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SHAPE MEMORY ALLOY -CHARACTERISTICS -PROPERTIES OF Ni-Ti ALLOY -APPLICATION OF MEMSTEAM MEMBERS13U252 -SUGUNESH V.P13U253 -SURIYA M13U254 -SWATHEE P.T13U255 -TAMILKUMARAN T.K13U256 -VAISHNAVI K.V13U257 -VARSHA ANAND13U258 -VISHNUPRIYAN Small memory alloys (sma)Have ability to return to a predefined shape when heatedsma- below its transition temperature has very low yeild and can be deformed into any shape which it will retainWhen heated above transition temperature changes crystal structure and returns to its original shape Thermal stability, practicability, supirior thermo mechanic performance Smas:- NiTi, Cu-Al-Ni , Ni-Mn-Ga,.Most of the sma 10C change in temperature initiates phase changePhase change: 1. Martensite soft and easily deformed phase of sma , occurs at low temperatureMolecular phase : twinned2.Austenite stronger sma,occurs at high temperatures

Ni-Ti ALLOYSBinary equiatomic compound of Ni-Ti alloy.They have more thermal stability,high ductility,better bio-compatibility. Heat treatment affects the the properties of Ni-Ti alloys. Density is 6.5 g/cm3 . Melting temperature in the range 1240 to 1310C. The transformation temperature can be modified from less than 100C to over 100C.

APPLICATIONS MEDICAL APPLICATIONS: -Microsurgical instruments. -As dental arch wires. -Repairing of bones.INDUSTRIAL APPLICATIONS: - As a valve in medical instruments and mass flow controllers. -As pipe connectors. Two way memory effect

Alloy remembers 2 shapes- low and high temperature (heating and cooling).Due to training-shape memory can learn to behave in a certain way.It is trained to remember to leave some reminders of the low temp condition in the high temp phases.Trained material heated to a very extent (amnesia).

One way memory effect Alloy is in cold state(below As).Can be deformed and will hold the shape till transition temperature.Upon heating, it regains its original shape.When it cools,it remains in its hot shape until its deformed again.Cooling does not produce macro change.Deformation is necessary to create low temperature shape.

Thermal stability, practicability, supirior thermo mechanic performance Smas:- NiTi, Cu-Al-Ni , Ni-Mn-Ga,.Most of the sma 10C change in temperature initiates phase changePhase change: 1. Martensite soft and easily deformed phase of sma , occurs at low temperatureMolecular phase : twinned2.Austenite stronger sma,occurs at high temperatures

Psuedo-elasticityFrames of reading glasses-undergo large deformations in their high temperature state and revert back when stress is removed-psuedo elasticity.The martensitic phase is generated by stressing the material in austenitic phase.Martensite phase is capable of large strains.With the removal of load, martensite reverts to austenite phase and material gains its original form.Nearly undestructible- no permanent deformation.Characteristics of smasShape memory effectPseudo elasticityShape memory effect:-Observed when the temperature of a piece of sma is cooled below Mf.This stage- completely martensite (easily deformed).After deformation, heating above Af reverts the material to its original shape.The heat transferred is the power driving the molecular rearrangement .Now, the martensite is converted to cubic austenite phase.

HysteresisThe difference between the transition temperatures upon heating and cooling That is:-Temperature at which material is 50% transformed to austenite upon heating.50% transformed to martensite upon cooling.This difference is about 20-30 c.

CONSUMER PRODUCTS: -Eye glass frame -Golf equipment in golf clubs -To produce working toys -used in safety instrument products. AUOTOMOTIVE APPLICATIONS: -As a thermostat , to open and close the valve for the water to flow through the cooling system. - As a sealing plugs for high temperature. ADVANTAGES:High power/weight ratio Noiseless and silent trainingHigh corrosion resistanceCan be controlled with electrical currentLIMITATIONS:Difficult to weldRelease of Ni acts as allergen and also a possible carcinogen.APPLICATIONS OF MEMS

APPLICATIONS OF MEMS INSENSORSMICROGRIPPERSOPTICAL APPLICATIONSBIOMEDICAL

SENSORSMEMS SensorsSensors are a major application for MEMS devices.Three primary MEMS sensorspressure sensorsinertial sensors (accelerometers, gyroscopes)MEMS sensors can be used in combinations with other sensors for multisensingapplications. For example, a MEMS can be designed with sensors to measure the flow rate of a liquid sample and at the same time identify any contaminates within the sample.

