基于背景纹影层析成像的高分辨率压力成像：MHz超声场的时空测量与水听器校准
High-resolution pressure imaging via background-oriented schlieren tomography: a spatiotemporal measurement for MHz ultrasound fields and hydrophone calibration
AI总结：
针对水听器测量超声压力场存在干扰声场、空间平均效应等局限，提出仅需背景图和相机的非接触式VT-BOS技术，可高时空分辨率测量MHz级、MPa量级超声场，还能估算水听器空间平均效应，测量范围可扩展，适用于血管流量测量、水听器校准等场景。
摘要：
本研究采用结合快速棋盘格解调与矢量层析成像的背景纹影技术（VT-BOS），测量了MHz级聚焦超声的时空压力场。水听器是水下超声局部压力测量的常用设备，但存在干扰声场、且会因空间平均效应影响压力测量结果的局限。为突破这些局限，我们提出VT-BOS这一非接触式声场测量技术，仅需一张背景图像和一台相机即可实现测量。实验中，VT-BOS对焦点宽度1.0 mm、频率4.55 MHz的聚焦声场进行测量，捕捉到了行波、反射波和驻波。我们探讨了该方法的三个核心特性：（1）VT-BOS与水听器测得的压力时间演化过程；（2）VT-BOS与其他技术在计算成本和空间分辨率上的差异；（3）VT-BOS的测量范围。结果表明，VT-BOS可成功量化时空声场，还能估算水听器在有限区域内的空间平均效应。VT-BOS以高时空分辨率测量数MPa的压力场，所需计算和测量时间更少。其可测量0.4至6.4 MPa的压力幅值，通过调整背景与目标的距离，测量范围有望扩展至0.3~201.6 MPa。VT-BOS是测量MHz频率、MPa量级声压的极具潜力的工具，对血管流量测量、水听器校准等应用至关重要。
英文摘要：
In this work, the spatiotemporal pressure field of MHz-focused ultrasound is measured using a background-oriented schlieren technique combined with fast checkerboard demodulation and vector tomography (VT-BOS). Hydrophones have been commonly employed to directly measure the local pressure in underwater ultrasound. However, their limitations include that they disturb the acoustic field and affect the measured pressure through the spatial averaging effect. To overcome such limitations, we propose VT-BOS as a non-contact technique for acoustic field measurements using only a background image and a camera. In our experiments, VT-BOS measures focused acoustic fields with a focal width of 1.0 mm and a frequency of 4.55 MHz, capturing traveling, reflected, and standing waves. We discuss three key features of this approach:(1) the temporal evolution of pressure measured by VT-BOS and hydrophones, (2) the differences in computational cost and spatial resolution between VT-BOS and other techniques, and (3) the measurement range of VT-BOS. The results demonstrate that VT-BOS successfully quantifies spatiotemporal acoustic fields and can estimate the hydrophones' spatial averaging effect over a finite area. VT-BOS measures pressure fields of several MPa with high spatiotemporal resolution, requiring less computational and measurement time. It is used to measure pressure amplitudes from 0.4 to 6.4 MPa, with the potential to extend the range to 0.3 ~ 201.6 MPa by adjusting the background-to-target distance. VT-BOS is a promising tool for measuring acoustic pressure in the MHz and MPa ranges, critical for applications such as vessel flow measurement and hydrophone calibration.
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