SENSORS AND ACTUATORS FOR

ENGINEERING APPLICATIONS

4.Magnetic and Electromagnetic sensors

by
N.Divya Manjira
Asst.Prof
SVR Engineering College

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Magnetic & Electromagnetic Sensors
 Inductive Sensors(LVDT, RVDT, Proximity Sensors)
 Hall Effect Sensors
 Magneto-resistive sensor
 Magneto-strictive sensor
Magnetic & Electromagnetic Actuators
 Motors as actuators (linear, rotational, stepping)
 Magnetic valves
 Magneto-strictive actuators
 Voice-call actuators(speaker, speaker-coil actuator)

Inductive Sensors :
 An inductive sensor is a device that uses the principle of electromagnetic
induction to detect or measure objects.
 An inductor develops a magnetic field when an electric current flows
through it; alternatively, a current will flow through a circuit containing an
inductor when the magnetic field through it changes.
 This effect can be used to detect metallic objects that interact with a
magnetic field. Non-metallic substances, such as liquids or some kinds of
dirt, do not interact with the magnetic field, so an inductive sensor can
operate in wet or dirty conditions.

Linear Variable Differential Transformer/ Transducer (LVDT) :

 LVDT is an inductive type passive transducer.
 It measures force in terms of displacement of ferromagnetic core of a
transformer.
 It converts translational or linear displacement into electrical voltage.
 It is also known as Linear Variable Differential Transducer.

Principle :
It is based on the principle of electro-magnetic induction.

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Construction :
 LVDT consist of cylindrical transformer where it is surrounded by one
primary winding in the centre of the former and two secondary windings at
the sides.
 The numbers of turns in both the secondary windings are equal, but they
are opposite to each other.
 The primary winding is connected to the ac source.
 A movable soft iron core slides within hollow former and therefore affects
magnetic coupling between primary and two secondary.

Working :
The working of LVDT by splitting the cases into 3 based on the iron core
position inside the insulated former.

Case 1: When no external force, the core reminds in the null position itself
without providing any movement then the voltage induced in both the
secondary windings are equal which results in net output is equal to zero.
V0=V1-V2=0
Case 2: When an external force is applied and if the steel iron core tends to
move in the left hand side direction then the emf voltage induced in the
secondary coil1 is greater when compared to the emf induced in the
secondary coil 2. Therefore, the net output will be
V0=V1-V2= +ve
Case 3: When an external force is applied and if the steel iron core moves
in the right-hand side direction then the emf induced in the secondary coil

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 2 is greater when compared to the emf voltage induced in the secondary
coil 1. Therefore, the net output voltage will be
V0=V1-V2= -ve

Applications :
1. Measurement of spool position in a wide range of servo valve
applications.
2. To provide displacement feedback for hydraulic cylinders.
3. To control weight and thickness of medicinal products viz. tablets or
pills.
4. For automatic inspection of final dimensions of products being packed
for dispatch.
5. To measure distance between the approaching metals during Friction
welding process.
6. To continuously monitor fluid level as part of leak detection system.
7. To detect the number of currency bills dispensed by an ATM.

Rotary Variable Differential Transformer/Transducer (RVDT) :

 RVDT is an electro-mechanical type of inductive transducer.
 It converts angular displacement into the corresponding electrical signal.
 As it is an AC controlled device, so there is no any electronics component
inside it.
 The coil of RVDT is designed to measure an angular position, so it is also
known as angular position sensor.

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  The electrical output of RVDT is obtained by the difference in secondary
voltages of the transformer, so it is called a Differential Transformer.
Principle :
It is based on the principle of electro-magnetic induction.
Construction :
 RVDT consists of primary and secondary windings similar to LVDT.
 The numbers of turns in both the secondary windings are equal, but they
are opposite to each other.
 The primary winding is connected to the ac source.
 It uses the Cam-shaped core (rotating core) for measuring the angular
displacement.

