made of nanocrystalline soft magnetic alloy thin strip stacks, and the stack thickness of the vertical section is greater than that of the horizontal section.

[0015] By adopting the above technical solutions, nanocrystalline soft magnetic alloy strips possess high permeability, high saturation magnetic flux density, and excellent flexibility. Compared to ferrite cores, they are less prone to breakage, improving antenna reliability under vibration and shock environments while enhancing magnetic moment. The saturation magnetic flux density of the nanocrystalline soft magnetic alloy strips is higher than that of ferrite, enabling the antenna to have greater power capacity. The stacking thickness of the vertical section is greater than that of the horizontal section, compensating for the insufficient cross-sectional area of ​​the surrounding magnetic circuit caused by the smaller circumference of the inner diameter side of the loop antenna. This makes the magnetic flux density more uniform throughout the entire surrounding magnetic circuit, thus helping to avoid local magnetic saturation.

[0016] Optionally, the number of air gaps on each vertical segment is multiple, and the multiple air gaps are evenly distributed along the circumference of the annular skeleton, and the air gaps are filled with non-magnetic gaskets.

[0017] By employing the above technical solution, multiple air gaps are uniformly distributed circumferentially along the ring frame, maintaining the symmetry of the surrounding magnetic circuit. This helps avoid magnetic flux distribution skew, enabling the antenna to obtain a near-omnidirectional radiation pattern in the horizontal plane. Distributing the total air gap width across multiple locations reduces the concentration of magnetic flux density at each air gap. Non-magnetic spacers fill the air gaps, maintaining precise spacing and structural stability.

[0018] Optionally, gradient transition zones are provided on both sides of the air gap, and the thickness of the vertical section in the gradient transition zone gradually decreases along the direction close to the air gap.

[0019] By adopting the above technical solution, the gradient transition region gradually reduces the thickness of the vertical section along the direction close to the air gap, achieving a gradual transition of magnetic permeability from a high value in the magnetic core to a low value in the air gap. This helps avoid abrupt changes in magnetic permeability at the air gap boundary. The gradual transition of magnetic permeability alleviates the magnetic flux density concentration phenomenon at the air gap edge, reduces the risk of local magnetic saturation, and makes the spatial distribution of the leakage magnetic field smoother. This is beneficial for improving the uniformity of the far-field radiation pattern and also helps reduce eddy current losses at the magnetic core edge.

[0020] Optionally, the partition plate is provided with a heat dissipation component, the two ends of which extend into the two adjacent winding grooves respectively.

[0021] By adopting the above technical solution, the heat dissipation component is set on the partition plate and extends to the two adjacent winding slots at both ends, so that the heat dissipation component can directly contact or approach the winding segments in the winding slots on both sides, and conduct the heat generated by the winding segments out through the partition plate, providing a heat dissipation channel for the inside of the antenna, which is beneficial to reduce the internal temperature rise of the antenna when it is working at high power.

[0022] Optionally, the partition plate has a heat-conducting hole extending through it along the axial direction. The heat dissipation assembly includes a first heat-conducting element and a second heat-conducting element. The first heat-conducting element is inserted into the heat-conducting hole, and the second heat-conducting element is radially embedded in the partition plate and connected to the first heat-conducting element. The two ends of the second heat-conducting element extend to the circumferential outer wall and circumferential inner wall of the annular skeleton, respectively.

[0023] By adopting the above technical solution, the first heat-conducting element is inserted into the heat-conducting hole and conducts heat axially, transferring the heat generated by the winding section to the upper and lower sides of the annular frame. The second heat-conducting element is radially embedded in the partition plate and connected to the first heat-conducting element, with its two ends extending to the outer and inner circumferential walls of the annular frame, respectively, conducting heat radially to the inner and outer sides of the annular frame. The first and second heat-conducting elements are interconnected, forming a parallel axial and radial heat dissipation path, improving the heat conduction efficiency from the heat source to the frame shell.

[0024] Optionally, a tuning capacitor is connected in series on the connecting wire between two adjacent winding segments, and the tuning capacitor is disposed on the partition plate.

