Lecture 3 Piezoelectric Materials (PDF Version)yyaman/avt086/Prasad/Eswar_Prasad_3.pdf ·...

Sensor Technology Limited

Piezoelectric Materials

• Piezoelectric Phenomena

— Piezoelectric Effect

— Modes of Vibration

— Terminology

• Materials and Processing

— Perovskite Materials

— Ceramic Processing

• Piezoelectric Applications

— Design Principles

— Application Examples

Lecture Outline

Piezoelectric Phenomena

• Piezoelectric behaviour can be manifested in two distinct

• ‘direct’ piezoelectric effect

• ‘converse’ piezoelectric effect

Piezoelectric Effect

• ‘Direct’ piezoelectric effect occurs when a piezoelectric

material becomes electrically charged when subjected to a

mechanical stress.

• These devices can be used to detect strain, movement,

force, pressure or vibration by developing appropriate

electrical responses, as in the case of force and acoustic

or ultrasonic sensors.

Direct Piezoelectric Effect

• ‘Converse’ piezoelectric effect occurs when the

piezoelectric material becomes strained when placed in an

electric field.

• This property can be used to generate strain, movement,

force, pressure or vibration through the application of

suitable electric field.

Converse Piezoelectric Effect

Terminology

• When an electric field is applied to a piezoelectric,

the material dimensions change in all three axes

under stress-free conditions. The d constant

also expresses the amount of charge developedrelative to the stress applied along a specific axis.

Piezoelectric Strain Constant d

• The d31 constant is defined as:

Piezoelectric Strain Constant d

axis 1 along applied Stressarea electrode per Charge

axis 3 along applied Fieldaxis 1 along Developed Strain

• The g constant expresses the electric fielddeveloped under open circuit conditions relative

to the stress applied along a specific axis. It

also expresses the amount of strain induced

relative to the applied electrical charge per unitarea.

Piezoelectric Stress Constant g

• The g31 constant is defined as:

Piezoelectric Stress Constant g

area electrodeper charge Appliedaxis 3 along developed Strain

axis 1 along applied Stressaxis 3 along developed Filed

Hysteresis and Strain

Piezoelectric and Electrostrictive Effect

Modes of Vibration

Crystal, Ceramics and Polymers

Type MaterialsSingle Crystals Quartz

Lead Magnesium Niobate(PMN-PT and PZN-PT)

Ceramics Lead Zirconate Titanate (PZT)Lead Metaniobate (LMN)Lead Titanate (LT)Lead Magnesium Niobate (PMN)

Polymers Polyvinylenedifluoride (PVDF)Composites Ceramic-polymer

Ceramic-glass

Longitudinal Strain vs.Field for VariousMaterials

Structure of Lead Zirconate Titanate Ceramics

A2+ (Pb, Ba)B4+ (Ti, Zr)O2-

BM400 Type I (Pb, Sr)(Zr, Ti)O3BM500 Type II Pb(Zr,Ti,Nb)O3

Se nsor Technology L imited

Soft Ceramics

Type of Piezoelectric Material Typical Properties

Soft Ceramics

Normally doped with NiobiumPentoxide or Lanthanum OxideLow Mechanical Q, High dielectricconstants and high chargesensitivity.

Examples of materials are:BM500 (Navy type II)BM527 (Navy type V)BM532 (Navy type VI)

Sensors, low power projectors,actuators, accelerometers.

Navy type ceramics refer to DOD-DTS-1376(SHIPS).

Se nsor Technology L imited

Hard Ceramics

Type of Piezoelectric Material Typical PropertiesHard Ceramics

Normally doped with Nickel, Iron orStrontium. Typical characteristicsare high mechanical Q, lowerdielectric constant, lower lossfactor, higher resistance todepoling.

Examples of material are:BM400 (Navy type I)BM800 (Navy type III)

High power transducers in sonar,ultrasonic cleaning, high-driveactuators, biological celldisrupters

Navy type ceramics refer to DOD-DTS-1376(SHIPS).

Electrostrictive Ceramics

Type of Piezoelectric Material Typical Properties

Electrostrictive Ceramics

Normally produced from doped leadmagnesium niobate., Available forabout five years now, thesematerials have almost nohysteresis, very high dielectricconstants, very high straincoefficients.

Materials:BM600 (Modified LeadMagnesium Niobate)

Mainly used in actuators andvery high power sonar projectors.

