1. Vibration Actuators and Sensors Professor Mike Brennan Institute of Sound and Vibration Research University of Southampton, UK

2. Active Vibration Control
WHY ?
Structures become lighter
Space and weight constraints
Actuators
Sensors
Controlled
Structure
Controller

3. Vibration actuators and sensors
Piezoelectric
Magnetostrictive
Electrodynamic
Hydraulic
Sensors
Piezoelectric
Controllability/Observability
Shaped actuators/sensors (spatial filtering)
Applications

4. Piezoelectric actuators and sensors
Piezoelectric effect
(sensor)
An electric field is generated
due to a change in dimensions
of a material
(Curie brothers 1880) + -
Converse Piezoelectric effect
(actuator)
A change in dimensions of
a material due to the
Application of an electric field

5. Polarisation of a piezoelectric material
Subject a piezoelectric material to a large voltage near the Curie temperature
then the dipoles align
dipole
Curie temperature is the temperature above which the material loses its piezoelectric property

6. Piezoelectric actuators and sensors
Property
PZT (PC5H) type VI
PVDF
Curie temperature (°C)
Longitudinal Young’s modulus (Nm-2)
Piezoelectric constant – d31 (mV-1)
Max E-field (Vm-1)
Piezoceramic (PZT)
Relatively stiff
Large piezoelectric constant
Piezopolymer (PVDF)
Relatively flexible
Large voltage capacity

7. Direct piezoelectric effect (sensor) (element in free-space)+ -

8. Indirect piezoelectric effect (actuator) (element in free-space)+ - + -
Poling axis

9. Conventional use of piezoelectric material in transducers
Used in accelerometers and force transducers. Generates an electrical
charge proportional to strain
Typical materials are polycystalline materials, e.g. barium titanate and
lead zirconate
Modes of deformation
ceramic + -
compression
shear
elongation q
piezoelectric
capacitance
Equivalent electrical circuit
Charge devices have a low capacitance
(high impedance) and hence require
pre-amp with a very high impedance

10. Practical Accelerometer Designs
Compression Type
Advantages
Few Parts / Easy to Fabricate
High Resonant Frequency
Disadvantages
Very high thermal transient
sensitivity
High base strain sensitivity

11. Practical Accelerometer Designs
Bending Type
Advantages
Few Parts
Small Size and Low Profile
Low Base Strain Sensitivity
Low Thermal Transient Sensitivity
Disadvantages
Low Resonant Frequency

12. Practical Accelerometer Designs
Shear Type
Advantages
Low Thermal Transient Sensitivity
Very Low Base Strain Sensitivity
Small Size
Disadvantages
???

13. Force Transducer Principle of Operation
The stress is related to the applied force by
and the stress is related to the strain by
Force, F
Material of
cross-sectional area A
and Young’s modulus E
Therefore the strain is related to the force by
As the electrical output is proportional to the strain, and the strain is
proportional to the applied force, then the electrical output is proportional
To the applied force

14. Piezoelectric Force Transducer
Preload stud
Electrical output
Piezoelectric element
Can be used in tension and compression
Fragile to moments

15. One-dimensional piezoelectric equations+
Piezoelectric
material of
thickness t
Conductive
electrodes -
The piezoelectric equations are
mechanical
electrical

16. Piezoelectric elements as strain sensors
The piezoelectric equations are 3 1 V C
Voltage generator C q
Charge generator

17. Flexural (bending) vibration sensorw b x
which evaluates to
If a flexural wavelength is much greater than l, then

18. Longitudinal vibration sensor
which evaluates to
If a longitudinal wavelength is much greater than l, then

19. 2-dimensional sensor 3 2 PVDF sensor 1 plate
Recall for the one-dimensional case (for no applied field)
For the two-dimensional case
Thus the electrical output is proportional to both S1 and S2

20. Strain or Strain-rate measurementC - + V
Piezoelectric sensor connected to a charge amplifier measures “strain” + - R V
Piezoelectric sensor connected to a current amplifier measures “strain rate”

21. Piezoelectric actuators
Single element
Stack
Connected electrically in parallel and
mechanically in series

22. Coupling an Actuator to a structure
The piezoelectric equation is

23. Coupling an Actuator to a structure
displacement
force
Increasing voltage
Max power transfer

24. Flat piezoelectric actuators
High displacement – Low force actuators

25. Some piezoelectric actuator configurations
Stacks
Fans
Curved actuators
Bimorphs (benders)

26. Amplified piezoelectric actuators

27. PZT actuators for beam vibration
actuators driven out-of-phase – bending vibration induced
PZT element
beam
PZT element
actuators driven in-phase – longitudinal vibration induced
PZT element
beam
PZT element

28. PZT actuators for beam vibration
actuators driven out-of-phase – bending vibration induced
PZT element
beam
PZT element M M
Ratio of
thicknesses
stiffnesses
Free strain

29. PZT actuators for beam vibration
actuators driven in-phase – longitudinal vibration induced
PZT element F
beam F
PZT element
Ratio of
stiffnesses
Free strain

30. Piezoceramic Elements
The two piezoelectric elements can be excited:
in phase to generate longitudinal vibration
out-of-phase to generate flexural vibration F F

31. Piezoceramic Elements
FLEXURAL VIBRATION
LONGITUDINAL VIBRATION
Works best at high frequencies when the length of the actuator is equal to half a wavelength

32. Excitation of a plate
PZT patch
plate

33. Controllability and Observability
Example - beam A
A sensor positioned at point A will observe modes 1 and 2 but not mode 3
An actuator positioned at point A can control modes 1 and 2 but not mode 3
Mode 1
Mode 2
Mode 3

