Low-frequency mechanical magnetoelectric antenna based on cantilever structureTechnical Field
The invention belongs to the technical field of low-frequency small-sized antennas, and particularly relates to a low-frequency mechanical magnetoelectric antenna based on a cantilever structure.
Background
In the field of radio waves, short wave signals attenuate fast, are not suitable for long-distance transmission, cannot propagate in water and are very easy to block by rock strata, and very low frequency radio waves have long wavelengths, can easily pass through the ground and the water surface of thousands of meters, and reach the propagation distance of thousands of meters in the air. However, the conventional low-frequency antenna relies on electromagnetic wave resonance, the size is usually larger than one tenth of the wavelength of electromagnetic waves, the size is equivalent to the wavelength, the transmitter needs a huge antenna array with a length of several kilometers, the cost is high, the communication bandwidth is low, the data transmission capacity is limited, and the conventional low-frequency antenna cannot be used for a mobile platform, so that the use of the conventional low-frequency antenna in a wireless communication system and a radar is greatly restricted.
In recent years, with the rapid development of miniaturization of communication electronic devices, most of electronic components have been miniaturized, and the miniaturization of conventional antennas has been achieved by sacrificing the bandwidth and gain of antennas, so that new electromagnetic wave radiation and reception mechanisms have been required to be developed to prepare antennas for further downsizing of antennas.
The principle of the mechanical antenna is that a strong electric field or magnetic field is generated by exciting a specific material having a certain electromagnetic property to periodically vibrate, thereby radiating electromagnetic waves into a space. The electromagnetic energy can be coupled by mechanical energy, and the wave speed of sound waves generated by mechanical vibration is smaller than the wave speed of electromagnetic waves (about 4-5 orders of magnitude smaller) on the basis of not changing the working frequency of the antenna, so that the size of the mechanical antenna can be reduced to one tenth or even one hundredth of that of a traditional antenna. The multiferroic mechanical magnetoelectric antenna is a novel miniaturized antenna designed according to the mechanism, and the magnetoelectric antenna (the size is as small as one thousandth wavelength) shows miniaturization of 1-2 orders of magnitude compared with the most advanced compact antenna under the condition that the performance is not degraded, so that the magnetoelectric antenna has great application prospect in a portable wireless communication system.
Recently, researchers at the university of california, los angeles division, virginia institute of technology, developed multiferroic mechanical magnetoelectric antennas by connecting a FeGa magnetostrictive rod in series with a piezoelectric actuator. Such an antenna does not require cumbersome capacitance and inductance for tuning while avoiding ohmic losses. Wherein the composite film comprises two parts of a magnetostrictive layer and a piezoelectric layer, utilizes magneto-acoustic-electric coupling to transmit and receive electromagnetic waves, and enhances the process by acoustic resonance of high quality factor. In the emitting process, voltage is applied to the piezoelectric layer, strain generated by the inverse piezoelectric effect is transferred to the magnetostrictive layer, and magnetization oscillation is excited and electromagnetic waves are radiated by the piezomagnetic effect. This way of generating an induced magnetic field by electro-acoustic-magnetic conversion of the magnetoelectric composite is also known as the reverse magnetoelectric effect. Experiments show that under the electric field intensity of 0.27MV/m, an antenna with the volume of 5cm3 can generate magnetic induction intensity of 1fT outside a distance of 1km, which is equivalent to magnetic moment change of 5.17 Am.
However, such a mechanical magneto-electric antenna based on a simple telescopic vibration mode still has its drawbacks. It is desirable to design a rf magnetoelectric antenna based on such a vibration mode, and the rf magnetoelectric antenna design currently prevailing in the academic world and industry is such a mode as FBAR antenna, transverse bulk wave resonant antenna, etc. However, for designing a magneto-electric antenna in a low frequency band, the mode is somewhat insufficient, and the main reason is that the resonant frequency of the telescopic vibration is in direct inverse relation with the size (length, width or thickness) of the antenna, that is, the lower the working frequency of the antenna is, the larger the size of the antenna is, especially in the ultra-low frequency band and the ultra-low frequency band, the size of the magneto-electric antenna designed based on the acoustic resonant mode can reach several meters or even hundreds of meters, and still is not miniaturized enough, and is not in accordance with the trend of the integration of the current electronic device, in addition, for materials, the magneto-electric composite material with the large size cannot be realized, not only the cost is too large, but also the current technology level is almost impossible, and the application of the magneto-electric composite material on the antenna in the low frequency band is limited.
