No description available.

Piezoelectric plate transducers are commonly used for the generation and detection of ultrasonic signals and have applications in, for example, non-destructive testing and medical imaging. A rigorous theoretical investigation of thermal noise in plate transducers has been undertaken with the aim of establishing the absolute limits of receiver sensitivity in terms of both Minimum Detectable Power (MDP) and Minimum Detectable Force (MDF). The central feature of the work has been the development of two independent theories which provide identical results. One theory is based on an electrical approach which makes use of an extensively modified version of Hayward's linear systems model of the piezoelectric plate transducer, along with the well known work of Johnson and Nyquist. The other theory is based on a mechanical approach which makes use of the less well known work of Callen and Welton. Both theories indicate that only two parameters are required in order to determine the MDP and MDF of an open circuit transducer. These parameters are the transducer's characteristic acoustic impedance and its mechanical quality factor. Significantly, the thermally limited sensitivity of an open circuit receiving transducer has been shown not to be related to its electromechanical coupling efficiency or any of its electrical properties. By applying the new theories it has been possible to design an ultra low noise ultrasonic receiver with wide ranging applications. Among other things, this receiver has been used to demonstrate the viability of a robust and truly practical air-coupled Lamb wave scanner suitable for detecting defects in thin plates which can be made from almost any type of material. The complete system has sufficient sensitivity to allow rapid scanning without the requirement for transducer matching layers or electronic signal averaging.

A new, two-dimensional model is presented for predicting the behaviour of tall, thin piezoelectric transducer structures, typical of those encountered in many ultrasonic phased array assemblies. Based on linear systems theory, the model may be represented in block diagram format, utilising feedback and feedforward loops to model mechanical and piezoelectric cross coupling, in addition to secondary and tertiary piezoelectric generation. As a result, the model permits a ready understanding of the electrical, mechanical and piezoelectric interactions which take place when two principal vibrational modes are present within a transducer structure. Comprehensive experimental and theoretical results are shown to produce close agreement, and compare favourably with alternative modelling strategies. It is considered that this novel approach will be of considerable benefit to the analysis and understanding of the transduction process within such structures.

BACKGROUND: Dental implants have been successful for the restoration of edentulous areas, but current techniques are inadequate in areas lacking sufficient bone volume. Piezoelectric surgery has shown encouraging effects on both osseous healing. A new wedge-shaped titanium PiezoImplant requires piezoelectric osteotomy. This study compares PiezoImplants to conventional threaded cylindrical shaped implants by microcomputed tomography and histology to assess osseointegration, tissue response, and alveolar ridge changes. METHODS: After 3 months post-extraction, 18 conventional cylindrical implants and 18 wedge-shaped PiezoImplants were placed using a split-mouth design in 3 adult mini pigs. The cylindrical implant sites were prepared for osteotomy with rotary instrumentation while the PiezoImplant sites were prepared with piezoelectric surgical inserts. One animal was sacrificed at 4, 8, and 12 weeks post operation. Quantitative µCT and histological analysis evaluated bone volume, osseointegration, and post-operative cellular events. RESULTS: The results of a multivariable linear regression model demonstrated that the PiezoImplants, arch location, and time were significant factors on higher BV/TV percentage. Bone to implant contact (BIC) analysis by high resolution microscopy and histomorphometry indicated osseointegration though intimate contact between implants and adjacent alveolar bone in both groups. The tissue response displayed no evidence of abnormal healing and the PiezoImplant was classified as a non-irritant. CONCLUSION: The combination of piezoelectric osteotomy and newly designed PiezoImplants had favorable effects on wound healing and osseointegration compared to conventional cylindrical implants. These novel wedge-shaped implants may be beneficial for narrow ridge spaces without additional ridge augmentation. Further research is needed to establish clinical validity.

University of Macau / Faculty of Science and Technology. / Department of Electromechanical Engineering

No description available.

The performance of smart structures depends on the electromechanical behaviour of piezoelectric sensors/actuators and the bonding condition along the interface, which connects the sensor/actuator and the host structures. This thesis documents a theoretical study of the influence of material parameters of the imperfect bonding layer on the coupled electromechanical characteristics of piezoelectric sensors/actuators. A one dimensional sensor/actuator model with an imperfect bonding layer, which undergoes a shear deformation, is proposed. The emphasis of the current study is on the local stress and strain fields near imperfectly bonded sensors/actuators and the load transfer. Analytical solutions based on the integral equation method are provided. Detailed numerical simulation is conducted to evaluate the influence of the geometry and the material mismatch of the adhesive layer upon the sensing/actuating process. The interfacial debonding and its effect upon the strain/stress distribution and the overall performance of the integrated structure are evaluated in detail.