34. Shaped piezoelectric film bonded to a beam structure
Cantilever
Mode 1
Mode 2
Simply supported

35. Modal filters

36. Modal filters experimental results
Point accelerance

37. Modal filters experimental results
Mode 1 filter
Mode 2 filter

38. Shunted Piezoelectric Absorber

39. The Smart Ski (ACX.com)

40. The Smart Ski (ACX.com)
Piezo patches

41. The Smart Bat (ACX.com) Fundamental bending mode (215 Hz)
                                          Second bending mode (670 Hz)                                           Third bending mode (1252 Hz)                                                                                
Fundamental bending mode (215 Hz)

42. The Smart Bat (ACX.com)

43. Electro / Magneto -Rheological Fluids
What are they ?
• micron sized, polarizable particles in oil
What do they do?
• Newtonian in absence of applied field
• develop yield strength when field applied
ER fluids respond to electric field
MR fluids respond to magnetic field

44. Magneto-Rheological Fluids - Applications
Ride Mode Switch
MR Fluid Damper
Sensor/Controller

45. Magneto-Rheological Fluids - Applications
Single Degree of Freedom System -
Heavy Duty Vehicle Suspended Seats
• off-highway, construction and agricultural vehicles
Acceptable motion transmitted
• class 8 trucks ("eighteen wheelers")
• buses
Sensor
Seat
Controller
Controllable shock absorber
Spring
Off-state
Random
pattern
On-State
Ordered
pattern
Road input

46. Change in Stiffness – shape memory alloys
Memory metal is a nickel-titanium alloy
This piece has been formed into the letters ICE, heat-treated, and cooled.
When the memory metal is pulled apart, it deforms. When placed into hot water, the metal "remembers" its original shape, and again forms the letters ICE.

47. Change in Stiffness – shape memory alloys
Soft
Stiff
Stiffness increases
With temperature

48. Change in Stiffness – shape memory alloys
Material whose Young’s modulus changes with temperature
Composite panel }
Embedded SMA wires
Activating the fibres (by passing a current through them and hence
causing a temperature change) causes local stiffening and hence the
natural frequencies can be shifted to avoid troublesome
excitation frequencies.

49. Active Control of Helicopter Vibrations/Structure-Borne Sound
Active control of rotor
vibrations at about 18 Hz
Active control of gearbox
noise at about 500 Hz

50. Active Control of Structural Response (Westlands, 1989)
Application of ACSR to the Westland/Agusta EH101 Helicopter.

51. Active Control of Rotor Vibration
Hydraulic actuators
Active control at rotor blade
passing frequency at
about 18 Hz + harmonics
Feedforward control
fuselage

52. ACSR - Actuator Installation for Production EH101• sa
Steel downtube
Composite
Compliant
Element
Titanium
Lug End
ACSR Actuator
Hydraulic Supply
Main Gearbox
Installation
Support Strut/ACSR Actuator
Assembly
Fwd

53. Magnetostrictive actuators
polepiece
Terfenol-D
Solenoid
coil
Ter – Terbium
Fe – Iron
Nol – Naval Ordinance Lab
D – Dysprosium
magnet
Needs to be pre-stressed
for good operation
Low voltages required
Similar performance to PZT
polepiece
Terfenol-D rod

54. Active Control of Gearbox Noise
Active control at gear meshing frequency
at about 500 Hz + harmonics
rotor
Feedforward control
magnetostrictive
actuators
fuselage

55. Active Control of Gearbox Noise
Without control
Real-time control
With control
Kinetic energy of receiving block
measured using 6 accelerometers

56. Active Control of Aircraft Noise
Original Equipment- 4 Tuned Vibration Absorbers per engine
Actuators 2 per engine

57. Active Control of Aircraft Noise (Lord Corporation)
Controller 1 in cargo bay 12”x8”x3.5” 5 lbs
Amplifier 1 in cargo bay 11”x18”x3.5” 17 lbs
Actuators 4 2 on each yoke 4.5”diax5” 15 lbs
Microphones 8 behind trim incorporated into actuator harness
Wire Harness from cockpit, overhead through cabin, to pylon 22 lbs

58. Active Control of Aircraft Noise
Attenuation is up to 8dBC
NVX™
OFF
SPL
(dBC)
NVX™ ON

59. Active Control of Aircraft Noise
NVX Systems reduce noise by reducing vibration
Data measured on pylon

60. Active magnetic bearings (SKF)
sensors
bearing
controller

61. Active Vibration isolation demonstration

62. Active Vibration isolation demonstration

63. Concluding Remarks Hydraulic Piezoelectric (PZT) Electrodynamic
Actuators and Sensors are required for all Active Control Systems:
Actuators used
Hydraulic
Piezoelectric (PZT)
Electrodynamic
Magnetostrictive
Sensors used
Accelerometers
Force gauges
PVDF
PZT

64. References
C.R. FULLER, S.J. ELLIOTT and P.A. NELSON Active Control of Vibration. Academic Press
P.A. NELSON and S.J. ELLIOTT Active Control of Sound. Academic Press
C.H. HANSEN and S.D. SNYDER Active Control of Noise and Vibration. E & F.N. Spon
R.L. CLARK, W.R. SAUNDERS and G.P. GIBBS Adaptive Structures. Wiley Interscience
A.V. SRINIVASAN and D. MICHAEL McFARLAND Smart Structures. Cambridge University Press