final presentation - 23-03-10

PINNA LUIGIPH.D COURSE IN NANOTECHNOLOGY

MARCH 2010

VIBRATION-BASED ENERGY SCAVENGING

FOR POWER AUTONOMOUS WIRELESS

SENSOR SYSTEMS

UNIVERSITY OF GENOAPH.D. SCHOOL IN

SCIENCE AND TECHNOLOGY FOR INFORMATION ANDKNOWLEDGE

Motivations

Motivations

CNW

Motivations

System on-chip

System on-chip

Power autonomous Wireless Sensor System

MotivationsThe battery, is the most limiting factor for the sizereduction and life time of Wireless Sensor Systems

– e.g. MICAz, AA batteries occupy the 90% of the device dimensions

System on-chip Tiny Fully integrated Pervasive Non-invasive Power-autonomous Communication-

autonomous Multifunctional and

high sensitive sensor arrays-based

PhD research Focus On

Solar

Thermoelectric

Electromagnetic (RF)

Mechanical Vibrations

Ambient energy sources

Solar

Thermoelectric

Electromagnetic (RF)

Mechanical Vibrations

– Available in many environments

• e.g. household goods, industrial machineries, automobiles, buildings, …

– Power densities near to solar cells for long period of operation (in terms of years)

Ambient energy sources

Electrostatic Relative motion between two conductors separated by a dielectric

Pros– Suitable to be easily miniaturized with micro-fabrication technologies

Cons– The capacitor must be pre-charged at its maximum capacitance point (electrostatic generators are

basically variable capacitors)– Low output current– High output impedance– Relatively high AC output voltage (till 220 V)

Electromagnetic Relative motion between a fixed coil and a moving magnet or vice versa

Pros– High output power density– High output current

Cons– Difficult to miniaturize due to the low quality magnets available and low resistance coils obtainable– Relatively low AC output voltage (< 1 V)

Piezoelectric Bender Generators Charge generation due to mechanical strain of the piezoelectric material

Pros– High quality thin layers of piezoceramic materials– High output power density– High AC output voltage

Cons– Low output current– High output impedance

Vibration-based generators

Electrostatic Relative motion between two conductors separated by a dielectric

Pros– Suitable to be easily miniaturized with micro-fabrication technologies

Cons– The capacitor must be pre-charged at its maximum capacitance point (electrostatic generators are

basically variable capacitors)– Low output current– High output impedance– Relatively high AC output voltage (till 220 V)

Electromagnetic Relative motion between a fixed coil and a moving magnet or vice versa

Pros– High output power density– High output current

Cons– Difficult to miniaturize due to the low quality magnets available and low resistance coils obtainable– Relatively low AC output voltage (< 1 V)

Piezoelectric Bender Generators Charge generation due to mechanical strain of the piezoelectric material

Pros– High quality thin layers of piezoelectric materials– High output power density– High AC output voltage

Cons– Low output current– High output impedance

Vibration-based generators

Ph.D research goal

The objective of the research activity has been to pursuethe design and development of a power-aware, integratedand self-powered vibration-based Power ManagementSystem for Piezoelectric Bender Generators (PBG)

Outline

Feasibility study

Development of the SPICE model of the Piezoelectric Bender Generator (PBG)

Design and SPICE analysis of an integrated Power Management System with the SPICE model of the PBG

Design, fabrication and experimental characterization of a prototype of the Power Management System

Experimental tests (preliminary)

Conclusions

Outline

Feasibility study



Design, fabrication and experimental characterization of the prototype of the Power Management System


Conclusions

L. Pinna, M. Valle, G. M. Bo, Experimental results of Piezoelectric Bender Generators for the energy supply of Smart Wireless Sensors, Proceedings of AISEM2008 –The XIII annual conference of Associazione Italiana Sensori E Microsistemi, Rome, 19th -21st of February 2008

Hypothesis: about the feasibility of powering a commercial WTPMS with a PBG every 5 minutes

