Ultrasound has been shown as an important tool in NDT applications, especially, in diagnostic imaging systems. The quality of ultrasonic imaging has close relations with the characteristics of acoustic waves generated by the ultrasonic transducers. In this thesis, the method of analysis, fabrication, and experiments for piezoelectric ultrasonic transducers are investigated. Also, the evaluation of piezoelectric composite materials for ultrasonic medical applications are carried out.
In chapter 2, the fundamental concepts and important performance parameters in the design of ultrasonic transducers are introduced. And, the functions of each component of the transducer in transmitting and receiving the ultrasonic waves are described.
In chapter 3, the internal losses of a piezoelectric resonator and layers are considered in the analysis of the performances of piezoelectric ultrasonic transducers. The piezoelectric resonator is represented by the transmission line model in terms of 5 effective parameters in which the attenuation coefficient is suggested to involve the internal losses of the transducer. The attenuation coefficients of PZT by our resonance method are in good agreement with those by pulse-echo method. By inserting these 5 model parameters into the developed simulation programs, the round trip insertion loss and pulse-echo response are calculated for the variation of important components of an ultrasonic transducer. These results give useful guidelines to design the ultrasonic transducers.
In chapter 4, PZT-polymer composite plates with 1-3 connectivity are considered, and the experimental study on the relation between electrical input impedance and vibration modes is performed. This composite transducer is verified to have a stable pulse-echo response for the variation of the thickness of matching layer. Even with a single matching layer, the pulse-echo response of the composite transducer has a broadband characteristic with the quality factor of 2.1. The experimental pulse-echo response is in good agreement with predicted one, and this fact confirms the effectiveness for biomedical applications.
In chapter 5, the operation and beam pattern of linear array are described. For the fabricated linear array with 33 elements, the electrical impedance, impulse response, cross coupling, and angular response are measured and discussed.