NONLINEAR RELAXATION SPECTROSCOPY USING A WHITE NOISE INPUT

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As a response to external force easily becomes nonlinear one in soft materials such as polymers and liquid crystal, the nonlinear relaxation spectroscopy is an useful method to investigate the dynamics of these materials. We have already developed the nonlinear dielectric relaxation spectroscopy in a frequency domain using a sinusoidal electric field as an input. But we have to repeat measurements to obtain a whole spectrum changing frequency and amplitude of an input signal.In this rresearch, we developed the measurement system of linear and nonlinear relaxation spectra using a pseudo white noise signal as an input, which is based on the nonlinear response theory of R.Wiener. We can obtain a whole nonlinear spectrum in a wide frequency range at the same time by this system. We applied this system to the nonlinear circuit made of an ideal diode and a low pass filter, and to a ferroelectric liquid crystal cell. We succeeded to measure the linear and nonlinear spectra of the nonlinear circuit in a short time. But we cannot obtain adequate nonlinear spectra for the liquid crystal sample due to the lack of the resolution of A/D converter in the FFT analyzer we used.We also developed the nonlinear electrooptical relaxation spectroscopy and applied this method to ferroelectric and antiferroelectric liquid crystals. We succeeded to obtain new information concerning to the dynamics of these material.In conclusion, we developed new nonlinear relaxation spectroscopies and showed the usefulness of these methods ini the study of dynamics of soft materials.