P1I-3 Measurement of Spectral Sound Field Parameters in Ultrasound Cleaning Baths using Piezo-electrical Hydrophones and Optical Fiber Tips

Despite the widespread use of ultrasound-supported cleaning in technology and manufacturing, general principles for its application and an efficient operation do not exist. Since the sound field is the cause and driving force of all processes, its measurement and characterization are the key to a better understanding and help in the selection of parameters for an economical operation of the devices. But sound field measurements in the appropriate frequency range from 20 kHz up to more than 1 MHz pose a number of problems, such as the interaction of too large sensor elements with the sound field and the risk of sensors being damaged by cavitation. Two types of sensor systems, based on piezo-electrical hydrophones and optical fiber tips which fulfil the requirements on accuracy and withstand high-power ultrasound fields and cavitation, were investigated. In experiments with an externally controlled cleaning bath working at reproducible conditions, the spatial distribution of spectral components of the sound field was determined. In addition, these parameters were related to the cavitation effect by means of an image analysis procedure of aluminum foil which was exposed to the same sound field. Based on the image of the foil, the perforations as well as the indentations were analyzed and quantified with special image processing software. The results of the correlation analysis reveal clear differences between the spectral parameters in relation to the erosion effect