A possible application of ferrofluid composites-a modulator for the millimetre wavelength range

Modulation of 3-mm-wavelength electromagnetic radiation has been achieved at low frequencies (2-60 Hz) using ferrofluid composites. Theoretical calculations have shown that it should be possible to modulate at higher frequencies under optimum conditions of ferrofluid viscosity, magnetization, and applied magnetic field. Some preliminary experimental results are presented which show that at low frequencies the modulation amplitude of a sub-50- mu m-thick composite is as high as 10% of a mechanical chopper. An estimation of the feasible upper-frequency limit is made.