Tham khảo tài liệu 'advances in piezoelectric transducers part 3', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Horn-Type Piezoelectric Ultrasonic Transducer Modelling and Applications 17 Length m Fig. 10. Vibration amplitude distribution along the length of the transducer proportional to the source strength International standard IEC 1998 Li et al. 2009 . Therefore in the present work a horn is applied to amplify the vibration velocity from the PZT crystal. And a ball or a short cylinder tip is attached at the distal end of the transmission wire to enhance the radiation area. AVG ELEMENT SOLUTION STEP 1 Fig. 11. Acoustic pressure pattern generated by the tip in the liquid Acoustic characterization The acoustic properties of the transducer were characterized qualitatively. As the acoustic pressure becomes larger and larger two phenomena might be observed around the tip of the transducer . cavitation and streaming Abramov 1994 1998 Young 1999 . Cavitation is the generation and burst of bubbles in the liquid due to the high amplitude of the acoustic 18 Advances in Piezoelectric Transducers pressure. Along with the burst of the bubbles is the high intensity shock wave and impinging of the liquid which is normally very strong and even sufficient to break a hard surface. Fig. 12 a shows the cavitation bubble clusters generated at the vibration tip in the silicon oil. The cluster is usually generated at the center of the surface and then flows away along the acoustic axis. When the distance becomes larger from the surface the bubbles might be agglomerating and floating upwards due to the buoyancy force. The cavitation threshold of the water is larger than silicon oil and is also frequency temperature and static pressure dependant Abramov 1994 1998 Young 1999 . Generally in water only when the acoustic field is very strong visible bubble clusters can be observed. The generation of the bubble cluster at the tip surface also proves that the highest intensity of acoustic energy is around the tip. This is consistent with the earlier theoretical analysis. The second important .
