A miniature surgical drill using ultrasonic/sonic frequency vibration

A study is presented of a miniature ultrasonic surgical drill designed for bone biopsy, based on an ultrasonic/sonic drill which converts high frequency to low frequency vibrations through a freely vibrating mass between an ultrasonic transducer-horn and a drill bit. For conventional surgical drilling using a rotary drill or an ultrasonic drill, considerable power is required to penetrate into bone and the efficiency is low. However, for ultrasonic/sonic drilling, sufficient acoustic energy is accumulated and then released through each impact to achieve precise drilling with a lower power requirement. The ultrasonic/sonic drill was originally invented for rock drilling in low gravity environments. In this study it is incorporated in a miniature ultrasonic surgical drill and the effective impulse delivered to the bone is used to evaluate the drilling performance. To develop a miniature surgical device based on maximising the effective impulse, optimisation of the ultrasonic horn and free-mass is first demonstrated. The shape and dimensions of the ultrasonic horn and free-mass are determined through FEA, which focuses on maximising the post-collision velocity of the free-mass. Then, the entire dynamic stack constituting the surgical drill device is modelled as a mass-spring-damper system to analyse the dynamic behaviour. The numerical model is validated through experiments, using a prototype drill, which record the velocity of the free-mass and the drilling force. The results of the numerical models and experiments indicate this miniature ultrasonic surgical drill can deliver sufficient impulse to penetrate bone and form the basis of an ultrasonically activated bone biopsy device

Nonlinear characterization of half and full wavelength power ultrasonic devices

It is well known that power ultrasonic devices whilst driven under elevated excitation levels exhibit nonlinear behaviors. If no attempt is made to understand and subsequently control these behaviors, these devices can exhibit poor performance or even suffer premature failure. This paper presents an experimental method for the dynamic characterization of a commercial ultrasonic transducer for bone cutting applications (Piezosurgery® Device) operated together with a variety of rod horns that are tuned to operate in a longitudinal mode of vibration. Near resonance responses, excited via a burst sine sweep method were used to identify nonlinear responses exhibited by the devices, while experimental modal analysis was performed to identify the modal parameters of the longitudinal modes of vibration of the assemblies between 0-80 kHz. This study tries to provide an understanding of the effects that geometry and material choices may have on the nonlinear behavior of a tuned device

Understanding nonlinear vibration behaviours in high-power ultrasonic surgical devices

Ultrasonic surgical devices are increasingly used in oral, craniofacial and maxillofacial surgery to cut mineralized tissue, offering the surgeon high accuracy with minimal risk to nerve and vessel tissue. Power ultrasonic devices operate in resonance, requiring their length to be a half-wavelength or multiple-half-wavelength. For bone surgery, devices based on a half-wavelength have seen considerable success, but longer multiple-half-wavelength endoscopic devices have recently been proposed to widen the range of surgeries. To provide context for these developments, some examples of surgical procedures and the associated designs of ultrasonic cutting tips are presented. However, multiple-half-wavelength components, typical of endoscopic devices, have greater potential to exhibit nonlinear dynamic behaviours that have a highly detrimental effect on device performance. Through experimental characterization of the dynamic behaviour of endoscopic devices, it is demonstrated how geometrical features influence nonlinear dynamic responses. Period doubling, a known route to chaotic behaviour, is shown to be significantly influenced by the cutting tip shape, whereas the cutting tip has only a limited effect on Duffing-like responses, particularly the shape of the hysteresis curve, which is important for device stability. These findings underpin design, aiming to pave the way for a new generation of ultrasonic endoscopic surgical devices

Nonlinear characterisation of power ultrasonic devices used in bone surgery

Ultrasonic cutting has existed in surgery since the 1950s. However, it was not until the end of the 20th century that advances in ultrasonic tool design, transduction and control allowed commercially viable ultrasonic cutting devices to enter the market. Ultrasonic surgical devices, like those in other power ultrasonic applications such as drilling and welding, require devices to be driven at high power to ensure sufficient output motion is produced to fulfil the application it is designed to perform. With the advent of novel surgical techniques surgeons require tuned ultrasonic tools which can reduce invasiveness while giving access to increasingly difficult to reach surgical sites. To fulfil the requirements of novel surgical procedures new tuned tools need to be designed. Meanwhile, it is well documented that power ultrasonic devices, whilst driven at high power, are inherently nonlinear and, if no attempt is made to understand and subsequently control these behaviours, it is likely that these devices will suffer from poor performance or even failure. The behaviour of the commercial ultrasonic transducer used in bone surgery (Piezosurgery® Device) is dynamically characterised through finite element and experimental methods whilst operating in conjunction with a variety of tuned inserts. Finite element analysis was used to predict modal parameters as well as stress levels within the tuned devices whilst operating at elevated amplitudes of vibration, while experimental modal analysis validated predicted resonant frequencies and mode shapes between 0-80kHz. To investigate the behaviour of tuned devices at elevated vibrational amplitudes near resonance, responses were measured whilst the device was excited via the burst sine sweep method. In an attempt to provide an understanding of the effects that geometry, material selection and wavelength of tuned assemblies have on the behaviour of an ultrasonic device, tuned inserts consisting of a simple rod horn design were characterised alongside more complex cutting inserts which are used in maxillofacial and craniofacial surgery. From these results the aim will be to develop guidelines for design of tuned inserts. Meanwhile, Langevin transducers, commonly known as sandwich or stack transducers, in their most basic form generally consist of four parts; a front mass, a back mass, a piezoceramic stack and a stud or bolt holding the parts together under a compressive pre-load. It is traditionally proposed that the piezoceramic stack is positioned at or close to the vibrational nodal point of the longitudinal mode, however, this also corresponds with the position of highest dynamic stress. It is also well documented that piezoceramic materials possess a low linear stress threshold, therefore this research, in part, investigates whether locating the piezoceramic stack away from a position of intrinsic high stress will affect the behaviour of the device. Through experimental characterisation it has been observed that the tuned devices under investigation exhibited; resonant frequency shifts, jump amplitudes, hysteretic behaviour as well as autoparametric vibration. The source of these behaviours have been found to stem from device geometry, but also from heating within the piezoceramic elements as well as joints with different joining torques

