Sensors and Actuators - Presentation with diagrams

Materials, Sensors, and Actuators in MEMS Technology Evolution
Microelectromechanical Systems (MEMS) technology has revolutionized various industries, including automotive, healthcare, aerospace, and consumer electronics. MEMS devices integrate mechanical and electrical components at the microscale, enabling precise sensing, actuation, and control. The evolution of MEMS has been significantly influenced by advancements in materials, sensors, and actuators. This document provides a comprehensive analysis of the role of materials, sensors, and actuators in the development of MEMS technology.

1. Introduction to MEMS Technology
MEMS technology refers to miniaturized mechanical and electro-mechanical devices fabricated using microfabrication techniques. These systems typically include sensors, actuators, and electronic components integrated onto a single chip. The advancements in MEMS technology have been driven by the development of novel materials, improved fabrication techniques, and enhanced sensor-actuator performance.

Key Features of MEMS Technology:
Miniaturization of mechanical components
Integration of electronic circuits and mechanical systems
High precision and sensitivity
Low power consumption
Cost-effective mass production
2. Materials in MEMS Technology
The choice of materials plays a crucial role in determining the performance, reliability, and efficiency of MEMS devices. MEMS materials can be broadly classified into structural materials, functional materials, and packaging materials.

2.1 Structural Materials
Structural materials form the backbone of MEMS devices and are responsible for mechanical strength, stability, and durability.

(a) Silicon-Based Materials
Single-Crystal Silicon (Si): The most widely used material in MEMS due to its excellent mechanical properties, low cost, and compatibility with semiconductor fabrication.
Polycrystalline Silicon (Poly-Si): Commonly used for microstructures such as beams, membranes, and cantilevers.
Silicon Carbide (SiC): Offers high-temperature stability and chemical resistance, making it suitable for harsh environments.
(b) Metal-Based Materials
Aluminum (Al): Used for interconnects and microstructures due to its good electrical conductivity and ease of deposition.
Gold (Au) and Platinum (Pt): Preferred for biomedical applications due to their biocompatibility.
Titanium (Ti): Provides high strength and corrosion resistance for specialized MEMS applications.
(c) Polymer-Based Materials
Polydimethylsiloxane (PDMS): Widely used in biomedical MEMS due to its flexibility and biocompatibility.
SU-8: A high-aspect-ratio photoresist polymer used in microfluidics and lab-on-a-chip applications.
Polyimide: Provides good mechanical and thermal properties for flexible MEMS applications.
2.2 Functional Materials
Functional materials exhibit specific electrical, magnetic, thermal, or optical properties that enhance MEMS device performance.

(a) Piezoelectric Materials
Lead Zirconate Titanate (PZT): Common

1. Sensors
1

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KNOWN TO UNKNOWN
Sensor
What is Sensor ?
•An element senses a variation in input energy to
produce
a variation in another source or same form of energy.
•A sensor acquires a physical parameter and converts
it into a signal suitable for processing
•e.g. optical, electrical, mechanical…

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Input signal output signal
SENSOR

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One energy form must be converted into the same or
another energy form with exactly the same information
content as the originating energy form.
Amplifier
Mic

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Types of Sensors
•Chemical sensors
•Magnetic sensors
•Mechanical sensors
acceleration,
position,
pressure,
rotation, etc.
•Temperature sensors

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Mechanical sensing elements
•Springs-convert a force or torque into displacement.
•A diaphragm , or a capsule, bellows bourdon tubes –
convert pressure into displacement.
•A bimetallic strip-convert temperature into
displacement.
•A mass damper system-used for measurement of
accelerations, velocity and displacement.

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Temperature sensors
Temperature is:
•One of the Fundamental parameter
•Indicates physical condition of matter
•Expresses degree of hotness or coldness

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Temperature measurement
•Change in physical or chemical state.
•Change in physical dimensions
•Change in electrical properties, mainly the change in
resistance
•Generation of e.m.f. at the junction of two dissimilar
metals.

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Methods of Temperature measurement
Electrical methods are:
•Most convenient
•Accurate

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Electrical methods Based on:
•Change in resistance with temperature.
•Generation of thermal e.m.f.
Temperature may be :
Resistance Thermometers-positive
temperature coefficient
Thermistors -Negative temperature coefficient

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Temperature sensors
•Thermistor
•Thermocouple

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Thermistor
•a type of resistor
•to measure temperature changes,
•the change in its resistance with changing
temperature.