Properties of Lead Zirconate Titanate Ceramics

Material ParameterPZT (II)BM500

PZT (VI)BM532

PZT (I)BM400

PZT (III)BM800

Dielectric Constant 1750 3250 1350 1000

Dissipation Factor%

2.0 2.0 0.4 0.2

Voltage Constant(g31) 10-3 Vm/N -11.5 -7.5 -10.5 -10.5

Charge Constant(d31) 10-12 C/N

-165 -250 -115 -80

Curie Temperature0C

360 210 350 325

Mechanic Q Factor 80 70 500 1000

Application PZT (II)BM500

PZT (VI)BM532

PZT (I)BM400

PZT (III)BM800

UnderwaterSonar ProjectorsHydrophonesDepth SoundersLinear Arrays

MeasurementLevel, FlowFlaw Detection (NDE)AccelerometersActuators

Application PZT (II)BM500

PZT (VI)BM532

PZT (I)BM400

PZT (III)BM800

MedicalTransducersSteilizers

r r rr r

IndustrialCleanersAlarmsWelders

Piezoelectric MaterialsPiezoelect ric Materials

Processing of Lead Zirconate Titanate Ceramics

Ball mill

Spray dry

Calcine up to 1200oC

Weigh outraw material

Ball mill to desiredparticle size

Spray dry

Forming process:(dry or isostatic press etc.)

Sinter firing

Grinding or lapping

Powder evaluation

Electroding

Polarizing

Testing

Polarization of Ceramics

Polarization in asingle crystal ofpiezoelectricceramics.

Piezoelectric ceramic -before polarization

Piezoelectric ceramic - after polarization

Standard Ceramic Configurations

Frequency discs Thickness discs

Plates and bars

Washers

Piezoelectric Tube Actuator

31dLWVL ••=∆

Electrode Configurations for Tube Actuators

Outer/InnerElectrodesSegmented

180 DegOption 001

OuterElectrode

Segmented180 Deg

Option 002

Outer/InnerElectrodesSegmented

90 DegOption 003

OuterElectrode

Segmented90 Deg

Option 004

Outer/InnerFullFace

ElectrodesOption 005

No Segmentation

Option 005

One Horizontal Line

Option 006

Horizontal/Vertical Segments

Option 007

Piezoelectric Stack Actuator

33dNVL ••=∆

33dLtV

••=

33••=

Actuator Displacement and Force Working Equations

Assumption: Same Electric Field in Ceramics

Displacement and Force for Stack Actuator

Electric Field Constraints

! Coercive Field

(~ 500V/mm)

! Flashover Limit in Air

(~ 1000V/mm)

0006.0≈∆LL

∴ would need 17mm stackfor 10µm displacement.

AreaF ×≈ 30(F in Newtons, Area in mm2)

For 15mm OD & 5mm ID:

NF 4600≈

For Field = 1000 V/mm

Note: Exceeding coercivefield limit requires DC bias toavoid depoling.

Bending Mode Actuator

LB V hB DB

LdVD •••=B

BBEB L

hWsdVF •••=

- 2 0 0 - 1 0 0 0 1 0 0 2 0 0

V o l tag e (V )

Parallel to Field

Perpendicular to Field

Electrostrictive Actuator

25 x 25 mm2

0.5 mm

A piezoelectric actuator of the same geometry and having the samedisplacements at 200V would require:

d33 = 1250pC/N; d31 = -460pC/N

Piezoelectric Composites

Piezoelectric composites consist of aceramic material embedded in a polymermatrix with a certain connectivity knownas 1-3 connectivity pattern. These elements offer several advantages oversingle-phase (monolithic) piezoelectricmaterials for such applications as

hydrophones and transducers. While not a flexible element, they canbe cut to very thin dimensions.

Piezoelectric Composites

1-3 composite

525±10%0.03 1475 ±5%0.62525-30%150kHz -1.5MHz

3250±10%0.031850±5%0.5870100150kHz -2MHz

Property

Dielectric ConstantK33T

Dissipation FactorN3Ke

Q (unloaded)Ceramic Volume

Frequency

Langevin-type transducers feature compactness, highenergy efficiency and a wide range of operatingtemperatures. These transducers use Lead ZirconateTitanate ceramic elements in a sandwich-typeconstruction (two to four discs), providing a ruggedunit capable of high efficiency and continuous operationat elevated temperatures.

Characteristic features:• Large amplitude• Low heat generation• Stability and durability• High efficiency• High output

Langevin Transducers

Langevin transducers can bebuilt from 18kHz to 70kHz forvarious end-user applications.

