基于水听器空间平均效应修正的高频声场定征方法研究

发布时间：2017-12-28 14:32

本文关键词：基于水听器空间平均效应修正的高频声场定征方法研究　出处：《哈尔滨工业大学》2017年博士论文　论文类型：学位论文

【摘要】：高频声场定征是先进医疗设备战略新兴产业发展的需要,水听器是用于水声声压探测的换能器件,广泛应用于超声医疗诊断设备的声场测量。随着高频超声医疗诊断设备应用中分辨率的提高和安全性指标的发展,对高频声场中声压、声功率及辐射力的测量精度、测量频率范围提出了越来越高的要求。根据超声医疗发展的要求,超声频率需至少达到几十兆赫兹量级。随频率升高所需水听器孔径越小,需达到微米量级,进一步造成声压灵敏度降低和制作工艺难度的提高;而随着频率的升高,声功率越微弱,接近现有溯源方法的本底噪声无法计量辐射力,这对利用水听器进行高频声场定征提出了新的挑战。本课题“基于水听器空间平均效应修正的高频声场定征方法研究”,在分析水听器孔径空间平均效应修正和声压灵敏度校准方法的基础上,研究了高频声场中声功率、辐射力定量方法,本文的主要工作如下:针对高频声场中水听器孔径空间平均效应引起声压低估愈发严重,而现有声场定征修正模型不完善的问题,本文提出一种基于瑞利积分-菲涅尔近似的空间平均效应评估方法。该方法利用瑞利积分描述换能器辐射声压,通过在水听器有效孔径上积分,采用级数展开和菲涅耳近似得到水听器空间平均作用下的声压解析解,并逐次分析了平面活塞换能器声轴、垂直于声轴平面上以及聚焦换能器声轴、焦平面内的空间平均效应对声压、声束宽度的影响。在此基础上,将研究结果拓展至衰减介质中水听器的空间平均效应分析,并对菲涅耳近似和聚焦声场中瑞利积分声压表示的有效区间进行了讨论。从而解决了高频声场探测中水听器的孔径空间平均效应修正模型不完善的问题,为实现动态位置反馈的高频声压、声束宽度的精密测量奠定基础。针对水听器声压灵敏度校准水环境中低频大位移振动造成零差干涉校准系统工作点漂移引起信号衰落,无法稳定开展40 MHz以上声压灵敏度校准的问题,本文提出一种基于外差干涉测量原理的水听器校准方法。该方法在综合分析了干涉仪中非线性误差抑制、光电接收器频率响应校准以及谐波场中水听器空间平均效应修正等不确定度分量的基础上,采用高频声光调制器进行光波移频,对载波信号高速数据采样后进行数字正交解调,避免了零差干涉校准中工作点漂移和锁相反馈电路易振荡的问题,将声压灵敏度校准频率上限拓展至60MHz。该水听器校准方法首先分析了水中质点振速与声压重建原理,揭示了质点振动位移/速度与声压之间的函数关系。然后对薄膜随声波运动跟随性进行分析,建立薄膜厚度与声压衰减之间严格的数学模型,以修正薄膜厚度对各频率点下声压测量的影响。将透声反光薄膜放置于水面,利用外差干涉仪测量薄膜振动位移以复现水声声压,该结构避免了声光共路过程中声光干涉效应的影响。针对微弱剂量高频超声功率接近现有测量方法本底噪声,声场参数中声功率及辐射力缺乏有效计量手段的问题,本文在实现水听器空间平均效应修正和声压灵敏度校准的基础上,提出一种基于动态位置反馈的水听器平面扫描声功率测量和建模结合的辐射力评估方法。该方法首先应用外差干涉仪对水听器进行声压灵敏度校准,考虑水听器空间平均效应修正,利用射线声学方法构建微粒在高频聚焦声场(单波束声镊)中三维受力模型,通过搭建声场扫描装置实测声功率和声束宽度,并将其带入辐射力模型,解决了高频声场中声功率和辐射力定量难题。在上述研究的基础上,本文设计和搭建了声场平面扫描系统和水听器声压灵敏度外差干涉校准系统,包括声光移频外差干涉仪、载波信号解调系统、光电二极管幅频响应校准等单元,并在此基础上对空间平均效应修正模型、水听器声压灵敏度校准及声功率测量等环节进行了实验测试与分析。测试结果与分析表明,搭建的水听器声压灵敏度外差干涉校准系统校准频率上限高达60MHz,扩展不确定度优于9.8%;搭建的声场平面扫描系统声束宽度测量分辨率可达0.1μm,在水听器声压灵敏度校准频率60 MHz范围内开展声功率测量,测量功率下限小于1 m W,可实现n N量级的辐射力定量研究。
[Abstract]:High frequency sound field identification is the need for the development of advanced medical equipment and strategic emerging industries. Hydrophone is a transducer for underwater acoustic pressure detection, and is widely applied to acoustic measurement of ultrasonic medical diagnostic equipment. With the improvement of the resolution and the development of safety index in the application of high frequency ultrasound medical diagnostic equipment, the measurement accuracy and frequency range of sound pressure, sound power and radiation force in high frequency sound field are increasingly demanding. According to the requirements of ultrasonic medical development, the ultrasonic frequency needs to be at least tens of megahertz orders. The hydrophone aperture is smaller with increasing frequency, required to achieve micron level, further decrease the difficulty of production technology and the pressure sensitivity increased; and with the increase of frequency, the sound power is weak, close to the existing tracing method is the background noise to measure radiation, the high frequency sound field characteristic has brought new challenges to the use of hydrophone. The sign method of "high frequency sound field hydrophone based on the effect of spatial average correction, based on the analysis of pore space average hydrophone effect correction and pressure sensitivity calibration method, study the quantitative methods of radiation acoustic power, high frequency sound field, the main work is as follows: according to the high frequency sound field space hydrophone aperture averaging effect the pressure caused by underestimation is increasingly serious, and the existing acoustic characterization of modified model problems, this paper puts forward a method for evaluating the Finel approximate Rayleigh integral - space based on average effect. The method described by Rayleigh integral transducer radiation pressure, the effective aperture integral in hydrophone, using Fresnel series expansion and approximate solution of pressure hydrophone under the action of analytical space averaging, and the successive analysis of plane piston transducer acoustic axis, perpendicular to the acoustic axis plane and focusing transducer axis and the focal plane space average the effect of sound pressure and sound beam width. Based on that, we extend the research results to the spatial mean effect analysis of the hydrophone in the attenuation medium, and discuss the effective interval between the Fresnel approximation and the Rayleigh integral acoustic pressure representation in the focused acoustic field. It solves the problem that