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A rotational piezoelectric energy harvester for efficient wind energy harvesting
Accepted Manuscript Title: A rotational piezoelectric energy harvester for efficient wind energy harvesting Authors: Jiantao Zhang, Zhou Fang, Chang Shu, Jia Zhang, Quan Zhang, Chaodong Li PII: DOI: Reference:
S0924-4247(17)30919-6 http://dx.doi.org/doi:10.1016/j.sna.2017.05.027 SNA 10136
To appear in:
Sensors and Actuators A
Received date: Revised date: Accepted date:
26-11-2016 6-5-2017 17-5-2017
Please cite this article as: Jiantao Zhang, Zhou Fang, Chang Shu, Jia Zhang, Quan Zhang, Chaodong Li, A rotational piezoelectric energy harvester for efficient wind energy harvesting, Sensors and Actuators: A Physicalhttp://dx.doi.org/10.1016/j.sna.2017.05.027 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
A rotational piezoelectric energy harvester for efficient wind energy harvesting Jiantao Zhang*, Zhou Fang, Chang Shu, Jia Zhang, Quan Zhang, Chaodong Li School of Mechatronic Engineering and Automation, Shanghai University, Shanghai 200072, China * E-mail:
[email protected]
HIGHLIGHTS: Harvesting wind energy to power the sensor nodes has evoked great interests. But the challenge in designing such wind energy harvesters is to improve the efficiency of energy harvesting for a wide range of wind speeds. In this research, a rotational piezoelectric energy harvester for efficiently harvesting wind energy is proposed. The piezoelectric (PVDF) beam generates electricity using the impact-induced vibration. But it is found that the energy output of the harvester doesn't always increase with increasing the wind speed. An analytical model is presented and simulated using finite element method. The transient responses of the piezoelectric beam subjected to an impulse pressure are obtained. The relationship between rms output voltage and excitation frequency is analyzed. To improve the harvester performance, the methods for the adjustment of the vibration frequency of the PVDF beam are proposed. The developed wind energy harvester can generate sufficient energy and does not require the excitation frequency to be close to the resonance frequency of the harvester. Since the dimension of the turntable and the position of the piezoelectric beam may be adjusted, large vibration amplitude of the beam can be obtained. So the harvester can effectively generate electricity.
ABSTRACT: A rotational piezoelectric energy harvester for efficiently harvesting wind energy is developed. The piezoelectric (PVDF) beam generates electricity using the impact-induced vibration. An analytical model is presented and simulated using finite element method. The transient responses of the piezoelectric beam subjected to an impulse pressure are obtained. The relationship between rms output voltage and excitation frequency is analyzed. It is found the impact frequency is an important factor for the harvester performance. When the impact frequency is beyond the critical one, the output power of the harvester will decrease with increasing the wind speed. To improve the harvester performance, the methods for the adjustment of the vibration frequency of the PVDF beam are proposed. The harvester can effectively scavenge the wind energy. A maximum rms voltage of 160.2 V and a maximum output power of 2566.4 µW were obtained at the wind speed of 14 m/s in configuration 2. Keywords: Piezoelectric, Wind energy harvesting, Impact-induced vibration, Finite element analysis 1. Introduction The recent technological advancement in wireless sensor and microelectronic technologies have led to the development of low-cost, low-power, multifunctional sensor nodes. These devices are being powered by the batteries. However, the batteries have finite storage capacities and need to be replaced periodically. In an attempt to solve this problem, harvesting energy from the environment has been explored to supplement or even replace batteries. The use of ambient energy, such as vibration, wind, sunlight, heat, has evoked great interests [1-4]. In particular, wind energy is a good source of electricity supply for its unique characteristics, such as clean, environmentally preferable, affordable and inexhaustible. Recently, many research works have been focused on the study of converting the wind energy to electricity [5-9]. Li et al. demonstrated that a cross-flow stalk-leaf configuration has better power generation performance, than a parallel-flow stalk-leaf. This study showed that the self-induced vibration of the trailing edge played the main role [10]. Zhao et al. proposed an arc-shaped piezoelectric generator which is capable of harvesting the energy from multi-directional winds [11]. Li et al. evaluated three distinct operation modes of piezoelectric energy harvester. It was showed that the Mode I is the most effective one. They attributed this result to large bending and torsion involved in this operation mode [12]. Yang et al. proposed a rotational piezoelectric wind energy harvester. The impact-induced resonance was used to improve the output power of the harvester [13]. Xia et al. showed that the resonance between the circuit and the piezoelectric flag’s flapping motion leads to a significant increase in the harvested energy [14]. Priya et al. demonstrated a piezoelectric windmill. The 12 piezoelectric bimorph transducers are utilized to harvest electrical energy [15]. The challenge in designing such wind energy harvesters is to improve the efficiency of energy harvesting for a wide range of wind speeds.
The rotational wind energy harvester has significant potential for effective energy harvesting, for its piezoelectric beam can produce a high bending deformation. In the aforementioned rotation energy harvesters, the piezoelectric ceramics are used. The piezoelectric ceramics have good voltage coefficient but are brittle, fragile and hard. Therefore, the piezoelectric ceramic beam cannot realize a large deformation and reductions of the energy harvesting efficiency are inevitable. In addition, the current research shows that the output performance of the rotational energy harvester increase with increasing the wind speed. Nevertheless, a different conclusion is found. 2. Structure of the piezoelectric energy harvester Motivated by the need for high-power density energy harvesters, we develop a rotational piezoelectric energy harvester that uses impact-induced vibration of a piezoelectric (PVDF) beam to harvest the wind energy. The harvester shown in Fig.1 consists of three piezoelectric cantilever beams embedded in an outer case. In order to improve the conversion efficiency of energy harvesting, a flexible piezoelectric material (PVDF) is adopted as the energy harvesting element, which shows a large deformation response and a wide range of vibration frequencies. A fan blade and a turntable are mounted on opposite ends of the rotating shaft. The blade number of the turntable is three. But it can be varied. The operation principle of the harvester is simple. As air flows past the harvester, the fan blade is caused to rotate and the turntable is driven through the rotating shaft. At this time, the turntable strikes the piezoelectric (PVDF) beam and causes the beam to undergo periodic oscillations. Accordingly, an electric field is produced. The harvesters with different numbers of piezoelectric (PVDF) beams are shown in Fig.2. There is only one piezoelectric (PVDF) beam in configuration 1, and there are three piezoelectric (PVDF) beams in configuration 2. The beam can be mounted in various positions on the outer case, as shown in Fig.2 (a). α is the mounting angle of the beam relative to the default position. When the beam is mounted in position 1, α is equal to 0. If the beam is mounted in position 2 (α is less than 0), its vibration amplitude is less. On the contrary, if the beam is mounted in position 3 (α is bigger than 0), its vibration amplitude is bigger. The developed wind energy harvester can generate sufficient energy and does not require the excitation frequency to be close to the resonance frequency of the harvester. However, some harvesters give appreciable response amplitude and energy output only if the dominant ambient vibration frequency is close to the resonance frequency of the harvester [16-19]. On the other hand, since the dimension of the turntable and the position of the piezoelectric beam may be adjusted, large vibration amplitude of the beam can be obtained. So the harvester can effectively generate electricity. 3. Analytical model The piezoelectric beam consists of a piezoelectric PVDF film and two protective coating, as shown in Fig.3. One end of the beam is fixed while the other end is free. It is assumed that l1, w1, and t1 are the length, the width, and the thickness of the protective coating layer. l2, w2, and t2 are the length, the width, and the thickness of the PVDF film. When the turntable strikes the piezoelectric (PVDF) beam causing it to deform, the mechanical strain generates charges in the piezoelectric layers. The electromechanical coupling behavior can be modeled as [20, 21]
M u Cu Ku F v C pv u Q
(1) (2)
where M is the mass matrix, C is the damping matrix, K is the stiffness matrix, u is the nodal displacement vector, F is the excitation force vector, is the electromechanical coupling matrix, v is the output voltage vector, C p is the piezoelectric element’s capacitance matrix, Q is the output electrical charge vector.
