A low-frequency mechanical magnetoelectric antenna based on cantilever beam structure

Abstract

The present invention belongs to the technical field of low-frequency small antennas, specifically relating to a low-frequency mechanical magnetoelectric antenna based on a cantilever beam structure. By setting the neutral plane of the magnetoelectric cantilever beam to coincide with the interface between the piezoelectric material layer and the magnetostrictive material layer, the present invention effectively solves the problem of polarization cancellation of the piezoelectric layer or magnetization of the magnetostrictive layer caused by the inappropriate positioning of the neutral plane during thickness bending vibration of the layered magnetoelectric composite material. This not only saves unnecessary material costs, but also further improves the inverse magnetoelectric coupling coefficient of the magnetoelectric composite material, while taking into account the operating frequency, impedance, and quality factor. The device can operate at frequencies ranging from tens of Hz to several kHz and can be reduced to the centimeter level, significantly reducing the size of a single antenna and promising the implementation of array antennas on mobile platforms.

Description

Technical Field

[0001] The present invention belongs to the technical field of low-frequency small antennas, and in particular relates to a low-frequency mechanical magnetoelectric antenna based on a cantilever beam structure. Background Art

[0002] In the field of radio waves, shortwave signals attenuate quickly, making them unsuitable for long-distance transmission, unable to propagate through water, and easily blocked by rock formations. Ultra-low frequency and very-low frequency radio waves, on the other hand, have longer wavelengths and can easily penetrate hundreds to thousands of meters above ground and across water, and can travel thousands of meters through air. However, traditional low-frequency antennas rely on electromagnetic wave resonance and are typically larger than one-tenth the wavelength of the wave, comparable in size to the wavelength itself. Transmitters require massive antenna arrays several kilometers long, resulting in high costs, low communication bandwidth, and limited data transmission capacity. This prohibitive effect on mobile platforms significantly restricts their use in wireless communication systems and radar.

[0003] In recent years, with the rapid development of miniaturization of communication electronic equipment, most electronic components have been miniaturized. However, traditional antenna miniaturization technologies are achieved at the expense of antenna bandwidth and gain. Therefore, in order to further reduce the size of antennas, it is necessary to develop new electromagnetic wave radiation and reception mechanisms to prepare antennas.

[0004] Mechanical antennas work by exciting special materials with specific electromagnetic properties into periodic vibrations, generating strong electric or magnetic fields that radiate electromagnetic waves into space. This coupling of mechanical energy to electromagnetic energy allows the size of mechanical antennas to be reduced to one-tenth or even one-hundredth of that of traditional antennas, without changing the antenna's operating frequency. This is because the speed of the acoustic waves generated by mechanical vibration is slower than that of electromagnetic waves (approximately 4-5 orders of magnitude slower). Multiferroic mechanical magnetoelectric antennas are a new type of miniaturized antenna designed based on this mechanism. These magnetoelectric antennas (as small as one-thousandth of a wavelength) achieve a 1-2 orders of magnitude reduction in size compared to state-of-the-art compact antennas without sacrificing performance, making them promising for applications in portable wireless communication systems.

[0005] Recently, researchers from the University of California, Los Angeles and Virginia Tech connected FeGa magnetostrictive rods in series with piezoelectric actuators to develop a multiferroic mechanical magnetoelectric antenna. This antenna does not require bulky capacitors and inductors for tuning, and can avoid ohmic losses. The composite film consists of two parts: a magnetostrictive layer and a piezoelectric layer. It uses magnetic-acoustic-electric coupling to transmit and receive electromagnetic waves, and enhances the process through acoustic resonance with a high quality factor. During the transmission process, a voltage is applied to the piezoelectric layer, and the strain is generated and transferred to the magnetostrictive layer through the inverse piezoelectric effect, which excites magnetization oscillations and radiates electromagnetic waves through the piezomagnetic effect. This method of generating an induced magnetic field by the conversion of electro-acoustic-magnetic of a magnetoelectric composite material is also called the inverse magnetoelectric effect. Experiments have shown that under an electric field strength of 0.27MV / m, a volume of 5cm 3 The antenna can generate a magnetic induction intensity of 1fT at a distance of 1km, which is equivalent to a magnetic moment change of 5.17Am.

