Design and Simulation of MEMS Cantilever Based ... - IEEE Xplore

National Conference on Recent Advances in Electronics & Computer Engineering, RAECE -2015, Feb.13-15, 2015, liT Roorkee, India

Design and Simulation of MEMS Cantilever Based Energy Harvester-Power Source for Piping Health Monitoring System Suresh s. Balpande and Rajesh S. Pande Department of Electronics Engg Shri Ramdeobaba College of Engineering & Management ,Nagpur-13 [email protected]

Ab stract

Industry without pipes cannot be imagined.

-

The Complex piping network produces noise due to fluctuations in pressure. High frequency noise produces excessive n o i s e and vibration causes failures of walls and instrumentation system used in pipes. In severe cases, the pipe itself can fracture. State-of-the-art piping systems

employ

sensor

nodes

for

piping

health

monitoring such abnormality. This kind of mechanism helps us to take preventive actions to avoid fluid wastage and accident. sensor nodes retain this information and periodically transmit it. These tasks require an average power budget of between about 0.1 microwatt and 1 milli-watt. Sensor nodes mounted on pipe driven by battery require frequent charging and replacement due to limited life span of battery. In many cases It is not convenient to charge or replace because of underground laying and huge count. The second reason for finding substitute to battery is the fact that energy density of batteries

increased by 8% whereas demand is 24 %.

This is the reason for short life span of electronics even though it c a n survive for few decades. T hus we need to think concretely for an alternate energy sources. Energy

pipes generates vibrations due to varIatIOns III flow, pressure etc. Steady-state vibration can be either low frequency « 300 Hz) or high frequency (> to 300 Hz). Low frequency vibration cause lateral displacement of the pipe, while high frequency vibration can cause flexural vibration of the pipe wall itself in addition to lateral pipe movement. Due to continuous flow of fluid at a particular f I 0 w a n d p r e s s u r e rate, pipe starts vibrating causes excessive noise and vibration. This is the reason for failures of pipe walls and instrumentation unit . In severe cases, the pipe itself can fracture which may create hazardous situation. In order to avoid damage of walls or fracture , sensor array is mounted on state-of-the-art piping system for continuous monitoring [1]. The sensor nodes as depicted in fig.1 are linked to server and generate alerts. This kind of mechanism helps us to take corrective actions in order to avoid w a s t a g e a n d accident [2-3] .

harvesters have attracted attention as the substitute for battery. An attempt has been made to design energy harvester using

the principle of piezoelectricity. Lead

free Zinc Oxide material is proposed as piezoelectric material. This work presents design and simulation of electromechanical

model.

Proposed

single

cantilever

harvester generates 22.25 microwatt of power for 1 KOhm load.

Cantilevers array can be employed

to

supply more power.

Index Ter ms- Piezoelectric harvester, Zinc Oxide, Piping system Fig.l Sensor Network

I. INTRODUCTION Industry or human life without pipes can not be imagined. It is used to connect one section of industry to other just like electrical wires. Pipes are the integral part of our life and there are numerous applications like water, LPG distribution system in non industrial applications. Fluid flowing through

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Fig.4 Mounting of Harvester at pipe joint[l]

Strained piezoelectric material generates voltage due to charge separation. The generated voltage is raised to desired level of voltage using voltage multiplier and stored in super capacitor which is considered to be replacement of battery[5] [6]. II . EH SYSTEM SCHEMATIC Fig.2 Self powered architecture of sensor node

The architecture of normal sensor node in which energy storage is battery as shown in fig.2. Sensor is used to get information of physical quantities processed by D SP processors and finally transmitted by radio transceiver to central unit [3]. There are many systems where it is very difficult in powering the nodes throughout life as the battery replacement is infeasible .Few examples are underground pipes, sensor node in concrete structure . There are thousands of situations where we can think of the operations once in a lifetime[4] . Generally instrumentation is done at every pipe joint to monitor health of the system depicted in fig.3. This is the place where energy harvester can be embedded with instrumentation unit i.e. sensor node. Mounting of energy harvester should be done properly as shown in fig.4 [1]. Harvester starts vibrating due to pressure ripples causes induction of strain m piezoelectric material.

The complete schematic of energy harvester is shown in fig 5. Storage device can be rechargeable battery in case of high duty cycle operation and feasibility of ?atte� replacement. In contrast to this ,super capacitor IS bemg used at rest of the applications . The piezoelectric generator is a simple mechanical beam structure with piezoelectric material as shown in fig.6. [1][2]. The electrical circuit i.e. Voltage �ultiplier c�mposed with ultra low threshold voltage dIOdes. ThiS subsystem is used to raise the voltage level of few millivolts to volts. The design parameters of the cantilever structure are chosen in such a way that it would be compatible to micro fabrication techniques [2]. VIBRATIONS

Fig.5. Block diagram of piezoelectric power harvester.