Working:
 Works based on the mutual induction principle.
 When AC excitation of 5-15V at a frequency of 50-400Hz is applied to the
primary windings of RVDT then a magnetic field is produced inside the
core.
 This magnetic field induces a mutual current in secondary windings.
 Then due to transformer action, the induced voltages in secondary
windings(S1&S2) are Es1 and Es2.
 Hence the net output voltage will be the difference between both the
induced secondary voltages.
Hence the output will be
Eo = Es1 – Es2
Now according to the position of core, there are three cases :

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Case 1 : When the core is at Null position.
When the core is at null position then the flux linkage with both the secondary
windings will be same. So the induced emf (Es1 & Es2) in both the windings
will be the same.
Hence the Net differential output voltage, E0 = Es1 – Es2 will be zero. It shows
that no displacement of the core.

Case 2 : When the core rotates in the clockwise direction.

When the core of RVDT rotates in the clockwise direction, then the flux with S1
will be more compared to S2. This means the emf induced in S1 will be more
than induced emf in S2.
Hence Es1>Es2 and net differential output voltage E0 = Es1 – Es2 will be
positive.
This means the output voltage E0 will be in phase with the primary voltage.
Case 3 : When the core rotates in the anti-clockwise direction.
When the core rotates in the anti-clockwise direction, then the flux linked with
S2 will be more compared to S1. This means the emf induced in S2 will be
more than the induced emf in S1.
Hence Es2>Es1 and net differential output voltage E0 = Es1 – Es2 will be
negative.

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This means the output voltage E0 will be in phase opposition with the primary
voltage.
Applications :
1. Used as actuators for controlling flight as well as engine.
2. Used as fuel valve as well as hydraulics.
3. Brake with a cable system.
4. Modern machine tools.
5. Wheel steering systems.
6. Weapon and torpedo system.
7. Engine fuel control system.
8. Aircraft and avionics.
9. Engine bleed air systems.
10. Robotics.

Proximity Sensors :
A proximity sensor is sensor able to detect the presence of nearby objects
without any physical contact. Proximity sensors often emits an electromagnetic
field or beam of electromagnetic radiation(infrared) and looks for change in the
field or return signal. The object being sensed is often referred to the proximity
sensor target.
Types of proximity sensors :
 Eddy Current
 Inductive
 Capacitive
 Optical
 Ultrasonic

Eddy current proximity sensors:

 Eddy current proximity sensors are used to detect non-magnetic but
conductive materials.
 They comprise of a coil, an oscillator, a detector and a triggering circuit.

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  Figure shows the construction of eddy current proximity switch.
 When an alternating current is passed through this coil, an alternative
magnetic field is generated.
 If a metal object comes in the close proximity of the coil, then eddy
currents are induced in the object due to the magnetic field.
 These eddy currents create their own magnetic field which distorts the
magnetic field responsible for their generation.
 As a result, impedance of the coil changes and so the amplitude of
alternating current.
 This can be used to trigger a switch at some pre-determined level of
change in current.
 These are relatively inexpensive, available in small in size, highly reliable
and have high sensitivity for small displacements.
Applications :
1. Automation requiring precise location.
2. Used in Machine tool monitoring.
3. Final assembly of precision equipment such as disk drives.
4. Used for Measuring the dynamics of a continuously moving target, such
as a vibrating element.
5. Drive shaft monitoring.
6. Vibration measurement.

Inductive proximity Sensor:

 Inductive proximity switches are basically used for detection of metallic
objects.
 Figure shows the construction of inductive proximity switch.

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  An inductive proximity sensor has four components; the coil, oscillator,
detection circuit and output circuit.
 An alternating current is supplied to the coil which generates a magnetic
field.
 When, a metal object comes closer to the end of the coil, inductance of the
coil changes.
 This is continuously monitored by a circuit which triggers a switch when a
preset value of inductance change is occurred.
Applications :
1. Industrial automation: counting of products during production or transfer.
2. Security: detection of metal objects, arms, land mines.
3. Also used in car washes.

Capacitive proximity Sensor :

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  Capacitive Proximity Sensors detect changes in the capacitance between
the sensing object and the Sensor.
 As per the name, capacitive proximity sensors operate by noting a change
in the capacitance read by the sensor.
 The amount of capacitance varies depending on the size and distance of
the sensing object.
 An ordinary Capacitive Proximity Sensor is similar to a capacitor with two
parallel plates, where the capacity of the two plates detected.
 When the object is at a preset distance from the sensitive side of the
sensor, an electronic circuit inside the sensor begins to oscillate.
 The rise or fall of such oscillation is identified by a threshold circuit that
drives an amplifier for the operation of an external load.
Applications :
used in many devices such as laptop track pads, digital audio players, computer
displays, mobile phones, mobile devices and others.

