Research On Broadband 1-3 Piezocomposite Transducers

Ultrasonic transducer is the key component in ultrasonic nondestructive examination and medical imaging system. For obtaining the better lateral resolution, the bandwidth of the transducer should be wide. This paper aims to discuss the method of designing broadband longitudinal wave ultrasonic transducer, whose center frequency is around 2.5MHz. The simulation and design method of piezoelectric transducer include circuit equivalent and finite element method. Obtaining accurate material parameters is the common basic premise of these methods.The 1-3 piezoelectric composite material is suitable for transducers working in low acoustic impedance medium, e.g. water, because of its advantages of low acoustic impedance, large electromechanical coupling coefficient, low lateral coupling and so on. The equivalent circuit of the piezoelectric film thickness vibration is derived. A practical method of determining piezoelectric material parameters using in designing thickness-expander transducers is introduced, which is based on the equivalent circuit of the piezoelectric film and impedance fitting. In detail, these parameters are kt (equivalent thickness-expander electromechanical coupling coefficient), Qm (mechanical quality factor), c (longitudinal wave velocity) and ε (relative clamped permittivity). Using this method, the parameters of a group piezoelectric composite materials with different volume fraction are obtained. They are useful in transducer designing and simulation.This paper introduces the KLM model and its improvement and the two port network equivalent theory. On the basis of these theories, the simulation of the transducer’s pulse echo is obtained. The evaluation function of the transducer is established. The optimization method of the transducer performance is discussed, especially the effect of the matching layer. It’s demonstrated that the thickness of the matching layer effect the transducer’s performance more than its acoustic impedance, and the acoustic attenuation of the matching layer has negative impact on the performance of the transducer. On the basis of the optimization result, 2.5MHz transducers are made, whose working media are respectively water and Polystyrene. Their-6dB relative bandwidths reach 94.3% and 100.8% respectively.