MEMS Pressure Sensor:MEMS pressure sensors use a flexible diaphragm as the sensing device. One side of the diaphragm is exposed to a sealed, reference pressure and the other side is open to external pressure. The diaphragm moves with a change in the external pressure.

MEMS Inertial Sensors :Newton's First Law of Motion (also referred to as the law of inertia) states, "An object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force.MEMS inertial sensors are designed to sense a change in an object's inertia, and then convert, or transduceinertial force into a measurable signal. They measure changes in acceleration, vibration, orientation and inclination. This is done through the use of micro-sized devices called accelerometers and gyroscopes. MEMS Accelerometers:The simplest MEMS accelerometer sensor is an inertial mass suspended by springs. The mass is deflected from its nominal position as a result of acceleration. This deflection of the mass is converted to an electrical signal as the sensor's output MEMS Gyroscopes: A gyroscope is generally a spinning wheel or disk with a free axis allowing it to take any orientation (below left). Some MEMS gyroscopes use a vibrating structure rather than the traditional rotating disk to determine orientation (see bottom right) MEMS in the Automotive Industry:MEMS pressure sensors sense, monitor and transmitTire pressureFuel pressureOil pressureAir flowAbsolute air pressure within the intake manifold of the engine 2.MICRO GRIPPERS:

Grippers or tweezers used in a variety of fields to clasp, pick up, and move micron to nanosizecomponents. The microgrippers(50 microns thick), developed by ZyvexCorporation, pick and place other microdevicesin an automated microassemblyprocess. The gripper on the left opens to 100 microns. The gripper on the right opens to 125 micronsMEMS Microgrippers3.OPTICAL APPLICATIONSThe objective for optical MEMS is to integrate optical, mechanical and electronic functions into one device. Optical MEMS have already been quite successful in display technologies. Two commercial devices Digital Mirror Devices and Grating Light Valve -redirect light to create high definition imaging from digital signals. Both of these devices are used in video projection systems such as rear and front projection televisions.Texas Instrument's Digital Mirror Devices (DMD) have been used for several years in a variety of projection systems including video projection and digital cinema. The technology is called digital light processing or DLPTM, a trademark owned by Texas Instruments, Inc.TIs DLP (digital light processing) System:A DMD is an array of micromirrors (left figure). Each micromirror (between 5um and 20um square) is designed to tilt into (ON) or away from (OFF) the light source. The mirror tilts when a digital signal energizes an electrode beneath the mirror. One mirror can be turned OFF and ON as many as 30,000 times per second. There are thousands of mirrors in an array with less than 1 mspacing between them. The DLP 1080p technology delivers more than 2 million pixels for true 1920x1080p resolution.The diagram on the right illustrates how the DLP system works

CROSSSECTION OF GLV FABRICATIONThe Grating Light Valve (GLV): The GLV device developed by Silicon Light Machines, is another micro optical based system. This microdevice consists of several silicon nitride ribbons coated with aluminum. A set of four ribbons (two fixed and two moveable) produce a 20 msquare pixel. The ribbons are held "up" by the tensile strength of the material (silicon nitride and aluminum). The moveable ribbons are "moved" up and down electrostatically. Electrodes are placed under the moveable ribbons. Variable voltages applied to the electrodes pull the ribbons down. When no voltage is applied, the tensile strength of the ribbon will allow it to snap back.GLVs are used in high definition TVs and are being investigated for use in masklessphotolithography.

MEMS ARE WIDELY USED IN VARIOUS DEPARTMENTS OF . MEDICALFIELDCell manipulation

Stomal cell interactions

Micro needles

Pressure sensor

Cardiology

Insulin micropumps

Endoscopic pillsClinical Laboratory Testing:The picture to the right shows a lab-on-a-chip (LOC). This device literally takes the laboratory testing of biomolecular samples (e.g. blood, urine, sweat, sputum) out of the typical medical lab and places it in the field and even at home. Using microfluidics and chemical sensors, this MEMS or bioMEMS can simultaneously identify multiples analytes (substances being analyzed). An example of a home LOC is the home pregnancy test. This bioMEMS uses a reactive coating that identifies a specific protein found in the urine of pregnant women.

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