In the twentieth century, materials scientists and engineers developed stronger and stronger permanent magnets – alnico magnets in the 1930s, ferrite (ceramic) magnets in the 1950s, and rare-Earth magnets in the 1970s and 1980s. The latest rare-Earth magnets, neodymium-iron-boron, are over a hundred times more powerful than the steel magnets available in the nineteenth century. Both ferrite magnets and the latest “neo” magnets have had a tremendous impact on modern technology, but they have also rejuvenated interest in the use of permanent magnets for magnetic therapy. Unlike earlier magnetic materials such as steel and alnico, the new magnets have great resistance to demagnetization. While earlier magnets had to be long to avoid being demagnetized by the internal fields produced by the poles at the ends, new magnets can be mounted in a variety of thin products that can be applied to the body with the magnetic field emanating from the surface.
Magnetic products are typically of two kinds: those whose north and south poles alternate, and those with only one pole facing out. Many magnetic therapy products have alternating arrays of north and south poles facing the patient. Some have detailed explanations of why a circular array of poles is optimal, while others offer poles in checkerboard or triangular arrays. Nikken, the Japan-based firm that has used a multilevel marketing scheme to expand from an annual business in the US of $3 million in 1989 to $210 million in 2010, primarily offers products with alternating poles.1
The difference between such multipolar and unipolar magnetic devices is the “reach” of the magnetic field. The field from even unipolar magnets decreases very rapidly with increasing distance from the magnet, but the field from multipolar magnets decreases much more rapidly. If multipolar magnets really have any effects on the human body, they will be limited to depths of penetration of only a few millimeters.2