The electrical displacement of the piezoelectric element can be expressed as
1 D1 0 0 0 0 d15 0 2 D 0 0 0 d 0 0 3 (3) 15 2 4 d d d 0 0 0 D3 31 31 33 5 6 where d31 , d33 , d15 are piezoelectric constants, 1 , 2 , 3 are the normal stresses along the x, y, z axis, 4 , 5 , 6 are the shear stresses. The vibrations of the piezoelectric beam exist mainly along the z axis. Therefore, the piezoelectric material is assumed to experience only a one-dimensional state of stress along the x axis. Then, the Eq. (3) can be written as D1 d311 (4) According to Gauss's law, the electric charge of the piezoelectric element can calculated as follows
Qe
s
(5)
D1da
where da is a differential area on the element domain s. 4. Simulation analysis An analytical solution for transient response of the piezoelectric (PVDF) beam under mechanical impulse loads can be studied by using Finite Element (FE) procedure. To simplify the analyzed model, two protective coating are merged into one. The material of the protective coating is polyethylene. The material and structural parameters of the piezoelectric beam are given in Table 1. The implemented matrices of the material properties of the PVDF piezoelectric material can be written as follows:
0 0.0105 0 0 0 0.0105 0 0 0.065 2 e C / m 0 0.0388 0 0.0388 0 0 0 0 0
(6)
11 0 0 0 11 0 1011 F / m 0 0 11
(7)
S
0 0 8.1 4.84 4.84 0 6.92 4.38 0 0 0 6.92 0 0 0 9 cE (8) 10 Pa 1.38 0 0 1.38 0 1.38 where e is piezoelectric coefficient matrix, S is dielectric constant matrix, and c E is stiffness matrix. The turntable strikes the piezoelectric (PVDF) beam and causes the beam to undergo periodic oscillations. It is assumed that an impulse pressure is applied at the surface of the protective coating layer. The voltages of the nodes on the top surface of the PVDF film are coupled. The coupling voltages are extracted. The transient response results at an excitation frequency of 75 Hz are shown in Fig. 4. Fig. 4(a) shows deflection history of the free end of the PVDF film. The maximum vibration amplitude of the free end is about 20 mm. The open circuit voltage generated by the piezoelectric film is shown in Fig. 4(b). The output peak-to-peak voltage is nearly 40 Vpp. In addition, the transient responses with excitation frequency from 65 Hz to 125 Hz are simulated. The root-mean-square (rms) of output voltage is calculated. Fig.5 shows rms output voltage versus excitation frequency from 65 Hz to 125 Hz. The rms output voltage firstly increases and then decreases with the excitation frequency. The maximum output voltage is about 29 V at excitation frequency of 95 Hz. 5. Experiment results The experimental setup is shown in Fig. 6. The PVDF film was provided by Measurement Specialties in USA. The wind speed in the wind tunnel was measured by a digital anemometer (TASI-8818, Tasi Electronic, Inc., Suzhou, JS, China). The generated voltage signal was collected by a digital storage oscilloscope (TBS 1102, Tektronix, Beaverton, Oregon, USA). The root-mean-square of voltage Vrms was measured over a period of approximately 5 s through the ×10 probe (10 MΩ). The average output power Po was calculated using the following formula [10]:
Po (Vrms )2 / R
.
(9)
When the beam is mounted in position 1 (α is equal to 0), the open circuit voltage signals at various wind speeds for two configurations were recorded and plotted in Fig.7. The three piezoelectric (PVDF) beams of the configuration 2 are connected in parallel in the experiment. The measured results can characterize the electrical outputs of the harvester under wind excitations with
various speeds. In configuration 1, periodic vibration is the main oscillating pattern of the piezoelectric beam at low wind speeds, and both the vibration amplitude and frequency increase with increasing the wind speed from 6 to 10 m/s. The reason is that, the rotational speed of the fan blade and the impact frequency of the turntable on the piezoelectric beam increase with increasing wind speed. But the vibration amplitude decreases at the wind speed of 14 m/s. In configuration 2, the oscillation of the piezoelectric beam is periodic and regular. The vibration amplitude and frequency increases with increasing the wind speed. It is found that the maximum peak-to-peak output voltage is around 508 Vpp at the wind speed of 14 m/s. In order to evaluate the energy harvesting capabilities of the harvesters, the rms voltage was measured as a function of wind speed and the output power was calculated using Eq. (9). As shown in Figs 8(a) and 8(b), Vrms and the output power of the two configurations first increase and then decrease with increasing the wind speed. Vrms peaks at 24 V and 160.2 V in configuration 1 and configuration 2, respectively, with corresponding wind speeds of 10 m/s and 14 m/s. The maximum output powers in configuration 1 and configuration 2 are 57.4 µW and 2566.4 µW respectively. When the wind speed exceeds a threshold value, Vrms and the output power of the two configurations start to decrease with increasing the wind speed. The reason is that, impact frequency of the turntable increases while the wind speed increases. When impact frequency reaches a threshold value, the piezoelectric beam cannot recover to its initial shape before the next impact occurs. Accordingly, the beam has a small vibration amplitude and cannot efficiently harvest energy at high wind speed. This is the reason why the output voltage decreases and becomes non-periodic response at 14 m/s in configuration 1, as shown in Fig 7(a). Furthermore, the experimental results of the configuration 1 as shown in Fig.8 (a) confirm the validity of the simulation analysis as shown in Fig. 5. In order to further study the relationship between the energy output and the wind speed, a Fourier transform (a spectrum analysis) is performed [12, 22-23]. The frequency content of the output voltages of two configurations at various wind speeds are shown in Fig.9. The dominant vibration frequency of the piezoelectric beam can be obtained from Fig. 9. It can be seen that the dominant vibration frequency of the beam increases with increasing the wind speed. There exists a critical vibration frequency for two configurations. The critical vibration frequencies in configuration 1 and configuration 2 are 95 Hz and 82 Hz respectively. If the vibration frequency is beyond the critical one, the output voltage and the output power of the harvesters will begin to decrease as the wind speed increases. On the contrary, if the vibration frequency does not exceed the critical one, the output voltage and the output power will increase with the wind speed. To improve wind energy harvesting efficiency in harvesters, the methods for the adjustment of the vibration frequency are described. The wind speed is different in various environments. Different harvesters may be fabricated according to the range of wind speeds. In a high wind speed situation, the fan blade and the turntable rotate at a high speed. As a result, the vibration frequency of the piezoelectric beam will increase and may be beyond the critical vibration frequency. Hence, the vibration frequency of the piezoelectric beam must be reduced in order to obtain a good output. There are