DT 2.1 Technical Principles p2

topics 2,3

what are smart materials (next few cards on this)

materials that react to a change in their environment such as temperature, light pressure or electrical input. reactions inc. change in colour, shape or resistance

define electroluminescent (or EL)

materials that provide light when exposed to a current

examples of electroluminescent materials

EL wire (thin copper wire core coated in phosphor powder - produces glowing light when exposed to AC)

EL flexible films or thin panels - light emitting phosphor sandwiched between pair of conductive electrodes and subjected to an AC to create light. brightness depends on voltage

other e.g. are LEDs, OLEDs, phosphorescent materials

Advantages of EL films replacing LCD displays

they are flexible, do not generate heat and are more reliable

define quantum tunnelling composite (QTC)

materials that can change from electrical conductors to insulators when under pressure

what is QTC and how does it work

flexible polymers that contain conductive nickel particles that can be either a conductor or insulator.

nickel particles make contact with each other and are compressed when force applied leading to increase in conductivity.

when force removed, material returns to original state and becomes electrical insulator

what are shape memory alloys (SMA)

SMAs return to original shape if heated

Nitinol is a common one made from titanium and nickel

uses of SMAs

medical applications like medical fastenings used in bone fractures

what is polymorph and how is it made

is a thermoforming polymer supplied in granular form. when heated in water to 62*C it softens and forms pliable volume of material which can be moulded and shaped.

solidifies on cooling and can be modelled and shaped

if reheated in water, becomes pliable again

uses of polymorph

useful for model making and prototyping

define photochromic pigment + e.gs

these change colour in response to light exposure

e.g. sunglasses - change in response to UV radiation

define thermochromic pigment + e.gs

change colour in response to change in heat and can be engineered to specific heat ranges

e.g. baby bottles to give indication of temp of milk

e.g. thermochromic mugs which respond to boiling water and change colour

define micro-encapsulation

tiny microscopic droplets containing various substances applied to fibres, yarns and materials, including paper and card.

protects and controls release of chemicals like vitamins, therapeutic oils, moisturisers, antiseptics, and anti-bacterial chemicals (released through friction)

define biomimicry

taking ideas from and mimicking nature - for inspiration for new materials, structures and systems

e.g. of biomimetic material

Fatskin, developed by Speedo, mimics shark’s sandpaper like skin by reducing drag in water used in performance enhancing swimwear

what are composites

when 2 or more materials are joined together to create a new enhanced material

1 material = the matrix, other = the reinforcement

what is carbon-fibre reinforced polymer (CFRP), how it is made, properties, uses

consists of woven carbon fibre strands encased in a polymer resin

carbon fibre strands = very high tensile strength and the polymer resin is lightweight and rigid

used in sports equipment like tennis rackets where strength to weight ratio is important

what is Kevlar, properties, uses

a lightweight flexible and extremely durable aramid fibre that has excellent resistance to heat, corrosion and damage from chemicals and a high tensile strength to weight ratio

often used in protective clothing like police body armour, where fibre often woven in a lattice that provides protection against knife attacks, bullets etc..

glass reinforced plastic (GRP) how its made, properties, uses

composite of glass fibres and a polyester resin

glass fibres create rigidity and the resin makes GRP tough and lightweight

is difficult to recycle because process of combining fibres and resin = irreversible

used in surfboards, canoes and car bodywork

what are technical textiles

engineered with specific performance characteristics that suit a particular purpose or function

define interactive (or integrated) textiles

fabrics that contain devices or circuits that respond and react with the user

e.g. of this

conductive fibres and threads (made from carbon, silver and steel) can be woven into textile fabrics and made into clothing or conductive threads that can be sewn into a product to connect to a circuit

define microfibres

extremely fine lightweight synthetic fibres, usually polyester or nylon

properties and e.gs of microfibres

excellent strength-to-weight ratio, water-resistance and breathability

used throughout textiles industry from clothing to cleaning cloths

what are phase-changing materials (PCMs) + an e.g.