[0025] By adopting the above technical solution, the tuning capacitor is connected in series on the connecting wire between adjacent winding sections, forming a resonant circuit with the inductance of the excitation coil. By adjusting the capacitance value of the tuning capacitor, the resonant frequency of the antenna can be adjusted to match the target operating frequency, thereby improving the current amplitude and radiation efficiency of the antenna at the operating frequency. The tuning capacitor is set on the partition plate, utilizing the structural space of the partition plate to achieve the integration of the tuning function without occupying additional space in the winding slot.

[0026] Optionally, the non-magnetic insulating material is an epoxy glass fiber composite material, and the excitation coil is wound with multi-strand Litz wire.

[0027] By adopting the above technical solutions, epoxy glass fiber composite materials possess high mechanical strength, excellent electrical insulation, and low dielectric loss characteristics, making them suitable as materials for ring-shaped skeletons. Multi-strand Litz wire, composed of multiple strands of fine-diameter enameled copper wire, can reduce the skin effect and proximity effect at high frequencies, lower AC resistance, and reduce copper loss.

[0028] Optionally, a heat-conducting layer is provided in the winding groove, the heat-conducting layer covering the winding segment and filling the gap between the winding segment and the magnetic layer.

[0029] By adopting the above technical solution, the heat-conducting layer covers the winding segment and fills the gap between the winding segment and the magnetic layer, eliminating the air gap between the winding segment and the magnetic layer, reducing contact thermal resistance, and enabling the heat generated by the winding segment to be effectively conducted to the magnetic layer and the partition plate. At the same time, after the heat-conducting layer is cured, it enhances the overall rigidity of the antenna's internal structure and improves the antenna's vibration resistance.

[0030] In summary, this application includes at least one of the following beneficial technical effects:

[0031] 1. The magnetic layer is set on the inner wall of the winding slot and forms a surrounding magnetic circuit around the winding slot. It surrounds the segment from multiple directions, reducing the demagnetization factor, improving the effective magnetic permeability, realizing the miniaturization of the antenna, and achieving controllable electromagnetic radiation through the air gap.

[0032] 2. The gradient transition region on both sides of the air gap gradually reduces the thickness of the vertical section, realizing a gradual transition of magnetic permeability, reducing the magnetic flux concentration phenomenon at the edge of the air gap, reducing the risk of local magnetic saturation, and helping to improve the uniformity of the radiation field distribution.

[0033] 3. Through the cooperation of the first and second heat-conducting components, a heat dissipation path that runs parallel to the axial and radial directions is formed, which improves the heat conduction efficiency from the heat source to the outer shell of the frame. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the overall structure of a miniaturized low-frequency loop antenna in Embodiment 1 of this application.

[0035] Figure 2 This is a block diagram of a miniaturized low-frequency loop antenna tuning and matching system according to Embodiment 1 of this application.

[0036] Figure 3 This is a schematic diagram of the overall structure of a miniaturized low-frequency loop antenna in Embodiment 2 of this application.

[0037] Figure 4 It is along Figure 3 A cross-sectional view along line AA in the middle.

[0038] Figure 5 It is along Figure 3 A cross-sectional view along the BB line.

[0039] Figure 6 yes Figure 5 A magnified view of a section at point C.

[0040] Explanation of reference numerals in the attached figures:

[0041] 1. Annular frame; 11. Annular winding cavity; 12. Partition plate; 121. Heat conduction hole; 13. Winding groove; 14. Heat dissipation assembly; 141. First heat conduction component; 142. Second heat conduction component; 15. Heat conduction layer; 16. Tuning capacitor; 2. Excitation coil; 21. Winding section; 3. Magnetic layer; 31. Horizontal section; 32. Vertical section; 33. Air gap; 34. Non-magnetic pad; 35. Gradient transition zone. Detailed Implementation

[0042] The following is in conjunction with the appendix Figure 1-6 This application will be described in further detail.

[0043] This application discloses a miniaturized low-frequency loop antenna.

[0044] It should be noted that, in the description of this invention, the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0045] Example 1: Refer to Figure 1 and Figure 2 A miniaturized low-frequency loop antenna includes a loop frame 1 and an excitation coil 2.

