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Ultrasound Transducers for High-power Application |
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02 Jan, 2016 |
Ultrasonic Transducer |
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High-power ultrasonic technology has used for a huge variety of applications due to its property of great safety and efficiency. Ultrasound transducers used in modern ultrasonic systems are almost based on the pre-stressed piezoelectric design, and tend to use at the low frequencies, because the available power is limited by mechanical stress in the oscilating parts. As a rule, ultrasound wave can be propagated in three phases of liquid, solid and gas. |
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High-power transducers applied in liquid & fluid medium |
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Power ultrasound in liquid treatment opens a door to a broad range of industries such as enhancement of chemical process, degassing for drink, extracting substance from plant, anti-fouling for heat exchanger and so on. The amplitude of vibration produced by the transducer is too low for practical use, so that
the horns(i.e. velocity transformer) are designed to magnify this amplitude in different shapes according to specific processing purpose which mainly includes disintegration, extraction, homogenization, emulsification, degassing and sonochemistry.
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Ultrasonic cleaning is the tranditional industrial application of power ultrasound. The constitution of cleaning system basically includes three parts: a generator, several transducers and a stainless steel tank, power density of ultrasonic oscillators is relatively low. Depends on the implosion of cavitation bubbles produced in fluid, dirt particles attached to parts can be removed thoroughly.
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High-power transducers applied in solid medium
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Plastic welding is the process of combination between two parts by wave energy in modern manufacturing. High frequency vibration generates heat to melt
plastic materials. The heat is produced within the plastic, so that the welding work can be rapidly and cleanly finished and requires no consumable.
Metal welding transducers are designed from the same principle of ultrasonics although the shape of the horns which transmit the ultrasound vibration into
plastic and metal are quite different. In addtion, not like plastic welding which is based on melting of the material, metal welding is accomplished via a
frictional action of the surfaces.
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The other major application in solid medium is ultrasonic cutting which does not require much pressure and sharp edge. The basic ultrasound cutting system
consists of ultrasound transducer, horn, cutting knife and generator. The horn amplify the vibration of the transducer, and the tool head (i.e. knife)
amplify the amplitude further. Under the action of power ultrasonic energy, the materials can be softened and melted immediately, in this case, even a
small cutting force will achieve the goal of cutting material. The vibrating blade created by ultrasound transducers can be applied in a wide range of
materials such as food, rubber, plastic sheets, paper products, etc.
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High-power transducers applied in gas medium
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The low acoustic impedance and the high absorption of the air medium. For an efficient transmission of energy, it is necessary to achieve a good impedance
matching between the transducer and the gas for large amplitudes of vibration. Besides, if we need a long range propagation, the vibrating source must has
highly directionality.
The flexural vibrating stepped plate is a new type of transducer which can generates high-density ultrasound energy with good directionality in gas medium.
The extensive surface of radiator provides the vibrating system which has a property of good impedance matching with air medium, all the elements of
transducer are designed to be resonant at a certain frequency.
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The air-borne ultrasound transducers have been widely applied in food drying industry, due to the good acoustic impedance matching between the vibrating plate
of the transducer and the food, ultrasonic cavitation inside the fluid can help to release the moisture which is strongly attached to the food material.
Besides, the rapid operating time and low temperature process can help the food are preserved very well.
Removal of small particles is another important application. For example, the coal dust with small size is difficult to remove by conventional separation
technology in power plant. The effect of high-intensity ultrasound energy can induces agglomeration processes to change the particles with small size (e.g.
smaller than 2.5 microns) into larger size, which can be easily precipitated with a conventional separator.
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