A (1) Explain the classification of smart materials.
ANS> Actively Smart:
They possess the capacity to modify their geometric or material properties under the application of electric, thermal or magnetic fields, thereby acquiring an inherent capacity to transduce energy.
• Piezoelectric
• Magneto strictive
• Shape memory alloys
• Electro-Rheological fluid, etc.
They can be used as force transducers and actuators
Passively Smart: Those smart materials that are not active are called passively smart materials. Although smart, they lack the inherent capability to transduce energy.
• Optic fibers
A(2) What is a smart system? Give an example. Explain the components of a Smart System?
ANS>
Actively Smart:
They possess the capacity to modify their geometric or material properties under the application of electric, thermal or magnetic fields, thereby acquiring an inherent capacity to transduce energy.
• Piezoelectric
• Magneto strictive
• Shape memory alloys
• Electro-Rheological fluid, etc.
They can be used as force transducers and actuators
Passively Smart: Those smart materials that are not active are called passively smart materials. Although smart, they lack the inherent capability to transduce energy.
• Optic fibers
Components of a smart system:
- Sensors: Smart systems rely on sensors to collect data from the environment. Sensors can include temperature sensors, humidity sensors, motion sensors, light sensors, or even more advanced ones like cameras or biometric sensors.
- Actuators: Actuators are responsible for carrying out actions or operations based on the decisions made by the smart system. Examples of actuators include motors, valves, switches, or even robotic arms.
- Connectivity: Smart systems often have connectivity features to enable communication between different components of the system or with external devices. This can include wireless technologies like Wi-Fi, Bluetooth, or Zigbee, allowing remote control and access.
- User Interface: Smart systems provide a user interface for interaction and control. This can be a mobile application, a web portal, voice commands, or even touch interfaces embedded in devices.
- Decision-Making: Smart systems utilize algorithms and decision-making techniques to process the collected data and generate appropriate actions or responses based on predefined rules or learning algorithms.
B) Write short notes on Piezoelectric materials & Shape memory materials.
ANS> Piezoelectric Material
- Materials that produce a voltage when stress is applied. (An applied mechanical stress will generate a voltage)
- Example: Quartz, BaTiO3, GaPO4
- The piezoelectric effect describes the relation between a mechanical stress and an electrical voltage in solids.
- In physics, the piezoelectric effect can be described as the link between electrostatics and mechanics.
- An LED is wired to a piezoelectric transducer. The LED briefly lights when the device is flicked & shows that electricity has been generated by stress and strain.
- The second generation of piezoelectric applications was developed during World War II. It was discovered that certain ceramic materials, known as ‘ferroelectrics’, showed dielectric constants up to 100 times larger than common-cut crystals and exhibited similar improvement in piezoelectric properties.
Reverse Piezoelectric effect
- An applied voltage will change the shape of the solid by a small amount (up to a 4% change in volume).
- Quartz watches, Piezoelectric US oscillator
Application of Piezoelectric effect
- In lighters or portable sparkers with a piezo fuze a sudden and strong pressure is used to produce a voltage. The spark then ignites the gas.
- A piezo motor is based on the change in mechanical shape of a piezoelectric material when an tension is applied. The material produces ultrasonic or acoustic vibrations and produces a linear or rotary motion.
- An alloy that remembers” its original, cold-forged shape. By heating it returns back to the re-deformed shape.
- SMAs are materials which can revert back to original shape & size on cooling by undergoing phase transformations.
- Shape memory alloys (SMA’s) are metals, which exhibit pseudo-elasticity and the shape memory effect.
- Examples: NiTiNOL (thermal), NiMnGa, Fe-Pd, Terfenol-D (Magnetic) CuZnSi, CuZnAl, CuZnGa, CuZnSn(actuator)
- The shape change involves a solid-state phase change involving a molecular rearrangement between Martensite and Austenite.
