To provide ultrasonic cleaning of inanimate objects, ultrasonic waves in a frequency range of between 15 kilohertz and 10 megahertz are applied to water in a tank with a power density between 15 and 7,000 watts per square centimeter. Asymmetric power waves are applied to avoid instability leading to...http://www.google.com.au/patents/US5305737?utm_source=gb-gplus-sharePatent US5305737 - Ultrasonic treatment system
