节点文献
球面聚焦超声高精度相控信号的设计与实现
【作者】 郭涛；
【导师】 张建秋；
【作者基本信息】 复旦大学 ， 电路与系统， 2010， 硕士
【摘要】 球面聚焦超声高精度相控信号在高强度聚焦超声(high intensity focused ultrasound, HIFU)治疗中起着举足重轻的作用,其精度直接影响到HIFU聚焦的声场增益和声场,其误差越大,声场增益越小,相应的声场强度偏差就越大,从而影响到整个HIFU治疗的最终治疗效果。球面聚焦超声相控信号设计中的难点主要体现在相差精度高,输出信号多等指标要求。若采取通常的时钟计数法,其精度由时钟频率决定,要实现高精度,时钟频率会很高,而时钟频率越高,电路功耗越大。此外,为了达到更高的精度,需要利用选择器选择不同相位的时钟边沿来触发信号的输出,若选择器的不同输入信号到达路径不同,它们各自的延时各不相关,这种绝对延时会影响输出信号的稳定。数字游标测量法是用来提高周期和时间间隔测量准确度的一种方法,该方法将测量的精度转换为时标脉冲周期和游标脉冲周期的差,其差值越小,测量的精度就越高。它可以在保证脉冲周期差值足够小(测量精度足够高)的前提下增大脉冲周期,降低时钟频率。据此,本文提出了一种既提高信号触发延时精度又保证时钟频率足够低的办法——数字游标定相法。FPGA芯片时钟资源丰富,通用管脚配置方便,是进行相控信号设计的理想选择。利用FPGA实现上述的方法,可以完成对球面超声高精度相控信号的设计与实现。针对球面相控阵聚焦超声换能器治疗系统的实际应用需求,我们扩展相关的通信与控制模块以及信号驱动模块,最后搭建了一个球面相控阵聚焦超声换能器的高精度相位控制系统。经过电路设计,印刷电路板绘制,软件实现等步骤,最终完成了高精度相位控制系统样机的制作。最后样机测试结果表明：提出的设计方法合理有效,构建的高精度相位控制系统能满足球面相控阵聚焦超声换能器的应用要求,为球面相控阵聚焦超声换能器的研制提供了技术基础。
【Abstract】 High-precision phased signals play an important role in spherical focused HIFU (high intensity focused ultrasound, HIFU) therapy, its accuracy directly affects the sound field and the sound field gain of HIFU focal area. The larger its error is, the smaller the sound field gain is, and the greater the bias of corresponding sound field strength, thus affecting the final treatment of the HIFU therapy.The design difficulties of the phased signals of spherical focused HIFU mainly include its high precision and excessive output channels. The accuracy of the normal clock count method is determined by the clock frequency, the higher accuracy we need, the higher the clock frequency we must take, and high clock frequency will lead to too much power consumption; besides, in order to get higher accuracy, selectors are needed to trigger the output by selecting the different phased clocks, and the uncorrelated delay paths of its input signals would affect the stability of output phased signals.The digital cursor measurement is usually used to improve the measure accuracy of the cycle and time interval, whose measure accuracy is determined by the difference of cycles between the standard clock pulse and the cursor clock pulse, the smaller the difference is, the higher the accuracy will be, so it not only increases the measure accuracy, but also reduce the clock frequency. Base on the digital cursor measurement, this thesis proposed a method, the digital cursor phased method.The FPGA becomes the ideal chip in the process of designing phased signals because of its rich clock resources and GPIO resources. Base on FPGA and the method we proposed, we can design and realize the phased signals of the spherical focused HIFU. For practical applications of spherical phased array focused ultrasound transducer (SPAFUT), we expanded the relevant communication and control module and signals driver module, finally we built a high-precision phase control system of SPAFUT.After circuit design, PCB layout, software design and other steps, the prototype of the high-precision phase control system was constructed based on the designed different modules. The test results of the prototype show that the proposed methods and techniques in this thesis can be used in the SPAFUT. The test results also show that the works of this thesis are of important signification for the further study of the SPAFUT.