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A virtual prototype focussed ultrasound surgery (FUS) transducer has been developed with finite element analysis (FEA) (OnScale, Redwood City, CA, USA) comprising a single piezocermic element and an acoustic Fresnel lens. The piezoceramic is supported by microbaloon filled epoxy to approximate an air backing. The transducer housing and Fresnel lens materials are photopolymer resins of the type used in mask stereolithography (mSLA) printers. The design is optimised in FEA for the materials used in the Fresnel lens and the active piezoceramic layer. Six piezoceramic materials produced by Meggitt A/S (Kvistgaard, Denmark) were characterised in FEA and the acoustic properties of the photopolymer resins were measured using a standard pulse-echo approach to find their sound speed and frequency-dependent attenuation. The piezoceramic materials characterised spanned four major types: soft (PZ29); hard (PZT4); a specialised composition for high intensity focused ultrasound (HIFU) (PZ54); and low acoustic impedance, porous (PZ36HD). Acoustic impedance matching between the active material and the lens allowed the porous piezoceramic with lower piezoelectric and coupling coefficients to reach a higher intensity, spatial peak temporal average, (I SPTA ) at the focus (3.6 kWcm−2) than the hard PZT (2.46 kWcm−2). The focal intensity improved when HIFU and soft PZT were used, producing 5.69 kWcm−2 and 6.35 kWcm−2respectively.

High-Q PIC 181 hard piezoceramic and high-k Mn:PIN-PMN-PT piezocrystal thickness extensional rings have been compared for use in the actuation of an ultrasonic scalpel for robotic endo-surgery. Measured material properties have been verified with both finite element analysis and laser vibrometry, to assess the materials' suitability for high power devices. Measured material properties have been verified with both finite element analysis and laser vibrometry, to assess material's suitability for high power devices. Measurements have shown a $k_{t}=0.25$ and $Q_{m}=2200$ , and $k_{t}=0.62$ and $Q_{m}=1100$ , for PIC 181 and Mn:PIN-PMN-PT respectively. Conventional bolted Langevin-style transducers (BLTs) have been successfully designed and built to resonate at 20 kHz for both piezomaterials. Modal parameters and performance have been modelled in FEA and measured via laser doppler vibrometry. When devices were excited with $\mathbf{50\ V}_{rms}$ at L1 a displacement of: $\mathbf{8}\ \mu\mathbf{m}$ and $\mathbf{7}\ \mu \mathbf{m}$ was measured for PIC-181 and Mn:PIN-PMN-PT BLTs respectively. Results suggest that a similar resonant frequency can be achieved with a shorter and equally functional device excited by Mn:PIN-PMN-PT piezocrystals.

The Badger Explorer is a rig-less oil and gas exploration tool which drills into the subsea environment to collect geological data. Drill spoil is transported from the front end of the system to the rear, where the material is compacted. Motivated by the need to develop a highly efficient compaction system, an ultrasonic compactor for application with granular geological materials encountered in subsea environments is designed and fabricated as part of this study. The finite element method is used to design a compactor configuration suitable for subsea exploration, consisting of a vibrating ultrasonic horn called a resonant compactor head, which operates in a longitudinal mode at 20 kHz, driven by a Langevin piezoelectric transducer. A simplified version of the compactor is also designed, due to its ease of incorporating in a lab-based experimental rig, in order to demonstrate enhanced compaction using ultrasonics. Numerical analysis of this simplified compactor system is supported with experimental characterisation using laser Doppler vibrometry. Compaction testing is then conducted on granular geological material, showing that compaction can be enhanced through the use of an ultrasonic compactor.

The class V transducer has found popularity in a diverse range of applications such as surgical and underwater projection systems, where high vibration amplitude for relatively low piezoceramic volume is generated. The class IV transducer offers the potential to attain even higher performance per volume than the class V. In this research, a miniaturized class IV power ultrasonic flextensional transducer is proposed. Simulations were performed using PZFlex finite element analysis, and electrical impedance analysis and experimental modal analysis were conducted for validation, where a high correlation between simulation and experiment has been demonstrated.

