KR101354158B1 - Vibration-driven eletromagnetic energy harvester - Google Patents

Abstract

The present invention relates to a vibration-driven electro-magnetic energy harvester comprising: a cylindrical housing forming a hollow portion therein; FR-4 springs installed at an upper end and a lower end of the housing respectively; an NdFeB permanent magnet positioned between the FR-4 springs for moving up and down within the hollow portion; and a coil part positioned near the NdFeB permanent magnet and wound around the circumferential surface of the housing. The coil part is made of the first to the third coils wound along a plurality of dent recesses formed equidistantly and spaced apart from each other on the circumferential surface of the housing. The first to the third coils generate different output voltages according to an input frequency, an input acceleration and a load resistance. The energy harvester according to the present invention generates an output of 1.59 mW at the acceleration of 0.2 g and the input frequency of 16 Hz. The present invention can design and produce the harvester with a high output at a low frequency, so can be used as an energy source for a small sized electronic device.

Description

Vibration-driven eletromagnetic energy harvester

The present invention relates to an electromagnetic energy harvester, and more particularly, to a high-efficiency vibration type electromagnetic energy harvester having high power at low frequencies with only linear movement of upper and lower while preventing left and right movement of permanent magnet based on FR-4 spring. It is about.

Currently, chemical batteries that convert energy generated through chemical reactions into electrical energy are widely used as power sources for portable electronic devices. Such chemical cells have advantages such as high energy density, small size, low cost, etc., but also have a problem in that limited lifetime, replacement or recharge is not easy.

Recently, the emphasis is on the development of pollution-free alternative energy. Examples of alternative energy sources include harvesting energy sources available from the environment such as solar, heat, wind and vibration. Harvesting energy technology is an eco-friendly green technology that does not emit pollutants while extracting energy from the surrounding environment. Its main applications are low power communication devices, sensor networks, implantable devices, and mobile devices that can be driven by small amounts of power. to be.

However, the above-described alternative energy, the power generation method using the sun, heat, wind, and the like has not yet a high conversion efficiency, but also takes a lot of equipment and management costs. In addition, the energy generation method is limited to the energy source of portable, wearable and portable small electronic devices.

On the other hand, the energy conversion method using the vibration is particularly applicable to a small power supply, there is an advantage that the device does not need to be exposed to the outside, it is advantageous to attach or insert the equipment. In addition, due to the potential for continuous use regardless of time and place, research is being actively conducted for use as power supplies such as small electronic devices, wireless sensor nodes (WSNs), and medical devices.

Representative power generation technology that collects energy using vibration is classified into electrostatic, piezoelectric, and electromagnetic according to materials and conversion methods.

Capacitive type is easy to integrate according to MEMS (micro electromechanical system) manufacturing process, but it is not suitable for small power supply because of low energy conversion efficiency and initial external voltage source.

Piezoelectric material is a piezoelectric material such as PZT or PVDF (polyfinylidenedifluoride) is used, it is easy to miniaturize, no external power source is required. However, there is a risk of piezoelectric material breaking because of its operation at high impedance and high frequencies of hundreds of kHz.

Electromagnetics, on the other hand, use the relative movement between an induction coil and a permanent magnet. Electromagnetic type is simple in structure and manufacturing, but it is difficult to integrate and has very low output voltage level. On the other hand, due to the structure of a simple mechanical resonator there is an advantage that can be designed with a very high energy conversion efficiency and low frequency.

Because of the advantage that low frequency electromagnetic design can be used in recent years, a lot of research has been made to use as an energy source of small electronic devices. In particular, considering that the vibration frequency generated in daily life is less than 100 kHz, it is preferable that the vibration type energy harvester is designed with a low electromagnetic frequency.

Research on electromagnetic energy harvesters is steadily being conducted. Various methods for improving the output power have been proposed.

By the way, the electromagnetic energy harvester to date uses a spring made of a specific material. The material used for the spring is silicon or copper. However, these materials have a high elastic modulus and the manufacturing process is complicated to design a spring that can accommodate low frequency.