[0046] The ring frame 1 is made of epoxy glass fiber composite material (FR4). Epoxy glass fiber composite material is a non-magnetic insulating material with the following characteristics: high mechanical strength, providing robust support for the precision coils bound to it and preventing coil deformation or loosening due to vibration; low coefficient of thermal expansion, ensuring dimensional stability at different temperatures and guaranteeing the stability of antenna inductance parameters; excellent electrical insulation, reliably isolating multi-layer, multi-turn coils and preventing inter-turn short circuits; strong environmental adaptability, not easily damaged, and able to withstand greater stress and vibration, far superior to ferrite materials.

[0047] In this embodiment, the outer diameter of the annular frame 1 is 54 cm, the inner diameter is 50 cm, and the axial height is 8 cm. An annular winding cavity 11 is formed on the annular frame 1. The annular winding cavity 11 is an annular cavity extending circumferentially along the annular frame 1 and is used to accommodate the excitation coil 2.

[0048] The excitation coil 2 is directly wound inside the annular winding cavity 11, and the excitation coil 2 is uniformly wound 12 turns on the annular frame 1. Through calculation and actual measurement, the inductance of this design at an operating frequency of 18kHz is approximately 125μH.

[0049] The excitation coil 2 is wound with Litz wire with a cross-sectional area of ​​20 mm². Under high power conditions, the larger cross-sectional area of ​​the wire can effectively reduce resistance, reduce ohmic losses, and avoid wire overheating and resonant frequency shift.

[0050] A loop antenna typically operates at its resonant frequency. To achieve resonant operation, a tuning and matching system is required. This system includes a signal generator, a signal processing unit, a power amplifier, matching capacitors, and the antenna itself.

[0051] The signal generator produces a radio frequency signal at the target frequency. The signal processing unit modulates, filters, amplifies, or shapes the signal to carry information and meet transmission requirements. The power amplifier significantly increases the signal power, enabling it to be effectively radiated through the antenna.

[0052] The matching capacitor and the antenna's inherent inductance form an LC resonant circuit, ensuring the antenna resonates at the operating frequency. This also achieves impedance matching between the power amplifier and the antenna, guaranteeing maximum power transmission. The antenna converts high-frequency electrical signals into electromagnetic waves that radiate into space. The system also includes a low-voltage power supply and a high-voltage power supply. The low-voltage power supply powers the small-signal circuits for signal generation and processing, while the high-voltage power supply provides a higher operating voltage for the power amplifier to meet high-power output requirements.

[0053] The resonant frequency is determined by the following formula:

[0054]

[0055] Calculations show that when the operating frequency is 18kHz and the inductance is 125μH, a matching capacitor of approximately 0.625μF needs to be connected in series. To adjust the resonant frequency, the capacitance of the matching capacitor can be changed: increasing the capacitance lowers the resonant frequency; decreasing the capacitance increases the resonant frequency. Through this tuning and matching system, the low-frequency electrical signal undergoes a series of processing steps and is ultimately converted into electromagnetic waves for effective radiation. The matching capacitor is a crucial component for adjusting the antenna's resonant frequency and ensuring the system's efficient operation.

[0056] The implementation principle of a miniaturized low-frequency loop antenna according to an embodiment of this application is as follows: When an alternating current is input to the excitation coil 2 through a tuning and matching system, the excitation coil 2 generates an alternating magnetic field. The matching capacitor and the inductance of the excitation coil 2 form an LC resonant circuit, which increases the current amplitude in the excitation coil 2 at the resonant frequency, thereby enhancing the magnetic field strength and radiation efficiency. The non-magnetic insulating material of the loop frame 1 provides stable mechanical support and electrical insulation, ensuring reliable operation of the antenna under various environmental conditions.

[0057] In this embodiment, the ring frame 1 is made of epoxy glass fiber composite material, which avoids the sharp increase in eddy current loss and hysteresis loss of the ferrite core at high frequencies, cuts off the macroscopic eddy current path, and greatly reduces the overall loss. This design achieves decoupling between antenna size and operating frequency, enabling an antenna with a diameter of about 50 cm to operate in the low frequency range of 10 kHz to 30 kHz, solving the problem of large size faced by traditional low frequency transmission systems.