- A temperature change of only about 100 C is necessary to initiate this phase change
Shape Memory Alloys
A. Cu-based Alloys
- Cu-Al-Ni with 14/14.5 wt.% Al and 3/4.5 wt.% Ni
- Cu-Sn approx. 15 at. % Sn
- Cu-Zn 38.5/41.5 wt.% Zn
B. Other shape memory alloys include:
- Ni-Ti (~55% Ni)
- Ag-Cd 44/49 at. % Cd
- Au-Cd 46.5/50 at. % Cd
- Fe-Pt approx. 25 at. % Pt
- Mn-Cu 5/35 at. % Cu
- Fe-Mn-Si
- Pt alloys
- Co-Ni-Al
- Co-Ni-Ga
- Ni-Fe-Ga
A) Explain with a neat sketch the silicon crystal growth by the Czochralski crystal puller method
ANS> • To demonstrate the methods of growing semiconductors, we will consider the crystal growth of silicon in detail first.
• Basically, the technique used for silicon crystal growth from the melt is the Czochralski technique.
• This starts from a pure form of sand (SiO2), known as quartzite, which is placed in a furnace with different carbon-releasing materials, such as coal and coke.
• Several reactions then take place inside the furnace and the net reaction that results in silicon is as follows:
• The silicon so-produced is known as metallurgical-grade silicon (MGS) which contains up to 2% of impurities.
• Subsequently, the silicon is treated with hydrogen chloride to form trichlorosilane (SiHCl3):
SiHCl3 is a liquid at room temperature. Fractional distillation of the SiHCl3 removes the impurities and the purified liquid is reduced in a hydrogen atmosphere to yield electronic- grade silicon (EGS) by the following reaction:
• EGS is a polycrystalline material of remarkably high purity and is used as the raw material for preparing high quality Si wafers. The Czochralski technique employs the apparatus shown in Figure 2.1.
• To grow a crystal, the EGS is placed in the crucible and the furnace is heated above the melting temperature of silicon. An appropriately oriented seed crystal (e.g. [100]) is suspended over the crucible in a seed holder.
• The seed is then lowered into the melt. Part of it melts but the tip of the remaining seed crystal still touches the liquid surface. The seed is next gently withdrawn, and progressive freezing at the solid–liquid interface yields a large single crystal.
• Absolute control of temperatures and pull rate is required for high quality crystals. A typical pull rate is a few millimeters per minute.
B(1) Explain the epitaxial growth of semiconductors.
ANS> In many situations, it may not be feasible to start with a silicon substrate to build a smart system.
- Instead, one could start with other possibilities and grow silicon films on the substrate by epitaxial deposition to ‘build the necessary electronics’.
- The method for growing a silicon layer on a substrate wafer is known as an epitaxial process where the substrate wafer acts as the seed crystal.
- Epitaxial processes are different from crystal growth from the melt in that the epitaxial layer can be grown at a temperature much lower than the melting point.
- Among various epitaxial processes, vapor phase epitaxy (VPE) is the most common.
- A schematic of the VPE apparatus and shows a horizontal susceptor made from graphite blocks.
- The susceptor mechanically supports the wafer and being an induction-heated reactor it also serves as the source of thermal energy for the reaction.
- Several silicon sources can be used, e.g. silicon tetrachloride (SiCl4), dichlorosilane (SiH2Cl2), trichlorosilane (SiHCl3) and silane (SiH4).
- The typical reaction temperature for silicon tetrachloride is 1200 C.
- The overall reaction, in the case of silicon tetrachloride, is reduction by hydrogen, as follows:
- SiCl4 (gas) + 2H2(gas) –>Si (solid) + 4HCl
- A competing reaction which occurs simultaneously is:
- SiCl4 (gas) + Si (solid) –> 2SiCl2(gas)
- silicon is deposited on the wafer, silicon is removed (etched).
- Therefore, if the concentration of SiCl4 is excessive, etching rather than growth of silicon will take place.
B(2) Explain the mechanism of UV curing of polymers.
- ANS> UV curing is based on photoinitiated polymerization, which is mediated by photo- initiators.
- These absorb UV light and convert the (light) energy into chemical energy in the form of reactive intermediates, such as free radicals and reactive cations, which subsequently initiate the polymerization.
- Typical photopolymer formulations contain a photo-initiator system, monomers and oligomers (or a polymer or polymers) to provide specific physical and/or processing properties.
- They may also contain a variety of additives to modify the physical properties of the light-sensitive compositions or the final properties of the cured photopolymers.