Set up

ATA6285/6286 WTPMS ATMEL– Supply: 2V to 3.6V– 20 kbps @ 64 bits @ 315 MHz– 5.05 msec @ 1 msec (Estimated measurement

requested time)– 17.4mW Power consumption (Estimated)

Experimental tests– @ different distance of the PBG from the

wheel center (9cm,16cm)– @ different car speed and the PBG

(50km/h,80km/h)– @ different PBG thickness (0.32mm,0.66mm)

Feasibility study: Wireless Tire Pressure Measurement System (WTPMS) powered by PBG


Some experimental results Est = 518 µJ Energy storage in 5 minutes @ Vcap = 2.2 V

(measured voltage)


Some experimental results Est = 518 µJ Energy storage in 5 minutes @ Vcap = 2.2 V

(measured voltage)

P = 103 mW @ 5.o5 msec

Outline

Feasibility study





Conclusions

Necessary an equivalent SPICE source which models the behavior of the PBG

Based on an electromechanical model which takes into account geometrical and physical parameters

The reciprocal interaction between PBG and scavengingsystem in terms of stress, strain rate, mechanical andelectrical powers at various loads can be studied andinvestigated

SPICE model of the PBG

Electromechanical model of the PBG

ElectromechanicalConversion

Block

Strain ratedS1/dt

Input Stress

Output Voltage

S Roundy and P K Wright, “A piezoelectric vibration based generator for wireless electronics”, Smart Materials Structures, Vol. 13, pp. 1131-1142, 2004

Stress developed as result of the input vibrations

K = geometrical constant [m-2]m = inertial massain = acceleration amplitudeω = vibration frequency

Inertia of the mass

MechanicalDamping

Mechanicalstiffness

Capacitance between

electrodes

Fin = main sinωt

σ

i

tKmaKF ininin ωσ sin==

nVVt

Yad

p

p =

−=

231σ

Mechanical -> Electrical Coupling

a = 1

a = 2

tp


Block

d31 = piezoelectric constantYp = piezoelectric material Young’s modulustp = thickness of the piezoelectric material

Input Stress

σ


i


+=

+=

331313

3311111

ETdD

EdTsST

E

ε

Constitutive equations for a linear piezoelectric material


( ) SASYdawli ipe == 31

Electrical -> Mechanical coupling

nVVt

Yad

p

p =

−=

231σ



Block

d31 = piezoelectric constantYp = piezoelectric material Young’s modulustp = thickness of the piezoelectric materialw = width of the piezoelectric materialle = length of the electrode

Input Stress

σ

i


+=

+=

331313

3311111

ETdD

EdTsST

E

ε

Constitutive equations for a linear piezoelectric material

( ) SASYdawli ipe == 31

Electrical -> Mechanical coupling

nVVt

Yad

p

p =

−=

231σ


SPICE model of the PBG

Luigi Pinna, Ravinder S. Dahiya, Maurizio Valle, SPICE model for piezoelectric bender generators, ICECS 2009, The 16th IEEE International Conference on Electronics, Circuits, and Systems, Hammamet, Tunisia, December 13th – 16th, pp. 587-590, 2009.

Input StresstKmaKF ininin ωσ sin==

Simulation results: MATLAB® vs SPICERoundy et al.

Optimized custom PBGVol. = 1cm3 (Device volume)f = 120 Hz (Vibration frequency)a = 2.5 m/s2 (Acceleration amplitude)

Simulation results: MATLAB® vs SPICE

Roundy et al.

Roundy et al.


