High sensitivity Fourier-transform rheology

The application of oscillatory shear strain leads, in the nonlinear regime, to the appearance of higher harmonic contributions in the shear stress res ponse. These contributions can be analyzed as spectra in Fourier space with respect to their frequencies, amplitudes and phase angles. In this article , we present several theoretical and practical aspects of measuring Fourier rheology spectra with high sensitivity. Using the hardware of a convention al rheometer, Fourier rheology spectra with a signal-to-noise ratio of abou t 18,000. 1 for a single acquisition were obtained. This allowed the observ ation of harmonics up to the 21st harmonic. Signal averaging can further in crease the sensitivity.