Nonlinear and hysteretic magnetomechanical model for magnetostrictive transducers

The growing interest on magnetostrictive materials for generation of strains and forces in smart structure systems motivates the development of increasingly accurate models of the performance of these materials as used in transducers. The proposed magnetomechanical model provides a characterization of the material magnetization as well as the strain and force output by a transducer in response to quasistatic applied magnetic fields. The model is built in three steps. In the first, the mean field model for ferromagnetic hysteresis originally developed by Jiles and Atherton is used to compute the magnetization arising from the application of magnetic fields. While this model provides an accurate characterization of the field-induced magnetization at constant stress, it is insufficient in cases where the stress state of the magnetostrictive driver varies significantly during operation. To model the stress-induced magnetization changes, or magnetomechanical effect, a \u27law of approach\u27 to the anhysteretic magnetization is considered. The magnetization hysteresis model in combination with this law of approach provides a more realistic representation of the bidirectional energy transduction taking place in magnetostrictive transducers. In the second step, an even-term series expansion posed in terms of the magnetization is employed to calculate the magnetostriction associated with magnetic moment rotations within domains. While the magnetostriction provides a good description of the total material strain at the low field levels where elastic dynamics are of secondary significance, it is highly inaccurate at higher drive levels, in which the elastic response gains significance. This elastic or material response is considered in the third and last step, by means of force balancing in the form of a PDE system with magnetostrictive inputs and boundary conditions consistent with the transducer mechanical design. The solution to this PDE system provides the longitudinal displacements and corresponding strains and forces generated by the magnetostrictive driver. Since the formulation precludes analytic solution, a Galerkin discretization is employed to express the PDE in the form of a temporal system, which is subsequently solved using finite difference approximations. The ability of the model to accurately characterize the magnetomechanical behavior of magnetostrictive transducers is demonstrated via comparison of model simulations with experimental measurements collected from two Terfenol-D transducers

The Roles of Piezoelectric Ultrasonic Motors in Industry 4.0 Era: Opportunities & Challenges

Piezoelectric Ultrasonic motors (USM) are based on the principle of converse piezoelectric effect i.e., vibrations occur when an electrical field is applied to piezoelectric materials. USMs have been studied several decades for their advantages over traditional electromagnetic motors. Despite having many advantages, they have several challenges too. Recently many researchers have started focusing on Industry 4.0 or Fourth Industrial revolution phase of the industry which mostly emphasis on digitization & interconnection of the entities throughout the life cycle of the product in an industrial network to get the best possible output. Industry 4.0 utilizes various advanced tools for carrying out the nexus between the entities & bringing up them on digital platform. The studies of the role of USMs in Industry 4.0 scenario has never been done till now & this article fills that gap by analyzing the piezoelectric ultrasonic motors in depth & breadth in the background of Industry 4.0. This article delivers the novel working principle, illustrates examples for effective utilization of USMs, so that it can buttress the growth of Industry 4.0 Era & on the other hand it also analyses the key Industry 4.0 enabling technologies to improve the performance of the USMs

On the Application of Mechanical Vibration in Robotics-Assisted Soft Tissue Intervention

