Transcript
1
MAGNETOMETERPRESENTEDBY
Ijaz Ul HaqM Bilal younisMoazam Ali
2
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.
3
OUTLINE Magnetometer data: what are we
measuring? Ground magnetic signatures of
Earth’s magnetic field Ring currents Auroral currents
4
MAGNETIC FIELDMEASUREMENT
magnetic field sensors can be divided into two components
I. vector componentII. Scalar magnitude types.
5
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.
7
MAGNETIC FIELD SENSOR
8
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.
9
Magnets produce magnetic fields. A magnetic field is a vector quantity with both magnitude and direction properties.
10
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
11
Magnetic fields are also produced by electric currents
12
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.
13
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
14
TYPES OF MAGNETOMETER There are two basic types of
magnetometer measurement1. Vector magnetometers 2. scalar magnetometers
15
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.
16
VECTOR MAGNETOMETERS Low-Field Vector Magnetometers
The Induction Coil Magnetometer
The Fluxgate Magnetomete
The SQUID Magnetometer
17
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.
18
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
19
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
20
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.
21
(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
22
THE FLUXGATE
The heart of the magnetometer is the fluxgate. It is the transducer that converts a magnetic field into an electric voltage
23
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
24
SCALAR MAGNETOMETERSThe two most widely used scalar magnetometers are the
1. proton precession2. optically pumped magnetometer
25
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
26
OUTLINE Magnetometer data: what are we
measuring? Ground magnetic signatures of
Earth’s magnetic field Ring currents Auroral currents
27
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
28
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
29
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
30
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.
31
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
32
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.
33
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]
34
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)
35
SOME IMAGES OF EARTH MAGNETIC FIELD
36
37
38
top related