In general the greater the magnetic
flux, the greater the efficiency of the shaker. Al-Ni-Co magnets
(an alloy of aluminum, nickel, and cobalt) became available in the
early 1930s and have been used in electrodynamic shakers until
the 1980s. In the mid ’80s rare-earth magnets became available,
and almost all modern shaker designs benefit from neodymium
magnets (based on an alloy of the rare earth metal neodymium,
iron, and boron).