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

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 literature
2) Research the potential applications of a switchable-mode ultrasonic transducer
3) Support the design and testing of torsional piezoelectric rings and investigate their incorporation into designs for a switchable-mode transducer
4) Develop FEA models in OnScale to design potential configurations of a switchable-mode ultrasonic transducer and to simulate their performance
5) Design, prototype, characterise and test a number of configurations with potential for controlled switchable responses, and validate the FEA models
6) Establish a range of performance tests to indicate the most promising transducer

FUSE has been designed to maximise impact in partnership with industry, international academics, and other organisations such as NPL and the NHS. It includes funded mechanisms to deal with opportunities in equality, diversity and integration (EDI) and in realisation of impactful outcomes.

EDI is aimed at realising the full potential of the talented individuals that join FUSE. Funding mechanisms include support for ten undergraduate internships to prime the pipeline into FUSE research studentships; part-time studentships reserved for people with specific needs to access this route; and talent scholarships for people from Widening Participation backgrounds. Additionally, cultural issues will be addressed through funded support for work life-balance activities and for workshops exploring the enhancement of research creativity and inventiveness through diversity.

People: As a community, FUSE will contribute to impact principally through its excellent training of outstanding people. At least 54 EngD and PhD graduates will emerge with very high value skills from the experience FUSE will provide in ultrasonics and through highly relevant professional skills. This will position them perfectly as future leaders in ultrasonics in the types of organisation represented by the partners.

Knowledge: FUSE will also create significant knowledge which will be captured in many different forms including industrial know-how, patents and processes, designs, and academic papers. Management of this knowledge will be integrated into the students' training, including data management and archival, and will be communicated effectively to those in positions to exploit it.

Economic Gain: In turn, the people and knowledge will lead to the economic impact that FUSE is ultimately designed to generate. The close interaction between the FUSE academics, its research students and industry partners will make it particularly efficient and, since FUSE includes both suppliers and customers, the transition from knowledge creation to exploitation will be accelerated.

Societal Benefit: FUSE is well placed to deliver a number of societal benefits which will reinforce our researcher training and external partner impacts. This activity encompasses new consumer products; improved public safety through advanced inspection across many industrial sectors; and new modalities for medical surgery and therapy. In addition, FUSE will provide engaging demonstrators to promote education in science, technology, engineering and maths, helping replenish the FUSE pipeline and supporting growth of the FUSE community far beyond its immediate members.

Impactful outcomes will gain from several specific funding mechanisms: horizon scanning workshops will focus on specific ultrasonic engineering application areas with industrial and other external participation; all FUSE students will have external partners and both industrial and international academic secondments will be arranged, as well as EngD studentships primarily in industry; and industry case studies will be considered. There will also be STEM promotion activity, funding ultrasonic technology demonstrators to support school outreach and public science and engineering events.