[0006] However, this mechanical magnetoelectric antenna based on a simple stretching vibration mode still has its drawbacks. For designing RF magnetoelectric antennas, basing it on this vibration mode is desirable. Currently, mainstream RF magnetoelectric antenna designs in academia and industry all adopt this model, such as FBAR antennas and transverse bulk wave resonant antennas. However, for designing low-frequency magnetoelectric antennas, this model is somewhat insufficient. The main reason is that the resonant frequency of the stretching vibration is directly and inversely proportional to the antenna size (length, width, or thickness). This means that the lower the antenna operating frequency, the larger the antenna size. Especially in the ultra-low and ultra-low frequency bands, magnetoelectric antennas designed based on this acoustic resonance mode can reach sizes of several meters or even hundreds of meters, which is still not small enough and does not conform to the current trend of electronic device integration. Furthermore, it is impossible to produce magnetoelectric composite materials of such large sizes. Not only is the cost prohibitive, but current processing technology is almost impossible to achieve, which limits its application in low-frequency antennas.

[0007] Layered magnetoelectric composite materials based on cantilever beam structures can also be used to realize magnetoelectric antenna functions. This type of magnetoelectric composite material works in the thickness bending vibration mode, and the frequency of the bending vibration is inversely proportional to the square of the length of the material (i.e.: ), which also means that bending vibration is the vibration with the lowest resonant frequency among all vibration modes. The size of a mechanical magnetoelectric antenna designed based on the thickness bending vibration mode will be two orders of magnitude smaller than that based on the longitudinal stretching vibration mode, which is undoubtedly good news for designers of low-frequency antennas. However, the bending vibration of a composite material can be regarded as the composite movement of two parts that perform extension and contraction vibrations on the same composite material at the same time. These two vibrations (extension and contraction vibrations) are divided by the neutral plane of the cantilever beam. Whether it is a piezoelectric material or a magnetostrictive material, the polarity of the polarization or magnetic moment changes generated by the extension and contraction vibrations are opposite, which means that if the neutral plane is in a layer of the magnetoelectric composite material, rather than directly appearing at the interface between the two layers of material, the electric polarization or magnetic moment changes generated in the layer will inevitably cancel each other out, resulting in a decrease in the magnetic induction intensity, thereby reducing the inverse magnetoelectric coupling coefficient of the magnetoelectric composite material.

[0008] The definition of the inverse magnetoelectric coupling coefficient is the change in magnetic induction intensity caused by a unit electric field. The design standard for the DARPA Microsystems Technology Office's "Mechanical Antenna" (AMEBA) program requires the magnetic induction intensity generated by a low-frequency magnetoelectric antenna at a distance of 1 km. Therefore, without changing the excitation electric field, a larger inverse magnetoelectric coupling coefficient results in a greater magnetic induction intensity and better antenna radiation performance. Summary of the Invention

[0009] In view of this, the present invention proposes a low-frequency mechanical magnetoelectric antenna based on a cantilever beam structure to solve the problem of polarization or magnetization canceling each other out due to different vibrations on both sides of the neutral plane, thereby improving the radiation efficiency of the magnetoelectric antenna and taking into account the operating frequency, impedance and quality factor.

[0010] The technical solution of the present invention is:

[0011] A low-frequency mechanical magnetoelectric antenna based on a cantilever beam structure, comprising: a piezoelectric material layer and a magnetostrictive material layer;

[0012] The piezoelectric material layer serves as the excitation end of the antenna transmitter, with its upper surface covered by a first silver metal layer used as an input electrode and its lower surface covered by a second silver metal layer used as an output electrode;

[0013] The magnetostrictive material layer serves as a response end and is located on the upper surface of the first silver metal layer;

[0014] The second silver metal layer, the piezoelectric material layer, the first silver metal layer and the magnetostrictive material layer together constitute a magnetoelectric composite material. One end of the magnetoelectric composite material is fixed and the other end is used as a free end to form a cantilever beam structure.

[0015] Furthermore, the thickness of the piezoelectric material layer and the magnetostrictive material layer should satisfy formula (1) to ensure that the neutral plane of the magnetoelectric cantilever beam is located at the interface between the piezoelectric material layer and the magnetostrictive material layer.

[0016]

[0017] In formula (1), t P represents the thickness of the piezoelectric layer, t M is expressed as the thickness of the magnetostrictive layer, represents the compliance coefficient of the piezoelectric layer under constant electric field strength, k represents the compliance coefficient of the magnetostrictive layer under constant magnetic field strength, 11,M It represents the longitudinal magnetostrictive coupling coefficient of the magnetostrictive layer.

