Submitted in partial fulfilment of the requirements for the Degree of Master of Technology: Mechanical Engineering, Durban University of Technology, 2011. / The objective of the present study was to investigate if piezoelectric techniques or sensors can be used in monitoring structural degradation. The study considers experimental results and analytical modelling of a ductile structure under tensile and cyclic loading. Throughout the project the emphasis was placed on the effectiveness of strain measuring sensors. Conventional tensile testing was conducted using a Lloyds testing machine. The testing machine was calibrated to have a lateral movement of 2mm/min (tension force). Rectangular plates were pulled in tension until failure. From that experimental data was produced for a uni-axial loading system. Cyclic testing was carried out using an in-house designed and manufactured fatigue machine. It produced a reciprocating load (force) of 25rad/s on a rectangular plate. Two different sensor measuring instruments (strain gauge and piezoelectric) were used. The strain gauge sensor was attached to a specimen and connected to a Wheatstone bridge. The piezoelectric sensor was attached to the specimen and then linked directly to the capturing system. From these two sensors experimental results were obtained and compared. The mathematical relationships for the rectangular plates were formulated using effective stress-strain behaviour based on the elastic and plastic behaviour of the plates. The analytical and experimental results were compared. Results from this investigation show that piezoelectric sensors can be useful for measuring fatigue failure on a ductile material.

A disadvantage with battery powered circuits is the fact that the battery sometimes can run out of power. If a button that can generate energy by applying mechanical work to it was applied instead of batteries, is it possible to enable a transmitter to stay active long enough to transmit data which can later by received and decoded? This thesis contains a study, in which how to effectively send data wirelessly between a transmitter and receiver module, without the use of any batteries or external power sources, only an energy harvesting push button is constructed and evaluated. There will also be a theoretical comparison between different transmission formats and which is more suitable for a task such as this.

published_or_final_version / Physics / Doctoral / Doctor of Philosophy

published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / Chemistry / Master / Master of Philosophy

The thesis deals with one major question: is it possible, using one piezoelectric sensor/vibrator, to detect a hard inclusion in a silicone rubber phantom? The question was approached with an open mind and the task was subdivided into three clearly identifiable parts: characterization of the piezoelectric sensor/vibrator (paper I), creating a model of the visco-elastic properties of a tissue-like material (phantom) in contact with the sensor/vibrator (paper II), and to detect the presence of a hard inclusion in the phantom (paper III). All vibrations of the sensor/vibrator and phantom was modeled using a finite element method (FEM). To minimize the computational time and to maximize the FEM model's ability to correctly reproduce the vibrations, a two-dimensional model system consisting of a cylindrical piezoelectric sensor/vibrator, emitting radial elastic waves in to a cylindrical disk-shaped phantom, was chosen. The piezoelectric sensor/vibrator was characterized using a parameter tuning procedure using harmonic overtones. The procedure enables tuning of the electro-elastic parameters of the sensor/vibrator so that the measured and calculated impedance frequency responses match. Silicone rubber was chosen as a phantom to mimic soft tissue. The properties of the phantom was modeled using a fractional derivative visco-elastic model. The hyperelastic effect at the first radial resonance of the sensor vibrator was corrected for by a compensating function. The high frequency complex visco-elastic modulus of the silicone rubber was determined using the transitions of standing Lamb waves in the phantom. The presence of a ring-shaped inclusion in the phantom, of polyamide, was detected using the change of the transitional Lamb wave patterns in the phantom. The tuning of the PZT5A1 sensor/vibrator parameters yielded a match between the calculated and the measured impedance spectra better than 0.54%. The average, complex, elastic modulus of three silicone rubber, Silgel 612, samples were: (0.97 + 0.009i) GPa  at 100 kHz and (0.97 + 0.005i) GPa at 250 kHz. The presence of a polyamide inclusion, PA6GPE, was detected in the phantom using multiple frequency footprints. / Denna avhandling berör frågan: är det möjligt, med en piezoelektrisk sensor/vibrator, att detektera ett hårt objekt inneslutet i en fantom av silikongummi? Frågan närmades utan begränsningar och uppgiften delades upp i tre tydliga delar: karaktäriseringen av den piezoelektriska sensorn/vibratorn (paper I), skapa en modell av det viskoelastiska uppförandet hos ett vävnadsliknande material (fantom) som står i kontakt med sensorn-/vibratorn (paper II) och att detektera förekomsten av ett hårt objekt inneslutet i fantomen (paper III). En finit element modell (FEM) skapades för att beräkna vibrationerna hos sensorn/vibratorn och fantomen. För att minimera beräkningstiden och maximera modellens förmåga att återge vibrationer på ett korrekt sätt, så skapades ett tvådimensionellt modellsystem bestående av en cylindrisk piezoelektrisk sensor/vibrator i kontakt med en cylindrisk fantom av silikongummi. Sensorn/vibratorn skickar radiella elastiska vågor in i fantomen. Den piezoelektriska sensorn/vibratorn karakteriserades med hjälp av en procedur som anpassar parametervärden med hjälp av övertoner. Proceduren möjliggör en justering av parametervärdena så att uppmätta och beräknade impedansspektra överensstämmer. En 'fractional derivative' modell av de viskoelastiska egenskaperna hos silikongummit skapades. De hyperelastiska egenskaperna vid första radiella resonansen blev kompenserade med hjälp av en sigmoidformad funktion. Den komplexa viskoelastiska modulen bestämdes för höga frekvenser med hjälp av transitioner hos stående Lambvågor i fantomen. Närvaron av ett hårt ringformat objekt i fantomen detekterades med hjälp av förändringar i mönstret hos de stående Lambvågorna. Justeringen av de piezoelektriska parametrarna hos elementet PZT5A1 gav som mest en skillnad på 0.54% mellan uppmätta och beräknade impedansspektra. Medelvärdet hos tre prov av silikongummit Silgel 612 av den komplexa elastiska modulen uppmättes till (0.97 + 0.009i) GPa  vid 100 kHz och (0.97 + 0.005i) GPa vid 250 kHz. Närvaron av ett hårt objekt, gjort av polyaramid (PA6GPE), detekterades i fantomen med hjälp av multifrekvensiella fotavtryck.