Previous research by the authors has demonstrated the efficacy of an ultrasonic bone biopsy device that operates in a longitudinal (L)mode. Ultrasonic longitudinal-torsional (L-T)coupled vibration has proven successful in several applications including ultrasonic surgical devices. In this work, an L-mode ultrasonic bone biopsy device was geometrically modified by introducing helical slits to degenerate the longitudinal vibration into a composite L-T motion. The performance of the L-T biopsy needle device was then compared with the L-mode needle device based on their ability to penetrate animal bone samples. Finite element analysis was used to design the L-T needle. The depth and pitch of the helical slits were systematically modified in the FEA model with the aim of maximizing the achievable torsional displacement while ensuring sufficient frequency spacing between the L-T mode and the neighboring flexural modes. Experimental modal analysis (EMA)of the fabricated ultrasonic device was used to identify the modal parameters and validate the FEA model. Comparative penetration tests showed that to achieve penetration with the L-mode device, the operator was required to apply a slow backward and forward rotation as well as the small forward force, to maintain a forward motion and avoid imprinting of the needle tip. The resulting hole was slightly conical with some micro-damage on the hole surface. The L-T mode device, however, could penetrate the same animal bone sample only applying a small forward force, hence simplifying the procedure, increasing precision and resulting in a cylindrical, less damaged hole surface.

Ultrasonic surgical devices are currently used in various soft and hard tissue surgeries. This study focuses on investigating how modifications of the device driving signal can affect the needle penetration speed. The penetration speed, and therefore time for extraction of a biopsy, should be comparable with a conventional trephine biopsy needle. The ultrasonic bone biopsy device was designed using finite element analysis (FEA) and tuned to operate in a longitudinal mode at 25 kHz. The device was manufactured and experimental modal analysis (EMA) was used to validate the FEA model and measure the modal parameters. A series of tests were carried out, based on the time to perform a 5mm penetration of the needle into a polyurethane foam which acts as a substitute trabecular bone material. During each penetration the temperature and time were recorded. Following this, the study focused on investigating power modulation techniques, as have been widely adopted for phacoemulsification where power modulation in cataract surgery delivers less ultrasound energy to the eye and hence improves visual rehabilitation. It is shown how modifications to the signal shape and power modulation techniques when driving the ultrasonic bone biopsy device effect the penetration speed of an ultrasonic needle device.

In this study, we introduce a new prototype ultrasonic cutting device for bone surgery based on a class V flextensional cymbal transducer, configured for use in power ultrasonics applications, which removes many of the geometrical restrictions on the cutting tip of Langevin-based transducers. The benefit of incorporating a cymbal transducer is that since the cutting blade itselfdoes not have to be tuned, blade design can focus more closely on delivering the best interaction with bone to provide a highly accurate cut. Small variations to the geometry of the blade do not affect the final resonance frequency. Also the ultrasonic device can be miniaturised to allow the design of devices for delicate orthopaedic procedures involving minimal-access surgery. Theresults show how the cymbal transducer, driven by a single piezoceramic disc, can excite sufficiently high vibration displacement amplitudes at lower driving voltages. This is achieved by adapting the configuration of the cymbal to remove the problem of epoxy layer debonding, and by optimising the cymbal end-cap and geometry through finite element modelling supported withexperimental vibration characterisation. Preliminary characterisations of the resulting prototype ultrasonic bone cutting device, which operates at around 25 kHz, illustrate the success of this novel device design.

