阅读说明：本技术 一种基于两端固定梁的磁场能量收集器 (Magnetic field energy collector based on two-end fixing beam ) 是由 储昭强 沈莹 高俊奇 孙泽尘 于 2021-08-17 设计创作，主要内容包括：本发明提出一种基于两端固定梁的磁场能量收集器,该能量收集器包括压电单元、永磁单元、横梁、夹具和基座,基座上设置有两个夹具,梁的中央固定有磁铁,磁铁的两侧对称固定有两个压电单元。本发明开发出一种新型的磁-力-电磁场能量采集器,打破了传统悬臂梁结构中工作频率与磁铁质量的强依赖关系,实现了50Hz微弱环境磁场(<1Oe)能量收集问题,结构稳定,应用面广,可以收集一般电线产生的磁场能。(The invention provides a magnetic field energy collector based on beams fixed at two ends, which comprises piezoelectric units, permanent magnet units, a cross beam, clamps and a base, wherein the base is provided with the two clamps, the center of the beam is fixed with a magnet, and two sides of the magnet are symmetrically fixed with the two piezoelectric units. The invention develops a novel magnetic-force-electromagnetic field energy collector, breaks through the strong dependence relationship between the working frequency and the magnet quality in the traditional cantilever beam structure, realizes the energy collection problem of a 50Hz weak environmental magnetic field (<1Oe), has stable structure and wide application range, and can collect magnetic field energy generated by common electric wires.)

1. The utility model provides a magnetic field energy collector based on both ends fixed beam, its characterized in that includes two piezoelectric material (1), magnet (2), roof beam (3), two anchor clamps (4) and base (5), be provided with two anchor clamps (4) on base (5), accompany roof beam (3) between two anchor clamps (4), the central authorities of roof beam (3) are fixed with magnet (2), the both sides of magnet (2) are located roof beam (3) symmetry and are fixed with two piezoelectric material (1).

2. The magnetic field energy harvester based on the two-end fixed beam according to claim 1, characterized in that the piezoelectric material (1) is a piezoelectric ceramic or a piezoelectric single crystal.

3. The magnetic field energy collector based on two fixed beams according to claim 1, characterized in that the size of the beam (3) is 160mm x 10mm x 0.5mm, the size of each piezoelectric material (1) is 40mm x 7mm x 0.3mm, and the distance between the two piezoelectric materials (1) is 13mm, which can ensure that the collector efficiency of the magnetic field energy collector is higher under the condition that the resonance frequency is kept at 50 Hz.

Technical Field

The invention relates to a magnetic field energy collector based on fixed beams at two ends, and belongs to the technical field of energy collectors.

Background

The technology of the internet of things plays a key role in the coming intelligent world. Wireless sensors and transceivers are typical components of the internet of things, which currently use batteries to power these internet of things devices, but when the number of network nodes exceeds trillions, maintenance and replacement of batteries will be nearly infeasible. Furthermore, charging or replacing batteries in harsh environments such as deep sea, high altitude, etc. is a challenging task. In this regard, energy harvesting technology can be viewed as an ultimate solution to replace batteries, implementing self-powered internet of things components, and thus providing long-term power for wireless sensor networks. Of the many collectable energy sources such as vibration, radiation, magnetic field/electric field, stray magnetic energy generated by power transmission cables, industrial machinery, household appliances, and the like is technically favored because of its fixed frequency of 50 or 60hz and its wide distribution.

Coil arrangements based on the principle of electromagnetic induction are generally employed to capture the magnetic field energy wasted in the surroundings, however, in the context of low frequency magnetic field energy harvesting, the output power of the coil is very limited. In contrast, a magneto-force-electric (MME) energy harvester is considered the most promising option for harvesting waste magnetic field energy. A typical magneto-mechanical-electric (MME) energy collector structure is a cantilever beam with a magnetic mass attached to its free end. When an external magnetic field perpendicular to the magnetization direction of the tip magnet is applied, a bending moment can be generated to excite a magnetic-force-electric (MME) energy collector, then the generated stress is transferred to the piezoelectric layer through elastic coupling, and finally, the piezoelectric effect is utilized to obtain electric output. In order to increase the output power of the magneto-electro-mechanical (MME) energy collector, the magneto-electric effect can be further integrated by using magnetostrictive multilayer structures (Metglas, FeGa and Ni). For example, Ryu et al reported a magneto-force-electric (MME) energy harvester composed of a low loss piezoelectric crystal and a textured magnetostrictive material that achieved a milliwatt output of 60Hz at 7Oe magnetic field.