The layered magnetoelectric composite material based on the cantilever structure can also be used for realizing the magnetoelectric antenna function. The magnetoelectric composite material of this structure operates in a thickness flexural vibration mode, and the frequency of flexural vibration is inversely proportional to the square of the length of the material (i.e.: ) This also means that one of all vibration modes has the lowest resonance frequency in bending vibration. The dimensions of a mechanical magneto-electric antenna designed according to the thickness bending vibration mode will be two orders of magnitude smaller than those based on the longitudinal stretching vibration mode, which is certainly a good news to the designers of low frequency antennas. However, the bending vibration of the composite material can be regarded as a resultant motion of the two parts of the stretching and shrinking vibration, respectively, on the same composite material at the same time. The two vibrations (extension and contraction vibrations) take the neutral plane of the cantilever beam as a demarcation point. The polarities of polarization or magnetic moment changes generated by stretching and shrinking vibration are opposite, which means that if a neutral plane is positioned in a certain layer of the magnetoelectric composite material, but not directly positioned on the interface of two layers of materials, the phenomena that the electric polarization or magnetic moment changes generated by the layer are mutually counteracted inevitably occur, and the magnetic induction intensity is reduced, so that the inverse magnetoelectric coupling coefficient of the magnetoelectric composite material is reduced.
According to the definition of the inverse magneto-electric coupling coefficient, namely the variation of the magnetic induction intensity caused by a unit electric field, the design standard requirement of the 'mechanical antenna' (AMEBA) project of the American DARPA microsystem technology office is the magnetic induction intensity generated by the low-frequency magneto-electric antenna at a distance of 1 km. Therefore, on the premise of not changing the excitation electric field, the larger the inverse magneto-electric coupling coefficient is, the larger the magnetic induction intensity induced by coupling is, and the better the radiation performance of the antenna is.
Disclosure of Invention
In view of this, the invention provides a low-frequency mechanical magnetoelectric antenna based on a cantilever structure, so as to solve the problem that polarities of the electric polarization or magnetization cancel each other on two sides of a neutral plane due to different vibrations, improve the radiation efficiency of the magnetoelectric antenna, and simultaneously consider the working frequency, impedance and quality factor.
The technical scheme of the invention is as follows:
A low-frequency mechanical magnetoelectric antenna based on cantilever structure comprises a piezoelectric material layer and a magnetostriction material layer;
The piezoelectric material layer is used as an excitation end of the antenna transmitter, the upper surface of the piezoelectric material layer is covered with a first silver metal layer used as an input electrode, and the lower surface of the piezoelectric material layer is covered with a second silver metal layer used as an output electrode;
The magnetostrictive material layer is used as a response end and is positioned 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 jointly form a magnetoelectric composite material, one end of the magnetoelectric composite material is fixed, and the other end of the magnetoelectric composite material is used as a free end to form a cantilever structure.
Furthermore, the thickness of the piezoelectric material layer and the thickness of the magnetostrictive material layer should satisfy formula (1) so as to ensure that the neutral plane of the magnetoelectric cantilever beam is positioned at the interface of the piezoelectric material layer and the magnetostrictive material layer.
In the formula (1), tP represents the thickness of the piezoelectric layer, tM represents the thickness of the magnetostrictive layer,Representing the compliance coefficient of the piezoelectric layer at constant electric field strength,Represents the compliance coefficient of the magnetostrictive layer under the constant magnetic field intensity, and k11,M represents the longitudinal electromechanical coupling coefficient of the magnetostrictive layer.
Further, the piezoelectric material layer is made of one of PZT-43, PZT-5H and PZN-PT.
Furthermore, the magnetostrictive material layer is made of iron gallium.
Further, one end of the magnetoelectric composite material is fixed by clamping with a clamp.
In principle, the method comprises the following steps:
The invention adopts a layered magnetoelectric composite material with a cantilever structure to form an acoustic resonator, and transmits strain from a piezoelectric layer to a magnetostrictive layer through mechanical wave resonance, and realizes the interconversion of acoustic characteristics and electromagnetic characteristics by utilizing electric-acoustic-magnetic coupling (inverse magnetoelectric effect). The working frequency of the structure is different from that of the traditional antenna, which depends on the wavelength of electromagnetic waves, and is also different from that of the mechanical magnetoelectric antenna with a simple telescopic vibration mode, which depends on the length of sound waves only, and is determined by the length and thickness of the sound waves, wherein the working frequency is inversely proportional to the square of the length of the sound waves and is directly proportional to the thickness.
The acoustic mode selected by the invention is a first-order bending vibration mode, and can be regarded as an in-plane acoustic mode when small-deflection vibration is considered. The piezoelectric phase and the ferromagnetic phase are coupled in-plane, and theoretical and experimental results show that the coupling mode has a larger coupling coefficient relative to the out-of-plane coupling mode, so that the antenna has higher antenna gain and transceiving efficiency.
