Don Raboud

Wide-bandwidth piezoelectric energy harvester with polymeric structure

A polymer based energy harvester with wide bandwidth is designed, fabricated and tested in this work. A polymer based structure has a lower resonance frequency compared to a silicon based structure with the same dimensions due to the much lower stiffness of polymeric materials. Therefore, a polymeric energy harvester is more useful for situations with lower ambient vibration frequencies. Aluminum nitride pads are fabricated on an SU-8 membrane to convert mechanical vibration of the membrane to electrical voltage. A new and scalable microfabrication process flow is proposed to properly fabricate piezoelectric layers on SU-8 structures. The nonlinear stiffness due to the stretching strain in the membrane provides a wider harvestable frequency bandwidth than conventional linear oscillators. Wideband energy harvesters are more useful for practical applications due to uncontrollable ambient vibration frequency. The load-deflection equation of the device is calculated using finite element simulation. This equation is then used in an analytical solution to estimate the nonlinear effect of the structure. A bandwidth of ~146 Hz is obtained for the fabricated device and a maximum open circuit voltage of 1.42 V, maximum power of 1.37 µW, and power density of 3.81 µW cm−2 were measured at terminal load of 357.4 kΩ under an excitation acceleration of 4 g. A power output of 10.1 µW and power density of 28.1 µW cm−2 was estimated using a synchronized switch harvesting on interface (SSHI) electrical interface with electrical quality factor of 5. In addition, the lumped element model has been employed to investigate the scaling effect on a polymeric circular diaphragm.

Bone impacted fibular free flap: a novel technique to increase bone density for dental implantation in osseous reconstruction.

Fibular free flap (FFF) bone has thick cortical bone surrounding a fatty marrow. The cortex has sufficient density for dental implantation, but the marrow limits bone stock. A novel technique was devised to increase bone density: the bone‐impacted fibular free flap (BIFFF). The purpose of this study was to: (1) describe the BIFFF technique; (2) evaluate the bone density of BIFFF; and (3) evaluate the stability/success of implants placed in BIFFFs.

Advanced System for Implant Stability Testing (ASIST)

This study presents the Advanced System for Implant Stability Testing (ASIST) which provides a non-invasive, quantitative measure of the stability of percutaneous implants used for craniofacial rehabilitation such as bone anchored hearing aids or dental implants. The ASIST uses an impact technique coupled with an analytical model which allows the measure to be independent of the system components. This paper presents a laboratory evaluation of the ASIST for the Oticon Medical Ponto and the Cochlear Baha Connect bone anchored hearing aid (BAHA) systems. There is minimal effect of abutment length on the ASIST Stability Coefficient (ASC) value, indicating that the method is able to isolate the interface properties from the overall system and the measurement is independent of attached components. Additionally, the ASIST was able to detect differences between different implant installations suggesting that it may be sensitive to changes in interface stiffness.

Finite-element modeling of shape memory alloy components in smart structures, part II: Application on shape-memory-alloy-embedded smart composite for self-damage control

For pt.I, see ibid., no.3, p.015-021 (2003). The finite element procedure proposed in part I was successfully used to model a smart-self-damage control system consisted of SMA wires embedded in a polymeric matrix. A parametric study was performed to investigate the effect of various parameters on the performance of the system. It was found that increasing current density speeds up the recovery process although it adds more heat to the system. Also, it was found that increasing wire diameters although speeds up the recovery process as well, it might cause harmful effects to the system by increasing the difference in CTE forces effect. Increasing number of activated wires was found to be beneficial as it reduces the amount of phase transformation and forces required per wire, and increases system sensitivity to small cracks. It is suggested that convection coefficient not to be too low or to high, and the initial temperature of the system to be as close to the Austenite start temperature as possible. It was also found that SMA wires prestraining have negligible effects if its not too low.

