anoop seminar ppt

7/27/2019 Anoop Seminar Ppt

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PRESENTED BY

ANOOP ANTONY

ROLL NO.:-10


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Differ from other detectors.

Hall sensors, AMR sensors, GMR sensors, SDT

sensors, Fluxgate sensors, SQUID magnetometers,Resonant magnetometers, Induction magnetometers,Magneto-electric sensors, Lorentz force magneticsensors.


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Made of high permeability, low power loss

materials.

They conduct the magnetic field more efficiently.

Disadvantages:- remenance, nonlinearity, dangerof saturation, and temperature dependence.

They are integrated into the package of some Hall

sensors and magneto resistors.

Also be used to deflect the sensing direction.


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Most important of magnetic sensors.

VH=IB


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Sensitivity of silicon sensors is typically 1 mV/mTfor a 1 mA current.

Hall sensors made using silicon-on-insulator (SOI)

technologynoise level 1T/Hz@1Hz.

Two-dimensional quantum-well multilayerheterostructures based on GaAsnoise level100nT/Hz@1Hz.

By using integrated CMOS Hall sensor noise level

can be 300nT/Hz@1Hz.


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ADVANTAGES

Immune to dust, dirt, mud, and water.

Non-contacting current sensor.

No additional resistance needed.

DISADVANTAGES

Magnetic flux from the surroundings may effect.Hall voltage is often on the order of millivolts.


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APPLICATIONS

Anti-lock braking systems

Proximity switching

Positioning

Speed detector

Current sensing


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AMR-Anisotropic magnetoresistive

Use Permalloy to make.

Commercially available AMR sensors use a

barber pole structure.Aluminum stripes sputtered on permalloy strips

deflect the direction of the current by 45.

Four meander-shaped elements are connected into

a Wheatstone bridge.Noise level of 200pT/Hz@1Hz.


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FlippingThe proper function of an AMR sensor is based on

the single domain state of the magnetic layer.

A good technique for this is periodical flipping.


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Magnetic Feedback For improving the accuracy of any magnetic

sensor is feedback compensation of the measured

field.

Modern AMR sensors have an integrated flatfeedback coil.

Crossfield Error

AMR sensors suffer from cross-field error.

V=2IRHy/(Hx+Ho)

R-maximum resistance change

I-bridgecurrent


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USES

Automotive wheel speed & crank shaft measurement

Compass navigation

Vehicle detection

Current sensing

Measure linear and angular position & displacement

in earths magnetic field


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GMR- Giant Magnetoresistive


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USES

Linear or rotary motion and speed detection

Linear or rotary position sensing

Magnetic field sensing

Current sensing

Angular sensing


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ADVATAGES

High spatial resolution

Very small

Require little power

Easily combined with other electronics

DISADVANTAGESHigh coercivity

Low linearity


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Measure DC and low-frequency AC fields.

Operation is based on modulation of thepermeability of the soft magnetic core.

Most fluxgates have a ring core and the same

direction of the excitation and measured fields.

Vacquier-type fluxgate, has two straight cores and

solenoidal windings.

standard method for fluxgate signal processing is

phase-sensitive detection of the second harmoniccomponent of the output voltage.

The best fluxgate magnetometers use Compact

Spherical Coil (CSC).


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Miniature Fluxgates

Common fluxgate sensors are quite large.

Three basic types of miniature fluxgate are:

1) CMOS-based devices with flat coils;

2) sensors with microfabricated solenoids;

3) PCB-based devices with solenoids


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Orthogonal Fluxgates

Main advantage of an orthogonal fluxgate is that it

needs no excitation coil.

Use of phase-sensitive detection of the outputvoltage gives a clear advantage for the

performance of the sensor.

Disadvantage-necessary excitation current is high.

Fundamental mode-uses DC biased excitation


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APPLICATIONS

Typical Flux Gate Sensor Applications include:

Proximity Sensing

Magnetic Field Measurement (Navigation,Geomagnetics)

Speed & Position Sensing


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SQUID- Superconducting Quantum Interference

Device


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Enough to measure the magnetic fields in living

organisms.

DC SQUIDS are less noisy than the RF SQUIDS.

SQUID measures only field changes.


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Proton magnetometers, Overhauser magnetometersand optically pumped magnetometers.

Very stable scalar devices & measure the absolute

field value.

Optical magnetometers are based on Zeemansplitting.

Proton magnetometers measure the precession

frequency of a proton or electron.

Any scalar magnetometer can be made vectorial byadding a rotating bias field and demodulating the

output


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Based on the Faraday induction law. Induction magnetometers naturally cannot measure

dc fields.

They have noise level of 2pT/Hz@1Hz.

Size is higher.


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GMI- Giant Magnetoindutive

GMI effect is based on the field-dependent change

of the penetration depth.

Temperature dependent

Gives low sensitivityCharacteristics are nonlinear and unipolar

APPLICATIONS

Compass modules for some mobile phones

Detecting microbeads


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A sandwich made from magnetostrictive and

piezoelectric materials.

The measured field causes strain in the

magnetostrictive layer.


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Lorentz force is proportional to the measured field

and the measuring current.

The motion is made periodic by applying an AC

measuring current.ADVATAGES

High linearity

Possibility to change their range widely


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There is a tradeoff between the size of a sensor and

its parameters.

In many applications, such as detection of

magnetic microbeads, micromagnetic scanningsensor size is an issue.

Large detection distance cannot be avoided,

parameters such as noise (detectivity) become

more important.


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