Optical Proximity Sensors/ Optical Encoders :

 Optical encoders provide digital output as a result of linear / angular
displacement.
 These are widely used in the Servo motors to measure the rotation of
shafts.
 It comprises of a disc with three concentric tracks of equally spaced holes.
 Three light sensors are employed to detect the light passing through the
holes.
 These sensors produce electric pulses which give the angular displacement
of the mechanical element e.g. shaft on which the Optical encoder is
mounted.
 The inner track has just one hole which is used locate the ‘home’ position
of the disc.
 The holes on the middle track offset from the holes of the outer track by
one-half of the width of the hole.
 This arrangement provides the direction of rotation to be determined.
 When the disc rotates in clockwise direction, the pulses in the outer track
lead those in the inner; in counter clockwise direction they lag behind.

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  The resolution can be determined by the number of holes on disc. With 100
holes in one revolution, the resolution would be 360/100 = 3.6 degree.
Applications :
1. Servo motors & Industrial automation
2. Medical & Lab Equipment
3. CNC machining , Robotics & Elevators
4. Rotating radar platforms
5. Flight simulators
6. Automated Guided Vehicles (AGV)
7. Off-Highway Vehicles (OHV)
8. Galvanometer scanners and Chemical dosing pumps
9. Sawmills, Pulp & paper mills
10. Used in Steel mills, Material handling & Textile manufacturing
11. Food & beverage
12. Printing & Packaging
13. Oil & gas production, Wind turbines.

The difference between Inductive and Capacitive Proximity Sensor :

 Inductive sensors use a magnetic field to detect objects. Capacitive sensors
use an electric field. In order to be sense by an inductive sensor an object

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 must be conductive. This limits suitable targets to metal objects (for the
most part). In order to be sense by a capacitive sensor the target doesn’t
need to be conductive.
 A capacitive sensor will react to an object acting as a dielectric material as
well as a conductive object. This makes metal and non-metal objects
suitable targets.

Hall Effect Sensors :

 The Hall effect sensor is a device that detects the presence of a magnetic
field.
 The sensor is typically made using a semiconductor material such as
gallium arsenide (GaAs), indium arsenide (InAs), or silicon (Si)

 The core of the sensor is a thin, flat semiconductor material known as the
Hall plate or Hall element. It's usually rectangular in shape and is the area
where the magnetic field is detected. This Hall plate is usually connected
to the sensor's circuitry.
 An electric current is passed through the Hall plate in a direction
perpendicular to the plane of the plate.

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  To protect the sensitive semiconductor material and circuitry, Hall effect
sensors are often encapsulated in a protective housing.
Principle :
It operates on the principle of the Hall effect, which describes the creation of a
voltage difference (Hall voltage) across an electrical conductor when subjected
to a magnetic field perpendicular to the current flow.
Working :
 When an external magnetic field is introduced perpendicular to the Hall
plate, it interacts with the current flowing through the plate. This
interaction causes the charge carriers (electrons or holes) in the
semiconductor material to be deflected, resulting in the accumulation of
charge on one side of the plate and a shortfall on the other side.
 Due to this charge separation caused by the magnetic field, a measurable
voltage difference, known as the Hall voltage, develops across the Hall
plate. The magnitude of the Hall voltage is proportional to the strength of
the magnetic field.
 The Hall voltage generated is then amplified and processed by the sensor's
circuitry to produce a usable output signal.
Applications :
1. Used for the measurement of fluid level in a container.
2. Used for the measurement of displacement and the detection of position
of an object.
3. Used in brushless DC motors to determine the rotor's position, enabling
precise control of motor speed and direction.
4. for measuring rotational motion in devices like computer hard drives,
robotics, and servo motors.
5. Used to measure both current and voltage in power systems.
6. Utilized in electronic compasses or magnetometers in smartphones,
navigation systems, and other devices.
7. Use in power electronics, battery management systems, and inverter
control circuits.
8. Also used in automotives for detecting the position of the throttle pedal,
gear shifters, and other controls.

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Magneto-resistive Sensors :
 Magneto-resistive sensors are devices used to detect and measure magnetic
fields.
 These sensors utilize the principle of magneto-resistance, which is the
change in electrical resistance of a material when subjected to an external
magnetic field.
 There are different types of magneto-resistive sensors, but main categories
are Anisotropic Magneto-Resistive (AMR) and Giant Magneto-Resistive
(GMR) sensors.

