Self-driven wireless magnetic sensing device based on friction nanogenerator

Abstract

The application provides a self-driven wireless magnetic sensing device based on friction nanogenerator, which comprises a non-magnetic aluminum alloy shell, a friction nanogenerating unit, a magnetostrictive driving unit and a tip discharge wireless transmitting unit. Under the excitation of environmental vibration, electrostatic charges are output and continuously accumulated. The magnetostrictive rod produces displacement corresponding to the magnetic field strength under the action of the external measured magnetic field, and the displacement drives the movement of the movable electrode through the elastic connecting piece. When the tip electric field strength reaches the breakdown threshold, tip discharge occurs. The external receiving end captures the electromagnetic wave signal through the LC resonant receiving circuit and demodulates the external magnetic field strength information, and simultaneously realizes wireless energy extraction through the rectification power supply circuit. The application does not need external power supply, uses environmental vibration energy as the self-driven source, and uses the external magnetic field strength as the sensing object, thereby realizing integrated integration and being suitable for power system remote node monitoring, ocean magnetic field detection and industrial field wireless magnetic field sensing and the like.

Description

Technical Field

[0001] This invention relates to the field of wireless sensing technology, and more specifically to a self-driven wireless magnetic sensing device based on triboelectric nanogenerator. Background Technology

[0002] Wireless magnetic field sensing and signal transmission technologies have wide applications in fields such as industrial IoT, structural health monitoring, marine exploration, and intelligent transportation. In typical scenarios such as remote node monitoring of power systems, bridge structural health sensing, and marine buoy data acquisition, sensor nodes are often distributed in remote locations or complex working environments, making wiring difficult and maintenance costs high, thus creating an urgent need for wireless self-powered magnetic field sensing systems.

[0003] Currently, most mainstream wireless sensing and power transmission solutions rely on batteries or wired power supplies. Battery power supply has several significant drawbacks: battery replacement and maintenance costs are high, and frequent maintenance in remote areas or complex operating conditions is not only labor-intensive and resource-intensive but also poses certain safety hazards; when the battery is depleted, node failure is likely to occur, and for critical monitoring nodes that need to operate continuously, the reliability of power supply cannot be guaranteed; the heavy metal pollution caused by discarded batteries is also inconsistent with the needs of the era of green development.

[0004] In magnetic field sensing, existing solutions typically employ active devices such as Hall effect sensors, fluxgate sensors, or magnetoresistive sensors. These require independent power supply units, signal conditioning circuits, and wireless RF transceiver modules, resulting in high system complexity and power consumption, making it difficult to achieve true self-drive and self-powering. Furthermore, traditional analog signals are susceptible to noise interference during long-distance wireless transmission, affecting the accuracy of magnetic field signal resolution at the receiving end.

[0005] Triboelectric nanogenerator (TNT), as an emerging technology that directly converts environmental mechanical vibration energy into electrical energy, has shown great potential in the field of self-powered sensing systems. However, existing wireless transmission schemes based on TNT still require additional signal modulation modules, resulting in limited system integration. How to organically integrate TNT, magnetostrictive magnetic field sensing, and wireless signal transmission to achieve a compact, integrated wireless magnetic field sensing and signal transmission device that requires no external power supply is a pressing technical problem in this field. To address the shortcomings of the existing technologies, this invention proposes a self-driven wireless magnetic sensing device based on TNT, organically integrating TNT, magnetostrictive magnetic field sensing, and tip discharge wireless transmission technologies. It uses environmental vibration energy as the self-powered energy source and the measured external magnetic field strength as the sensing object. Through the magnetostrictive effect, the magnetic field strength is converted into mechanical displacement, which then modulates the discharge gap and the electromagnetic wave resonant frequency, achieving passive wireless sensing of the external magnetic field. This provides a new solution to the aforementioned technical challenges. Summary of the Invention

[0006] To achieve the above objectives, this invention proposes a self-driven wireless magnetic sensing device based on triboelectric nanogenerators, comprising: The non-magnetic aluminum alloy shell has an electromagnetic wave radiation window, and all functional units are located inside the shell. The non-magnetic aluminum alloy shell is filled with dry nitrogen or inert gas. The triboelectric nanogenerator unit includes a vertically stacked mass block, an upper friction layer, a lower friction layer, and a spring. The upper friction layer is composed of an upper plate, an upper copper foil, and a fluorinated ethylene propylene film stacked sequentially from top to bottom. The lower friction layer is composed of a lower copper foil, a substrate, and a lower plate stacked sequentially from top to bottom. The lower plate is fixed to the bottom plate of the outer shell. The spring is vertically arranged, with its lower end connected to the lower plate and its upper end connected to the upper plate to support the mass block. The mass block is located above the upper friction layer, and the upper and lower friction layers are arranged facing each other. Under the excitation of external environmental vibration, the mass block forms a continuous contact-separation reciprocating motion with the help of the restoring force of the spring, causing the upper and lower friction layers to periodically generate static electricity and continuously output electrostatic charge. A magnetostrictive drive unit includes a magnetostrictive rod, a fixed base, and an elastic connector. The fixed base is fixed to the outer shell plate. The magnetostrictive rod is fixed by the fixed base, with one end near the triboelectric nanogenerator unit being the fixed end and the other end away from the triboelectric nanogenerator unit being the free end. One end of the elastic connector is fixedly connected to the free end of the magnetostrictive rod. Under the action of an external measured magnetic field, the magnetostrictive rod generates an axial elongation displacement corresponding to the magnetic field strength, and outputs this displacement through the elastic connector. A tip discharge wireless transmitting unit includes a horizontally opposite movable electrode and a reference electrode. The reference electrode is fixedly connected to the inner wall of the housing by a fixing block. The other end of the movable electrode is fixedly connected to the elastic connector, and its tip is opposite to the tip of the reference electrode, forming an adjustable discharge gap between the two electrode tips. The elastic connector transmits the axial elongation displacement of the magnetostrictive rod to the movable electrode to change the discharge gap; The charge accumulation circuit guides the electrostatic charge generated by the triboelectric nanogenerator unit to the active electrode and the reference electrode through wires for continuous accumulation. When the tip electric field strength reaches the breakdown threshold, tip discharge occurs, and the excited electromagnetic wave is radiated outward through the electromagnetic wave radiation window. The external receiver receives the electromagnetic waves and performs energy extraction and frequency signal demodulation.