- The photopolymerization reactions fall into two categories, i.e. radical photopolymerization and cationic photopolymerization.
- Generally, acrylates are associated with free-radical polymerization while epoxies are typical of cationic curing.
- The most commonly used reactive monomeric materials are low-molecular-weight unsaturated acrylate or methacrylate monomers that can be made to cross-link with the use of a radical-generating photo-initiator.
- The practical applications of cationic initiated cross-linking of monomeric materials with epoxy and/or vinyl ether functionalities have significantly increased with the development of new UV sensitive, high-efficiency photo-initiators which generate cationic species.
- Once the photo-initiator (PI) absorbs light, it is raised to an electronically excited state, PI*.
- The lifetimes of the PI* states are short, generally less than 106 s.
A(1) Explain in detail about Piezoelectric sensor.
ANS> Generation of electrical potential in response to applied mechanical stress.
Derived from Greek word piezo meaning squeeze Transducer converts one form of energy into another. Transduction is from mechanical energy to electrical energy.
Many piezoelectric materials are known to exist.
Quartz, tourmaline, ceramic (PZT), GAPO4 and many others.
The word ‘piezo‘ is derived from the Greek word for pressure.
The piezoelectric effect was discovered by Jacques and Pierre Curie in 1880.
Found that electricity is produced when mechanical stress is applied.
Mechanical compression changes the dipole moment creating voltage.
Directions of compression or tension generates voltage of the same polarity as the poling voltage
A(2) Discuss about Magnetostrictive sensors.
ANS> Certain ferromagnetic materials show deformation when subjected to a magnetic field.
- This phenomenon, commonly known as magnetostriction, is reversible and is also called the ‘Joule and Villari effects’.
- In their demagnetized forms, domains in a ferromagnetic material are randomly oriented.
- However, when a magnetic field is applied these domains become oriented along the direction of the field.
- This orientation results in microscopic forces between these domains, hence resulting in deformation of the material.
- By reciprocity, mechanical deformation can cause orientation of the domains, so resulting in induction at the macroscopic level.
- The elongation is quadratically related to the induced magnetic field and hence is strongly non-linear.
- Apart from the ferroelectric bar, a Magnetostrictive transducer consists of a coil and a magnet Figure (a).
- It is now possible to translate this electrical equivalent circuit to a electromechanical circuit, as shown in Figure (b).
- This has electrical and mechanical components connected to an electromechanical transformer.
- The ratio of the ‘turns’ of this transformer is decided by the amount of coupling.
- This has electrical and mechanical components connected to an electromechanical transformer.
The electromechanical coupling for the Magnetostrictive transducer shown in Figure (a) relates the induced voltage V at the terminals of the coil with the rate of change in displacement at the free end of the bar:
V=fracgΔENRmx
where gΔ is the Magnetostrictive strain modulus, E is the Young’s modulus of the material, Rm is the total ‘reluctance’ of the magnetic circuit and N is the number of turns in the coil.
The ratio on the right-hand side of Equation represents the electromechanical coupling.
B(1) Write down the applications of semiconductor-based sensors.
ANS> Here are the applications of semiconductor-based sensors.
Environmental Monitoring: Semiconductor sensors help measure and monitor things like temperature, air quality, and humidity in the environment, which is important for understanding weather conditions and air pollution.
Industrial Automation: These sensors are used in factories to measure and control factors like temperature, pressure, and flow, ensuring machines and equipment work properly and efficiently.
Medical and Healthcare: Semiconductor sensors are used in medical devices to monitor vital signs like heart rate, blood pressure, and body temperature, helping doctors and nurses care for patients.
Automotive Applications: In cars, these sensors are used to measure things like air flow, temperature, and pressure in the engine, as well as detect movements and help control the vehicle’s stability.
Consumer Electronics: Semiconductor sensors are found in devices like smartphones and gaming consoles to detect touch inputs, motion, and gestures, making the devices more interactive.
Energy and Power Systems: These sensors help monitor and control variables like voltage, current, and temperature in power systems, ensuring efficient and reliable electricity generation and distribution.