Anisotropic Magneto-Resistive (AMR) Sensors:

 AMR sensors use materials like permalloy (an alloy of nickel and iron)
that exhibit a change in resistance when the direction of an applied
magnetic field changes.

 In these sensors, a thin strip or film of the magneto-resistive material is

placed between conductive layers, forming a Wheatstone bridge
configuration.
 When there's no external magnetic field present, the resistance across the
bridge is balanced. But, when a magnetic field is applied perpendicular to
the film, the resistance of the material changes due to the rotation of the
magnetic domains within the material.

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  This change in resistance causes an imbalance in the Wheatstone bridge,
resulting in an output voltage that can be measured and used to determine
the strength and direction of the magnetic field.

Giant Magneto-Resistive (GMR) Sensors:

 GMR sensors use multiple layers of ferromagnetic and non-magnetic
materials.
 The GMR effect occurs when thin layers of ferromagnetic material are
separated by non-magnetic conductive layers.
 When these layers are arranged in a specific manner, they exhibit a
significant change in electrical resistance in response to an applied
magnetic field.
 When a magnetic field is applied, it causes the magnetic domains in the
ferromagnetic layers to align or misalign, affecting the electron spin
scattering at the interfaces between the layers, resulting in a significant
change in resistance.

 This change in spin-dependent electron scattering results in a substantial

change in the overall resistance of the GMR material. By measuring this
change in resistance, the strength and direction of the magnetic field can be
determined.
 GMR sensors are more sensitive than AMR sensors and can detect smaller
changes in magnetic fields.

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Applications of Magneto-resistive Sensors :
1. used in security systems for proximity detection, tamper detection in doors
and windows, and in anti-theft devices.
2. Used in aerospace and defence applications for navigation, attitude control,
and sensing magnetic fields.
3. in industrial automation for detecting the presence of metallic objects,
monitoring the position of machinery parts, and ensuring proper alignment
in manufacturing processes.
4. Used in biomedical devices and healthcare equipment for applications like
magnetic resonance imaging (MRI) systems.
5. Utilized in the automotive sector for various purposes including speed
sensing, anti-lock braking systems (ABS), gear position sensing, throttle
and pedal position sensing, and steering angle sensing.
6. Used in automotive applications for wheel speed sensors, gear tooth
sensors, and rotational position sensors.
7. Used in magnetic field sensing applications such as compasses,
magnetometers, and magnetic encoders.

Magneto-Strictive Sensor :
 A magneto-strictive sensor is a device that utilizes the magnetostriction
phenomenon to measure various physical quantities such as displacement,
stress, pressure, or torque.
Principle :
It operates based on the principle of magnetostriction, which refers to the
property of certain materials to change their shape or dimensions when
subjected to a magnetic field.
 The sensor consists of a magnetostrictive wire or waveguide made of a
magnetostrictive material such as nickel, iron, or cobalt.
 There is a transducer, usually a coil or solenoid that wraps around the
magnetostrictive wire.
 The magnetostrictive wire and the transducer are enclosed within a
protective housing or enclosure.

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Working :
 An electrical current pulse is sent through the wire via a transducer,
creating a magnetic field that induces mechanical strain.
 This strain generates ultrasonic stress waves traveling along the wire at the
speed of sound in the material.
 When the stress waves encounter a discontinuity or change in the material,
they reflect back toward the sensor.
 By measuring the time it takes for these waves to travel to and return from
the point of interest, the sensor calculates the distance or the parameter
being measured.
 The accurate timing enables accurate determination of displacement,
stress, or pressure.
Applications :
1. Used for precise position and displacement sensing in manufacturing
equipment, robotics, and machinery.
2. Employed in automotive industries for measuring suspension movements,
pedal position, throttle control, and other critical components.
3. Used to monitor structural integrity by measuring structural deformations,
vibrations, or strains in buildings, bridges.
4. Used in medical equipment such as in infusion pumps.
5. Employed for monitoring and controlling various mechanisms in aircraft,
missiles, and defence systems.
6. Utilized in industries like oil and gas, chemical processing, and food
production for accurate liquid level measurement in tanks and containers.