[0007] Furthermore, in the upper friction layer, the fluorinated ethylene propylene film is located at the bottom layer and faces the lower friction layer, the upper copper foil is stacked on top of the fluorinated ethylene propylene film, and the upper plate is located at the top layer and is fixedly connected to the bottom surface of the mass block; In the lower friction layer, the lower copper foil is located on the uppermost layer and is opposite to the fluorinated ethylene propylene film. The substrate layer is stacked below the lower copper foil, and the lower plate is located on the lowermost layer and is fixed to the bottom plate of the outer casing. The lower copper foil also serves as a charge collection electrode and is electrically connected to the charge accumulation circuit. The mass of the mass block ranges from 1 to 5 g; the spring constant is 0.5 to 2 N / mm.

[0008] Furthermore, the charge accumulation circuit includes a rectifier module and a charge accumulation circuit. The rectifier module is electrically connected to the lower copper foil and the upper copper foil, respectively. After rectifying the alternating pulse current output by the triboelectric nanogenerator, the electrostatic charge is guided by the charge accumulation circuit to the active electrode and the reference electrode via wires, so that the charge on the two electrodes continues to accumulate.

[0009] Furthermore, the elastic connector is made of polytetrafluoroethylene (PTFE), with one end fixedly connected to the free end of the magnetostrictive rod and the other end fixedly connected to the movable electrode, so as to convert the axial elongation displacement of the magnetostrictive rod into the displacement of the movable electrode in the horizontal direction toward or away from the reference electrode; the magnetostrictive rod is made of terbium-dysprosium iron, and its length change ∆L satisfies the following condition with respect to the external measured magnetic field strength H: ; Where λs is the saturation magnetostriction coefficient, L is the initial length of the magnetostrictive rod, and H0 is the characteristic field strength.

[0010] Furthermore, both the active electrode and the reference electrode are needle-shaped electrodes with a tip curvature radius of 5–20 micrometers; the tips of the active electrode and the reference electrode are arranged opposite each other along the normal direction of the electromagnetic wave radiation window, and the discharge gap between the two tips is continuously adjusted within the range of 10–200 micrometers according to the strength of the external measured magnetic field; the electromagnetic wave resonant frequency corresponding to the discharge gap adjustment is tuned within the range of 10–40 MHz, with a tuning accuracy better than 1 MHz.

[0011] Furthermore, the resonant frequency of the electromagnetic wave The electrode spacing d satisfies the following mapping relationship: ; Where c is the speed of light. The equivalent dielectric constant is the discharge environment between the two electrodes; the resonant frequency f is negatively correlated with the electrode spacing d, that is, the resonant frequency f decreases when the spacing d increases, and the resonant frequency f increases when the spacing d decreases; the equivalent dielectric constant εeff is determined by the dielectric properties of the gas filling the shell and the inter-electrode medium between the two electrodes.

[0012] Furthermore, the external receiving end includes an LC resonant receiving circuit and a rectifier power supply circuit; the resonant frequency of the LC resonant receiving circuit matches the frequency of the electromagnetic wave emitted by the tip discharge wireless transmitting unit, and electromagnetically couples with the electromagnetic wave through an inductor coil to capture the electromagnetic wave pulse signal and demodulate the signal through frequency feature identification; the rectifier power supply circuit is connected to the output terminal of the LC resonant receiving circuit, and supplies power to the load after collecting induced charge, rectifying and stabilizing the electromagnetic wave energy.

[0013] Furthermore, the two ends of the spring are respectively fixedly connected to the upper surface of the lower plate and the lower surface of the mass block. The natural frequency of the spring-mass block structure is matched with the dominant frequency of the ambient vibration in the range of 0.1 to 200 Hz by adjusting the elastic coefficient of the spring or the mass of the mass block. When the spring-mass block structure resonates, the contact-separation motion amplitude between the upper and lower friction layers is the largest, and the charge density per unit area generated by triboelectric charging is 10 to 50 μC / m².

[0014] Furthermore, the outer shell is a closed shell made of non-magnetic aluminum alloy material, the electromagnetic wave radiation window is opened on the side wall of the outer shell facing the tip of the reference electrode, and the electromagnetic wave radiation window is covered with a polytetrafluoroethylene film to achieve hermetically sealed packaging; the interior of the outer shell is filled with dry nitrogen or inert gas to prevent electrode oxidation and unintended discharge.