The prior art generally employs magnetic fields of strength above 5Oe to demonstrate the energy harvesting performance of a typical magneto-force-electric (MME) energy harvester. The world health organization recommends that the threshold value of 50/60hz magnetic field level accessible to the public be 1Oe, and that the magnetic field strength at 30 cm for most household appliances is also below this threshold value. Although a considerable energy output can be obtained by placing a magnetic-force-electric (MME) energy collector close to the magnetic source, the side effects on industrial equipment or household appliances will greatly limit the practical application. In addition, the magnet at the free end in the MME energy collector with the cantilever beam structure has large flexibility, and contributes to most of the kinetic energy of the system. In this case, the free end magnet mass is highly correlated to the resonant frequency of the MME cantilever. In order to maintain a constant resonant frequency of 50/60Hz, it is difficult to increase the weak magnetic response capability by increasing the mass of the magnet while maintaining the rigidity of the system. On the other hand, cantilever beams are also susceptible to buckling under asymmetric support when a heavier free end mass is added. Therefore, a novel magnetic-force-electric (MME) energy harvester needs to be developed to break through the strong dependence relationship between the working frequency and the magnet mass in the traditional cantilever beam structure, and achieve 50Hz weak environmental magnetic field (<1Oe) energy collection.

Disclosure of Invention

The invention aims to solve the technical problems in the background art, provides a novel magnetic-force-electromagnetic field energy collector, breaks through the strong dependence relationship between the working frequency and the magnet quality in the traditional cantilever beam structure, realizes the energy collection problem of a 50Hz weak environmental magnetic field (less than 1Oe), has stable structure and wide application range, can collect magnetic field energy generated by a common wire, and is applied to power supply of an internet of things sensor, magnetic energy collection of an electrified lead and detection of an alternating current sensor.

The invention provides a magnetic field energy collector based on beams fixed at two ends, which comprises two piezoelectric materials, a magnet, a beam, two fixtures and a base, wherein the base is provided with the two fixtures, the beam is clamped between the two fixtures, the magnet is fixed in the center of the beam, and the two sides of the magnet are positioned on the beam and are symmetrically fixed with the two piezoelectric materials.

Preferably, the piezoelectric material is a piezoelectric ceramic or a piezoelectric single crystal.

Preferably, the brass beam has dimensions of 160mm x 10mm x 0.5mm, each piezoelectric material has dimensions of 40mm x 7mm x 0.3mm, and the two piezoelectric materials are spaced apart by 13mm, which ensures a higher collector efficiency of the magnetic field energy collector at a resonance frequency of 50 Hz.

The magnetic field energy collector based on the fixed beams at the two ends has the beneficial effects that:

1. the invention utilizes the second-order vibration mode of the beams fixed at the two ends, and the permanent magnet in the middle provides driving force on one hand, and reduces the natural frequency of the system by increasing the equivalent mass of the beams on the other hand. The structural design has the advantages that: 1) the deflection of the middle part of the second-order vibration mode of the fixed beams at the two ends is small, and the contribution of the mass of the magnet to the equivalent mass of the system is obviously reduced compared with a cantilever beam. Therefore, the mass of the magnet can be ensured to be increased, and meanwhile, the system rigidity does not need to be improved to the same extent, so that the weakening of the coupling effect of the system is avoided; 2) the stability and rigidity of the beam are increased compared with the traditional cantilever beam, so that more permanent magnets are supported and placed; 3) under a weak field, the increase of the permanent magnet is beneficial to improving the driving force of the beam, so that the power output under a low field is enhanced.

2. The cantilever beam structure is innovative in structural theory, and a novel two-end clamping structure is adopted instead of the traditional cantilever beam structure.

3. The invention can generate higher output electric power in a small magnetic field of 50Hz and below 1 Oe.

4. The invention has stable structure and wide application range, and can collect magnetic field energy generated by common wires.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate embodiments of the invention and, together with the description, serve to explain the invention and not to limit the invention.

