Design and Simulation of Cantilever Based MEMS Bimorph Piezoelectric Energy Harvester

Mechanics, Materials Science & Engineering, April 2017 – ISSN 2412-5954

Design and Simulation of Cantilever Based MEMS Bimorph Piezoelectric Energy Harvester19 G.K.S. Prakash Raju1, P. Ashok Kumar1, Vanaja Aravapalli2, K. Srinivasa Rao3,a 1 – M. Tech, KL University, Dept of ECE, Green Fields-522502, India 2 – Tirumala Engineering College, Dept of AS & H, Narasaraopeta-522601, India 3 – Professor & Head of MERG, KL University, Dept of ECE, Green Fields-522502, India a – gorantlaraju02@gmail.com, drksrao@kluniversity.in DOI 10.2412/mmse.16.9.490 provided by Seo4U.link

Keywords: cantilever beam, MEMS, Piezo-electric bimorph, power consumption, proof mass.

ABSTRACT. Piezoelectric generators designed for harvesting vibratory energy are usually based on mechanical resonators, cantilever beams for instance, able to effectively transmit ambient energy to the active materials. In this paper, we have designed and simulated a rectangular piezoelectric energy harvester, which consists of cantilever, proof mass, piezoelectric bimorph with different lead-zirconate-titanate (PZT) materials (PZT-5A, PZT-5H, PZT-5J, PZT-7A, PZT8) using COMSOL Multiphysics, (Finite Element Analysis) FEM Tool. The performance of the device mainly engrossed with the power-optimization by varying the materials and varying the dimensions of the proof mass and dimensions of piezoelectric bimorph. This model describes the consumption of the power dependence with the mechanical acceleration, frequency response and helps in the load behaviour for power optimization. The designed device will be used in aircraft engine and car engine. We observed from the simulated results, a rectangular piezoelectric energy harvester with PZT5H material gives optimal power. Comparable with the conventional devices, MEMS based energy harvesting device is optimized with 33.3% of power.

Introduction. Now-a-days, researchers are mainly concentrating on the reduction in size, area, cost and power consumption of sensors and complementary metal oxide semiconductor (CMOS) electronic circuitry research lines on battery recharge via available power sources. Energy harvesters can be operating as battery rechargers in various environments, such as wireless communication systems, wireless sensors, houses and military applications. The possibility to bypass replacing exhausted batteries is highly attractive for wireless networks [1-2], due to maintenance of battery check and restoration are relevant.

There are several mechanisms for converting vibrational mechanical energy to electrical energy. The most important are electrostatic, electromagnetic and piezoelectric. Among the three mechanisms, piezoelectric transduction principle offers higher power density compared to electrostatic transduction and electromagnetic transduction. A majority of current research has been done on piezoelectric conversion due to the low complexity of its analysis and fabrication. For electrostatic transduction principle, which initially we need to provide the polarization and for electromagnetic transduction principle which are having some limitations in the magnet miniaturization [3]. Marin et al. have discussed about the scaling of output power as a function of effective material volume (v) for different mechanisms. By taking account into some equations for the respective conversion mechanisms, the output power of the electromagnetic mechanism is proportional to v2, while the piezoelectric mechanism is proportional to v3/4. Thus, at smaller scales, the piezoelectric mechanism becomes more attractive as compared to electromagnetics.So, piezoelectric is well suited than 19

© 2017 The Authors. Published by Magnolithe GmbH. This is an open access article under the CC BY-NC-ND license http://creativecommons.org/licenses/by-nc-nd/4.0/

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electrostatic and electromagnetic transduction principle for MEMS implementation [4]. Piezoelectric energy harvester generators produces very low power in the range of milliwatts or microwatts due to the mechanical properties. Here, stress is very large, strain is small and piezoelectric materials may work up to hundreds of kilohertz. The mechanical vibrations of the cantilever beam are in the range of 0.1 Hz – 1 kHz . In this paper, the design and simulation of a piezoelectric energy harvester based MEMS sensor has been performed. The simulations should be performed by varying the materials and by varying dimensions of piezoelectric structure components. From all the designs performed, the PZT-5H material energy harvester gives optimal power.

