A new high‐frequency rheometer based on the torsional waveguide technique

A new high‐frequency rheometer for measuring mechanical properties of fluids with viscosities as low as 0.5 mPa s is described. The operation is based on the torsional waveguide technique. The torsional motion is generated by a bismuth and germanium oxide Bi12GeO20 piezoelectric crystal. A specific numerical processing is developed for rapid computation of acoustic attenuation and phase retardation. Dynamic viscosity of several Newtonian liquids is determined at 98 kHz. The accuracy of acoustic measurements is better than 1%, and the resolution in terms of the Maxwell relaxation time is 2×10−8 s. The apparatus is used successfully for measuring the viscoelastic moduli G’ and G‘ of polystyrene‐isobutylmethylketone solutions.