This study presents a basis for the analytical and experimental procedures as well as design techniques required in achieving adaptive structures for active structural acoustic control (ASAC). Test structures studied in this work included a baffled simply supported beam and a baffled simply supported plate which were subjected to a harmonic input disturbance created physically with a shaker and modelled by a point force input. Structural acoustic control was achieved with piezoelectric actuators bonded to the surface of the test structure. The primary focus of this work was devoted to studying alternative sensing techniques in feed forward control applications. Specifically, shaped distributed structural sensors constructed from polyvinylidene fluoride (PVDF), distributed acoustic near-field sensors constructed from PVDF, and accelerometers were explored as alternatives to microphones which are typically implemented as error sensors in the cost function of the control approach. The chosen control algorithm in this study was the feed forward filtered-x version of the adaptive LMS algorithm. A much lower level of system modelling is required with this method of control in comparison to state feedback control methods. As a result, much of the structural acoustic coupling (i.e. system modelling) must be incorporated into the sensor design. / Ph. D.

Two rapid-response thin-film heat flux gage systems have been used to measure time-resolved unsteady heat transfer signals. The Heat Flux Microsensor is a passive gage which measures the temperature difference across a thin thermal resistance. The second sensor, an actively powered gage operated by a constant temperature anemometer, measures heat flux by measuring dissipated power. These gages have frequency performance windows of 50 kHz and 250 Hz, respectively. Each gage was calibrated for both steady and unsteady response. They were then placed at a flow stagnation point. A velocity probe is positioned outside the boundary layer adjacent to the gage. Simultaneous monitoring of these signals allowed the time-resolved documentation of the effects of local freestream turbulence on boundary layer heat transfer. The resulting time traces indicate a direct correlation between the turbulent velocity fluctuations and heat flux variation. The effects of apparent single-frequency turbulent components are isolated on both the velocity and heat flux signals. These signals are analyzed to determine their relative amplitude and phase characteristics. The results are compared to similar relationships characterized in regularly pulsating laminar flow regimes. / Master of Science

Two new fiber optic magnetostrictive phase modulators and magnetometers using the highly magnetostrictive rare-earth iron compound Tb_xDy_l-xFe₂ are investigated. They demonstrated to have a high sensitivity, dynamic range, minimum field detectability, and a better structural suitability than metallic glasses. For the first sensor, the experimental linear phase shifting coefficient was 1.102 rad/Vp-m with the corresponding phase shift nonnalized to the magnetic field of 0.306 radiO-m. For the second sensor, the experimental linear phase shifting coefficient was 0.5 rad/Vp-m with the corresponding phase shift nonnalized to the magnetic field of 0.136 rad/G-m. A minimum detectable phase shift of better than 1 μrad was obtained, which corresponds to 2 μG/m for a 4 Hz bandwidth and 1 μG/â HZ per meter of fiber interaction length. The projected minimum detectable magnetic field for 30 meters, for the first sensor, is thus seen to be 3pT/â HZ. The experimental results presented have clearly demonstrated the utility of the Terfenol based magnetostrictive fiber optic phase modulator and magnetometer. / Master of Science

A microprocessor based air pressure controller is discussed. The particular implementation was designed around an existing pressure measurement, and display unit. The unit is controlled by a 6809 microprocessor. It is shown that due to the many functions that the unit must perform and control, a microprocessor based system is a good choice. The controller is economical since it uses standard chips, yet it is very accurate since it uses state of the art pressure transducers. Experimental results and the user friendly interface will also be discussed. A commented listing of the controller software, and the circuit diagrams are appended. / Master of Science

During the initial heating of hydraulically bonded castable refractories, dehydration of cement phases causes build-up of high levels of internal steam pressure. If this pressure exceeds material strength, explosive spalling results. A probe capable of measuring internal steam pressures"in-situ" has been developed and tested. Correlation of cement calorimetry and pressure data suggests that castable heating schedules can be modified to reduce explosive spalling. / Master of Science