After the technical scheme is adopted, the invention has the following beneficial effects:
The invention has simple and effective design concept and is easy to realize, under the condition that the performance parameters of the existing materials can not be changed, the neutral plane of the magnetoelectric cantilever beam is just set to be the interface between the piezoelectric material layer and the magnetostrictive material layer, thereby effectively solving the problem that polarities are mutually offset when the piezoelectric layer polarization or the magnetostrictive layer polarization occurs due to unsuitable position of the neutral plane when the layered magnetoelectric composite material is subjected to thickness bending vibration, saving unnecessary material cost, further improving the inverse magnetoelectric coupling coefficient of the magnetoelectric composite material, and simultaneously taking the working frequency, impedance and quality factor into consideration. The device can work at tens of Hz to KHz, the size can be reduced to the order of centimeters, the size of a single antenna is greatly reduced, and the array antenna is expected to be realized on a mobile platform.
Drawings
Fig. 1 is a schematic diagram of a low-frequency mechanical magnetoelectric antenna based on a cantilever structure according to the present invention.
Fig. 2 is a schematic diagram of a micro-area deformation simulation result of the magnetoelectric antenna under electric excitation.
Fig. 3 is a simulation diagram of magnetization cancellation in the magnetostrictive layer of the magnetoelectric antenna under electric excitation, wherein (a) is cancellation and (b) is no cancellation.
Fig. 4 is a simulation graph of magnetic induction intensity with frequency when magnetization in a magnetostrictive layer of a magneto-electric antenna is cancelled under electric excitation, wherein (a) is cancelled, and (b) is not cancelled.
Detailed Description
The technical scheme of the invention is described in detail below with reference to the accompanying drawings.
The invention is used for solving the problem that polarities of the piezoelectric layer or the magnetostrictive layer are mutually offset when the cantilever structure magnetoelectric composite material is subjected to thickness bending vibration, thereby remarkably improving the inverse magnetoelectric coupling coefficient and improving the radiation capacity of the antenna.
Examples
As shown in FIG. 1, the magneto-electric antenna based on cantilever first-order bending resonance comprises a piezoelectric material layer and a magnetostrictive material layer, wherein a first silver metal layer is covered on the upper surface of the piezoelectric material layer, the magnetostrictive material layer is positioned 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 is an input electrode, the second silver metal layer is an output electrode, the piezoelectric material layer is used as an excitation end of an antenna transmitter, the magnetostrictive material layer is used as a response end, and one end of a magneto-electric composite material formed by 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 of the magnetostrictive material layer is used as a free end, so that a cantilever structure is formed.
In order to generate in-plane extensional strain, piezoelectric materials are required to have a sufficiently large component of piezoelectric coefficient d31 or d32, and alternative materials are PZT-43, PZT-5H, 110 tangential PZN-PT single crystals, etc. The magnetostrictive material should be selected from materials with piezomagnetic system not less than 10-8 m/A, such as iron gallium (FeGa) and the like.
The excited resonant mode in the magnetoelectric antenna of this example belongs to the thickness bending vibration mode, the displacement of the mass point, i.e. the deflection of the material, is along the thickness direction of the material, and the propagation direction of the vibration is along the length direction of the material. The piezoelectric layer excited by voltage performs periodic mechanical vibration, and simultaneously drives the magnetostrictive layer to perform periodic mechanical vibration through strain-stress coupling to induce the magnetostrictive layer to generate periodic magnetic moment change.
The piezoelectric material layer selected in this example is PZT-43, and compared with PZT-5H, although the component of the piezoelectric coefficient d31 is slightly smaller than that of the piezoelectric material layer, the piezoelectric material layer has a quality factor higher than 1000, and theory and experiment show that, considering the contribution degree to the inverse magneto-electric coupling coefficient, when the large piezoelectric coefficient and the high quality factor of the material are not compatible, the high quality factor is preferentially selected, the magnetostrictive material layer is iron gallium (FeGa), wherein the lengths of the PZT-43 and the FeGa are 4cm, and according to the theoretical condition that the longitudinal combined force based on the free end of the cantilever structure should be 0, the relationship between the thickness of the piezoelectric material layer and the magnetostrictive material layer is satisfied when the neutral plane of the magneto-electric cantilever is just the interface of the piezoelectric material layer and the magnetostrictive material layer through integral calculation: the optimal thickness ratio relation between the simple longitudinal stretching vibration magnetostriction layer and the piezoelectric layer under the low-frequency condition is as follows: Wherein the method comprises the steps ofAndThe elastic flexibility components under the constant electric field of the piezoelectric layer and the constant magnetic field intensity of the magnetostrictive layer are respectively obtained, the electromechanical coupling coefficient of the material of the piezoelectric layer and the electromechanical coupling coefficient of the material of the magnetostrictive layer are respectively obtained, therefore, when the neutral plane of the magnetoelectric cantilever beam is just the interface between the piezoelectric material layer and the magnetostrictive material layer, the total thickness of the magnetoelectric composite material is set to be 1mm, the thickness of PZT-43 is 0.9mm, the thickness of FeGa is 0.1mm, and when the optimal thickness ratio relation between the simple longitudinal stretching vibration magnetostrictive layer and the piezoelectric layer under the low frequency condition is applied, the thickness of PZT-43 is 0.7mm, the thickness of FeGa is 0.3mm, and the neutral plane of the magnetoelectric cantilever beam appears in the FeGa layer. The low-frequency condition of the longitudinally extending and contracting vibration magnetostrictive layer and the piezoelectric layer means that the longitudinally extending and contracting vibration magnetostrictive layer and the piezoelectric layer have non-resonant frequencies and are far smaller than the resonant frequencies.
