The usefulness of ultrasonics as a diagnostic medical tool is now an established fact. There have been, however, some limitations on spatial resolution, that is, fine azimuthal resolution can be obtained in sacrifice of target range, consequently some kind of compromise between them has been carried out in the design of ultrasonic transducers. In order to overcome this difficulty, electronic focusing of the ultrasonic beam has been introduced either on transmission or on reception. When focusing on reception, a dynamic focusing arrangement could be implemented to achieve virtually perfect focus at each range in turn with only a single transmitted pulse. The purpose of this paper is to analyze the directional pattern of dynamic focusing transducers (abbreviated by DFT) and to give some instructions for the design of DFT. The outline of the DFT analyzed in this paper is shown in Fig. 1, where an annular array of ultrasonic transducers is used to receive the reflected ultrasonic signals and an element of the annular array is used to transmit the ultrasonic pulses. The radii of the annular transducers are given by α√<i> (i=1, 2, …, n), where α is a constant and i is the number labeled to the transducer and n is the number of transducers. The received signals from the transducers are passed through the phase shifters so as to obtain coincidence of the phases of the received signals and the sum of the phase-shifted signals is used as the output of the DFT. The axial intensity of the DFT is shown in Fig. 2, where β-kα^2/4r_0 is used as a parameter (k:wavenumber of ultrasonic waves, r_0:radius of curvature of the DFT), and the target range (taken as the width between -20 dB points) of the curves in Fig. 2 is arranged in Fig. 3 (b), where the maximum target range is obtained in case of β=1. 5 if the total area of the DFT is kept constant. The half power width of the DFT is shown in Fig. 4, where the abscissa shows (n+2i_T-1)^<-1/2> (i_T is the number of the transducer used as the transmitter, 1&le;i_T&le;n), consequently a smaller half width is obtained if a larger valve of i_T is adopted. The sidelobe level of the DFT is shown in Fig. 5, where the parameter u=kα^2 (1/r-1/r_0)/2 is shown along the abscissa, and as can seen from these figures, it is possible to reduce the sidelobe level by properly choosing the number of the transmitting transducer. The influence of quantization on axial intensity, half power width, and sidelobe level is shown in Figs. 6〜8 respectively. In these figures, m shows the quantized number of the shifted phase and &lrtri;u shows the interval between the switching of the phase shifters and the maximum deviation of the directional characteristics due to the quantization is plotted in these figures.

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This paper describes a method of male to female voice conversation as an application of speech analysis and synthesis by liner predication. The method was demonstrated in the open house of the NHK Technical Research Lab's in 1975, where a synthesized female voice was presented, the original of which was a sentence from a weather forecast announcement spoken by a male announcer. The average format frequencies of female voices are approximately 1. 2 times as high as those of male voice as shown in Fig. 2, and the average bandwidths of the first format of female voices is approximately 1. 3 times as wide as that of male voices as shown in Fig. 3. In this experiment, both the pole frequencies and the bandwidths of the input speech spectra were multiplied by 1. 3 by simply setting the sampling frequency of the D/A converter at the value of 1. 3 times as high as that of the A/D converter. It is known that the pitch frequency of female voices is approximately twice as high as that of male voices, and that the optimal pitch frequency region exists corresponding to format frequencies. Therefore, we tried several multiplying factors for pitch frequencies between 1. 7 and 2. 5 and decided for 2. 1 as the best by an informal listening test. To soften the shrillness of the synthesized voice, we designed a filter to compensate for the difference of the glottal wave forms between female voice and male voice, the input-output relation of which is given by (9). In a standard case, in which the shorter of the rising time and the falling time of the glottal wave form of female voices is twice as long as that of male voice, the difference of the glottal wave forms can be compensated by a filter with the frequency characteristics shown in Fig. 4. The spectra of the vowel segments of the male voice used in this experiment have dips around 2 kHz, which corresponds to the rising time (or falling time) of 0. 5 ms. The optimum value, determined by an informal listening test, for the constant τ of the compensating filter appearing in (10) was also approximately 0. 5 ms. The synthesized voice has excessive amplitude in one part as shown in Fig. 7. To remove this deficiency, a saturating operation was performed on the intensity of the driving signal. By this method we obtained an almost satisfactory female voice without any different processing for each phoneme.

