| Medical ultrasond transducer is of vital importance in the whole ultrasonic imaging system, which can directly affect the image performance of the ultrasonic imaging system. As the development of piezoelectric materials, the improvement of production process and computer, the ultrasonic frequency of ultrasonic diagnosis is higher. High frequency ultrasond transducer(central frequency >20MHz), especially the high frequency focused ultrasound transducer can increase the imaging resolution of the target area. The High frequency ultrasound transducer has a broad application prospect in the Biological Microscope Ultrasonic(UBM), Photoacoustic Imaging(PAI), Intravascular Ultrasound( IVUS), small animal experiments and other applications. In this paper, the high performance 1-3 type piezoelectric composites were prepared. By shaping the piezoelectric composite materials the spherically and cylinder line focusing ultrasonic transducer were successfully fabricated. The main work included in this paper is shown as follow:(1) Firstly, the basic structure of ultrasond transducer, including the material and the characteristics of each component are analyzed and classified, The results show that the 1-3 type piezoelectric composites are more suitable for high frequency focusing ultrasonic transducers than the single phase piezoelectric materials, because of its high mechanical coupling coefficient, low acoustic impedance, low dielectric constant, low dielectric constant, low mechanical quality factor, better flexibility and controllability;(2) Secondly, the mechanical and acoustic properties of 1-3 type piezoelectric; composite materials is simulated based on the W.A Smith model. The results show that when the volume fraction is range from 30%~80% the mechanical and acoustic properties of the piezoelectric composite materials is changed. The electromechanical coupling coefficient is almost 1.5 times of a single phase piezoelectric ceramics(general piezoelectric ceramics), and the acoustic velocity increases with the increase of the volume fraction of piezoelectric ceramics phase;(3)Thirdly, the fine particles of alumina particles with different volume fractions is doped in RTV615 silicone rubber. And the acoustic properties such as the sound velocity, acoustic attenuation, acoustic impedance are both studied in a theoretical simulation based on the Devaney-Levinc model and the experimental verification;(4) At last, a self-focus high frequency(center frequency is near 50MHz) ultrasound transducer is fabricated. The time domain waveform and sound field characteristics are tested and analyzed. Results show that the two kinds of focused ultrasound transducer both have better focusing characteristics(focus depth <10mm) and spatial resolution(lateral and axial resolution are both less than 200um). For the future medical ultrasound diagnosis application such as distinguishing fine structure of the superficial tissue, the application of small animal experiment and photoacoustic imaging, the fabricated ultrasound transducer has an promising important application value. |
