The artificial magnets are broadly divided into two main categories, namely : Electromagnets and Permanent magnets.
The electromagnets are magnets which work when electricity is applied to them and have no power of their own to act without electricity. Electromagnets are used in electric machines, generators and motors and are utilised in various industries. These are used for loading and unloading iron- equipment on ships, for magnentic cranes, and magnetic brakes in trams.
These are also used for separating iron scraps from other non-magnetic substances, as well as in amplifiers, armatures, bells, buzzers, circuit breakers, contact rectifiers, electronics, loud speakers, reed relays, radios, storage devices, tele-communications, transformers, etc. Electromagnets are also used by surgeons for extracting iron splinters from eyeballs and other parts of body.
Permanent magnets, as their name shows, remain permanently magnetised once they are charged with electric current and are used without electricity applied to them every time they are put to use. They do not lose their magnetism if they are properly preserved with keepers attached to them for many years. If not stocked with keepers, these may, however, lose some force of their magnetism, in due course of time—say in some years, but these can be remagnetised and the decreased force of their strength restored to them. If they are recharged every 5-6 years, they work for 100 years—even more.
Different Shapes, Sizes, Designs and Strength
The permanent magnets are made of different alloys and are of different shapes, sizes, and designs. These also have different magnetic strength. The strength of the magnets depends upon the proportion, quantity and quality of the different metallic alloys which are mixed for making them.
The most commonly manufactured and used shapes and designs of the permanent magnets are given here. The sizes differ according to the requirements and the purposes for which they are made.
1. Bar magnets.
2. Cylindrical solid magnet.
3. Cylindrical magnets with holes.
4. Ring magnets.
5. Rectangular magnets with holes and without holes.
6. Chuck magnets.
7. Arc or Crescent magnents.
8. U-shaped magnents.
9. Horse-shoe magnets.
10. Square magnets with holes or without holes.
11. Cup shape covered magnets.
The above shapes are but examples of the magnets which are generally produced by the manufacturing companies. In fact, permanent magnets can be made, with the alloys already in use, according to any given measurements or specifications to suit any purpose, in any shape, size, design or strength.
Generally permanent magnets are made for industrial, commercial and educational purposes but some of them can be utilised for medical purposes also. They are however of low strength and are not therefore of great use for the purpose of treatment. The author has, after his long experience, developed some special magnets for treatment of chronic diseases.
In some cases, the magnets are attached to the parts of machinery while in some other cases, they are encased in other metallic covers and are then used. When these are so encased, their magnetic power is increased manyfolds. One example of such magnets is the complete magnetic kit or unit prepared for loud speakers. Such magnetic packages are used in many other kinds of machinery also.