Ultrasonic Horn Designs and Properties

Ultrasonic horns (also called sonotrodes, waveguide radiators, ultrasonic resonators and probes) are devices used to amplify the vibration amplitudes provided by ultrasonic transducers and deliver the acoustic energy to the processed liquids. ISM supplies several types of high-efficiency ultrasonic horns as parts of its laboratory, bench and industrial-scale liquid processors.

Conventional Ultrasonic Horn Conventional Horn

Conventional horns (CH) are suitable for small-scale process investigations. Able to provide very high ultrasonic amplitudes and power densities, these horns cannot deliver significant amounts of total power to liquids because their output tip diameters are small, which limits cavitation zone volumes they are able to generate. These horns, therefore, are not appropriate for commercial-scale liquid processing, but are recommended for laboratory-scale data collection prior to scale-up.

Full-Wave Barbell Ultrasonic Horn Full-Wave Barbell Horn

Full-Wave Barbell HornProcess scale-up requires switching to horns with larger output tip diameters, able to output the ultrasonic energy into greater volumes of working liquids while still maintaining high amplitudes. Full-wave Barbell horns (FBH) are appropriate for large-scale batch liquid processing and investigations. These devices can have large output tip diameters (up to about 60 mm) and are able to generate very high ultrasonic amplitudes and power densities, creating large cavitation zones and delivering substantial amounts of power to liquids. When inserted up to their lower nodal point, these horns produce one major cavitation zone under the output tip. Downward liquid streaming in the cavitation zone helps mixing the liquids during batch mode operation.

Scaling up processes with full-wave Barbell horns leads to an increase in liquid processing capacity approximately proportional to (Dfbh/Dch)2, where Dfbh and Dch are the FBH (after the scale-up) and CH (before the scale-up) output tip diameters, respectively. For example, if conventional ultrasonic horn has an output tip diameter of 12 mm and the full-wave Barbell horn operating at the same amplitude has an output tip diameter of 60 mm, the productivity-rate increase factor after the scale-up will be 25.

Half-Wave Barbell Horn Half-Wave Barbell Horn

Half-Wave Barbell HornHalf-wave Barbell horns (HBH) are ideal for industrial-scale flow-through liquid processing. These devices can have large output tip diameters (up to about 50 mm) and generate high ultrasonic amplitudes and power densities, creating large cavitation zones and delivering very high power to liquids. These horns produce two major cavitation zones (under and above the output section) ensuring that no liquid is able to bypass the active treatment zone as it flows through the reactor chamber.

HBH devices generate both downward and upward liquid streaming, which helps mixing the liquids inside a batch or flow-through reactor. HBH devices are smaller than FBH devices, making it possible to design more compact systems. The cumulative cavitation area produced by these horns is very large (approximately double of that produced by an FBH with the same tip diameter). Scaling up processes with half-wave Barbell horns leads to an increase in liquid processing capacity approximately proportional to 2(Dhbh/Dch)2, where Dhbh and Dch are the HBH (after the scale-up) and CH (before the scale-up) output tip diameters, respectively. For example, if conventional ultrasonic horn has an output tip diameter of 12 mm and the half-wave Barbell horn operating at the same amplitude has an output tip diameter of 50 mm, the productivity-rate increase factor after the scale-up will be approximately 35.

Half-Wave Barbell Horn with an Opening Half-Wave Barbell Horn with an Opening

Half-Wave Barbell Horn with an OpeningHalf-wave Barbell horns with an opening (HBHO) are the right choice for industrial-scale flow-through liquid processing where extremely high power deposition is required. These devices can have large-diameter output sections and generate high ultrasonic amplitudes and power densities, creating very large cavitation zones and delivering extremely high power to liquids. The output surface areas of these devices are further increased by hollow regions in their output sections.

These horns produce two major cavitation zones (under/inside and above the output section) ensuring that no liquid is able to bypass the active treatment zone as it flows through the reactor chamber. The lower zone experiences an additional effect of cavitation focusing, due to concentric expansion-contraction which occurs simultaneously with the longitudinal motion of the output section. HBHO devices generate both downward and upward liquid streaming, which helps mixing the liquids inside a batch or flow-through reactor. Scaling up processes with HBHO devices leads to an increase in liquid processing capacity, which depends on the shape and size of the hollow section and is greater than 2(Dhbho/Dch)2, where Dhbho and Dch are the HBHO (after the scale-up) and CH (before the scale-up) output tip diameters, respectively. For example, if conventional ultrasonic horn has an output tip diameter of 12 mm and the half-wave Barbell horn with an opening operating at the same amplitude has an output tip diameter of 50 mm, the productivity-rate increase factor after the scale-up will be greater than 35.

Half-Wave Barbell Booster

Half-Wave Barbell BoosteHalf-wave Barbell boosters (HBB) can be connected between a transducer and a horn to modify the horn’s effective gain factor (amplify or reduce). The HBB device's gain (when used as an amplifier, as shown on the left) or reduction (when connected in the opposite direction) factor should be multiplied by the horn's gain factor to obtain the resulting assembly’s gain factor. HBB devices can also be used as assembly length extenders and to provide additional clamping support.

It is important to point out that in order for an FBH, HBH or HBHO device to permit direct process scale-up, during which the ultrasonic amplitude and other parameters are maintained while the processed liquid volume is increased, it is necessary to make sure that the power to be delivered to the working liquid is made available by the processor’s generator and transducer. For example, a CH with an output tip diameter of 12 mm, operating at the amplitude of 90 microns in water under normal conditions draws approximately 70 - 100 W of power. An FBH with a 33 mm output tip diameter operating at the same amplitude will draw approximately 800 - 1,000 W. An FBH with a 60 mm output tip diameter will draw approximately 2,500 - 3,000 W.