Low-frequency transmitting-receiving magnetoelectric coupling integrated antenna and preparation method thereof

Abstract

The invention relates to a low-frequency transmitting-receiving magnetoelectric coupling integrated antenna and a preparation method thereof. The low-frequency transmitting-receiving magnetoelectric coupling integrated antenna comprises a transmitting antenna unit and a receiving antenna unit, the transmitting antenna unit comprises an L-T type magnetoelectric composite material structure, the L-T type magnetoelectric composite material structure is formed by compounding at least one piezoelectric material layer and at least two magnetostriction material layers symmetrically arranged on the two sides of the piezoelectric material layer through a bonding layer, and the magnetization direction of magnetostriction materials is in the length direction of the composite material structure. The polarization direction of the piezoelectric material is along the thickness direction of the composite material structure; the receiving antenna unit comprises an MLT type magnetoelectric composite material structure, the MLT type magnetoelectric composite material structure comprises a plurality of piezoelectric material sheets which are in electrode series connection in a plane and at least one magnetostriction material layer which is compounded on at least one main surface of the piezoelectric material sheets which are in series connection through a bonding layer, and a permanent magnet which is used for providing a direct current bias magnetic field is arranged on the MLT type structure. According to the low-frequency transmitting-receiving magnetoelectric coupling integrated antenna, the effective working frequency is reduced to the target VLF frequency band through the L-T and MLT structures.

Description

Technical Field

[0001] This invention relates to the field of wireless communication and sensing technology, specifically to a low-frequency transmit-receive magnetoelectric coupling integrated antenna and its fabrication method. Background Technology

[0002] Very low frequency (30-300 kHz) electromagnetic waves exhibit minimal attenuation in conductive media such as seawater and soil, making them ideal for cross-medium wireless communication. However, traditional antennas in this frequency band are constrained by the Chu-Harrington limit, often resulting in bulky and inefficient devices that are difficult to integrate into modern portable or embedded equipment.

[0003] Mechanical antennas generate radiation by driving the mechanical motion of charges or magnetic dipoles, providing a new path to overcome the aforementioned limitations. Among them, mechanical antennas based on magnetoelectric (ME) composite materials utilize their multi-field coupling characteristics of magneto-elastic-electricity to efficiently convert electrical energy into electromagnetic radiation through acoustic resonance within the material, or to generate a highly sensitive electrical response under weak magnetic fields. Theoretically, they can operate at dimensions much smaller than the wavelength of electromagnetic waves. However, existing technologies have significant shortcomings: 1) High-performance ME antennas often rely on externally strong bias magnetic fields (such as Helmholtz coils), resulting in bulky systems; 2) The high resonant frequency and narrow bandwidth of the materials make them difficult to adapt to low-frequency communication; 3) Robust design and fabrication processes for practical application environments (such as pressure and humidity) are not well studied; 4) There is a matching problem between the high-voltage driving nonlinearity of the transmitting unit and the weak signal detection of the receiving unit.

[0004] Therefore, there is an urgent need to develop a magnetoelectric coupling antenna and method with high integration, good low-frequency characteristics, strong environmental adaptability, and a well-defined fabrication process. Summary of the Invention

