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BACKGROUND: Bone decortication is essential to activate bone based on the Regional Acceleratory Phenomenon (RAP), a post-injury transient bone remodeling phenomenon. The Piezoelectric knife with low ultrasonic frequency has been shown to cut bone with minimal invasive effect on soft tissues, less inflammatory response compared to conventional Bur that causes trauma leading to excessive inflammation. Previous studies have shown that using graft materials for Guided Bone Regeneration (GBR) had a significant beneficial effect on the healing process and the thickness of new bone formation. This study hypothesized that the piezoelectric knife would create a better tissue response to different graft materials compared to conventional carbide bur with grafts or the graft alone. MATERIAL & METHOD: Eighteen 9-10 week male Sprague-Dawley rats (300-350g) were purchased from Charles River Laboratories. This study was approved by Boston Medical Center Institutional Animal Care and Use Committee. The piezoelectric knife (BS1 insert) of the Piezotome 2 (Acteon) was used for deep decortication and compared to a conventional carbide osteotomy bur (#1/2) with Mucograft (Geistlich) or OsteoGen (Impladent, Ltd) graft materials, Onlay graft material alone served as a control. Digital dentistry using Cone Beam Computed Tomography (CBCT) located and allowed precise cut of the area of interest without detached the surrounding soft tissue. Tissues collected from day 7 and day 28 were sectioned and stained with Hematoxylin/Eosin or Masson trichome stains. RESULTS: The Cone Beam Computed Tomography (CBCT) scans significantly increased the success rate in locating and cutting the area of interest. Hematoxylin & Eosin staining showed on day 7 that piezoelectric knife activated a broad bone response and less inflammatory response. While recruiting and enlarging chondrocytes to the Mucograft area which will turn to new bone. The use of OsteoGen combined with a piezoelectric knife resulted in thickening in the cortical bone around and above the defect area. CONCLUSION: Piezoelectric knife with Mucograft healed faster compared to bur or graft alone. The piezoelectric knife resulted in significantly increased bone thickness when combined with OsteoGen.

Hybrid actuation is an expanding field in which several systems, such as a mechanical, electrical, hydraulic, pneumatic, and/or thermal, among others, are integrated in order to combine certain aspects of each system, and achieve a better and more efficient performance under certain operating conditions. The concept of piezohydraulic actuation takes advantage of the high force capabilities that piezoceramics have and combines it with the operation at high frequencies, in order to achieve the hydraulic actuation of a system under a specified stroke and force. High frequency rectification translates the low stroke of a piezoelectric stack into a desired amount of stroke per unit time. Thus, the low displacement, oscillatory motion of the piezoelectric device (coupled with a high frequency operation) is translated into a unidirectional motion of a hydraulic cylinder. As part of this research, a benchtop piezohydraulic unit has been developed and the concept of piezohydraulic actuation has been demonstrated. The effective bidirectional displacement of a hydraulic cylinder through the actuation of a piezoelectric stack has been achieved. A lumped parameter model is developed in order to simulate the dynamics of the hydraulic system and of the entire piezohydraulic unit. The model did approximate the response of the piezohydraulic unit under a one-sided operation. Time response analysis is performed through the frequency spectrum comparison of the measured and the simulated data. Then a two-stage cycle simulation is used to model the pumping operation of the unit. Discrepancies were obtained between the model and the actual system for the single-ended piezohydraulic unit, nonetheless, a good approximation has been achieved for the pumping operation of the double-ended unit under certain conditions. Furthermore, several factors have been identified that may limit the operation of the piezohydraulic unit. First, the need of high displacement actuators often comes with the requirement of high voltage operation along with high current consumptions. Thus, the amplifier becomes the first limitation to overcome. Second, is the response of the controlled valves. The highest valve operating frequency and their time response will set the limit on the piezohydraulic unit. And finally, once these limitations are overcome, the unit is eventually limited by the dynamics of the fluid and the hydraulic system itself. Attenuation in the frequency response, or the operation near resonance and the possibility of cavitation, are some of the aspects that eventually will limit the operation of the piezohydraulic unit. A custom made, high displacement stack is used along with a custom made switching amplifier. The current system is being limited by the second factor, the solenoid valves. Nonethelss the analysis performed has addresed the relevant issues required for the design and use of another set of controlled valves. Finally, the eventual limitation from the hydraulic system has been determined through the analysis of the fluid dynamics of the system. The analysis does not account for potential cavitation, and future operations at high frequencies should take it into account. / Master of Science