[0018] Furthermore, the piezoelectric material layer is made of one of PZT-43, PZT-5H and PZN-PT.

[0019] Furthermore, the magnetostrictive material layer is made of iron gallium.

[0020] Furthermore, one end of the magnetoelectric composite material is fixed by clamping it with a clamp.

[0021] In principle:

[0022] This invention uses a layered magnetoelectric composite material with a cantilever beam structure to form an acoustic resonator. Mechanical wave resonance transfers strain from the piezoelectric layer to the magnetostrictive layer, leveraging electro-acoustic-magnetic coupling (the inverse magnetoelectric effect) to achieve mutual conversion of acoustic and electromagnetic properties. Unlike traditional antennas, which depend on the wavelength of electromagnetic waves, and mechanical magnetoelectric antennas with simple telescopic vibration modes, which depend solely on the length of the acoustic wave, this structure's operating frequency is determined by both the length of the acoustic wave and its thickness. It is inversely proportional to the square of the acoustic wave length and directly proportional to the thickness.

[0023] The acoustic mode selected in this invention is a first-order bending vibration mode, which can be considered an in-plane acoustic mode when considering small deflection vibrations. The piezoelectric and ferromagnetic phases couple in-plane. Theoretical and experimental results show that this coupling mode has a larger coupling coefficient than the out-of-plane coupling mode, resulting in higher antenna gain and transmit / receive efficiency.

[0024] After adopting the above technical solution, the present invention has the following beneficial effects:

[0025] The design concept of this invention is simple, effective, and easy to implement. When existing material performance parameters are already fixed and cannot be changed, the neutral plane of the magnetoelectric cantilever beam is set exactly at the interface between the piezoelectric and magnetostrictive material layers. This effectively solves the problem of polarization cancellation between the piezoelectric layer polarization and the magnetostrictive layer magnetization caused by the improper positioning of the neutral plane during thickness bending vibration of the layered magnetoelectric composite material. This not only saves unnecessary material costs, but also further improves the inverse magnetoelectric coupling coefficient of the magnetoelectric composite material, while also taking into account the operating frequency, impedance, and quality factor. The device can operate in the range of tens of Hz to several kHz and can be reduced to the centimeter level, significantly reducing the size of a single antenna and promising the implementation of array antennas on mobile platforms. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a schematic structural diagram of a low-frequency mechanical magnetoelectric antenna based on a cantilever beam structure described in the present invention.

[0027] Figure 2 Schematic diagram of the simulation results of micro-area deformation of the magnetoelectric antenna under electric excitation.

[0028] Figure 3 Simulation diagram of magnetization cancellation in the magnetostrictive layer of the magnetoelectric antenna under electrical excitation, where (a) is with cancellation and (b) is without cancellation.

[0029] Figure 4 This is a simulation diagram of the change of magnetic induction intensity with frequency when the magnetization in the magnetostrictive layer of the magnetoelectric antenna is offset under electrical excitation, where (a) is with offset and (b) is without offset. DETAILED DESCRIPTION

[0030] The technical solution of the present invention is described in detail below with reference to the accompanying drawings.

[0031] The present invention is used to solve the problem of polarity cancellation when the piezoelectric layer polarization or the magnetostrictive layer polarization of the cantilever beam structure magnetoelectric composite material undergoes thickness bending vibration, thereby significantly improving its inverse magnetoelectric coupling coefficient and enhancing the radiation capability of the antenna.

[0032] Example

[0033] like Figure 1As shown, this embodiment provides a magnetoelectric antenna based on the first-order bending resonance of a cantilever beam, comprising a piezoelectric material layer and a magnetostrictive material layer. A first silver metal layer is covered on the upper surface of the piezoelectric material layer, and the magnetostrictive material layer is located on the upper surface of the first silver metal layer. A second silver metal layer is covered on the lower surface of the piezoelectric material layer. The first silver metal layer serves as an input electrode, and the second silver metal layer serves as an output electrode. The piezoelectric material layer serves as an excitation end of the antenna transmitter, and the magnetostrictive material layer serves as a response end. One end of the magnetoelectric composite material composed of the magnetostrictive material layer, the first silver metal layer, the piezoelectric material layer, and the second silver metal layer is fixed, and the other end is free, thereby forming a cantilever beam structure.

