Production of an ultrasonic equipment with a high output power has been attempted by braze-bonding of ferrite vibrators to it using the active metal method. This paper describes evaluation for the braze-bonding strength of ferrite vibrators by acoustic vibration methods. A composite vibrator is constructed by braze-bonding or by adhering with an epoxy resin of two ferrite vibrators at each surface for acoustic radiation. Each vibrator is driven at the fundamental resonant frequency so that the maximum breaking stress occurs at the jointed surface. On this condition, acoustic duration tests at high vibration amplitudes for a long time and temperature characteristics measurements are carried out for each vibrator. The braze-bonded vibrator is shown to be more than twice as strong as the resinadhered vibrator and thermally more stable for temperature rises up to 120℃. A ferrite vibrator brazed with a metal plate is attached to a water tank and driven at a high vibration amplitude for a long time for an ultrasonic power test into water. The vibrator works stably for 200 hours at the driving power density of 12. 5W/cm^2, which is nearly four times as large as the power rating of commercial ferrite vibrators for single-sided radation into water.

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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.

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