| Medical high-frequency(>15MHz) ultrasound transducers having the very high image resolution, can provide rich imaging information for clinical diagnosis and biological tissue research. It is the main development direction of medical ultrasonic in domestic and abroad.In this paper, the simulation design and preparation process of high-frequency linear array transducer are systematically researched. Main work includes the following aspects:The model of 2-2 piezoelectric composite is built, and the harmonic response analysis is operated using COMSOL. By research the relationship of thickness and frequency, the frequency constant of resonance and anti-resonance is obtained 1510 MHz?um and 2060MHz?um, respectively. By research the influence of W/T(the width to thickness aspect ratio of ceramic pillar) on vibration mode of composite, the result is found that deleterious mode-coupling can be avoided, when W/T is less than 65%. In addition, The proper array element size and volume ratio of piezoelectric matrix can make the electromechanical coupling coefficient of piezoelectric composites as high as 0.7 above. Simulation results show that the array element size value should is close to half of the acoustic wavelength in composite materials. An optimum design method of 2-2 piezoelectric composite based on finite element method is proposed. The 2-2 piezoelectric composite is suited to fabricate center frequency 15 MHZ transducer is designed. The acoustic field of 2-2 piezoelectric composite is simulated using COMSOL. It is found that the optimal matching layer thickness is a quarter wavelength.Ultrafine 2-2 PZT-5H/Epoxy piezoelectric composite is prepared. The fracture risk of piezoelectric phase is effectively reduced by using an improved “dice-and-fill” method.Ni Cr/Au electrodes are sputtered over the composite. The performance of composite is measured and characterized using Agilent 4294 A precision impedance analyzer. Single thickness coupling, high electromechanical coupling coefficient, low acoustic impedance,and moderate mechanical and electrical loss are achieved. The result shows it is suited to fabricate high-frequency linear array ultrasonic transducer.Six samples of matching layer are prepared by mixing 5.9 um alumina with Epo-Tek 301A/B epoxy resin. The law that changes in acoustic impedance of matching layer with volume fraction of alumina is obtained. The result shows when the volume fraction of alumina is changed in 0-25%, and the acoustic impedance of matching layer will increase from 3.08 to 5.24 Mrayl. A method that can be used to fabricated high frequency(> 15MHZ) linear array ultrasonic transducer is put forward. The technical solution is:(1) a electrode is sputtered over 2-2 piezoelectric composite, then the composite elements including three sub-element are cut into 10 um along kelfs to separate the electrodes;(2) the flexible circuits with hollow pin are used to interconnection;(3) tungsten powder/ epoxy backing is cast, until is completely cured, then grind the backing flat;(4) lapping piezoelectric composite to specified thickness, sputtering electrode, connecting ground wire;(5) matching layer is cast, until is completely cured, then is lapped to specified thickness;(6) prepare acoustic lens;(7) Encapsulation and measurement. The difficulties of piezoelectric composite preparation, elements interconnection and matching layer preparation are effectively solved by this method. Multiple samples of high-frequency linear array transducer are successfully fabricated. The pulse-echo center frequency is15.1MHz and the measured-6d B bandwidth is 64.7%. The results achieve promising performance. The oscillation time of pulse echo is only 0.6 us, and elevation focal point is near 20.7mm. It suggests that the preparation method is an effective way in fabricating high-frequency linear array transducers. |
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