Andrew Mathieson

The influence of piezoceramic stack location on nonlinear behavior of langevin transducers

Power ultrasonic applications such as cutting, welding, and sonochemistry often use Langevin transducers to generate power ultrasound. Traditionally, it has been proposed that the piezoceramic stack of a Langevin transducer should be located in the nodal plane of the longitudinal mode of vibration, ensuring that the piezoceramic elements are positioned under a uniform stress during transducer operation, maximizing element efficiency and minimizing piezoceramic aging. However, this general design rule is often partially broken during the design phase if features such as a support flange or multiple piezoceramic stacks are incorporated into the transducer architecture. Meanwhile, it has also been well documented in the literature that power ultrasonic devices driven at high excitation levels exhibit nonlinear behaviors similar to those observed in Duffing-type systems, such as resonant frequency shifts, the jump phenomenon, and hysteretic regions. This study investigates three Langevin transducers with different piezoceramic stack locations by characterizing their linear and nonlinear vibrational responses to understand how the stack location influences nonlinear behavior.

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.

In vitro performance testing of two arcuate oscillating saw blades designed for use during tibial plateau leveling osteotomy

OBJECTIVE To test the cutting performance of 2 commercially available oscillating saws designed for use during tibial plateau leveling osteotomy (TPLO) and to evaluate the influence of saline irrigation on cutting performance. STUDY DESIGN In vitro experimental study. SAMPLE POPULATION Composite polyurethane test blocks (n=40); 24 m TPLO saw blades. METHODS Controlled force cutting tests were performed using custom-made laminated bone substitute blocks to model the canine proximal tibia. Half of the trials were irrigated with 0.9% saline solution. Outcome measures were test block temperature (measured 1.5 m from the cutting zone), cutting rate, and cutting surface wear. Durability was measured by recording change in performance over multiple consecutive trials. RESULTS The Synthes blade cut the test blocks with ∼64% less heat generation and at a 63% faster cutting rate compared with the Slocum blade. Although wear of the Synthes blade was ∼50% greater after 19 uses, this did not negatively impact cutting performance. Saline irrigation produced no significant effect on peak cutting temperature but significantly reduced cutting rate for both saws. CONCLUSIONS Our results favor the Synthes blade in terms of cutting performance and the Slocum blade in terms of wear resistance.

Feasibility of lead-free piezoceramic based power ultrasonic transducers

Lead-based piezoceramics are currently the most widely used transduction material in power ultrasonic applications. Directives such as the Restriction of Hazardous Substances (RoHS and RoHS2) regulate the sale of electrical and electronic equipment containing hazardous substances, such as lead, entering the European marketplace. However, lead-based piezoceramics have been exempt due to the lack of a genuine lead-free equivalent. Lead-free piezoceramics were first developed in the 1950s, however their relatively poor properties when compared to PZT left them largely neglected until the implementation of the European directive. This study investigates the incorporation of a modern lead-free piezoceramic, a variant of bismuth sodium titanate (BNT), into a commercial power ultrasonic transducer used in semiconductor wire bonding. It is reported that a device containing BNT was capable of forming wire bonds, and that the lead-free transducer exhibited properties that could make them suitable in other power ultrasonic applications.

Analysis of Lead-Free Piezoceramic-Based Power Ultrasonic Transducers for Wire Bonding

Since the 1950s, lead zirconate-titanate (PZT) has been the dominant transduction material utilized in power ultrasonics, while lead-free piezoceramics have been largely neglected due to their relatively poor piezoelectric and electromechanical properties. However, the implementation of environmental directives that regulate and control the use of hazardous materials, such as lead, triggered a search for new high-performance lead-free piezoceramics. Recent advances have led to lead-free piezoceramics exhibiting properties similar to PZT, but despite this, reports utilizing these novel piezoceramics in practice are limited. This research employs a modified variant of bismuth sodium titanate (BNT) in a power ultrasonic transducer used for metal welding during the manufacture of semiconductors. The important factors for transducer reliability and performance are investigated, such as piezoceramic aging and stack preload level. It is reported that BNT-based transducers exhibit good stability, and can withstand a stack preload level of 90 MPa without depoling. Although the BNT-based transducers exhibited larger dissipative losses compared to identical PZT8-based transducers, the tool displacement gain was larger under constant current conditions. Semiconductor wire bonds which satisfied the commercial quality control requirements were also formed by this BNT-based transducer.