Fig.3 Installation of Instrumentation unit at pipe joint

� Housing

1

For 0.25 micro gram tip mass Material

0.0

2.0

4.0

6.0

8.0

10.0

Time (s)

12.0

14

ZnO PZT

8

910

0.6

AIN

5

1100

0.4

GaAs

6.5

1000

0.6

Fig.8. Output voltage levels of multiplier circuit

19 acceleration applied for cantilever for all these materials

This circuit is used to multiply and rectify the input voltage based on diodes and capacitors. The output voltage of the micro-power generator is often smaller than the threshold voltage of the standard diode. To

185


overcome this problem, we proposed a novel low

Piezoelectric analysis

C.

threshold diodes based on DTMOS (Dynamic threshold MOS ) technology. This technology can be realized by

50

connecting gate, drain and bulk together [12]-[14]. The

40

plot shows that output is multiplied by factor 6 . The

30

input voltage of 200mV p-p was applied and observed

>20

the output of 1.2 V dc .

i 10

E

1'"

i

0 .g �-10

V. RESULTS AND DISCUSSION A.

IT]

Meshed model of geometry

-20 -30 -40 500

1000

1req

1500

Fig 10 Electrical Potential harvested by single Cantilever

It is observed that-45 mV to +50 mV peak is generated by single cantilever at 1kHz frequency which is very closed to first mode of973 Hz frequency.

Fig 9

Meshing of Cantilever

Free tetrahedral meshing with extremely fine is used in order to get accurate results. B.

Eigen Frequency analysis

1

973Hz

2

8..2KHz

3

12.92 KHz

4

39.01KHz

5

77KHz

6

127K hz

500 Fig

1000

1500

2000

2500

3000

3501

II Displacement vs frequency plot

Maximum 8 urn displacement is noted at 1000 Hz frequency. This kind of analysis is important to know maximum displacement in Z direction. One can decide reliability, stopper arrangement and spacing between base and cantilever out of this analysis. Von mises analysis shown in fig.12 is to get average value of stress on cantilever. Stress level is different at different point and directions. This analysis gives the aggregate effect . Von misses stress analysis is important to know stress level sustained by structure. 2.25 MPa stress value can be easily sustained by silicon

This analysis is carried out for computing resonant modes of the structure. Vertical acceleration of 1g was applied as body load at free end .The result shows mode 1 of 973 Hz as a mode of interest because maximum output is achieved for mode only.

186


Point Graph: von Mises stress (MPa)

freq(S)=2000 Isosurface: Electric potential (mV) Arrow: Electric field A1.9!

0.5

500

1000

1500

2000

2500 freq

3000 n

Fig 12 Von mises stress vs Frequency

Fig 15. Electric Field along the length

D. tP

Cantilever fabrication process flow

Process Editor - [C:/Coventor /DeslgnJiles/demo/Devlces/balpande:5Irtest.proc] Edit

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Fig 13. Design of cantilever array

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Layer Name

Step Name

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Thermal Oxidation 5i02

2

Planar Fill

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Generic Wet Etch

4

Planar Fill

5

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6

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7

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Mask Name

litho 1 cavityanchor

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+

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Point Graph: Electric potential (mV)

Fig.16 Fabrication Process steps

150

1, P Type \"Jafer 100

2. T h e r m al 0xidation(Dry)

6. ZnO Deposition

3. Sacrificial layer deposition

-50

7. Top electrode deposition

o

500

1000

1500

4. Optical Lithoeraphy 2000

2500 1req

3000

Fig 14. Output voltage vs frequency plot of array of cantilever

5. Cantilever-anchor deposition

In order to generate more voltage array configuration is preferred . It is observed that 160 mV is harvested at lOOO

8. Removal of sacrifiallayer

Fig.17 Fabrication Process Flow of harvester

HZ frequency for array of 4 cantilever. Electrical

Cantilever fabrication process steps and

field indicates that maximum voltage is induced at fixed

flow is

presented in Fig 16 and 17. ZnO piezoelectric material deposition with aluminum electrodes with parallel plate

end where material experience maximum stress.

arrangement is proposed in this work [15][16].

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[11] A Harb , " Energy harvesting : state-of-the-art," Journal of

VI. CONCLUSION AND FUTURE WORK

renewable energy , Elsevier, June 2010 ,pp 1-14.

This work is

focused on developing more realistic

[12] S. Saadon, O. Sidek ,"A review of vibration-based MEMS

MEMS structures. Proposed harvester can generate 22

piezoelectric energy

microwatt of power. The commercial sensor node

management ,52, Elsevier, August 2010, pp 500-504.

require power budget of about 0.1 microwatt to 1 milliwatt per node over a period of

[13] Henry A Sudano, Daniel

3-5 seconds. This

2004 ,pp 1-28.

power budget sensor node. In future, this work will be for

maximizing

power

by

1. Inman, "Estimation of electric

charge output for piezoelectric energy harvesting" Strain Journal,

shows that proposed Energy Harvester can drive low continued

harvesters," Journal of Energy conversion and

[14] S. Balpande, B.Lande, U.Akare, Laxman Thakre "Modeling of

optimizing

cantilever based power harvester as an innovative source of power

geometry , formation of cantilever array so that sensor

for RFTD Tag" in proceedings of 2nd IEEE International conference ,

node of higher power budget i.e. commercial sensor

G.H.Raisoni College of Engineering, Nagpur [Decl6-18, 2009]

node with 1 milliwatt of power requirement .

[15]

R.

Pande,

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