Security Systems: Semiconductor sensors are used in security systems to detect intrusions, fires, and gas leaks, providing early warnings and enhancing safety.
Aerospace and Defense: These sensors are used in aircraft and military equipment for navigation, altitude sensing, and missile guidance, ensuring accurate and safe operations.
Food and Agriculture: Semiconductor sensors are used in the food industry to monitor temperature and humidity during storage and transportation, ensuring food quality. In agriculture, they help monitor soil moisture and climate for better crop management.
These applications highlight how semiconductor-based sensors are used in different fields to measure and monitor important factors, enabling safer, more efficient, and more convenient technologies.
B(2) Compare Piezoelectric and Piezoresistive sensors.
ANS>
| Piezoelectric Sensors | Piezoresistive Sensors |
| Convert mechanical stress/strain into electrical charge | Change in electrical resistance due to mechanical stress/strain |
| Piezoelectric crystals or ceramics | Semiconductor materials (e.g., silicon) |
| High sensitivity | Moderate sensitivity, may require signal conditioning |
| Less affected by temperature variations | More sensitive to temperature changes |
| Wide frequency response | Limited frequency response |
| Highly linear within their specified range | Non-linear response, requires calibration or compensation |
| Wide dynamic range | Limited dynamic range |
| Stable over time and usage | Susceptible to drift and aging effects |
| Suitable for high-frequency and dynamic measurements, acoustic sensing, ultrasonic applications | Ideal for static or low-frequency measurements, pressure sensing, force measurement in mechanical systems |
| Generally higher cost due to specialized materials | Lower cost due to the use of common semiconductor materials |
- Explain in details with neat sketch about Electro-strictive transducers
ANS>
Electrostrictive transducers are devices that convert electrical energy into mechanical displacement or strain in response to an applied electric field. They utilize a phenomenon called electrostriction, where the dimensions of certain materials change when subjected to an electric field. Here’s a detailed explanation of electrostrictive transducers:
Introduction : Electrostrictive transducers are used to convert electrical energy into mechanical motion or strain by utilizing the electrostriction effect.
Types : There are various types of electrostrictive transducers, including:
- Lead Zirconate Titanate (PZT) : PZT is a commonly used electrostrictive material with high coupling coefficients and wide frequency response. It is widely employed in applications such as ultrasonic transducers and actuators.
- Terfenol-D : Terfenol-D is another popular electrostrictive material known for its high magnetostrictive properties. It finds applications in sonar systems, acoustic sensors, and vibration control devices.
- Galfenol : Galfenol is a newer electrostrictive material that exhibits a combination of magnetostrictive and electrostrictive properties. It is being explored for applications in energy harvesting and sensors.
Working Principle : Electrostrictive transducers work based on the principle that certain materials undergo dimensional changes when exposed to an electric field. When an electric field is applied, the material deforms or expands, producing mechanical motion or strain.
Applications : Electrostrictive transducers find applications in various fields, including:
- Ultrasonic Transducers : Electrostrictive transducers are used to generate and receive ultrasonic waves in medical imaging, non-destructive testing, and industrial applications.
- Actuators : These transducers are employed as actuators in precision positioning systems, robotics, and adaptive optics.
- Vibration Control : Electrostrictive transducers can be used for active vibration control in structures and systems, reducing unwanted vibrations and enhancing stability.
- Sonar Systems : They are utilized in sonar systems for underwater communication, navigation, and detection of objects.
- Energy Harvesting : Electrostrictive materials are being explored for energy harvesting applications, where mechanical strain is converted into electrical energy.
- Acoustic Sensors : Electrostrictive transducers are used in acoustic sensors for detecting and measuring sound waves.
Advantages : Electrostrictive transducers offer advantages such as high sensitivity, broad frequency response, and the ability to operate in harsh environments.
Limitations : Limitations include the need for high voltage for actuation, limited strain range, and the requirement for efficient cooling in some cases.
electrostrictive transducers play a crucial role in various fields, enabling the conversion of electrical energy into mechanical motion or strain, and finding applications in ultrasonic transducers, actuators, vibration control, sonar systems, energy harvesting, and acoustic sensors.
B)Explain in details with neat sketch about Magnetostrictive transducers.
