File:RabinowJacob 049.jpg

Close-up of filling hole in the upper driven plate of the first practical model of the NBS magnetic fluid clutch showing the visible change in the fluid, demagnetized and magnetized. In the view at left, the driving plate turns freely in the demagnetized mixture of powdered iron and oil between the upper and lower driven plates. When the clutch is energized, right, the magnetic flux acts on the iron powder suspended in the oil, and the mixture forms a virutally solid mass. When the driving plate is revolved, the shearing action on the iron-oil mixture is readily visible. By varying the magnetic flux in the fluid any degree of slippage between the driving and driven plates may be obtained. This constitutes the basic principle of the new clutch which, because of its sensitivity and apparently negligible wear, appears to offer many advantages for a wide variety of clutch applications.

Jacob Rabinow invented the Magnetic Particle Clutch in 1947 during his work on ordnance at the National Bureau of Standards. The particle clutch used a mixture of light lubricating oil and powdered carbonyl iron inside a chamber connecting two free spinning plates. When an electromagnet attached to the chamber was energized, the iron particles would magnetize and attract each other, producing an almost solid mass, which locked the plates together. Controlling the magnetic flux would control the amount of torque between the plates. Because Rabinow invented the Magnetic Particle Clutch as part of his work at the National Bureau of Standards, the United States Government owned the U.S. patent. However, in partnership with his brother Joseph, Rabinow did file for patents in 22 foreign countries. Due of the simple design, precise torque control, smooth operation, and long life, the device found wide application. It was used in Renault and Subaru automobiles in Europe and Japan, in airplane controls, and in the disc file of the IBM RAMAC computer.