Outline

Feasibility study





Conclusions

Power Management System

AC-DC full-wave bridge rectifierActive vs Diode Bridge Rectifier

– Advantages

Lower Power Consumption

Lower voltage drop across active device than diode (0.7 V)

Advantage for low power systems

Design flexibility

– Drawbacks

Control circuits for active devices

Circuit complexity (fully active)

The use of only two active devices in place of two of the fourdiodes aimed to develop a simple circuit

Semi-Active Bridge Rectifier

CONTROLCIRCUIT


PBG generates high output voltageNecessary a HV process technology up to 50 V


CONTROLCIRCUIT



Self-starting thanks to the intrinsic VDMOS diodes (bd1, bd2)


CONTROLCIRCUIT




Self-starting thanks to the intrinsic VDMOS diodes (bd1, bd2)

DC-DC converterDC-DC switching converter

– An active device - controlled by a controller circuit -transforms the input rectified voltage to a square-wave with adjustable duty-cycle

– A passive filter - with inductor and capacitor - extracts the average of the square wave signal, which corresponds to the DC output voltage value

– Pros• High efficiency• Step-up and step-down• Flexibility of the control

circuits design• Smart switching control circuits

– Cons• Complex control circuits Step-down Buck Converter

– Generates a Vout < Vin

SW

Steady-state: switch closedDC-DC converter

∫ −=∆

=−=

ontoutinonL

LoutinL

dtVVL

I

dtdiLVVV

)(1,

∫−=∆

=−=

offtoutonL

LoutL

dtVL

I

dtdiLVV

1,

Steady-state: switch opened

SW on

SW off

DC-DC converter

inout

loadin

inout

offon

on

PPDIIDVV

D

DutyCycleTT

TD

===

∈

=+

=

)1,0(

inoutinripple

rippleinrippleinoffon

onout

tout

toutin

DVtVDVv

tvDVtvVtt

ttV

dtVL

dtVVL

offon

≈⇒<<

+=++

=

=−− ∫∫

)(

)()()(

01)(1

SWSW on

SW off

DC-DC converter controller

DC-DC CONVERTERCONTROL

BLOCK

DC-DC converter controller

VOLTAGELEVEL

SHIFTER

DRIVER

Vrec

DRIVER

DC-DC converter controllerVrec

DC-DC voltage regulatorVrec

If Vout < Vref Vctrl -> Low Vrec-Vctrlsw ≤ 3.3V

If Vout > Vref Vctrl -> High Vrec-Vctrlsw = 0

SW3 -> ON

SW3 -> OFF

SPICE analysisSPICE ideal AC voltage source

Reference Inverter• Wp = 2.25 µm• Lp = 0.5 µm• Wn = 1 µm• Ln = 0.5 µm

Vrec

Vrec

SPICE analysis

Vripple = 0.5%

idriv = 850 µA (Current consumption)

SPICE indipendent AC voltage source

Vrec

SPICE analysis

DC-DC voltage regulator with PBG as source


Roundy et al.


DC-DC voltage regulator with PBG as sourceiPBG ~ 200 µA

Roundy et al.


3.3 V


CURRENT-AWARE OPTIMIZEDReference Inverter

•Wp = 1.25 µm•Lp = 2.2 µm•Wn = 0.5 µm (minimum width)•Ln = 2.2 µm

Self-Powered DC-DC voltage regulator

idriv ≅ 90 µA (Current consumption)

SPICE analysis results

Luigi Pinna, Ravinder S. Dahiya, Fabrizio De Nisi, Maurizio Valle, Analysis of Self-Powered Vibration-Based Energy Scavenging System, ISIE 2010, The IEEE International Symposium on Industrial Electronics, Bari, Italy, July 4th – 7th, 2010, (accepted)

Pout,PBG PRloadPMechRload

VP

iVP

SnAP

RloadRload

PBGout

ini

Mech

2

,

=

⋅=

⋅= σ3.3 V DC

SPICE analysis resultsSTRAIN RATE, dS1/dt

STRESS

PIEZOCERAMIC

PIEZOCERAMIC

1

2

3

S1σ1

S1σ1

Efficiency of the voltage

regulator

Pout,PBG PRload

η = PRload / Pout,PBG

SPICE analysis resultsPBG OUTPUT CURRENT

Outline

Feasibility study





Conclusions

• On ASIC -> Only the key components – semi-active bridge and buck converter switching part

• On PCB -> LC filter and switches control circuits– Necessary a design flexibility for the experimental tests– Design corrections could be needed– Errors can be easily found and corrected