In the drawings:

fig. 1 is a schematic structural diagram of a magnetic field energy collector based on two end fixing beams according to the present invention.

Fig. 2 is a resonance mode diagram of the magnetic field energy collector based on the fixed beams at two ends when the magnetic field energy collector works.

FIG. 3 is a schematic size diagram of a magnetic field energy collector based on two end fixed beams according to the present invention; where a represents the piezoelectric material length, L represents the brass beam length, and s represents the distance of the two piezoelectric materials from the center of the beam.

FIG. 4 is a load output power diagram of the magnetic field energy collector based on the fixed beams at two ends under the 50Hz alternating current magnetic field.

Fig. 5 is a comparison of the mode of a cantilever beam magnetic-force-electric (MME) energy collector with a two-end clamped magnetic-force-electric (MME) energy collector, wherein (a) represents the operating mode of the cantilever beam magnetic-force-electric (MME) energy collector; (b) representing the working mode of a two-end clamping magnetic-force-electric (MME) energy collector; (c) and (3) showing the output comparison of the cantilever beam structure and the MME energy collector with the two-end clamping structure in the resonance state.

Fig. 6 is a stress-deflection distribution diagram of a magnetic field energy collector based on two fixed beams, wherein (a) shows a stress analysis diagram of a magnetic-force-electric (MME) energy collector clamped at two ends, (b) shows a bending moment diagram of a beam, and (c) shows a deflection distribution of the beam.

The piezoelectric ceramic material comprises 1-piezoelectric material, 2-magnet, 3-beam, 4-clamp and 5-base.

Detailed Description

The following detailed description of embodiments of the invention is provided in conjunction with the appended drawings:

the first embodiment is as follows: the present embodiment is explained with reference to fig. 1 to 6. The magnetic field energy collector based on the beams fixed at two ends 1 comprises two piezoelectric materials 1, two magnets 2, a beam 3, two clamps 4 and a base 5, wherein the two clamps 4 are arranged on the base 5, the beam 3 is clamped between the two clamps 4, the magnet 2 is fixed in the center of the beam 3, and the two sides of the magnet 2 are positioned on the beam 3 and symmetrically fixed with the two piezoelectric materials 1.

The piezoelectric material 1 is piezoelectric ceramic. The piezoelectric ceramic is PZT ceramic. The magnet 2 is an N35 magnet. The clamp 4 is a stainless steel clamp. The beam 3 is a brass beam.

The working principle of the magnetic field energy collector based on the fixed beams at the two ends is as follows:

fig. 5(b) shows the mode of operation of a two-end clamped magneto-force-electric (MME) energy harvester, as shown in fig. 5, in which a permanent magnet is mounted in the center of a beam with its magnetization direction upward, and in response to an external magnetic field parallel to the length direction of the beam, a second-order bending mode can be excited. Compared to cantilever-structured magneto-force-electric (MME) energy collectors (fig. 5(a)), symmetric support and small deflection of the attached magnets is achieved in a two-end clamped magneto-force-electric (MME) energy collector. Here, a symmetrical support with a magneto-dynamic-electric (MME) energy collector clamped at both ends can withstand heavier magnets and be stable in case of strong vibrations. The small deflection can reduce the kinetic energy of the magnet, so that the resonant frequency of the two-end clamping magnetic-force-electric (MME) energy collector is less influenced by the weight change of the magnet. Thus, clamping a magneto-force-electric (MME) energy harvester at both ends may allow for the addition of more permanent magnets and thus increased bending moments. Thus, power output performance can be enhanced with low amplitude magnetic field excitation (<1Oe) at a fixed operating frequency (FIG. 5(c))

Force analysis of a two-end clamped magnetic-force-electric (MME) energy harvester is shown in figure 6(a),

concentrated moment is loaded on the beam through the magnet, and can be obtained according to moment balance and stress balance:

wherein M is_eBending moment applied to the beam for the central magnet, M_AAnd M_BRespectively the bending moment of the two clamping ends, F_AAnd F_BThe concentrated force at the two clamping ends, l is the beam length.