Ultrasonic bone cutting is known to offer advantages over more conventional techniques, however ultrasonic surgical devices for hard tissues are currently limited to small bone procedures. This study investigates the potential benefits of an ultrasonically assisted sagittal saw, and explores two designs based on incorporating planar ultrasonic transducers in sagittal saw blades. Designs were developed using finite element analysis (FEA) and were subsequently characterised using experimental modal analysis (EMA). Both blades were tuned to operate in a longitudinal mode of vibration. The dynamic response characterisations were measured and compared, using a harmonic analysis involving bi-directional frequency sweeps through the tuned longitudinal resonance at increasing excitation levels. The blades were tested in a linear loading rig, where they were drawn across a fixed piece of bone substitute material, mimicking a typical cut of a sagittal saw. Each blade was tested first with no ultrasonic excitation, and then under ultrasonic excitation. The depth of cut and the current draw of the drive actuator was recorded for comparison of performance. The results of the tests show that the current draw remained constant for control and ultrasonically excited cuts, whilst one design demonstrated a greater depth of cut for an ultrasonically excited blade.Ultrasonic bone cutting is known to offer advantages over more conventional techniques, however ultrasonic surgical devices for hard tissues are currently limited to small bone procedures. This study investigates the potential benefits of an ultrasonically assisted sagittal saw, and explores two designs based on incorporating planar ultrasonic transducers in sagittal saw blades. Designs were developed using finite element analysis (FEA) and were subsequently characterised using experimental modal analysis (EMA). Both blades were tuned to operate in a longitudinal mode of vibration. The dynamic response characterisations were measured and compared, using a harmonic analysis involving bi-directional frequency sweeps through the tuned longitudinal resonance at increasing excitation levels. The blades were tested in a linear loading rig, where they were drawn across a fixed piece of bone substitute material, mimicking a typical cut of a sagittal saw. Each blade was tested first with no ultrasonic excitation, ...

The class V cymbal is a flextensional transducer commonly used in low-power ultrasonic applications. The resonance frequency of the transducer can be tailored by the choice of end-cap and driver materials, and the dimensions of the end-caps. The cymbal transducer has one significant limitation which restricts the operational vibration amplitude of the device. This is the limit imposed by the mechanical strength of the bonding agent between the metal end-cap and the piezoceramic driver. Therefore, when there is an increase in the input power or displacement, the stresses in the bonding layer can lead to debonding, thereby rendering the cymbal transducer ineffective for high-power ultrasonic applications. In this paper, several experimental analyses have been performed, complemented by the use of Abaqus/CAE finite element analysis, in order to develop a high-power ultrasonic cutting device for bone surgery using a new configuration of cymbal transducer, which is optimised for operation at high displacement and high input power. This new transducer uses a combination of a piezoceramic disc with a metal ring as the driver, thereby improving the mechanical coupling with the metal end-cap.

This study investigates combining longitudinal and torsional (L–T) vibration responses at the output face of a Langevin transducer. A mode degeneration method is adopted that converts the longitudinal response excited by the axially poled piezoceramic discs in the transducer into combined L–T vibration in the transducer front mass using geometric modifications of the wave path. The study uses three techniques; numerical, analytical, and experimental, in order to estimate and validate transducer electro-mechanical parameters for different geometric modifications, and also to evaluate transducer performance for different excitation levels in terms of the desired L–T response. A finite element (FE) analysis is used to optimise the mechanical structure of the transducer while the analytical model, which is based on an equivalent-circuit approach, is used to estimate the electrical impedance spectra and to confirm some of the FE calculations prior to fabrication. These models are then validated through an experimental characterization of the vibration response and impedance response and the results show that the operating frequency and torsionality can be tailored through modification of the transducer geometry.

Finite element (FE) model of die necking process of an aluminium hollow thin cylinder has been developed. The input parameters of material properties and coefficient of friction, µ for the model have been deducted from our previous experimental study. Later the models have been validated against experimental data as reported in the previous studies. For the die necking process, the FE model has successfully to predict how much the original diameter of the aluminium hollow cylinder can be maximised necked with and without applying ultrasonic vibration. FE models showed that the application of ultrasonic vibration during the necking process has reduced buckling of the cylinder body if compared to the necking process without ultrasonic. The benefit of applying ultrasonic vibration in sheet metal forming process has been related to the reduction of interface friction between die and specimen.