two methods used to reduce the vibration frequency of the beam. The first is to adjust the mounting angle of the beam, as shown in Fig.2 (a). If the beam is mounted in position 3, the resistance to the motion of the turntable will be increased. Then, rotational speed of the turntable and the vibration frequency of the beam are decreased, even if the wind speed is high. But the cut-in wind speed of the harvester (threshold wind speed required to start the harvester) is raised. The second is to reduce the blade number of the turntable. The impact frequency of the turntable on the piezoelectric beam will be decreased with reducing the blade number. Accordingly, the vibration frequency of the beam is diminished. Generally, the output power of the harvester should increase with the wind speed as long as the vibration frequency of the beam is not higher than the critical one. In a low wind speed situation, if the beam is mounted in position 2, the resistance to the motion of the turntable will be decreased and the cut-in wind speed of the harvester will be reduced. We can adjust the mounting angle of the beam and the blade number of the turntable according to the variation range of the environment wind speed so that the harvester can efficiently harvest wind energy. 6. Conclusion In conclusion, this study demonstrates a rotational piezoelectric energy harvester. The fan blade and the turntable rotate with the blowing wind. The turntable strikes the piezoelectric (PVDF) beam, and the impact induces the beam to vibrate. Accordingly, the piezoelectric element generates electricity. The number of piezoelectric (PVDF) beam can be varied. An analytical model for analyzing the piezoelectric (PVDF) beam is presented and simulated using finite element method. The transient responses and the generated voltage of the piezoelectric beam subjected to an impulse pressure are obtained. The relationship between rms output voltage and excitation frequency is analyzed. To evaluate the energy harvesting capabilities, the output performance of the two configurations was measured. The harvester can effectively scavenge the wind energy. A maximum rms voltage of 160.2 V and a maximum output power of 2566.4 µW were obtained at the wind speed of 14 m/s in configuration 2. In addition, it is found that if the impact frequency (the dominant vibration frequency of the piezoelectric beam) is beyond the critical one, the output power of the harvesters will decrease as the wind speed increases. In order to improve the harvester’s performance, the methods for the adjustment of the vibration frequency of the beam are proposed. In general, the developed harvester does not require the excitation frequency to be close to the resonance frequency of the device. The large vibration amplitude of the piezoelectric beam can be
easily obtained by adjusting the structural parameters. The increased power of the harvester could be obtained in the future by developing the high efficient flexible piezoelectric materials such as PVDF-TrFE, ZnO and AlN [24, 25]. Acknowledgment This research was supported by the National Natural Science Foundation of China (No. 51305248, No. 51577112, No. 51605271), Shanghai Natural Science Foundation of China (No. 13ZR1416900), and the Training Project for Young Teachers in Shanghai Colleges and Universities (No. ZZSD13051). References [1] A. Bibo, M. Daqaq, Investigation of concurrent energy harvesting fromambient vibrations and wind using a single piezoelectric generator, Applied Physics Letters, 102(2013) 243904. [2] Q. Leng, L. Chen, H. Guo, J. Liu, G. Liu, C. Hu, et al., Harvesting heatenergy from hot/cold water with a pyroelectric generator, Journal of Materials Chemistry A, 2(2014) 11940-7. [3] C. Bowen, H. Kim, P. Weaver, S. Dunn, Piezoelectric and ferroelectricmaterials and structures for energy harvesting applications, Energy & Environmental Science, 7(2014) 25-44. [4] M. Kim, S. Hong, D.J. Miller, J. Dugundji, B.L. Wardle, Size effect of flexible proof mass on the mechanical behavior of micron-scale cantilevers for energy harvesting applications, Applied Physics Letters, 99(2011) 243506. [5] F. Ewere, G. Wang, B. Cain, Experimental investigation of galloping piezoelectric energy harvesters with square bluff bodies, Smart Materials and Structures, 23(2014) 104012. [6] L. Zhao, L. Tang, Y. Yang, Enhanced piezoelectric galloping energy harvesting using 2 degree-of-freedom cut-out cantilever with magnetic interaction, Japanese Journal of Applied Physics, 53(2014) 060302. [7] Y. Yang, L. Zhao, L. Tang, Comparative study of tip cross-sections for efficient galloping energy harvesting, Applied Physics Letters, 102(2013) 064105. [8] A. Abdelkefi, Z. Yan, M.R. Hajj, Modeling and nonlinear analysis of piezoelectric energy harvesting from transverse galloping, Smart Materials and Structures, 22(2013) 025016. [9] H.D. Akaydin, N. Elvin, Y. Andreopoulos, The performance of a self-excited fluidic energy harvester, Smart Materials and Structures, 21(2012) 025007. [10] S. Li, J. Yuan, H. Lipson, Ambient wind energy harvesting using cross flow fluttering, Journal of Applied Physics, 109(2011) 026104. [11] J. Zhao, J. Yang, Z. Lin, N. Zhao, J. Liu, Y. Wen, et al., An arc-shaped piezoelectric generator for multi-directional wind energy harvesting, Sensors and Actuators A: Physical, 236(2015) 173-9. [12] D.J. Li, S. Hong, S. Gu, Y. Choi, S. Nakhmanson, O. Heinonen, et al., Polymer piezoelectric energy harvesters for low wind speed, Applied Physics Letters, 104(2014) 012902. [13] Y. Yang, Q. Shen, J. Jin, Y. Wang, W. Qian, D. Yuan, Rotational piezoelectric wind energy harvesting using impact-induced resonance, Applied Physics Letters, 105(2014) 053901. 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Li, A scalable concept for micropower generation using flow-induced self-excited oscillations, Applied Physics Letters, 96(2010) 144103. [20] Q. Wang, X. Pei, Q. Wang, S. Jiang, Finite element analysis of a unimorph cantilever for piezoelectric energy harvesting, International Journal of Applied Electromagnetics and Mechanics, 40(2012) 341-51. [21] S. Paquin, Y. St-Amant, Improving the performance of a piezoelectric energy harvester using a variable thickness beam, Smart Materials and Structures, 19(2010) 105020. [22] M. Carrara, J. Kulpe, S. Leadenham, M. Leamy, A. Erturk, Fourier transform-based design of a patterned piezoelectric energy harvester integrated with an elastoacoustic mirror, Applied Physics Letters, 106(2015) 013907. [23] H. Kim, S. Lee, C. Cho, J.E. Kim, B.D. Youn, Y.Y. Kim, An experimental method to design piezoelectric energy harvesting skin using operating deflection shapes and its application for self-powered operation of a wireless sensor network, Journal of Intelligent Material Systems and Structures, 26(2015) 1128-37. [24] C. T. Pan, Z. H. Liu, Y. C. Chen, C. F. Liu. Design and fabrication of flexible piezo-microgenerator by depositing ZnO thin films on PET substrates. Sensors and Actuators A: Physical, 159 (2010): 96-104. [25] N. Jackson, A. Mathewson. Enhancing the piezoelectric properties of flexible hybrid AlN materials using semi-crystalline parylene. Smart Materials and Structures, 26 (2017): 045005.