[0015] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention provides a self-driven wireless magnetic sensing device based on triboelectric nanogenerator. The triboelectric nanogenerator directly converts environmental vibration energy into electrical energy and continuously replenishes electrostatic charge to the tip electrode, completely eliminating the dependence on batteries or wired power sources. This fundamentally eliminates the reliability risks of system failure due to power depletion and is suitable for long-term unattended remote deployment scenarios.

[0016] 2. This invention provides a self-driven wireless magnetic sensing device based on triboelectric nanogenerators. The tip discharge directly excites electromagnetic waves to radiate outwards, eliminating the need for independent modulation circuits, RF transceiver chips and their power supply units in traditional wireless transmission schemes. This significantly reduces system complexity and power consumption, and realizes the integrated design of triboelectric nanogenerators, magnetostrictive magnetic field sensing and tip discharge wireless transmission.

[0017] 3. This invention provides a self-driven wireless magnetic sensing device based on triboelectric nanogenerators. The strength of the external magnetic field being measured is directly converted into the axial displacement of a magnetostrictive rod through the magnetostrictive effect, thereby changing the electrode spacing and the electromagnetic wave resonant frequency, and accurately mapping the magnetic field strength into a frequency-coded signal. The noise immunity of the frequency-coded signal is significantly better than that of the traditional amplitude signal, significantly improving the reliability and resolution accuracy of magnetic field sensing signal transmission in complex electromagnetic environments.

[0018] 4. This invention provides a self-driven wireless magnetic sensing device based on triboelectric nanogenerator. The natural frequency of the spring-mass structure can be flexibly adjusted within the range of 0.1 to 200 Hz by adjusting the spring parameters or the mass of the mass block to match the main vibration frequency of different environments such as machine tool vibration, ocean wave fluctuations, road surface excitation, and bridge vibration. When resonance occurs, the triboelectric charging efficiency is significantly improved, enabling the device to maintain continuous and stable charge accumulation and tip discharge under various complex working conditions, and possessing excellent environmental adaptability.

[0019] 5. This invention provides a self-powered wireless magnetic sensing device based on triboelectric nanogenerators. The external receiver simultaneously possesses an LC resonant receiving circuit and a rectifier power supply circuit. The former is responsible for identifying and demodulating the electromagnetic wave resonant frequency, enabling wireless extraction of information on the strength of the external magnetic field being measured. The latter performs induced charge collection and voltage stabilization processing on the received electromagnetic wave energy, enabling wireless power supply to external low-power nodes. This allows the device to have the dual functions of transmitting magnetic field sensing signals and wireless energy transmission, expanding its application scope in self-powered sensing nodes such as industrial IoT, structural health monitoring, and marine exploration. Attached Figure Description

[0020] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0021] Figure 1 A schematic diagram of the structure of this invention; Figure 2 Schematic diagram of simulation results of the tip field strength changing with magnetic induction intensity in this invention Figure 3 This is a schematic diagram of the simulation results of the change of electromagnetic wave resonant frequency with magnetic induction intensity in this invention; Figure 4 This is the electromagnetic wave spectrum diagram of the tip discharge in this invention; Figure 5 This is a simulation diagram of the detection equivalent circuit in this invention; Figure 6 It is the real-time tracking response of the resonant frequency under a dynamic magnetic field; Figure 7 This is a schematic diagram of the signal transmission process in this invention; The diagram shows: 1. Non-magnetic aluminum alloy shell; 2. Spring; 3. Lower copper foil; 4. Base; 5. Lower plate; 6. Magnetostrictive rod; 7. Drive circuit; 8. Reference electrode; 9. Fixing block; 10. Charge accumulation circuit; 11. Mass block; 12. Upper plate; 13. Upper copper foil; 14. Fluorinated ethylene propylene film; 15. Movable electrode; 16. Elastic connector; 17. Fixing base; 18. Electromagnetic radiation window. Detailed Implementation

[0022] The technical solution of the present invention will be more clearly and completely explained below with reference to the accompanying drawings and through the description of preferred embodiments of the present invention.

[0023] Figure 1 This is a schematic diagram of the self-driven wireless magnetic sensing device based on triboelectric nanogenerator of the present invention. The device is entirely encapsulated in a non-magnetic aluminum alloy shell 1. One side of the shell 1 has an electromagnetic wave radiation window 18 covered with a polytetrafluoroethylene film. The interior is filled with dry nitrogen gas (dew point below -40 °C) and then sealed to maintain the stability and consistency of the tip discharge environment. The device consists of three functional parts from left to right: a triboelectric nanogenerator unit, a magnetostrictive drive unit, and a tip discharge wireless transmission unit. Each unit works in concert through mechanical and electrical connections, forming a four-level linkage mechanism of "environmental vibration excitation—triboelectric nanogenerator self-drive—external measured magnetic field driving magnetostrictive displacement output—tip discharge wireless transmission," realizing the wireless sensing and signal transmission functions of external magnetic fields.