Piezoelectric energy harvesters in the road pavement are developed and studied to collect energy from the passing vehicles. A numerical model based on the Westergaard's stress model is proposed to calculate the three dimensional stress distribution in the pavement and the power generation from the piezoelectric harvesters placed inside the pavement. Piezoelectric patch, plate and beam harvesters are designed. Based on proposed numerical models, simulations are conducted to reveal the effects of vehicle velocity as well as the location and size of the Piezo-electric harvesters on the generated power. Optimally designed plate energy harvester attached with four cantilever harvesters generates up to around 28 W electrical power with the assumption of continuum vehicle passing the pavement by 22.2 m/s. This power can be used to collect enough energy in 2 hours to raise the ice temperature with the thickness of 1 cm, covering a 5 m wide road by 20 degree Celsius. / February 2017

The objective of this research is to develop a wearable device that could harvest waste mechanical energy of the human hand movement and utilize this energy to suppress wrist tremors. Piezoelectric material is used to measure the hand movement signals, and the signal of wrist tremor is filtered to be utilized to suppress the tremor. In order to conduct the experiment of energy harvesting and tremor suppression, an experimental rig was fabricated. Two types of piezoelectric materials, PVDF (polyvinylidene fluoride) films and MFC (macro fiber composite) films, are used to harvest mechanical energy and used as actuators to suppress hand tremors. However, due to some shortages of the materials, these two types of materials are not used as actuators to suppress the wrist tremors. Thus, we use Matlab Simulink to simulate the tremor suppression with AVC (active vibration control) algorithm.

Resonators are one of the most important parts of electronic products. They provide a stable reference frequency to ensure the operation of these products. Recently, the electronic products have the trend of miniaturization, which rendered the size reduction of the resonators as well [1]. Better design of the resonators relies on a better understanding of the crystals' nonlinear behavior [2]. The nonlinearities affect the quality factor and acoustic behavior of MEMS (Micro-Electro-Mechanical-System) and nano-structured resonators and filters [3]. Among these nonlinear effects, Drivel Level Dependence (DLD), which describes the instability of the resonator frequency due to voltage level and/or power density, is an urgent problem for miniaturized resonators [2]. Langasite and GaPO4 are new promising piezoelectric material. Resonators made from these new materials have superior performance such as good frequency-temperature characteristics, and low acoustic loss [2]. In this thesis, experimental measurements of drive level dependence of langasite resonators with different configurations (plano-plano, single bevel, and double bevel) are reported. The drive level dependence of GaPO4 resonators are reported as well for the purpose of comparison. The results show that the resonator configuration affects the DLD of the langasite resonator. Experiments for DLD at elevated temperature are also performed, and it was found that the temperature also affects the DLD of the langasite resonator.

Real-time, bedside observation of patient clotting is essential in various surgeries in the operating room (OR), but specifically during cardiac surgeries. The objective of this thesis is to design and test a new piezoelectric device that can be used for viscoelasticity measurement with time as a Point of Care (POC) test. Slow turnaround times (TAT) of current methods to monitor blood viscoelastic changes in patients have led to excessive bleeding and the need for blood transfusions in many situations (Despotis et al, 1997). This study shows that the phase shift produced by a resonator sensor can be related to the viscosity of a liquid. By monitoring a phase shift between an actuator and sensor pair, a numeric relationship can be generated and suffice as a calibration curve for each probe. At a calculated error averaging a maximum of 2%, and coefficient of determination and correlation coefficient exceeding 0.95, two probes have been tested in various glycerin solutions and prepared for whole blood experimentation. They have also been tested in varying temperatures to simulate effectiveness in a dynamic environment, similar to that of clotting whole blood.