Biographies Jiantao Zhang is an associate researcher in the School of Mechatronic Engineering and Automation of Shanghai University. He received the B.S. and M.S. degrees from Hefei University of Technology, China, in 2002, 2005 and the Ph.D. degree from Nanjing University of Aeronautics and Astronautics, China, in 2009. His research interests include energy harvesting, piezoelectric transducers, actuators, and ultrasonic motors. Zhou Fang was born in Anhui, China. He received the B.Sc. degree in mechanical engineering and automation from Shanghai University, Shanghai, China, in 2015. He is currently pursuing his M.Sc. degree in machinery manufacturing and automation at Shanghai University. His research interests include piezoelectric materials, sensors, and wind energy harvester.
Chang Shu was born in Jiangxi, China. He received the B.Sc. degree in mechanical engineering and automation from Shanghai University, Shanghai, China, in 2014. He is currently pursuing his M.Sc. degree at Shanghai University. His research interest is in piezoelectric energy harvesting. Jia Zhang was born in Changsha, China. He received the B.Sc. degree in mechanical design manufacturing and automation from Changsha University, Changsha, China, in 2015. He is currently pursuing his M.Sc. degree in mechanical engineering at Shanghai University. His research interest is in energy harvesting. Quan Zhang received his PhD and B. Eng. from Nanjing University of Aeronautics and Astronautics (NUAA), in 2014 and 2009, respectively. He is a lecturer in School of Mechatronic Engineering and Automation, Shanghai University (SHU). His research interests are mainly focused on vibration control of flexible robot and piezoelectric based precision driving system. Chaodong Li is currently a professor and doctoral tutor in School of Mechatronic Engineering and Automation, Shanghai University. He received a B.Eng. degree in 1982 from Anhui University of Technology and M.E degree in 1988 from University of Science and Technology LiaoNing. In 1999, he received a Ph.D. degree from Nanjing University of Aeronautics and Astronautics. His research interests include piezoelectric and elastic wave theory and applications, linear micro-motor technology, dynamics of structures, analysis and design of ultrasonics.
Outer case
Piezoelectric (PVDF) beam
Fan blade
Turntable
Rotating shaft Fig.1. Schematic diagram of the rotational piezoelectric energy harvester.
(a)
(b) 2 α 1 3
Fig.2. Schematic illustration of two different operation modes: (a) configuration 1, (b) configuration 2. z Protective coating PVDF Film Protective coating
0
l1
x
l1
x
y w1
0
Fig.3. Structure of the piezoelectric beam
(a)
25
Displacement（mm）
20 15 10 5 0 -5 -10 -15 -20 -25
0
Output voltage（V）
(b)
0.1
0.2
0.3
0.4
0.5
0.3
0.4
0.5
Time(s) 30 20 10 0 -10 -20 -30
0
0.1
0.2 Time(s)
Fig. 4. Simulation results: (a) deflection of the free end of the PVDF film. (b) output voltage of the PVDF film.
Rms output voltage（V）
40 35 30 25 20 15 10 5 0 60
70
80
90
100
110
120
130
Excitation frequency (Hz)
Fig.5. Rms output voltage versus excitation frequency from 65 Hz to 125 Hz
Po (Vrms )2 / R
.
(9)
Fig.6. Photo of the experimental setup.
6m/s
10m/s
14m/s
6m/s
Time(0.05s-interval) Configuration 1 10m/s
14m/s
Open-Circuit Voltage(V)
40 20 0 -20 -40 -60 -80 -100
300 Open-Circuit Voltage(V)
200 100 0
-100 -200 -300 Time(0.05s-interval) Configuration 2
Fig.7. Output voltages of two modes at various wind speeds: (a) configuration 1, (b) configuration 2.
(a) 180
Configuration 1 Configuration 2
Output Vrms（V）
160
160.2
140 120 100 80
60
24.0
40 20 0
4
6
8
10
12
14
16
Wind Speed（m/s）
(b) Output Power（µW）
3000
Configuration 1 Configuration 2
2500
2566.4
2000
1500
1000
500
57.6 0
4
6
8
10
12
Wind Speed（m/s）
14
16
Fig.8. (a) rms voltage (Vrms) as a function of the wind speed. (b) output power as a function of the wind speed.
(b) Configuration 2
(a) Configuration 1 30
4m/s
25 20
15 10
21
5 0 30
Voltage Amplitude(V)
25
76
20
7m/s
15 10
5 0 30
95
25
10m/s
20
15 10 5
0 30
13m/s
25 20 15
10
135
5 0
0
50
100
150
200
200 180 160 140 120 100 80 60 40 20 0 200 180 160 140 120 100 80 60 40 20 0 200 180 160 140 120 100 80 60 40 20 0 200 180 160 140 120 100 80 60 40 20 0
250
10m/s 65
12m/s
74
82
14m/s
15m/s 140
0
50
100
150
200
250
Frequency(Hz) Fig.9. Frequency content of the output voltages of two modes at various wind speeds: (a) configuration 1, (b) configuration 2.