Accordingly, there is a need to manufacture springs of electromagnetic energy harvesters using materials that are easy to design at low frequencies. In other words, when the vibration type electromagnetic energy harvester is attracting attention as a power source of a portable small electronic device, when a person moves, the frequency band of motion generated in each part of the human body is low frequency with an acceleration of 1 to 10 Hz and about 0 to 1 G. Research and development of a spring-loaded energy harvester capable of low frequency design to have high energy conversion efficiency is required.

On the other hand, the electromagnetic energy harvester produces electrical energy by using the relative movement between the induction coil and the permanent magnet, as described above, the permanent magnet must be moved linearly to produce a relatively high output power.

To this end, it is necessary to linearly move in the vertical direction while preventing the left and right movement of the permanent magnet.

Accordingly, an object of the present invention is to solve the above problems, to provide a vibration type electromagnetic energy harvester having a high output at a low frequency by moving linearly in the vertical direction while preventing the left and right movement of the permanent magnet.

According to a feature of the present invention for achieving the above object, a cylindrical housing having a hollow portion formed therein; First and second springs installed on upper and lower ends of the housing; A magnet positioned between the first spring and the second spring and vertically moving in the hollow part; And a coil unit configured to wind an outer circumferential surface of the housing corresponding to the position of the magnet and generate an electromotive force according to the vertical movement of the magnet.

The first spring and the second spring, characterized in that made of FR-4 material.

The magnet is characterized in that the NdFeB permanent magnet.

A plurality of grooves are formed on the outer circumferential surface of the housing at predetermined intervals, and the coils of the coil unit are wound around the grooves, respectively.

The groove is partitioned and formed in an upper / middle / lower position while being spaced apart by a predetermined interval along the longitudinal direction of the housing, and the first to third coils wound around the upper / middle / lower position are input frequency (input). Output vlotage occurs differently according to frequency, input acceleration, and load resistance.

The output voltage value according to the input frequency is the highest in the first coil and the lowest in the second coil.

When the input acceleration increases, the output voltage values of the first to third coils also increase.

As the load resistance changes, the output voltage of the first coil and the third coil increases, but the output voltage of the second coil is zero.

The output power according to the change in the load resistance is characterized in that the output of 1.59 mW at 0.2 acceleration (g) and 16 Hz input frequency.

According to the vibration type electromagnetic energy harvester configured as described above, the FR-4 spring is mounted on the upper and lower ends of the cylindrical housing, and the NdFeB permanent magnet is configured to move up and down between the FR-4 springs. In addition, the coil is wound around the outer peripheral surface of the housing at grooves formed at regular intervals.

Accordingly, the spring applied to the energy harvester can be manufactured for a low frequency, and the linear movement of the NdFeB permanent magnet occurs in the vertical direction while preventing the left and right movements, thereby providing a high output.

In other words, the energy harvester according to the present embodiment generates an output of 1.59 mW at 0.2 acceleration (g) and 16 Hz input frequency, and it is confirmed that an output of approximately 10 times or more is obtained compared to other vibration type electromagnetic energy harvesters.

Therefore, it is possible to provide a high efficiency generator capable of operating at a low frequency, can be utilized as an energy source optimized for portable or mobile small electronic devices can be expected to be marketable and economical.

1 is a cross-sectional view showing a structure of a vibration type electromagnetic energy harvester according to a preferred embodiment of the present invention
2 is a diagram showing resonance frequencies of materials for spring shapes;
Figures 3a and 3b is a view showing a geometric example of the FR-4 spring applied to the vibration type electromagnetic energy harvester of the present invention
Figure 3c is a perspective view showing an example of the FR-4 spring according to the present invention
Figures 4a to 4c is a view showing the shape change according to the mode of the magnet and FR-4 spring in accordance with the present invention
5 is a graph showing the maximum displacement amount of the magnet according to the input frequency in accordance with the present invention
6 is a graph showing an output voltage vs. an input frequency according to an embodiment of the present invention;
7 is a graph illustrating an output voltage versus an input acceleration according to an embodiment of the present invention.
8A and 8B are graphs illustrating output voltages and output powers of the first to third coils according to the change of the load resistance according to an embodiment of the present invention.