ANS>
Magnetostrictive transducers are devices that convert electrical energy into mechanical vibrations using the magnetostrictive effect. This effect occurs in certain materials that change their shape or dimensions when exposed to a magnetic field.
Introduction : Magnetostrictive transducers utilize the magnetostrictive effect, where a material changes its shape or dimensions when subjected to a magnetic field.
Operating Principle : When an electrical current is passed through a magnetostrictive material, it produces a magnetic field that causes mechanical vibrations in the material.
Types : There are two main types of magnetostrictive transducers: Terfenol-D transducers and Galfenol transducers. Terfenol-D is a rare-earth metal alloy, while Galfenol is an iron-gallium alloy.
- Terfenol-D Transducers : Terfenol-D transducers are known for their high sensitivity and large displacement capabilities. They find applications in sonar systems, vibration sensors, and high-precision positioning devices.
- Galfenol Transducers : Galfenol transducers offer improved mechanical properties and lower costs compared to Terfenol-D. They are used in applications such as energy harvesting, vibration energy converters, and sensing devices.
Applications : Magnetostrictive transducers have diverse applications including:
- Sonar and underwater acoustics: They are used in hydrophones and underwater navigation systems.
- Non-destructive testing: Magnetostrictive transducers are employed for inspecting structures, detecting flaws, and measuring material properties.
- Actuators and sensors: They find use in precision positioning, robotics, haptic feedback systems, and active vibration control.
- Energy harvesting: Magnetostrictive transducers can convert mechanical vibrations or strain energy into electrical energy for power generation.
- Magnetic field sensing: They can be used for measuring magnetic fields and as part of magnetic field sensors.
- Material characterization: These transducers assist in determining material properties, such as elasticity and magnetic behavior.
Advantages : Magnetostrictive transducers offer high sensitivity, fast response times, broad bandwidth, and the ability to operate in harsh environments.
Limitations : They may require high magnetic fields or current levels to achieve desired performance, and some materials used in magnetostrictive transducers are expensive or less readily available.
Magnetostrictive transducers utilize the magnetostrictive effect to convert electrical energy into mechanical vibrations. They have applications in sonar, non–destructive testing, precision positioning, energy harvesting, magnetic field sensing, and material characterization.
Que 5>
A) Explain in detail about Capacitive sensors.
ANS> Capacitive sensors are devices that measure changes in capacitance to detect the presence or proximity of objects.
They work based on the principle of capacitance, which is the ability of a capacitor to store electrical charge.
Capacitive sensors can be categorized into two types: proximity sensors and touch sensors.
Proximity capacitive sensors detect the presence or absence of an object without physical contact.
Touch capacitive sensors are designed to respond to physical touch or proximity and are commonly used in touchscreens and touch-sensitive buttons.
Capacitive sensors utilize an oscillating electrical field and measure changes in capacitance caused by the presence or proximity of an object.
They can detect a wide range of materials, including conductive and non–conductive substances.
Capacitive sensors have various applications, including:
- Touchscreens in smartphones, tablets, and other electronic devices.
- Proximity detection in automatic faucets, automatic doors, and elevators.
- Object detection and positioning in industrial automation and robotics.
- Liquid level sensing and fluid flow measurement.
- Human presence detection for energy-saving purposes in lighting and heating systems.
- Automotive applications such as occupant detection, keyless entry systems, and touch-sensitive controls.
Capacitive sensors offer advantages such as high accuracy, durability, and immunity to environmental factors like dust and moisture.
They can operate through various materials, including glass, plastic, and thin barriers.
Capacitive sensors find widespread use due to their versatility and reliability in a wide range of applications.
B) Write down the importance of Carbon nano-tube sensors in MEMS based applications.
ANS>
C)Explain about Acoustic sensors.
ANS> Acoustic sensors detect and measure sound waves in the environment, converting sound energy into electrical signals.
Common types of acoustic sensors include microphones, ultrasonic sensors, hydrophones, and vibration sensors.
Microphones are used in audio recording, communication systems, and voice–controlled devices.
Ultrasonic sensors measure distance and detect objects in industrial automation and robotics.
Hydrophones detect underwater sounds for marine research and sonar systems.
