Development of a New Ultrasonic Probe with High Capability of Axial and Lateral Resolution

本研究项目的目的是研制一种在轴向和横向上都具有高分辨率的新型超声换能器。研究结果如下：(1)建立了压电板厚度振动模式的等效网络，该网络中的压电参数是渐变的。该网络与均匀平板的网络形式相同，但两个换能器的换能器比和电容都是频率相关的。(2)利用等效网络模型对功能梯度超声换能器的性能进行了理论研究。传递函数和脉冲响应清楚地表明了功能梯度板在产生短超声脉冲方面的有效性。(3)设计并制作了一种加权锥形有限衍射束换能器，该换能器采用沿厚度方向改变陶瓷体积分数的压电复合材料。该换能器是采用带有锥形叶片的“骰子填充”技术制造的。陶瓷的体积分数从77%到23%不等。为了便于制作，在极化过程中采用了变迹。(4)在水中对换能器的性能进行了测试。用直径17.5 mm、锥角173°、工作频率3.1 MHz的换能器，在~100 mm的轴向范围内获得了接近均匀的~6分贝、~8个波长的波束宽度。尖峰脉冲激励也表明，该换能器具有比传统换能器更宽的频带。

The purpose of this research project is to develop a new type of ultrasound transducer that has a high resolution capability in both axial and lateral directions. The results obtained in this project are as follows :(1) A new equivalent network has been devised for thickness vibration modes in piezoelectric plates in which the piezoelectric parameter is graded. The network has the same style as that derived for a uniform plate, however, the values of the two transformer ratios and the capacitances are all frequency dependent.(2) The performance of functionally-graded ultrasound transducers has been studied theoretically using the equivalent network model. The transfer functions and impulse responses have clearly shown the effectiveness of the functionally-graded plates for generation of a short ultrasonic pulse.(3) A limited-diffraction-beam transducer of weighted conical type has been designed and fabricated using a piezoelectric composite with varying fraction of the ceramic volume in the thickness direction. The transducer has been fabricated using the "dice-and-fill" technique with a tapered blade. The volume fraction of ceramic has been varied from 77% to 23%. Apodization in the poling process has been employed to facilitate the fabrication.(4) The performance of the transducer has been tested in water. It has been confirmed that an almost uniform -6 dB beamwidth of 〜8 wavelengths has been obtained in the axial range of 〜100 mm using a transducer 17.5 mm in diameter and 173° in conical angle operating at 3.1 MHz. It has also been shown by a spike-pulse excitation that the transducer has the frequency bandwidth wider than that of a conventional transducer.