Hereinafter, an embodiment of a vibration type electromagnetic energy harvester according to the present invention will be described in detail with reference to the accompanying drawings.

First, it should be noted that the vibration type electromagnetic energy harvester of the present embodiment provides a high output power and a low resonant frequency, and is manufactured according to ANSYS-FEM (Finite element model) structural analysis. In addition, the structure of the FR-4 spring and NdFeB permanent magnet, which are the components of the vibration type electromagnetic energy harvester, is defined as a spring-mass system.

1 is a cross-sectional view showing the structure of a vibration type electromagnetic energy harvester according to a preferred embodiment of the present invention. As shown in FIG. 1, the vibration type electromagnetic energy harvester (hereinafter, referred to as 'energy harvester') 100 includes a housing 110, a magnet 120, a spring 130, a coil part 140, and a jig. 140).

The housing 110 forms a shape and a skeleton of the body, and the body substantially forms the outer shape of the energy harvester 100. The body is formed in a cylindrical shape, the hollow portion 112 is formed in the vertical direction therein to enable the vertical movement of the magnet 120. In addition, a copper coil 140 is wound around the outer circumferential surface of the housing 110, in which a plurality of grooves 114 are formed to stably wind the copper coil 140. The groove 114 is divided into three regions, such as an upper / middle / lower region, in the longitudinal direction of the housing 110. And the housing 110 is made of teflon (teflon).

The hollow part 112 of the housing 110 accommodates a magnet 120 that moves up and down along the hollow part 112. The magnet 120 of this embodiment is a cylindrical NdFeB permanent magnet (denoted as '120') having excellent magnetic flux density. The magnet 120 is located at the center of the spring 130 to increase the deflection and inertia of the magnet 120. In an embodiment the magnet has a mass of 27.5 g.

First and second springs 130a and 130b are mounted on upper and lower ends of the housing 110. The spring 130 is made of FR-4 material. In the following description, spring and FR-4 spring are used in the same sense, and the same reference numerals will be given. FR-4 is a material used as the main material of PCB (Printed Circuit Board) substrate, and has a low elastic modulus lower than that of silicon (Si) and copper, which has been conventionally used, and thus is easy to manufacture for low frequency springs. Their modulus of elasticity is 150 GPa for silicon, 120 GPa for copper, and 15 GPa to 20 GPa for FR-4. In the electromagnetic transducer, the resonant frequency of the spring-mass system, which is a vibration system consisting of spring and mass, depends on the spring and mass, and the material of the spring affects the function of the energy harvester. Because it acts as. Meanwhile, the spring 130 made of FR-4 may be manufactured in a spiral or curved shape due to low spring constant, high amplification, low stress, and the like. And CNC 3D modeling is used in the manufacture of the spring 130 in the embodiment.

In the present embodiment, the FR-4 spring 130 has a first spring 130a and a second spring 130b installed at the top and bottom of the magnet 120, respectively. By using two FR-4 springs as described above, it is possible to extend the fatigue failure and to move the magnet 120 linearly in the vertical direction while preventing the movement in the left and right directions.

The coil part 140 is wound around the plurality of recesses 114 formed in the housing 110. The coil part 140 is composed of the first to third coils 140a to 140c, and is made of copper, and the diameter of the coil in the embodiment is 0.1 mm. The first to third coils 140a to 140c are portions that generate electromotive force by the change of the magnetic field according to the relative position change of the magnet 120 moving up and down in the hollow part 112. The first to third coils 140a to 140c generate output voltages differently according to an input frequency, an input acceleration, and a load resistance, respectively. This will be described through simulation results to be described later.

The jig 150 made of a plastic material is coupled to the top and bottom of the housing 120. The jig 150 serves to fix the first spring 130a and the second spring 130b in the hollow part 112.

As described above, the energy harvester 100 according to the present embodiment is characterized in that the FR-4 springs 130 are installed at the upper and lower ends of the housing 110, respectively. The three coils 140a to 140c are respectively wound in the upper, middle, and lower regions of the housing 110 to generate different output values according to the relative position change of the up and down moving magnet 120.