A booster horn can be used togenerate greater displacementfrom the transducer.

Applications:• Ultrasonic cleaning• Ultrasonic degreasers• Cell disrupters• Ultrasonic machining• Plastics welding• Underwater acoustics• Non-destructive evaluation• Atomizers• Ultrasonic scalpel

The electrical condition of an unstressed medium under

the influence of an electric field is defined by two

quantities - the field strength E and their dielectric

displacement D. These two are related by the equation:

D = ε E

where ε is the permittivity of the medium.

Piezoelectric Relations

The mechanical condition of the same medium at zero

electric field strength can be defined by two mechanical

quantities - applied stress T and strain S.

S = sT

where s is the compliance of the medium.

Piezoelectricity involves the interaction between the

electrical and mechanical behaviour of the medium, and

the interaction can be described by linear relationships

between these two.

S = sE T + dE

D = dT + εT E

1. Energy Conversion Mechanism

An externally applied electric field causes a change in the

dielectric polarization in the material which in turn causes

an elastic strain. The generating action takes place when

an elastic strain causes a change in the polarization that

induces a charge on the electrodes.

Principles of Application

2. Transducer Operating Environment

The acoustic properties of the medium (air, water or ice)

are very important in the design of transducers.

Transducers must also withstand the severe effects of

sea water, biological activity, hydrostatic pressure, and

extreme temperature conditions.

3. Conversion Criteria

The following are the general performance criteria for the transducers.

• Linearity. The output of the transducer is a linear function of the

input.

• Reversibility. The transducer must convert energy in either direction.

• Passivity. All the output energy from the transducer is obtained from

the input energy - electrical or acoustical.

Applications

Mechanical toElectricalConversion

! Phonograph cartridges! Microphones! Vibration sensors! Accelerometers! Photoflash actuators! Gas igniters! Fuses

Applications - Piezoelectric Igniters

NTK Ceramics, Japan, 1986.

Hydrophones

Applications - Diver Communication SystemsOcean technology S

ystems, 1990

Applications - Marine Mammal Listening Systems

Applications - Consumer Products

Applications

Electrical toMechanicalConversion

! Valves! Micropumps! Earphones and speakers! Ultrasonic cleaners! Emulsifiers! Sonic transducers

Applications - Piezoelectric Audiotone Transducers

Figure A. Layered structure with ceramic bonded to metal diaphragm. Radialmode of vibration produces a bending effect.Figure B. Alternating voltage produces convex and concave distortions in thediaphragm. Displacement of the diaphragm is in the order of microns.

Applications - Liquid Atomization Devices

1. Vibration; 2. Cavitation; 3. Misting4. Ultrasonic Humidifier.

Liquid Atomizing Nozzle from Sono-Tek Corporation. Fineliquid sprays are used in material processing industry suchas the manufacture of solar cells to provide thin uniformcoatings.

Applications - Liquid Atomization DevicesData from

Sono-Tek

Cavitation (at lower power levels)

Misting(at increased power levels)

Applications - Depth Sounders

NTK Technical Ceramics, 198

Applications - Sonar Applications

Applications - Low Frequency Sonar

Sonar Dome

Applications - Low Frequency Sonar

Detail of the Sonar Transducerand the components of thesystem.Raytheon, 1984.

Applications - Ultrasonic MotorS

hinsei, 1996

Applications

Electrical-Mechanical-ElectricalConversion

! Surface acoustic wave devices! Delay lines! Filters! Oscillators! Transformers

Applications - Flash Blindness Goggles

TransducerSX100

DepthCompensator

MatchingNetwork

PowerAmplifierShield

SignalProcessor

PowerDistribution

LithiumBatteryPack

AnodizedAluminumHousing

Underwater Communications

Communication with Marine Mammals

Transducer

Battery

ControlBox

Cable &Reel

Marine Mammal Communications

Transmitter Receiver/Monitor

Conclusions

NTK Technical Ceramics, 198

• Reviewed Piezoelectric Phenomena

— Piezoelectric Effect, Modes of Vibration, Terminology

• Materials and Processing

• Piezoelectric Applications

— Application examples using mechanical to electrical conversion, electricalto mechanical conversion, and electrical-mechanical-electrical conversionhave been discussed.

Conclusions

Lecture 3 Piezoelectric Materials (PDF Version)yyaman/avt086/Prasad/Eswar_Prasad_3.pdf ·...

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