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A new geometrically unique ultrasonic motor (USM) was designed using finite element modeling (FEM). A USM operates by vibrating a drive tip in an elliptical motion while it is in periodic contact with a driven surface. Piezoelectric elements are used to create the elliptical motions and are driven near a resonant frequency to create the needed displacements for the motor to operate. An idea for a motor frame was conceived that consisted of an arch, a center ground, and two piezoelectric elements connected to the center ground. End caps were added between the frame and the piezoelectric elements to reduce the stress of the elements. Legs located at the bottom of were used to increase the rigidity. Several FEM programs were written to design the motor and to predict its performance. The FEM motor model exceeded the performance characteristics of the benchmark Nanomotion HR1. The model predicted a linear motor capable of pushing up to 5 N and a maximum speed of 0.4 m/s. A prototype frame was built out of tool steel and run against an oxide ceramic plate. The USM prototype's piezoelectric elements did not provide the expected displacements in the motor frame as determined by the FEM. The discrepancy was determined to be caused manufacturing errors. Soft glue layers were thicker than expected on each side of the piezoelectric elements causing a large amount of compliance inline with the piezoelectric motion. An additional unexpected layer of glue between the end cap and frame increased the compliance inline with the piezoelectric elements even more. It was also determined that even if the motor had been assembled properly that Hertzian displacement would have caused a 1/3 decrease in piezoelectric motion. The prototype frame's steady state displacements were approximately 20% of the expected output from the FEM models. The motor was still able to achieve a maximum speed of 55.6 mm/s and a push force of 0.348 N at a preload of 6 N. It is expected that a motor assembly correctly dimensioned and manufactured and designed to minimize Hertzian displacement would result in a significantly better performing prototype.

Resonance frequency detuning (RFD) is a piezoelectric-based vibration reduction approach that applies to systems experiencing transient excitation through the system*s resonance—for example, turbomachinery experiencing changes in rotation speed, such as on spool-up and spool-down. This technique relies on the inclusion of piezoelectric material and manipulation of its electrical boundary conditions, which control the stiffness of the piezoelectric material. Resonance frequency detuning exploits this effect by intelligently switching between the open-circuit (high stiffness) and short-circuit (low stiffness) conditions as the excitation approaches resonance, subsequently shifting the natural frequency to avoid this resonance crossing and limit the response. The peak response dynamics are then determined by the system*s sweep rate, modal damping ratio, electromechanical coupling coefficient, and, most importantly, the trigger (represented here in terms of excitation frequency) that initiates the stiffness state switch. This thesis identifies the optimal frequency-based switch trigger over a range of sweep rates, damping ratios, and electromechanical coupling coefficients. With perfect knowledge of the system, the optimal frequency-based switch trigger decreases approximately linearly with the square of the coupling coefficient. Furthermore, phase of vibration at the time of the switch has a very small effect; switching on peak strain energy is marginally optimal. In practice, perfect knowledge is unrealistic and an alternate switch trigger based on an easily measurable parameter is necessary. As such, this thesis also investigates potential methods using the open-circuit piezoelectric voltage response envelope and its derivatives. The optimal switch triggers collapse to a near linear trend when measured against the response envelope derivatives and, subsequently, an empirical control law is extracted. This control law agrees well with and produces a comparable response to that of the optimal control determined using perfect and complete knowledge of the system.

Multifunctional "self-sensing" materials at the frontiers of current research are generally designed to gather only a single type of information (such as quasi-static strain data). This project introduces a new sensor that is both multifunctional and dual-response, indicating its ability to not only perform in mechanical and sensing functions but also in its ability to sense multiple types of response. The proposed new class of sensing materials, comprised of nanocomposite polymer foams, exhibits measurable piezoresistive and quasi-piezoelectric phenomena in the form of change in resistance and voltage generation in response to deformation, respectively. An initial sampling of the envelope of dual-response nanocomposite foam sensors is mapped. The sensing materials can also be tailored to provide desired mechanical compliance and damping. Nanocomposite foam sensors decrease in resistance with increased strain in both static and cyclic compression environments. The quasi-piezoelectric voltage response of nanocomposite foam sensors increases linearly with compression frequency. A circuit and signal demodulation system was developed enabling simultaneous capture of a dual-response foam sensor's change in resistance and voltage generation. Measuring the two responses provides both long-term and immediate performance and health status of mechanical systems, enabling improved monitoring and decreased risk of failure.

This thesis explores the effects of two assumptions commonly used in mathematical models related to a piezoelectric damping method known as State Switching. The technique relies on changing the stiffness state of a piezoelectric patch through control of the electrical boundary conditions. The transition between stiffness states is assumed to occur instantaneously and in concurrence with the switch event. In actuality, the transition will occur over a finite time and will trail behind the switch event by a finite time. For these assumptions to be valid, the effects of switch duration and delay on the performance of the State Switching method must be examined. The vibration reduction for various switch duration/delay values was calculated using a numerical solver; the results of the simulations were used to provide a range in which the two aforementioned assumptions produce negligible error, defined here as a 10% decrease in method performance. Switch durations of more than 3% of the forcing period lead to significant performance decrease, for most values of damping and coupling coefficient. Results of the switch delay simulations were counter-intuitive and require further examination and validation.

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