Actuator &

Sensory Devices
based on HBLS
Smart Materials

Bishakh Bhattacharya
Department of Mechanical Engineering
Indian Institute of Technology, Kanpur
 What is a Transducer?
Fundamental mechanism for both sensing and actuation is energy
transduction – conversion of signal/energy. Primary forms are grouped into two
categories:

Multicomponent transduction, utilizes “action at a distance” behavior

between multiple bodies.
eg:
Electromagnetic transduction, typically based upon the Lorentz equation and
Faraday’s law, and electrostatic interaction, typically based upon Coulomb’s
law.

Deformation-based / Solid-state transduction, mechanics-of-material

phenomena: crystalline phase changes or molecular dipole alignment.

Piezoelectric effects, shape memory alloys, and magnetostrictive,

electrostrictive materials.

Micro-scale systems currently dominated by electrostatic and electromagnetic

interactions.
Relative position of Actuators and Sensors
in an Intelligent System
Two Important Components: Energy Controller
and Energy Converter

Ref. Book. H. Janocha (ed): Actuators

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 The first Piezoelectric Device!
• In a modern quartz
watch, the crystal
resonator is
shaped as a small
tuning fork that
vibrates at the
frequency of
32,768 Hz!
Follow up: two very common smart actuators

• Thin Disk Buzzer

• Amplified Piezo
Actuator
 Smarter Actuators for
Automobiles
• Current trend in Automotive Electronics is to
use actuators for functions which require
faster, more powerful and highly precise
motion.
• Initiated application of Piezoelectric
Actuators and Rheological Fluids for the
control of Fuel Injection and Vibration
control.
• Simple Unimorph/Bimorph/Discs are not
popular in the industrial scale due to lack of
efficiency, displacement and safety.
 Piezo Diesel Injectors were developed to
reduce emissions by making the
combustion of fuel within the cylinder
more efficient (specially for Diesel
Engines)

As a Piezo injector performs faster, it can carry out

more injections per cylinder stroke and allows for higher
fuel system pressures. This improves the atomisation of
the diesel, giving improved spray momentum and
greater accuracy. Furthermore, the technology allows
for greater flexibility with regard to the start of injection
and the relevant time interval between individual
injection events. In addition, the new piezo injectors
developed are found to be smaller in size and lower in
weight compared to the traditional injectors

improved combustion control, less fuel consumption,

reduced noise, improved engine performance, and a
considerable reduction in emissions.

Cut-out of a Piezoelectric Fuel Injector from EPCOS

(TDK) [Ref. Sealand-Turbo-Diesel Asia]
Comparison of Different Actuation Speeds

Type Device Accuracy Response

Pneumatic Motor Degrees 10 secs
Hydraulic Motor Degrees 1 sec
Electro-magnet Stepper 10 µm 0.1 sec
Piezoelectric Actuator 0.01µm 0.0001 sec

Magnetostrictive Actuator 0.01µm 0.001 sec

Piezoelectric Ultrasonic minutes 0.001 sec

 Issues with PZT
• A relatively high electric field is necessary
to develop an equivalent system with
associated high voltage requirement to
generate appreciable or useful strain.
• Example: PZT block of height 1mm, apply
1KV field, d33 = 600 m/pV, strain 6x10-4
and corresponding displacement is the
same magnitude in mm.
 How can we Maximize the
Displacement?
Consider a multilayered piezoelectric stack of
length l and number of layers n, which is subjected
to a voltage V.

Neglecting elastic deformation, total displacement

available from a ‘n’ layered stack will be:

Δ = ( l x d X V/(l/n)) = d x V x n

Total displacement is directly proportional to the

number of layers n!
 Multilayer Actuators
• Typical layer thickness is about 50µm
• Typical strain available 0.1%
• Hence, for a 100 mm stack actuator with
2000 piezo-eletcric layers and an applied
voltage of about 100V, the displacement
will be: 10 x 10-9 x 100 x 2000 = 200 µm
• Blocking force = 100 kgf
• Lifetime = 1011 cycles
Major Applications of Multilayers
• Precision Positioners (order of 0.1 !")
• Miniature Ultrasonic Motors (USMs)
(< 1cm)
• Adaptive Mechanical Dampers
 Advantages of Multilayered
Piezoelectric Actuators
• Requires less voltage
• Produces larger deformation/displacement
• Safer to use
• High Life Cycle
• Lighter and More Compact
• Concurrent engineering – advantages
from the development of multi-layered
capacitors
A Typical Multilayer Configuration
Mechanically Series Connection
Mechanically Parallel
Connection
Series Modelling of the
Electrical System
Parallel Connection of the
Electrical System
 Governing Criteria
• The PZT actuators showing higher mechanical
compliance should be modelled as a series assembly of
springs;
• those with higher stiffness can be modelled with a
parallel assembly of springs.
• In the electrical domain, PZ actuators having faster
response time should be modelled with a series
assembly of the capacitors;
• those showing higher robustness to electrical
disturbances can be modelled with a parallel circuit
Comparison of Mechanical and
Electrical Models
 Other important properties
• The resonating frequency of a fixed-free
multilayer actuator is given by:
1 #
fn =
and response time !" = $ %
&
2 l r S33
D