Ultrasonic cutting for surgical applications

This chapter investigates the application of ultrasonic cutting in surgical procedures, reviewing its origins to the current art. The mechanisms of ultrasonic cutting of both soft and mineralized tissues are discussed with reference to device design, experimental characterization, and clinical use. Finally, integrating new materials in devices, including transduction materials and shape memory alloys, as well as novel transducer designs, illustrate the future trends of ultrasonics in surgical cutting devices.

Optimization of Ultrasonic Horns for Momentum Transfer and Survivability in High-Frequency/Low Frequency Planetary Drill Tools

Drilling tools for planetary landers must operate with a minimum of applied preload and deliver little torque to the drillstring, given the limited ability of small landers to react these loads. Several proposed drill systems use a vibrating ultrasonic horn to excite a slower oscillatory motion in a free-mass beneath, which in turn impacts upon a cutting bit, delivering the energy of many high-frequency cycles in fewer but more powerful blows with significant effective impulse. In this paper a range of ultrasonic horns with differing taper are presented and their respective ability to deliver momentum, expressed as a change in velocity ΔV, to a free-mass are reviewed. The subsequent behavior of the dynamic stack, which consists of the horn, the free-mass and the cutting bit, is analysed and maximization of the ΔV is shown, amongst other considerations, to be associated with improved drilling performance. However it is recognized that the application of significant ΔV to a free-mass is associated with high stress at the tip of the horn, independent of horn shape optimization. Spalling of the horn material, typically titanium alloy, is predicted by finite-element analysis of a contact event and recorded experimentally with high-speed photography. To prevent this damage titanium nitride (TiN) coating, plasma nitride diffusion (PND), and combined TiN coating and PND treatment of the titanium alloy, as well as solid caps of silicon carbide/titanium matrix composite (TMC) and polycrystalline diamond (PCD), are investigated to determine the protection they offer the horns. Modified horns are subjected to drilling loads and the damage inspected under an electron microscope. Polycrystalline diamond is shown to resist damage extremely well and an ultrasonic horn capped with this material is designed and manufactured. However, this horn does not perform well compared to titanium alloy, TiN-coated and PND-treated horns and significant energy losses are recorded at the horn/cap interface.

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 the 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 utilizes micrometric vibrations generated at the distil tip of a full-wavelength resonant ultrasonic device, while the second utilizes 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 behavior of the devices identified through experimental techniques closely match the behavior calculated through numerical and finite-element analysis 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.

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 end-effectors. The devices investigated in this study, designed using finite element analysis, have been experimentally characterized to identify their impedance and resonant characteristics.

An ultrasonically assisted sagittal saw for large bone surgeries

Large bone cutting surgeries are predominantly undertaken using sagittal saws, whereas ultrasonic devices are currently limited to small shallow cuts in bone, for example in maxillofacial surgeries. Given the known benefits of ultrasonic cutting, this study considers an approach of superimposing ultrasonic vibration on a sagittal saw blade motion by designing the saw as a planar transducer. Finite element modeling was used to establish piezoceramic and blade geometries, culminating in two designs, one for a longitudinal-mode transducer and one for a lateral-mode transducer. The two resulting planar transducers were manufactured, with the piezoceramic plates bonded to the blades using a high strength epoxy. Impendence plots confirmed the tuned ultrasonic frequency for each transducer. The ultrasonic vibration amplitude of the blade was also measured, although was limited by the device tracking and drive system. Initial cutting tests carried out on a sagittal saw test rig demonstrated small reductions in cut temperature and cut time compared with control blades. These are very early, but promising results for developing this new surgical technology.