As the broad implementation and use of wireless sensor nodes in Internet of Things (IOT) devices increase over the years, securing personal data becomes a growing issue. Physical unclonable functions (PUFs) and random number generators (RNGs) provide methods to generate security keys for data encryption. Transducers used in the energy harvesting systems of wireless sensor nodes, can generate the PUFs and RNGs. These transducers include piezoelectric devices (piezo), thermoelectric generators (TEG) and solar cells. This research studies the electrical properties of transducers at normal and low operating levels for electrical responses that can be used in PUF generation and random number generation respectively. The PUF generation discussed in this study analyzes the resonance frequency of 10 piezos, and the open-circuit voltages of 5 TEGs and 5 solar cells. The transducers are tested multiple times over a 10-day period to evaluate PUF reproducibility and reliability characteristics. The random number generation is accomplished by applying a low-level vibration, thermal or light excitation to each respective transducer. The generated electrical signals are amplified and digitally processed and analyzed using the National Institute of Standards and Technology (NIST) Statistical Test Suite. The experiment results for the PUF generation are promising and indicate that the piezos are the better choice due to their stable frequency output. Each transducer was able to produce random numbers and pass the NIST tests, but the TEGs passed the NIST tests more often than the other transducers. These results offer a preliminary basis for transducers to be used directly in security applications. / Master of Science / As the broad implementation and use of wireless sensor nodes in Internet of Things (IOT) devices increase over the years, securing personal data becomes a growing issue. Physical unclonable functions (PUFs) and random number generators (RNGs) provide methods for securing data. Transducers used in the energy harvesting systems of wireless sensor nodes, can be used to generate the PUFs and RNGs. These transducers convert vibrations, light and heat into electricity. This research studies the electrical properties of transducers at normal and low operating levels for responses that can be used in PUF generation and random number generation respectively. The PUF generation discussed in this study analyzes the different electrical properties of each transducer. The transducers are tested multiple times over a 10-day period to gather an adequate amount of data. Producing the same output every single time is imperative for PUFs. The random number generation is accomplished by applying a low input vibration, heat or light to each respective transducer. The generated electrical signals are amplified and digitally processed to be analyzed using software. The experiment results for the PUF generation are promising and indicate that the transducers that convert vibrations to electrical energy are the better choice due to their consistent output. Each transducer was able to produce random numbers and pass the required tests. These results offer a preliminary basis for transducers to be used directly in security applications.

No description available.

A technique for calculating bulk ultrasonic fields which uses implicit difference equations to evaluate the parabolic approximation to the Helmholtz equation is described. The parabolic approximation assumes that the field varies much faster in the transverse directions than in the direction of propagation and results in a partial differential equation which is formulated as a pure i initial value problem . Finite difference equation descriptions are derived for one-dimensional, cylindrically symmetric problems and for more general two-dimensional problems. A Fourier stability analysis is performed on the simpler numerical scheme to determine acceptable values for parameters such as the grid spacing and increment step sizes. Several example calculations for each geometry are presented to demonstrate the usefulness of this parabolic-difference equation technique in transducer modeling. Included in these examples are gaussian, rectangular, circular, and concentric ring amplitude distributions, as well as uniform and focused phase distributions. In many cases, qualitative agreement between the numerical results and analytic diffraction theory predictions can be observed. An experimental system is developed for the detection of acoustic fields in water using a dual beam differential interferometer which is scanned through a large tank. The output from this system is proportional to the average difference in refractive index sampled by the two beams and is effectively integrated along the path of the beams through the specimen. An algorithm is presented which reconstructs a radial profile of the measured field from the integrated data assuming cylindrical symmetry. Raw, averaged, and reconstructed data is given for scans taken in the far-field of a circular, uniform transducer. / M.S.