A number of architectures for a hollow Langevin ultrasonic transducer are proposed and evaluated. One of these is optimised by finite element modelling and is then manufactured and analysed experimentally. The preload on the transducer ceramics is increased and the effect on the performance is measured. At maximum preload the results of an experimental modal analysis are used to determine the natural frequency and response of both the operating longitudinal mode and unwanted bending modes. The performance of the hollow transducer is compared to a solid commercial transducer containing the same volume of piezoceramic material. The efficiency is shown to be comparable. Higher ultrasonic displacement amplitudes are achieved with the hollow transducer although a lower Q-factor is found.

This paper presents a study of the effects of superimposing ultrasonic vibrations on the lower platen in tension and compression tests of aluminium. By measuring the oscillating force response as well as the static force, it is shown that the experimentally derived stress–strain data from these tests does not satisfy the description of a simple oscillatory stress superposition model. Finite element models of tension and compression tests are created and a description of the contact friction condition is included for the compression test model. By incorporating ultrasonic vibration of the lower platen for an interval during plastic deformation, the finite element model predicts that the stress–strain relationship satisfies a simple oscillatory stress superposition model. The finite element models are then developed further to investigate the predicted stress–strain relationship if a softer material model is incorporated only during the interval of ultrasonic excitation. For the tension test model, this allows the predicted stress–strain data to match the experimentally derived data. For the compression test model, by combining a softer material model description with a change in the coefficient of friction at the contact surface, only during the interval of ultrasonic excitation, the finite element model predicted stress–strain data matched the experimentally derived stress–strain data. The study indicates that it is not sufficient to explain the effects of ultrasonic excitation in metal forming processes only in terms of oscillatory stress superposition and contact friction.

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.

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.

The performance of an ultrasonic cutting device critically relies on the interaction of the cutting tool and the material to be cut. A finite element (FE) model of ultrasonic cutting is developed to enable the design of the cutting blade to be influenced by the requirements of the toolmaterial interaction and to allow cutting parameters to be estimated as an integral part of designing the cutting blade. In this paper, an application in food processing is considered and FE models of cutting are demonstrated for toffee; a food product which is typically sticky, highly temperature dependent, and difficult to cut. Two different 2D coupled thermal stress FE models are considered, to simulate ultrasonic cutting. The first model utilises the debond option in ABAQUS standard and the second uses the element erosion model in ABAQUS explicit. Both models represent a single blade ultrasonic cutting device tuned to a longitudinal mode of vibration cutting a specimen of toffee. The model allows blade tip geometry, ultrasonic amplitude, cutting speed, frequency and cutting force to be adjusted, in particular to assess the effects of different cutting blade profiles. The validity of the model is highly dependent on the accuracy of the material data input and on the accuracy of the friction and temperature boundary condition at the blade-material interface. Uniaxial tensile tests are conducted on specimens of toffee for a range of temperatures. This provides temperature dependent stress-strain data, which characterises the material behaviour, to be included in the FE models. Due to the difficulty in gripping the tensile specimens in the test machine, special grips were manufactured to allow the material to be pulled without initiating cracks or causing the specimen to break at the grips. A Coulomb friction condition at the bladematerial interface is estimated from experiments, which study the change in the friction coefficient due to ultrasonic excitation of a surface, made from the same material as the blade, in contact with a specimen of toffee. A model of heat generation at the blade-toffee interface is also included to characterise contact during ultrasonic cutting. The failure criterion for the debond model assumes crack propagation will occur when the stress normal to the crack surface reaches the tensile failure stress of toffee and the element erosion model uses a shear failure criterion to initiate element removal. The validity of the models is discussed, providing some insights into the estimation of contact conditions and it is shown how these models can improve design of ultrasonic cutting devices.

