Smart Wind Turbine Blades
Sensor Team
Cassel, Fraser, Larsen,
McCrummen, Sarrazin
ME 580 – Smart Structures

ME 580 – Smart Wind Turbine Blades – Sensor Team
Objective:
• Gather and support development for sensors in wind turbine blades.
• Investigate multiple types of sensors to allow for monitoring or measuring:
– Structural Loads
– Tip Deflection
– Damage
– Environmental Aspects

ME 580 – Smart Wind Turbine Blades – Sensor Team
• Current Data and
Usage

ME 580 – Smart Wind Turbine Blades – Sensor Team
What to Sense
Strain
Displacement
Vibration
Temperature
Pressure
Impact
Acceleration
Ultrasonic
Humidity/Moisture
Why to Sense
Composite failure
Monitor blade stress
Tip deflection
Vibration absorption
Temperature effects on materials
Wind pressure
Air flow
Natural wind frequencies/gusts
Hail/Rain intensity
Natural wind frequencies/gusts
Wind loading vs. energy generation
Non-destructive for delamination
Prevention of system degradation
Strain Gage Piezoresistive Piezoelectric Optical
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ME 580 – Smart Wind Turbine Blades – Sensor Team
Piezoelectric Sensing
• 4 Types
– Single Crystal
• Original
– Ceramic
• Similar to single crystal
– Polymer (PVDF)
• Flexible, poor for actuation
– Active Fiber Composite
(AFC)
• Subset of Ceramic
• Flexible
• Compromise

ME 580 – Smart Wind Turbine Blades – Sensor Team
Piezoelectric Sensors
• Wide frequency range
• High voltage output (particularly
PVDF)
– No power supply needed
• PVDF has low acoustic impedance, good for adhesives
• High compliance in PVDF
• Flexible, thin, easily manipulated

ME 580 – Smart Wind Turbine Blades – Sensor Team
Piezoelectric Sensor
• Drawbacks/Considerations
– Temperature range for PVDF: -40 to 80/100 °C (Not as bad for PZT)
– Strong pyroelectric effect
– Inability to actuate large displacements
– Inability to sense static load
– Capacitive effect of unloaded area
– Crosstalk if both driving signal and sensing

ME 580 – Smart Wind Turbine Blades – Sensor Team
Piezoelectric AFC
• Ceramic-Polymer composite
• Advantages: can custom design properties
– Tradeoffs
– Properties determined by:
• Ceramic type
• Polymer Properties
• Volume fraction

ME 580 – Smart Wind Turbine Blades – Sensor Team
Impact Sensing
• Weather Detection
– Active control
– Damage prevention
• Wind Gust Detection
– Active control
• PVDF appropriate if surface mounted
– Thin
– Sensitive

ME 580 – Smart Wind Turbine Blades – Sensor Team
Vibration Sensing
• Vibration hurts performance/strength
– Active control
• Most sensors can detect
• Primary considerations: Wide frequency range, Cost
• PVDF good for surface mount

ME 580 – Smart Wind Turbine Blades – Sensor Team
Ultrasonic/NDT
• Piezoelectric typically used.
• PVDF good if done during operation
• 1/64th in. smallest size
• Depth small for small flaw

ME 580 – Smart Wind Turbine Blades – Sensor Team
Metal Foil Gauges
• Uses wire resistance change to compute strain
• Most commonly used gauge in engineering
• Can use strain to compute stress, torque, and pressure

ME 580 – Smart Wind Turbine Blades – Sensor Team
Metal Foil Gauges Advantages
• Strain and Pressure gages
• Widely available
• Cheap
• Easy to apply
• Easy to use

ME 580 – Smart Wind Turbine Blades – Sensor Team
Metal Foil Gauges Disadvantages
• Must be properly bonded
• Sensitive to temperature changes
• Maximum strain limited to foil material used (3%)
• Size limitations
• Can change resistance over time
(creep)
• Susceptible to fatigue

ME 580 – Smart Wind Turbine Blades – Sensor Team
Piezo-resistive Sensing – Basic Structure http://www.microsystems.metu.edu.tr/piezops/piezops.html

ME 580 – Smart Wind Turbine Blades – Sensor Team
Piezo-resistive Sensing – Background
• Types of measurement
– Pressure
– Force
• Higher sensitivity than standard strain gage
• Pressure Sensor Calibration
• Able to be microfabricated http://www.ceatec.com/2007/en/visitor/ex_must_detail.html?exh_id=E070209 http://cooperinst.thomasnet.com/Asset/lpm562.pdf