[0024] The triboelectric nanogenerator unit is the self-powered energy source of the entire device, requiring no external power supply. It converts environmental mechanical vibration energy into electrical energy through a mechanism combining triboelectric charging and electrostatic induction, and outputs it externally in the form of electrostatic charge. The triboelectric nanogenerator unit adopts a vertical stacked structure, consisting of the following layers from top to bottom: a mass block 11 (made of stainless steel, weighing approximately 2g), an upper plate 12, an upper copper foil 13 (20 μm thick, 20 mm × 20 mm in area), and a fluorinated ethylene propylene film 14 (35 μm thick, 20 mm × 20 mm in area) forming the upper friction layer; the lower friction layer is composed of a lower copper foil 3 (80 μm thick, also serving as a charge collection electrode), a substrate 4, and a lower plate 5 stacked from top to bottom, with the lower plate 5 fixed to the bottom plate of the outer shell 1; a spring 2 (made of stainless steel, with an elastic coefficient of 1 N / mm, symmetrically arranged on both sides of the stack) is fixedly connected to the upper surface of the lower plate 5 at its lower end, and supports the lower surface of the mass block 11 at its upper end. The upper copper foil 13 and the fluorinated ethylene propylene film 14 are located at different positions in the triboelectric sequence: the upper copper foil 13 is biased towards the side that is more likely to lose electrons, while the fluorinated ethylene propylene film 14 is biased towards the side that is more likely to gain electrons. When external environmental vibration excitation acts on the device, the mass block 11 forms a continuous contact-separation reciprocating motion with the restoring force of the spring 2, driving the periodic contact-separation between the upper and lower friction layers. Electrons on the surface of the upper copper foil 13 migrate to the surface of the fluorinated ethylene propylene film (FEP) 14, eventually making the surface of the upper copper foil 13 positively charged and the surface of the fluorinated ethylene propylene film 14 negatively charged, continuously outputting electrostatic charge to the outside. The natural frequency of the spring-mass block structure can be flexibly adjusted within the range of 0.1 to 200 Hz by adjusting the parameters of spring 2 or the mass of mass block 11 to match the main vibration frequencies of different environments such as machine tool vibration (about 50 Hz), ocean wave fluctuations (about 0.1 to 0.25 Hz), road surface excitation (broadband), and bridge vibration (1 to 10 Hz). When resonance occurs, the charge density per unit area generated by triboelectric charging can reach 10 to 50 μC / m², providing a sufficient energy basis for subsequent charge accumulation and discharge.

[0025] The triboelectric nanogenerator unit is connected to the tip electrode via a charge accumulation circuit. The rectifier module of the charge accumulation circuit is electrically connected to the upper copper foil 13 and the lower copper foil 3, respectively. After rectifying the alternating pulse current output by the triboelectric nanogenerator unit, the electrostatic charge is guided via the charge accumulation circuit 10 to the active electrode 15 and the reference electrode 8 through wires for continuous accumulation, providing charge reserves for subsequent tip discharge. The charge accumulation circuit 10 uses polyimide material as the insulating substrate, with a volume resistivity of not less than 10¹. 6 Ω·cm can effectively prevent charge leakage and ensure the stable retention of charge on the electrode.

[0026] The magnetostrictive drive unit is the core component of the entire device, converting the external measured magnetic field into mechanical displacement output. A cylindrical terbium-dysprosium iron (Terfenol-D) magnetostrictive rod 6 is selected as the sensing and drive element. Terbium-dysprosium iron is composed of terbium, dysprosium, and iron atoms in a specific ratio, and contains a large number of magnetic domain structures. Its saturation magnetostriction coefficient λs is approximately 1500 ppm, and its characteristic field strength H0 is approximately 8 kA / m, exhibiting excellent magnetomechanical conversion characteristics. The magnetostrictive rod 6 is reliably fixed to the inner wall of the outer shell 1 by an aluminum alloy fixing base 17 with M4 screws. The end closer to the triboelectric nanogenerator unit is the fixed end, and the end farther away from the triboelectric nanogenerator unit is the free end. The elastic connector 16 is made of polytetrafluoroethylene (PTFE), with one end bonded to the free end of the magnetostrictive rod 6 and the other end bonded to the movable electrode 15. The elastic connector 16 has a length of 5 mm. Polytetrafluoroethylene (PTFE) material possesses excellent elasticity and corrosion resistance, effectively buffering the stress generated during the expansion and contraction of the magnetostrictive rod 6, preventing electrode deformation due to stress concentration, and ensuring the stability and repeatability of the discharge gap adjustment process. Under the influence of an external measured magnetic field, the magnetic domains within the magnetostrictive rod 6 align along the magnetic field direction, causing the material lattice to elongate axially. Macroscopically, this manifests as an increase in the axial length of the rod by ΔL, which is transmitted to the movable electrode 15 via the elastic connector 16. The constitutive relationship between the expansion and contraction amount ΔL of the magnetostrictive rod 6 and the strength H of the external measured magnetic field is as follows: ; Where λs is the saturation magnetostriction coefficient (taken as 1500 ppm), L is the length of the magnetostrictive rod 6, and H0 is the characteristic field strength (taken as 8 kA / m). This nonlinear hyperbolic tangent relationship indicates that the expansion and contraction increase approximately linearly in the low magnetic field range and tend to saturate in the high magnetic field range, providing a stable magnetomechanical conversion response over a wide range, with a device response time not exceeding 10 ms. The greater the external measured magnetic field strength, the greater the axial elongation of the magnetostrictive rod 6, the greater the displacement of the movable electrode 15 towards the reference electrode 8, the smaller the discharge gap, and the higher the corresponding electromagnetic wave resonant frequency, thus achieving a precise mapping of the external magnetic field strength to the frequency signal.

