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MAGNETOMETERPRESENTEDBY

Ijaz Ul HaqM Bilal younisMoazam Ali

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MAGNETOMETER Definition

Magnetometer are measurement instruments used for two general purposes: to measure the magnetization of a magnetic material like a ferromagnet, or to measure the strength and, in some cases, the direction of the magnetic field at a point in space.

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OUTLINE Magnetometer data: what are we

measuring? Ground magnetic signatures of

Earth’s magnetic field Ring currents Auroral currents

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MAGNETIC FIELDMEASUREMENT

magnetic field sensors can be divided into two components

I. vector componentII. Scalar magnitude types.

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MAGNETIC FIELD FUNDAMENTALS The vector types can be further divided into

sensors that are used to measure low fields (<1 mT) and high fields (>1 mT).

Instruments that measure low fields are commonly called magnetometers

High-field instruments are usually called gaussmeters.

Magnetic field sensors are divided into two categories based on their field strengths and measurement

Range: magnetometers measure low fields and gaussmeters measure high fields.

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MAGNETIC FIELD SENSOR

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MAGNETIC FIELD FUNDAMENTALS An understanding of the nature of

magnetic fields is necessary in order to understand the techniques used for measuring magnetic field strength. The most familiar source of a magnetic field is the bar magnet.

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Magnets produce magnetic fields. A magnetic field is a vector quantity with both magnitude and direction properties.

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The field it produces is shown in Figure. Magnetic field is a vector quantity; that is, it has both a magnitude and a direction.The field of a bar magnet or any other magnetized object, when measured at a distance much greater than its longest dimension, is described by EquationH = 3 ( m × ar ) ar – m / r³

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Magnetic fields are also produced by electric currents

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MAGNETOMETER Definition

Magnetometer are measurement instruments used for two general purposes: to measure the magnetization of a magnetic material like a ferromagnet, or to measure the strength and, in some cases, the direction of the magnetic field at a point in space.

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OBJECTIVES Magnetometers are widely used for

measuring the Earth's magnetic field and in geophysical surveys to detect magnetic anomalies of various types

They are also used militarily to detect submarines

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TYPES OF MAGNETOMETER There are two basic types of

magnetometer measurement1. Vector magnetometers 2. scalar magnetometers 

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1. VECTOR MAGNETOMETERS  Vector magnetometers measure the

vector components of a magnetic field measure the component of the

magnetic field in a particular direction, relative to the spatial orientation of the device.

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VECTOR MAGNETOMETERS Low-Field Vector Magnetometers

The Induction Coil Magnetometer

The Fluxgate Magnetomete

The SQUID Magnetometer

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THE INDUCTION COIL MAGNETOMETER

The induction or search coil, which is one of the simplest magnetic field sensing devices, is based on Faraday’s law.

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This law states that if a loop of wire is subjected to a changing magnetic flux, f, through the area enclosed by the loop, then a voltage will be induced in the loop that is proportional to the rate of change of the flux:

e (t )= - dɸ / dt

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Induction or search coil sensors consist of a loop of wire (or a solenoid), which may or may not surround a ferromagnetic core. (a) Air core loop antenna; (b) solenoid induction coil antenna with ferromagnetic core

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THE FLUXGATE MAGNETOMETER The fluxgate magnetometer has been

and is the workhorse of magnetic field strength instruments both on Earth and in space. It is rugged, reliable, physically small, and requires very little power to operate.

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(a) and ring core (b) fluxgate sensors, the excitation field is at right

angles to the signal winding axis. This configuration minimizes coupling between the excitation field and the signal winding

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THE FLUXGATE

The heart of the magnetometer is the fluxgate. It is the transducer that converts a magnetic field into an electric voltage

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2. SCALAR MAGNETOMETERS  Total field magnetometers or scalar

magnetometers measure the magnitude of the vector magnetic field

measures the total strength of the magnetic field they are subject to

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SCALAR MAGNETOMETERSThe two most widely used scalar magnetometers are the

1. proton precession2. optically pumped magnetometer

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PROTON PRECESSION

They have a limited magnetic field magnitude measurement range: typically 20 mT to 100 mT. And they have limitations with respect to the orientation of the magnetic field vector relative to the sensor element

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OUTLINE Magnetometer data: what are we

measuring? Ground magnetic signatures of

Earth’s magnetic field Ring currents Auroral currents

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EARTH’S MAGNETIC FIELDS The Earth's magnetic field is both expansive

and complicated. It is generated by electric currents that are deep within the Earth and high above the surface. All of these currents contribute to the total geomagnetic field

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CONTINUE In some ways, one can consider the Earth's

magnetic field, measured at a particular instance and at a particular location, to be the superposition of symptoms of a myriad of physical processes occurring everywhere else in the world.

Magnetic fields are vectors: they have a strength (magnitude) and a direction just like velocity

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MAGNETIC FIELD STRENGTH

The strength of a magnetic field is the magnetic flux density, B.

The units of magnetic flux density is the Tesla or the Gauss

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1 Tesla (T) = 104 Gauss (G)

The most powerful magnets in the world are

superconducting electromagnets. These

magnets have magnetic fields of around 20 T.

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CONTIUE • Earth’s magnetic field is

0.000 052T = 52,000 nanotesla (nT) = 0.5 gauss (G)

• 1 nanotesla = 10-9 T

• Changes in Earth’s magnetic field are typically 5-100 nT

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TESLA The applied magnetic field will be one

tesla when one coulumb charge enters in it perpendicularly with velocity 1 m/s and experience 1N magnetic force.

Also Wb/m2 is the unit of magnetic field.

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HOW MAGNETOMETERS WORK

Magnetometer measures the magnetic field it is applied to. The magnetometer outputs three magnitudes: X, Y and Z. From these three values you can construct the magnetic field vector (magnitude and direction) B= [X, Y, Z]

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COORDINATE SYSTEMS Because magnetic fields have a

direction, in order to communicate about magnetic fields, we need to define a coordinate system.

Three main coordinate systems are used for magnetometer data: – Geographic (XYZ)– Geomagnetic (XYZ or HDZ -

BEWARE!!)– Compass-type (HDZ)

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SOME IMAGES OF EARTH MAGNETIC FIELD

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