(SEM-VII) THEORY EXAMINATION 2022-23 MICRO & SMART SYSTEMS

SECTION A – Short Answers (2 Marks Each)

(a) Difference between Microsystems and MEMS

Microsystems are miniaturized systems combining sensors, actuators, electronics, and control, whereas MEMS (Micro-Electro-Mechanical Systems) mainly focus on micro-scale mechanical structures integrated with electronics.

(b) Smart systems

Smart systems are systems that can sense, process, decide, and respond to environmental changes using sensors, actuators, and control logic.

(c) Applications of smart materials and microsystems

Applications include automotive sensors, biomedical devices, inkjet printers, aerospace systems, robotics, consumer electronics, and structural health monitoring.

(d) Self-generating transducer

A self-generating transducer produces its own electrical output without external power, such as piezoelectric and thermocouple sensors.

(e) Micromachining process

Micromachining is the fabrication of micro-scale structures using techniques like photolithography, etching, and deposition on silicon wafers.

(f) Dynamic range

Dynamic range is the ratio of the maximum measurable signal to the minimum detectable signal of a sensor.

(g) Applications of piezo-resistive pressure sensor

They are used in automotive pressure sensing, biomedical devices, industrial process control, and MEMS pressure sensors.

(h) Use of Hall Effect sensors

Hall Effect sensors are used to measure magnetic field, current, position, and speed in automotive and industrial applications.

(i) Difference between tactile and non-tactile sensors

Tactile sensors require physical contact to sense parameters, while non-tactile sensors operate without direct contact, such as optical or ultrasonic sensors.

(j) Intelligent sensor

An intelligent sensor integrates sensing, signal processing, decision making, and communication capabilities in a single unit.

SECTION B – Long Answers (10 Marks Each)

(Attempt any three in exam; answers provided for all)

(a) Silicon capacitive accelerometer

A silicon capacitive accelerometer consists of a movable proof mass suspended by micro-fabricated beams. Acceleration causes displacement of the mass, changing capacitance between fixed and movable electrodes. This change is converted into an electrical signal. Advantages include high sensitivity, low power consumption, and compatibility with IC fabrication.

(b) Goals and applications of integrated microsystems

The goals of integrated microsystems are miniaturization, low power consumption, high reliability, and mass production. Applications include biomedical implants, automotive airbag systems, environmental monitoring, and consumer electronics.

(c) Smart-material systems and their evolution

Smart materials can change their properties in response to external stimuli like stress, temperature, or electric field. Examples include piezoelectric materials, shape memory alloys, and magnetostrictive materials. Their evolution led from passive materials to adaptive structures and finally to fully integrated smart systems.

(d) Micromachined transducers and micro-manufacturing evolution

Micromachined transducers convert physical quantities into electrical signals using micro-fabrication techniques. Evolution of micro-manufacturing includes bulk micromachining, surface micromachining, and deep reactive ion etching (DRIE). Applications include pressure sensors, accelerometers, and micro-actuators.

(e) Sensors, actuators, and systems

Sensors detect physical parameters, actuators convert electrical signals into mechanical action, and systems integrate sensors, actuators, and control electronics to perform intelligent tasks. Key features include accuracy, sensitivity, reliability, and fast response.

SECTION C – Long Answers (10 Marks Each)

3(a) Piezoelectric inkjet print head and characteristics

Piezoelectric inkjet print heads use piezoelectric actuators to generate pressure pulses that eject ink droplets. Characteristics include precise droplet control, high resolution, low power consumption, and suitability for a wide range of inks.

3(b) Piezo-resistive pressure sensor

This sensor operates on the principle that resistance of piezo-resistive material changes with applied stress. It consists of a silicon diaphragm with diffused resistors. Advantages include high sensitivity and easy integration with electronics.

4(a) Advanced processes for micro-fabrication

Advanced processes include LIGA, DRIE, nano-lithography, wafer bonding, and laser micromachining. These processes enable fabrication of high-aspect-ratio and complex micro-structures.

4(b) Emerging trends in silicon wafer processing

Trends include SOI wafers, ultra-thin wafers, 3D integration, nano-scale patterning, and improved surface treatment techniques.

5(a) Poisson effect and anticlastic curvature of beams

Poisson effect is the lateral strain produced when a material is stressed longitudinally. Anticlastic curvature refers to bending of a beam in the opposite direction due to Poisson’s ratio.

5(b) Modeling of coupled electromechanical systems

Coupled electromechanical systems are modeled using energy methods and constitutive equations that relate electrical and mechanical domains, enabling analysis of sensors and actuators.

6(a) Residual stress and stress gradients

Residual stress is locked-in stress present without external load, while stress gradient is the variation of stress across thickness. Stress gradients cause bending or warping in micro-structures.

6(b) Integration of Microsystems and microelectronics

Integration allows sensors and actuators to be fabricated along with signal processing circuits on a single chip, improving performance, reliability, and reducing size and cost.

7(a) Microsystems packaging

Microsystems packaging protects devices from environment, provides electrical interconnections, and ensures mechanical stability. Techniques include wafer-level packaging and hermetic sealing.

7(b) Mechanical, electrostatic, and magnetic domains

Mechanical domain deals with force and displacement, electrostatic domain with voltage and capacitance, and magnetic domain with magnetic fields and flux. These domains interact in smart systems.