The simulation modeling is carried out on two magnetoelectric cantilevers Liang Tianxian with different thickness ratios in the example by utilizing COMSOL Multiphysics finite element simulation software, the piezoelectric material is modeled by a piezoelectric constitutive equation, the magnetic material is modeled by a piezomagnetic constitutive equation, and the simulation modeling method can be used for simulating dynamic bidirectional coupling among electricity, sound and magnetism. The cantilever beam vibrates in the length-thickness plane, and the width is far smaller than the length, so that the width almost has no influence on the vibration state, the two-dimensional model is enough to meet the simulation requirement, the simulation speed and model convergence are facilitated to be improved, and the specific results are as follows:
Fig. 2 is a simulation result of resonance deformation of the magnetoelectric antenna under electric excitation. As can be seen from the simulation result graph, this is a typical first order bending resonance mode.
Fig. 3 (a) is a simulation result when magnetization in the magnetostrictive layer of the magnetoelectric antenna is cancelled under electric excitation. The upper rectangle is FeGa and the lower rectangle is PZT-43, wherein the arrow on the figure is oriented to indicate the direction of magnetization, and from the simulation results it can be seen that when the neutral plane is present in the magnetostrictive layer, rather than just at the interface of the piezoelectric layer and the magnetostrictive layer, the magnetization directions of the magnetic layers on both sides of the neutral plane are exactly opposite, which also means that the magnetization of the magnetic layers is cancelled. This is due to the fact that the magnetic layer on one side of the neutral plane is vibrating in extension (or contraction) and the magnetic layer on the other side is vibrating in opposite directions.
Fig. 3 (b) is a simulation result when magnetization in the magnetostrictive layer of the magnetoelectric antenna is not canceled under electric excitation. Also, the arrow on the graph is oriented to indicate the direction of magnetization, and it can be seen from the simulation result that when the neutral plane just appears at the interface between the piezoelectric layer and the magnetostrictive layer, the magnetizations in the magnetostrictive layer are all oriented to the same direction, which also means that no cancellation of the magnetizations occurs in the magnetic layer, which is a phenomenon that is expected to be seen. Since all the magnetostrictive layers are on one side of the neutral plane, the magnetostrictive layers only vibrate in the same stretching or shrinking mode at the same time, and the magnetization directions are consistent.
FIG. 4 is a graph showing the change of the inverse magnetoelectric coefficient with frequency in the magnetostrictive layer of the magnetoelectric antenna under electric excitation. The two figures are compared with each other, and it can be found that when the magnetization in the magnetostrictive layer is not counteracted, the variation of the magnetic induction intensity is actually larger than when the magnetization in the magnetostrictive layer is counteracted. At the same time, the magnetic flux in the magnetic layer changes the most when the acoustic resonance frequency is observed, which is the result of strengthening the magneto-electric coupling by the acoustic resonance.
The working frequency of the device is 315Hz, and the electromagnetic wavelength in the frequency band is about 952.4 km. The size of the low-frequency mechanical magnetoelectric antenna based on the cantilever structure can be 40 multiplied by 6 multiplied by 1mm through reasonable design, and is far smaller than the sizes of the traditional electric resonance antenna and the simple telescopic vibration mechanical magnetoelectric antenna.
It should be noted that the actual device is not limited to the width, thickness, and aspect ratio in the examples. Because these parameters can be adjusted for specific materials, expected operating frequencies, etc., as long as the neutral plane of the layered magnetoelectric composite material of the cantilever structure is ensured to be just the interface between the piezoelectric material layer and the magnetostrictive material layer.
It should be noted that the actual device is not limited to the material configuration in the example, and the piezoelectric material with high piezoelectric coefficient is selected, and the magnetic material with high magnetic permeability and high magnetostriction helps to further improve the radiation performance of the antenna.