[0027] The tip discharge wireless transmitting unit is the core functional unit for realizing wireless magnetic field sensing and signal transmission, including a horizontally opposed movable electrode 15 and a reference electrode 8. Both the movable electrode 15 and the reference electrode 8 are made of copper, with the tip curvature radius controlled at 10 μm (±2 μm) to ensure a high concentration of the local electric field at the tip, guaranteeing the stability and repeatability of the discharge process. The movable electrode 15 is connected to the free end of the magnetostrictive rod 6 via an elastic connector 16, allowing it to undergo axial displacement according to changes in the strength of the external measured magnetic field. The reference electrode 8 is fixedly connected to the inner wall of the outer shell 1 via a polyimide insulating bracket, maintaining its position. Its tip faces the tip of the movable electrode 15, forming an adjustable discharge gap between the two electrode tips. The initial electrode spacing d0 is set to 100 μm. The elastic connector 16 transmits the axial displacement output by the magnetostrictive rod 6 to the movable electrode 15, allowing the discharge gap between the two electrodes to be continuously adjusted within the range of 10–200 μm according to the strength of the external measured magnetic field. Both the movable electrode 15 and the reference electrode 8 are prepared using an electrochemical etching method.

[0028] When the triboelectric nanogenerator continuously replenishes electrostatic charge to the active electrode 15 and the reference electrode 8 through the charge accumulation circuit 10, and the electric field strength between the tip electrodes reaches the air breakdown threshold (approximately 3 × 10⁻⁶), 6 When the voltage reaches V / m, electrical breakdown occurs between the two tips, resulting in tip discharge. The accumulated charge is rapidly released in the form of a pulse current. During the discharge process, the violent movement of the charge excites high-frequency electromagnetic waves, and its physical mechanism follows the Maxwell-Ampère equations: ; Where H is the magnetic field strength vector, J is the conduction current density vector, D=εE is the electric displacement vector, ε is the dielectric constant, and E is the electric field strength vector. dl is the displacement current density; dl is the current density along the closed loop. The line element vector dS is the surface element vector of the surface S. The transient electric field generated by the tip discharge causes a displacement current density. The dramatic changes in the displacement current term drive the radiation of high-frequency electromagnetic waves, providing the energy and signal basis for the transmission of wireless magnetic field sensing signals.

[0029] Resonant frequency of electromagnetic waves The physical mapping relationship between the electrode spacing d and the electrode is as follows: ; Where c is the speed of light. The equivalent dielectric constant of the discharge environment is given. This relationship shows that the resonant frequency is negatively correlated with the electrode spacing: when the electrode spacing d decreases from 200 μm to 10 μm, the resonant frequency increases from 10 MHz to 40 MHz, with a tuning accuracy better than 1 MHz. Since the electrode spacing is determined by the strength of the external magnetic field being measured, the electromagnetic wave resonant frequency essentially encodes the information of the external magnetic field strength, realizing a precise mapping of magnetic field parameters to frequency signals. The generated electromagnetic waves are emitted outward through the electromagnetic wave radiation window 18. The external receiver captures the electromagnetic wave pulse signal through an LC resonant receiving circuit via electromagnetic coupling, generating a peak response at the resonant frequency, identifying frequency characteristics, and demodulating the external magnetic field strength. Simultaneously, the electromagnetic wave energy is collected by induced charge and regulated through a rectifier power supply circuit, realizing wireless energy extraction. Under normal electromagnetic conditions, the effective signal transmission distance is not less than 50 m, and the response time is not more than 10 ms.

[0030] In one specific embodiment, a cylindrical terbium-dysprosium magnetostrictive rod 6 with a length L = 50 mm and a diameter of 8 mm is selected. Both ends are mechanically polished to a surface roughness Ra not exceeding 0.4 μm. The fixed end of the magnetostrictive rod 6 is reliably fixed to the inner wall of the outer casing 1 using an aluminum alloy mounting base 17 with M4 screws. One end of the elastic connector 16 is bonded and fixed to the free end of the magnetostrictive rod 6, and the other end extends through the side of the mounting base 17 and is bonded and fixed to the movable electrode 15, achieving synchronous driving of the displacement of the movable electrode 15. A copper metal tip electrode is prepared using an electrochemical etching method, controlling the tip curvature radius to be 10 μm (±2 μm). The movable electrode 15 and the reference electrode 8 are arranged horizontally opposite each other. The movable electrode 15 is connected to the elastic connector 16, and the reference electrode 8 is fixedly connected to the inner wall of the outer casing 1 via a polyimide insulating bracket. The initial electrode spacing d0 is set to 100 μm.

