Li Xuan, Stritch Thomas, Manley Kevin, Lucas Margaret
IEEE Trans Ultrason Ferroelectr Freq Control. 2021 Jul;68(7):2543-2553. doi: 10.1109/TUFFC.2021.3065207. Epub 2021 Jun 29.
Minimally invasive surgery offers opportunities for reduced morbidities, faster postoperative recovery, and reduced costs, and is a major focus of surgical device innovation. For ultrasonic surgical devices, which offer benefits of high precision, low force, and tissue selectivity in surgical procedures, there exist laparoscopic ultrasonic shears for minimally invasive surgeries that combine tissue cutting with vessel hemostasis and sealing functions. Another approach to laparoscopy that could enable new procedures, and increase the sites of surgeries that could be reached by an ultrasonic device, involves integrating a miniature ultrasonic tool with a flexible surgical robot. However, miniaturization presents challenges in delivering the ultrasonic vibrational energy required to cut hard and soft tissues, partly due to the concomitant small volume of piezoelectric material. This article aims to provide insights into the trade-offs between transducer size, volume of piezoceramic material, resonance frequency, and the achievable displacement amplitude of devices that, consistent with current ultrasonic surgical tools, are based on a bolted Langevin transducer (BLT) and tip. Different configurations of BLTs are studied, including a cascaded version, simple bar versions, and BLTs with different front mass geometries. Results show that a BLT with a larger number of piezoceramic rings exhibits a higher coupling coefficient [Formula: see text] but with the compromise of a lower mechanical Q and stronger nonlinear response at increasing excitation levels. Displacement amplitude is reduced considerably when a BLT is excited at a higher harmonic, where the PZT rings are maintained at a nodal plane, and the resonance frequency shift at increasing excitation levels increases significantly. The electromechanical and dynamic characteristics of a cascaded transducer excited in its third longitudinal mode (L3) are almost equivalent to a much shorter version of a BLT driven at the same frequency but in its first longitudinal mode (L1), showing that a cascaded BLT can be a realistic proxy for studying the dynamics of small BLT devices. A new figure of merit is proposed that is the product of Q , [Formula: see text], and gain, which [Formula: see text] accounts for the gain of cylindrical BLTs which is shown not to be unity. It also proves effective as it incorporates the key factors affecting the achievable displacement amplitude of a BLT, including for BLTs with gain profiles in the front mass. The order of highest to lowest amplitude of a series of six gain-profile BLTs matches the order estimated by the figure of merit. It is shown that a BLT with a stepped profile front mass can achieve displacement that has the potential to cut hard or soft tissue and exhibits the smallest shifts in resonance frequency at increasing excitation levels.
微创手术为降低发病率、加快术后恢复和降低成本提供了机会，是手术器械创新的一个主要重点。对于在手术过程中具有高精度、低作用力和组织选择性优势的超声手术器械，存在用于微创手术的腹腔镜超声剪刀，其将组织切割与血管止血及密封功能相结合。腹腔镜手术的另一种方法，即能够实现新手术并增加超声设备可到达的手术部位，涉及将微型超声工具与柔性手术机器人集成。然而，小型化在提供切割硬组织和软组织所需的超声振动能量方面带来了挑战，部分原因是压电材料的体积随之变小。本文旨在深入探讨换能器尺寸、压电陶瓷材料体积、共振频率以及与当前超声手术工具一致的基于螺栓朗之万换能器（BLT）和尖端的设备可实现的位移幅度之间的权衡。研究了不同配置的BLT，包括级联版本、简单棒状版本以及具有不同前端质量几何形状的BLT。结果表明，具有更多压电陶瓷环的BLT表现出更高的耦合系数[公式：见正文]，但折衷的是较低的机械品质因数以及在激励水平增加时更强的非线性响应。当BLT在更高谐波下激励时，位移幅度会大幅降低，此时压电陶瓷环保持在节点平面，并且在激励水平增加时共振频率偏移会显著增加。在其第三纵向模式（L3）下激励的级联换能器的机电和动态特性几乎等同于在相同频率下以其第一纵向模式（L1）驱动的短得多的BLT版本，这表明级联BLT可以作为研究小型BLT设备动力学的现实替代方案。提出了一个新的品质因数，它是品质因数Q、[公式：见正文]和增益的乘积，其中[公式：见正文]考虑了圆柱形BLT的增益，结果表明其不为1。它也被证明是有效的，因为它纳入了影响BLT可实现位移幅度的关键因素，包括前端质量具有增益分布的BLT。一系列六个具有增益分布的BLT的振幅从高到低的顺序与品质因数估计的顺序相匹配。结果表明，前端质量具有阶梯状分布的BLT能够实现有可能切割硬组织或软组织的位移，并且在激励水平增加时共振频率的偏移最小。
