Switchable Permanent Magnets

Get a grip…or don’t

Permanent magnets are among the most useful components of our technological age. They provide a constant, reliable source of energy for many magnetic circuits without the need for external electric currents.

Advances in metallurgy and magnetic technology in the last two decades have resulted in the availability of magnetic materials with unprecedented power — most notably “Rare Earth” magnets, some of which exhibited holding strength more than 100 times their own weight. These breakthroughs have remained virtually unnoticed by the wider public, mainly because these new, superior rare earth magnets generally were used as replacements for magnetic materials in existing products. The rare earth magnets perform the same tasks, only with reduced size, in modified products. New products and markets have not emerged because of the major drawback of permanent magnets: Their energy output is fixed and therefore they cannot be employed if a variation in the magnetic field strength is required.

Previous attempts to overcome this shortcoming of permanent magnets resulted in bulky, complicated-to-manufacture or uneconomical designs. The early use of switchable permanent magnets was limited to very special applications, as they were unsuitable for general purposes and therefore never attracted much attention. Thus, until recently, the common choices for most applications remained electromagnets, except where the limit of all electrical systems came into play—that is, where electricity was not constantly available, or where access was too complex, costly or unsafe.

The Magswitch, from the company of the same name in Port Macquarie, NSW, Australia, is a device designed for integration in many applications hitherto reserved to electromagnets: hydraulic, pneumatic or other means of operation. The company claims that the Magswitch can hold in excess of 250 times its own weight. According to their literature, one typical version weighs less than 200 grams but can hold over 50 kilograms (though holding performance likely will be reduced if parts being held or lifted are uneven, odd-shaped or varied in surface condition).

Besides being a viable replacement for electromagnets in some applications, Magswitch solves some of the mechanical and cost problems associated with earlier, bulky attempts to broaden the use of permanent magnets. Its simple design uses few parts and a basic switching mechanism to activate the magnetic power of the unit. The device comprises two diametrically magnetized cylindrical-shaped magnets encased in a hard magnetic housing. One of the magnets is fixed in position; the other is capable of rotating. A moveable handle or lever is attached to the housing, in order to rotate the free magnet 180 degrees. This aligns the polar aspects of both magnets and activates the full magnetic attraction of the unit.

This device appears to be well-suited for applications requiring temporary but reliable joining, such as holding welding joints, building joists, signs, wall hangers, clamps and adhesives. Latches and locks are other potential applications, from simple enclosure doors to complex locking mechanisms. Still other uses include magnetic sensors, switches and solenoids. The product offers the benefits of low cost, lower part counts, variable strength and direction of magnetic attraction, durability, and temperature- and weather-tolerance. The intrinsic safety and independence from any external power source allows the Magswitch in many cases to replace existing electromagnets in accordance with the need to develop ecological sustainability and improved performance.

—RM