magnetic particle clutch
英[mæɡˈnetik ˈpɑ:tikl klʌtʃ]美[mæɡˈnɛtɪk ˈpɑrtɪkəl klʌtʃ]
A magnetic particle clutch is a special type of electromagnetic clutch which does not use friction plates. Instead, it uses a fine powder of magnetically susceptible material (typically stainless steel) to mechanically link an otherwise free wheeling disc attached to one shaft, to a rotor attached to the other shaft.