The science of effects of sound vibrations beyond the limit of audible frequencies. Used for dust, smoke, and mist precipitation; preparation of colloidal dispersions; cleaning of metal parts, precision machinery, fabrics, etc. Friction welding, formation of catalysts, degassing and solidification of molten metals, extracting flavor oils in brewing, electroplating, drilling hard materials, fluxless soldering, nondestructive testing. Also used for investigation of physical properties, determination of molecular weights of liquid polymers, degree of association of water, and for inducing chemical reaction. A developing application is the use of ultrasonic vibration in diagnostic medicine.