Development of Broadband Utrasonic Transducer for High Temperature Use

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An ultrasonic transducer which can emit an ultrasound with arbitrarily specified frequency from a vibrating plate has bee developed for its high temperature use. A ferromagnetic plate is electromagnetically driven by alternative attractive and repulsive forces between static magnet and alternatively induced magnetic field. A typical material for the purpose is a rectangular iron plate with high magnetic Curie point of 770 ℃ that is fairly high compared with normal piezo-elastic material for ultrasonic transducer. The plate with a small yet strong neodymium magnet (say 0.4t) in its center was placed in front of an electromagnetic pole which was imposed with a high frequency alternative current with 40-80 W. The electromagnetically oscillating plate can emit an ultrasound with the same frequency imposed. The intensity and frequency of the irradiated sound was measured with the use of an ultrasonic meter or a microphone. FFT analysis indicated that the sound had the same frequency. The various effects of frequency and current imposed, and thickness and distance of the vibrating plate on the sound intensity were investigated. The vibrating modes for the resonant situations were tried to find by the remote-observation of heat generation in the plate by using a high resolution thermo-viewer. The sound with a level of 20kPa could be also indirectly generated in the water bath as a molten metal. Although the fundamentals of the newly developed ultrasonic device for high temperature use were investigated and reported here, we further need additional research such as a system for cooling liquid through which an ultrasound would be transmitted. In this report, sound based key technologies and the better designing of expected systems using radiation force and acoustic cavitation are discussed as well.