Monitoring and controlling of insects are of great scientific and engineering interests based on the potential impacts on environments, search and rescue operations, and robotics design. This research focuses on studying insects’ locomotive behavior by employing noninvasive piezoelectric sensors and presenting a conceptual method of locomotion control. To do so, polyvinylidene fluoride thin sheets are used as bending sensors at the joints of a cockroach’s legs. Approaches include development of polymeric sensors; laboratory in vitro testing of sensors and cockroaches; and methodology to control them. This research successfully built an experimental foundation for sensor and roach testing and developed a methodology for roach locomotion control. This research links engineering and entomology potentially having impacts in the mentioned arenas. Testing showed that piezoelectric films, such as polyvinylidene fluoride (PVDF), can serve as motion sensors for the legs, providing frequency and range of motion of each of the roach’s legs. The film is thin enough to provide as little resistance to motion to prevent altering the roach’s natural walking patterns. Testing also showed that using the insect’s instinct to physically touch an unknown object can be used as a directional control method. By using this natural response, a device can be fit on the roach capable of guiding the roach in any direction desired. This thesis is organized to present a brief introduction on the history and need for biomimetic robots. This section is followed by the research objectives and an introduction to polyvinylidene fluoride and the piezoelectric properties that allow it to become a sensor. A brief description of the roach anatomy and physiology is presented that will provide baseline of information needed to proceed with the project. We finish with an explanation of the testing of sensors on the roach and a novel method to control the roach walking orientation.

This research entails the synthesis and characterization of a novel class of materials which incorporate both magnetic and piezoelectric characteristics. The composite is made up of the piezoelectric polymer PVDF and magnetic nanoparticles. The testing samples are produced using a spin casting process. The characterizations of the samples were performed using X-ray diffraction, Atomic force microscopy, linear staging, Dynamic mechanical analysis, Differential scanning calorimetry, and Fourier transform Infra-Red. X-ray diffraction and Atomic force microscopy showed that the presence of the Fe3O4 particles have no effect on the crystallinity of the polymer matrix, therefore allowing for the incorporation of inclusions without directly affecting the piezoelectric property. Changes in the thermal characteristics of the polymer matrix, observed using Differential scanning calorimetry, indicated increases in the thermal conductivity of the composite. Decreases in the heat of melting and crystallization were also observed and further solidified the conclusion that the presence of the Fe3O4 nanoparticles changes the thermal behavior of the polymer. It was observed from the DMA results caused an increase in the storage modulus of the polymer matrix which is related to an increase in the material's ability to store energy. Linear staging results showed that the presence of the nanoparticles had an effect on the mechanical properties of the composites and altered the time dependent voltage output readings. These results were used to calculate the energy capabilities of the composite material and it was found that the composites showed greater energy outputs with increasing amounts of nanoparticles. Interaction was observed between the embedded particles and an external magnetic field, which was found to decrease the energy outputs of the composites. This research showed enhancements in the composite material's energy outputs in comparison to the pure PVDF samples. This research also showed that the embedded nanoparticles interacted with an exteriorly applied magnetic field. This observation introduces a new dimension of possible activation processes for piezoelectric devices which have been largely based on physical forms of activation. PVDF which is widely used in research and applications for its superior output capabilities has been enhanced in this research and shown to have capabilities to exhibit higher energy outputs.

In this thesis, the feasibility of inverse evaluation of piezoelectric parameters by using piezoelectric beam¡¦s natural frequencies is presented. Generally, all the piezoelectric parameters are not measured simultaneously. In other words, the interactive effects between the piezoelectricity and strain are not all included. The piezoelectric beam¡¦s natural frequencies are analyzed by the inverse evaluation of piezoelectric parameters associated with the optimization algorithm. The dynamic model for piezoelectric beam is proposed by using Hamilton¡¦s principle in this study. The corresponding eigenvalue problems of different piezoelectric beams are formulated and solved by employing differential quadrature method (DQM). The genetic optimization algorithm is employed to optimize all piezoelectric parameters from the measured natural frequencies. Optimization of piezoelectric parameters of piezoelectric beam under the boundary conditions of fix-fix ends and fix-free ends are investigated. The robustness of program is also demonstrated through several numerical examples. The results demonstrate the method of this study applied to determine piezoelectric parameters by using natural frequencies is feasible and practicable.