Mechanical vibration as a way of transmitting energy has been an interesting subject to study. While cyclic oscillation is usually associated with fatigue effect, and hence a detrimental factor in failure of structures and machineries, by controlled transmission of vibration, energy can be transferred from the source to the target. In this thesis, the application of such mechanical vibration in a few surgical procedures is demonstrated. Three challenges associated with lung cancer diagnosis and treatment are chosen for this purpose, namely, Motion Compensation, tumor targeting in lung Needle Insertion and Soft Tissue Dissection: A robotic solution is proposed for compensating for the undesirable oscillatory motion of soft tissue (caused by heart beat and respiration) during needle insertion in the lung. An impedance control strategy based on a mechanical vibratory system is implemented to minimize the tissue deformation during needle insertion. A prototype was built to evaluate the proposed approach using: 1) two Mitsubishi PA10-7C robots, one for manipulating the macro part and the other for mimicking the tissue motion, 2) one motorized linear stage to handle the micro part, and 3) a Phantom Omni haptic device for remote manipulation. Experimental results are given to demonstrate the performance of the motion compensation system. A vibration-assisted needle insertion technique has been proposed in order to reduce needle–tissue friction. The LuGre friction model is employed as a basis for the study and the model is extended and analyzed to include the impact of high-frequency vibration on translational friction. Experiments are conducted to evaluate the role of insertion speed as well as vibration frequency on frictional effects. In the experiments conducted, an 18 GA brachytherapy needle was vibrated and inserted into an ex-vivo soft tissue sample using a pair of amplified piezoelectric actuators. Analysis demonstrates that the translational friction can be reduced by introducing a vibratory low-amplitude motion onto a regular insertion profile, which is usually performed at a constant rate. A robotics-assisted articulating ultrasonic surgical scalpel for minimally invasive soft tissue cutting and coagulation is designed and developed. For this purpose, the optimal design of a Langevin transducer with stepped horn profile is presented for internal-body applications. The modeling, optimization and design of the ultrasonic scalpel are performed through equivalent circuit theory and verified by finite element analysis. Moreover, a novel surgical wrist, compatible with the da Vinci® surgical system, with decoupled two degrees-of-freedom (DOFs) is developed that eliminates the strain of pulling cables and electrical wires. The developed instrument is then driven using the dVRK (da Vinci® research kit) and the Classic da Vinci® surgical system

Experimental investigations of the Mach-effect for breakthrough space propulsion

This research was conducted within the framework of the SpaceDrive project funded by the German Aerospace Center to develop propellantless propulsion for interstellar travel. The experiments attempted to measure mass fluctuations predicted by the Mach-effect theory derived from General Relativity and observed through torsion balance measurements by Woodward (2012). The combination of such mass fluctuations with synchronized actuation promises propellantless thrust with a significantly better thrust-to-power ratio than photon sails. Thus, experiments using different electromechanical devices including the piezoelectric Mach-effect thruster as tested by Woodward et al. (2012) were pursued on sensitive thrust balances. The tests were automated, performed in vacuum and included proper electromagnetic shielding, calibrations, and different dummy tests. To obtain appropriate driving conditions for maximum thrust, characterization of the experimental devices involved spectrometry, vibrometry, finite element analysis, and circuit modeling. Driving modes consisted of sweeps, resonance tracking, fixed frequency, and mixed signals. The driving voltage, frequency, stack pre-tension, mounting, and thruster