Comparison of implant stability measurement devices for bone-anchored hearing aid systems

Statement of problem. The success of implants for bone‐anchored hearing aids (BAHA) relies on proper osseointegration at the bone‐implant interface. Clinical evaluation of implant stability is important in prescribing loading, identifying the risk of failure, and monitoring the long‐term health of the implant. Purpose. The purpose of this in vitro study was to evaluate 2 measurement systems for BAHA implant stability: the most commonly used, Osstell implant stability quotient (ISQ), and a newly developed advance system for implant stability testing (ASIST). Material and methods. BAHA implants (Oticon Medical Ponto and Cochlear BAHA Connect systems) were installed in plastic materials with adhesive to simulate implants integrated in bone with varying levels of interface stiffness. Different lengths of BAHA abutments were used with each implant specimen, and stability measurements were obtained with both the Osstell ISQ and the ASIST systems. The measurement systems were evaluated in terms of sensitivity to differences in interface stiffness and the effect of abutment length on the stability measurement. Repeated measures ANOVA followed by post hoc t tests were used for the comparisons with a Bonferroni adjusted alpha value of .05/15 = .003 to control for potential type 1 errors. Results. Changing the abutment length of a single implant installation had minimal effect on the ASIST stability coefficient, whereas large variations were observed in the Osstell implant stability quotient (ISQ). The Osstell showed a clear relationship of decreasing ISQ with increasing abutment length for both the Oticon Medical and the Cochlear implant systems. Both the ASIST and the Osstell were found to be sensitive to changes in interface properties, with the ASIST being more sensitive to these changes. Conclusions. The ASIST system is more sensitive to changes in interface properties and shows smaller variation because of changes in abutment length than the Osstell ISQ system.

Application of the advanced system for implant stability testing (ASIST) to natural teeth for noninvasive evaluation of the tooth root interface

In this paper we present the development of the Advanced System for Implant Stability Testing (ASIST) for application to natural teeth. The ASIST uses an impact measurement combined with an analytical model of the system and surrounding support to provide a measure of the interface stiffness. In this study, an analytical model is developed for a single-rooted natural tooth allowing the ASIST to estimate the stiffness characteristics of the periodontal ligament (PDL). The geometry and inertia parameters of the tooth model are presented in two ways: (1) using full CT scans of the individual tooth and (2) using an approximate geometry model with estimates of only the tooth length and diameter. The developed system is evaluated with clinical data for patients undergoing orthodontic treatment. This study shows that ASIST technique can be applied to natural teeth to estimate the stiffness characteristics of the PDL. The developed system can provide a valuable clinical tool for assessment of tooth stability properties and PDL stiffness in a variety of clinical situations such as dental trauma, orthodontics, and periodontology.

Optimizing Energy Output of Piezoelectric Microcantilevers

This work presents some new methods in optimizing electrical energy, harvested using a micro piezoelectric cantilever. Both mechanical and electrical aspects have been considered. Mechanically, two items have been considered to maximize the generated voltage: geometry of the cantilever and placement of the electrodes. It has been shown that for given sizes of length and width of the harvester and for a given natural frequency, the output voltage can be increased by adjusting the thickness of the beam and the proof mass and consequently increasing the amplitude of vibration. As well, the placement of the electrodes plays a very important role in optimizing output voltage. It has also been shown that piezoelectric cantilevers with shorter top electrodes induce higher voltage than cantilevers with longer top electrodes. Overall results agree with the analytical equations reported in literature so far. Moreover, distribution of top electrodes along the width of the cantilever has been taken into consideration. It has been shown how output voltage can be approximately doubled by using two narrower top electrodes along the width of the cantilever. All analysis in this work was carried out in ANSYS. In this research, to improve the electrical efficiency, diodes have been considered in the circuit to reduce electrical losses in comparison to rectifiers which have been used in conventional harvesters. Applying these methods to particular test cases, a 71% increase in output voltage was observed for the case of geometry optimization, a 116% increase was observed for the case of shortening the top electrode and losses in the electrical circuit were reduced by approximately 50% by using diodes comparing to using rectifiers. While these results focused on cantilever based harvesters, the ideas contained are equally applicable to other structures.Copyright

Nonlinear Coupled Field Finite Element Procedure for Modeling of Shape Memory Alloy Components in Multi-physics Applications

In this paper, we introduce a one-dimensional finite element procedure for modeling shape memory alloy components used in multi-physics based applications including MEMS and biomedical applications. The procedure addressed in this paper is based on a sequential solution of two main finite-element procedures which are then combined after each iteration. The procedure was applied to model an SMA wire and the results were compared with corresponding numerical and experimental results from the literature for different loading cases and boundary conditions. The results showed very good agreement with both experimental and numerical results. The procedure was found to be capable of capturing system characteristics such as structural and thermal non-linearity, variable SMA material properties and the ability to model coupled electrical, thermal and structural loading and boundary conditions and was general enough to be extensible to various geometrical shapes and different SMA constitutive models.