Limits and opportunities for miniaturising ultrasonic surgical devices based on a Langevin transducer

Li, X. , Stritch, T., Manley, K. and Lucas, M. (2021) Limits and opportunities for miniaturising ultrasonic surgical devices based on a Langevin transducer. IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, 68(7), pp. 2543-2553. (doi: 10.1109/TUFFC.2021.3065207)

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Abstract

Minimally invasive surgery offers opportunities for reduced morbidities, faster post-operative 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 haemostasis 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, miniaturisation 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 paper 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 keff 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 3rd longitudinal mode (L3) are almost equivalent to a much shorter version of a BLT driven at the same frequency but in its 1st 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, keff2 and gain, which 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.

Item Type:Articles
Additional Information:The research was supported by funding from the EPSRC Impact Acceleration Account with co-funding by Stryker (EP/R511705/1), and an EPSRC Programme Grant (Ultrasurge – Surgery enabled by Ultrasonics, EP/R045291/1).
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Lucas, Professor Margaret and Li, Dr Xuan
Authors: Li, X., Stritch, T., Manley, K., and Lucas, M.
College/School:College of Science and Engineering > School of Engineering > Systems Power and Energy
Journal Name:IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control
Publisher:IEEE
ISSN:0885-3010
ISSN (Online):1525-8955
Published Online:10 March 2021
Copyright Holders:Copyright © 2021 The Authors
First Published:First published in IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control 28(7):2543-2553
Publisher Policy:Reproduced under a Creative Commons License

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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
300671Surgery enabled by ultrasonicsMargaret LucasEngineering and Physical Sciences Research Council (EPSRC)EP/R045291/1ENG - Systems Power & Energy
304896EPSRC-IAA: Early Stage Commercialisation of a PET Imaging Agent for the Detection of Cardiovascular Disease and CancerAndrew SutherlandEngineering and Physical Sciences Research Council (EPSRC)EP/R511705/1Chemistry