Next, with respect to FR-4, which is a material of the spring employed in the energy harvester 100 of the present embodiment, the relative resonant frequency values of silicon, aluminum, and copper used as materials of the existing spring will be described. This is a reference to Figure 2, Figure 2 is a diagram showing the resonant frequency for each material for the spring shape. 2 shows the resonant frequency values of FR-4, silicon, aluminum and copper.

As described above, in order to design an energy harvester 100 having a high output at a low frequency, the material of the spring 130 must overcome durability such as fatigue failure and also provide characteristics for low modulus or high tensile force. . The material satisfying these conditions is FR-4 material and is used as the material of the spring in this embodiment.

Referring to FIG. 2, it can be seen that the FR-4 material exhibits the lowest resonant frequency in the first to third resonant modes. In other words, when comparing the resonant frequency in each resonant mode with other materials, such as silicon, aluminum, and copper, FR-4 has a value of 16.25 차 in primary mode, 75.24 2 in secondary mode and 91.96 ㎐ in tertiary mode. It can be seen that this has a relatively low resonant frequency value than the other three materials, silicon, aluminum, and copper described above.

Figures 3a and 3b is a view showing a geometric example of the FR-4 spring 130 applied to the vibration type electromagnetic energy harvester of the present invention, Figure 3a is a curve-type FR-4 spring, Figure 3b is An example of a right type FR-4 spring is shown.

For these two types of FR-4 springs 130, the maximum stresses that affect the fatigue life of the spring-mass meter are 182 MPa and the right angle type FR-4 springs. Was found to be 246 MPa.

As a result, it can be seen that the maximum stress is 64 MPa higher than that of the rectangular FR-4 spring, compared to the curved FR-4 spring. Here, the maximum stress value is a value extracted from the curve and the right angle region of the FR-4 spring 130.

On the other hand, Figure 3c shows an example of the FR-4 spring according to the present invention in a perspective view. As shown in the figure, the FR-4 spring 130 is formed in a thin film form and is positioned at the top and bottom of the magnet 120. And in the embodiment FR-4 spring 130 is made of 1 mm wide and 200 ㎛ thick. In addition, the gaps between the beams, the inner diameter and the outer diameter are formed to be 1 mm, 17 mm and 20 mm, respectively. Of course, the above-described numerical value is only one embodiment, and it will be obvious that it can be manufactured in a different size.

4a to 4c is a view showing a change in shape according to the mode of the magnet and the FR-4 spring in accordance with the present invention.

That is, the shape when the resonance frequency of the primary resonance mode of the FR-4 spring is 16.25 Hz is shown in FIG. 4A, and the shape when the resonance frequency of the secondary resonance mode of the FR-4 spring is 75.24 Hz is shown in FIG. 4B, the shape when the resonant frequency of the third resonance mode of the FR-4 spring is 91.96 Hz is shown in FIG. 4C.

5 is a graph showing the maximum displacement amount of the magnet according to the input frequency.

Referring to FIG. 5, it can be seen that the maximum displacement of the FR-4 spring 130 occurs in the primary mode (16.25 Hz) in which the magnet 120 moves downward (z-axis) in the coil direction when 2.36 mm. .

That is, the magnet 120 is positioned 1 mm higher or lower in the center of the first coil 140a and the third coil 140c. Under the conditions of gravity, the magnet 120 moves 0.8 mm downward.

Accordingly, the upper edge portion of the magnet 120 has a gap of about 0.2 mm with the center of the first coil 140a, and the lower edge portion of the magnet 120 has a 1.8 mm gap with the center of the third coil 140c. there is a gap.

Next, a test process for the vibration type electromagnetic energy harvester according to the present embodiment will be described.

The equipment and conditions used to measure and analyze the output of energy harvesters are as follows. In order to generate and control a vibration signal, a signal generator, a controller, an amplifier, a vibration accelerometer, a vibrator, and an oscilloscope are included. According to the embodiment, the signal generator 'SCO-01P', the controller 'LAS-200', the amplifier 'PA25E-CE', the vibration accelerometer 'IEPE-8341', the vibrator 'LDS-V201-M4', the measuring instrument Uses 'LeCroy'.