The bending moment diagram of the whole beam obtained by the above formula is shown in fig. 6(b),

the bending moment M is a second derivative of the deflection w, and the deflection distribution is obtained based on a beam deflection second-order differential equation and boundary conditions (EI is the bending rigidity of the beam):

and the longitudinal displacement of each point on the beam of the magnetic-force-electric (MME) energy collector clamped at two ends meets the wave equation:

the velocity at each point is therefore:

the magnet is equivalent to two mass points at the position of the mass center, and the integral kinetic energy gamma is calculated:

where ρ and A are the density and cross-sectional area of the beam, m, respectively₀And m₁The mass of the beam and the magnet respectively, so that the equivalent mass m of the system can be obtained by the formula_eq：

Meanwhile, the equivalent stiffness of the beam can be obtained by calculating the first-order resonance state of the beam:

the equivalent mass and the equivalent stiffness of the cantilever beam are respectively as follows:

by comparison, the magnet has much smaller equivalent mass ratio and much larger rigidity compared with the traditional cantilever beam, which means that the two-end clamping magnetic-force-electric (MME) energy collector can bear more magnets and thus increase the output power.

As shown in fig. 3, the length a of PZT ceramic, the length L of brass beam and the distance s between PZT in the energy collector are optimized to ensure that the collector of the energy collector has higher efficiency and can work stably under the condition that the resonant frequency is kept at 50 Hz. Through experimental comparison, the increase of the length a of the PZT ceramic is found to increase and then decrease the energy collection efficiency, and the optimal length is about 40 mm; the length of the brass beam influences the resonance frequency, and the length is set to be 16cm, which is more suitable; the energy collection efficiency increases and then decreases with an increase in the PZT ceramic pitch s, and the energy recovery efficiency at a small field of 13mm is optimized.

The sizes of the currently manufactured 50Hz two-end clamping energy collector are respectively as follows: the brass beam 3 is 160mm × 10mm × 0.5mm in size, the PZT ceramic is 40mm × 7mm × 0.3mm in size, and the PZT ceramic is 13mm apart. The output power of the energy collector under an alternating magnetic field of 50Hz is shown in figure 4.

As can be seen from FIG. 4, the optimum load output of the energy collector can be more than 1mW at a weak field of 1Oe, and can be nearly 400 μ W at a weak field of less than 0.5 Oe.

In order to solve the technical problem, the invention provides a magnetic field energy collector based on fixed beams at two ends, and the magnetic field energy collector generates a second-order bending mode to obtain the surrounding magnetic field energy through the moment excitation of the center of a bridge. Firstly, structural parameters of the magnetic field energy collector based on the fixed beams at two ends are optimized, and power output (0.4mW) under the excitation of a low-frequency (93Hz) and low-amplitude (0.48Oe) magnetic field is realized. Then, by further adding the additional magnet weight to 66g, a magnetic field energy collector based on two end fixed beams suitable for 50Hz magnetic field energy harvesting was prepared.

The experimental results prove that: at magnetic fields of 0.48 and 0.96Oe, the average power of the magnetic field energy harvester based on the two end fixed beams was 0.37 and 0.98mW, respectively, and at the low field range (<1Oe), the output power was increased by about 250% compared to the previously reported MME energy harvester.

Compared with the traditional MME cantilever beam, the maximum deflection is theoretically calculated by considering equivalent mass and spring constant, and the principle that the output power of the magnetic field energy collector based on the fixed beams at two ends is greatly improved is disclosed. The low-amplitude (0.48Oe) magnetic field of 50Hz was also successfully used to continuously power temperature/humidity sensors, which indicates the great potential of magnetic field energy collectors based on two-end fixed beams in the application field of the internet of things.

The invention has the advantages of innovating the structure theory, abandoning the traditional cantilever beam structure and adopting a novel two-end clamping structure, overcoming the prejudice of the prior art and being capable of generating higher output electric power in a small magnetic field intensity below 1 Oe. Stable in structure, the range of application is wide, can collect the magnetic field energy that general electric wire produced.

The above-mentioned embodiments further explain the objects, technical solutions and advantages of the present invention in detail. It should be understood that the above-mentioned embodiments are only examples of the present invention, and are not intended to limit the present invention, and that the reasonable combination of the features described in the above-mentioned embodiments can be made, and any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.