基于光声多普勒频谱标准偏差的自相关碳颗粒横向流速测量  

Transverse flow velocity measurement of carbon particles based on photoacoustic Doppler standard deviation calculated with autocorrelation method

作　　者：卢涛[1] 白薇薇[1] LU Tao;BAI Weiwei(College of Electrical Engineering, Henan University of Technology, Zhengzhou 450001, China)

机构地区：[1]河南工业大学电气工程学院,河南郑州450001

出　　处：《中国医学物理学杂志》2018年第5期598-601,共4页Chinese Journal of Medical Physics

基　　金：河南省自然科学基金(162300410054);河南省属高校基本科研业务费专项(2015RCJH13)

摘　　要：为了测量与超声探头信号接收轴线相垂直的碳颗粒悬混液的流速,采用多普勒频谱的标准偏差估计频带展宽,频谱标准偏差由自相关方法计算。光声信号由波长532 nm重复频率20 Hz的脉冲激光激励,由中心频率10 MHz的聚焦超声换能器采集。碳颗粒悬混液由微量注射泵驱动,时域光声信号经希尔伯特变换为复信号后进行自相关计算,多普勒频宽的标准偏差由若干序列A扫的自相关平均得到。对比之前基于序列A扫的互相关方法,所提出方法的优点是自相关中的信号时移大小可自定义,如时移量远小于信号扫描间隔,可避免信号混叠,避免互相关中对重复频率为数千赫兹脉冲激光的需求。该方法的可行性通过测量横向流速为5.0~8.4 mm/s的碳颗粒悬混液的频谱标准偏差得到初步验证,实验结果显示信号的自相关结果在测量范围内呈现线性分布趋势。In order to measure the flow velocity of carbon particle suspension perpendicular to the receiving axis of ultrasound transducer, the standard deviation of photoacoutic Doppler frequency spectrum which was calculated with an autocorrelation method was used to estimate the bandwidth broadening. A 532 nm pulsed laser with the repetition frequency of 20 Hz was used as a pumping source to generate photoacoustic signals which were then detected using a focused ultrasound transducer with a central frequency of 10 MHz. The suspension of carbon particles was driven by a micro-injection syringe pump. The photoacoustic signals in time domain were transformed into complex photoacoustic signals using Hilbert transformation before autocorrelation calculation. The standard deviation of Doppler bandwidth was calculated by averaging the autocorrelation results of several sequential A scans. Compared with the previously reported cross-correlation method based on sequential A scans, the advantage of the proposed method is that the time delay in autocorrelation can be customized. If the time delay was chosen much less than the time interval between the sequential A scans, aliasing can be avoided, moreover, the requirement for high laser repetition frequency up to several k Hz in cross-correlation was avoided. The feasibility of the proposed method is preliminarily demonstrated by measuring the standard deviation of the carbon particle suspension with a transversal flow velocity from 5.0 to 8.4 mm/s. The experimental results revealed that the autocorrelation results were approximately distributed linearly within the measuring range.

关 键 词：光声多普勒 横向流速测量 频谱展宽 标准偏差 碳颗粒悬混液 

分 类 号：Q631[生物学—生物物理学]