Investigation of mechanisms to control the longitudinal and torsional mode vibration response of an ultrasonic transducer

在超声装置中，纵向(L)和扭转(T)振动联合运动是很常见的。组合运动在设备的输出面或尖端提供LT振动。作为研究方案基础的这类设备的例子包括用于行星探测的超声波钻头、用于骨活检的超声针和超声波焊接设备。商业上的例子包括超声波手术剪刀和超声乳化设备。在这些示例中，换能器基于传统的朗之万式配置。然后，有许多不同的方法来激发LT运动。一种是通过L波的退化，它沿着L波的路径切割和扭曲一些槽或螺旋线，从而产生一个不均匀的截面，使得一部分波转换成T波，而其余部分不变地传播通过该截面。第二种方法是通过调谐L模和T模以使这两个模在同一频率下被共振激发来耦合这两个模。另一种模式耦合方法另外使用了两组压电元件，其中一组产生L振动，而第二组产生T振动。LT设备还可以基于在换能器本身中传递LT运动，或者在模式退化设备的情况下，通过在连接到传统朗之万换能器输出面的超声波喇叭中引入几何特征来实现。如果LT运动是在换能器本身中传递的，这可以通过两组不同极化的压电环(一个激励L，另一个激励T运动)或通过在前质量中加入螺旋或开槽结构来实现。然而，在所有情况下，通常很少控制装置的扭转力(定义为尖端的切向与轴向振动位移的比率)。还有一种商业化的超声乳化装置，它只依赖尖端的T型振动。目前产品的一个空白是可切换模式换能器，可以在同一设备上以相同的共振频率单独激励L和T运动。本博士将探索一系列可以提供这种可切换模式超声换能器的配置，包括通过结合不同极化的压电陶瓷元件。将执行的主要任务包括：1)回顾目前商业上开发的或在文献中发表的可用LT器件2)研究可切换模式超声换能器的潜在应用3)支持扭转压电环的设计和测试，并调查它们与可切换模式换能器设计的结合4)在OnScale中开发有限元模型以设计可切换模式超声换能器的潜在配置并模拟其性能5)设计、原型、表征和测试具有可控可切换响应潜力的许多配置并验证有限元模型6)建立一系列性能测试以确定最有希望的换能器

Combining longitudinal (L) and torsional (T) vibration motion is common in ultrasonic devices. The combined motion deliver LT vibrations at the output face or tip of the device. Examples of such devices that have been the basis of research programmes include ultrasonic drills for planetary exploration, ultrasonic needles for bone biopsy, and ultrasonic welding devices. Commercial examples include ultrasonic surgical shears and phacoemulsification devices. In these examples, the transducer is based on a conventional Langevin configuration. There are then a number of different approaches to exciting the LT motion. One is through L-wave degeneration that creates a non-uniform section, by cutting and twisting a number of slots or a helix along the path of the L-wave such that part of the wave converts into a T wave whilst the remaining part propagates unchanged through the section. A second approach is to couple the L mode and a T mode by tuning the two modes to be excited in resonance at the same frequency. Another mode coupling approach additionally uses two set of piezoelectric elements, where one set generates L vibration whilst the second set generates T vibration. LT devices can also be based on delivering LT motion in the transducer itself or, in the case of mode degeneration devices, by introducing the geometrical features in an ultrasonic horn attached to the output face of a conventional Langevin transducer. Where LT motion is delivered in the transducer itself, this can be via two sets of differently poled piezoelectric rings (one exciting L and the other exciting T motion) or by incorporating a helical or slotted structure in the front mass. In all cases, however, there is often little control of the torsionality of the device (defined as the ratio of tangential to axial vibrational displacement of the tip). There is also a commercialised phacoemulsification device that relies only on T mode vibrations of the tip. A gap in current offerings is a switchable-mode transducer, where L and T motions can be excited independently in one device at the same resonance frequency. This PhD will explore a range of configurations that can deliver such a switchable-mode ultrasonic transducer, including through the incorporation of differently poled piezoceramic elements.The main tasks to be carried out include:1) A review of the currently available LT devices developed commercially or published in the literature2) Research the potential applications of a switchable-mode ultrasonic transducer3) Support the design and testing of torsional piezoelectric rings and investigate their incorporation into designs for a switchable-mode transducer4) Develop FEA models in OnScale to design potential configurations of a switchable-mode ultrasonic transducer and to simulate their performance5) Design, prototype, characterise and test a number of configurations with potential for controlled switchable responses, and validate the FEA models6) Establish a range of performance tests to indicate the most promising transducer