Vibration sensors monitor structural integrity and machine condition.
Acoustic sensors have various applications, including:
- Audio recording, public address systems, and telecommunication devices.
- Monitoring machine condition and detecting faults in industries.
- Measuring noise levels and analyzing soundscapes in environmental monitoring.
- Intrusion detection and surveillance in security systems.
- Monitoring respiratory function and performing ultrasound imaging in medical applications.
- Noise cancellation, parking assistance, and collision warning systems in the automotive industry.
- Enhancing the entertainment and gaming experience in musical instruments, gaming peripherals, and virtual reality systems.
Acoustic sensors provide valuable capabilities for detecting and analyzing sound waves, leading to improved monitoring, communication, and analysis of acoustic information.
D )Explain with neat sketch of Piezoelectric transducers.
ANS> There are certain materials that generate electric potential or voltage when mechanical strain is applied to them or conversely when the voltage is applied to them, they tend to change the dimensions along certain plane. This effect is called as the Piezoelectric Effect.
The piezoelectric transducers work on the principle of Piezoelectric Effect. When mechanical stress or forces are applied to some materials along certain planes, they produce electric voltage. This electric voltage can be measured easily by the voltage measuring instruments, which can be used to measure the stress or force.
The voltage output obtained from the materials due to piezoelectric effect is very small and it has high impedance. To measure the output some amplifiers, auxiliary circuit and the connecting cables are required.
Materials used for the Piezoelectric Transducers
There are various materials that exhibit piezoelectric effect. The materials used for the measurement purpose should posses desirable properties like stability, high output, insensitive to the extreme temperature and humidity and ability to be formed or machined into any shape.
But none of the materials exhibiting piezoelectric effect possesses all the properties.
Examples of Piezoelectric Material The materials are : Barium Titanate, Lead zirconate titanate (PZT), Rochelle salt, Quartz.
Construction and working:
The figure shows a conventional piezoelectric transducer with a piezoelectric crystal inserted between a solid base and the force summing member.
If a force is applied on the pressure port, the same force will fall on the force summing member.
Thus a potential difference will be generated on the crystal due to its property. The voltage produced will be proportional to the magnitude of the applied force.
E)Compare the electromagnetic transducers and electrodynamics transducers.
ANS>
| Electromagnetic Transducers | Electrodynamics Transducers |
| Based on electromagnetic induction | Based on electromagnetic induction |
| Coil of wire, magnetic field source, and mechanical element | Permanent magnet, voice coil, and diaphragm |
| Speakers, microphones, generators, transformers, motors, sensors | Loudspeakers in audio systems |
| Wide range of frequencies | Primarily designed for audio frequencies |
| Varies depending on design and application | Efficiency can be affected by various factors |
| Transformers, electric motors, microphones, generators | Dynamic loudspeakers, headphones, car audio systems |
F) Write down the applications of Actuators in MEMS and NEMS based applications
ANS> Actuators in MEMS and NEMS applications have several important uses:
Micromirror Arrays : They control tiny mirrors in display and projection systems, ensuring high-quality images.
Inkjet Printers : Actuators create pressure pulses to eject ink droplets onto paper, enabling precise printing.
Optical Switches : Actuators move optical fibers or waveguides, allowing for efficient signal switching in communication systems.
Microvalves : Actuators regulate fluid flow in microfluidic devices, enabling precise control in lab-on-a-chip systems.
Microgrippers and Microtools : Actuators manipulate and handle micro-objects or samples in various applications.
Microactuated Probes : Actuators enable controlled movement and positioning of probe tips in nanoscale imaging systems.
Biomedical Devices : Actuators play a role in drug delivery, implants, and diagnostic systems, allowing for controlled substance release.
Energy Harvesting : Actuators convert ambient energy into electrical power, providing a source for low-power electronics and sensors.
Adaptive Optics : Actuators correct optical aberrations in real-time, improving image quality in telescopes and high-resolution imaging.
Vibration and Noise Control : Actuators actively counteract vibrations and reduce noise in MEMS-based systems, enhancing performance.
These applications demonstrate the versatility and importance of actuators in MEMS and NEMS technology.