Analysis of Cross Shaped Cantilever with C Shaped Proof Mass for Vibration Energy Harvesting

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ScienceDirect Materials Today: Proceedings 5 (2018) 21343–21349

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ICSEM 2016

Analysis of Cross Shaped Cantilever with C Shaped Proof Mass for Vibration Energy Harvesting Sampath Na , Ezhilarasi Db a

Research scholar, National Institute of Technology, Tiruchirappalli-620015, Tamilnadu, India b Assistant Professor , National Institute of Technology, Tiruchirappalli-620015, Tamilnadu, India.

Abstract

A novel energy harvesting structure with C shaped proof mass is proposed to enhance the harvested power from the vibration. Analysis has been carried out using numerical simulation for the structures with rectangular and C shaped proof mass by keeping the volume of proof mass constant. The resonant frequency , generated voltage and power of the cross shaped cantilever beam are studied by using COMSOL.It has been proved that the cross shaped cantilever beam with C shaped proof mass produce high voltage and high power as compared to cross shaped cantilever with rectangular proof mass for the given input vibration. © 2018 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of INTERNATIONAL CONFERENCE ON SMART ENGINEERING MATERIALS (ICSEM 2016).

Keywords: vibration energy harvesting; cross shaped unimorph cantilever beam; resonant frequency; electric potential; rectangular mass; C shaped proof mass. 1. Introduction: Most of the vibrational energy harvesting system proposed in the literature are designed to extract power at their resonance frequency. These resonance based generator harvest more energy when excitation frequency is matching with ambient excitation frequency of harvester and deviation between two frequencies reduces the output power. Generally a tip mass is attached at the free end of the beam tune resonance frequency harvester to that of excitation frequency. This kind of manual tuning is not suitable for practical application. Hence there is a need to increase bandwidth of harvester by suitable design and also low frequency vibration is quite common in the environment and designing a harvester which occupies less space has low frequency vibration is a challenging task. In the reference [1] new Pi shaped piezo electric harvester is proposed and it consists of rectangular piezo ceramic and Pi shaped elastic body which is attached on the top surface of the elastic beam to harvest random vibration

2214-7853 © 2018 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of INTERNATIONAL CONFERENCE ON SMART ENGINEERING MATERIALS (ICSEM 2016).

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energy and their performance characteristic of the Pi shaped were studied depending on the elastic body thickness, ceramic size and input applied forced on the each elastic beam. A activated theta type based piezo electric energy harvester designed by Byeong-Ha Lee et al. consists of two hat-shaped elastic bodies and rectangular piezo electric ceramic plate to harvest power from lower frequency vibration [2]. In reference [3] a flexible longitudinal zigzag structure capable of vibrating in both X and Z direction to improve the efficiency of energy harvester under low frequency input vibration.To increase the bandwidth (22.2 Hz-35.25Hz) of the harvester in reference (Dauda Sh. Ibrahim1et al.) the authors investigated the magnetically coupled two cantilever structure and analyzed the effect of distance between beam an output power analytically and experimentally. A ‘S’ shaped PZT cantilever is proposed and designed in reference ( Iman Mehdipour and Francesco Braghin ) is increase the output power compare to normal rectangular structure. Guided beam cantilever structure fixed from four end and having proof mass at the center is proposed by (Jung-Hoon Lima et al.) to have stable, reliable and improved response as compared single beam structure. The proof mass supported with four beam enable the structure sustained higher stress value due to high amplitude vibration also provides higher stiffness to the structure result in lower displacement which improve life time of the harvester.Conventional piezo electric energy harvester methods can able to produce the maximum energy when the beam is vibrating in transverse direction at resonant frequency to overcome this limitation by Renwen Chena et al. [7]. Designed a multi directional piezo electric vibration energy harvester to extract higher energy from different direction. Furthermore the structure dimension was optimized to maximize energy conversion efficiency. The cross shaped piezo electric generator is proposed and fabricated by Jung-Hoon Lima et al. [8] to extract energy from low frequency vibration sources. In this article [9], the voltage and frequency characteristic of four types of cross connected with multi cantilever (three, four, six, eight) are investigated. Among the structures, three cantilever is produced maximum output compared to the other cross shaped cantilever due to the higher stress transmission in the three cantilever structure. In this paper, the cross shaped cantilever beam with C shaped proof mass proposed and modeled using COMSOL to harvest energy from low vibration and also enhance output voltage. The performance characteristics such as resonance frequency, voltage and power are studied by changing beam and piezo dimensions and proof mass at the free end of each beam. 2. Structure: The structure of cross shaped cantilever with rectangular and C shaped proof mass is shown in fig (1.a, b). This structure is mechanically more stable than other multi beam structures [10].The cross shaped energy harvester consists of four piezoelectric attached composite beam is analyzed by adding different proof mass at the free end of each beam. Aluminum cantilevers of thickness 1mm and width of 15mm are used. The piezo ceramic of the thickness 0.5mm and 15mm width is placed nearly the fixed end of the cantilever beams with rectangular and C shaped proof mass is attached at the tip of the beams. The generator is designed to have with cross shaped Centro symmetric four cantilever legs are attached on the center of the elastic body [9].When the base vibration is applied to the center point of harvester, vibration energy is equally transmitted to the each cantilevers of structure. Since the dimension of the cantilever beams are same, upon excitation beam vibrate with same frequency and amplitude of displacement. The resonant frequency of the harvester can be tuned by changing beam length, beam width, and adding different proof mass.