[0058] Example 2: Refer to Figure 3 and Figure 4The difference between this embodiment and embodiment 1 is that it also includes a magnetic layer 3, and a number of partition plates 12 are provided on the annular frame 1 at intervals along the axial direction to improve the effective magnetic permeability and equivalent magnetic dipole moment of the antenna, thereby further enhancing the radiation performance of the antenna.

[0059] A closed annular winding cavity 11 is formed on the annular frame 1 around its own axis. A partition plate 12 is coaxially disposed within the annular winding cavity 11, dividing it into multiple winding slots 13 arranged axially. In this embodiment, three partition plates 12 are provided, evenly dividing the annular winding cavity 11 into four winding slots 13. A wire-passing channel is provided on the partition plate 12, and adjacent winding slots 13 are connected through the wire-passing channel. In other embodiments, the number of partition plates 12 can be adjusted according to actual needs, for example, one, two, four, or more partition plates 12 can be provided.

[0060] The number of magnetic layers 3 is equal to the number of winding slots 13, and each magnetic layer 3 is disposed on the inner wall of a corresponding winding slot 13, and each magnetic layer 3 forms a surrounding magnetic circuit around the corresponding winding slot 13.

[0061] In this embodiment, the magnetic layer 3 is made of a stack of nanocrystalline soft magnetic alloy thin strips, that is, multiple nanocrystalline soft magnetic alloy thin strips are stacked sequentially and fixed with an adhesive to form a magnetic layer 3 with a certain thickness. The stacked structure helps to reduce eddy current losses in the thin strips.

[0062] The typical composition of nanocrystalline soft magnetic alloy strips is an iron-silicon-boron-copper-niobium alloy, obtained through amorphous rapid quenching and subsequent nanocrystalline annealing. Nanocrystalline soft magnetic alloy strips possess the following key performance characteristics: high initial permeability, exceeding 80,000; high saturation magnetic flux density, approximately 1.24 Tesla, far exceeding the 0.3 to 0.5 Tesla of traditional manganese-zinc ferrites; lower core loss than ferrites; and excellent flexibility, capable of bending and adhering to the surface of a framework without breakage, exhibiting significantly better impact and vibration resistance than ferrites.

[0063] In other embodiments, the magnetic layer 3 can also be made of a stack of iron-based amorphous alloy strips, which also have high magnetic permeability, good flexibility and high saturation magnetic flux density.

[0064] The magnetic layer 3 includes a horizontal section 31 and a vertical section 32. The horizontal section 31 is disposed on the inner walls of the winding groove 13 on both sides along the axial direction of the annular frame 1, that is, the inner walls of the top and bottom surfaces of the winding groove 13. The vertical section 32 is disposed on the inner walls of the winding groove 13 on both sides in the radial direction, that is, the inner walls of the inner diameter surface and the inner walls of the outer diameter surface of the winding groove 13. The horizontal section 31 and the vertical section 32 are connected end to end to form a surrounding magnetic circuit.

[0065] It should be noted that in this embodiment, the description is based on the example of the ring skeleton 1 being placed vertically. The horizontal segment 31 refers to the magnetic layer segment extending perpendicular to the axis, and the vertical segment 32 refers to the magnetic layer segment extending parallel to the axis.

[0066] The specific connection method can be: the end of the horizontal segment 31 extends to the top or bottom of the end face of the vertical segment 32 to form an overlap, or the ends of the horizontal segment 31 and the vertical segment 32 are connected to each other. The overlap method helps to ensure the continuity of the magnetic circuit at the corner and reduce the magnetic resistance at the corner.

[0067] In this embodiment, the stacking thickness of the vertical segment 32 is greater than that of the horizontal segment 31. Since the circumference of the inner wall of the loop antenna is smaller than that of the outer wall, the magnetic flux density at the inner wall is higher under the same magnetic flux, making it easier to reach magnetic saturation first. The vertical segment 32 is located on both radial sides of the winding slot 13, and its cross-sectional area is limited by the axial height and stacking thickness of the winding slot 13. Designing the stacking thickness of the vertical segment 32 to be greater than that of the horizontal segment 31 increases the magnetic circuit cross-sectional area of ​​the vertical segment 32 and reduces the magnetic flux density at the vertical segment 32. The horizontal segment 31 is located on both axial sides of the winding slot 13, and its radial width is larger, which can compensate for the insufficient thickness. This differentiated thickness design makes the magnetic flux density at various points along the entire surrounding magnetic circuit more uniform, avoiding local magnetic saturation and improving the antenna's power capacity and operational stability.