[0031] The triboelectric nanogenerator unit adopts a vertical stacked structure, consisting of, from top to bottom: a mass block 11 (stainless steel, approximately 2 g), an upper plate 12, an upper copper foil 13 (20 μm thick, 20 mm × 20 mm in area), and a fluorinated ethylene propylene film 14 (35 μm thick, 20 mm × 20 mm in area), forming the upper triboelectric layer; the lower triboelectric layer is composed of a lower copper foil 3 (80 μm thick, serving as a charge collection electrode), a substrate 4, and a lower plate 5 stacked sequentially from top to bottom, with the lower plate 5 fixed to the bottom plate of the outer shell 1; a spring 2 (stainless steel, elastic coefficient 1 N / mm, symmetrically arranged on both sides of the stack) is fixedly connected at its lower end to the upper surface of the lower plate 5, and its upper end supports the lower surface of the mass block 11. The upper copper foil 13 and the lower copper foil 3 are respectively connected to the rectifier module of the charge accumulation circuit through wires; after rectification, the electrostatic charge is guided by the charge accumulation circuit 10 to the active electrode 15 and the reference electrode 8 for continuous accumulation. A polyimide insulating substrate is laid between the fluorinated ethylene propylene film 14 and the lower copper foil 3, with a volume resistivity of not less than 10¹. 6 Ω·cm, ensuring no significant leakage during charge accumulation. Each unit is placed in a non-magnetic aluminum alloy casing 1, filled with dry nitrogen gas (dew point below −40 ℃), and then sealed. A 20 mm × 10 mm electromagnetic radiation window 18 is opened on one side of casing 1, covered with a polytetrafluoroethylene film to achieve hermetic sealing. The overall structure is as follows. Figure 1 As shown, the device consists of a triboelectric nanogenerator unit, a magnetostrictive actuation unit, and a tip discharge wireless transmission unit, from left to right. Each unit works together through mechanical and electrical connections.

[0032] The aforementioned device was fixed to the bed of a CNC milling machine and placed in an external magnetic field environment. The machine tool's operating speed of 3000 r / min corresponds to a characteristic vibration frequency of approximately 50 Hz and an acceleration amplitude of approximately 2–5 m / s². Mass 11 reciprocates vertically with the vibration of the machine bed. Since the natural frequency of spring 2-mass 11 is pre-tuned to around 50 Hz, the system experiences resonant amplification, resulting in a measured charge density of approximately 18–25 μC / m² and a charge accumulation time constant of approximately 0.5 s. Figure 2 As shown in the relationship between tip field strength and magnetic field strength, the tip field strength increases nonlinearly and exponentially with the increase of the external measured magnetic field strength. This characteristic stems from the physical mechanism that the increased external magnetic field leads to an increase in the elongation of the magnetostrictive rod 6, a decrease in the electrode spacing, and a subsequent nonlinear increase in the local electric field at the tip. Figure 3 As shown in the relationship between resonant frequency and magnetic field strength, the resonant frequency increases linearly with the increase of the external measured magnetic field strength, and the two show a stable positive correlation with a linear correlation coefficient R² greater than 0.98; the response time is approximately 8 ms; after 30 consecutive measurements, the standard deviation of the resonant frequency is less than 0.5 MHz, indicating good repeatability of the device. Figure 4As shown in the electromagnetic spectrum of the tip discharge, two characteristic peaks exist in the spectrum: the main peak is located at 40 MHz with an amplitude of approximately 0.28 V, corresponding to the fundamental frequency discharge resonance at the initial electrode spacing; the secondary peak is located at 100 MHz with an amplitude of approximately 0.12 V, representing the harmonic component of the discharge pulse. These results verify the accurate sensing and wireless transmission capabilities of this device in external magnetic field sensing scenarios.

[0033] In another specific embodiment, keeping other parameters constant, the position of the movable electrode 15 was manually adjusted using a precision displacement stage, and the electrode spacing d was sequentially set to 10 μm, 20 μm, 50 μm, 100 μm, 150 μm, and 200 μm. At each spacing, the triboelectric nanogenerator unit was driven at a contact separation frequency of 50 Hz, and the resonant frequency of the tip discharge electromagnetic wave was recorded. The resonant frequency exhibited a hyperbolic decay trend with increasing electrode spacing: a spacing of 10 μm corresponded to a resonant frequency of approximately 40 MHz, a spacing of 50 μm to approximately 28 MHz, a spacing of 100 μm to approximately 20 MHz, and a spacing of 200 μm to approximately 10 MHz. The measured frequencies at each point highly matched the theoretical predictions of the formula f=c / (4d√εeff), with a tuning range covering 10–40 MHz and a tuning accuracy better than 1 MHz. Under a constant external magnetic field of 150 mT, using... Figure 5 The LC resonant receiver circuit shown is used for wireless signal reception. This circuit consists of a power supply VCC (2.0 V), current-limiting resistors R1 (1 TΩ) and R2 (100 Ω), inductors L1 and L2 (2 μH each), a resonant capacitor C1 (4 pF), a frequency counter XFC1, and an oscilloscope XSC1. The resonance condition satisfies f0 = 1 / (2π√LC). It receives tip discharge signals through electromagnetic coupling, generating a peak response at the resonant frequency. The LC resonant receiver circuit is placed at different distances, and the signal-to-noise ratio (SNR) is recorded as a function of distance. In a low electromagnetic interference environment, the signal transmission distance can reach 50 m, the SNR is greater than 15 dB, and the measured resonant frequency of the frequency counter XFC1 deviates from the theoretical value by less than 0.3 MHz. After rectifying the received electromagnetic wave energy, the rectifier power supply circuit can provide a continuous and stable wireless power output for external low-power sensing nodes (power consumption approximately 10–100 μW).

