New developments of high power ultrasonic transducers

【摘要】：正In high power ultrasonic applications and underwater sound field,the longitudinally composite piezoelectric sandwich transducer(which is also called the Langevin transducer since it was invented by French scientist Langevin ) has been widely used.In this kind of transducers,the active piezoelectric ceramic elements were polarized and sandwiched between two metal end masses in the longitudinal direction.The direction of electric polarization,the external exciting electric field and the mechanical vibration is the same and along the longitudinal axis of the transducer.It has the advantages of large power,high sound intensity,flexible mechanical structure and high mechanical strength.However,the longitudinal composite transducer also has some disadvantages.Among these disadvantages,the limit for the output power and the acoustic radiation direction is the most important.Since the dimension limitation imposed by the one-dimensional longitudinal vibrational theory in the analysis of the longitudinal composite transducer,the radial dimension should be much less than the longitudinal dimension. Generally speaking,the radial dimension should be less than the quarter of the longitudinal wavelength.In this case, the sound radiation direction is one-dimensional and in the longitudinal direction.This condition determines that the radiation area of the transducer cannot be very large and therefore very large output acoustic power is difficult to get by using a single transducer.In order to produce very large ultrasonic and sonic power,transducer array can be used as in ultrasonic cleaning and sonar systems.In the transducer array,it is required that the resonance frequency and the impedance of the transducers should be the same as far as possible.