[0068] Reference Figure 5 and Figure 6 An air gap 33 is provided on the vertical section 32, preferably on the side of the circumferential outer wall of the vertical section 32. The circumferential outer wall faces the external space of the antenna, and the radiation window is unobstructed, which is conducive to the leakage of magnetic flux into the external space and the formation of far-field radiation. In other embodiments, the air gap 33 may also be provided on the side of the circumferential inner wall of the vertical section 32, or air gaps 33 may be provided on both the circumferential inner wall and the circumferential outer wall of the vertical section 32.

[0069] Multiple air gaps 33 are provided, and the multiple air gaps 33 are evenly distributed along the circumference of the annular frame 1. In this embodiment, four air gaps 33 are provided. The four air gaps 33 are evenly distributed to maintain the symmetry of the surrounding magnetic circuit, avoid the magnetic flux distribution deviation, and enable the antenna to obtain an approximately omnidirectional radiation pattern in the horizontal plane. Distributing the total air gap width across multiple locations reduces the concentration of magnetic flux density at each air gap. In other embodiments, the number of air gaps 33 may also be two, three, six, or other numbers.

[0070] In a completely closed magnetic circuit, all magnetic flux is confined within the high-permeability magnetic layer 3, resulting in a weak magnetic field outside the core, making effective far-field radiation difficult to generate. When an air gap 33 is provided on the vertical section 32, the magnetic flux is forced to leave the high-permeability magnetic layer 3 at the air gap 33 and enter the low-permeability air or non-magnetic medium. At the air gap 33, the magnetic field lines are no longer confined within the narrow cross-section of the core but instead diffuse outwards, forming a leakage magnetic field component extending into free space. When an alternating current is passed through the excitation coil 2, these time-varying magnetic fields leaking into free space will induce an electric field, thereby generating electromagnetic waves that propagate outwards, achieving energy radiation.

[0071] The air gap 33 is filled with a non-magnetic gasket 34. The non-magnetic gasket 34 can be made of polytetrafluoroethylene, alumina ceramic sheet, or other non-magnetic materials with low dielectric constant. The non-magnetic gasket 34 maintains the precise spacing and structural stability of the air gap 33, while preventing mechanical deformation at the air gap 33.

[0072] Reference Figure 4 and Figure 6 A gradient transition region 35 is provided on both sides of each air gap 33. The thickness of the vertical section 32 within the gradient transition region 35 gradually decreases along the direction close to the air gap 33. Since the thickness of the magnetic layer 3 is positively correlated with the equivalent permeability at that location, the gradual decrease in thickness achieves a gradual transition of permeability from the high value of the magnetic core to the low value of the air gap. This effectively avoids abrupt changes in permeability at the boundary of the air gap 33, reduces the risk of local magnetic saturation, makes the spatial distribution of the leakage magnetic field smoother, and helps to improve the uniformity of the far-field radiation pattern. At the same time, it helps to reduce eddy current losses at the edge of the magnetic core.

[0073] In this embodiment, the gradient transition region 35 is implemented as follows: the vertical segment 32 is composed of multiple layers of nanocrystalline soft magnetic alloy thin strips. Within the gradient transition region 35, along the direction close to the air gap 33, the length of each layer of nanocrystalline soft magnetic alloy thin strips gradually decreases, so that the total thickness of the stack decreases in a step-like manner. The more steps there are, the closer it is to a continuous gradient effect, and it can be flexibly adjusted according to manufacturing precision requirements.

[0074] The excitation coil 2 includes multiple winding segments 21, the number of which is equal to the number of winding slots 13. Each winding segment 21 is wound in a corresponding winding slot 13 and located within the surrounding magnetic circuit. Adjacent winding segments 21 are electrically connected in series through connecting wires passing through the wire passage.