orientation were also varied. Lastly, different amplifier electronics were tested as well, including Woodward’s original equipment. Experiments on the double-pendulum and torsion balances with a resolution of under 10 nN and an accuracy of 88.1 % revealed the presence of force peaks with a maximum amplitude of 100 nN and a drift of up to 500 nN. The forces mainly consisted of switching transients whose signs depended on the device’s orientation. These force transients were also observed in the zero-thrust configurations. No additional thrust was observed above the balance drift, regardless of the driving conditions or devices tested. In addition, finite element and vibrometry analysis revealed that the vibration from the actuator was transmitted to the balance beam. Moreover, simulations using a simple spring-mass model showed that the slower transient effects observed can be reproduced using small amplitude, high-frequency vibrations. Hence, the forces observed can be explained by vibrational artifacts rather than the predicted Mach-effect thrust. Then, centrifugal balance experiments measured the mass of a device subjected to rotation and energy fluctuations, with a precision of up to 10 µg and a high time resolution. The measurements relied on piezoelectric- and strain gauges. Their calibration methods presented limitations in the frequency range of interest, resulting in discrepancies of up to 500 %. However, the tests conducted with capacitive and inductive test devices yielded experimental artifacts about three orders of magnitude below the mass fluctuations of several milligrams predicted by the Mach-effect theory. Although the piezoelectric devices presented more artifacts due to nonlinearity and electromagnetic interaction, all rotation experiments did not show the expected dependence on the rotation frequency. In summary, the search for low thrust and small mass fluctuations consisted of challenging experiments that led to the development of innovative and sensitive instruments, while requiring a careful consideration of experimental artifacts. The results analysis led to the rejection of mass fluctuations and thrusts claimed by Woodward’s Mach-effect theory and experiments. The quest for breakthrough space propulsion must thus continue a different theoretical or experimental path.:List of Figures List of Tables List of Abbreviations List of Variables and Symbols 1. Introduction 1.1 Research Motivation 1.2 Objectives 1.3 Content Overview 1.4 Team Work 2. Literature Review 2.1 Fundamentals of Space Propulsion 2.2 Mach’s Principle 2.3 Woodward’s Mach-effect Theory 2.3.1 Derivation of the Mass Fluctuation Equation 2.3.2 Design of a Mass Fluctuation Thruster 2.4 Woodward-type Experiments 2.5 Force and Transient Mass Measurements 3. Electromechanical Characterization 3.1 Piezoelectric Actuators 3.1.1 Basic Properties 3.1.2 Actuator Design 3.1.3 Mach-effect Thruster Devices 3.1.4 Magnetostrictive Actuator 3.1.5 Numerical Analysis of MET Behavior 3.1.6 Vibrometry Analysis 3.1.7 Impedance Spectroscopy 3.1.8 Circuit Modeling 3.1.9 Predictions 3.2 Electronics 3.2.1 Description 3.2.2 Characterization 3.3 Torsion Balances 3.3.1 Description 3.3.2 Characterization 3.3.3 Simulation 3.4 Double-pendulum Balance 3.4.1 Description 3.4.2 Characterization 3.5 Laboratory Setup 3.5.1 Vacuum Chambers 3.5.2 Software and Test Setup 4. Thrust Balance Experiments 4.1 Torsion Balance I Test Results 4.1.1 Dummy Tests 4.1.2 CU18A 4.1.3 MET03 4.1.4 MET04 4.1.5 Discussion 4.2 Torsion Balance II Test Results 4.2.1 Dummy Tests 4.2.2 MET05 4.2.3 Beam Vibration 4.2.4 Discussion 4.3 Double-pendulum Balance Test Results 4.3.1 Dummy Tests 4.3.2 MET03 4.3.3 Discussion 5. Centrifugal Balance Experiments 5.1 Centrifugal Balance 5.1.1 Description 5.1.2 Centrifugal Devices 5.1.3 Predictions 5.2 Transducer Calibration 5.2.1 Quasi-Static Calibration I 5.2.2 Quasi-Static Calibration II 5.2.3 Dynamic Calibration 5.3 Centrifugal Balance Test Results 5.3.1 Characterization 5.3.2 CD01 5.3.3 CD02 5.3.4 CD03 5.3.5 CD04 5.3.6 CD05 5.4 Discussion & Error Analysis 6 Conclusions 6.1 Research Summary 6.2 Further Research Appendix A Appendix B Bibliograph