Theory: Piezoelectric Generator. A majority of the energy harvesters has been designed and simulated with piezoelectric materials i, e Lead zirconate titanate (PZT) and Aluminium nitride (ALN) but most of the researchers has been using PZT because of the high piezoelectric coefficent and dielectric constant, it produces optimal power and less will be used Aliminium nitride (ALN) because of the material deposition and compatable with CMOS fabrication process. The materials will be chosen according to the users requirements. The energy flow diagram for the design structure as shown below.

Environment Excitation Energy

Mechanical Vibrational Energy

Mechanical Loss 

Unmatched mechanical impedance



Damping factor

Electrical Energy Output

Electrical Energy Generated

Mechanical – Electrical Transduction Loss 

Coupling factor



Piezoelectric coefficient

Electrical Loss 

Unmatched electrical impedance

Fig. 1. Energy flow of piezoelectric generator.

The source excitation is converted into cyclic oscillations through mechanical assembly due to this there is a loss of some energy through unmatched mechanical impedance, damping and backward reflection followed by the cyclic mechanical oscillations are converted into cyclic electrical energy through the piezoelectric effect. Due to this there is a loss of some energy through electromechanical losses of piezoelectric material. Electromechanical coupling factor (k) represents the efficiency of the conversion process from mechanical energy to electrical energy and then followed by generated electrical energy is conditioned through rectification and dc/dc conversion. This step results in some losses due to power consumption by the circuit.

Designing of Device Structure. This model analyses a simple “seismic” energy harvester, which is designed to generate electrical energy from the local variations in acceleration. The cantilever based energy harvester has two ends. One end is fixed with piezoelectric bimorph and other end is connected to vibrating machinery with proof mass. To ensure the same voltage on the external electrodes of the cantilever beam, even though the above and below the stress is of opposite sign with the help of applied load. The below conFig.uration needs, the bimorph has ground electrode inside within it and MMSE Journal. Open Access www.mmse.xyz 86

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coincident with neutral plane of the beam. The schematic structure of of the piezoelectric energy harvester, dimensions and materials of the designed structure are tabulated as shown below.

Table. 1. Dimensions, Materials of the designed structure Component

Material

Dimensions (mm)

Colour

Anchor or Die

Structural Steel

1×1

Orange

Electrodes

Lead_Zirconate_Titanate (PZT-5A)

21×0.06

Green

Piezoelectric Bimorph

Structural Steel

21×0.04

Orange

Proof or Seismic Mass

Structural Steel

4×1.7

Orange

Proof Mass Piezoelectric Bimorph Bimorph

Electrodes Anchor or Die Fig. 2. Schematic structure of energy harvester.

Principle of operation. For a typical energy harvester, anchor is fixed at one end of cantilever while other end of the cantilever is free to move with proof mass. A input force ( in the form of load) is applied at a one end of cantilever, beam will vibrates up and down due to electrostatic force and a mechanical energy is produced. The produced mechanical energy is converting in to the electrical energy with the piezoelectric principle. A voltage (V) will be measured at the two electrodes of the beam. The power (P) can be calculated as P = V2rms/R = V2/2R

(1)

where V – voltage induced; R – load resistance Results and Analysis. This designed model performs three analysis of the piezoelectric energy harvester are power and DC voltage as a function of frequency, electrical load and acceleration. First, the power output is shown as a function of frequency with a fixed electrical load. Then the DC voltage is shown linear as a function of acceleration and at last the power output is analysed as a function of electrical load. From the analysis of the device, the input mechanical power and output electrical power is plotted and peak voltage is induced across the piezoelectric bomorph (in V) at 77Hz with

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respect to frequency, when the energy harvester is excited by a sinusoidal acceleration with electrical load of 12kΩ.

Fig. 3. Mechanical, electrical power (mW) and peak voltage (V) w.r.t the frequency.