• Where, ρ is the density and S33 denotes

the compliance modulus
• For example, one 1 cm sample will have
resonating frequency about 100 kHz and
response time in milli seconds.
How multi-layers are developed?
• Two common techniques – Cut and Bond
and Tape-Casting
• In cut and bond technique PZT wafers are
cut (typical thickness 0.2mm) and bond with
intermittent metal foils. Major draw back is
that this is a labor intensive process.
• In tape-casting method, ceramic green
sheets are printed with electrodes and
cofired. There are various ways of
electrically connecting such layers.
Reference:
J. Pritchard, C. R. Bowen,
and F. Lowrie, 2000
Various electrode configurations

Inter-digital Plate Through

Configuration Configuration
 Some more configurations

Inter-digital Electrode with

configuration with slit Gap
 Design Issues: Electrode
Configuration
• Inter-digital Configuration is the most
common and best suitable for mass
production. However, due to non-uniform
electric field present towards the edges –
stress concentration can occur which may
lead to failure.
• All other configurations are developed to
make the electric field more uniform and
hence reduce the stress concentration.
Acoustic Emission Test
 Design Issues: Inactive Area
• Limited Strain is developed at the edge of
the inter-digitated pattern
d 31bulk
d 31eff =
S e te
[1 + ]
St
• Where, d31eff is the effective coupling
constant, S and t are the compliance
modulus and thickness of piezo while the
ones with e-subscript denote that of
electrode.
 Design Issues: Delamination
• Delamination can occur between the
electrodes and the piezo layers due to
binder burn-out, inadequate adhesion
between the electrode and the ceramics
and thermal expansion mismatch during
sintering.
• Solution:
– Control of Organic Binder
– Decreasing the Metal Powder Surface Area
 Design Issues: Effect of
Composition
• Increase in Grain size increases
piezoelectric effect but reduces the
fracture toughness, also increases
hysteresis and dielectric loss
• For electrodes – Ag-Pd alloy or Copper-
Nickel Alloy are better as they have less
thermal mismatch.
Design Issues: Heat Generation
• Heat Generation during operation of such
actuator could be expressed as:
U f vactuator
DT =
k (T ) A

• ΔT – change in temperature, U dielectric

loss per driving cycle per volume fraction, f
– driving frequency, v – actuator volume,
k- conduction coefficient and A – CS area
Further Amplification of Force?
Cymbals
Range of Derivatives of APA
A Comparison of Piezo Actuators
Device Driving Displaceme Force Cost
Voltage nt (µm) (N)
(V)

MLA 100 10 900 High

Bimorph 100 35 1 Low

Rainbow 450 20 3 Medium

Cymbal 100 40 15 Low

Moonie 100 20 3 Medium

Types of Wafer based PZT Devices
 A Comparison
Actual Market Demand: 100 μm displacement, 100 N force, and
100 μs response.

For multilayer: About 100 thin piezoelectric ceramic sheets are

stacked together, has the advantages of low driving voltage (100
V), quick response (10 μs), high generative force (1 kN), and high
electromechanical coupling.
However, the displacement, on the order of 10 μm, is not
sufficient for some applications.

For Benders: large bending displacement of several hundred μm is

possible, but it has relatively low response time (1 ms) and
generative force (1 N)
 Even more for Electrostrictors
Consider a multilayered electrostrictive stack of
length l and number of layers n, which is subjected
to a voltage V.

Neglecting elastic deformation, total displacement

available from a ‘n’ layered electrostrictor will be:

Δ = [ l x d X (V /(l/n))2 ] = (d/l )x V2 x n2

Total displacement is directly proportional to the

number of layers n2 !
 Types of USM Devices based on Drives
• Rigid Displacement Devices
- the strain is induced unidirectionally along the direction of the applied
DC field

• Resonating Displacement Devices

- the alternating strain is excited by an AC field at the mechanical
resonance frequency (USMs).

The Rigid Displacement device can be further divided into two types:
servo displacement transducers (positioners), controlled by a feedback
system through a position-detection signal, and pulse drive motors
operated in a simple on/off switching mode, exemplified by inkjet
printers.
 Material Requirements

• The material requirements for these classes of devices

are somewhat different, and certain compounds will be
better suited to particular applications.
• The USM, for instance, requires a very hard piezoelectric
with a high mechanical quality factor QM, to suppress
heat generation.
• The servo displacement transducer suffers most from
strain hysteresis and, therefore, a PMN electrostrictor is
used for this purpose.
• The pulse drive motor requires a low permittivity material
aimed at quick response with a certain power supply (a
high-power supply is expensive from the practical device
application viewpoint!) rather than a small hysteresis,
hence, soft PZT piezoelectrics are preferred.
 Better Piezoelectric Material
Lead Magnesium Niobate / Lead
Titanate (PMN-PT)

A Piezo and an Electrostrictor [Uchino, 2003]

Perovskite Lead Lanthanum Zirconate Titanate (PLZT) ceramic

is actually Lanthanum doped PZT and typically known as
PLZT (100x/100y/100(1-y)).
Special reference for this lecture
• Micro-mechatronics by Uchino &
Giniewicz, Marcel, Dekker
• Kato, Fine Ceramics Technology
• Pritchard, Bowen, Lowrie; Multilayer
Actuators: A Review, British Ceramic
Transactions, 2001

Acknowledgement: Mr. G. Tripathi of the SMSS Lab for the experiment