2-2 piezocomposite materials are widely used for ultrasonic transducers in medical ultrasound imaging and underwater acoustics. An important issue in 2-2 piezocomposite transducer designs is to avoid spurious lateral modes. We proposed a new method to solve the lateral mode problem in this paper. A 30-element 2-2 piezocomposite transducer composed of PZT-5H and five different types of polymers were studied by using ANSYS finite element software. Using a 2-D model of the transducer the electrical admittances were calculated within the interested frequency range. The results show that there is a strong coupling between the thickness mode and the first lateral mode when any one type of polymer is used in the transducer design. However, the lateral mode is greatly suppressed when all of these polymers are used, and the electromechanical coupling coefficient for the thickness mode is also increased. The analysis further shows that the reduction of the lateral mode is only related tothe shear velocity of the polymer, while the density and longitudinal velocity of the polymer have little effect on it.
In this paper, the elastic properties of passive materials (matching, backing and lens materials) for ultrasound transducers are explored at room temperature in the frequency range of 25 - 65 MHz using the ultrasonic spectroscopy method. Alumina/EPO-TEK 301 and tungsten/EPO- TEK 301 composites were fabricated and measured. Experimental results display a monotonic rise in acoustic impedance of the composites with the addition of the particle filler. However, there was an attenuation peak occurring at about 8% volume fraction of particle filler. The acoustic impedance of the compositions was modeled. And additional passive materials were fabricated and measured. The measured results showed that materials having high attenuation also had large velocity dispersion, and low attenuation materials displayed low velocity dispersion.
It was found that the ferroelectric coercive field of LiNbO<SUB>3</SUB>, both in forward and reverse direction, vary with time after domain inversion. The existence of an internal field decaying as e<SUP>-t/(tau</SUP> ) is proposed, and the related coefficients are fitted.