The input mechanical, electrical power and DC voltage is harvested from the device as a function of electrical load resistance at an acceleration of 1 g oscillations at 77 Hz. The peak in energy harvested corresponds to an electrical load of 12kΩ.

Fig. 4. Power harvested from the device as a function of electrical load resistance at an acceleration of 1 g oscillating at 77 Hz. The DC voltage and mechanical/electrical power output versus the magnitude of the mechanical acceleration at a fixed frequency of 77 Hz with a load impedance of 12 kΩ. The voltage increases linearly with the load, while the harvested power increases quadratically.

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Fig. 5. DC voltage, mechanical and electrical power verses acceleration at a fixed frequency of 77 Hz with a load impedance of 12 KΩ.

The simulation results with different materials is shown below.

Table 2. Comparison of energy harvester simulation results with various materials.

Material

PZT-5° PZT-5H PZT-5J PZT-7A PZT-8

Frequency response M.P (mW) 1.3 0.8 1.2 3.4 1.7

E.P (mW) 1.3 0.8 1.2 3.4 1.7

Voltage (Volts) 5.5 4.5 5.3 9 6.5

Load dependence M.P (mW) 1.4 0.8 1.2 2.9 1.7

E.P (mW) 1.4 0.8 1.2 2.6 1.7

Voltage (Volts) 6.2 7 7 8 8

Acceleration dependence M.P (mW) 5 3.6 4.7 9 5.8

E.P (mW) 5 3.6 4.7 8.6 5.8

Voltage (Volts) 10 9.5 10 14 12.5

M.P – Mechanical power in, E.P – Electrical power out.

From the above table, when compared to all other materials PZT-5A (Lead-zirconate-titanate) material gives optimal mechanical and electrical power.

The energy harvester device is mainly depends on two parameters namely, load resistance and acceleration. Based on these parameters power can be calculated. Here we have shown the comparsion between theoritical and simulated results.

Table 3. Theoritical and simulation calculations of the electrical power at 12 KΩ Frequency 60 65 70 72 74 77 80 85 90

Power (mW) Theoretical simulation 0.03 0.04 0.06 0.09 0.20 0.23 0.32 0.37 0.58 0.60 0.86 0.90 0.54 0.58 0.17 0.18 0.06 0.0

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Fig. 6. Comparing theoritical and simulated results of the energy harvester.

Summary. In this paper, the design and simulation of a piezoelectric energy harvester based MEMS sensor has been performed. Here, the design and simulation has been observed by varying the materials and by changing the dimensions of piezoelectric bimorph and dimensions of proof mass of the rectangular cantilever beam. From all the above designs performed, the PZT-5H material energy harvester gives optimal power. The optimal power will be 0.9 mW at 77 Hz References [1] Kim Sang-Gook, Shashank Priya, Isaku Kanno. “Piezoelectric MEMS for Energy Harvesting.”

MRS Bulletin 37.11 (2012): 1039–1050. Web. © Materials Research Society 2012.

[2] Jornet, J.M.; Akyildiz, I.F. Joint energy harvesting and communication analysis for perpetual wireless nanosensor networks in the terahertz band. IEEE Trans. Nanotechnol. 2012, 11, 570–580.

[3] Renato Caliò, Udaya Bhaskar Rongala, Domenico Camboni, Mario Milazzo, Cesare Stefanini, Gianluca de Petris and Calogero Maria Oddo. “Piezoelectric Energy Harvesting Solutions.” Sensors 2012 [4] Bridget Cunningham, Optimizing the Power of a Piezoelectric Energy Harvester, www.comsol.co.in/blogs/optimizing-the-power-of-a-piezoelectric-energy-harvester/

Cite the paper G.K.S. Prakash Raju, P. Ashok Kumar, Vanaja Aravapalli, K. Srinivasa Rao (2017). Design and Simulation of Cantilever Based MEMS Bimorph Piezoelectric Energy Harvester. Mechanics, Materials Science & Engineering, Vol 9. doi:10.2412/mmse.16.9.490

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