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In this report, we took notice of the erosion effects of an ultrasonic cavitation produced in the gap between parallel planes, i. e. between the test piece and the acoustic irradiation surface of step horn, and examined the effects of the distance of the planes and the static pressure. Cavitation effects are affected by the excitation mode of an ultrasonic transducer, i. e. ultrasonic burst pulse excitation mode and continuous one. Therefore, in this report the experimental results using the ultrasonic burst pulse are also shown. Ferrite transducers (28 kHz) were attached to a 1/2 wavelength-resonant step horn of stainless steel, and excited by an oscillator or a function generator and a 500-watts-type broad band power amplifier. As a test piece of this experiment we used a circular plate of aluminum, whose thickness is 1 mm and diameter is 30 mm. Temperature of this experiment was held at 15±1℃ by a cooling coil that was set in the pressure vessel. Using the continuous irradiation of ultrasound, we held first the hap between the test piece and the horn tip to be constant, and examined the change of erosion weight loss under elevated pressure (Fig. 3). If the gap is from 0. 44 mm to 2. 63 mm, the erosion weight loss has a sharp maximum at an elevated pressure of several atmospheres. If the gap is above 4. 38 mm, the weight loss has also some maximum, but its value is not so large. In case the gap was kept constant at 0. 44 mm, we examined how the peak values of erosion weight loss change with the ultrasonic irradiation time (Fig. 4), and ascertained that the peak values appear under pressure of several atmospheres regardless of the irradiation time. There are few reports on the cavitation erosion under elevated pressure. Sirotyuk, using a 560 kHz transducer, and Angona, using a 30 kHz transducer, examined the erosion weight loss of some test pieces set in an acoustic focal region, and showed that the erosion weight loss has its maximum at some elevated pressure. Our results are similar to theirs in spite of different experimental conditions. Experiment on the cavitation erosion using some ultrasonic burst pulses was only made by Plesset, who showed that he could get more erosion weight loss than by the continuous radiation method under some conditions. Using a function generator and a broad band power amplifier, we obtained arbitrary ultrasonic burst pulses. The gap between the test piece and the irradiated surface of the horn was held 0. 44 mm wide. In this experiment we adjusted the irradiation time so as to the net irradiation time to be constant. When the irradiation time is kept constant at 5 minutes, the erosion weight loss of the test piece gets its maximum under pressure of several atmospheres, and by elevating the static pressure the weight loss gradually decreases to zero (Fig. 7). When we use the ultrasonic burst pulse irradiation, the erosion weight loss is nearly the same as in the continuous one under low pressure, but becomes larger than the continuous irradiation under high pressures. In case the rest time and elevated pressure are constant of 20 msec and 4 kg/cm^2, respectively, changing the time of burst pulse we made an experiment of the erosion weight loss (Fig. 8). We have got the results that the erosion weight loss gets its maximum when the ratio of burst time and rest time of the pulse is 1/2, and by decreasing the ratio, the erosion weight loss diminishes rapidly, and by increasing the ratio, it approaches to a half of its maximum value.

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Almost of all the sounds around us in everyday life -speech, musical sounds, surrounding noises and others- suffer ever changes in frequency and in amplitude. There are some evidences showing that the changes in frequency convey more important informations than the changes in amplitude do. From this point of view, the thresholds of audibility of frequency change in brief tones with some typical patterns of the changes were measured. With these results obtained and the related facts after other authors, a functional model of detecting mechanism of frequency change was presented. The results obtained are as follows. 1) For three patterns of frequency change, rising ramp, convex triangle and rising step as shown in Fig. 1, the thresholds were determined through the constant method. The initial frequency was 1 kHz. The results are shown in Fig. 2 (a) - (c) where the threshold is defined as the frequency deviation (&lrtri;f) of the variable tone for 75% correct detection. The average results of the subjects show that it becomes harder to detect the change as the duration decreases and also harder to detect the change according to the order of the pattern of rising step, rising ramp and convex triangle in the range of duration (20-300 msec) used. 2) The thresholds were also determined for the pattern of rising ramp and convex triangle for each initial frequency of 250, 1 k and 4 kHz. Two subject's groups participated in the experiment for each pattern of the change separately. The parameters of stimuli are shown in Table 1 and the results are in Fig. 3. Although there are differences in the normalized thresholds (&lrtri;f/f_i) between the patterns of change, the curves of the thresholds, which vary with the duration, for both patterns are similar in each initial frequency. For each pattern with the initial frequency of 4 kHz, thresholds are kept constant for tones of longer duration than about 100 msec. This is not the case with other initial frequencies. 3) The functional model of detecting mechanism of frequency change is shown in Fig. 4. The weighting network in the model is composed of a low pass filter of a simple RC network with a time constant of 13 msec, the inverse transfer function of which is seen in Fig. 5. The comparisons were made of the calculated thresholds by the model with the measured ones in the experiment of 1). The calculated thresholds are roughly the same as the measured ones as in Fig. 6. The comparisons were also made of the results after the model with the results of the experiment in which the frequency change of rising ramp occurred in a portion of the tone burst of 0. 5 sec. The parameters of stimuli used in the experiment are presented in Table 2. Fig. 7 shows that the calculated thresholds and the measured ones have the same inclination although the former ones are lower than the latter ones when the frequency changes occur abruptly near the onset of the burst.

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