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 7. Integrated into systems requiring precise motion control, such as in CNC
machines, servo motors, and robotic arms.
8. Employed in energy meters and smart grid systems for accurate
monitoring of electrical parameters like voltage, current, and power
distribution.

Motors as Actuator :
Linear Motor :
 A linear motor is an electromagnetic device that produces linear (straight
line) motion.
Principle:
Linear motors work on the interaction between magnetic fields and electric
currents.
 Linear motor consists of two main parts: a stator (stationary part) and a
mover (moving part).
 The stator typically contains a series of coils arranged in a line, while the
mover consists of a permanent magnet or another set of coils.

Working:
 When electric current is applied to the coils in the stator, they create a
magnetic field.

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  The interaction between the magnetic fields generates a force along the
length of the motor. This force pushes or pulls the mover, causing it to
move in a linear direction.
 The motion of the mover can be controlled by adjusting the intensity and
direction of the current flowing through the stator coils.
 By varying the current, the speed and direction of the linear motor can be
precisely controlled.
Applications :
1. Used in Computer Numerical Control (CNC) machines.
2. Utilized in semiconductor manufacturing, 3D printing, and other
automated processes.
3. Employed in robotic systems.
4. Used in medical devices like MRI (Magnetic Resonance Imaging)
machines and CT (Computed Tomography) scanners.
5. Utilized in various aircraft components, including control surfaces, flight
simulators, and aerospace manufacturing equipment.
6. Used in laboratory equipment, such as spectrometers, microscopy stages,
and other analytical instruments.
7. Used in controlling the movement of medical instruments such as surgical
robots or automated drug delivery systems.

Rotational Motors :
 Rotary motors are electromechanical devices that convert electrical energy
into mechanical motion, resulting in rotational movement.
Principle :
They operate based on the principle of electromagnetism, where the interaction
between magnetic fields and electric currents produces rotational movement.
 It consists of two main parts: the stator and the rotor.
 The stator generates a magnetic field using stationary magnets or coils of
wire (windings) through which electric current flows.
 The rotor, which is the rotating part of the motor, contains a coil of wire
that interacts with the magnetic field created by the stator.
 Bearings are also used to support and allow smooth rotation of the rotor
shaft within the stator.

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  The motor components are often enclosed within a housing or casing.
Working :
 When a direct current (DC) is applied to the motor, it passes through the
wire windings of the rotor. The direction of the current creates a magnetic
field around the rotor coil.
 The rotor's magnetic field interacts with the magnetic field produced by
the stator. According to the principles of electromagnetism, this interaction
generates a force that causes the rotor to rotate.
 As long as the electrical current is supplied to the motor, the rotor will
continue to rotate, converting electrical energy into mechanical motion.
 The speed and torque of the motor can be controlled by adjusting the
voltage or current supplied to the motor windings.
The widely used rotary electric motors are AC motors, DC motors and stepping
motors.
Applications :
1. Motors are used in blenders, mixers, food processors, and other kitchen
appliances.
2. Used in electric cars, scooters, and bicycles.
3. Used in satellite positioning, solar array deployment, and various control
systems in space missions.

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 4. Utilized in devices like electric toothbrushes, DVD drives, hard disk
drives, and other consumer electronics.
5. Used in hydroelectric power plants to generate electricity from flowing
water.
6. Used in medical devices such as pumps, surgical tools, imaging machines,
and mobility aids.
7. Motors are also used in electric boats, ships, and underwater vehicles for
propulsion.

Stepping Motors :
 A stepping motor is a type of electric motor that divides a full rotation into
a number of equal steps.
 It converts electrical pulses into mechanical rotation.
 There are typically two main types of stepping motors: the permanent
magnet (PM) stepper motor and the hybrid stepper motor.
Principle :
The principle of operation of a stepping motor involves the interaction between
the electromagnetic fields in the motor's coils and a permanent magnet rotor.
 The stepper motor consists of a stator and a rotor.
 The rotor carries a set of permanent magnets, and a stator has the coils.

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  The shaft is connected to the rotor and extends outside the motor. It's the
part that transmits the mechanical output of the motor to the external
system or load.
 The coils on the stator are connected to the motor's control system through
wires.
Working:
 When a current flows through the coils in a particular sequence, it
generates electromagnetic fields that attract the teeth of the rotor's
permanent magnet.
 As the coils are energized in a sequence, the rotor aligns itself with the
changing magnetic fields, causing it to rotate in discrete steps.