A surgical bone biopsy needle using ultrasonic-sonic frequency vibration

This thesis presents a surgical needle designed for bone biopsy, based on an ultrasonic-sonic drilling mechanism. Bone biopsy is an invasive diagnostic procedure where a bone sample is extracted for clinical analysis. For conventional bone biopsy methods, closed biopsy is normally adopted and uses a core needle. An intact and viable biopsy sample is required for clinical analysis. However, a particular limitation of closed biopsy is that the microarchitecture of the biopsy sample can be easily damaged due to the large force which is applied through the core needle to penetrate bone. In some cases, the bone biopsy samples are fractured or crushed during the biopsy process. Power ultrasonic surgical devices have improved many aspects of bone cutting procedures, such as lower cutting force, higher accuracy, and better preservation of the tissue around the cutting site. In this study, an ultrasonic-sonic needle (US needle) system is designed and used to extract an intact biopsy sample and the penetration performance is evaluated by the effective impulse delivered to the target. The ultrasonic-sonic drilling mechanism was originally invented for rock drilling in low environments. In the US needle system, a free mass oscillates between an ultrasonic transducer-horn and a surgical needle, converting the ultrasonic frequency vibration of the horn to sonic frequency vibration of the needle. Compared to other ultrasonic surgical devices that directly transfer the ultrasonic vibrations from the cutting tip to the tissue, the US needle allows sufficient time between impacts with the free mass for the tip vibration amplitude to be re-established in the horn. This can maintain penetration progress of the needle into bone, where the rate of progress has been shown to be proportional to the effective impulse delivered by the needle to the bone. To maximise the effective impulse, a numerical model is developed to simulate the dynamic behaviour of the needle system and optimise the US needle. To build the US needle system, the design and optimisation of the ultrasonic transducer-horn were investigated with the finite element method and experimental modal analysis, ensuring that the transducer-horn operates at the tuned frequency (50kHz) with a pure longitudinal mode. The configuration of the ultrasonic horn determines the momentum transferred to the free mass and hence also affects the effective impulse delivered to the target. The shape and dimensions of the ultrasonic horn were determined through the finite element model of the ultrasonic horn impacting the free mass, which focused on maximising the post-collision velocity of the free-mass. The dynamic components of the US needle were also investigated. A numerical model representing the dynamic behaviour of the needle system was developed, allowing the optimisation of each dynamic component, maximising the effective impulse delivered to the target. Each dynamic component of the US needle was modelled as a mass-spring-damper (MSD) system, which constituted the whole system dynamic model. The numerical model was validated by experiments using a prototype needle. The free-mass velocity, needle velocity and impact force predicted by the numerical model were compared with the results measured from experiments using 3D laser Doppler vibrometry, an ultra-high speed camera and a load cell, respectively. The numerical model results exhibit good agreement with the experimental results, indicating the numerical model can be used as a predictive tool to evaluate the performance of the US needle when different configurations are implemented. The configuration of the US needle is studied to maximise the effective impulse by the numerical model, through optimisation of the mass of the free mass, spring rate and spring pre-load. An optimised configuration of the US needle was determined by the numerical model and validated by experiments. The resulting prototype of the needle device was tested in ovine femur in vitro and was demonstrated to retrieve a cortical bone biopsy sample with a more cylindrical geometry, smoother surface and more intact sample than a cortical biopsy sample retrieved using a conventional trephine needle. Moreover, the penetration performance of the US needle was also compared with an ultrasonic resonant needle where the ultrasonic transducer and surgical needle resonate at the same frequency

Design of Ultrasonic Processing Device for Aluminum Surfaces

The work in this thesis examines the design possibility of a device capable of harnessing ultrasonic oscillations through resonance such that it can be applied onto an aluminum surface to produce a compressive residual stress field. Particularly to solve the common industry issue of fatigue life failures around stress concentration areas such as holes and shape discontinuities. Purchase of a pre-assembled ultrasonic transducer was used to simplify the project, however the design research focuses on developing a Sonotrode or Horn capable of amplifying and focusing ultrasonic oscillations onto a sample surface. The development includes iterative analytical, numerical, and experimental design to achieve the final result. MatLab and Comsol software were used for analytical and numerical simulation models. Three iterations of physical designs were conducted including full steel body, combined aluminum and steel, and aluminum and carbide material design methods. The first two iterations were unsuccessful in achieving resonance due to incorrect design assumptions which lead to a mismatch in frequency resonance and a significant increase in system electrical impedance due to mass. The third iteration used a complete aluminum body with multi-stepped shape design and an attached carbide insert for tip hardness. A 200W precision ultrasonic driver and analyzer device made by Piezo Drive combined with a Laser Doppler Vibrometer was used for monitoring electrical and mechanical system response during operation. The result of this study shows that after true system resonance is achieved, maximum tip displacement occurs at the same frequency, and can be increased by increasing applied input voltage to the transducer

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

High temperature ultrasonic gas flow sensor based on lead free piezoelectric material