[0005] The technical problem this invention aims to solve is to address the shortcomings of existing magneto-electro-mechanical antennas in terms of low-frequency operation, integration, environmental adaptability, and fabrication processes. It provides a low-frequency transmit-receive magneto-electric coupled integrated antenna and its fabrication method, specifically a miniaturized antenna operating in the very low frequency (VLF) band and its fabrication method. This antenna achieves electromagnetic signal transmission and reception based on the magneto-electric coupling effect of magnetostrictive / piezoelectric composite materials, making it particularly suitable for underwater communication, underground detection, and complex electromagnetic environments. The antenna fabricated using this method features low operating frequency, compact size, high sensitivity, strong radiation capability, and eliminates the need for bulky external biasing equipment.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] This invention provides a low-frequency transmit-receive magnetoelectric coupling integrated antenna, comprising a transmitting antenna unit and a receiving antenna unit. The core of the transmitting antenna unit is an LT-type magnetoelectric composite material structure. This structure consists of a piezoelectric material as an intermediate layer, with at least one layer of magnetostrictive material symmetrically bonded to its upper and lower surfaces via adhesive layers, forming a sandwich configuration of "magnetostrictive / adhesive layer / piezoelectric / adhesive layer / magnetostrictive". The easy magnetization axis of the magnetostrictive material is along the length of the composite material, and the polarization direction of the piezoelectric material is along the thickness direction; this is the LT longitudinal magnetization-transverse polarization mode. A single transmitting antenna unit can be constructed by electrically connecting one or more such LT structural elements in parallel or series to adjust its total impedance and equivalent magnetic moment. The core of the receiving antenna unit is an MLT-type magnetoelectric composite material structure. This structure employs a composite design of multi-layer stacking and in-plane series connection: specifically, multiple strips of piezoelectric material are connected in series along their length in a plane, with electrodes at both ends; at least one layer of magnetostrictive material is bonded to at least one main plane of this series piezoelectric array via an adhesive layer; simultaneously, permanent magnets are placed at both ends or specific locations of the MLT structure to provide a DC bias magnetic field that allows the magnetostrictive material to operate within its optimal piezomagnetic coefficient range. This structure aims to achieve a balance between high charge output coefficient and low intrinsic capacitance to improve low-frequency sensitivity.

[0008] Furthermore, the piezoelectric material in the LT-type structure is a "hard" lead zirconate titanate (PZT-8) ceramic with a high mechanical quality factor Qm > 1000, and its dimensions are, for example, 70 mm in length, 20 mm in width, and 0.5 mm in thickness; the magnetostrictive material is a high-permeability amorphous alloy strip, Metglas 2605A, with a thickness of 25 μm. This combination ensures the stability and high energy conversion efficiency of the transmitting unit under a high driving electric field. Further, the piezoelectric material in the MLT-type structure is a relaxor ferroelectric single crystal PMN-PT with a high piezoelectric coefficient and d31 > 1000 pC / N, and the single crystal size is, for example, 37 mm in length, 2 mm in width, and 0.5 mm in thickness; the magnetostrictive material is also preferably a Metglas amorphous strip. The permanent magnet can be neodymium iron boron or ferrite magnetic sheet, and its size is determined according to the required bias magnetic field strength of 6-10 Oe.

[0009] Furthermore, the present invention provides an array system comprising the aforementioned antenna elements. This system, through a specific array design, significantly improves the overall radiated power, receiving sensitivity, and omnidirectionality. The transmitting antenna array is composed of multiple transmitting antenna rods arranged in a certain topology. Each transmitting antenna rod integrates multiple, not less than 20, of the aforementioned LT-type magnetoelectric composite material elements, which are electrically connected in parallel to reduce the equivalent impedance of a single antenna rod and enhance its local magnetic dipole moment. Sixteen such antenna rods are further arranged to form a transmitting array, and all antenna rods are synchronously excited by the same high-voltage driving source.

[0010] In the transmitting array, the antenna rods can be arranged with non-uniform spacing. This design effectively suppresses electromagnetic coupling between adjacent radiating elements, including mutual inductance and parasitic capacitance coupling, thereby avoiding the reduction in radiation efficiency and the "saturation" phenomenon of field strength synthesis caused by coupling, ensuring that the radiation intensity of the array effectively increases with the number of elements. The receiving antenna array adopts a tri-axis orthogonal omnidirectional detection architecture. The array consists of three receiving antenna rods, which are arranged perpendicularly and orthogonally in space along the X, Y, and Z axes of the Cartesian coordinate system. Each receiving antenna rod integrates at least one of the aforementioned MLT-type receiving antenna elements. This orthogonal configuration ensures that the array can capture incident magnetic field signals from any direction in space without blind spots and decompose them into three orthogonal components, providing complete vector magnetic field information for subsequent signal processing and communication demodulation, greatly enhancing the system's signal acquisition capability and communication reliability in complex electromagnetic environments.