 By energizing one or more of the stator phases, a magnetic field is

generated by the current flowing in the coil and the rotor aligns with this
field.
 By supplying different phases in sequence, the rotor can be rotated by a
specific amount to reach the desired final position.
 At the beginning, coil A is energized and the rotor is aligned with the
magnetic field it produces.
 When coil B is energized, the rotor rotates clockwise by 60° to align with
the new magnetic field and the same happens when coil C is energized.
 The stator teeth indicate the direction of the magnetic field generated
by the stator winding.
Applications :
1. Utilized in automotive systems for functions like controlling airflow in
HVAC systems, engine management systems.
2. Used in printers, scanners, disk drives, and various consumer electronics.

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 3. Used in scientific instruments, telescopes, and test equipment.
4. Utilized in textile machinery for controlling the movement of the fabric,
yarn winding, and other related processes.
5. Used in various medical devices like blood analysers, imaging systems,
and laboratory automation equipment.
6. Used in robotic systems and 3D printing.
7. Used in Computer Numerical Control (CNC) machines for cutting,
milling, engraving, and other machining processes.

Magnetic Valves:
 Magnetic valves, also known as solenoid valves, are electromechanical
devices used to control the flow of liquids or gases in a system.
 They consist of a coil of wire wound around a hollow core, called a
solenoid, which generates a magnetic field when an electric current passes
through it.

Solenoid
Spring

 And a movable plunger or armature inside the solenoid.

Principle of operation :
 When the solenoid is not energized (no current flowing through the coil),
the plunger or armature inside the solenoid is in a resting or default
position due to a spring or other mechanical means.
 In this state, the valve is closed, and no flow is permitted between the
inlet and outlet ports.
 When an electric current is applied to the coil, it generates a magnetic
field around the solenoid.

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  This magnetic field attracts the plunger or armature, causing it to move
against the spring force or other mechanical resistance.
 As the plunger moves, it opens a pathway for the fluid or gas to flow
from the inlet to the outlet ports.
 The valve remains open as long as the solenoid is energized and
generating the magnetic field.
 When the electrical current to the coil is cut off, the magnetic field
dissipates.
 The spring or mechanical force returns the plunger to its resting position,
thereby closing the valve and stopping the flow.
Applications :
1. Used in food processing and beverage production for controlling the flow
of liquids and gases and mixing of ingredients .
2. Employed in waste management systems, in sewage treatment plants and
waste disposal facilities.
3. Used in oil refineries and gas processing plants.
4. Employed in agricultural equipment and irrigation systems to control the
flow of water, fertilizers, and other agricultural chemicals.
5. Used in vehicles for controlling fuel flow in engines.
6. Used in anesthesia machines, analytical instruments, chromatography
systems, and liquid handling systems.
7. help in controlling the temperature and pressure in HVAC systems.

Magneto-strictive Actuators :
 A magnetostrictive actuator is a type of device that converts electrical
energy into mechanical motion or force using the magnetostrictive effect.
 The magnetostrictive effect refers to the property of certain materials to
change shape or dimensions when subjected to a magnetic field.
Principle :
Operate based on the principle of magneto-striction.
 These actuators typically consist of a magnetostrictive material, such as a
ferromagnetic alloy or a rare-earth element.
 This magnetostrictive material surrounded by a coil of wire that carries an
electrical current.

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  The coil serves as an electromagnet and generates the magnetic field
required to induce the magnetostrictive effect in the material.
Working :
 When an electrical current passes through the coil of wire, it generates a
magnetic field around the magnetostrictive material.
 The generated magnetic field causes the magnetostrictive material to
change shape or dimensions.
 This change occurs due to the alignment of magnetic domains within the
material, resulting in mechanical strain or deformation.
 As the magnetostrictive material changes its shape or length, it creates
mechanical movement.
 This movement can be harnessed and utilized depending on the design of
the actuator.
 By varying the intensity and direction of the electrical current passing
through the coil, the strength and orientation of the magnetic field can be
controlled.
 This control allows for good regulation of the mechanical movement or
force produced by the actuator.
Applications :
1. Used in applications, such as in robotics, machine tools, and optical
systems.