The review of current technologies for measurement of gas velocity in stack flow applications is undertaken and it is shown that the ultrasonic time-of-flight method is the most suitable and offers a number of advantages over alternatives. Weakness of current piezoelectric based transducers are identified as the inability to operate at temperatures above 400 °C due to limitation of piezoelectric materials used, and a case for development of an alternative high temperature material is put forward. A novel and highly enhanced, lead free piezoelectric material, suitable for continuous operation at temperatures above 400 °C has been engineered for ultrasonic gas velocity sensor applications. Structural modification of pure bismuth titanate (Bi4Ti3O12) or BIT compound, through multi-doping at the Ti-site, has been found to enhance piezoelectric properties accompanied with a mild reduction in Curie temperature, Tc. Initially, compounds doped with tungsten and chromium were found to increase the piezoelectric coefficient (d33) from around 5 pC N¯¹ in pure bismuth titanate, to above 20 pC N¯¹ in doped compounds. This increase is attributed to lower conductivity and improved poling conditions. Further increases in d33 (up to 35 pC N¯¹) were then realised through controlled grain growth and reduction in conductivity for niobium, tantalum and antimony doped compounds. The Curie temperature of the material with best properties is found to be 667 °C, which is a slight reduction from 675 °C for pure bismuth titanate ceramic. The enhancements in modified bismuth titanate achieved in present work allow the material to be considered as suitable for high temperature ultrasonic transducer applications. Integration of bismuth titanate material into a working high temperature transducer is then considered and the investigation of suitable, high temperature bonding method is undertaken. It is shown that reactivity of bismuth titanate with the titanium based fillers makes brazing unsuitable as a bonding method between piezo-ceramics and stainless steel. A novel assembly method, using liquid gallium as an electrically conductive bond, and a mechanical restraint for the piezo actuator is then presented as an alternative with the potential to reduce the negative effects of differences in thermal expansion coefficients between constituents of the transducer assembly.This work was supported by funding from the EPSR

Ultrasonically assisted penetration through granular materials for planetary exploration

Space exploration missions often use drills or penetrators to access the subsurface of planetary bodies. Protected by the conditions experienced at the surface, these regions have potentially been untouched for millennia. As such, the subsurface is a very attractive option for scientific goals, be it the search for extra-terrestrial life, to examine the history of the planet, or to utilise underground resources. However, many issues arise in such a task. Every other rocky body in our solar system possesses a surface gravity lower than our own, resulting in a lower available weight for a spacecraft to ‘push’ on a penetrating device. Add to this the low power availability and complications regarding remote operation, and this becomes a very difficult process to achieve. Mole devices which burrow through the ground whilst tethered to a surface-station to provide power and data have shown great promise in this regard. Using an internal mass to ‘hammer’ themselves into the ground, special care is required to ensure internal components are not damaged, and that they can arrive at their target depth in a reasonable period of time. There is continuous development in these types of drilling and penetrating technologies and anything that can penetrate with a lower weight-on-bit (WOB), and consume less power, could potentially be extremely useful for these situations. High powered ultrasonic vibrations have been shown to reduce operational space and forces required in cutting bones for surgery. Additionally, they have been successful in reducing WOB requirements for drilling devices through rocky substrates. To maximise penetration depth, it is often favourable to progress though granular material rather than solid rock, however this also provides its own set of problems. This work looks at applying ultrasonic vibration to penetrating probes for use in granular material, with the aim of utilising it in low gravity or low mass scenarios. Before this can be done however, the regolith used for testing must be fully characterised and consistent preparation methods established, ensuring that all other effects are accounted for. An ultrasonically tuned penetrator was designed and manufactured, and the effects it had on the surface of sand were investigated using a high-speed camera and optical microscope. It was found that regions of sand immediately surrounding the penetrator were highly fluidised, localising any deformations to a small radial distance. Penetration tests were then conducted that showed ultrasonic vibration significantly reduces the penetration forces and therefore the overhead weight required, in some cases by over an order of magnitude. A similar effect was seen in power consumption, with some instances displaying a lowered total power draw of the whole system. Experiments were then conducted in a large centrifuge to examine the trends with respect to gravity. Gravitational levels up to 10 g were tested, and the general trend showed that ultrasonic penetration efficiency indeed increased at lower gravities, suggesting that the force reduction properties would be enhanced at lower levels of g. Finally, the first steps to applying this technique as a fully-fledged penetration device were conducted. These tests oversaw combining ultrasonic vibration with the established hammering mechanism used by mole devices. Comparing this against a purely hammering penetration, it was found that the addition of ultrasonic improved performance significantly, greatly reducing the number of strikes required to reach the same penetration depth. To conclude, the work presented in this thesis shows the potential that ultrasonic vibration can have with advancing low gravity/low mass penetrating devices. Reducing both the weight and power requirements can be a huge boon to small spacecraft, and the potential use as subsurface access or anchoring devices makes it an attractive avenue for future research and development