  We present a flexible set-up for determining the rheology of visco-elastic
materials which is based on the mechanical response of a magnet deposited at
the surface of a slab of material and excited electromagnetically. An
interferometric measurement of the magnet displacement allows one to reach an
excellent accuracy over a wide range of frequency. Except for the magnet, there
is no contact between the material under investigation and the apparatus. At
low frequency, inertial effects are negligible so that the mechanical response,
obtained through a lock-in amplifier, directly gives the material complex
modulus. At high frequency, damped waves are emitted and the rheology must be
extracted numerically from a theoretical model. To validate the design, the
instrument was used to measure the rheology of a test PDMS gel which presents
an almost perfect scale free response at high frequency.
