How do Ultrasonic Homogenisers Work?
Ultrasonic Cell Disrupters, also called Sonicators or Sonifiers® operate on a different principle than mechanical shear homogenizers. They are extremely effective on hard to disrupt samples and for producing smaller particle size distribution within a sample. Some of the samples that are typically sonicated or sonified are bacteria, spores, tough animal tissue, soil samples, nanostructures, and liposomes.
There are three main components of a laboratory Ultrasonic Homogenizer; an electronic generator which provides the power, a transducer which converts the signal to mechanical energy and a horn or probe where the processing takes place.
The electronic generator, which is located in the base of the unit, gets its power from an AC line. The generator transforms this electrical power to a 20 KHz signal that drives the transducer or converter. This signal is outside of normal human hearing ranges so it is not audible in this form of energy.
The converter or transducer contains piezoelectric crystals. These crystals are able to convert the electrical signal that the generator produces into a mechanical energy or vibration. This mechanical vibration is amplified and is used to drive the horn.
The vibration of the crystals is transmitted down the length of the horn or probe causing it to longitudinally expand and contract all the way to the end of the probe. The tip of the probe is the area where the highest level of activity will be occurring. The longitudinal vibration in the tip causes the sample to cavitate meaning thousands of tiny bubbles form and collapse as the tip continues to vibrate. This cavitation creates the energy that causes the sample to disrupt and break down into smaller particles which is responsible for the sound that is heard during sonication.
The probes are typically manufactured out of titanium as this metal can withstand the expansion and contraction caused by the longitudinal vibration. As with any metal, over time the probe can begin to erode or become pitted. It is important to clean the probe after each use and dry it to keep it from eroding. Erosion or pitting on a probe can decrease the effectiveness of the sonication so it is important to inspect the probe after 8-10 hours of use and polish it with a fine emery cloth.
Probes come in different diameter tip sizes to enable very small to large samples to be processed. A tip with a very small diameter will have a very high intensity for processing as all the energy is focused on a very small area. However, the size of the tip will limit the area of the cavitation and which will limit the sample size. A larger tip will have a lower intensity as the energy is spread out over a larger surface area. However, the area of cavitation or processing area is larger thus allowing for more sample to be processed.
When looking at what type of sonicator is needed for an application, it is important to look at power output along with probe size. Power is measured in Watts or Wattage and the higher the wattage the more power the Ultrasonic Homogenizer can produce. Small samples will not need high power because the size of the probe will be small and the intensity of the smaller probes is much higher than the larger probes. Large samples or samples with higher viscosities may require higher power to produce results as the Ultrasonic has to drive a larger probe with less intensity or energy at the tip.
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