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Thermocouple
• interchangeable
•They have standard connectors and
•can measure a wide range of temperatures.

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Pressure sensing elements: Definition
•it is not possible to transform the measurable
quantity into an electrical quantity directly.

•a primary sensing element senses the measurable
quantity
•transforms into a form of physical quantity to a
transducer is used.

•The mechanical elements are used to transform the
force or pressure into displacement.

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Pressure Sensing Elements
•The commonly used pressure sensitive devices
are:
–Diaphragms
–Capsule
–Bellows
–Bourdon tubes

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Pressure sensors-uses
•To measure pressures of gases or liquids
•a wide range of uses in
industrial
commercial and
consumer applications.

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Diaphragms
•Pressure sensing elastic elements in pressure
transducer is diaphragm.
•Characteristics:
–ruggedness,
–excellent stability and
–reliability.
•Made from elastic metal alloys.

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•Most commonly used pressure sensing element.
•Thin circular plate stretched and fastened at its
periphery.
•Responds to pressure values ranging from few
millimeters of water column to several atmosphere.

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•Selecting suitable metal depends on:
•temperature range
•effects of shock and vibration
•frequency response requirements.

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Types of Diaphragms
•Flat type.
Diaphragms

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Corrugated type:
•used for larger deflection requirements

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Capsule
•consists two identical annular corrugated metal
diaphragms
•sealed together at the periphery to form a shell – like
enclosure.
•One diaphragm to admit the pressure to be measured.
•Other diaphragm is linked to a mechanical number.
•the difference of the inner and outer pressure is
proportional to displacement of mechanical number.

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Capsule
Capsule Diaphragms

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BURDON TUBE
TYPES OF BURDON TUBES
•C-Type

•Spiral type
•Twisted tube type
•Helical type

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1. C-Type
Tube cross section
Pressure
Displacement

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2.Spiral
3.Twisted tube

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4.Helical

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C-type Bourdon tube
Socket
link
pressure
pointer
scale

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•Pressure applied to the inside of the Bourdon tube
expands or contracts the entire tube, and moves the
pointer.
•Angular deflection measured with mechanical
pointer.
•Deflection varies with, ratio, tube length, difference of
pressures, radius of curvature, tube well thickness,
material used

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Advantages:
•Low cost
•Simple construction
•High pressure range
•High accuracy except at low pressure
•Easily adapted for obtaining electrical outputs.
Disadvantages:
•More sensitive to shock and vibrations than diaphragms
•Hence they are used for static measurements.
•Their use is limited to precision measurements unto a
pressure of 3 MN/m
2

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BELLOWS
•consists of a thin walled cylindrical shells with deep
convolution.
•sealed at one end.
•The sealed end moves axially when pressure is
applied to the other end.
•convolutions vary from 5to 20.
•Materials:
•Brass, bronze, beryllium copper ,alloys of nickel and
copper, steel..
•used for low pressure measurements.

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•Bellows
100
pressure
Calibrated
scale

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Sensor-Applications
•Sensors are omnipresent.

•embedded in our bodies, automobiles, airplanes,
cellular telephones, radios, chemical plants,
industrial plants and countless other applications.
•Without the use of sensors, there would be no
automation !

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•Traffic and security surveillance
•Blind spot detection
•Light activation.
•New truck weighing systems, Etc.
•Food testing
•Vehicle dynamic system
•Patient monitoring
•Carpet cleaning etc.,

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Summary
We have discussed about:
•Sensor, definition
•Various types of sensors
•Temperature sensors
•pressure sensors
•Pressure sensing elements
•Applications of sensor.

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QUIZ

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•Bourdon type pressure sensor belongs to
which type of sensor classification?
a) Thermal sensor
b) Electronic sensor
c) Mechanical sensor
d) Temperature sensor

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Frequently asked questions in
examination
•Define what is meant by sensing elements?
•Explain the function Diaphragms as sensing device.
•Explain the function of Bellows as sensing device.
•Explain the construction and working of a bourdon
tube to measure pressure.

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