[0034] In order to generate in-plane stretching strain, the piezoelectric material needs to have a sufficiently large piezoelectric coefficient d 31 or d 32 Component, the available materials are PZT-43, PZT-5H, 110 tangential PZN-PT single crystal, etc. Magnetostrictive materials should be selected from the piezomagnetic system ≥10 -8 Materials with m / A numbers, such as iron gallium (FeGa).

[0035] The resonant mode excited in this example's magnetoelectric antenna is a thickness-bending vibration mode. The displacement of the particle, or the deflection of the material, is along the thickness, while the vibration propagates along the length. The voltage-induced periodic mechanical vibration of the piezoelectric layer simultaneously drives the magnetostrictive layer through strain-stress coupling, inducing periodic changes in the magnetostrictive layer's magnetic moment.

[0036] The piezoelectric material layer selected in this example is PZT-43. Compared with PZT-5H, its piezoelectric coefficient d 31 The component is slightly smaller than the latter, but it has a quality factor higher than 1000. Theory and experiments show that, considering the contribution to the inverse magnetoelectric coupling coefficient, when a large piezoelectric coefficient and a high quality factor of the material cannot be achieved at the same time, the high quality factor should be given priority. The magnetostrictive material layer is iron gallium (FeGa). Among them, the length of PZT-43 and FeGa is 4 cm. According to the theoretical condition that the longitudinal net external force at the free end of the cantilever beam structure should be 0, the integral calculation shows that when the neutral plane of the magnetoelectric cantilever beam is exactly the interface between the piezoelectric material layer and the magnetostrictive material layer, the relationship between the thickness of the piezoelectric material layer and the magnetostrictive material layer should be: The optimal thickness ratio of the magnetostrictive layer and the piezoelectric layer under simple longitudinal stretching vibration at low frequency is: in and The elastic compliance component of the piezoelectric layer under a constant electric field, the elastic compliance component of the magnetostrictive layer under a constant magnetic field, the electromechanical coupling coefficient of the piezoelectric layer, and the electromagnetism coupling coefficient of the magnetostrictive layer, respectively. Therefore, when the neutral plane of the magnetoelectric cantilever beam is exactly at the interface between the piezoelectric and magnetostrictive material layers, and the total thickness of the magnetoelectric composite material is set to 1mm, the thickness of the PZT-43 is 0.9mm, and the thickness of the FeGa is 0.1mm. When applying the optimal thickness ratio relationship for the simple longitudinal telescopic vibration magnetostrictive layer and the piezoelectric layer at low frequencies, the thickness of the PZT-43 is 0.7mm, and the thickness of the FeGa is 0.3mm. At this time, the neutral plane of the magnetoelectric cantilever beam appears in the FeGa layer. It should be noted that the low-frequency condition of the longitudinal telescopic vibration magnetostrictive layer and the piezoelectric layer refers to the situation where the longitudinal telescopic vibration magnetostrictive layer and the piezoelectric layer are at a non-resonant frequency and are far less than the resonant frequency.

[0037] Using COMSOL Multiphysics finite element simulation software, we simulated and modeled two magnetoelectric cantilever antennas with different thickness ratios. The piezoelectric material was modeled using the piezoelectric constitutive equation, while the magnetic material was modeled using the piezomagnetic constitutive equation. This approach can be used to simulate the dynamic bidirectional coupling between electricity, acoustics, and magnetism. Since the cantilever vibrates within its length-thickness plane, and its width is much smaller than its length, the width has almost no effect on the vibration state. Therefore, a two-dimensional model is sufficient for simulation requirements and helps improve simulation speed and model convergence. The specific results are shown below:

[0038] Figure 2 The simulation results of the resonant deformation of the magnetoelectric antenna under electrical excitation are shown in the figure. As can be seen from the simulation results, this is a typical first-order bending resonance mode.

[0039] Figure 3 (a) shows the simulation results of magnetization cancellation in the magnetostrictive layers of a magnetoelectric antenna under electrical excitation. The upper rectangle is FeGa, and the lower rectangle is PZT-43. The arrows in the figure indicate the direction of magnetization. The simulation results show that when the neutral plane appears in the magnetostrictive layer, rather than at the interface between the piezoelectric and magnetostrictive layers, the magnetization directions of the magnetic layers on either side of the neutral plane are opposite, indicating that the magnetization of the magnetic layers cancels out. This is because the magnetic layer on one side of the neutral plane is vibrating in an expansion (or contraction) direction while the magnetic layer on the other side is simultaneously vibrating in the opposite direction.