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 2. control the flow of fluids by precisely opening or closing valves or
regulating pump mechanisms.
3. Employed to counteract vibrations in various structures or machinery.
4. Utilized in systems where components need to adjust their shape or
position dynamically.
5. Used in mirrors, lenses, or other optical elements, ensuring accurate
alignment and focusing.
6. Used in ultrasonic applications, such as ultrasonic cleaning systems,
ultrasonic welding, and medical devices like ultrasonic surgical tools.
7. Also employed in sensors and transducers for measuring stress, strain,
pressure, and torque due to their ability to change dimensions in response
to magnetic fields.

Voice Call Actuators :

 A voice coil is a linear actuator, that moves a mass along a line.
 Voice coils were originally developed for loud speakers for the
conversion of electrical energy into sound wave through the use of a
diaphragm.
 Loud speakers were used to amplify or create a louder voice, thus the
name “voice coil” stuck.
 But, the voice coils designed to move larger masses in other applications
are called “voice coils.”

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  VCA are the simplest type of electric motors.
 Voice coils typically consist of :
• a non-magnetic centre pole,
• a cylindrical coil connected to the power supply,
• and an outer cylindrical permanent magnet.
Principle :
Operate by producing Lorentz forces.
Working :
 If a conductor (wire) carrying electric current is placed in a magnetic
field, a force is generated on the wire at right angles to both the direction
of current and magnetic flux.
 The Lorentz force is proportional to the product of the magnetic field and
the current, in a direction perpendicular to both of them
 Since the permanent magnet flux density field is fixed, the direction of
the linear displacement depends on the polarity of input current.
 This linear displacement of the diaphragm converts electric current into
sound energy.

Speaker Actuator :
A speaker actuator is a device that converts electrical signals into sound waves,
allowing us to hear audio.
Principle :
It operates on the principle of electromagnetism.
 When an electrical current passes through the voice coil, it creates a
magnetic field around the coil.
 The magnetic field generated by the voice coil interacts with the
permanent magnet. The interaction between these magnetic fields creates a
force, causing the voice coil (and the attached diaphragm/cone) to move
back and forth.
Construction :
 It consist of a permanent magnet, typically made of materials like ferrite,
placed at the core of the speaker assembly.
 The coil of wire attached to a diaphragm or cone.

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  The voice coil is the part that interacts with the magnetic field generated
by the magnet.
 The diaphragm or cone is a flexible material attached to the voice coil. It
moves back and forth to produce sound waves.

Working :
 An electrical audio signal, representing sound waves, is fed into the
speaker system. This signal varies in voltage and frequency according to
the sound being reproduced.
 As the electrical signal fluctuates, the current passing through the voice
coil changes accordingly.
 These changes in the current create a varying magnetic field around the
voice coil.
 The interaction between this changing magnetic field and the fixed
magnetic field of the permanent magnet causes the voice coil to move,
which, in turn, moves the attached diaphragm or cone.
 As the diaphragm or cone moves back and forth rapidly in response to the
electrical signal, it pushes and pulls on the air surrounding it.
 The movement of the diaphragm or cone creates compressions and rare
fractions in the air, generating sound waves that correspond to the
original audio signal.
 The frequency and amplitude of the electrical signal determine the
frequency and volume (loudness) of the produced sound.

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 Applications :
1. Used in stereo systems, home theatre setups, soundbars, headphones, and
earphones to reproduce music, movies, games, and other forms of
entertainment.
2. These are fundamental in telecommunication devices like smartphones,
landline phones, and communication systems.
3. These systems include speakers installed in car doors, dashboards,
headrests, and other parts of the vehicle to provide music, navigation
prompts, hands-free calling, and other audio functionalities.
4. Used in medical devices such as ultrasound machines, diagnostic
equipment, patient monitoring systems, and hearing aids.
5. Utilized for alarms, warning systems, signalling devices, and
communication systems to convey important information or alerts in
noisy environments in industries.
6. Smart speakers, virtual assistants, and other IoT devices often integrate
speaker actuators to provide voice prompts.
In essence, the term "speaker" generally encompasses the entire audio-
producing device, while the "speaker coil actuator" or "voice coil" is a specific
part or component within the speaker responsible for the conversion of
electrical energy into mechanical movement to create sound waves.

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