In this presentation you will know what is magnetism and types of magnetism like Para magnetism, diamagnetism and ferromagnetism with their examples also what are requirements of magnets with their types like permanent magnets , resistive and superconducting magnets with their advantage and disadvantages

1. MAGNETS AND ITS
TYPES
By – Bhavana Katiyar
PRN – 19040121027
B.Sc.MT 3rd YEAR (5th Semester)

2. MAGNETISM
The types of magnetism are defined in the following sections:
PARAMAGNETISM
1. They exhibit a weak attraction to an external magnetic
field.
2. Weakly magnetized in the same direction of magnetic
field.
3. Known as having a small positive magnetic
susceptibility.
4. An example of a paramagnetic substance is oxygen,
gandolium
FERROMAGNETIS
M
1. They have a large positive magnetic susceptibility
2. Are powerfully attracted to an external magnetic
field.
3. Such substances are used to make permanent
magnet.
4. An example of a ferromagnetic substance is iron.
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3. 1. They exhibit a weak repulsion to an external
magnetic field.
2. Known as having a small negative magnetic
susceptibility.
3. Diamagnetic elements have atoms in which all
electrons are evenly paired.
4. Examples of diamagnetic substances include
water and inert gasses
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DIMAGNETISM

4. MAGNETS
There are six main requirements, each of
which presents technological challenges:
1. The field strength (flux density) must be high.
2. The fringe field having a strength of 0.5 mT (5 G).
3. The field must be spatially homogenous to a very high degree.
4. The homogeneity must extend over a large spherical imaging volume
(40 cm).
5. The field must be temporally stable.
6. The weight and bulk of the magnet must be kept at a level that does
not pose any problems.
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5. TYPES OF MAGNETS
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6. 1. PERMANENT MAGNET
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1. Permanent magnets consist of ferromagnetic substances that have
magnetic susceptibility greater than 1.
2. Large blocks of ferrous metal are used to generate the magnetic field.
3. Such magnets are largely maintenance-free and consume no electric
power or cryogens (i.e., liquid helium and nitrogen)
4. MR magnets are made up of alnico, which is alloy of aluminium,
nickel and cobalt.

7. Advantages :
- It does not require electrical power or cryogenic cooling.
- Open design: children, obese and claustrophobic patients scanned with ease.
- Interventional and dynamic procedures are possible.
Disadvantage :
- Their low-field strength of about 0.15 - 0.4 t restrict their use to diagnostic imaging.
- Longer scan times.
- Sensitive to temperature changes.
- System cannot be switched off
- Limited field strength thus low SNR ratio.
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8. 2. RESISTIVE MAGNETS
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1. In a resistive magnet, an electrical current is passed through a loop of wire
and generates a magnetic field.
2. Resistive magnets are therefore also called electromagnets.
3. They are only magnetic as long as there is an electrical current flowing
through them.
4. Compared with permanent magnets, they achieve a higher field strength.
5. Used in horizontal or vertical field systems.

9. ADVANTAGES :
• They are lighter in weight than permanent magnets
• Good patient acceptance.
• No refrigerants necessary.
• Machines can be switched off.
DISADVANTAGES :
• The operational costs of the resistive magnet are quite high due to the large
quantities of power required to maintain the magnetic field.
• Limited field strength.
• Limited signal-to-noise ratio.
• scan times are longer.
• High electric power consumption.
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10. 3. SUPERCONDUCTING MAGNET
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1. Superconducting magnets are the ones most widely
used in MR machines at the present time.
2. Superconductive MRI magnets use a solenoid-shaped coil
made of alloys such as niobium/titanium or niobium/tin
surrounded by copper.
3. The direction of the main magnetic field runs horizontally like
that of the resistive system, from the head to the feet of the
magnet.
4. Liquid helium is the cryogen of choice for superconducting
magnets

11. ADVANTAGES :
• High signal-to-noise ratio and homogeneity.
• High magnetic field strengths with low power requirements are achievable.
• The operating costs are low.
• Advanced applications and optimum image quality are possible
DISADVANTAGE :
• There are high capital costs.
• Fringe fields are significant, so shielding is necessary.
• Tunnel design renders this unsuitable for large or claustrophobic patients.
• Interventional and dynamic studies are difficult.
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12. THANK YOU
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