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研究了不同尺寸吸收体产生的光声压的频谱特性:对于厘米量级、毫米量级和几百个微米量级的吸收体,产生光声压频谱的主要范围分别约为20~300 kHz、70 kHz~2.5 MHz和 400 kHz~20 MHz;讨论了不同频率范围的光声信号对重建图像的影响,低频段的光声信号能反映物体的非边界区域,而高频段的光声信号能突出物体的细微结构,尤其是物体的边界特征。提出了不同尺寸的吸收体要选用或设计不同带宽范围的探测器进行检测的方法,当探测器的带宽范围与光声压频谱范围基本吻合时,损失的频率成份较少,重建的光声图像效果较好,这一结论在仿真和实验结果中都得到了证明。实验用的光源为 YAG激光器,波长为 532 nm,重复频率为 30 Hz,脉宽为7 ns,探测器为针状的PVDF膜水听器,接收面积的直径为1 mm。
The spectral characteristics of photoacoustic pressure generated by absorbers of different sizes were studied: for the centimeter, millimeter and hundreds of micron absorbers, the main range of the photoacoustic pressure spectrum is about 20 ~ 300 kHz, 70 kHz ~ 2.5 MHz and 400 kHz ~ 20 MHz. The effect of photoacoustic signals in different frequency ranges on reconstructed images is discussed. The low-frequency photoacoustic signals can reflect the non-boundary regions of the objects, while the high-frequency photoacoustic signals can highlight The fine structure of objects, especially the boundary features of objects. A method of detecting or selecting detectors with different bandwidths for different sizes of absorbers is proposed. When the bandwidth of the detector is basically in agreement with the spectrum range of photoacoustic pressure, the frequency components lost are less, and the reconstructed photoacoustic images The effect is better, this conclusion has been proved in the simulation and experimental results. The experimental light source was a YAG laser with a wavelength of 532 nm, a repetition frequency of 30 Hz and a pulse width of 7 ns. The detector was a needle-shaped PVDF hydrophone with a receiving area of 1 mm in diameter.