As an analysis condition using this, frequency, vibration acceleration, and load resistance were measured as input values, and the output voltage Vrms output from the first coil 140a to the third coil 140c of the coil unit 140 was measured.

6 is a graph illustrating an output voltage versus an input frequency according to an embodiment of the present invention.

As shown in FIG. 6, the output voltages of the first to third coils 140a to 140c generate the largest output value when the input frequency is 16 Hz. In particular, at 0.2 acceleration g and 16 kHz input frequency, the first coil 140a has a 2.56 Vrms value, the third coil 140c has a 2.24 Vrms value, and the second coil 140b has a 0.72 Vrms value. Of course, when the first to third coils 140a to 140c are connected in series, it can be seen that an output voltage value of 5.52 Vrms occurs.

7 is a graph illustrating an output voltage versus an input acceleration according to an embodiment of the present invention.

Referring to FIG. 7, it can be seen that as the input acceleration increases, the output voltages of the first to third coils 140a to 140c also increase steadily. The output voltage of the first coil 140a is higher than that of the second coil 140b and the third coil 140c, which are different from each other.

8A and 8B are graphs illustrating output voltages and output powers of the first to third coils according to a change in the load resistance according to an exemplary embodiment of the present invention.

8A shows an output voltage value according to the load resistance. As shown in the drawing, the first coil and the third coil 140a to 140c correspond to the increase in the load resistance, and thus the output voltage is also increased. On the other hand, in the second coil 140b located in the center of the housing 110, even if the load resistance increases, the output voltage is zero or generates a value low enough to be close to zero.

8b shows the output power value according to the load resistance. Referring to FIG. 8B, when the load resistance is 1.66 kW, the power of 1.59 kW is output.

Based on the experimental results, the vibration-type electromagnetic energy harvester 100 according to the present embodiment generates an output of 1.59 mW at an acceleration of 0.2 g and 16 Hz, and a power density of 1.125 mW /. As cm ³ g ² , it can be seen that high power can be provided at a low frequency. This can be confirmed more clearly through the following [Table 1].

That is, Table 1 summarizes the results of comparing the frequency, power, and power density of the energy harvester according to the present embodiment and other conventional electromagnetic electromagnetic energy harvesters (EMEH) disclosed in the related fields. .

Rearch group Frequency (Hz) Power (mW) NPD (mW / cm ³ g ² ) G.Hatipoglu and H.Urey (1) 24.4 0.4 1.7 * 10 ^-2 Yang et.al. (2) 369 3.2 * 10 ^-3 - N.G.Elvin, A.A. Elvin (3) 112.25 - 1.7 * 10 ^-3 S.Cheng, D.P.Arnold (4) 9.2 0.55 2.3 * 10 ^-2 C. Cepnik et al. (5) 50 13.4 - P. Wang et al. (6) 280.1 21.2 * 10 ^-3 1.01 * 10 ^-1 Ching et al. (7) 110 0.83 8.7 * 10 ^-3 Pan et al. (8) 60 0.1 8.6 * 10 ^-1 Von Buren et al. (9) 20 2.5 * 10 ^-2 9.6 * 10 ^-3 Beeby et al. (10) 52 4.6 * 10 ^-3 4.48 * 10 ^-8 The
Energy harvester 16 1.59 1.125

Referring to [Table 1], the energy harvester 100 of the present invention has a lower resonance frequency and a higher output power and power density than those of the conventional energy harvesters disclosed in the papers (1) to (10). It can be seen that. In other words, approximately 10 times more output is obtained.

Meanwhile, in order to compare the performance with the energy harvester of the present invention, the papers (1) to (10) disclosed in Table 1 referring to the conventional vibration type electromagnetic energy harvester are as follows.

