The Applications of Smart Materials in Hydraulic Machineries: Combination of Piezoelectricity and Bubbles
By Xiaojian Ma, Biao Huang, Guoyu Wang
Due to the secondary Bjerknes force, the bubbles migrate towards the wall, generate the toroidal shape, and then form high-speed jet, which causes high impulsive pressure [1]. Jacques, a French physicist, discovered the piezoelectricity in 1880 [[2]] (http://www.science20.com/profile/news_staff). The combination of piezoelectricity and bubbles can be considered as a smart material to solve harmful cavitation phenomenon in hydraulic machineries.
The impulsive pressure of bubble collapse applied on the piezoelectric materials can induce the internal generation of electrical charge, which causes electric potential difference. Based on this direct piezoelectric effect, the cavitation bubbles will be real-timely detected in intensity and magnitude. The system of collapsing bubble – piezoelectricity is treated as a trigger switch of pressure or feed-back system.
On the other hand, the shape of piezoelectric material can be changed by inputting alternating current, due to its inverse piezoelectric effect. As known, bubble migration is closely influenced by deformable and elastic boundaries [3]. So it’s possible to actively control the direction of bubble migration and then eliminate cavitation by changing alternative current.
The application of piezoelectricity and bubbles will also be a perfect combination in the ultrasonic cleaning [[4]] (http://www.sciencedirect.com/science/article/pii/S1350417716301699), underwater explosion [5], and medical therapeutics [[6]] (http://www.sciencedirect.com/science/article/pii/S1350417716302917), etc.
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