Sferruzza Jean-Pierre, Birer Alain, Chavrier Françoise, Cathignol Dominique
INSERM, Lyon, France.
IEEE Trans Ultrason Ferroelectr Freq Control. 2002 Oct;49(10):1453-60. doi: 10.1109/tuffc.2002.1041087.
New clinical concepts in lithotripsy demand small shock heads. Reducing the size of piezoelectric shock heads will be possible only if the pressure generated at the surface of each transducer can be increased so that the total pressure at the focus remains the same. To solve this problem, different solutions were proposed. For example, it has been demonstrated that piezocomposite material, as opposed to piezoceramic material, allows the generation of a higher surface pressure before breaking, mainly because radial modes are dramatically reduced. In addition, in a previous paper, we showed the feasibility of generating high-pressure pulse waves without increasing the transducer voltage by using sandwiched transducers, which are a stack of two or more transducers. Some discrepancies appeared, however, between the pressure measured at the surface of the front transducer and the arithmetic sum of the pressures generated by each transducer constituting the stack. In fact, development of such stacked transducers capable of generating surface pressures in the range of 2 to 5 MPa is very complex, which may explain why no aging tests have been reported in the literature thus far. In the first part of this paper, we theoretically determine the importance of the electroacoustical coupling between the two transducers on the generated surface pressure. We show that pressure losses due to these electroacoustical couplings are less than 5%. Experimental measurements done on a stacked transducer assembled and tightened in a castor oil-filled tank are in excellent accordance with the theoretical measurements. Using this assembly technique, it was possible to obtain, on average, out of four elements, a pressure of 7.5 MPa for the duration of 4 million shocks, which would allow the treatment of approximately 1000 patients.
碎石术的新临床概念需要小型冲击头。只有当每个换能器表面产生的压力能够增加，以使焦点处的总压力保持不变时，才有可能减小压电冲击头的尺寸。为了解决这个问题，人们提出了不同的解决方案。例如，已经证明，与压电陶瓷材料相比，压电复合材料在破裂前能够产生更高的表面压力，主要是因为径向模式显著减少。此外，在之前的一篇论文中，我们展示了通过使用夹层换能器（由两个或更多换能器堆叠而成）在不增加换能器电压的情况下产生高压脉冲波的可行性。然而，在前部换能器表面测得的压力与构成堆叠的每个换能器产生的压力的算术和之间出现了一些差异。事实上，开发能够产生2至5兆帕表面压力的这种堆叠换能器非常复杂，这可能解释了为什么迄今为止文献中尚未报道老化测试。在本文的第一部分，我们从理论上确定了两个换能器之间的电声耦合对产生的表面压力的重要性。我们表明，由于这些电声耦合导致的压力损失小于5%。在一个装满蓖麻油的水箱中组装并拧紧的堆叠换能器上进行的实验测量与理论测量结果非常吻合。使用这种组装技术，平均从四个元件中，在400万次冲击的持续时间内可以获得7.5兆帕的压力，这将允许治疗大约1000名患者。