Table 1 Geometric and material parameters of the piezoelectric beam Parameter
PVDF film
Protective coating
Mass density /kgm-3 Elastic modulus/GPa Poisson’s ratio Length×width×thickness /mm3
1780 anisotropy 0.28 30×12.5×0.02
920 1.07 0.44 41.5×16.3×0.2
S0924-4247(17)30919-6 http://dx.doi.org/doi:10.1016/j.sna.2017.05.027 SNA 10136
To appear in:
Sensors and Actuators A
Received date: Revised date: Accepted date:
26-11-2016 6-5-2017 17-5-2017
Please cite this article as: Jiantao Zhang, Zhou Fang, Chang Shu, Jia Zhang, Quan Zhang, Chaodong Li, A rotational piezoelectric energy harvester for efficient wind energy harvesting, Sensors and Actuators: A Physicalhttp://dx.doi.org/10.1016/j.sna.2017.05.027 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
A rotational piezoelectric energy harvester for efficient wind energy harvesting Jiantao Zhang*, Zhou Fang, Chang Shu, Jia Zhang, Quan Zhang, Chaodong Li School of Mechatronic Engineering and Automation, Shanghai University, Shanghai 200072, China * E-mail:
[email protected]
HIGHLIGHTS: Harvesting wind energy to power the sensor nodes has evoked great interests. But the challenge in designing such wind energy harvesters is to improve the efficiency of energy harvesting for a wide range of wind speeds. In this research, a rotational piezoelectric energy harvester for efficiently harvesting wind energy is proposed. The piezoelectric (PVDF) beam generates electricity using the impact-induced vibration. But it is found that the energy output of the harvester doesn't always increase with increasing the wind speed. An analytical model is presented and simulated using finite element method. The transient responses of the piezoelectric beam subjected to an impulse pressure are obtained. The relationship between rms output voltage and excitation frequency is analyzed. To improve the harvester performance, the methods for the adjustment of the vibration frequency of the PVDF beam are proposed. The developed wind energy harvester can generate sufficient energy and does not require the excitation frequency to be close to the resonance frequency of the harvester. Since the dimension of the turntable and the position of the piezoelectric beam may be adjusted, large vibration amplitude of the beam can be obtained. So the harvester can effectively generate electricity.
ABSTRACT: A rotational piezoelectric energy harvester for efficiently harvesting wind energy is developed. The piezoelectric (PVDF) beam generates electricity using the impact-induced vibration. An analytical model is presented and simulated using finite element method. The transient responses of the piezoelectric beam subjected to an impulse pressure are obtained. The relationship between rms output voltage and excitation frequency is analyzed. It is found the impact frequency is an important factor for the harvester performance. When the impact frequency is beyond the critical one, the output power of the harvester will decrease with increasing the wind speed. To improve the harvester performance, the methods for the adjustment of the vibration frequency of the PVDF beam are proposed. The harvester can effectively scavenge the wind energy. A maximum rms voltage of 160.2 V and a maximum output power of 2566.4 µW were obtained at the wind speed of 14 m/s in configuration 2. Keywords: Piezoelectric, Wind energy harvesting, Impact-induced vibration, Finite element analysis 1. Introduction The recent technological advancement in wireless sensor and microelectronic technologies have led to the development of low-cost, low-power, multifunctional sensor nodes. These devices are being powered by the batteries. However, the batteries have finite storage capacities and need to be replaced periodically. In an attempt to solve this problem, harvesting energy from the environment has been explored to supplement or even replace batteries. The use of ambient energy, such as vibration, wind, sunlight, heat, has evoked great interests [1-4]. In particular, wind energy is a good source of electricity supply for its unique characteristics, such as clean, environmentally preferable, affordable and inexhaustible. Recently, many research works have been focused on the study of converting the wind energy to electricity [5-9]. Li et al. demonstrated that a cross-flow stalk-leaf configuration has better power generation performance, than a parallel-flow stalk-leaf. This study showed that the self-induced vibration of the trailing edge played the main role [10]. Zhao et al. proposed an arc-shaped piezoelectric generator which is capable of harvesting the energy from multi-directional winds [11]. Li et al. evaluated three distinct operation modes of piezoelectric energy harvester. It was showed that the Mode I is the most effective one. They attributed this result to large bending and torsion involved in this operation mode [12]. Yang et al. proposed a rotational piezoelectric wind energy harvester. The impact-induced resonance was used to improve the output power of the harvester [13]. Xia et al. showed that the resonance between the circuit and the piezoelectric flag’s flapping motion leads to a significant increase in the harvested energy [14]. Priya et al. demonstrated a piezoelectric windmill. The 12 piezoelectric bimorph transducers are utilized to harvest electrical energy [15]. The challenge in designing such wind energy harvesters is to improve the efficiency of energy harvesting for a wide range of wind speeds.
The rotational wind energy harvester has significant potential for effective energy harvesting, for its piezoelectric beam can produce a high bending deformation. In the aforementioned rotation energy harvesters, the piezoelectric ceramics are used. The piezoelectric ceramics have good voltage coefficient but are brittle, fragile and hard. Therefore, the piezoelectric ceramic beam cannot realize a large deformation and reductions of the energy harvesting efficiency are inevitable. In addition, the current research shows that the output performance of the rotational energy harvester increase with increasing the wind speed. Nevertheless, a different conclusion is found. 2. Structure of the piezoelectric energy harvester Motivated by the need for high-power density energy harvesters, we develop a rotational piezoelectric energy harvester that uses impact-induced vibration of a piezoelectric (PVDF) beam to harvest the wind energy. The harvester shown in Fig.1 consists of three piezoelectric cantilever beams embedded in an outer case. In order to improve the conversion efficiency of energy harvesting, a flexible piezoelectric material (PVDF) is adopted as the energy harvesting element, which shows a large deformation response and a wide range of vibration frequencies. A fan blade and a turntable are mounted on opposite ends of the rotating shaft. The blade number of the turntable is three. But it can be varied. The operation principle of the harvester is simple. As air flows past the harvester, the fan blade is caused to rotate and the turntable is driven through the rotating shaft. At this time, the turntable strikes the piezoelectric (PVDF) beam and causes the beam to undergo periodic oscillations. Accordingly, an electric field is produced. The harvesters with different numbers of piezoelectric (PVDF) beams are shown in Fig.2. There is only one piezoelectric (PVDF) beam in configuration 1, and there are three piezoelectric (PVDF) beams in configuration 2. The beam can be mounted in various positions on the outer case, as shown in Fig.2 (a). α is the mounting angle of the beam relative to the default position. When the beam is mounted in position 1, α is equal to 0. If the beam is mounted in position 2 (α is less than 0), its vibration amplitude is less. On the contrary, if the beam is mounted in position 3 (α is bigger than 0), its vibration amplitude is bigger. The developed wind energy harvester can generate sufficient energy and does not require the excitation frequency to be close to the resonance frequency of the harvester. However, some harvesters give appreciable response amplitude and energy output only if the dominant ambient vibration frequency is close to the resonance frequency of the harvester [16-19]. On the other hand, since the dimension of the turntable and the position of the piezoelectric beam may be adjusted, large vibration amplitude of the beam can be obtained. So the harvester can effectively generate electricity. 3. Analytical model The piezoelectric beam consists of a piezoelectric PVDF film and two protective coating, as shown in Fig.3. One end of the beam is fixed while the other end is free. It is assumed that l1, w1, and t1 are the length, the width, and the thickness of the protective coating layer. l2, w2, and t2 are the length, the width, and the thickness of the PVDF film. When the turntable strikes the piezoelectric (PVDF) beam causing it to deform, the mechanical strain generates charges in the piezoelectric layers. The electromechanical coupling behavior can be modeled as [20, 21]
M u Cu Ku F v C pv u Q
(1) (2)
where M is the mass matrix, C is the damping matrix, K is the stiffness matrix, u is the nodal displacement vector, F is the excitation force vector, is the electromechanical coupling matrix, v is the output voltage vector, C p is the piezoelectric element’s capacitance matrix, Q is the output electrical charge vector.