[0075] In this embodiment, the excitation coil 2 is wound with multi-strand Litz wire. Litz wire is composed of multiple strands of fine-diameter enameled copper wire, which can reduce the skin effect and proximity effect under high-frequency operation, lower AC resistance, and reduce copper losses. The total cross-sectional area of ​​the multi-strand Litz wire is 15mm² to 25mm², achieving a balance between conductivity and space occupation in the winding slot 13, ensuring sufficient current carrying capacity without excessively occupying the limited space of the winding slot 13.

[0076] Unlike the excitation coil 2 in Embodiment 1, in this embodiment, the excitation coil 2 is divided into multiple winding segments 21 by the partition plate 12 and wound in each winding slot 13. Segmented winding has the following advantages compared with concentrated winding: it reduces the potential difference between adjacent turns and improves insulation reliability; it makes the magnetic flux distribution in the annular winding cavity 11 more uniform; and it shortens the distance from each coil segment to the nearest heat dissipation channel, which is beneficial for heat dissipation.

[0077] A heat-conducting hole 121 is axially through-hole on the partition plate 12. A heat dissipation assembly 14 is provided on the partition plate 12, which includes a first heat-conducting element 141 and a second heat-conducting element 142. The first heat-conducting element 141 is inserted into the heat-conducting hole 121. In this embodiment, the first heat-conducting element 141 is a copper pillar or a copper through hole, with its two ends extending into the winding grooves 13 on both sides of the partition plate 12. The first heat-conducting element 141 conducts heat axially, transferring the heat generated by the winding segment 21 to the upper and lower sides of the annular frame 1. Multiple heat-conducting holes 121 can be distributed radially and circumferentially along the partition plate 12, and correspondingly, multiple first heat-conducting elements 141 are also provided.

[0078] The second heat-conducting element 142 is radially embedded in the partition plate 12 and connected to the first heat-conducting element 141. In this embodiment, the second heat-conducting element 142 is a copper strip or a micro heat pipe, which extends radially, with its two ends extending to the outer and inner circumferential walls of the annular frame 1, respectively. The second heat-conducting element 142 conducts heat radially to both the inner and outer sides of the annular frame 1. Multiple second heat-conducting elements 142 can be distributed circumferentially along the partition plate 12.

[0079] The first heat-conducting element 141 and the second heat-conducting element 142 are interconnected, forming a heat dissipation path that is parallel in both the axial and radial directions. The second heat-conducting element 142 extends radially and is approximately orthogonal to the main flow direction (circumferential direction) of the magnetic flux, which helps to reduce eddy current losses in the second heat-conducting element 142.

[0080] A thermally conductive layer 15 is disposed within the winding groove 13. The thermally conductive layer 15 covers the winding segment 21 and fills the gap between the winding segment 21 and the magnetic layer 3. The thermally conductive layer 15 can be made of a thermally conductive potting compound, such as thermally conductive silicone. The thermally conductive potting compound is liquid during potting, which can fully fill the irregular gap between the winding segment 21 and the magnetic layer 3, and forms a solid thermally conductive layer 15 after curing.

[0081] The thermally conductive layer 15 eliminates the air gap between the winding section 21 and the magnetic layer 3, reducing contact thermal resistance and allowing the heat generated by the winding section 21 to be more effectively conducted to the magnetic layer 3 and the partition plate 12. Simultaneously, after curing, the thermally conductive layer 15 enhances the overall rigidity of the antenna's internal structure and improves its vibration resistance. The thermal conductivity of the thermally conductive layer 15 is preferably not less than 1.5 Kelvin per meter, and the dielectric strength is preferably not less than 15 kV per millimeter to ensure good thermal conductivity and electrical insulation performance.

[0082] A tuning capacitor 16 is connected in series on the connecting wire between two adjacent winding segments 21. The tuning capacitor 16 is disposed on the partition plate 12. In this embodiment, the tuning capacitor 16 is a surface-mount high-voltage ceramic capacitor, which is fixed to the surface of the partition plate 12 by welding, and its two leads are respectively welded to the connecting wire of the two adjacent winding segments 21. The partition plate 12 is provided with a groove for mounting the tuning capacitor 16, and the depth of the groove matches the thickness of the tuning capacitor 16 so that the tuning capacitor 16 is embedded in the groove and does not protrude from the surface of the partition plate 12.

