Smart Materials

[seminar class]

presented by:
John Summerscales

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Smart materials
“smart responds to a stimulus with one predictable action”
l normal materials have limited responses
l smart materials have appropriate responses
l ... but response is the same every time
Smart materials
l smart materials have appropriate responses
 photochromic glass
• darkens in bright light
 low melting point wax in a fire sprinkler
• blocks the nozzle until it gets hot
 acoustic emission
• sounds emitted under high stress
 embedded optical fibres
• broken ends reflect light back
 microporous breathable fabrics
l Waterproof clothing
l Goretex®
l micro-porous expanded PTFE
discovered in 1969 by Bob Gore
l ~ 14 x 1012 micropores per m².
l each pore is about 700x larger than
a water vapour molecule
l water drop is 20,000x larger than a pore
Goretex:
Intelligent structures (IS)
“intelligent responds to a stimulus with a calculated response and different possible actions”
l composites made at low temp
l \ can embed additional components
l control can decide on novel response
Intelligent structures (IS)
l embed three elements of the system:
l sensors
signal processing and control
l actuators
l Sensors
l strain gauges
l microdieletric interdigitated sensors
l optical fibres
l piezoelectric crystals
l shape memory alloys
l electro-rheological fluids
l giant magnetoimpedance (GMI) wires
Signal processing
l issues with data fusion for large sensor arrays
Control
l proportional integral derivative (PID)
 proportional:
output = (gain x error) + bias
 integral:
output = gain x (error + ∫error w.r.t. time)
 derivative:
output = gain x derivative x de/dt
l advanced systems ...
Advanced control
l proportional integral derivative (PID)
l fuzzy logic control (FLC)
 sliding mode control
l artificial neural networks (ANN)
l genetic algorithms (GA)
l knowledge-based systems/
artificial intelligence/expert systems
Actuators
l hydraulic, pneumatic and electric
l piezoelectric crystals
 shape changes when voltage applied
l shape memory materials
 shape changes at a specific temperature
 alloys = SMA .... polymers = SMP
l magneto-rheological (MR) fluids
 viscosity changes with magnetic field
l electro-rheological (ER) fluids
Magneto-rheological (MR) fluids
Electro-rheological (ER) fluids
Intelligent Structures: applications
l artificial hand
 SMA fingers controlled by
nerve (myoelectric) signals
l vibration damping
 apply electric field to ER fluid
l skyscraper windows
 acoustic emission warning system
Biomimetics
l a.k.a bionics, biognosis
l the concept of taking ideas from nature to implement in another technology
 Chinese silk cultivation begins c.4000BC
• Colin Thubron, Shadow of the Silk Road, Chatto & Windus, 2006.
 Daedalus' wings - early design failures
l gathering momentum due to the
ever increasing need for
sympathetic technology
Biomimetics
l “inspiration rather than imitation”
Janine Benyus.
l “design inspired by nature”
BioNIS thematic network
Biomimetics
l Notable innovations from understanding nature
 Velcro
 Gecko tape
 Lotus effect self-cleaning surfaces
 Drag reduction by shark skin
 Platelet TechnologyTM for pipe repair
 Smart-fabric
 ElekTex™
Biomimetics
l Velcro
 small hooks enable seed-bearing burr
to cling to tiny loops in fabric
Gecko tape
l Inspiration from the remarkable hairs that allow geckos to hang single-toed from sheer walls and walk along ceilings
l researchers at the University of California - Berkeley, created an array of synthetic micro-fibres that uses very high friction
to support loads on smooth surfaces.
l Biomimetics: Lotus effect
l most efficient self-cleaning plant
= great sacred lotus
(Nelumbo nucifera)
l mimicked in paints and
other surface coatings
l pipe cleaning in oil refineries (Norway)
Biomimetics
l Lotus effect self-cleaning surfaces
l surface of leaf water droplet on leaf
l Image from http://library.thinkquest27468/e/lotus.htm
l drag reduction by shark skin
 special alignment and grooved structure
of tooth-like scales embedded in shark skin
decrease drag and thus
greatly increase swimming proficiency
 Airbus fuel consumption down 1½%
when “shark skin” coating applied to aircraft
Platelet TechnologyTM
l Brinker Technology Platelet TechnologyTM
l discrete particles released into pressurised pipe flow
l when particles encounter modified flow at a leak, fluid forces entrain them into the leak and hold them against the pipe wall
l seals and marks the position of the leak for subsequent detection.
l brinker-technology.com animation and video links now dead L
Smart-fabric
l pine-cone model
l adapts to changing temperatures
by opening when warm or shutting tight if cold
ElekTex™
l looks and feels like a fabric
l capable of electronic x-y-z sensing
l fold it, scrunch it or wrap it
l lightweight, durable, flexible
l cost competitive
l cloth keyboards and keypads