[0011] This invention provides a method for fabricating the above-mentioned magnetoelectric composite antenna.

[0012] (1) The fabrication method of the LT type transmitting antenna unit includes the following steps: Material pretreatment: Clean and cut the piezoelectric ceramic sheet PZT-8 and the magnetostrictive alloy strip Metglas to the design size. Adhesive preparation: Mix two-component epoxy resin, type 105 & 206, with a mass ratio of 5.3:1. Lamination and composite: Apply adhesive evenly to the surface of the piezoelectric sheet, cover with the magnetostrictive strip, and form a symmetrical laminate. Vacuum pressure curing: Place the laminated assembly into a vacuum bag to remove air bubbles, and then apply uniform pressure in a fixture to cure at room temperature for 12-24 hours. Electrode lead-out and integration: Weld electrode leads; connect multiple cured LT elements in parallel and encapsulate them in a protective shell. (2) The fabrication method of the MLT type receiving antenna unit includes the following steps: Piezoelectric single crystal string preparation: Connect the polarized PMN-PT single crystal in series with conductive adhesive. Magnetostrictive layer composite: Apply adhesive to the surface of the series piezoelectric array and attach multiple layers of Metglas thin strips. Bias magnet assembly: Permanent magnets are bonded to both ends of the composite structure so that the magnetic field direction is along the length direction. Shielding encapsulation and circuit integration: The sensitive element is placed in a grounded shield shell and the output terminal is connected to a low-noise charge amplifier circuit board. (3) Array integration: Multiple transmitting units are arranged in parallel with non-uniform spacing to form a transmitting array; three receiving units are orthogonally mounted on a rigid frame to form a triaxial receiving array.

[0013] Furthermore, all bonding processes are performed in a vacuum degassing environment to ensure interface bonding quality and thickness uniformity. Furthermore, the charge amplification circuit employs a low-noise operational amplifier, and its feedback network capacitor C... f Approximately 100pF, resistance R f Approximately 10MΩ is optimized for a 30kHz operating frequency.

[0014] Furthermore, the present invention provides an array system including the aforementioned antenna and its application in low-frequency communication. The system operates in an air environment at a frequency of 30-32 kHz. The transmitting array can generate a radiated magnetic field of not less than 2 pT, rms at a distance of 100 meters, the receiving array noise equivalent magnetic field is less than 50 fT / √Hz, the signal-to-noise ratio exceeds 10000 under 1 nT signal excitation, and it supports command communication of not less than 5 bps.

[0015] The beneficial effects of this invention are as follows:

[0016] Low frequency and miniaturization: The unique LT and MLT structure design, combined with material parameter optimization, reduces the effective operating frequency to the target VLF band of 30kHz, and utilizes the advantages of acoustic wavelength to achieve a significant reduction in antenna size.

[0017] High performance indicators: Through process control, the transmitting unit has high radiation efficiency under high voltage drive, and the receiving unit has high sensitivity and low noise due to the MLT series structure and integrated bias magnet, resulting in excellent overall performance indicators.

[0018] The process is reliable and consistent: the well-defined step-by-step preparation method, especially the vacuum degassing and pressure curing process, ensures the interfacial coupling strength and performance consistency of the magnetoelectric composite material, laying the foundation for mass production.

[0019] High environmental adaptability: Modular packaging design, such as ABS shell and waterproof connector, makes the antenna easy to integrate and withstand complex environments, such as underwater pressure, improving engineering practicality.

[0020] Attached Figure Description Figure 1 The diagram shows the structure of the LT-type transmitting antenna unit (a) and the sensitive element (b) in an embodiment of the present invention.

[0021] Figure 2 This is a schematic diagram of the MLT-type receiving antenna structure and a schematic diagram of the sensitive element structure in an embodiment of the present invention.

[0022] Figure 3 This is a schematic diagram of the antenna transmitting array in an embodiment of the present invention.