Ultrasonic cutting is an established technology in the cutting of food products. As the high-cost components of an ultrasonic cutting system are the ultrasonic generator and transducer, some designs have concentrated on running several cutting blades from a single power source. This strategy is undoubtedly economic, but problems remain with reliability. Blade failure during cutting is a common problem in ultrasonic systems and therefore strategies are proposed to reduce stress levels at the failure locations. Many alternative blade profiles are investigated using finite element (FE) models, which are validated by experimental modal analysis (EMA) using a 3D laser Doppler vibrometer (LDV). Combining three strategies can reduce the stress level at the failure location on cutting blades. The first investigates the blade profile at the failure location with the aim of incorporating sufficient gain at reduced stress levels. The second concentrates on detuning the block horn and blades in order to move the longitudinal node away from the highest stressed section of the blade. Finally, a redesign of the block horn is studied in order to eliminate the effects of blade flexural vibrations in the longitudinal cutting mode.

In ultrasonic devices consisting of serially coupled tuned components, components whose tuned length dimension is large compared to other dimensions, or components with profiles designed for high gain, the response of the device during operation is often characterised by modal interactions, and especially the excitation of combination resonances. The effects on ultrasonic devices are high noise levels, component failures and poor operating performance. In this paper, energy exchanges between modes are characterised to illustrate the adverse effects of combination resonances. Design solutions are proposed to eliminate these effects which concentrate on reducing the number of modes. In particular, a novel half-wavelength three-blade cutting system tuned to the first longitudinal mode has been designed by finite element modelling. An experimental investigation demonstrates that the measured response does not show evidence of modal interactions.

A validated finite element analysis is described for the upsetting of a cylindrical specimen between two parallel rigid dies, where the workpiece is exposed to kinematic and radial or longitudinal ultrasonic oscillatory loading conditions. Numerical results are presented to show the effects of variation in several parameters on the die-specimen interface for Plasticine, and how stress superposition, temperature and friction reduction contribute to the reduced deformation forces, for both radial and longitudinal die oscillation directions.

On-line condition monitoring is widely used to detect failure mechanisms in large highvoltage three-phase induction motors. The high-voltage winding is installed in a complex, stator core structure which vibrates due to electromagnetic forces. Insulation degradation can be diagnosed via on-line monitoring of partial discharges but the fundamental cause is often mechanical damage due to stator vibration. This paper presents results of an investigation into the natural vibratory response of the complete stator assembly. Results from finite element models of complex stator assemblies, including the frames, are supported by experimental measurements. These include freely suspended stator cores as in previous studies, and also now introduce the much more realistic condition of the complete stator assembly securely bolted on to a solid baseplate. The knowledge gathered in this study will aid the application of a vibration monitoring strategy to detect stator core vibration which can lead to winding insulation damage.

Ultrasonic block horns are prone to reliability problems associated with modal activity close to the tuned operating frequency. This paper presents an approach to block horn design, which relies on two laser based vibration measurement techniques, electronic speckle pattern interferometry (ESPI) and laser doppler velocimetry (LDV) modal analysis, to validate finite element (FE) models. Block horn vibration characteristics are interpreted from experimental and theoretical data such that successful horn redesign can be achieved from modifications to the FE models.

The behaviour of the cancellous bone surrogate material, rigid polyurethane foam (PUF), subject to power ultrasonic vibration excitation has been studied, with the purpose of identifying a methodology to investigate the effects that ultrasonic surgical devices have on biological tissue materials. To characterise the vibrational response to ultrasonic excitation, non-contact measurement of the full in-plane displacement field of PUF plate specimens was performed by combining the use of an ultra-high speed camera and 2D digital image correlation. To investigate the thermal response, an infrared camera was used in real time to detect the temperature field. The measured surface displacement and strain fields of the PUF specimens and the thermal response are compared with data from an analytical model, and two different finite element models using Abaqus and PZFlex. The close agreement between calculated and measured data provides initial confidence in the use of the models for predicting the effects of ultrasonic excitation on tissue materials. The measurement data demonstrate the success of the experimental method for measuring vibrational responses in a hard tissue surrogate material at the ultrasonic frequencies associated with power ultrasonic surgical devices.