ASIC and test PCB design

D1

D2

SW1

D3

SW2

SW3

1.465 mm

1.45

78 m

mASIC design (AMIS I3T50u technology)

TEST CHIP CORE

ESD PROTECTIONS p-channel VDMOS (LFPDM50)

Dimensioned to have the same Ron

(i.e. 16 Ω) of VFNDM50

Wtot = 3600µm @ 1mA @

|Vgs|=3.3V

Floating poly Diode (FID50U)

Vd @Id=1mA

Wanode = 21 µm @ m=1

->Rd=653Ω @ m=80

n-channel VDMOS (VFNDM50)

• Wchannel=40 µm

• Ron=Vds/Ids @ Vgs=3.3V

@ Ids=1mA->Ron=16 Ω @ Wtot = 750 µm

Ref: PBG T226-H4-303XVoc = ±36Vppf = 400 HzPout = 7.2 mWrms

EXTERNAL SUPPLY

Test PCB design and validation Vctrlsw

Vrec

Vout

Test PCB design and validation

START UP TEST RECTIFIER SWITCHES TEST

VO1

AC1 G1

Test PCB design and validation AC1 VO1

VO1

VO1

G1

TESTCHIP

OUTPUT VOLTAGE LOAD POWER


REGULATED VOLTAGE

INPUT POWER


TESTCHIP

η = Pin / Pout

Outline

Feasibility study



Design, fabrication and experimental characterization of the Power Management System


Conclusions

• PBG1– 63.5x31.8x.66 mm3

– Iron proof mass 220g– ~32Hz resonance frequency

Experimental tests (preliminary)• PBG2

– 31.8x3.2x.51 mm3

– Iron proof mass 16g– ~60Hz resonance

frequency

Shaker Tira TV50018 controlled by LabView

AluminumSupports

• Test 1• PBG1 Vout (Pout) vs.

resistive load • Vibrations @ ~33 Hz


PRload


~33 Hz

Measured results:

Problems related to the experimental Set-up

• Support structure

• Issues in the PBG

• Test 2• PBG1 Voc vs. Frequency

of Vibrations

• Test 3• PBG2 Voc vs. Frequency

of Vibrations

~63 Hz

Plastic Support


~32 Hz

Experimental tests (preliminary)Test 4: Rectified PBG output

voltage• PBG1 connected to the

Test Board • Vibrations @ ~33 Hz

Experimental tests (preliminary)Test 5: 3.3V regulated output

voltage @ 1 μF capacitive load

• PBG1 connected to the Test Board

• Vibrations @ ~33 Hz

Outline

Feasibility study



Design, fabrication and experimental characterization of the Power Management System


Conclusions

ConclusionsThe developed SPICE model of the PBG has shown the

importance to have an equivalent model in SPICE of the vibration-based transducerBetter estimation of the behavior of the system with respect to

the use of simple equivalent PBG models

The developed SPICE model of the PBG has shown the importance to have an equivalent model in SPICE of the vibration-based transducerBetter estimation of the behavior of the system with

respect to the use of simple equivalent PBG modelsAnalysis of the reciprocal interaction among

mechanical and electrical parametersEvaluation of the current, voltage and power

generated by a PBG when connected to the power management systemOptimization of the power management system

Conclusions

Power Management System architectures

Conclusions

PROPOSED ARCHITECTURE

Proposed Power Management System architecture Innovative and Simple approach PBG + Semi-active bridge rectifier +Voltage regulator

Self-powered (SPICE version) Validated the well working of the prototype Test Chip and Test

board Efficiency of the system could be improved

• Optimization of the Voltage Level Shifter circuit• Design of the integrated comparator

• Should be designed to work in the sub-threshold region

• Low power and current consumption (order nW and nA )

• Solve the problem of the generation of a stable voltage reference in input to the driver comparator

Conclusions

Further experimental tests are necessary to validate and optimize the SPICE model of the PBG

• Inclusion of various losses - dielectric, piezoelectric and viscoelastic - might be necessary

Careful study is needed to be conducted • Set up of the experiments

Conclusions

final presentation - 23-03-10

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