[0034] In another specific embodiment, the device is fixed to a marine buoy structure and placed in the external magnetic field environment to be monitored, simulating ocean wave frequencies of 0.1–0.25 Hz and accelerations of approximately 0.5–2 m / s². Resonant amplification is achieved by tuning the natural frequency of spring 2-mass block 11 to approximately 0.2 Hz, with a measured charge density per unit area of ​​approximately 12–20 μC / m² and a charge accumulation time constant of approximately 1 s. Under the influence of the external magnetic field being measured, the magnetostrictive rod 6 outputs axial displacement, and the movable electrode 15 moves accordingly. The electrode spacing dynamically changes with the external magnetic field strength within the range of 10–150 μm, corresponding to a resonant frequency that is tuned in real-time between approximately 15–40 MHz, with a tuning accuracy better than 1 MHz. Figure 6 As shown, the upper subplot displays the waveform of the measured external magnetic field strength H(t); the lower subplot displays the corresponding resonant frequency f(t) response waveform. f(t) and H(t) are positively correlated—when H(t) reaches its peak value, f(t) reaches its peak value at approximately 40 MHz; when H(t) drops to its trough value, f(t) drops to its trough value at approximately 15 MHz; the center value of f(t) is approximately 27 MHz. Both track synchronously with a phase delay of approximately 8 ms, meeting the technical requirement of a response time not exceeding 10 ms. The device can maintain continuous discharge under weak vibration excitation conditions and is suitable for wireless magnetic field sensing and wireless power supply applications in marine environments.

[0035] The device operated continuously for 72 hours under stable external magnetic field conditions, recording the resonant frequency every hour. The results showed that the resonant frequency drift was less than ±0.5 MHz, demonstrating that the device, protected by an inert gas-sealed enclosure and a polyimide insulating substrate, exhibits stable tip discharge environment, reliable charge accumulation-discharge cycles, and good long-term operational stability. This meets the requirements for long-term, uninterrupted wireless sensing and monitoring of external magnetic field parameters. The signal transmission process of this device is as follows: Figure 7 As shown.

[0036] The above-described specific embodiments are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Various modifications, substitutions, and improvements made by those skilled in the art to the technical solutions of the present invention based on the provided textual description and drawings, without departing from the design concept and spirit of the present invention, should all fall within the scope of protection of the present invention. The scope of protection of the present invention is determined by the claims.

Claims

1. A self-driven wireless magnetic sensing device based on triboelectric nanogenerators, characterized in that, include: The non-magnetic aluminum alloy shell (1) has an electromagnetic wave radiation window (18), and each functional unit is located inside the shell (1). The non-magnetic aluminum alloy shell (1) is filled with dry nitrogen or inert gas. The triboelectric nanogenerator unit includes a vertically stacked mass block (11), an upper friction layer, a lower friction layer, and a spring (2). The upper friction layer is composed of an upper plate (12), an upper copper foil (13), and a fluorinated ethylene propylene film (14) stacked from top to bottom. The lower friction layer is composed of a lower copper foil (3), a substrate (4), and a lower plate (5) stacked from top to bottom. The lower plate (5) is fixed to the bottom plate of the outer shell (1). The spring (2) is vertically arranged, with its lower end connected to the lower plate (5) and its upper end connected to the upper plate (12) to support the mass block (11). The mass block (11) is located above the upper friction layer, and the upper and lower friction layers are arranged facing each other. Under the vibration excitation of the external environment, the mass block (11) forms a continuous contact-separation reciprocating motion with the help of the restoring force of the spring (2), so that the upper and lower friction layers periodically generate static electricity and continuously output electrostatic charge to the outside. The magnetostrictive drive unit includes a magnetostrictive rod (6), a fixed base (17), and an elastic connector (16). The fixed base (17) is fixed to the bottom plate of the outer shell (1). The magnetostrictive rod (6) is fixed by the fixed base (17). The end of the rod that is close to the triboelectric nanogenerator unit is the fixed end, and the end that is away from the triboelectric nanogenerator unit is the free end. One end of the elastic connector (16) is fixedly connected to the free end of the magnetostrictive rod (6). The magnetostrictive rod (6) generates an axial elongation displacement corresponding to the magnetic field strength under the action of the external measured magnetic field, and outputs the displacement through the elastic connector (16). The tip discharge wireless transmitting unit includes a horizontally opposed active electrode (15) and a reference electrode (8). The reference electrode (8) is fixedly connected to the inner wall of the outer shell (1) by a fixing block (9). The other end of the active electrode (15) is fixedly connected to the elastic connector (16), and its tip is opposite to the tip of the reference electrode (8). An adjustable discharge gap is formed between the tips of the two electrodes. The elastic connector (16) transmits the axial elongation displacement of the magnetostrictive rod (6) to the movable electrode (15) to change the discharge gap. The charge accumulation circuit is used to guide the electrostatic charge generated by the triboelectric nanogenerator unit to the active electrode (15) and the reference electrode (8) through wires for continuous accumulation. When the tip electric field strength reaches the breakdown threshold, tip discharge occurs, and the excited electromagnetic wave is radiated outward through the electromagnetic wave radiation window (18). The external receiver receives the electromagnetic waves and performs energy extraction and frequency signal demodulation.

