The ARMA(autoregressive and moving-average)model provides an effective means for precise representation of the production process of speech signals, especially the nasals and fricative consonants. A stable and efficient estimation of ARMA parameters was accomplished directly from the speech signal using the SEARMA(simultaneous estimation of ARMA parameters)method proposed by the authors. In order to trace the temporal variation of the poles and zeros with a high accuracy, a method was also proposed for adaptive control of the location and the length of an analysis interval. The paper describes a theoretical relationship among the location and the length of an analysis interval and the convergence of estimated parameters, for stationary and non-stationary speech signals. The effects of adaptive control of an analysis interval are also investigated by analysis of both synthetic and natural speech signals.
In this paper, a novel tomographic system for imaging the nonlinear parameter B/A which is closely related to the detailed properties of tissue is described. In our system, relatively high intensity scanned low frequency ultrasonic pumping waves are used to illuminate the object under observation so that sound pressure over the object field is modulated sinusoidally. A low intensity high frequency probe beam is propagated perpendicular to the pumping waves. The phase of the probing wave is modulated in proportion to the integral of the product of nonlinear parameter B/A and the pressure of pumping waves, which varies sinusoidally along the probe beam. This phase change provides a Fourier component of the distribution of the nonlinear parameter B/A for the spatial frequency corresponding to the wave length of the pumping wave. By changing the frequency of the pumping waves, a set of spatial Fourier coefficients of the distribution of the nonlinear parameter B/A is obtained. Inverse operation gives the image along the probe beam. If the probe beam is scanned mechanically, the entire cross-section image is obtained. Several images of the nonlinear parameter of biological objects are obtained. Experimental results show the usefulness of this method.
An ultrasonic equipment with magnetostrictive ferrite vibrator can supply an increased ultrasonic output power with increasing bonding-strength between ferrite vibrator and its water tank or its metallic horn, etc. For this purpose, a novel solder-jointing method is developed for a ferrite vibrator. In this method, a ferrite surface is reduced to a metallic state before soldering, using a titanium alloy power, so that soldering on it can be easily done. The bonding-strengh of this method for ferrite-to-ferrite boding is compared with that of adhering method with an epoxy-resin, using acousic vibration methods. It is found that the former is more thermally stable and more than twice as strong as the latter. In an ultrasonic radiation test into water, a ferrite vibrator solder-jointed by this method is found to work stably for 24 hours at 15 W/cm^2 corresponding to five times of power rating for commercial ferrite vibrators. These results indicate that this method can give far stronger bonding-strength than the usual epoxy-resin adhering method dose.