The design of an ultrasonic cutting blade is presented in this study. The blade is designed as a cutting tool for orthopaedic surgery. It is tuned at a frequency of 35kHz and in the first longitudinal mode. Finite element analysis was carried out to investigate the blade dynamic parameters and its structural behaviour. Two prototypes of the design were manufactured and experimentally tested. This included experimental modal analysis to reveal the actual modal behaviour of the blades and cutting experiments to observe the overall performance and temperature accumulated. The temperature of the cutting area during the test was monitored by a thermal imaging camera and the cutting samples were examined afterwards. The analysis and experimental work conducted have demonstrated that the blade was operating efficiently at the desired frequency. However, a relatively high temperature of the cutting blade was observed which has stimulated further design modification.

Ultrasonic tools are used for a variety of cutting applications in surgery and the food industry, but when they are applied to harder materials, such as rock, their cutting performance declines because of the low effective impulse delivered by each vibration cycle. To overcome this problem, a technique known as high-frequency/low-frequency (or alternatively, ultrasonic/sonic) drilling is employed. In this approach, an ultrasonic step-horn is used to deliver an impulse to a free mass which subsequently moves toward a drilling bit, delivering the impulse on contact. The free mass then rebounds to complete the cycle. The horn has time between impacts to build significant vibration amplitude and thus delivers a much larger impulse to the free mass than could be delivered if it were applied directly to the target. To maximize the impulse delivered to the target by the cutting bit, both the momentum transfer from the ultrasonic horn to the free mass and the dynamics of the horn/free mass/cutting bit stack must be optimized. This paper uses finite element techniques to optimize the ultrasonic horns and numerical propagation of the stack dynamics to maximize the delivered effective impulse, validated in both cases by extensive experimental analysis.

The Cymbal transducer consists of an inner piezoelectric disk mechanically coupled to two thin metal endcaps on each of its faces by an epoxy. This miniature flextensional transducer is an emerging technology that has been used principally in underwater applications for large area and restricted volume transmit and receive arrays. This paper is focused on the use of this transducer in power ultrasonics applications. Based on previous studies of ceramic and metal cymbal configurations, a new improved model has been analyzed to evaluate the differences and advantages against the traditional cymbal. For this purpose, a theoretical electro-mechanical analysis and finite element analysis (FEA) have been realized. The aim of this work is to develop a new double ceramic half-cymbal prototype for high power ultrasonic cutting applications.

The use of ultrasonic excitation of tools and dies in metal forming and joining operations has been the subject of ongoing research for many years. However, the lack of understanding about the effects of ultrasonic vibrations on the forming process has resulted in difficulties in maximising the benefits and applications of this technology. In particular, experimental characterisations of the effects of superimposing ultrasonic oscillations have largely relied on interpretations of measurements of the mean forming load, which have been insufficient. In this research, a simple forming test is designed and the effects of superimposing ultrasonic vibrations on the die, which is tuned to a longitudinal mode at 20 kHz, are studied via force‐displacement measurements, which rely on a piezoelectric transducer to monitor the oscillatory force, and finite element analysis.

Nasa funded studies have proven that ultrasonics is a viable technology for extraterrestrial drilling. Previous research by the authors has indicated that ultrasonic longitudinal-torsional coupled vibrations may improve rock excavation. In this study, two approaches to the development of torsional output from a Langevin transducer are pursued: coupling the longitudinal mode with a torsional mode and degenerating the longitudinal mode to output torsional motion at the tip using helical flutes cut into the sides of the horn. The amplitude of the output motion and the electrical properties of the horn whilst these modes are being driven are investigated and the findings are validated experimentally.

Tuned cylindrical radial mode ultrasonic horns offer advantages over ultrasonic probes in the design of flow-through devices for bacterial inactivation. This study presents a comparison of the effectiveness of a radial horn and probe in the inactivation of Escherichia coli K12. The radial horn is designed using finite element analysis and the predicted modal parameters are validated using experimental modal analysis. A validated finite element model of the probe is also presented. Visual studies of the cavitation fields produced by the radial horn and probe are carried out using luminol and also backlighting to demonstrate the advantages of radial horns in producing a more focused cavitation field with widely dispersed streamers. Microbiological studies show that, for the same power density, better inactivation of E. coli K12 is achieved using the radial horn and, also, the radial horn offers greater achievable power density resulting in further improvements in bacterial inactivation. The radial horn is shown to be more effective than the probe device and offers opportunities to design in-line flow-through devices for processing applications.

