An ultrasonic bath is often used to clean jewellery. The jewellery to be cleaned is placed in the tub of the device filled with liquid and a cleaning agent. A generator supplies several ultrasonic transducers with high-frequency energy, which are attached to the walls of the device or directly to the tub. The energy is then introduced as ultrasound over the liquid so that a uniform, strong, non-static sound field is created. Another method of ultrasonic cleaning is the variant with immersion transducers suspended in the liquid. So-called plate transducers can also be used for an ultrasonic bath. The frequencies for ultrasonic cleaning are usually in a range between 20 kHz and 2 MHz. The frequency is determined by the structure or the smallest opening to be cleaned. In water, the wavelength should be less than half as large as the opening diameter, otherwise the ultrasound cannot penetrate the surface. It will then be closed and particles cannot be removed.