Medical high frequency focused ultrasound transducer

Importance of medical ultrasond transducer shown 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 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 ultrasonic biological microscope (UBM),photoacoustic ifnaging(PAI)，intravascular ultrasound(IVUS)，small animal experiments and other applications.In this paper,the high performance of 3 type piezoelectric composites were prepared.the piezoelectric composite materials are the spherically and cylinder line ultrasonic high focusing piezo were successfully fabricated.The main work included in this paper shown as follow:

    (l)Firstiy,the basic structure of ultrasond transducer,including the material and the characteristics of each component are analyzed and classified,The results show that the 3 type piezoelectric composites are more suitable for high frequency HIFU hemisphere focusing piezoelectric 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 3 type piezoelectric has simulated composite materials .The results show that when the volume fraction range from 30% to 80%the mechanical and acoustic properties of the ultrasonic hifu piezo transducer composite materials changed.The electromechanical coupling coefficient almost is 1.5 times of a single phase piezoelectric ceramics,and the acoustic velocity increases with the increasing of the volume fraction of piezoelectric ceramics phase.

    (3)Thirdly,the fine particles of alumina particles with different volume fractions are doped in RTV615 silicone rubber.And the properties of high focusing piezo pickups such as the sound velocity,acoustic attenuation,acoustic impedance are both studied inatheoretical simulation based on the devaney of Levinc model and the experimental verification.

  (4)At last,high frequency self -focusing (center frequency is 15 - 50MHz)HIFU piezo 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 is <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 photo acoustic imaging,the fabricated HIFU piezoelectric crystal transducer has an promising important application value.