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

纵向(L)和扭转(T)相结合的振动运动在超声波装置中很常见。这种组合运动在设备的输出面或尖端处传递低强度振动。这些设备已经成为研究计划的基础，包括用于行星探测的超声波钻，用于骨活检的超声波针，以及超声波焊接设备。商用的例子包括超声手术剪和超声乳化装置。在这些例子中，换能器是基于传统的朗格万结构。然后有许多不同的方法来刺激左心室运动。一种是通过l波退化产生非均匀截面，通过沿l波路径切割和扭曲一些槽或螺旋，使部分波转换成T波，而其余部分不变地通过截面传播。第二种方法是通过调谐L模式和T模式，使其在相同频率上共振激发，从而耦合L模式和T模式。另一种模态耦合方法另外使用两组压电元件，其中一组产生L振动，另一组产生T振动。LT设备也可以基于在换能器本身传递LT运动，或者在模式退化设备的情况下，通过在附加到传统朗格万换能器输出面上的超声波喇叭中引入几何特征。在换能器本身传递LT运动的情况下，可以通过两组不同极性的压电环（一个激励L运动，另一个激励T运动）或通过在前质量中结合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度（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，它只依赖于尖端的T型振动。当前产品中的一个空白是可切换模式换能器，其中L和T运动可以在同一谐振频率下在一个器件中独立激发。本博士将探索一系列可以提供这种可切换模式超声波换能器的配置，包括通过结合不同的极化压电陶瓷元件。要进行的主要任务包括：1)审查目前可用的商业开发或在文献中发表的LT设备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，并研究将其纳入可切换模式换能器的设计4)在OnScale中开发FEA模型，以设计可切换模式超声换能器的潜在配置并进行模拟5)设计，原型，表征和测试具有控制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，以指出最有前途的传感器

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