(One). Hatipoglu G and Urey 2010 FR-4 based electromagnetic energy harvester for wireless sensor nodes Smart Mater . Struct . 19 015022-015032

(2). Yang B, Lee C, Xiang W, Xie J, He JH, Kotlanka RK, Low SP and Feng H 2009 Electromagnetic energy harvesting from vibrations of multiple frequencies J. Micromech . Microeng . 19 035001

(3). Elvin NG and Elvin AA 2011 An experimentally validated electromagnetic energy harvester J. Sound Vib . 330 2314-2324

(4) Cheng S and Arnold DP 2010 A study of a multi-pole magnet generator for low-frequency vibrational energy harvesting J. Micromech . Microeng. 20 025015

(5) Cepnik C, Radler O, Rosenbaum S, Stohla T and Wallrabe U 2011 Effective optimization of electromagnetic energy harvesters through direct computation of the electromagnetic coupling, Sensors Actuators A 167 416-421

(6) Wang P, Liu H, Dai X, Yang Z, Wang Z and Zhao X 2012 Design, simulation, fabrication and characterization of a micro electromagnetic vibraton energy harvester with sandwiched structure and air channel J. Microelectro. 43 154-159

(7) Ching NNH, Wong HY, Li wj, lEONG PHW and Wen Z 2002 A laser micro-machined multi-modal resonating power transducer for wireless sensing systems Sensors Actuators A 97-98 685-690

(8) Pan CT, Hwang YM and Hu HL 2006 Fabrication and analysis of a magnetic self-power microgenerator J. Magn . Magn . Mater . 304 394-396

(9) Buren TV and Troster G 2007 Design and optimization of a linear vibration-driven electromagnetic micro-power genereator Sensors Actuators A 135 765-775

(10) Beeby SP, Torah RN, Tudor MJ, Glynne-Jones P, O'Donnell T, Saha CR and Roy S 2007 A micro electromagnetic generator for vibration energy harvesting J. Micromech . Microeng . 17 1257-1265

As described above, this embodiment is a vibration type electromagnetic energy harvester comprising two FR-4 springs, NdFeB permanent magnets, and a copper coil wound in three regions while preventing the left and right movement of the permanent magnets Up and down movement shows that the output is several times higher than conventional energy harvesters at low frequencies.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, It will be apparent that modifications, variations and equivalents of other embodiments are possible. Therefore, the true scope of the present invention should be determined by the technical idea of the appended claims.

110 housing 112 hollow part
114: groove 120: magnet
130: FR-4 spring 140: coil

Claims (9)

A cylindrical housing having a hollow portion formed therein;
First and second springs installed at upper and lower ends of the housing and made of FR-4;
A magnet positioned between the first spring and the second spring and vertically moving in the hollow part; And
Vibrating electromagnetic energy harvester comprising a coil unit for winding the outer peripheral surface of the housing corresponding to the position of the magnet, and generates an electromotive force according to the vertical movement of the magnet. delete The method of claim 1,
The magnet is a vibration type electromagnetic energy harvester, characterized in that the NdFeB permanent magnet. The method of claim 1,
The outer circumferential surface of the housing is formed with a plurality of grooves spaced at a predetermined interval,
The groove is a vibration type electromagnetic energy harvester, characterized in that the coil of the coil unit is wound. 5. The method of claim 4,
The recess is formed by partitioning the upper / middle / lower position spaced apart a predetermined interval along the longitudinal direction of the housing,
The first to third coils wound in the grooves of the upper, middle and lower positions may have an output voltage according to an input frequency, an input acceleration, and a load resistance. Vibration type electromagnetic energy harvester, characterized in that each occurs differently. The method of claim 5, wherein
The output voltage value according to the input frequency is the highest in the first coil, the lowest in the second coil is characterized in that the vibration type electromagnetic energy harvester. The method of claim 5, wherein
The vibration type electromagnetic energy harvester, characterized in that as the input acceleration increases, the output voltage values of the first to third coils also increase. The method of claim 5, wherein
The output voltage of the first coil and the third coil increases according to the change of the load resistance, but the output voltage of the second coil is zero. The method of claim 5, wherein
The output power according to the change of the load resistance is a vibration type electromagnetic energy harvester, characterized in that the output of 1.59 mW at 0.2 acceleration (g) and 16 Hz input frequency.

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