| Ultrasound diagnostic technology is one of the most important medical diagnostic technologies and has broad prospects for development. It has the advantages of portable, simple style, repeatability, real-time, accuracy, cheap and other characteristics relative to other medical imaging techniques. Endoscopic ultrasonography system is a novel ultrasound diagnostic technique. A high-frequency ultrasound transducer was combined with ordinary endoscopic. Mucosal surfaces of the body cavity could be observed by endoscopic. And at the same time, tissues of body organs and adjacent organs could be scanned by ultrasound transducer. The transducers of the current products which made by major research institutions and medical equipment companies of China were driven by a motor to scan. Although this scanning method just need a simple transducer, the endoscopy requires high-precision mechanical connection, susceptible to damage, and further the obtained image is not stable enough.The parameters of 2-2 piezoelectric composites were determined and optimized by simulation software COMSOL in this paper. According to the simulated parameters, piezoelectric composites were fabricated by improved dicing-filling. The surfaces of materials were fabricated by dual-stage grinding. The surface electrodes of 2-2 piezoelectric composites were fabricated by magnetron sputtering. A layer of NiCr alloy film was coated to increase the adhesion between the composite and the electrode layer. The characters of composites were analyzed and compared to the simulation results. The structure of the radial array ultrasonic transducer was designed by three-dimensional modeling software, and the fabricating process of transducer was made accorded to the structure. The sizes and parameters of each part of the transducer were analyzed and calculated. A radial array ultrasonic transducer was fabricated. The acoustic performances of transducer were tested by pulse transmitting and receiving instrument and oscilloscope. The piezoelectric array elements were arranged around endoscopy so that human tissue could be scanned by 360° ultrasound without motors. It highlighted the "electronic scanning" technical points, more advanced the "mechanical scanning" technology stage. It came into the ranks of the advanced international level. The following main results were obtained in this paper:(1) The simulation results of 2-2 piezoelectric composites made by COMSOL show:The composites have a simple vibration mode when the thickness of composites is 0.16mm, the height of the sub-array elements is 8mm, width of the sub-array elements is 0.16mm, pitches of the sub-array elements is 0.2mm. The susceptance curve of composites was made by COMSOL, and the frequency of the minimum susceptance is 9.1MHz. It was closed to the real composite material which has a minimum susceptance frequency of 8.84MHz. The above results show that composite simulated by COMSOL is credible.(2) The piezoelectric ceramic column collapse was prevented by using improved cutting and filling method to fabricate composite materials, and it reduced materials defect rate. The distance of two adjacent cutting slots increased from 0.2mm to 0.6mm, then improving the cutting precision and high frequency composites can be fabricated. The electrodes fabricated by magnetron sputtering method have strong adhesion, uniform structure, excellent performance, etc. The thickness of films also can be controlled by adjusting the sputtering power and sputtering time. The finished materials have a relative dielectric constant of 121.3, acoustic impedance of 24.5 Mrayl, electromechanical coupling coefficient of 0.581, mechanical quality factor of 26.25, and excellent performance. They can meet the requirements of high-quality radial array ultrasonic transducer.(3)The radial array ultrasonic transducer was fabricated by 2-2 type piezoelectric composite materials has 40 array elements, center frequency of 5.1MHz, focal length of 50.1 mm, and the during of echo pulse time is short. Its-6dB bandwidth can be reached 62.7%. These performance parameters closed to the well-known foreign company’s new product. It is proved that fabricated radial array ultrasonic transducer by utility-type perfusion method is feasible. |
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