Radulescu E G, Lewin P A, Wójcik J, Nowicki A, Berger W A
Department of Electrical and Computer Engineering, School of Biomedical Engineering, Drexel University, 3141 Chestnut Street, MS Biomed. 7-727, Philadelphia, PA 19104, USA.
Ultrasonics. 2004 Apr;42(1-9):367-72. doi: 10.1016/j.ultras.2003.11.019.
The influence of finite aperture and frequency response of piezoelectric ultrasonic hydrophone probes on the Thermal and Mechanical Indices was investigated using a comprehensive acoustic wave propagation model. The experimental verification of the model was obtained using a commercially available, 8 MHz, dynamically focused linear array and a single element, 5 MHz, focused rectangular source. The pressure-time waveforms were recorded using piezoelectric polymer hydrophone probes of different active element diameters and bandwidths. The nominal diameters of the probes ranged from 50 to 500 microm and their usable bandwidths varied between 55 and 100 MHz. The Pulse Intensity Integral (PII), used to calculate the Thermal Index (TI), was found to increase with increasing bandwidth and decreasing effective aperture of the probes. The Mechanical Index (MI), another safety indicator, was also affected, but to a lesser extent. The corrections needed were predicted using the model and successfully reduced the discrepancy as large as 30% in the determination of PII. The results of this work indicate that by accounting for hydrophones' finite aperture and correcting the value of PII, all intensities derived from the PII can be corrected for spatial averaging error. The results also point out that a caution should be exercised when comparing acoustic output data. In particular, hydrophone's frequency characteristics of the effective diameter and sensitivity are needed to correctly determine the MI, TI, and the total acoustic output power produced by an imaging transducer.
利用综合声波传播模型，研究了压电超声水听器探头的有限孔径和频率响应对热指数和机械指数的影响。使用市售的8MHz动态聚焦线性阵列和单个5MHz聚焦矩形源对该模型进行了实验验证。使用不同有源元件直径和带宽的压电聚合物水听器探头记录压力-时间波形。探头的标称直径范围为50至500微米，其可用带宽在55至100MHz之间变化。发现用于计算热指数（TI）的脉冲强度积分（PII）随着探头带宽的增加和有效孔径的减小而增加。另一个安全指标机械指数（MI）也受到影响，但程度较小。使用该模型预测了所需的校正，并成功地将PII测定中的差异降低了30%。这项工作的结果表明，通过考虑水听器的有限孔径并校正PII值，可以校正所有从PII导出的强度的空间平均误差。结果还指出，在比较声学输出数据时应谨慎。特别是，需要水听器的有效直径和灵敏度的频率特性来正确确定MI、TI以及成像换能器产生的总声学输出功率。
