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22-02-2009, 01:46 AM
1. Introduction
The advent of integrated circuits, which became possible because of the tremendous progress in semiconductor technology, resulted in the low cost microprocessor. Thus if it is possible to design a low cost sensor which is silicon based then the overall cost of the control system can be reduced .We can have integrated sensors which has electronics and the transduction element together on one silicon chip. This complete system can be called as system-on-chip .The main aim of integrating the electronics and the sensor is to make an intelligent sensor, which can be called as smart sensor. Smart sensors then have the ability to make some decision. Physically a smart sensor consists of transduction element, signal conditioning electronic and controller/processor that support some intelligence in a single package. In this report the usefulness of silicon technology as a smart sensor, physical phenomena of conversion to electrical output using silicon sensors, characteristics of smart sensors. A general architecture of smart sensor is presented.
2. Definition
Smart sensors are sensors with integrated electronics that can perform one or more of the following function logic functions, two-way communication, make decisions.
3. Usefulness of Silicon Technology in Smart Sensor
There are very convincing advantages of using silicon technology in the construction of smart sensor. All integrated circuits employ silicon technology. A smart sensor is made with the same technology as integrated circuits. A smart sensor utilizes the transduction properties of one class of materials and electronic
properties of silicon (GaAs). A transduction element either includes thin metal films, zinc oxide and polymeric films. Integrating electronics circuits on the sensor chip makes it possible to have single chip solution. Integrated sensors provide significant advantages in terms of overall size and the ability to use small signals from the transduction element. The IC industry will get involved in smart sensor if a very large market can be captured and the production of smart sensor does not require non-standard processing steps.
3.1 Signal conversion effects
We know that silicon shows a suitable physical signal conversion effect. Many of the physical effects of silicon can be used in making sensors. Based on these effects, different types of sensors can be constructed which can be used for measuring different physical and chemical measurand.
Table1 below shows how different non electrical signal in which we can classify different measurand and Table 2 shows the physical effects for sensors in silicon.
One problem with silicon is that its sensitivities to strain, light and magnetic field show a large crosssensitivity to temperature. When it is not possible to have silicon with proper effect, it is possible to deposit layers of materials with desired sensitivity on the top of a silicon substrate. Thus we can have a magnetic field sensor by depositing Ni-Fe layer on the top of a silicon substrate.
3.2 Different Silicon Sensors Employing Above Effects
Radiant Signal Domain
Silicon can be used to construct a sensor for sensing wide range of radiant signal from gamma rays to infrared. Silicon can be used for the fabrication of photoconductors, photodiode, and phototransistor or to detect nuclear radiation.
Mechanical Signal Domain
Silicon can be used for measuring force and pressure because of the piezo resistance effect. This effect is large because the average mobility of electrons and holes in silicon is strongly affected by the application of strain. Silicon can also be used for the measurement of air or gas velocities. If we slightly heat a silicon structure having two temperature measuring devices, and is brought into airflow then the resulting a temperature difference is proportional to the square root of the flow velocity. Combining a piezo resistor, diffused in a cantilevered beam or a piezoelectric layer with silicon can make a miniature accelerometer. By photoelectric principle one can find angular position by employing two photodiodes (i.e. one for X co-ordinate and other for Y).
Thermal Signal Domain
We know that all electron devices in silicon show temperature dependence, this property of silicon can be used for the measurement of temperature. This can be achieved by using two bipolar transistors with a constant ratio of emitter current. Another way of measuring temperature is to integrate thermocouples consisting of evaporated aluminium films and diffused p-type and n-type layers. This is possible because Seebeck in silicon is very large.
Magnetic Signal Domain
Silicon is a non “magnetic material but it can be used for the construction of Hall plates and transistor structures that are sensitive to magnetic fields. These sensors are constructed by depositing a thin magnetic Ni-Fe film on top of silicon chip that also contains electronic circuits.
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[attachment=10834]
SMART MATERIALS AND SENSORS
ABSTRACT
Now days, smart materials have found an important place in the modern engineering applications. Smart materials or intelligent materials system include integration of sensors, actuators and control with a material or structural component possesses intelligent and life features .The development of smart material is inspired by the biological structure systems and their basic characteristics of functionality, efficiency, precision, self - repair and durability. Smart materials are not only singular materials but also Hybrid composites or integrated systems of materials.
Shape Memory Alloys are one of the major categories of smart materials which after being strained at certain temperature revert back to the original shape because of unique properties such as Shape Memory effect, Pseudo elasticity and high damping capacity. These properties in smart hybrid composites provide them the tremendous potential for creating new paradigms for material-structural interactions and demonstrate various successes in engineering applications like Aeronautical engineering, in medical fields like Vascular stents and Osteosynthesis etc., and in commercial fields also.