Design of a slender tuned ultrasonic needle for bone penetration

This paper reports on an ultrasonic bone biopsy needle, particularly focusing on design guidelines applicable for any slender tuned ultrasonic device component. Ultrasonic surgical devices are routinely used to cut a range of biological tissues, such as bone. However the realisation of an ultrasonic bone biopsy needle is particularly challenging. This is due to the requirement to generate sufficient vibrational amplitude capable of penetrating mineralised tissue, while avoiding flexural vibrational responses, which are known to reduce the performance and reliability of slender ultrasonic devices. This investigation uses finite element analysis (FEA) to predict the vibrational behaviour of a resonant needle which has dimensions that match closely to an 8Gx4inch bone marrow biopsy needle. Features of the needle, including changes in material and repeated changes in diameter, have been included and systematically altered to demonstrate that the location of and geometry of these features can significantly affect the resonant frequency of bending and torsional modes of vibration while having a limited effect on the frequency and shape of the tuned longitudinal mode. Experimental modal analysis was used to identify the modal parameters of the selected needle design, validating the FEA model predictions of the longitudinal mode and the close flexural modes. This verifies that modal coupling can be avoided by judicious small geometry modifications. Finally, the tuned needle assembly was driven under typical operational excitation conditions to demonstrate that an ultrasonic biopsy needle can be designed to operate in a purely longitudinal motion

Ultrasonic Biopsy Needle Based on the Class IV Flextensional Configuration

This study builds on previous research by the authors, where the design of a miniaturized class IV transducer configuration and adaption for including an end-effector for use in biopsy are investigated. Device design has focused on the generation of displacement uniformity across the output surface of the transducer. This has the aim of maximizing device reliability and minimizing nonlinear responses that could adversely affect the performance of devices incorporating endeffectors. The devices investigated in this study, designed using finite element analysis, have been experimentally characterized to identify their impedance and resonant characteristics

An Empirical Exploration of Exchange Rate Target-Zones

In the context of a flexible-price monetary exchange rate model and the assumption of uncovered interest parity, we obtain a measure of the fundamental determinant of exchange rates. Daily data for the European Monetary System are used to explore the importance of non-linearities in the relationship between the exchange rates and fundamentals. Many implications of existing "target-zone" exchange rate models are tested; little support is found for existing non-linear models of limited exchange rate flexibility.

Ultrasonic needles for bone biopsy

Bone biopsy is an invasive clinical procedure where a bone sample is recovered for analysis during the diagnosis of a medical condition. When the architecture of the bone tissue is required to be preserved, a core-needle biopsy is taken. Although this procedure is performed while the patient is under local anaesthesia, the patient can still experience significant discomfort. Additionally, large haematoma can be induced in the soft tissue surrounding the biopsy site due to the large axial and rotational forces which are applied through the needle to penetrate bone. It is well documented that power ultrasonic surgical devices offer advantages of low cutting force, high accuracy and preservation of soft tissues. This paper reports a study of the design, analysis and test of two novel power ultrasonic needles for bone biopsy that operate using different configurations to penetrate bone. The first utilises micrometric vibrations generated at the distil tip of a full-wavelength resonant ultrasonic device, while the second utilises an ultrasonic-sonic approach where vibrational energy generated by a resonant ultrasonic horn is transferred to a needle via the chaotic motion of a free-mass. It is shown that the dynamic behaviour of the devices identified through experimental techniques closely match the behaviour calculated through numerical and FEA methods, demonstrating that they are effective design tools for these devices. Both devices were able to recover trabecular bone from the metaphysis of an ovine femur, and the biopsy samples were found to be comparable to a sample extracted using a conventional biopsy needle. Furthermore, the resonant needle device was also able to extract a cortical bone sample from the central diaphysis, which is the strongest part of the bone, and the biopsy was found to be superior to the sample recovered by a conventional bone biopsy needle

Macroalgal Monitoring in the Great Bay Estuary: 2018 Annual Report

Since 2013, the abundance and taxa of intertidal macroalgae have been assessed at fixed locations throughout the Great Bay Estuary in New Hampshire. Algal abundance may be influenced by environmental conditions such as nutrient levels, water temperature, light and invasive species. Therefore, abundance of different algal groups can provide insights into the overall health of the estuary and signal ecological change. In 2018, intertidal abundance data for percentage cover and biomass were collected, as planned, from five of the eight sites. For the first time, subtidal sampling arrays were also incorporated at all four sites in Great Bay proper to monitor macroalgae at lower elevations and to collect data on eelgrass communities coexisting with the algae