Many experiments have been performed by various investigators concerning the erosion of metals caused by the ultrasonic cavitation, there being many factors which affect this phenomenon. The authors conducted the following experiment in this paper. The cylindrical testpiece of aluminum, 18 mm in diameter and 20 mm in length, is set in front of the radiating surface of a stainless-steel solid-horn driven by a bolt-clamped Langevin-type piezoelectric (PZT) transducer. The dc voltage or the dc pulse voltage is applied between the testpiece and the radiating surface of the horn, with the testpiece as cathode or anode. The weight loss of the testpiece by erosion under irradiation of ultrasound and application of voltage, is measured. The erosion first increases slightly then decreases rather sharply with the increase of the dc current in case the testpiece is cathode (Fig. 3). The behavior is more complex when the testpiece is anode : the erosion first increases slightly, then decreases and finally increases almost linearly as the dc current increases (Fig. 7). Also an experiment with dc pulse current has been performed with the testpiece as cathode, but no difference is observable between the dc current and the dc pulse current, provided that the total amount of current is the same (Fig. 3 and Fig. 6). When the dc voltage is applied, with the testpiece as anode and without ultrasonic irradiation, a linear increase in erosion is observed with the increase of the dc current (Fig 7). It is concluded that the large difference in erosion of the aluminum testpiece acording as the testpiece is cathode or anode, is mainly due to the effect of the electrolytic erosion, while the mechanical effect of the cavitation is equally reduced in both cases the testpiece is cathode and anode. Although the mechanism is not ascertained as yet, the reduction of the mechanical effect of cavitation is presumably due to the electrolytic production of large gas bubbles preventing cavitation.

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The construction, function, displaying method, and example of display of a three-dimensional on-line displaying system for sound spectrogram are shown. In this system, frequency analysis (FFT) is done by a computer, and its results (frequency spectrogram) are displayed on a color picture tube changing the magnitude of frequency component to colors. Following two systems are presented : 1) A system using a large-type computer HITAC-5020 in which the data-input and analysis are carried out by means of "off-line", and the data-output and display of the analyzed results are carried out by means of "on-line". 2) A system using a small-type-computer HITAC-10 in which all steps from input to display are carried out by means of "on-line". It is shown that former system 1) is suitable for displaying the abundant data and latter 2) is suitable for handling the input data required to obtain quick response. Two methods of display are shown. One is the moving-pattern method in which the spectrograms are displayed continuously an electric news-sign-board. The other is a method Combined with the above-mentioned one and the standing-pattern displaying method in which the analyzed results to be given intermittently and slowly are able to display continuously and slowly in the same timing as the analyzed results. The arrangement of color is decided so that each color assigned to each step of intensity is sensed continuously and at equal intervals on the sensory response. In this system, 15 steps of color are used, and red color is selected in order to correspond to the highest step of intensity and blue color to the lowest one. A fragment of the effect of these systems is shown with an example of analysis and display for the sailing sound of tanker.

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