encapsulated droplets on fibres and materials that change between liquid and solid within a temperature range

absorb energy during the heating process (returning to liquid) and release energy to environment during cooling (returning to solid)

e.g. cold weather clothing - encapsulated into fabric, allow body heat to be stored and then released when needed

what are breathable fabrics (+commonly used one) properties, uses

Gore-Tex consists of 3 or more fabrics laminated together with the breathable hydrophilic membrane in the middle (this is a solid structure that stops water passing though but at the same time can absorb and diffuse fine water vapour molecules)

means sweat and perspiration and permeate out but moisture from rain etc.. cant enter

therefore used in high performance clothing and footwear - helps regulate body temp by maintaining constant temp by allowing flow of air in and out

how is sun-protective clothing made and further enhanced - why does this work

clothes are made from tightly woven or knitted fabrics as this is most effective at blocking out the sun’s harmful UV rays as gaps much smaller preventing rays getting through

elastane fibres used to reduce spaces further making fabrics even more protective

define aramid fibres, Nomex as a n example + properties of Nomex

aramid fibres - non-flammable heat resistant fibre

Nomex is an aramid synthetic fibre primarily used where heat and flames resistance is essential. e.g. firefighters’ uniform and racing car drivers’ clothin

extremely strong and can withstand very extreme conditions

what are geotextiles

woven or bonded, synthetic or natural, permeable fabrics made originally for use with soil with the ability to filter, separate, protect and drain

uses of geotextiles

in civil engineering, road and building construction and maintenance

e.g. control of coastal erosion and drainage; and control of embankments on the sides of roads

what is Rhovyl + properties

non-flammable, synthetic fibre which is crease resistant, has good thermal and acoustic properties, is anti-bacterial and comfortable to wear

uses of Rhovyl

construction of fibre gives fabric ability to wick away moisture like perspiration through fabric.

also dries quickly and does not retain odours making it ideal for socks

what is a system

a set of parts which work together to provide functionality to a product

purpose of electronic systems

to provide functionality to products and processes

what are subsytems

electronic systems can be broken down into these

and can then be classified as inputs, processes and outputs

subsystem - the interconnected parts of a system

what are system/block diagrams + signals

to show how subsystems are connected and signals flow between them

signals = digital or analogue

what can process subsystems be made from

microcontrollers, microprocessors, computers

define microcontroller

a miniaturised computer, programmed to perform a specific task, and embedded in a product

what is an Integrated circuit (IC)

e.g. microcontroller

a miniaturised, highly complex circuit with small pin connections in a single component

some functions programming devices can do + example applications for these

counting - sports scoreboard, digital clock, pedometer

switching - night light, electric kettle, automatic door

timing - security light, burglar alarm, cooking timer

what does a sensor do + name the 2 types

produces an electrical signal which can be analogue or digital

define digital sensor

a sensor that detects yes/no or on/off situations

define analogue sensors

sensor used to measure how big a physical quantity is. e.g. light and temperature

what is an LDR + uses

an analogue sensor used to sense light level

used in streetlamps, night lights, digital clocks (for brightness control), CCTV cameras (to switch to night vision mode)

what is a thermistor + uses

an analogue sensor to sense temperature

used in ovens, room thermostats, electric heaters and car engines

2 types of thermistors

negative temperature coefficient (NTC) type: resistance falls as temp increases

PTC type: resistance increases as temp increases

what does an output subsystem do

converts electrical signals into a desired function

types of output subsystems + uses

buzzers - produce sound outputs. useful for providing feedback that a user has pressed a button.

found in burglar alarms, microwave ovens, dishwashers and kitchen timers

LED produces a light output. available in range of colours, sizes, shapes

used as an indicator (i.e. as a ‘power on’ light in a product), or as a source of illumination e.g. torch

resistor must be used with an LED to limit current flow or LED will burn out

define feedback + why

achieving precise control by feeding information from an output back into the input of a control subsystem

allows a microcontroller to monitor the effect of the changes it makes to its output devices in order to achieve precise control over a system

an e.g. of feedback

why is reprogramming microcontrollers useful

allows for updates, improvements and adjustments to the operation of devices without needing to replace hardware

enhances functionality and can adapt to new requirements

egs of products including microcontrollers

toasters, TVs, microwave ovens, hi-fi systems and cars

what is a Programmable interface controller (PIC)

a microcontroller used in many products - due to ease of use

define program (in terms of microcontroller)

a set of instructions which tells the microcontroller what to do

define subroutines(or macros)

a small sub-program within a larger program