[0023] Figure 4 The diagram below shows the antenna radiation direction in an embodiment of the present invention. (a) shows the position of the antenna in the spherical coordinate system, and (b) shows the radiation pattern of the transmitting antenna in the xz plane.

[0024] Figure 5 This is a schematic diagram of the radiation intensity frequency response characteristic test curve of the transmitting antenna unit in an embodiment of the present invention.

[0025] The specific implementation methods are described below with reference to the accompanying drawings and test examples. These embodiments are not intended to limit the scope of protection of this invention.

[0026] Example 1:

[0027] The assembly and radiation performance testing of the transmitting antenna array were conducted according to the preparation method described in this invention. Twenty LT-type magnetoelectric composite material units (PZT-8, 70×20×0.5mm in size, with a Metglas 2605A strip thickness of 25μm) were fabricated and connected in parallel to form a single transmitting antenna unit, which was then packaged. Sixteen such transmitting antenna units were mounted on a support frame, with non-uniform spacing between units to reduce mutual coupling, thus forming the transmitting antenna array. Test 1: Unit frequency response and radiation intensity. In an open area, a fixed peak-to-peak AC driving voltage of 140Vpp was applied to a single transmitting antenna unit. At a distance of 3 meters from its radiation center, the radiated magnetic induction intensity was measured using a calibrated standard magnetic field receiving coil, yielding the following results: Figure 5 The frequency response curve is shown. The results show a significant mechanical resonance peak at 31.4 kHz, with a radiation intensity B_peak reaching approximately 5.8 nT, rms. Based on the near-field radiation model of a magnetic dipole, B ∝ 1 / r^3, the radiation intensity contribution of this element at a distance of 100 meters is estimated to be approximately 6.7 fT, meeting the element specification requirement of ≥7 fT @100m. The measured -3dB bandwidth Δf is approximately 110 Hz.

[0028] Example 2:

[0029] The integration and sensitivity testing of the receiving antenna array were conducted according to the fabrication method described in this invention. Three MLT-type receiving antenna sensing elements, PMN-PT single-crystal series composites with multiple Metglas layers and ferrite magnets attached to both ends, were fabricated. Each sensing element was encapsulated in a shielded shell with grounded copper foil and connected to a low-noise charge amplifier circuit board (C). f =100pF, R f =10MΩ). Three encapsulated receiving units (i.e., "black tubes") were precisely mounted orthogonally along the X, Y, and Z axes on a hollow bakelite frame to form a receiving antenna array. Test 1: Sensitivity and Noise. A single receiving antenna unit was placed inside a high-magnetic shielding cylinder. First, a standard Helmholtz coil was driven using a precision current source to generate a calibration magnetic field with a frequency of 31.4kHz and a known intensity of 1 nT (rms). The output voltage Usignal of the receiving unit was measured, and its voltage sensitivity S = Usignal / 1 nT was calculated. The average of multiple measurements yielded S ≈ 520 mV / nT. Subsequently, the excitation magnetic field was turned off, and the background noise voltage spectral density Vn at the output of the receiving unit was measured using a dynamic signal analyzer. At 31.4kHz, Vn ≈ 20.8 μV / √Hz. Therefore, the noise equivalent magnetic field NEM = Vn _ / S ≈ 40 fT / √Hz, which meets the design specification of ≤50 fT / √Hz.

[0030] Example 3:

[0031] System integration and communication function verification were conducted by deploying the transmitting antenna array of Example 1 and the receiving antenna array of Example 2 in an open field, with a horizontal spacing of 100 meters. The communication system was established as follows: the transmitting end's host computer generated a 5bps random binary command sequence, modulated the carrier wave with 2FSK (f1=31.3kHz, f2=31.5kHz), and drove the transmitting array through a power amplifier. At the receiving end, the output of the three-axis receiving array was synchronously acquired by a data acquisition card, and the signal was synthesized, demodulated, and decoded using software algorithms. Test results: The system stably established a communication link. During a continuous test lasting one hour, the bit error rate (BER) was statistically less than 1×10⁻⁶. -5 This enables reliable low-speed command transmission. This embodiment verifies the completeness and feasibility of the antenna system of the present invention, from materials, elements, array to system application.