Sampath N , Ezhilarasi D/ Materials Today: Proceedings 5 (2018) 21343–21349

Fig. 1. (a) Cross shaped cantilever with rectangular mass;

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(b) Cross shaped cantilever with C shape proof mass.

Piezoelectric attached thin beam undergoing transverse vibration is obtained using Euler Bernoulli beam theory [9] and is written as,

2 x 2

  2w 2w EI x x, t A x     2  x, t   f  x, t           (1)    x 2    x  

Where, f (x, t) is the external input force applied to the cantilever beam, E is Young’s modulus, I(x) - The moment of inertia of the beam section about the y axis, ρ - density of the beam, and A - cross-sectional area of the beam. 3. FEM analysis: The proposed cross shaped cantilever with rectangular and C shape proof mass is analyzed using finite element method (FEA) to determine the correlation between output characteristics with respect to the dimension of the harvester. A free tetrahedron meshing method is used for creating mesh model. In this structure center point is considered as fixed constraint. First modal analysis and their corresponding resonance frequency is studied for cross shaped cantilever, simulation is carried out using COMSOL software as depicted in figure 2. The vertical color bar represents the modal displacement (mm) of each point along the cantilever. Here first mode resonant frequency is consider for dynamic studies to get maximum displacement and output power.

(a)

(b)

Fig 2: First mode resonant frequency of the cross shaped cantilever with rectangular and C shaped proof

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Sampath N , Ezhilarasi D/ Materials Today: Proceedings 5 (2018) 21343–21349

4. Simulation Result and Discussion: From the simulation result it is observed that the maximum displacement and electric potential is obtained at the first mode resonance frequency of 37.97Hz and 40.63Hz for the structure with rectangular and C shaped proof mass respectively. Second analysis study about how the frequency response characteristics were studied by changing the dimension of the cantilever.

(a) Resonant frequency Vs Beam length

(b) Open circuit voltage Vs Beam width

(c) Resonant frequency Vs Open circuit voltage

Fig 3: Resonant frequency and output voltage variation against beam length of cross shaped cantilever

From the figure 3 a-c) it can be observed that when the beam length is increased from 40mm-240mm by keeping width and thickness of the beam as constant, the resonant frequency is reduced and open circuit voltage across the piezo patch is increased. Harvester with rectangular proof mass generated maximum output voltage 7.52V when the length of the beam are 240mm at its resonance frequency of 7.52Hz. Harvester with C shaped proof mass generated maximum output voltage 8.25V when the length of the beam are 234mm at its resonance frequency of 8.6Hz. Similar analysis is carried out by increasing the width from 5mm to 15mm by keeping length and thickness as constant, the corresponding change in resonant frequency and open circuit voltage across the piezo patch is shown in fig4 a-b) .The output voltage initially increase with increase in width after 7mm it start to decrease. Harvester with rectangular proof mass generated maximum output voltage 6.36V when the width of the beam are 15mm at its resonance frequency of 36.84Hz. Harvester with C shaped proof mass generated maximum output voltage 7.89V when the width of the beam are 7mm at its resonance frequency of 8.6Hz as shown fig 4.c.

(a) Resonant frequency Vs Beam width

(b)

Open circuit voltage Vs Beam width

(c) Resonant frequency Vs open circuit voltage

Fig 4: Resonant frequency and output voltage variation against beam width of cross shaped cantilever

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Finally, we have to analysis the effect of output voltage and resonant frequency of both structure due to the variation of parameter of piezo electric device (PZT-5H).In figure (5.a) shows that, the output voltage of the structure is depend on the piezo electric patch .when piezo length is increased then output voltage is increased after that it goes to decrease by varying the piezo length from 40mm-120mm.The output voltage of piezo patch decreased while increasing width of piezo patch from 5mm-15mm as shown in figure 7b.The open circuit voltage start to increase first and then it reduced when the thickness of piezo electric patch is raised from 0.5mm-5mm as shown in figure 5.c.Based on the simulation result shown that, the cross shaped cantilever with C shaped proof mass with same weight is designed to improve the output voltage and output power for low frequency environmental vibration in COMSOL software. The properties and dimension of cross shaped cantilever beam as mention in the table 1.

a) Open circuit voltage Vs Piezo length

b) Open circuit voltage Vs Piezo width

c) Open circuit voltage Vs Piezo thickness

Fig 5: Resonant frequency and output voltage variation against piezo length, width and thickness of cross shaped cantilever Table 1: Properties and Dimension of the cross shaped cantilever

Substrate : Aluminium

Piezoelectric material: PZT-5H

69

70

Poisson Ratio

0.22

0.33

Density ρs (kgm-3)

