分析了移相在宽带多普勒流剖面仪(Broadband Acoustic Doppler Current Profiler,BBADCP)中的误差表现,确定了BBADCP使用移相方式的适用条件。从宽带编码信号特征出发,分析了移相造成的时域“错位”和频域频谱幅值不均匀衰减、功率谱密...分析了移相在宽带多普勒流剖面仪(Broadband Acoustic Doppler Current Profiler,BBADCP)中的误差表现,确定了BBADCP使用移相方式的适用条件。从宽带编码信号特征出发,分析了移相造成的时域“错位”和频域频谱幅值不均匀衰减、功率谱密度分散现象,确定了影响阵列输出的变量分别为:中心频率、带宽、编码阶数、重复次数、相邻阵元时延;从波束指向和宽度、阵列输出信噪比损失、测频误差三个方面考虑,综合分析了移相波束形成在上述变量变化时的表现。仿真发现,增加中心频率与带宽的比值、提高阵元数量且阵元间距在λ/2时,波束指向准确、宽度理想,阵列输出信噪比损失较小,同时发现,在低信噪比条件下,应尽可能减小归一化带宽以保证移相测频结果的准确性。展开更多
In order to measure the flow velocity of carbon particle suspension perpendicular to the receiving axis of ultrasound transducer, the standard deviation of photoacoustic Doppler frequency spectrum is used to estimate ...In order to measure the flow velocity of carbon particle suspension perpendicular to the receiving axis of ultrasound transducer, the standard deviation of photoacoustic Doppler frequency spectrum is used to estimate the bandwidth broadening, and the spectrum standard deviation is calculated by an auto-correlation method. A 532 nm pulsed laser with the repetition rate of 20 Hz is used as a pumping source to generate photoacoustic signal. The photoacoustic signals are detected using a focused PZT ultrasound transducer with the central frequency of 10 MHz. The suspension of carbon particles is driven by a syringe pump. The complex photoacoustic signal is calculated by Hilbert transformation from time domain signal before auto-correlation. The standard deviation of the Doppler bandwidth broadening is calculated by averaging the auto-correlation results of several individual A scans. The feasibility of the proposed method is demonstrated by measuring the spectrum standard deviation of the transversal carbon particle flow from 5.0 mm/s to 8.4 mrn/s. The experimental results show that the auto-correlation result is approximately linearly distributed within the measuring range.展开更多
文摘分析了移相在宽带多普勒流剖面仪(Broadband Acoustic Doppler Current Profiler,BBADCP)中的误差表现,确定了BBADCP使用移相方式的适用条件。从宽带编码信号特征出发,分析了移相造成的时域“错位”和频域频谱幅值不均匀衰减、功率谱密度分散现象,确定了影响阵列输出的变量分别为:中心频率、带宽、编码阶数、重复次数、相邻阵元时延;从波束指向和宽度、阵列输出信噪比损失、测频误差三个方面考虑,综合分析了移相波束形成在上述变量变化时的表现。仿真发现,增加中心频率与带宽的比值、提高阵元数量且阵元间距在λ/2时,波束指向准确、宽度理想,阵列输出信噪比损失较小,同时发现,在低信噪比条件下,应尽可能减小归一化带宽以保证移相测频结果的准确性。
基金supported by the Joint Funds of the National Natural Science Foundation of China(No.U1204612)the Natural Science Foundation of He’nan Educational Committee(No.13A416180)
文摘In order to measure the flow velocity of carbon particle suspension perpendicular to the receiving axis of ultrasound transducer, the standard deviation of photoacoustic Doppler frequency spectrum is used to estimate the bandwidth broadening, and the spectrum standard deviation is calculated by an auto-correlation method. A 532 nm pulsed laser with the repetition rate of 20 Hz is used as a pumping source to generate photoacoustic signal. The photoacoustic signals are detected using a focused PZT ultrasound transducer with the central frequency of 10 MHz. The suspension of carbon particles is driven by a syringe pump. The complex photoacoustic signal is calculated by Hilbert transformation from time domain signal before auto-correlation. The standard deviation of the Doppler bandwidth broadening is calculated by averaging the auto-correlation results of several individual A scans. The feasibility of the proposed method is demonstrated by measuring the spectrum standard deviation of the transversal carbon particle flow from 5.0 mm/s to 8.4 mrn/s. The experimental results show that the auto-correlation result is approximately linearly distributed within the measuring range.
