Ultrasonic vibrations are high-frequency sound waves beyond the range of human hearing.
Optimum Conditions and Mode of Action for Ultrasonics:
Ultrasonic waves or wave's frequencies above 15000 cycles per second, can cause bacteria to caviatate. Cavitation is the formation of a partial vacuum in a liquid—in this case, the fluid cytoplasm in the bacterial cell. Bacteria so treated disintegrate, and their proteins are denatured.
When propagated in fluids, ultrasonic vibrations cause the formation of microscopic bubbles, or cavities, and the water appears to boils. Some observers call this "cold boiling." The cavities rapidly collapse and send out shock waves. Microorganisms in the fluid are quickly disintegrated by the external pressures. The formation and implosion of the cavities are known as cavitation. (Figure) illustrates this process.
Ultrasonic vibrations are valuable in research for breaking open tissue cells and obtaining their parts for study. A device called the cavitron is used by dentists to clean teeth, and ultrasonic machines are available for cleaning dental plates, jewelry, and coins. A major appliance company has also experimented with an ultrasonic washing machine. Many research laboratories us e ultrasonic probes for cell disruption and hospitals use ultrasonic devices to clean their instruments. When use with an effective germicide, an ultrasonic device may achieve sterilization, but the current trend is to use ultrasonic vibrations as a cleaning agent and follow the process by sterilization in an autoclave.
Limitations of Method:
As a sterilizing agent, ultrasonic vibrations have receive minimal attention because liquid is required and other method are more efficient.