7800

7500

-

-190 Pm/V

Properties Young Modulus (GPa)

Piezo electric constant

5. Power output of cross shaped cantilever beam: The theoretical output power is calculated by Po= V2o/Rl

Where Po, Vo, Rl are the output power, the voltage across the load and the load resistance connected across the harvester. Simulation studies carried out for cross shaped cantilever beam under same vibration condition and proof mass values between 5g-60g. The variations of power versus proof mass for the cross shaped cantilever with rectangular and C shape proof mass harvesters are shown in figure. 6; Maximum output power of 11.80µW(each piezo patch) is obtained for cross shaped cantilever with C shaped proof mass and maximum power

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of 7.13 µW(each piezo patch) is achieved for cross shaped cantilever with rectangular proof mass under same proof mass and vibration condition. From which it is understood that the cross shaped cantilever with C shaped proof mass can able to generate more voltage compared to rectangular proof mass as shown in the Table 2.

Fig 6. : Variations of the output power versus proof mass for the cross shaped cantilever with rectangular and C shaped mass Table 2: Results obtained from simulation for the cross shaped cantilever with rectangular and C shaped mass Proof mass(g)

Cross shaped cantilever with rectangular proof mass structure Frequency(Hz) OCV voltage(V)

5.37 10.75 21.50 32.28 43.01 53.75

36.84 26.48 17.75 13.05 9.94 7.77

6.35 6.34 6.38 6.30 6.38 6.40

Cross shaped cantilever with C shaped proof mass structure Frequency(Hz) OCV voltage(V)

40.69 31.35 22.91 18.87 16.39 14.69

7.05 6.95 6.51 6.43 6.35 6.44

Load Resistance (kΩ)

Output power (µW) in each piezo patch. Rectangular proof mass

10 20 30 40 50 60

7.18 7.13 4.87 3.49 2.56 1.91

C shaped proof mass 10.70 11.80 8.15 7.09 6.43 6.29

6. Conclusion: The cross shaped cantilever beam with C shaped proof mass is modelled using COMSOL software to analyses the frequency response characteristics in low frequency application and also finite element analysis is carried out by altering beam, piezo dimension and proof mass to optimize the structure for maximum output voltage to enhance the generated power. From the numerical result, it is found that the proposed structure gives better performance, as compared to the cross shaped cantilever with rectangular proof mass in the frequency range of 5Hz - 100Hz. The maximum power of the harvester is found to be 11.80 µW from each piezoelectric patch) at 31.35Hz. References: 1.

Byeongha Lee, SeongSuJeong, SeongkyuCheon, YongwooHa, MinhoPark, TaegoneParkn, Generating characteristics of a tension activated π-shaped piezoelectric harvester, Ceramics International,41 (2015)S695–S701.

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2.

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Byeong-Ha Lee, Seong-Su Jeong and Tae-Gone Park, Generating Characteristics of a Theta-type Piezoelectric Energy Harvester, Journal of the Korean Physical Society, Vol. 66, No. 7, April 2015, pp. 1110∼1114. 3. Shengxi Zhou1,2,Weijia Chen2,3, Mohammad H Malakooti2, Junyi Cao1 and Daniel J Inman2, Design and modelling of a flexible longitudinal zigzag structure for enhanced vibration energy harvesting, Journal of Intelligent Material Systems and Structures,1–14, 2016. 4. Dauda Sh. Ibrahim1 · Asan G. A. Muthalif1 · N. H. Diyana Nordin1 · Tanveer Saleh1, Comparative study of conventional and magnetically coupled piezoelectric energy harvester to optimize output voltage and bandwidth , springer,Microsyst Technology ,23 May 2016,5 July 2016. 5. Iman Mehdipour and Francesco Braghin, Innovative Piezoelectric Cantilever Beam Shape for Improved Energy Harvesting, Shock & Vibration, Aircraft/Aerospace, and Energy Harvesting, Volume 9, 2015. 6. Shanky Saxena1, · Ritu Sharma1 · B. D. Pant, Design and development of guided four beam cantilever type MEMS based piezoelectric energy harvester, springer,Microsyst Technology, april 2016. 7. Renwen Chena,∗, Long Rena, Huakang Xiaa, Xingwu Yuana, Xiangjian Liuba, Energy harvesting performance of a dandelion-like multi-directional piezoelectric vibration energy harvester, Sensors and Actuators A 230 (2015) 1–8 8. Jung-Hoon Lima, Seong-Su Jeonga, Na-Ri Kim, Seong-Kyu Cheona, Myong-Ho Kimb, Tae-Gone Park,Design and fabrication of a cross-shaped piezoelectric generator for energy harvesting,Ceramics International, S641–S645,2013. 9. Seong-Su Jeong and Tae-Gone Park, Generating the Characteristics of a Modified Unimorph-type Piezoelectric Harvester, Journal of the Korean Physical Society, Vol. 65, No. 2, July 2014, pp. 205∼210. 10. Shahruz S M '' Design of mechanical band-pass filters with large frequency bands for energy scavenging'' Mechatronics 16 523–31, 2006.