[0083] The tuning capacitor 16 and the inductance of the excitation coil 2 form a resonant circuit. By selecting a suitable capacitance value for the tuning capacitor 16, the resonant frequency of the resonant circuit can be matched with the target operating frequency of the antenna. In the resonant state, the current amplitude in the excitation coil 2 increases, thereby enhancing the magnetic flux and leakage magnetic field strength, and improving the radiation efficiency of the antenna. Compared with the method in Embodiment 1 where the matching capacitor is placed in an external matching circuit, this embodiment integrates the tuning capacitor 16 on the partition plate 12, realizing the integration of the tuning function, without occupying additional space in the winding slot 13, and shortening the connection path between the capacitor and the coil, thus reducing the influence of parasitic inductance.

[0084] The antenna in this embodiment can adopt a closed structure, making it suitable for harsh environments such as underwater and underground. Internal heat is primarily dissipated through solid-state heat conduction paths. These heat dissipation paths include:

[0085] The first-stage heat dissipation path is from the heat source to the partition plate 12. The Joule heat generated when the winding section 21 is working is conducted through the heat-conducting layer 15 to the partition plate 12 and the magnetic layer 3 that are in contact with it.

[0086] The second-level heat dissipation path involves axial and radial conduction within the partition plate 12. After entering the partition plate 12, heat is conducted axially to the upper and lower sides of the annular frame 1 via the first heat-conducting element 141, and simultaneously radially to the outer and inner circumferential walls of the annular frame 1 via the second heat-conducting element 142. These two parallel heat dissipation paths improve the thermal conductivity from the heat source to the frame shell.

[0087] The third-level heat dissipation path is from the frame shell to the external environment. The heat collected on the outer wall of the annular frame 1 exchanges heat with the external environment through the outer surface of the frame. Depending on the application scenario, heat dissipation fins can be installed on the outer surface of the annular frame 1 to enhance heat dissipation, or the annular frame 1 can be attached to the cold plate of the equipment platform for conduction heat dissipation.

[0088] The implementation principle of Example 2 is as follows: When the radio frequency power source inputs alternating current to the excitation coil 2, each winding segment 21 generates an alternating magnetic field in its corresponding winding slot 13. The alternating magnetic field excites alternating magnetic flux in the magnetic layer 3. The magnetic flux circulates along the surrounding magnetic circuit, passing sequentially through the horizontal segment 31 and the vertical segment 32, forming a closed magnetic flux loop. The magnetic layer 3 constrains the magnetic flux from four directions—axial and radial—concentrating the magnetic flux within the surrounding magnetic circuit.

[0089] When the magnetic flux flows through the air gap 33 on the vertical section 32, it is forced to leave the high-permeability magnetic layer 3 and enter the low-permeability air medium. Magnetic field lines diffuse at the air gap, and a portion of the flux leaks into the free space outside the antenna as a leakage magnetic field. Within the gradient transition region 35 on both sides of the air gap 33, the magnetic flux gradually transitions from the magnetic core into space. The time-varying leakage magnetic field induces an electric field in the free space, which in turn induces a magnetic field, generating and propagating outwards alternately to form electromagnetic wave radiation.

[0090] The tuning capacitor 16 is connected in series on the connecting wire between adjacent winding sections 21, forming an LC resonant circuit with the inductance of the excitation coil 2. When the frequency of the input signal matches the resonant frequency, the current amplitude in the resonant circuit reaches its maximum value, the alternating current flowing through the excitation coil 2 increases, the magnetic flux in the surrounding magnetic circuit increases accordingly, and the leakage magnetic field strength leaking into free space at the air gap 33 also increases.

[0091] During continuous antenna operation, alternating current flowing through winding section 21 generates Joule heat, and alternating magnetic flux in magnetic layer 3 generates core loss heat. The heat is conducted through thermally conductive layer 15 to partition plate 12 and magnetic layer 3, and then conducted axially through first thermally conductive element 141 and radially through second thermally conductive element 142 on partition plate 12, finally converging on the outer wall of annular frame 1 and dissipating into the external environment.