When dealing with vibration analysis at ultrasonic frequencies it is necessary to consider carefully the techniques to be used and the parameters to be monitored. Conventional sensors and their associated electronics invariably are designed with linear characteristics in the audible range only. Ultrasonic machines cannot readily be adapted to monitor the transmission line forces as interruption of the system's geometry will detune the system. This paper presents the approach taken to analyse an ultrasonically excited thick cylinder using finite element analysis, electronic speckle pattern interferometric analysis and modal analysis supported by software for structural modification.

Using a single-blade ultrasonic cutting device, a study of ultrasonic cutting of three very different materials is conducted using specimens of cheese, polyurethane foam and epoxy resin. Initial finite element models are created, based on the assumption that the ultrasonic blade causes a crack to propagate in a controlled mode 1 opening, and these are validated against experimental data from three point bend fracture tests and ultrasonic cutting experiments on the materials. Subsequently, the finite element model is developed to represent ultrasonic cutting of a multi-layered material. Materials are chosen whose properties allow a model to be developed that could represent a multi-layer food product or biological structure, to enable ultrasonic cutting systems to be designed for applications both in the field of food processing and surgical procedures. The model incorporates an estimation of the friction condition between the cutting blade and the material to be cut and allows adjustment of the frequency, cutting amplitude and cutting speed.

The application of ultrasonics in metal forming applications has been shown to reduce the forming load significantly in many research studies. The load reduction has been related to the stress superposition effect, rise in temperature and change in the friction condition between the specimen and die interfaces. This paper reports an investigation into the effects of superimposed ultrasonic oscillation of the die in compression tests on aluminium specimens. In particular, a finite element model is developed to simulate uniaxial compression and to model the effects of a change in the friction boundary condition when ultrasonic excitation is applied to the lower platen. The model predictions of the stress–strain relationship can be compared with test data to provide some insights into the effects of the interfacial condition. The paper shows how the analysis of the test data, combined with finite element models of ultrasonic compression test simulations, allows some initial conclusions to be drawn regarding the influence of the interfacial friction during ultrasonic compression.

This paper describes a preliminary study of the influence of ultrasonics on the boundary conditions associated with the equipment walls in a soft solid forming operation using Plasticine as a material model. A detailed finite element analysis is described involving the upsetting of a cylindrical specimen between two parallel rigid dies with kinematics and ultrasonic oscillatory loading conditions. A series of squeeze flow experiments has been conducted to validate the finite element models. The oscillation parameters were measured using a 3D laser Doppler vibrometer to complement the measurement of reaction forces.

This paper describes the modelling of the indentation of an elasto-viscoplastic material. The finite element code ABAQUS was used to study the bulk mechanical, thermal and interface frictional characteristics for rigid wedge indenters. A series of simulations has been performed at a constant velocity to prescribed depths of penetration for a range of wedge surface temperatures and semi-included angles. Selected experimental data are provided as a basis for validating the numerical simulation. In the simulations, the constitutive behaviour of the model material Plasticine is treated as non-linear elasto-viscoplastic, in which the stress scales linearly with the elastic strain and non-linearly with the plastic strain rate. The results demonstrate that the FE simulations agree well with the experimental data of displacement, strain and stress for all the range of wedge angles and temperatures examined.

A wedge indentation test has been carried out, in which an ultrasonic vibration was superimposed at a frequency of 20 kHz to investigate the effects of ultrasonic vibration on the indentation mechanics of Plasticine. A finite element simulation was employed as basis for interpreting the experimental data. The model incorporated material and geometric non-linearity and the slide line method for modeling contact problems. The finite element results show that stress superposition only accounts for part of the load reduction measured under superimposed ultrasonic vibration, and that there are no temperature changes during the process. Consequently, the reduction in indentation load may be attributed to a combination of stress superposition and friction reduction.

