Frequently Asked Questions
What is Ultrasonics?
Although sound is the sensation perceived by the sense of hearing, it is not always audible. Ultrasound literally means beyond sound; sound above the human audible spectrum. The frequency of a sound is the number of cycles of a sound wave in one second. Frequency is measured in units called hertz (Hz). Since 18 kHz (18,000 Hertz/cycles) per second is the approximate upper limit of human audibility, ultrasonics refers to sound (acoustic waves) beyond that frequency. 20 kHz is the most effective frequency for liquid processing applications.
What are the differences between an ultrasonic processor and an ultrasonic bath?
The ultrasonic intensity within a bath is low power, location dependent, and inconsistent, due to many factors. With an ultrasonic processor, processing is significantly faster and highly reproducible, due to the fact that the energy at the probe tip is high intensity, focused and adjustable.
20 KHZ or 40 KHZ?
40 kHz is commonly used for ultrasonic cleaning and atomization because the droplet size at that frequency is half that generated at 20 kHz. However, the frequency of choice for most ultrasonic liquid processing applications is 20 kHz, because the amplitude at the probe tip and the resulting cavitation is more effective for liquid processing. 40 kHz may be effective for small volumes and some short duration applications such as many OEM situations.
With ultrasonic processing, are there any limitations?
Yes - viscosity, temperature and liquid characteristics. As the viscosity of the material increases, its ability to transmit vibrations decreases. Typically, the maximum viscosity at which a material can be processed effectively is 4000 cps. With standard systems, the practical upper limit on temperature is approximately 65°C. Solid tipped probes can be used with both aqueous solutions and low surface tension liquids (e.g. solvents), however probes with replaceable tips are only used with aqueous samples.
Which instrument should I use?
The 500 and 750 watt units are the most versatile because they can process both large and small volumes – as little as 250μl with a microtip, and as much as 1 liter with a 1” (25 mm) probe. Additionally, they can process many liters per hour on a flow-through basis when used with a continuous flow cell. If your sample volume is small, a 130 watt unit is likely the best option. The 1500 or 2500 watt units are recommended for large scale and industrial applications.
Replaceable or solid tip?
Replaceable tip probes have threaded ends and when the tip is worn out it can be unscrewed and replaced. Replaceable tip probes are only used with aqueous samples. If you sonicate a solution that contains organic solvents, alcohols or any low surface tension liquid, the liquid will seep inside this threaded tip (regardless of how tight the connection is attached). Once liquid gets inside the tip, it will loosen and cause the system to display an overload error. If the application requires solvents or low surface tension liquids, you must use a solid tip probe. Solid tip probes can be used for any type of liquid. Note all microtips are solid. Only ½” diameter probes or larger are available with a replaceable tip.
Which probe is best suited for my application?
The larger the probe diameter and higher the amplitude, the larger the volume that can be processed. Smaller probes are needed to fit into smaller vessels. See probe listings for guidelines and contact us for assistance in selecting the correct options.
How deep should the probe be inserted?
If the tip is not submerged enough the sample will foam or bubble. If the tip is submerged too deep, it will not circulate the sample effectively. Foaming can also be caused when the amplitude setting is too high. All the conditions described will result in extended processing times and poor outcomes. Adjust the probe depth to avoid splashing and foaming while still maintaining vigorous sample mixing.
Can probes be manufactured to any length?
No. Probes are made to resonate at a specific frequency (half a wavelength or multiples of half wavelength). 20 kHz probes are approximately 5” (127 mm) long and can be made longer in 5” (127 mm) increments.
Wattage display vs. amplitude setting?
Power is the measure of the electrical energy that is being delivered to the converter. It is measured in watts and displayed on the sonicatorʼs screen. At the converter, the electrical energy is transformed into mechanical energy. It does this by exciting the piezoelectric crystals causing them to move in the longitudinal direction within the converter. This conversion from electrical into mechanical energy causes a motion that travels through the horn/probe causing the tip to move up and down.
The distance of one movement up and down is called its amplitude. The amplitude is adjustable. Each probe has a maximum amplitude value. For example, with a ½” diameter probe at setting 100%, the probe will achieve an amplitude of approximately 115μm. At setting 50% the amplitude is approximately 57μm. Note this value is approximate and not perfectly linear. Sonics measures the amplitude of each probe at 100% and these values are published in the brochure.
Amplitude and intensity have a direct relationship. If you operate at a low amplitude setting, you will deliver low intensity sonication. If you operate at a high amplitude setting, you will have high intensity sonication. In order to be able to reproduce results, the amplitude setting, temperature, viscosity and volume of the sample are all parameters that need to remain consistent. The amplitude, not the power, is most critical when trying to reproduce sonication results.
Power has a variable relationship with amplitude/intensity. For example, sonicating water at setting 50% requires less wattage when compared to a viscous sample (such as honey). For both samples the amplitude/intensity is the same but the power/wattage will differ because the viscous sample will require more watts in order to drive the horn. The viscous sample puts a heavier load on the probe so they system must work harder to vibrate up and down at the same intensity. Small fluctuations in the wattage display during sonication is normal.