The electrical displacement of the piezoelectric element can be expressed as
1 D1 0 0 0 0 d15 0 2 D 0 0 0 d 0 0 3 (3) 15 2 4 d d d 0 0 0 D3 31 31 33 5 6 where d31 , d33 , d15 are piezoelectric constants, 1 , 2 , 3 are the normal stresses along the x, y, z axis, 4 , 5 , 6 are the shear stresses. The vibrations of the piezoelectric beam exist mainly along the z axis. Therefore, the piezoelectric material is assumed to experience only a one-dimensional state of stress along the x axis. Then, the Eq. (3) can be written as D1 d311 (4) According to Gauss's law, the electric charge of the piezoelectric element can calculated as follows
Qe
s
(5)
D1da
where da is a differential area on the element domain s. 4. Simulation analysis An analytical solution for transient response of the piezoelectric (PVDF) beam under mechanical impulse loads can be studied by using Finite Element (FE) procedure. To simplify the analyzed model, two protective coating are merged into one. The material of the protective coating is polyethylene. The material and structural parameters of the piezoelectric beam are given in Table 1. The implemented matrices of the material properties of the PVDF piezoelectric material can be written as follows:
0 0.0105 0 0 0 0.0105 0 0 0.065 2 e C / m 0 0.0388 0 0.0388 0 0 0 0 0
(6)
11 0 0 0 11 0 1011 F / m 0 0 11
(7)
S
0 0 8.1 4.84 4.84 0 6.92 4.38 0 0 0 6.92 0 0 0 9 cE (8) 10 Pa 1.38 0 0 1.38 0 1.38 where e is piezoelectric coefficient matrix, S is dielectric constant matrix, and c E is stiffness matrix. The turntable strikes the piezoelectric (PVDF) beam and causes the beam to undergo periodic oscillations. It is assumed that an impulse pressure is applied at the surface of the protective coating layer. The voltages of the nodes on the top surface of the PVDF film are coupled. The coupling voltages are extracted. The transient response results at an excitation frequency of 75 Hz are shown in Fig. 4. Fig. 4(a) shows deflection history of the free end of the PVDF film. The maximum vibration amplitude of the free end is about 20 mm. The open circuit voltage generated by the piezoelectric film is shown in Fig. 4(b). The output peak-to-peak voltage is nearly 40 Vpp. In addition, the transient responses with excitation frequency from 65 Hz to 125 Hz are simulated. The root-mean-square (rms) of output voltage is calculated. Fig.5 shows rms output voltage versus excitation frequency from 65 Hz to 125 Hz. The rms output voltage firstly increases and then decreases with the excitation frequency. The maximum output voltage is about 29 V at excitation frequency of 95 Hz. 5. Experiment results The experimental setup is shown in Fig. 6. The PVDF film was provided by Measurement Specialties in USA. The wind speed in the wind tunnel was measured by a digital anemometer (TASI-8818, Tasi Electronic, Inc., Suzhou, JS, China). The generated voltage signal was collected by a digital storage oscilloscope (TBS 1102, Tektronix, Beaverton, Oregon, USA). The root-mean-square of voltage Vrms was measured over a period of approximately 5 s through the ×10 probe (10 MΩ). The average output power Po was calculated using the following formula [10]:
Po (Vrms )2 / R
.
(9)
When the beam is mounted in position 1 (α is equal to 0), the open circuit voltage signals at various wind speeds for two configurations were recorded and plotted in Fig.7. The three piezoelectric (PVDF) beams of the configuration 2 are connected in parallel in the experiment. The measured results can characterize the electrical outputs of the harvester under wind excitations with
various speeds. In configuration 1, periodic vibration is the main oscillating pattern of the piezoelectric beam at low wind speeds, and both the vibration amplitude and frequency increase with increasing the wind speed from 6 to 10 m/s. The reason is that, the rotational speed of the fan blade and the impact frequency of the turntable on the piezoelectric beam increase with increasing wind speed. But the vibration amplitude decreases at the wind speed of 14 m/s. In configuration 2, the oscillation of the piezoelectric beam is periodic and regular. The vibration amplitude and frequency increases with increasing the wind speed. It is found that the maximum peak-to-peak output voltage is around 508 Vpp at the wind speed of 14 m/s. In order to evaluate the energy harvesting capabilities of the harvesters, the rms voltage was measured as a function of wind speed and the output power was calculated using Eq. (9). As shown in Figs 8(a) and 8(b), Vrms and the output power of the two configurations first increase and then decrease with increasing the wind speed. Vrms peaks at 24 V and 160.2 V in configuration 1 and configuration 2, respectively, with corresponding wind speeds of 10 m/s and 14 m/s. The maximum output powers in configuration 1 and configuration 2 are 57.4 µW and 2566.4 µW respectively. When the wind speed exceeds a threshold value, Vrms and the output power of the two configurations start to decrease with increasing the wind speed. The reason is that, impact frequency of the turntable increases while the wind speed increases. When impact frequency reaches a threshold value, the piezoelectric beam cannot recover to its initial shape before the next impact occurs. Accordingly, the beam has a small vibration amplitude and cannot efficiently harvest energy at high wind speed. This is the reason why the output voltage decreases and becomes non-periodic response at 14 m/s in configuration 1, as shown in Fig 7(a). Furthermore, the experimental results of the configuration 1 as shown in Fig.8 (a) confirm the validity of the simulation analysis as shown in Fig. 5. In order to further study the relationship between the energy output and the wind speed, a Fourier transform (a spectrum analysis) is performed [12, 22-23]. The frequency content of the output voltages of two configurations at various wind speeds are shown in Fig.9. The dominant vibration frequency of the piezoelectric beam can be obtained from Fig. 9. It can be seen that the dominant vibration frequency of the beam increases with increasing the wind speed. There exists a critical vibration frequency for two configurations. The critical vibration frequencies in configuration 1 and configuration 2 are 95 Hz and 82 Hz respectively. If the vibration frequency is beyond the critical one, the output voltage and the output power of the harvesters will begin to decrease as the wind speed increases. On the contrary, if the vibration frequency does not exceed the critical one, the output voltage and the output power will increase with the wind speed. To improve wind energy harvesting efficiency in harvesters, the methods for the adjustment of the vibration frequency are described. The wind speed is different in various environments. Different harvesters may be fabricated according to the range of wind speeds. In a high wind speed situation, the fan blade and the turntable rotate at a high speed. As a result, the vibration frequency of the piezoelectric beam will increase and may be beyond the critical vibration frequency. Hence, the vibration frequency of the piezoelectric beam must be reduced in order to obtain a good output. There are two methods used to reduce the vibration frequency of the beam. The first is to adjust the mounting angle of the beam, as shown in Fig.2 (a). If the beam is mounted in position 3, the resistance to the motion of the turntable will be increased. Then, rotational speed of the turntable and the vibration frequency of the beam are decreased, even if the wind speed is high. But the cut-in wind speed of the harvester (threshold wind speed required to start the harvester) is raised. The second is to reduce the blade number of the turntable. The impact frequency of the turntable on the piezoelectric beam will be decreased with reducing the blade number. Accordingly, the vibration frequency of the beam is diminished. Generally, the output power of the harvester should increase with the wind speed as long as the vibration frequency of the beam is not higher than the critical one. In a low wind speed situation, if the beam is mounted in position 2, the resistance to the motion of the turntable will be decreased and the cut-in wind speed of the harvester will be reduced. We can adjust the mounting angle of the beam and the blade number of the turntable according to the variation range of the environment wind speed so that the harvester can efficiently harvest wind energy. 