An investigation through experiments and finite element analysis (FEA) has been carried out to study the effects of applying ultrasonic oscillations to the lower platen in forming tests for two different metals. Previous research has shown that by applying ultrasonic vibrations to the lower platen in compression tests on pure aluminium specimens, the resulting stress-strain relationship can be characterised by a temporary effective softening of the material properties during intervals of ultrasonic excitation. The current research demonstrates this effect in two different metal specimens and additionally shows that finite element simulations can be used to model the behaviour in terms of both volume and surface effects. In this study, the ultrasonic excitation was introduced both prior to and post yield and the process simulations were developed in the FEA software Abaqus. The data recorded from experiments and predicted by the FEA illustrate how ultrasonically assisted metal forming can result in a lowering of the static flow stress, consistent with the effective material softening proposed previously in studies of the acoustoplastic effect.

A Class V cymbal flextensional transducer is composed of a piezoceramic disc or ring sandwiched between two cymbal-shaped shell end-caps. These end-caps act as mechanical transformers to convert high impedance, low radial displacement of the piezoceramic into low impedance, large axial motion of the end-cap. The cymbal transducer was developed in the early 1990's at Penn State University, and is an improvement of the moonie transducer which has been in use since the 1980's. Despite the fact that cymbal transducers have been used in many fields, both as sensors and actuators, due to its physical limitations its use has been mainly at low power intensities. It is only very recently that its suitability for high amplitude and high power applications has been studied, and consequently implementation in this area of research remains undeveloped. This paper employs experimental modal analysis (EMA), vibration response measurements and electrical impedance measurements to characterise two variations of the cymbal transducer design, both aimed at incorporation in ultrasonic cutting devices. The transducers are fabricated using the commercial Eccobond 45LV epoxy adhesive as the bonding agent. The first cymbal transducer is of the classic design where the piezoceramic disc is bonded directly to the end-caps. The second cymbal transducer includes a metal ring bonded to the outer edge of the piezoceramic disc. The reason for the inclusion of this metal ring is to improve the mechanical coupling with the end-caps. This would therefore make this design particularly suitable for power ultrasonic applications, reducing the possibility of debonding at the higher ultrasonic amplitudes. The experimental results demonstrate that the second cymbal design is a significant improvement on the more classic design, allowing the transducer to operate at higher voltages and higher amplitudes, exhibiting a linear response over a practical power ultrasonic device driving voltage range. The results also show that the device can be accurately tuned using finite element modelling and that the cymbal exhibits a modal response as predicted by the finite element models.

Radially oscillating dies can be designed for reducing friction forces in metal forming processes. The cylindrical dies are prone to reliability problems due to the inherent dense modal activity close to the tuned operating mode. The determination of die vibration characteristics is critical to successful die design and a design strategy that relies on validated finite element modelling is therefore proposed. This paper discusses the adaptation of vibration analysis techniques to ultrasonic modal parameter estimation and proposes a redesign strategy to improve the reliability of ultrasonic dies.

Since the 1950's researchers have carried out investigations into the effects of applying ultrasonic excitation to metals undergoing elastic and plastic deformation. Experiments have been conducted where ultrasonic excitation is superimposed in complex metalworking operations such as wire drawing and extrusion, to identify the benefits of ultrasonic vibrations. This study presents a finite element analysis of ultrasonic excitation applied to the extrusion of a cylindrical aluminium bar. The effects of friction on the extrusion load are reported for the two excitation configurations of radially and axially applied ultrasonic vibrations and the results are compared with experimental data reported in the literature.

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.

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.

When dealing with vibration analysis at ultrasonic frequencies it is necessary to consider carefully the techniques to be used and the parameters to be monitored. Conventional sensors and their associated electronics invariably are designed with linear characteristics in the audible range only. Ultrasonic machines cannot readily be adapted to monitor the transmission line forces as interruption of the systems geometry will detune the system. This paper presents the approach taken to analyse an ultrasonically excited thick cylinder using finite element analysis, electronic speckle pattern interferometric analysis and modal analysis supported by software for structural modification.