Claims

1. A low-frequency transmit-receive magnetoelectric coupling integrated antenna, characterized in that, The system includes a transmitting antenna unit and a receiving antenna unit. The transmitting antenna unit includes an LT-type magnetoelectric composite material structure, which is composed of at least one piezoelectric material layer and at least two magnetostrictive material layers symmetrically arranged on both sides of the piezoelectric material layer, bonded together by an adhesive layer. The magnetization direction of the magnetostrictive material is along the length direction of the composite material structure, and the polarization direction of the piezoelectric material is along the thickness direction of the composite material structure. The receiving antenna unit includes an MLT-type magnetoelectric composite material structure, which includes multiple piezoelectric material sheets with electrodes connected in series in a plane, and at least one magnetostrictive material layer bonded to at least one main surface of the series piezoelectric material sheets by an adhesive layer. A permanent magnet for providing a DC bias magnetic field is provided on the MLT-type structure.

2. The low-frequency transmit-receive magnetoelectric coupling integrated antenna according to claim 1, characterized in that, The piezoelectric material in the LT-type structure is lead zirconate titanate PZT-8 piezoelectric ceramic, and the magnetostrictive material is iron-based amorphous alloy thin strip; the piezoelectric material in the MLT-type structure is lead magnesium niobate-lead titanate PMN-PT relaxor ferroelectric single crystal.

3. The low-frequency transmit-receive magnetoelectric coupling integrated antenna according to claim 1 or 2, characterized in that, One of the transmitting antenna units is electrically connected in parallel from multiple of the LT-type magnetoelectric composite material structures.

4. A transmitting antenna array, characterized in that, It is composed of multiple transmitting antenna elements as described in any one of claims 1-3 arranged in an array.

5. A receiving antenna array, characterized in that, It is composed of receiving antenna elements as described in any one of claims 1-3, arranged orthogonally along the three-dimensional rectangular coordinate direction in space.

6. A method for fabricating a low-frequency transmit-receive magnetoelectric coupling integrated antenna as described in claim 1, characterized in that, This includes the fabrication of the transmitting antenna element and the receiving antenna element; The fabrication of the transmitting antenna unit includes: (1) Fabrication of LT structural elements: After cleaning the piezoelectric material sheet and the magnetostrictive material strip, an adhesive is coated on the surface of the piezoelectric sheet, and the magnetostrictive strip is covered. After vacuum degassing and pressure curing, an LT-type magnetoelectric composite material element is formed; (2) Unit integration: Multiple LT-type elements are connected in parallel and packaged to form a transmitting antenna unit; The fabrication of the receiving antenna unit includes: (3) Fabrication of MLT sensitive elements: Multiple piezoelectric single crystal electrodes are connected in series; an adhesive is coated on the surface of the series piezoelectric array, and a magnetostrictive material layer is composited; a permanent magnet is assembled to provide a bias magnetic field to form an MLT-type sensitive element; Packaging and circuit integration: The MLT sensitive element is placed in a shielding shell and its output terminal is connected to a low-noise charge amplifier circuit.

7. The preparation method according to claim 6, characterized in that, In the preparation of the LT structural unit, the adhesive used is a two-component epoxy resin, and the curing conditions are room temperature curing for 12-24 hours under vacuum and pressure.

8. The preparation method according to claim 6, characterized in that, In the fabrication of the MLT sensing element, the permanent magnet is assembled at both ends of the sensing element, and its magnetic field direction is along the length direction of the sensing element.

9. A method for fabricating a transmitting antenna array, characterized in that, Multiple transmitting antenna elements prepared by any one of claims 6-8 are mechanically fixed and electrically connected in parallel according to a preset non-uniform spacing topology.

10. A method for fabricating a receiving antenna array, characterized in that, Three receiving antenna units, which are prepared by the method of any one of claims 6-8 and have integrated charge amplification circuits, are mounted on the same rigid frame in a pairwise orthogonal manner.

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