the correction model of the aperture spatial mean effect of hydrophone is not perfect in the high frequency acoustic field detection, and lays the foundation for the precise measurement of the high frequency sound pressure and the beam width of the dynamic position feedback. For the low frequency acoustic pressure sensitivity of hydrophone calibration in the water environment caused by large displacement vibration calibration system working point zero differential interference drift caused by signal fading, unable to carry out more than 40 MHz stable pressure sensitivity calibration problem, this paper presents a calibration method of hydrophone heterodyne interferometry principle based on water. The method in the comprehensive analysis of the interferometer nonlinear error suppression, photoelectric receiver frequency response calibration and hydrophone space harmonic field average effect correction based on the degree of uncertainty component, wave frequency shift using high frequency acousto-optic modulator, the carrier signal high speed data sampling digital quadrature demodulation, avoiding the problem of interference point the calibration drift and PLL feedback circuit easy oscillation zero difference, the pressure sensitivity calibration frequency limit is extended to 60MHz. The calibration method of the hydrophone first analyzes the principle of the velocity of vibration and the sound pressure reconstruction in the water, and reveals the function relation between the vibration displacement / velocity of the particle and the sound pressure. Then we analyze the follower of the film with the sound wave motion, establish a strict mathematical model between the thickness of the film and the sound pressure attenuation, so as to correct the influence of the thickness of the film on the sound pressure measurement at all frequencies. The transonic reflective film is placed on the water surface. Heterodyne interferometer is used to measure the vibration displacement of the membrane to reproduce the underwater acoustic pressure. The structure avoids the influence of acousto-optic interference in the acousto-optic common path. According to the background noise of the existing measurement methods to high frequency ultrasonic power weak acoustic power and radiation dose, the acoustic parameters in the lack of effective means of measurement problems, based on the realization of the hydrophone space average effect correction and pressure sensitivity calibration, evaluation method is proposed with dynamic position feedback sensor plane scanning acoustic power measurement and modeling based on the radiation force. This method used the pressure sensitivity of hydrophone calibration of heterodyne interferometer, considering the hydrophone space average effect, construction of particles in high frequency focused sound field using ray method (single beam acoustic tweezers) in three-dimensional force model, through building a sound field scanning device the measured acoustic power and beam width, and brought it into the radiation force model to solve the acoustic power and radiation of high frequency sound field quantitative problem. On the basis of the above research, this paper design and build a sound field scanning system and acoustic pressure sensitivity of hydrophone heterodyne interferometric calibration system, including acousto optical frequency heterodyne interferometer, the carrier signal demodulation system, photodiode frequency response calibration unit, and based on the spatial averaging effect correction model, and the acoustic pressure sensitivity of hydrophone calibration power measurement and other aspects of the testing and analysis of experiments. Analysis and test results show that the acoustic pressure sensitivity of hydrophone heterodyne interferometer calibration frequency calibration system is up to 60MHz, the expanded uncertainty is less than 9.8%; to build the field of the plane beam scanning system for measuring the width of the resolution can reach 0.1 M, conduct sound power measurement in the frequency range of 60 MHz acoustic pressure sensitivity of hydrophone calibration, measurement of power limit less than 1 m W, radiation quantitative research can achieve n N level.
【学位授予单位】：哈尔滨工业大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TB565.1

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