6. Conclusion In conclusion, this study demonstrates a rotational piezoelectric energy harvester. The fan blade and the turntable rotate with the blowing wind. The turntable strikes the piezoelectric (PVDF) beam, and the impact induces the beam to vibrate. Accordingly, the piezoelectric element generates electricity. The number of piezoelectric (PVDF) beam can be varied. An analytical model for analyzing the piezoelectric (PVDF) beam is presented and simulated using finite element method. The transient responses and the generated voltage of the piezoelectric beam subjected to an impulse pressure are obtained. The relationship between rms output voltage and excitation frequency is analyzed. To evaluate the energy harvesting capabilities, the output performance of the two configurations was measured. The harvester can effectively scavenge the wind energy. A maximum rms voltage of 160.2 V and a maximum output power of 2566.4 µW were obtained at the wind speed of 14 m/s in configuration 2. In addition, it is found that if the impact frequency (the dominant vibration frequency of the piezoelectric beam) is beyond the critical one, the output power of the harvesters will decrease as the wind speed increases. In order to improve the harvester’s performance, the methods for the adjustment of the vibration frequency of the beam are proposed. In general, the developed harvester does not require the excitation frequency to be close to the resonance frequency of the device. The large vibration amplitude of the piezoelectric beam can be
easily obtained by adjusting the structural parameters. The increased power of the harvester could be obtained in the future by developing the high efficient flexible piezoelectric materials such as PVDF-TrFE, ZnO and AlN [24, 25]. Acknowledgment This research was supported by the National Natural Science Foundation of China (No. 51305248, No. 51577112, No. 51605271), Shanghai Natural Science Foundation of China (No. 13ZR1416900), and the Training Project for Young Teachers in Shanghai Colleges and Universities (No. ZZSD13051). References [1] A. Bibo, M. Daqaq, Investigation of concurrent energy harvesting fromambient vibrations and wind using a single piezoelectric generator, Applied Physics Letters, 102(2013) 243904. [2] Q. Leng, L. Chen, H. Guo, J. Liu, G. Liu, C. Hu, et al., Harvesting heatenergy from hot/cold water with a pyroelectric generator, Journal of Materials Chemistry A, 2(2014) 11940-7. [3] C. Bowen, H. Kim, P. Weaver, S. Dunn, Piezoelectric and ferroelectricmaterials and structures for energy harvesting applications, Energy & Environmental Science, 7(2014) 25-44. [4] M. Kim, S. Hong, D.J. Miller, J. Dugundji, B.L. Wardle, Size effect of flexible proof mass on the mechanical behavior of micron-scale cantilevers for energy harvesting applications, Applied Physics Letters, 99(2011) 243506. [5] F. Ewere, G. Wang, B. Cain, Experimental investigation of galloping piezoelectric energy harvesters with square bluff bodies, Smart Materials and Structures, 23(2014) 104012. [6] L. Zhao, L. Tang, Y. Yang, Enhanced piezoelectric galloping energy harvesting using 2 degree-of-freedom cut-out cantilever with magnetic interaction, Japanese Journal of Applied Physics, 53(2014) 060302. [7] Y. Yang, L. Zhao, L. Tang, Comparative study of tip cross-sections for efficient galloping energy harvesting, Applied Physics Letters, 102(2013) 064105. [8] A. Abdelkefi, Z. Yan, M.R. Hajj, Modeling and nonlinear analysis of piezoelectric energy harvesting from transverse galloping, Smart Materials and Structures, 22(2013) 025016. [9] H.D. Akaydin, N. Elvin, Y. Andreopoulos, The performance of a self-excited fluidic energy harvester, Smart Materials and Structures, 21(2012) 025007. [10] S. Li, J. Yuan, H. Lipson, Ambient wind energy harvesting using cross flow fluttering, Journal of Applied Physics, 109(2011) 026104. [11] J. Zhao, J. Yang, Z. Lin, N. Zhao, J. Liu, Y. Wen, et al., An arc-shaped piezoelectric generator for multi-directional wind energy harvesting, Sensors and Actuators A: Physical, 236(2015) 173-9. [12] D.J. Li, S. Hong, S. Gu, Y. Choi, S. Nakhmanson, O. Heinonen, et al., Polymer piezoelectric energy harvesters for low wind speed, Applied Physics Letters, 104(2014) 012902. [13] Y. Yang, Q. Shen, J. Jin, Y. Wang, W. Qian, D. Yuan, Rotational piezoelectric wind energy harvesting using impact-induced resonance, Applied Physics Letters, 105(2014) 053901. [14] Y. Xia, S. Michelin, O. Doaré, Resonance-induced enhancement of the energy harvesting performance of piezoelectric flags, Applied Physics Letters, 107(2015) 263901. [15] S. Priya, C.-T. Chen, D. Fye, J. Zahnd, Piezoelectric windmill: a novel solution to remote sensing, Japanese Journal of Applied Physics, 44(2004) L104. [16] S. Roundy, On the effectiveness of vibration-based energy harvesting, Journal of Intelligent Material Systems and Structures, 16(2005) 809-23. [17] A. Erturk, D.J. Inman, A distributed parameter electromechanical model for cantilevered piezoelectric energy harvesters, Journal of Vibration and Acoustics, 130(2008) 041002. [18] J.M. Renno, M.F. Daqaq, D.J. Inman, On the optimal energy harvesting from a vibration source, Journal of Sound and Vibration, 320(2009) 386-405. [19] D.S. Clair, A. Bibo, V. Sennakesavababu, M.F. Daqaq, G. Li, A scalable concept for micropower generation using flow-induced self-excited oscillations, Applied Physics Letters, 96(2010) 144103. [20] Q. Wang, X. Pei, Q. Wang, S. Jiang, Finite element analysis of a unimorph cantilever for piezoelectric energy harvesting, International Journal of Applied Electromagnetics and Mechanics, 40(2012) 341-51. [21] S. Paquin, Y. St-Amant, Improving the performance of a piezoelectric energy harvester using a variable thickness beam, Smart Materials and Structures, 19(2010) 105020. [22] M. Carrara, J. Kulpe, S. Leadenham, M. Leamy, A. Erturk, Fourier transform-based design of a patterned piezoelectric energy harvester integrated with an elastoacoustic mirror, Applied Physics Letters, 106(2015) 013907. [23] H. Kim, S. Lee, C. Cho, J.E. Kim, B.D. Youn, Y.Y. Kim, An experimental method to design piezoelectric energy harvesting skin using operating deflection shapes and its application for self-powered operation of a wireless sensor network, Journal of Intelligent Material Systems and Structures, 26(2015) 1128-37. [24] C. T. Pan, Z. H. Liu, Y. C. Chen, C. F. Liu. Design and fabrication of flexible piezo-microgenerator by depositing ZnO thin films on PET substrates. Sensors and Actuators A: Physical, 159 (2010): 96-104. [25] N. Jackson, A. Mathewson. Enhancing the piezoelectric properties of flexible hybrid AlN materials using semi-crystalline parylene. Smart Materials and Structures, 26 (2017): 045005.
