Ultrasonic Homogenizer Selection Guide

Ultrasonic Processing

High-intensity ultrasonic processors are extremely versatile and can safely process a variety of organic and inorganic materials in a range of volumes. Typical applications include sample preparation, cell lysing, disaggregation, homogenization, particle size reduction, soil testing, acceleration of chemical reactions, defoaming, and atomization.

The ultrasonic power supply (generator) converts 50/60 Hz voltage to high frequency electrical energy. This energy is transmitted to the piezoelectric transducer within the converter or tank where it is changed to mechanical vibrations.

These vibrations from the converter are intensified by the probe, creating pressure waves in the liquid. This action forms millions of microscopic bubbles (cavities) that expand during the negative pressure excursion and implode violently during the positive excursion. This phenomenon, called cavitation, produces the powerful shearing action at the probe tip and causes the molecules in the liquid to become intensely agitated.

Variables to Consider

The following variables must be considered to achieve efficient cell disruption with probe-style ultrasonic processors:

Probes: All probes, including those with replaceable tips, are tuned to resonate at 20 kHz, ±50 Hz. Low-surface tension liquids can penetrate the interface between the probe and the tip and carry Particulates into the threaded section, isolating the tip from the probe. If the tip is isolated or removed, the probe will not resonate at 20 kHz and the power supply will fail. To prevent this from happening, when processing low-surface tension liquids, such as solvents, always use a solid probe.

In ultrasonic processing, the higher the wattage and the larger the probe diameter, the greater the volume you can process. Also, the larger the tip diameter, the larger the volume you can process, but at reduced intensity.

Tip Amplitude and Intensity: Adding a tip to the end of the probe amplifies the longitudinal vibrations of the converter. Greater amplification, or "gain", creates more intense cavitation and greater disruption. Typical maximum tip amplitudes are 30 to 250 µm and the resulting output intensities are in the range of 200 to 2000 W/cm2 (compared to about 1 W/cm2 for ultrasonic cleaners).

Temperature: Cavitation is most effective at low temperatures. The intense agitation of ultrasonic processing can, over time, result in elevated temperatures that might damage sensitive biological samples. The temperature of your sample suspension should be as low as possible; ideally, the sample should be kept just above its freezing point. Use a cooling cell to prevent unwanted sample warming.

Power: Power is the energy required to drive the radiating surface of a given probe at a particular amplitude and frequency. Larger probes require higher power. While it is the intensity of cavitation that breaks the cells and emulsifies liquids (not the total power applied to the system), higher power is required to process larger liquid volumes and to process against higher liquid viscosities and pressures.