2. The self-driven wireless magnetic sensing device based on triboelectric nanogenerator according to claim 1, characterized in that: In the upper friction layer, the fluorinated ethylene propylene film (14) is located at the bottom layer and faces the lower friction layer, the upper copper foil (13) is stacked on top of the fluorinated ethylene propylene film (14), and the upper plate (12) is located at the top layer and is fixedly connected to the bottom surface of the mass block (11). In the lower friction layer, the lower copper foil (3) is located on the uppermost layer and is opposite to the fluorinated ethylene propylene film (14). The substrate (4) is stacked below the lower copper foil (3). The lower plate (5) is located on the lowermost layer and is fixed to the bottom plate of the outer shell (1). The lower copper foil (3) also serves as a charge collection electrode and is electrically connected to the charge accumulation circuit. The mass of the mass block (11) is in the range of 1 to 5 g; the elastic coefficient of the spring (2) is 0.5 to 2 N / mm.

3. The self-driven wireless magnetic sensing device based on triboelectric nanogenerator according to claim 1, characterized in that: The charge accumulation circuit includes a rectifier module and a charge accumulation circuit (10). The rectifier module is electrically connected to the lower copper foil (3) and the upper copper foil (13) respectively. After rectifying the alternating pulse current output by the triboelectric nanogenerator unit, the electrostatic charge is guided by the charge accumulation circuit (10) to the active electrode (15) and the reference electrode (8) respectively through the wires, so that the charge on the two electrodes continues to accumulate.

4. A self-driven wireless magnetic sensing device based on triboelectric nanogenerator according to claim 1, characterized in that: The elastic connector (16) is made of polytetrafluoroethylene. One end of it is fixedly connected to the free end of the magnetostrictive rod (6), and the other end is fixedly connected to the movable electrode (15) to convert the axial elongation displacement of the magnetostrictive rod (6) into the displacement of the movable electrode (15) in the horizontal direction toward or away from the reference electrode (8). The magnetostrictive rod (6) is made of terbium-dysprosium iron, and its length change ∆L satisfies the following condition with respect to the external magnetic field strength H: Where λs is the saturation magnetostriction coefficient, L is the initial length of the magnetostrictive rod, and H0 is the characteristic field strength.

5. The self-driven wireless magnetic sensing device based on triboelectric nanogenerator according to claim 1, characterized in that: Both the active electrode (15) and the reference electrode (8) are needle-shaped electrodes with a tip curvature radius of 5 to 20 micrometers. The tip of the active electrode (15) and the tip of the reference electrode (8) are arranged opposite each other along the normal direction of the electromagnetic radiation window (18). The discharge gap between the two tips is continuously adjusted in the range of 10 to 200 micrometers according to the strength of the external magnetic field being measured. The electromagnetic resonant frequency corresponding to the discharge gap adjustment is tuned in the range of 10 to 40 MHz with a tuning accuracy better than 1 MHz.

6. A self-driven wireless magnetic sensing device based on triboelectric nanogenerator according to claim 5, characterized in that: The resonant frequency f of the electromagnetic wave satisfies a mapping relationship with the electrode spacing d: Where c is the speed of light. The equivalent dielectric constant of the discharge environment between the two electrodes; the resonant frequency f is negatively correlated with the electrode spacing d, that is, the resonant frequency f decreases when the spacing d increases, and the resonant frequency f increases when the spacing d decreases; the equivalent dielectric constant The dielectric properties of the gas filling the outer shell (1) and the inter-electrode medium between the two electrodes are jointly determined.

7. The self-driven wireless magnetic sensing device based on triboelectric nanogenerator according to claim 1, characterized in that: The external receiver includes an LC resonant receiving circuit and a rectifier power supply circuit. The resonant frequency of the LC resonant receiving circuit matches the frequency of the electromagnetic wave emitted by the tip discharge wireless transmitting unit. It electromagnetically couples with the electromagnetic wave through an inductor coil, captures the electromagnetic wave pulse signal, and demodulates the signal through frequency feature identification. The rectifier power supply circuit is connected to the output terminal of the LC resonant receiving circuit. It performs induced charge collection, rectification, and voltage regulation on the electromagnetic wave energy before supplying power to the load.

8. The self-driven wireless magnetic sensing device based on triboelectric nanogenerator according to claim 1, characterized in that: The two ends of the spring (2) are fixedly connected to the upper surface of the lower plate (5) and the lower surface of the mass block (11), respectively. The spring (2) and the mass block (11) constitute a spring-mass block structure. The natural frequency of the spring-mass block structure is matched with the main frequency of environmental vibration in the range of 0.1 to 200 Hz by adjusting the elastic coefficient of the spring (2) or the mass of the mass block (11). When the spring-mass block structure resonates, the contact-separation motion amplitude between the upper and lower friction layers is the largest, and the charge density per unit area generated by triboelectric charging is 10 to 50 μC / m².

9. The self-driven wireless magnetic sensing device based on triboelectric nanogenerator according to claim 1, characterized in that: The outer shell (1) is a closed shell made of non-magnetic aluminum alloy material. The electromagnetic radiation window (18) is opened on the side wall of the outer shell (1) facing the tip of the reference electrode (8). The electromagnetic radiation window (18) is covered with a polytetrafluoroethylene film to achieve hermetically sealed packaging. The interior of the outer shell (1) is filled with dry nitrogen or inert gas to prevent electrode oxidation and unintended discharge.

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