[0092] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A miniaturized low-frequency loop antenna, characterized in that, include: An annular frame (1) is made of non-magnetic insulating material. An annular winding cavity (11) is formed on the annular frame (1). Several partition plates (12) are spaced apart along the axial direction on the annular frame (1). The partition plates (12) are coaxially arranged in the annular winding cavity (11). The partition plates (12) divide the annular winding cavity (11) into multiple winding slots (13) arranged along the axial direction. A wire passage is opened on the partition plate (12). Adjacent winding slots (13) are connected through the wire passage. The number of magnetic layers (3) is equal to that of the winding grooves (13). One magnetic layer (3) is disposed on the inner wall of one winding groove (13). The magnetic layer (3) forms a surrounding magnetic circuit with an air gap (33) along the cross-sectional direction of the winding groove (13). The excitation coil (2) includes winding segments (21), the number of which is equal to the number of winding slots (13). One winding segment (21) is wound in a corresponding winding slot (13) and located in the surrounding magnetic circuit. Adjacent winding segments (21) are electrically connected in series through connecting wires passing through the wire passage.

2. The miniaturized low-frequency loop antenna according to claim 1, characterized in that: The magnetic layer (3) includes a horizontal section (31) and a vertical section (32). The horizontal section (31) is disposed on the inner wall of the winding groove (13) on both sides of the axial direction of the annular skeleton (1). The vertical section (32) is disposed on the inner wall of the winding groove (13) on both sides of the radial direction. The horizontal section (31) and the vertical section (32) are connected end to end to form the surrounding magnetic circuit. The air gap (33) is disposed on the vertical section (32).

3. The miniaturized low-frequency loop antenna according to claim 2, characterized in that: The magnetic layer (3) is made of nanocrystalline soft magnetic alloy thin strip stacks, and the stack thickness of the vertical section (32) is greater than the stack thickness of the horizontal section (31).

4. The miniaturized low-frequency loop antenna according to claim 2, characterized in that: The number of air gaps (33) on each vertical segment (32) is multiple, and the multiple air gaps (33) are evenly distributed along the circumference of the annular skeleton (1). The air gaps (33) are filled with non-magnetic gaskets (34).

5. The miniaturized low-frequency loop antenna according to claim 2, characterized in that: The air gap (33) is provided with gradient transition zones (35) on both sides, and the thickness of the vertical section (32) in the gradient transition zone (35) gradually decreases along the direction close to the air gap (33).

6. The miniaturized low-frequency loop antenna according to claim 1, characterized in that: The partition plate (12) is provided with a heat dissipation component (14), and the two ends of the heat dissipation component (14) extend into the two adjacent winding grooves (13).

7. The miniaturized low-frequency loop antenna according to claim 6, characterized in that: The partition plate (12) has a heat conduction hole (121) through it along the axial direction. The heat dissipation assembly (14) includes a first heat conduction element (141) and a second heat conduction element (142). The first heat conduction element (141) is inserted into the heat conduction hole (121). The second heat conduction element (142) is embedded in the partition plate (12) along the radial direction and connected to the first heat conduction element (141). The two ends of the second heat conduction element (142) extend to the outer circumferential wall and the inner circumferential wall of the annular skeleton (1), respectively.

8. The miniaturized low-frequency loop antenna according to claim 1, characterized in that: A tuning capacitor (16) is connected in series on the connecting wire between two adjacent winding segments (21), and the tuning capacitor (16) is disposed on the partition plate (12).

9. The miniaturized low-frequency loop antenna according to claim 1, characterized in that: The non-magnetic insulating material is epoxy glass fiber composite material, and the excitation coil (2) is wound with multi-strand Litz wire.

10. The miniaturized low-frequency loop antenna according to claim 1, characterized in that: A heat-conducting layer (15) is provided in the winding groove (13). The heat-conducting layer (15) covers the winding section (21) and fills the gap between the winding section (21) and the magnetic layer (3).

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