A sensibilidade eletromecânica dos transdutores de eletretos poliméricos resulta em muitas aplicações na engenharia, que motivaram a produção industrial de um filme não homogêneo e eletricamente carregado, denominado filme eletromecânico ou EMFi (ElectroMechanical Film). Um dispositivo alternativo a este EMFi, produzido em nosso laboratório, foi o resultado de uma bolha de ar homogênea termoformada, unida por dois filmes de teflon FEP. Este dispositivo possui uma estrutura similar ao EMFi, mas permite cavidades homogêneas a serem predefinidas e distribuídas no momento em que o dispositivo é produzido, diferindo das células no EMFi com tamanhos diversos e dispersas no interior do filme industrial. A possibilidade de controlar a geometria das bolhas de ar tornou possível o desenvolvimento de um modelo, empregado como uma ferramenta de projeto. A resposta eletromecânica deste transdutor foi modelada e então apresentada neste trabalho. Este modelo analítico avalia o desempenho destes transdutores com somente uma bolha termoformada, para efeitos de simplificação, baseado em capacitores em série, em função da deformação mecânica e da carga elétrica retida no polímero. São representados dinamicamente com parâmetros elétricos e mecânicos, definidos à medida que operam como sensores ou atuadores, com respeito ao limites impostos pela aplicação especificada. O gráfico da resposta em freqüência mostra a freqüência de ressonância e a largura da faixa para meia-amplitude que determina o coeficiente de amortecimento que não pode ser obtido diretamente do modelo analítico. Este gráfico também permite comparar a freqüência natural obtida graficamente com aquela calculada pelo modelo, tornando mais confiável o modelo desenvolvido para o transdutor. Finalmente, melhorias na instrumentação e em condições mais adequadas para os testes são sugeridas, bem como métodos alternativos para trabalhos futuros. / The electromechanical sensibility of polymeric electrets transducers yields many engineering applications which have motivated industrial production of a non-homogeneous and electrically charged film, the so-called electromechanical film (EMFi). An alternative device for this EMFi that has been produced in our laboratory was a homogeneous thermo-formed air bubbles bonded with two teflon FEP films. This device has a structure similar to the EMFi, but allows the homogeneous voids to be pre-defined and distributed at the moment the device is produced, differing the EMFi voids with diverse sizes and dispersed into the industrial film. The possibility to control the air bubbles geometry makes possible the development of a model to be used as a design tool. The electromechanical response of this transducer has been modeled and is presented in this work. Such analytical model evaluates the transducers performance using just a single thermo-formed bubble for simplification purposes, based on series capacitors, which are function of the mechanical deformation and electrical charge trapped in the polymer. They are represented dynamically, with electrical and mechanical parameters being defined as they work as sensors or actuators, regarding the limits imposed by the specified application. A frequency response plot shows the resonance frequency and the bandwidth for the half amplitude, which determines the damper coefficient that cannot be obtained directly from the analytical model. This plot also allows comparison of the natural frequency obtained graphically with the calculated one using the model, making more reliable the transducer model developed. Finally, instrumentation improvements and more suitable test conditions are suggested, as well as alternative methods for future works.

Pulsed ultrasound Doppler velocimetry proved to be capable of measuring velocities accurately (relative error less than 0.5 percent). In this research, the limitations of the method are investigated when measuring: in channels with a small thickness compared to the transducer diameter, at low velocities and in the presence of a flow reversal area. A review of the fundamentals of pulsed ultrasound Doppler velocimetry reveals that the accuracy of the measured velocity field mainly depends on the shape of the acoustic beam through the flow field and the intensity of the echo from the incident particles where the velocity is being measured. The ultrasonic transducer turned out to be most critical component of the system. Fundamental limitations of the method are identified. With ultrasonic beam measurements, the beam shape and echo intensity is further investigated. In general, the shape of the ultrasonic beam varies depending on the frequency and diameter of the emitter as well as the characteristics of the acoustic interface that the beam encounters. Moreover, the most promising transducer to measure velocity profiles in small channels is identified. Since the application of pulsed ultrasound Doppler velocimetry often involves the propagation of the ultrasonic burst through Plexiglas, the effect of Plexiglas walls on the measured velocity profile is analyzed and quantified in detail. The transducers ringing effect and the saturation region caused by highly absorbing acoustic interfaces are identified as limitations of the method. By comparing measurement results in the small rectangular channel to numerically calculated results, further limitations of the method are identified. It was not possible to determine velocities correctly throughout the whole channel at low flow rates, in small geometries and in the flow separation region. A discrepancy between the maximum measured velocity, velocity profile perturbations and incorrect velocity determination at the far channel wall were main shortcomings. Measurement results are improved by changes in the Doppler angle, the flow rate and the particle concentration. Suggestions to enhance the measurement system, especially its spatial resolution, and to further investigate acoustic wave interactions are made.