[0040] Figure 3(b) shows the simulation results for the case where there is no magnetization cancellation in the magnetostrictive layer of the magnetoelectric antenna under electrical excitation. Again, the arrows in the figure indicate the direction of magnetization. The simulation results show that when the neutral plane is located at the interface between the piezoelectric and magnetostrictive layers, the magnetizations in the magnetostrictive layers all face the same direction, indicating no magnetization cancellation in the magnetic layers, which is the expected phenomenon. This is because the magnetostrictive layers are all on one side of the neutral plane, so at any given moment, they only experience the same extension or contraction vibration, with the magnetizations facing the same direction.

[0041] Figure 4 The graph below shows the frequency variation of the inverse magnetoelectric coefficient in the magnetostrictive layer of a magnetoelectric antenna under electrical excitation. Comparing the two graphs reveals that the change in magnetic flux density is indeed greater when the magnetization in the magnetostrictive layer is not offset than when the magnetization in the magnetostrictive layer is offset. Furthermore, it can be observed that the magnetic flux change in the magnetic layer is greatest at the acoustic resonance frequency, a result of the enhanced magnetoelectric coupling caused by acoustic resonance.

[0042] It should be noted that the device operates at a frequency of 315 Hz, where the electromagnetic wavelength is approximately 952.4 km. Through proper design, the low-frequency mechanical magnetoelectric antenna based on a cantilever beam structure can be reduced to a size of 40 × 6 × 1 mm, significantly smaller than traditional electric resonant antennas and simple telescopic vibration mechanical magnetoelectric antennas.

[0043] It should be noted that actual devices are not limited to the width, thickness, and aspect ratio shown in the examples. These parameters can be adjusted to suit specific materials, desired operating frequencies, and other factors, as long as the neutral plane of the layered magnetoelectric composite material in the cantilever structure is precisely at the interface between the piezoelectric and magnetostrictive layers.

[0044] It should be noted that actual devices are not limited to the material configurations in the examples. Selecting piezoelectric materials with high piezoelectric coefficients and magnetic materials with high magnetic permeability and high magnetostriction can help further improve the radiation performance of the antenna.

Claims

1. A low-frequency mechanical magnetoelectric antenna based on a cantilever beam structure, comprising a piezoelectric material layer and a magnetostrictive material layer, characterized in that: The piezoelectric material layer serves as the excitation end of the antenna transmitter, with its upper surface covered by a first silver metal layer used as an input electrode and its lower surface covered by a second silver metal layer used as an output electrode; The magnetostrictive material layer serves as a response end and is located on the upper surface of the first silver metal layer; The second silver metal layer, the piezoelectric material layer, the first silver metal layer and the magnetostrictive material layer together constitute a magnetoelectric composite material, and one end of the magnetoelectric composite material is fixed and the other end is free to form a cantilever beam structure; The thickness of the piezoelectric material layer and the magnetostrictive material layer should satisfy formula (1) to ensure that the neutral plane of the magnetoelectric cantilever beam is at the interface between the piezoelectric material layer and the magnetostrictive material layer; Among them, t P represents the thickness of the piezoelectric layer, t M is expressed as the thickness of the magnetostrictive layer, represents the compliance coefficient of the piezoelectric layer under constant electric field strength, k represents the compliance coefficient of the magnetostrictive layer under constant magnetic field strength, 11,M It represents the longitudinal magnetostrictive coupling coefficient of the magnetostrictive layer.

2. The low-frequency mechanical magnetoelectric antenna based on a cantilever beam structure according to claim 1, characterized in that: The piezoelectric material layer is made of one of PZT-43, PZT-5H and PZN-PT.

3. The low-frequency mechanical magnetoelectric antenna based on a cantilever beam structure according to claim 1, characterized in that: The magnetostrictive material layer is made of iron gallium.

4. A low-frequency mechanical magnetoelectric antenna based on a cantilever beam structure according to any one of claims 1 to 3, characterized in that: A method for fixing one end of the magnetoelectric composite material is to clamp it with a clamp.

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