ME 580 – Smart Wind Turbine Blades – Sensor Team
Piezo-resistive Sensing – Pros and Cons
• Pros
– Low fabrication cost
– Varying pressure levels can be achieved
– High sensitivity (>10mV/V)
– Good data linearity at constant temp.
• Cons
– Requires significant amount of power
– Low output signal
– Strong drift of offset with temperature

ME 580 – Smart Wind Turbine Blades – Sensor Team
Piezo-resistive Sensing – Conclusion
• Not Recommended
– Ideal placement is blade exterior
• Temperature change affects data collection
• Possible weather damage to sensor
– Required, potentially bulky equipment
• Power source
• Data collection device / Wireless emitter
– Uses
• Only designed for pressure and force data collection
– Recommendation
• Use a sensor that is more versatile

ME 580 – Smart Wind Turbine Blades – Sensor Team
Fiber Optic Sensors

ME 580 – Smart Wind Turbine Blades – Sensor Team
Fiber Optics

ME 580 – Smart Wind Turbine Blades – Sensor Team
Types of Cores
• Glass Cores • Plastic Cores

ME 580 – Smart Wind Turbine Blades – Sensor Team
Total Internal Reflection
• Cladding material less dense than core material.
• The critical angle is less than the angle of incidence for the core and cladding combination.

ME 580 – Smart Wind Turbine Blades – Sensor Team
Fiber Optic Sensor Pros
• Essentially passive
• Immune to Electrical
Interference
• Low Weight
• Flexibility
• Long Transmission
Distances
• Low Material
Reactivity
• Electrical Insulation
• Electromagnetic
Immunity
• Multiple Sensor
Multiplexing
• Multi-Functionality
• Good in Harsh
Environments
• Capable of Fitting in
Small Areas

ME 580 – Smart Wind Turbine Blades – Sensor Team
Fiber Optic Sensor Cons
• Expensive
– Need:
– Fiber optic cable
– Polarized light emitter
– Interrogator Unit/Receiver
• Newer Technology
• Not time tested
• Limited Availability
• Few suppliers

ME 580 – Smart Wind Turbine Blades – Sensor Team
Sensing Capabilities
• Strain
• Displacement
• Vibration
• Temperature
• Leak Detection
• Pressure

ME 580 – Smart Wind Turbine Blades – Sensor Team
Sensing Capabilities

ME 580 – Smart Wind Turbine Blades – Sensor Team
FBG Working Principle
• Sensors created by Fiber Bragg Grating
– An intense UV source “inscribes” a periodic variation of refractive index into the core of an optical fiber. A special germanium-doped silica fiber is used due to its photosensitivity.
– Variations in the fiber change the reflected and transmitted response within the optical fiber. The fiber responds to strain and temperature initially, and different orientations allow for multiple sensing options.

ME 580 – Smart Wind Turbine Blades – Sensor Team
Fiber Bragg Grating

ME 580 – Smart Wind Turbine Blades – Sensor Team
Strain Measurement

ME 580 – Smart Wind Turbine Blades – Sensor Team
Bragg Grating Configurations

ME 580 – Smart Wind Turbine Blades – Sensor Team
Types of Configurations

ME 580 – Smart Wind Turbine Blades – Sensor Team
Sensor Multiplexing Multiple
Functions

ME 580 – Smart Wind Turbine Blades – Sensor Team
Data Collection and Utilization
• Data Collection Options
– Slip Ring
– Brushless Slip Ring
– Rolling Ring
– Liquid Filled Slip Ring
– Wireless

ME 580 – Smart Wind Turbine Blades – Sensor Team
Data Collection
• Brushless Slip Ring
– Continuous Data Collection Ability
– Improved lifespan
• Rolling Contacts reduce friction, reduce wear
– Minimizes wire tanglage
– HoneyBee Robotics

ME 580 – Smart Wind Turbine Blades – Sensor Team
Recommendations
Test sleeve made from combination of PVDF film and fiber optic sensors.
• PVDF film senses wind loading.
• Fiber Optic Sensors acquire resulting strains/stresses on blade.

ME 580 – Smart Wind Turbine Blades – Sensor Team
Recommendations
• Lab testing
– Cantilever beam distributed load
• Include tension and compression
– Consider bank of hydraulic actuators applying load conditions, and perhaps even a cam system to apply concurrent vibration

ME 580 – Smart Wind Turbine Blades – Sensor Team
Questions?