Magnets are actually quite simple materials, but they have a profound yet distinctive impact on human technology and life. From the discovery of natural lodestone in ancient times to today’s super magnets, which have found applications in nearly all high-tech fields, they possess specific features that have given rise to many innovations throughout history.
The Science of Magnets
What constitutes a magnet is a magnetic field. The atomic structure of the said material decides this. In the case of ferromagnetic materials, spins and orbital angular momentum of the electrons align towards certain directions, creating tiny magnetic moments. As the tiny magnetic moments align within the materials, their net macroscopic magnetic field appears. A magnet has two poles: North and South, which can be considered endpoints of the magnetic field, and, hence, they follow the rule of “like poles repel, opposite poles attract.
Magnets are usually characterized by the measure of their magnetic flux density. Their operation also relies upon the material’s coercivity and remanence, which in turn reflect how the magnet performs in certain applications.
The History and Cultural Significance of Magnets
The history of magnets goes back to ancient China and Greece in the 6th century BC. It was also discovered by humans in the shape of natural magnetite. The ancient Chinese classic “Guanzi” records guiding the compass with magnets, while the Greek philosopher Thales of Miletus described the remarkable phenomenon of magnets attracting iron. Natural magnets were used by early sailors to construct the earliest compasses, which laid the basis for navigation and geographical exploration.
In the Middle Ages, the understanding of magnets was broadened to encompass their primitive applications in navigation as well as their mysterious signs. After the opening of electromagnetism in the 19th century, Michael Faraday and James Clerk Maxwell put forward hypotheses concerning the very nature of the magnetic fields; thus, they were the ones to start the modern magnetic technology.
Types and Properties of Magnets
The two broad classifications of magnets, according to the source of magnetism and the purpose of their use, are permanent magnets and soft magnets. Modern magnets also use different materials and shapes to meet the requirements in different fields.
Magnet Shape and Design
The shape of a magnet directly influences its magnetic field distribution and application effectiveness. Common magnet shapes include:
Bar Magnets: A classic magnet shape, commonly used in educational experiments and basic industrial applications.
Disc and Ring Magnets: Ring magnets are used in speakers and microphones due to their uniform magnetic field distribution.
Curved magnets: Designed specifically for rotors in electric motors and generators, their curved shape optimizes the matching of the magnetic field to the mechanical structure.
Square magnets: Commonly used in industrial equipment requiring a strong and concentrated magnetic field.
Neodymium (NdFeB) Magnets
Neodymium magnets, also known as “super magnets,” are the strongest permanent magnets on Earth, and they have widely diverse applications today. In electroacoustics, they are used to power high-fidelity loudspeakers and headphones. They are very relevant in electric vehicle motors for permanent magnet rotor-type designs, thus achieving high energy conversion efficiency. Other common applications include aerospace navigation systems, computer hard disks, and medical devices, such as MRI machines, in which high strength directly relates to accuracy and reliability.
Ferrite Magnets
They are relatively inexpensive, not prone to corrosion, and play an important role in many devices. Their applications extend from electricity meters and generators, where they serve to provide a uniform field for the magnetic field, to telephones and loudspeakers for sound production, and even to microwave and radar equipment used in signal processing. They form the basis of modern audio and data storage technology in the magnetic cores of recorders and pickups.
Samarium Cobalt (SmCo) Magnets
Soft magnets: Soft magnets are fabricated from soft iron or silicon steel and show magnetism only if an external current or magnetic field is applied. The magnetism vanishes quite fast when the supplying current is turned off. Electromagnets are extensively utilized in machines like transformers, electric bells, and electromagnetic relays.
Alnico Magnets
Alnico magnets demonstrate good temperature stability and resistance to corrosion. They are widely applied in motors and sensor devices, where reliable performance in variable temperature conditions is needed. It is also possible to use them in medicine. This is further evidence of such a diverse application of alnico magnets in the field of acoustics.