Biographies Jiantao Zhang is an associate researcher in the School of Mechatronic Engineering and Automation of Shanghai University. He received the B.S. and M.S. degrees from Hefei University of Technology, China, in 2002, 2005 and the Ph.D. degree from Nanjing University of Aeronautics and Astronautics, China, in 2009. His research interests include energy harvesting, piezoelectric transducers, actuators, and ultrasonic motors. Zhou Fang was born in Anhui, China. He received the B.Sc. degree in mechanical engineering and automation from Shanghai University, Shanghai, China, in 2015. He is currently pursuing his M.Sc. degree in machinery manufacturing and automation at Shanghai University. His research interests include piezoelectric materials, sensors, and wind energy harvester.
Chang Shu was born in Jiangxi, China. He received the B.Sc. degree in mechanical engineering and automation from Shanghai University, Shanghai, China, in 2014. He is currently pursuing his M.Sc. degree at Shanghai University. His research interest is in piezoelectric energy harvesting. Jia Zhang was born in Changsha, China. He received the B.Sc. degree in mechanical design manufacturing and automation from Changsha University, Changsha, China, in 2015. He is currently pursuing his M.Sc. degree in mechanical engineering at Shanghai University. His research interest is in energy harvesting. Quan Zhang received his PhD and B. Eng. from Nanjing University of Aeronautics and Astronautics (NUAA), in 2014 and 2009, respectively. He is a lecturer in School of Mechatronic Engineering and Automation, Shanghai University (SHU). His research interests are mainly focused on vibration control of flexible robot and piezoelectric based precision driving system. Chaodong Li is currently a professor and doctoral tutor in School of Mechatronic Engineering and Automation, Shanghai University. He received a B.Eng. degree in 1982 from Anhui University of Technology and M.E degree in 1988 from University of Science and Technology LiaoNing. In 1999, he received a Ph.D. degree from Nanjing University of Aeronautics and Astronautics. His research interests include piezoelectric and elastic wave theory and applications, linear micro-motor technology, dynamics of structures, analysis and design of ultrasonics.
Outer case
Piezoelectric (PVDF) beam
Fan blade
Turntable
Rotating shaft Fig.1. Schematic diagram of the rotational piezoelectric energy harvester.
(a)
(b) 2 α 1 3
Fig.2. Schematic illustration of two different operation modes: (a) configuration 1, (b) configuration 2. z Protective coating PVDF Film Protective coating
0
l1
x
l1
x
y w1
0
Fig.3. Structure of the piezoelectric beam
(a)
25
Displacement（mm）
20 15 10 5 0 -5 -10 -15 -20 -25
0
Output voltage（V）
(b)
0.1
0.2
0.3
0.4
0.5
0.3
0.4
0.5
Time(s) 30 20 10 0 -10 -20 -30
0
0.1
0.2 Time(s)
Fig. 4. Simulation results: (a) deflection of the free end of the PVDF film. (b) output voltage of the PVDF film.
Rms output voltage（V）
40 35 30 25 20 15 10 5 0 60
70
80
90
100
110
120
130
Excitation frequency (Hz)
Fig.5. Rms output voltage versus excitation frequency from 65 Hz to 125 Hz
Po (Vrms )2 / R
.
(9)
Fig.6. Photo of the experimental setup.
6m/s
10m/s
14m/s
6m/s
Time(0.05s-interval) Configuration 1 10m/s
14m/s
Open-Circuit Voltage(V)
40 20 0 -20 -40 -60 -80 -100
300 Open-Circuit Voltage(V)
200 100 0
-100 -200 -300 Time(0.05s-interval) Configuration 2
Fig.7. Output voltages of two modes at various wind speeds: (a) configuration 1, (b) configuration 2.
(a) 180
Configuration 1 Configuration 2
Output Vrms（V）
160
160.2
140 120 100 80
60
24.0
40 20 0
4
6
8
10
12
14
16
Wind Speed（m/s）
(b) Output Power（µW）
3000
Configuration 1 Configuration 2
2500
2566.4
2000
1500
1000
500
57.6 0
4
6
8
10
12
Wind Speed（m/s）
14
16
Fig.8. (a) rms voltage (Vrms) as a function of the wind speed. (b) output power as a function of the wind speed.
(b) Configuration 2
(a) Configuration 1 30
4m/s
25 20
15 10
21
5 0 30
Voltage Amplitude(V)
25
76
20
7m/s
15 10
5 0 30
95
25
10m/s
20
15 10 5
0 30
13m/s
25 20 15
10
135
5 0
0
50
100
150
200
200 180 160 140 120 100 80 60 40 20 0 200 180 160 140 120 100 80 60 40 20 0 200 180 160 140 120 100 80 60 40 20 0 200 180 160 140 120 100 80 60 40 20 0
250
10m/s 65
12m/s
74
82
14m/s
15m/s 140
0
50
100
150
200
250
Frequency(Hz) Fig.9. Frequency content of the output voltages of two modes at various wind speeds: (a) configuration 1, (b) configuration 2.
Table 1 Geometric and material parameters of the piezoelectric beam Parameter
PVDF film
Protective coating
Mass density /kgm-3 Elastic modulus/GPa Poisson’s ratio Length×width×thickness /mm3
1780 anisotropy 0.28 30×12.5×0.02
920 1.07 0.44 41.5×16.3×0.2