The main advantages of shape memory alloys are, they are Bio-compatible, strong and good corrosion resistant. They generally have high power to weight ratio and can withstand large amount of recoverable strain and when heated above transition temperature, they can exert high recovery stresses of 700MPa which can be used to perform work.
In this paper, we are presenting one of the major categories of smart materials, SMAs, their properties, different types of SMAs and their applications in various fields
SHAPE MEMORY ALLOYS
INTRODUCTION:
Shape memory alloys are metals that, after being strained, at a certain temperature revert back to their original shape. A change in their crystal structure above their transformatations temperature causes them to return to their original shape.
SMAs enable large forces (generated when encountering any resistance during their transformation) and large movements’ actuation, as they can recover large strains.
SMAs exhibit two very unique properties pseudo-elasticity and the shape memory effect. Typical Alloys which exhibit these properties are Ni-Ti alloy, Iron base SMA alloy, Copper base SMA alloy, Super Elastic glasses etc.,
SHAPE MEMORY EFFECT:
The ability of SMAs to return to their original shape after heating to their transformation temperature after having been deformed is termed as “shape memory effect”. This is due to the change in the crystalline structure during the transition from martensitic phase to austenitic phase.
Martensite is the relatively soft and easily deformed phase of shape memory alloys, which exists at lower temperatures. The molecular structure in this phase is twinned as shown in the middle of figure. Upon deformation this phase takes on the second form shown in figure2, on the right. Austenite, the stronger phase of shape memory alloys, occurs at higher temperatures. The shape of the Austenite structure is cubic, shown on the left side of figure2.The un-deformed Martensite phase is the same size and shape as the cubic Austenite phase on a macroscopic scale, so that no change is visible in shape memory alloys until the Martensite is deformed.
The Shape Memory effect is observed when the temperature of SMA is cooled to below the temperature Mf. At this stage the alloy is completely composed of Martensite which can be easily deformed. The original shape of SMA can be recovered simply by heating the SMA above the temperature Af.
The shape memory effect is currently being implemented in:
Coffeepots
The Space Shuttle
Thermostats
Vascular Stents
Hydraulic Fitting (for Airplanes)
PSEUDO-ELASTICITY:
Pseudo-elasticity occurs in SMAs when the alloy is completely composed of Austenite. It occurs without change in temperature. The load on the SMA is increased until the Austenite becomes transformed into Martensite due to the loading (as shown).
The loading is absorbed by the softer Martensite, but as soon as loading is decreased the Martensite begins to transform back to Austenite since the temperature of the SMAs is still above Af, and the wire springs back to its original shape.
Some Applications of pseudo-elasticity is used are:
Eyeglass Frames
Medical tools
Cellular phone Antenna
Orthodontic Arches
FEW SHAPE MEMORY ALLOYS:
NICKEL-TITANIUM ALLOY:
Ni-Ti alloys are the most used SMA. It is an equiatomic compound of Ni-Ti, whose transformation temperature can range between -100 & 110C. It has great shape-memory strain (up to 8%),is thermally stable and has excellent corrosion resistance. Because of the reactivity of Ti, all melting of it must be done in a vacuum.
COPPER BASE SMA ALLOY (Cu-Zn-Al & Cu-Al-Ni):
Cu-Zn-Al and Cu-Al-Ni alloys are commercially available SMAs. Their transformation temperature ranges between -180 & 200C and -140 & 100 C respectively. They are cheaper than Ni-Ti alloys can be melted in air with ease and have a shape-memory strain up to 4-5%. Hot work in air is well suitable, while cold work is suitable only for low Al content alloys (<6% wt).
SUPER ELASTIC GLASSES:
These glasses are made from a super elastic metal alloy. Therefore, they can be bended quite drastically without permanent damage. The glasses utilize the super elastic property of Ni-Ti alloys.
IRON BASE SMA ALLOYS:
The most important Iron based shape memory alloy is Fe-Mn-Si. They base shape-memory effect on a different physical principle than conventional SMAs. They can recover only less than 4% strain.
APPLICATIONS:
The pseudo elasticity and Shape memory effect are being applied to a wide variety of applications in a number of different fields. Some of them are:
Aeronautical Engineering
Medical Applications
Commercial applications
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plz send me this as soon as possible
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thanks for this great help.
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Smart Sensor
[attachment=17907]
Bi-directional MODBUS page link to DCS
Analyzer returns MEASUREMENT and STATUS value for control action
DCS sends commands and key process parameters
Product TYPE Sets:
Measurement parameters
Calibration equation (model)
Process STATE Sets:
Instrument response (“Auto” cruse control)
Rapid process change = short time constant
Stead state=long time constant
DCS signal triggers raw data save when:
Routine samples pulled for lab analysis (low frequency activity)
Non-standard conditions exist
DCS initiates calibration update based on:
Lab data
Corresponding instrument data
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plz send me full report of the above topic
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Hi,
Please send me the seminar report on smart sensor.
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