Development And Detecting Of An Air-Coupled Piezoelectric Ceramic Ultrasonic Transducer

Ultrasound is difficult to propagate in air and the application of ultrasound is limited because the serious mismatch of acoustic impedance between transducer material and air. Then air-coupled ultrasonic transducer has become the research focus of air ultrasonic technology. In order to improve the propagating efficiency of ultrasonic waves in air, there are a variety of air-coupled ultrasonic transducer research methods. Based on previous researches, an air-coupled piezoelectric ultrasonic transducer with mode conversion is developed in this paper and is trying to be used in the medical area. Seven aspects are studied in this paper:① Learned the related knowledge about air-coupled ultrasonic transducer designed its basic structure which consisted of two parts: driving system and vibration system. The driving system is the excitation source that provides a driving power for the transducer. The vibration system has four parts:the backing, the piezoelectric ceramic stack, the exponential amplitude transformer and the bending vibration disk.② Designed the driving system and tested it, including the driver circuit and the feedback loop. The driver part stimulates the transducer to emit ultrasound. The feedback loop collects voltage and current signals of the transducer and tracks the resonant frequency of the transducer automatic by phase-locked loop.③ Designed the vibration system and chose appropriate materials for each parts of the vibration system. Calculated the sizes of each parts of the vibration system by their resonant frequency equation so that every part can work at the same resonant frequency, and then the transducer can work at the optimal operating condition.④ Connected the finished vibration system to the driving system and debugged the output frequency of the signal source to make the transducer work at resonant state, and then the resonant frequency of transducer is 33.3 KHz.⑤ Tested and detected the transducer, including the output signal of piezoelectric ceramic stack and vibration system, analysis of the pitch circle, the radiated acoustic pressure of disc. The results showed that every part of the transducer is in good working condition.⑥ Detected the transducer by using schlieren method. The results showed that the bending vibration disk became thicker significantly and the acoustic field couldn’t be seen. Its causes were analyzed.⑦ Processed an arc radiation plate, detected its resonant frequency and radiated acoustic pressure, compared it with the disc. The results showed that the vibration of disc was more ideal than the arc radiation plate.An air-coupled piezoelectric ceramic ultrasonic transducer with feasible theory and easy-using feature has been presented in this paper. Experiments results showed that the transducer could work normally and get higher radiated acoustic pressure at very low driving power. After thorough research, it will be expected to apply in the healthcare area, such as physiotherapy and drug penetration, and has a high prospect.